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BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(4107 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: cam option
Posted by: BlownMGB-V8
Date: August 12, 2008 05:48PM

Looks like I may be trying to hit a moving target here. May have a deal on some Carrillo rods and Venolia pistons and obviously if that happens redline is going to go up, probably to the 6500-7000 range. But I'd like to keep the valve lift under .500 if it's feasible, and as mentioned shoot for max economy at the same time. Those are some pretty conflicting demands right there and I don't think it'd be possible without the blower. But I do love an engine that will wind up so why not go for it? I'm thinking wide lobe centers, minimum overlap, and near stock lift and duration on the intake, say around .400 on the lift, and then max out the lift and duration on the exhaust. I'll have to see what clearance my exhaust valves have at the seals and I'd prefer not to have to notch the pistons.

I have little doubt the end result will be a custom grind but I'm not concerned about that, I just want to get in the ballpark with the specs before I talk to the cam grinders. Wonder if Racer Brown is still around?

Jim


Wotland
Wotland Wotland

(104 posts)

Registered:
01/07/2008 08:14AM

Main British Car:


Re: cam option
Posted by: Wotland
Date: August 20, 2008 05:04AM

Hello Nick, sorry was away.

Cam figures : BTDC/ABDC/BBDC/ATDC
Last figure give you the duration. Two figures when In/Ex duration is different.

LCA (lobe centre angle) : (duration/2) - valve opening point for the inlet or closing point for the exhaust
LSA (lobe separation angle) : (inlet LCA + exhaust LCA)/2

If I can give you an advice contact Rob at V8Developments in UK. This is the man for stroked Rover V8. He created an 5.5 with custom 3.7'' stroker crank and 3.8'' bore [www.v8developments.co.uk]


NixVegaGT
Nicolas Wiederhold
Minneapolis, MN
(659 posts)

Registered:
10/16/2007 05:30AM

Main British Car:
'73 Vega GT 4.9L Rover/Buick Stroker

authors avatar
Re: cam option
Posted by: NixVegaGT
Date: August 20, 2008 09:18AM

WOW that's a lot more specific information. I like that method WAY better. Why don't we do it? I mean, you can get a card from Crower website, which is great, but most don't have that information readily available. I couldn't find anything specific like that about Isky. Is that because they want to keep it a secret?

I love it when the only information is: Street-strip or Race cam. WOW that's helpful. OKů I'm starting to sound like a crotchity beeotch.

My point is: Thanks Dimitri.


NixVegaGT
Nicolas Wiederhold
Minneapolis, MN
(659 posts)

Registered:
10/16/2007 05:30AM

Main British Car:
'73 Vega GT 4.9L Rover/Buick Stroker

authors avatar
Re: cam option
Posted by: NixVegaGT
Date: August 23, 2008 09:54AM

OK I got my cam specs from Woody at the Wedge Shop. It makes a lot more sense now:

LCA: 108║
Overlap: 74║
Timing: 35/71/75/39

Clearance Hot: 0.023

Lift: .544/.544

Adv Duration: 286/294


Specs @ 0.050:

Overlap: 38
Timing: 17/53/21/57

Duration: 250/253

It's a solid lifter cam. Custom ground to get the LCA. What Woody was saying to me over the phone is it's a 340 cam not 314 like I thought I heard. At the time I thought he was either talking about the lobe lift or the adv. duration. It's actually the lobe lift. It's got some pretty wicked lift. Hopefully I will clearance OK. 286/294 makes a lot more sense to me. We'll see how it all assembles.

Thanks again for the help guys.


Wotland
Wotland Wotland

(104 posts)

Registered:
01/07/2008 08:14AM

Main British Car:


Re: cam option
Posted by: Wotland
Date: August 28, 2008 06:44AM

Hello Nick,
I found back an very good article from Rob about cams in Rover V8 :

