MG Sports Cars

engine swaps and other performance upgrades, plus "factory" and Costello V8s

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BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5830 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: 340 upgrade
Posted by: BlownMGB-V8
Date: May 28, 2008 09:17AM

No reply from Art, guess I'll have to call him.

We got back from Nashville with the Jag IRS for the roadster over the weekend. It's an '81 from an XJ6 and has 2.88 gears and posi, at least the wheels both turn the same way when I turn one so it looks like it does. Haven't verified with the tag yet. Everything appears to be in pretty good shape. Brake rotors are not worn noticeably, brake pads look good, worn down maybe 1/3 and e-brake pads don't look worn at all. A little grease/grime at the pivot points but not excessive. So I think I got good value and it should break down as expected. Looks like a unit from a low mileage car. I pressure washed off the worst of the grime and the rest isn't much. Have to get it broken down in the next day or two so it can be narrowed concurrently with the one for the Roadmaster. I'd say if you buy one of these take your time and find a good one, it'll pay off. I may not end up using the 2.88 gears but I'll probably start out with them and see how the car runs.

Jim


V6 Midget
Bill Young
Kansas City, MO
(1337 posts)

Registered:
10/23/2007 09:23AM

Main British Car:
'73 MG Midget V6 , '59 MGA I6 2.8 GM, 4.0 Jeep

authors avatar
Re: 340 upgrade
Posted by: V6 Midget
Date: May 28, 2008 10:51AM

Sounds like a good rear for your car. I think you'll probably have to change the 2.88s. With a 25 to 26 inch rear tire you'd only be turning around 1800 rpm with a V8 type T5. With an automatic I don't know, don't have the overdrive ratio for that one. I had a 2.78 rear in the Midget with the V6 T5 and had to change it out to a lower ratio, was turning so low on the highway that it would bog on the hills a bit. Installed a 3.43 and it's much better, but around a 3.27 would be ideal. About the same for your combination I would think. I found this calculator on line that really helps me figure out what gears I need to use to match the tire and trans combination. [www.f-body.org] It already has the GM and a lot of other transmissions preprogrammed which helps a lot.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5830 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: 340 upgrade
Posted by: BlownMGB-V8
Date: May 28, 2008 12:09PM

Looks like 71@1800rpm's Bill. Could be a little slow, but with the 340 and the blower I just might have the torque to get away with it. A lot would depend on what I end up with for shift control. I now have a spare Megasquirt controller since I'm scrapping out the old I-H truck and I could probably use that to control shift solenoids and line pressure. That has me wondering what else I really need other than accumulators. There's lots of passages in a valve body but if it's under computer control much of that should be redundant or unnecessary I'd think. I've worked with hydraulics and with air logic, even done some hydraulic design. Maybe it's time to consider building a computer interface. The megasquirt could control the lock-up clutch too, should be able to treat it as another gear or as a splitter shift in 3rd and 4th (2nd maybe, not sure about that). The idea would be for automatic function at part throttle and paddles that give a ratchet-shift type function overriding the auto control. I haven't forgotten about the pseudo "clutch" function either, it's good to be able to disengage the driveline if you overcook it in the corners.

Anyway, I'm still waiting for the final damages on the heads, have to tear down and reassemble the short block, and build a blower intake. So it ain't happening today, and tomorrow don't look good either.

Jim


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5830 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: 340 upgrade
Posted by: BlownMGB-V8
Date: June 05, 2008 01:32AM

I've gotten some work done on the Jag IRS, got it mostly broken down but one of the hub splines is resisting my advances. Well I've been meaning to hook up a hydraulic unit to the press which will give it more umph and it looks like I'll have to do that before I go any further. In the meantime here are a couple of photos.

MVC-614S.JPG

The next one shows a stock Jag cage in the MG location.

MVC-615S.JPG

Not a terribly good fit.

Jim


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5830 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: 340 upgrade
Posted by: BlownMGB-V8
Date: July 03, 2008 06:33PM

I'm happy to be able to say I've made some more progress on the 340 build. Dale Spooner (Motion Machine in Danville, Va) finished up the head work sooner than I expected and shipped them to me. I'll say one thing for Dale, he does mighty good work. He pressure checked the castings, installed bronze sleeves in the valve guides, and machined the guides for Rover style seals.
MVC-680S.JPG
MVC-681S.JPG
Plus as you can see doing a nice job of bead blasting.
I've been working on assembly. I removed the good valve springs from my old Buick 215 heads and will use them, I just have to decide on how much preload to give them. Seated pressure will be in the range of 80-100 lbs but which end of the range depends on installed height. I've lost the specs and CC no longer sells that cam they came with as an off the shelf item. So I did a little testing'