I will come to cams and what i think are good and bad in a bit, firstly what are you trying to achieve is to get the engine to fill its total cylinder capacity throughout its rev range, easy said impossible to do unfortunately,
The first place to start is the cylinder heads, a real good flowing pair of cylinder heads means you dont need such a viscous cam to make decent horsepower!, unfortunately this is what lets the rover engine down big time, even in the 500 TVR heads the valves are just no where near big enough to flow the air that is required, so we are left with trying to make some decent bhp and driveabillity with a cam.
LIFT,
basically as much lift as you can get the better your engine will perform through the whole rev range regardless of cc's, the rover head flows it most cfm when the valve is something like 700 thou from is seat, the reality here is no rover cam lifts that far because it just cant, 600 is about its max, lift is related to duration, you cant have lots of lift with little duration as the valve will be being opened so quick that the cam follower willjust dig into the side of the cam profile and break, so with a 600 though lift you are going to need 320 deg of duration, what you now have is a full circuit race cam that will only make power from 5000 rpm upwards!
DURATION
Duration is the time the valve is lifted of its seat, to little you will have no power too much the car will drive like a pig, However duration, lca "lobe center angle, and overlap are all related, its not so much the duration that kills driveabillity its the overlap, just 10 deg can make or break the engine!, so duration make bhp lift makes both, as i said in the other post i am only going into road engines!.
The lca is the angle between full lift on the inlet and full lift on the exhaust lobe, by making this wider you can tame the cam for the same given duration, however what will happen is the came with the wider lca will idle better drive smoother make more bhp and have a wider torque curve, the cam with the smaller lca will only have a benefit in the mid range, around peak torque. so in my honest opinion for a road cam i like to go for around 285-290 deg of duration with a wide lca around 114, this to make a good road sports cam, you can drive it down the shops with no hunting and use it on a track day as well, the same cam on a 108 lca will make it more peaky in the mid range, but you will have to keep changing gears in slow traffic and it will drop of the cam quicker too, peak power will be around the same but where the 114 will still be making dood power at say 6500 rpm the 108 will be dead and buried and need a gear change, a race car is totaly different i would spec a a cam to work in the rev range i wanted and make the most of that rev range.
mc1 good idle, excellent drive ability, reasonable bhp.
mc2 poor ish idle, poor ish drive abilty good mid range, good bhp.
h404 very poor idle, crap driveability, good mid range, excellent bhp
stealth very good idle, very good drive ability, ok ish mid range, good bhp.
Piper 270 ok idle good mid range crap bhp
piper 285 crap idle, poor drive ability, very good mid range,ok bhp, falls off the cam very quickly
piper 300 crap idle crap drive ok mid range good bhp
kent 200 very good idle good drive poor every where else
218 good idle good drive good mid range poor bhp
214 ok idle ok drive ok mid range ok bhp
224 poor idle, poor drive, good mid range, good bhp
234 crap idle crap drive, good mid range, excellent bhp,
These are all based on the fact that you will be running standard management systems and a plenum, there are of course many more cams out there but these are the general ones you will buy.
So to sum things up a bit, if you want a good low down nice driving torque cam go for a cam with a max of around 270 deg duration and a lca of around 112 deg.
if you arent bothered with idle qualities and want a good mid range cam go for one with a low lca and around 280 deg of duration.
if you want a track day cam or fast road cam go for around 300 deg and around 110 lca
if you want a good all rounder go for around 285 deg and wide 114 lca, both kent and piper will make cams to what you want within reason so give them a call, the piper 285 for instance, loses nearly 25 bhp over the 404 at the top end, this on a controlled dyno not a rolling road, but it gains around 10 ftlb at around 200-3000 rpm, but if you asked piper to gring it on an lca 0f say 110 you would only be losing around 10 bhp at peak,300but gaining around 20 ftlb at 2000-3000.
Also please note cams cannot be judged against other cams on rolling roads, espiecially different rolling roads, there are too many varients, all the way from the air filter to the oil in your gearbox and diff!!!!!
Throttle bodies against plenums and cams!!
What i breifly said earlier with overlap cams, this will murder an engine running a plenum, where as on throttle bodies it tends to smooth thigs out a bit, take a single plenum all 8 cylinders draw from this one opening, not a proplem there in fact it is good as each cylinder can draw as much air as it wants with no restictions as far as air flow is concerned. The BIG DOWNSIDE TO A PLENUM, on the overlap period part of the cam, this is where both exhaust and inlet valve are open at the same time, ie at the end of the exhaust stroke where the piston is forcing the burnt gas out the exhaust port the inlet valve opens before the exhaust is shut, instead of the unwanted rubbish going out the exhaust it is sent back up past the inlet valve and into the plenum, this is more agrivated by the fact that the next cylinder is sucking hard and will suck the waste out of the disposing cylinder into the good one, the problem here becomes that it is not fresh and lacks oxygen, so instead of the new cylinder getting a good charge of fresh air and fuel, it has 20 or 30% of nothing that cant be ignited, hence poor combustion poor idle and low power, This is only at low ish rpm, at high rpm you have the advantage that the exuast manifolds are "should" be scavenging the fresh inlet charge into the cylinder, if you have the money to go to throttle bodies then this is where the biggest gain is going to come in the low to mid range, on the overlap period each cylinder can only contamite its own cylinder, and part of this will be lost to the atmosphere anyway, so genearly lets say at below 3000 rpm a plenum is giving a cylinder 70% of fresh charge to be ignited a set of throttle bodies will be giving 90% at the equivalent rpm all this = more ftlb of torque, just be carefull you dont go too small on the throttle bodies or this will hurt the top end breathing, you have gone from a 72 mm plenum and as i said each cylinder will see 72 mm down to what ever size your throttle bodie is.

Hope it helps you.


Dan Jones
Dan Jones
St. Louis, Missouri
(196 posts)

Registered:
07/21/2008 03:32PM

Main British Car:
1980 Triumph TR8 3.5L Rover V8

Re: cam option
Posted by: Dan Jones
Date: August 29, 2008 02:11PM

> basically as much lift as you can get the better your engine will perform
> through the whole rev range regardless of cc's,

That assumes the high lift lobe shape lends itself to the maximum RPM
you are after. Most cam grinders typically have two primary families
of lobe shapes (along with a host of others for specialized applications
like racing classes with lift limitations or stock lifter requirements,
etc.). The first family of lobe shapes are optimized for shorter rocker
ratios or lower RPM when used with longer rocker ratios. These are
sometimes referred to as high torque grinds. The second family of lobes
are ones designed for higher RPM and/or longer rocker arm ratios (1.7:1
to 1.8+:1).

> the rover head flows it most cfm when the valve is something like 700
> thou from is seat

Not on any Rover or Buick 215/300 head I've ever had on the flow bench.
Stock Rover heads plateau by 0.5" lift and even my ported Buick 300
heads with 1.775" intake valve peaked at 0.550" lift. This is largely
a consequence of the valve diameter. That said, a cam with higher lift
means more time spent near (or above) the heads peak flow.

> lift is related to duration, you cant have lots of lift with little duration
> as the valve will be being opened so quick that the cam follower will just
> dig into the side of the cam profile and break, so with a 600 though lift
> you are going to need 320 deg of duration, what you now have is a full
> circuit race cam that will only make power from 5000 rpm upwards!

That's lobe lift. Valve lift is lobe lift times the rocker arm ratio
so you can get greater lift from the same cam by increasing rocker arm
ratio. Unfortunately, the stock Rover ratio is 1.6:1 and no larger
ratios are easily (read affordable) available. On another engine I'm
currently working on, the stock ratio is 1.73:1 with 1.8:1 optional.
For that engine (351C Ford stroker), I had to go to shorter rocker
arm ratios (1.7:1 intake and 1.6:1 exhaust) to keep lift under 0.620"
(the limit the BBC beehive valve springs can tolerate), even with a
street cam (hydraulic roller).

For flat tappet cams, the maximum lobe lift slope is determined by the
diameter of the lifter. Unfortunately, the Rover diameter is 0.842"
(same as other GM V8's such as the small block and big block Chevys,
Pontiac and Buick V8's). Small and big block Ford V8's use a larger
0.875" diameter and Chrysler and AMC V8's use an even larger diameter
of 0.904". One way around the lifter diameter limitation is to use
mushroom tappets which have a face that is larger than the lifter
diameter. The downside is the lifters have to go in from the bottom
sied of the block, before the crankshaft goes in.

> Duration is the time the valve is lifted of its seat, to little you will have
> no power too much the car will drive like a pig, However duration, lca "lobe
> center angle, and overlap are all related, its not so much the duration that
> kills driveabillity its the overlap, just 10 deg can make or break the engine!

Overlap is much more important than duration. Overlap is the period when
both intake and exhaust valve are open.

> The lca is the angle between full lift on the inlet and full lift on the
> exhaust lobe, by making this wider you can tame the cam for the same given
> duration

Because you've decreased the overlap. Overlap is the combination of duration
and LCA. The best approach is to pick the total overlap to set your desired
RPM range, choose the optimal LCA for your particular engine and then duration
will fall out of the equation.

> however what will happen is the cam with the wider lca will idle
> better drive smoother make more bhp and have a wider torque curve,

A wider LCA does not necessarily make better peak or average HP.

> the cam with the smaller lca will only have a benefit in the mid range,
> around peak torque.

In many engines, particularly Rover storker engines, tighter lobe centers
will make better power across the rev range.

> so in my honest opinion for a road cam i like to go for around 285-290 deg
> of duration with a wide lca around 114, this to make a good road sports cam,
> you can drive it down the shops with no hunting and use it on a track day
> as well,
>
> the same cam on a 108 lca will make it more peaky in the mid range, but
> you will have to keep changing gears in slow traffic and it will drop off
> the cam quicker too, peak power will be around the same but where the 114
> will still be making dood power at say 6500 rpm the 108 will be dead and
> buried and need a gear change,

That's not a apples-to-apples comparison. For a valid comparison, you
need to have equivalent overlap. In the above example, the 108 LCA cam
has far great overlap so tunes in at a higher RPM. If 108 is the optimal
lobe center, then reducing the duration so the overlap is equivalent will
yield a cam that makes much better average power under the curve than the
114 LCA cam.