Installed height in the 215 heads was 1.625" and at that height the spring pressure is just over 80 lbs. At 1.600 it's around 100. I have to get some more shim washers to get uniform heights (within.016") but I can easily hit that range, the question being whether I should aim more for the high end or the low end. Less pressure means longer cam life, while more means more rev potential. The 215 was good for 7 grand without valve float but the valves were a little smaller and therefore lighter, however I don't expect the engine to ever go over 6500, though I do like a comfortable safety margin. I'll admit it's a little nit picky but as long as I'm doing it I might as well optimize it where I can.

I made this neat little valve spring micrometer out of an old motorcycle fork tube end and plug. It has 1.0mm threads so that's .040" per turn. I made an index mark at 1.600 and another at 1.625" and filed a flat in the first exposed thread for a reference. It works real slick. I don't really need the other graduations since 1/64 is probably the thinnest shim washer anyway and I can guestimate in between the marks pretty well. I'll post a photo of that tomorrow.

Jim


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5830 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: 340 upgrade
Posted by: BlownMGB-V8
Date: July 04, 2008 02:28PM

Here are a couple shots of my homemade valve spring micrometer.

MVC-684S.JPG
MVC-683S.JPG

I decided to go ahead and put the valve springs in using the shims I had. It gives me a range of installed heights between 1.610 and 1.630 which puts me between 80 and 90 lbs on seated pressure. That should be just fine. The depth Dale cut the seal seats to, gives me a max lift of .540 which should be more than I'll ever need. I haven't checked the coil bind height yet but I think that'll be fine too. I plan to run a near stock cam in this engine, but if I do anything different from that it'll be a custom grind with more lift on the exhaust side and possibly less overlap. Anyway here's a shot of the heads with the valvecovers in place.

MVC-685S.JPG

I'm not real sure what the compression will be on this motor but it will be up there I think. More work to do on that. Since the heads have been decked I should cc them but the nominal chamber size is 54. The block has the 10-1/4:1 pistons but the pistons in my high compression 215 Buick block come closer to the deck and it had 37 cc heads, and a slightly smaller dish so it'll be hard to say until I take volume measurements. The increase in bore size makes a difference too. Then the block needs to be disassembled and checked, then reassembled using better fasteners. The ones the reman company used were a mix-n-match set and I'm not real big on mismatched parts, plus going with ARP might add some strength where it will do some good.

Jim


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5830 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: 340 upgrade
Posted by: BlownMGB-V8
Date: July 11, 2008 12:08AM

I cc'd the chamber and piston today, got 52cc for the chamber (it has been milled) and 22cc for the bore, so going online to a CR calculator it looks like my ratio with these pistons will be between 9-1/2 and 10:1 depending on what I use for head gaskets. Over on the V8Buick board they've got a group buy going for MLS (multi-layer steel) head gaskets for the 350 and I inquired if they could be used for this engine. Should handle the sealing tasks well enough, but there also may be a combo available that uses a sealed pressurized tube as the compression seal. More expensive of course but a permanent solution. With the blower it could be a good idea. I'll post when I have prices.

The heads and valve covers are painted, I used clear engine enamel which gives a sort of dark grey color to the beadblasted aluminum but it should stay cleaner. The rocker shafts from my first 215 Buick still look practically new and they're cleaned up and ready to install. Now the way is clear to begin teardown and reassembly of the 340. One of the big advantages of an iron block is that I needn't be too concerned about the threads in the block, particularly for the main caps and the head bolts. I will however need to be sure I have some thick heat treated washers for the head bolts, and studs might not be a bad idea. Well, I'll get to play with that some after the V8 meet.

Jim



BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5830 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: 340 upgrade
Posted by: BlownMGB-V8
Date: July 20, 2008 11:33PM

Some new info from TA Performance:
"Once the 455 block is done we will start working on the rest of the projects that we have planned which include 350 heads and SP intake." (7-16-08)
"The order that I know of from talking with dad is 455 Block, Rover head (and possibly a new version of the V6 head based off of the Rover head), 350 head, 350 SP intake."

So it seems we'll be getting some new choices reasonably soon. The "Rover" head design is to be based on the successful TA Buick V6 head design (currently capable of 1700 hp in twin turbo racing trim), so it's interesting to see that they are considering doing a new V6 design at the same time. This is likely to be a VERY exceptional head. Expect to pay somewhere around say $2500 a set complete. Quite competitive with Wildcat. Plus it should be possible to put the "Rover" heads on the Buick 350 block.