In "Be the Camshaft Expert" (July 2006 issue of Popular Hot Rodding),
David Vizard presented some rules of thumb for selecting cam specs based
upon what he's learned in developing a cam selection program. An online
version of that article can be found here:

[www.popularhotrodding.com]

The program was reportedly 18 years in the making and uses data gathered
from several thousand cam tests. The basic idea is that cam overlap sets
the RPM range in which an engine will best operate and the total overlap
is a function of the cam duration and lobe center angle (LCA). If you
know the ideal LCA and the RPM range you wish to operate in, the duration
will fall out. In the article, Vizard presents graphs of cubic inch
displacement (CID) per cylinder per inch of valve diameter versus ideal LCA.
The graphs are for inline valve heads with compression ratios between 9:1
and 11:1. If canted valve heads are used, the ideal LCA is 2 degrees less.
The optimal LCA is also adjusted for compression ratios outside the assumed
range. Once ideal LCA is known, you pick your desired overlap via
application:

1. Street towing 10 to 40 degrees
2. Regular street 30 to 60 degrees
3. Street Performance 50 to 75 degrees
4. Street/Strip 70 to 90 degrees
5. Amateur Race 85 to 100 degrees
6. Professional Race 95 to 115 degrees

Overlap is the period when both intake and exhaust valves are open and serves
to set the RPM range over which the cam will be best suited. More overlap
means a rougher idle and poorer low end response due to reversion of the
exhaust charge into the intake plenum as well as loss of "effective"
compression ratio (compression is literally blown out the exhaust port at
low RPM). Where you fall in the overlap range is a function of valve size
per cubic inch. Big valves on a 302 use the low end, a 350 with typical size
valves use the mid-point, big inch small block or big block, use the right
hand side. Given the small valve size of the Rover/Buick aluminum V8's,
we'd typically use the larger overlap value (right hand side). Once LCA and
overlap are known, duration falls out of the equation. Lift is determined
by the intake valve diameter.

In the article, Vizard presented the results of a test demonstrating the
importance of picking the right LCA:

[www.popularhotrodding.com]
[www.bacomatic.org]

Ideal LCA for that engine was 108 degrees. Narrowing to 105 degrees made
similar power but had noticeably worse idle and low speed characteristics.
Widening to 111 degrees lost power. Another LCA test was performed on a
302 Small-Block Ford and repeated on a stroked (347 CID) version of the same
engine:

[www.popularhotrodding.com]

"When used in the 302, the 276/280 roller hydraulic cam on a 110 LCA proved
optimal, as even a 1 degree change either way produced worse results. Using
a SCAT stroker kit, this engine was stretched to 347 inches and re-tested
with the original 110 LCA cam. The stroker kit really helped both power and
torque. When the 110 LCA was replaced with a more appropriate 108 LCA cam,
the output made a further jump to the tune of some 20 lb-ft and 20 hp. The
108 cam in the 347 gave as much in terms of idle and vacuum as did the 110
LCA in the 302. Dozens of tests such as this show conclusively that the
overlap and LCA--not the duration--are the first steps toward generating a
cam spec."

At low speed, lots of overlap is bad as it hurts low end but overlap helps
as the RPM increases. To a degree, you can offset overlap with static
compression. Another point raised in the article is that, for most V8's with
reasonable heads, the ability to raise low speed torque with compression
increase holds to around 285 to 290 degrees (at lash point) of cam duration.
After that, drop off is faster than an increase in compression can recover.
In another article ("Compression Comprehension") about running up to 12:1
compression on pump gas, Vizard presented the results of a compression test:

[www.bacomatic.org]

"When used in conjunction with a bigger cam, increased compression can
work wonders for the entire curve. When a 265-degree cam (gray curve)
was substituted for a 285-degree cam (blue curve), a substantial drop
in low-speed output was seen. Raising the CR from 9:1 to 12:1 recovered
almost all the lost low end and gave a further increase in top-end
output"

I wrote a little computer program based upon the article. The required
inputs for the simplified program are:

bore diameter (in inches)
crankshaft stroke (in inches)
intake valve diameter (in inches)
static compression ratio
canted or inline valve heads
desired overlap (picked from the ranges listed above)

Some results for various Rover/Buick combos are presented below. Vizard's
cam selection program is not available to the general public but I know for
a fact it takes much more into consideration than the simplified rules
presented above. A friend has run his program and it uses actual head flow
data, port size (length and cross-sectional areas), valve diameters, rocker
ratios, desired idle vacuum, compression, bore, stroke, fuel octane,
thermostat temperature, rod length and more. Basically, it attempts to feed
the "air pump" in the most efficient manner, given the parameters entered.
What it doesn't do is tell you what ramp rates you need. The recommendation
is to use the most aggressive ramp you can tolerate for your application.
However, more aggressive lobe shapes are noisier, wear more quickly and are
harder on valvetrain parts so that neds to be taken into consideration as
well.

The simplified program assumes you'll use the same lobe profile for intake
and exhaust. There's an implicit assumption that the exhaust flow is
reasonable compared to the intake. Vizard also suggests the rocker ratio
on exhaust is best kept 0.1 to 0.2 of a ratio lower than the intake ratio.
The exhaust is under higher pressure and blows down early in the lift cycle
plus the exhaust is less sensitive to valve acceleration than the intake but
is sensitive to duration. I noticed in last year's Engine Masters Competition,
most of the entries were using shorter rocker ratios. If an existing cam's
LCA is too wide, higher ratio rockers may increase output. For rocker ratios
between 1.5 to 1.9, each 0.1 ratio increase on the intake, the LCA needs to
be spread by 0.75 to 1. Be aware there are cases where the ideal lobe center
may be too narrow for acceptable street manners. For instance, when stroking
an engine (keeping all other variables constant), Vizard suggests tightening
the LCA up by a degree for something like every 16 cubic inches increase in
displacement. That will lead to very tight lobe centers which may not be
acceptable for certain applications. For instance, an engine equipped with
mass-air EFI (which will measure reversion flow as if it were induction flow)
might not be too happy with 104 degree lobe centers. Vizard's full-up
program allows you to specify idle vacuum to get around problems like that
but the simplified program doesn't have that sort of flexibility.

Another thing to be aware of is that narrow lobe separation angles require
an efficient exhaust with minimal back-pressure. If you have a bunch of
back-pressure (from things like restrictive mufflers or headers that turn
down sharply at the exhaust port exit) it will hurt a narrow lobe separation
angle engine more than a wide one. A quote from the article drives home this
point home:

"Let's make one thing clear here: Big (but not excessive) overlap is a prime
key to big power numbers, but only if your exhaust system sucks. Literally.
If you have ever heard that an engine needs a little backpressure, you might
want to ask yourself why an engine would want an exhaust system that literally
pushes exhaust back into the combustion chamber rather than sucking it out.
The simple answer is, it doesn't. If a big-overlap, big-cammed engine has an
exhaust system with any measurable backpressure, the price paid is a big drop
in output."

If your exhaust system is restrictive, it may be wise to err on the side of
a wider LCA or shorter duration.

Since large valved heads tend to increase flow through high lift levels,
the lift recommended by Vizard's rules may be excessive for heads equipped
with large valves. The recommendation is to use a lift consistent with your
reliability goal (higher lift wears valves, guides and seats more quickly).
However, for small valve heads, like our little Rover/Buick aluminum V8's,
the maximum lift is reasonable. In the range of 2 valve pushrod V8's, our
Rovers are at the small valve diameter (per displacement) end of the spectrum
but, based upon my limited experience, the simplified program seems to give
pretty reasonable trends. As a starting point, you could do worse. Woody
Cooper has had a lot of experience with custom cams in Rovers of various
displacements and I believe his experience parallels Vizards predictions.

Cam specs for Rover/Buick street performance assuming 75 degrees overlap
and 9:1 to 11:1 compression ratio:

CID Bore x Stroke Intake duration / LCA / Lift
Valve
Diameter

215 (3.50 x 2.8) 1.5 298 / 112 / 0.45 to 0.52
219 (3.52 x 2.8) 1.5 298 / 111 / 0.45 to 0.52
215 (3.50 x 2.8) 1.625 298 / 112 / 0.48 to 0.56
266 (3.53 x 3.4) 1.5 288 / 107 / 0.45 to 0.52
266 (3.53 x 3.4) 1.625 292 / 109 / 0.48 to 0.56
292 (3.70 x 3.4) 1.625 288 / 107 / 0.48 to 0.56
292 (3.70 x 3.4) 1.775 292 / 109 / 0.53 to 0.62
297 (3.73 x 3.4) 1.775 292 / 108 / 0.53 to 0.62

Note that the durations used here are seat-to-seat duration (similar to
advertised or SAE duration, not duration at 0.050").

Okay, so that's the theory. Here's some of the practice side from an
engine builder friend of mine...