I have the teardown table set up and am ready to disassemble the short block. Since this was a new reman everything should go smoothly and the biggest decisions I face are whether to try getting a set of forged pistons for it, what cam to use, and what fasteners. Like Carl, I really like a free winding engine and the temptation to go with forged pistons is huge. Getting them might be another matter entirely. Luckily for me I have no deadlines.

Jim


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5830 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: 340 upgrade
Posted by: BlownMGB-V8
Date: July 21, 2008 08:44PM

Running into a bit of trouble on the reman 340 short block, basically shoddy workmanship and mismatched/damaged parts. It's unfortunate, and promises to be expensive to fix. Well, at least I'm glad I didn't put it together like that. I'm back to looking at my options, one of which is to go with a seasoned 350 and start from scratch, fit it with the early cam using adapter bearings and use the 300 heads. At least (forged) pistons would be easier to find, the rods would match, the crank should be undamaged, the cam and crank bores should be straight, etc. It's a setback that I'm not at all happy about but in the long run it could be a benefit if I can show how to use a 350 Buick as the foundation for a BOP/R swap. Anybody got a good running old 350 Buick they want to sell cheap?

Jim


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5830 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: 340 upgrade
Posted by: BlownMGB-V8
Date: July 22, 2008 01:21PM

Turns out I have a spare 340 crank and 6 rods so using this block depends mostly on the straightness of the cam bores, though I will continue to look for a good running 350 Buick because... they are a little lighter, a little bigger, and a LOT more common. I would need adapter cam bearings to be able to use the early cam and will report cost and source for those when I have it. Today I pick up a 350 head gasket and will report back on how it matches up with the 300 head. I will be fabricating an intake but for others, the solution is to use an intake for one of the smaller engines and spacer plates. The exhaust will remain unchanged. Then in a year or so when TA brings out their new Rover style heads that would be a bolt-on swap.

So how about that guys? Big flow aluminum heads that fit a Buick 350 short block and use the RV8 style headers? An aluminum intake couldn't be that far behind.

Jim


MG four six eight
Bill Jacobson
Wa state
(299 posts)

Registered:
10/23/2007 02:15AM

Main British Car:
73 MGB Buick 215, Eaton/GM supercharger

Re: 340 upgrade
Posted by: MG four six eight
Date: July 30, 2008 01:15AM

Jim

Any thoughts of using those ported 300 heads on a Rover 4.6L block? With it's cross-bolted main line and a head stud kit, I would think it should handle a fair amount of boost. :-)

Bill


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5830 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: 340 upgrade
Posted by: BlownMGB-V8
Date: July 30, 2008 10:18AM

I think that would work just fine Bill. But the 340 represents a very inexpensive upgrade to 5.7L size. The weight penalty is offset by extra strength in the block as well, and no worries of pulled out threads.

Incidentally, it appears that use of a 350 block will probably require a custom grind cam since 340/300/215 pusrods are splayed to clear the two center ports and 350 pushrods are splayed to clear paired intakes between the front pair and the back pair. Only the cam maker would know for sure.

Jim


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5830 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: 340 upgrade
Posted by: BlownMGB-V8
Date: August 19, 2008 08:02PM

More changes. I've been very disappointed with the quality of the reman 340 and have decided not to use the crank, rods or pistons. There's just too much damage and mismatch to satisfy me. Instead I'll use a spare crank I have on hand and get it cleaned up .010 under by a reputable shop, and after a lot of investigation I've settled on a set of rods and pistons. It turns out that good used NASCAR rods can be had for anywhere from 100-400 bucks a set, but they tend to be either too short, too wide, or have too small or too large of a big end. The rods used in the 340 are a whopping 6.4" long. It looked like I'd have to cut down a set of SBC take outs, IF I could find them in a 6.4 or 6.5" length. That was before I talked to the Venolia rep. During that discussion it came to light that the Buick has a pin height considerably longer than what they like to see for custom pistons. At I think 1.85", there's plenty of room to get it down to the 1.2-1.3" height they more commonly see. And Venolia custom forged slugs can be had for $73 each. That may sound like a lot but it buys great peace of mind, its a couple hundred less than what I've been seeing for the set, and it'd be a shame to spoil the engine for want of a few hundred bucks. (To paraphrase Barrie Robinson)