If you set up a cam on blocks or centers and use a lifter jig, or plot
it out on paper, it quickly becomes apparent that the range of actual
lobe profiles is sharply limited. For flat tappet cams, the diameter of
the lifter or the length and curvature of the finger follower defines
the limits of possible profiles. Once your pressure line gets to the
edge of the follower, there's no more to be had. For rollers, the
diameter of the roller is your limiting factor. Eventually the pressure
line reaches the height of the axle, and spits the roller off to the side.

That's geometry. It does make a difference; that's why flat tappet
racing lobes are specified by lifter diameter, and why rollers go to
inverted flanks.

Then you need ramps to take up the slack on opening, and to keep from
pounding things on closing. That further restricts allowable profiles.

Then you come to the big real-world part - wear. For a flat tappet,
wear is pretty much a function of load at the pressure line. That's why
Detroit cams are all so wimpy. They had to last 75,000 or more miles
without wearing to the point where they had to be replaced. For
hydraulic rollers, oil viscosity and pressure are your main limits,
where leakdown starts to change the valve motion significantly from the
lobe motion. And remember, that's assuming a 10 year old car that still
has the oil it left the factory with, in a worst-case service condition,
like pulling a camping trailer in New Mexico in the summer.

For a "performance" cam, longevity is sacrificed first. You can load
the cam more heavily, and shorten the ramps, and pick up lots of "free"
power by kicking the valves open faster and closing them sooner.
Competition Cams is infamous for this; some of their more aggressive
street cams seldom saw more than 20,000 miles before rounding off lobes
or hollowing lifter bases. They *did* perform as advertised. Note
that Comp recommends armor-faced lifters for flat tappet lobes that
require heavy spring rates.

For "street" cams, you have to assume the stock valvesprings are being
used, because a largish fraction of your customers *will* insist on
running them. Getting more area under the curve with stock springs is
a damned good trick; you can whack it off the seat, but you have to stop
lifting early and carefully to keep the valvetrain together at max lift,
and you have to set the valve down carefully to keep it from bouncing.

Drag cams are quite specialized now, which is why you see the lobes
separated from circle track stuff. Longevity on a cutting-edge drag cam
is often less than a dozen runs for a flat tappet. For solid rollers,
lifter failure happens first.

Power is cheap. Longevity is what costs the big money.

Crane and Isky like to talk about stepped lobes to handle harmonic
motion of the valvetrain bits, and other crap like that. It's just
marketing; on the dial indicator, it's all a smooth curve.

What's creepy is to mike a brand new cam, and find .005" difference in
lobe height from smallest to largest. Kind of makes me laugh at Crane,
which claims accuracy down to *millionths* when tossing cams into the
grinder...

Extended exhaust duration only adds overlap, with its attendant idle
and emissions problems. All-out racers use long exhaust durations for
scavenging, but that ruins your fuel economy on the street. It's primarily
a drag race trick to keep the power from dropping off quickly after power
peak. On the street, a symmetrical profile or even a short exhaust will
run just as well and with a lot more tractability. On the street, extended
exhaust profiles date back to the 15-psi-backpressure old-style catalytic
convertor days; they are obsolete.

Overlap creates a lot of internal EGR during cruise which is great for fuel
economy if the spark is advanced enough. In the BMW world, intake and
exhaust cam profiles are either the same, or the intake gets the bigger cam.
Independent runner intake manifolding can withstand a lot more overlap without
trashing the low speed torque and tractability than a standard plenum carb
intake.

Dan Jones


Moderator
Curtis Jacobson
Colorado USA
(3776 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

authors avatar
Re: cam option
Posted by: Moderator
Date: August 29, 2008 02:35PM

One of these days I'm gonna succeed in convincing Dan to write articles for BritishV8 instead of (or in-addition-to) putting so much effort and information into message-board posts. They'd be such a valuable reference and they'd probably reach so many more people. (Tables and charts would also be easier to integrate.)

Awesome and thought provoking information!

A bit overwhelming though, for non-motorheads like me...



NixVegaGT
Nicolas Wiederhold
Minneapolis, MN
(659 posts)

Registered:
10/16/2007 05:30AM

Main British Car:
'73 Vega GT 4.9L Rover/Buick Stroker

authors avatar
Re: cam option
Posted by: NixVegaGT
Date: August 30, 2008 01:35AM

An interesting feature I wanted to also mention is the lobe lift at .34 is just about as big as it looked like you could make it without making the camshaft weak. As it is, the back side of the lobe is almost even with the main shaft of the cam and in some places looks like it is at the diameter of the main shaft.

I'm starting to reconsider running E85 again. Do you think there is any difference in cams for that? Probably not but interesting to thing about. I think after I CC the heads and get a clear understanding of my actual CR I'll decide. I figure if I'm under 11:1 gasoline. If I'm over that I might consider E85 again. I initially threw out the idea because of the expense in converting a carb for it but the are getting less expensive now.

Just tossing in wrenches. LOL!


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(4107 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: cam option
Posted by: BlownMGB-V8
Date: September 01, 2008 09:35PM

Good stuff Dan. It's really great to have someone around who ponders and really understands these things. But what happens when you add boost? I mean just from reading your post and having not yet followed the links...(I will, count on that) it would almost sound like I'd be better off to just stick with a stock cam. Here I am thinking that it'd be an advantage to help the exhaust side since the intake is getting a boost (literally) and you up and say extended duration on the exhaust ain't all that great shakes.

But I'm looking for the practical solution. Something to let me take advantage of the Scat rods, Venolia pistons, CC springs and Eaton blower but keep the economy and driveability of the 10 to 11:1 CR. But I don't want to make a study of it, just want to find a decent bump stick.

340 Buick, stock '64 300 heads.

Jim


NixVegaGT
Nicolas Wiederhold
Minneapolis, MN
(659 posts)

Registered:
10/16/2007 05:30AM

Main British Car:
'73 Vega GT 4.9L Rover/Buick Stroker

authors avatar
Re: cam option
Posted by: NixVegaGT
Date: September 02, 2008 10:09AM

Jim I would try calling Woody: 1-508-880-5448 OR email him: Woody@TheWedgeshop.com

He's got a lot of practical cam experience since the late sixties. He might have a good thought or two on it or he may know a good resource.

Whatever your findings, post'em. I'd be really interested in knowing. Not for my project but I just love to know why things work the way they do.

Thanks for staying in the thread.


Dan Jones
Dan Jones
St. Louis, Missouri
(196 posts)

Registered:
07/21/2008 03:32PM

Main British Car:
1980 Triumph TR8 3.5L Rover V8

Re: cam option
Posted by: Dan Jones
Date: September 02, 2008 09:50PM

> One of these days I'm gonna succeed in convincing Dan to
> write articles for BritishV8 instead of (or in-addition-to)
> putting so much effort and information into message-board
> posts. They'd be such a valuable reference and they'd
> probably reach so many more people. (Tables and charts
> would also be easier to integrate.)

One of these days I'll get around to finishing one of those
articles but things are very busy at the moment. Outfitting
the new shop and running the dyno program are taking up
most of my free time.

Dan Jones


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(4107 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: cam option
Posted by: BlownMGB-V8
Date: September 04, 2008 09:35AM

I emailed Woody and he is going to see what he can come up with. He feels the challenge might be to get 7 grand out of the stock alloy 300 heads.

Incidentally Nick, have you checked your rod to cam clearance? I'm out of space. I'll have to grind the shoulders of the rods to keep from hitting the cam lobes, they just graze with the stock cam. I think that's going to limit my lift to very near stock. I don't think Woody will be happy. Wonder how much clearance you need? I'd think about .020" would do it.

Jim


NixVegaGT
Nicolas Wiederhold
Minneapolis, MN
(659 posts)

Registered:
10/16/2007 05:30AM

Main British Car:
'73 Vega GT 4.9L Rover/Buick Stroker

authors avatar
Re: cam option
Posted by: NixVegaGT
Date: September 04, 2008 12:33PM

Interesting! I am about to start assembling the bottom end. I will be careful and post what I find. I figure I'm about three weeks away from that.

Thanks Jim!


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(4107 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: cam option
Posted by: BlownMGB-V8
Date: September 04, 2008 02:24PM

Glad to help.
I wish I had some input on what is considered adequate clearance between the cam and the rods. I'm thinking .020-.030" would do it.

I could get that by reducing the base circle of my cam and get a more performance oriented grind in the process. Currently I have a 1.175" base circle, 1.020" minor diameter and 1,425" lobe for .250" lift (.400 at the valve) so if I reduced the lobe height by .030" to get clearance and then reduced the base circle to get lift back it would seem I could go as high as .490" at the valves and possibly even get a little more duration. Does this make sense?

Jim


MGBV8
Carl Floyd
Kingsport, TN
(2019 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
79 MGB, Buick 215

authors avatar
Re: cam option
Posted by: MGBV8
Date: September 05, 2008 12:11AM

The Chevy stroker guys say .050". The BIG stroke engines go with .080" due to crankshaft flex. I would use the smaller base circle cam as a last resort.



BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(4107 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: cam option
Posted by: BlownMGB-V8
Date: September 05, 2008 08:52AM

Thanks Carl, that really helps. I do think we're looking at last resorts here, the only other option is to mill down the shoulders of the rods and with them already finely balanced I just hate to do that, plus there isn't a whole lot to be gained there before getting into the threads. I may end up doing both though.

Disadvantages of a reduced base circle? Can't really be a strength thing since the weak points are the minor diameter and I wouldn't be changing that. It used to be pretty common practice to regrind cams. Even at .050" clearance I think there's still room for .500" lift and I don't expect to need more than that.

Jim


Dan Jones
Dan Jones
St. Louis, Missouri
(196 posts)

Registered:
07/21/2008 03:32PM

Main British Car:
1980 Triumph TR8 3.5L Rover V8

Re: cam option
Posted by: Dan Jones
Date: September 05, 2008 03:56PM

> Here I am thinking that it'd be an advantage to help the exhaust side
> since the intake is getting a boost (literally) and you up and say
> extended duration on the exhaust ain't all that great shakes.

Vizard's cam rules apply to normally aspirated engines.
Different rules apply to supercharged engines.

> But I'm looking for the practical solution. Something to let me take
> advantage of the Scat rods, Venolia pistons, CC springs and Eaton
> blower but keep the economy and driveability of the 10 to 11:1 CR.

You've got some mis-matched parts there that make specifying a cam
difficult. You're trying to vent a 340 cubic inch engine plus
boost through a 1.3" exhaust valve. You're limiting lobe lift
bacause of a rod clearance issue and your trying to run boost on
top of high compression on pump gas.

> Disadvantages of a reduced base circle?

Might be worth a call to Erson (Steve Tanzi) if Woody doesn't have
a call in for you already. If the cam core has been heat-treated
already, there is a limit to how far you can grind before breaking
through the heat treat.

Dan Jones


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(4107 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: cam option
Posted by: BlownMGB-V8
Date: September 05, 2008 08:49PM

I take it you disapprove. I don't mind that, but perhaps it would help a bit if you better understood where I'm coming from. To start with I really don't need more power than I have right now with the 215. I have other goals in mind. But since it *is* a 350 (340 + .050") I might as well bump it up a little. Did I state the power goal? 400hp is not a lot to ask from a 350, even normally aspirated. Why do I want it to turn 7 grand? Because I *like* it. Not because I expect a big power boost above 5000. Why am I putting a blower on it? To overcome the restriction of those small valves you mentioned. Why am I using such small valves? Two reasons, money and money. Gas and machine work. The high compression is also for the first of those two reasons, plus low end torque. The intercooler is for the low octane fuel. (Who said I was going to run regular in it? That would be a switch.) Also, I want a cast iron block, and I want to put a Buick 340 in my MGB.

This car may very well never see another drag strip, but it *will* be taking on the back roads of KY and West By God Virginny. For that I don't need as much power as I have now. Heck even without the blower this engine might blow the doors off the 215.

I do appreciate your comments. I would appreciate them even more if they were more to the point. I know quite well this is a challenging application. Convention has been thrown out the window. I'm on a quest here to get what *I* want and that's a long ways from the mainstream.

Jim


hoffbug
Tony Hoffer
Minnesota
(267 posts)

Registered:
10/15/2007 05:25PM

Main British Car:
Land rover 4.6 Buick 300 hybrid ( in progress)

Re: cam option
Posted by: hoffbug
Date: September 10, 2008 01:48PM

FYI..
Harold Brookshire former owner of Ultradyne and designer for Reed, Lunati, and others offered up this cam info.


I have a very reliable solid lifter cam of the following specs:

.020 282/292
.050 248/255
.200 155/162
valve lift, 1.6s
.536"/.551"
LCA as wanted...

This would be a healthy cam in an engine of that size...
It has gone over 100,000 miles in street SBCs, and needs the valves adjusted at least once a year.....
I also have much more aggressive solid lifter cam lobes.
The lowest lifts I have with rollers are about .550" with 1.5s.

Cores for the Buick 215/300/340 are available, but from a supplier.
It will take 5 to 7 working days to have in the shop.
Mike, who was my shop foreman at UltraDyne for 19 years, and who now is shop foreman and Landis operator at Lunati, reminded me that the cores do not have a lot of meat on them, and the cam will need to be ground straight-up, with no advance.
Costs? Around $220 right now.
If I can help, please let me know......

Harold Brookshire

662-562-4933


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(4107 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: cam option
Posted by: BlownMGB-V8
Date: September 10, 2008 04:31PM

Interesting. I don't really want to run a solid lifter cam because I have no provision for lash adjustment. Lift will have to be limited to .500 on a 1.020" base circle to leave .050" rod clearance. The cam used for inspection has a 109* LCA and .250" lift at the lobe. (.400 at the valve).

I would like to keep the intake lobe reasonably mild for good driveability and economy and run an agressive exhaust lobe to allow better evacuation of the cylinder under boost.

Jim
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