Well, that really opened up the rod choices (not much) because Venolia had some leeway in where to put the pins so I began anew looking at rods, and I came across 3 sets of NEW H-beam forged and fully machined rods in a 7" length on ebay for $359 a set. The cake on the icing was that these rods used a *Buick* rod bearing insert. When I checked I learned that they use the bearings that fit the V6 Buick, meaning the exact same ones as used in the SBB! Further that meant a pin height of about 1.25, right in the recommended range. The only possible downside seems to be that the piston pins are a .750" diameter, and there is some question about Buick rods using a .094" offset, still not sure what that refers to. It was really more than I wanted to pay, but with those rods and pistons the bottom end would be darned near bullet proof and, well it'd be a shame to ruin the engine for want of a few hundred dollars... So I ordered them.

What are these mystery rods? Flathead Ford! Regularly available for around $500 a set and sometimes for less. So with that I've significantly increased the cost of my engine but I've also significantly increased both reliability and performance potential. Don't know why I'd need the performance, it's not like I drive it that hard or anything but I guess it'll be good insurance. Having an extra thousand or so on the redline could be fun too, I already know the valve springs can handle it.

So when the rods come in I'll check to make sure they won't hit the cam, enlarge the oil pickup holes in the block and then it'll be time to send it out for fine tuning. Probably the bore will go to about .050 over to square them up, deck the block, align hone the mains and check the cam bores for straightness, then order the pistons, have the crank ground and everything balanced. By the time that's done it'll no longer be such a "cheap upgrade" but it'll be no worse than a comparable chevy or ford of like displacement, especially when considering what it would cost to change over. Displacement should be 350 cu.in.

Jim


MGBV8
Carl Floyd
Kingsport, TN
(3789 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB, Buick 215

authors avatar
Re: 340 upgrade
Posted by: MGBV8
Date: August 26, 2008 11:27AM

Quote:
and there is some question about Buick rods using a .094" offset, still not sure what that refers to...

I think they have confused offset rods with wrist pin offset.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5830 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: 340 upgrade
Posted by: BlownMGB-V8
Date: September 03, 2008 11:54PM

I believe Carl is correct.

The rods finally came in and they are some fine pieces.

MVC-733S.JPG

I fit one up to the crank to check the cam clearance and it looks like a little work is going to be needed on the end of the threaded boss for the upper rod capscrew.

MVC-735S.JPG

There should be just enough meat there to get clearance, but that is with a stock cam so I'll be limited on lift. Good thing I'm putting a blower on it. One other alteration that's needed is the squirt hole for lubricating the cam lobes. As you can see in this last shot there is none, but I'm thinking about a 1/16" hole drilled straight through at the parting line should do the trick.

MVC-734S.JPG

Jim



Citron
Stephen DeGroat
Lugoff, SC
(365 posts)

Registered:
10/23/2007 09:43PM

Main British Car:
1970 MGBGT V6, 7004R, AC, matching trailer 3.1 liter

Re: 340 upgrade
Posted by: Citron
Date: September 05, 2008 09:22PM

We Chevy strokers use a cam ground on a smaller base circle to get the rod clearance. Could you do that?
I have built 3 Chevy 383 using the small base circle cams from Comp Cams.
No problems so far.

Steve


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5830 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: 340 upgrade
Posted by: BlownMGB-V8
Date: September 08, 2008 08:11PM

That's a good idea Steve. It looks like I'll be doing that plus clearancing the rods. In fact I've already done most of the work that the rods needed. First, there was no oil spurt hole so I used a 1/16" zip wheel to cut the hole and a countersink to cut a pathway around the alignment dowell for the oil to find its way out.

MVC-739S.JPG

MVC-742S.JPG

Then there were two cylinders where there was serious interference with the cam, that would be on #6 and 8 cylinders. There was no way that just a reduced base circle cam was going to do the trick. But by knocking the corner off the shoulder of the rod I got them to clear and the reduced base circle cam will give the needed clearance. All 8 rods were machined the same.

MVC-749S.JPG

Then the upper rod bolt had to get a large chamfer to clear so I made up a fixture and cut them on the lathe.

MVC-748S.JPG

Finally, the big end is .023" wider than the stock rod so I will need to machine them down just a bit. Then they will go to Dale for resizing and balancing. Dale clued me in that most of the Scat and Eagle rods he sees are improperly torqued when honed from the factory so these may need some rework. Rather do it now than later.

Out of curiosity we put them on the shipping scale to compare to the stock rods and the weight was the same. I would not have thought so but how are you going to argue with a digital scale? Of course on these rods the weight is concentrated at the big end whereas the stock rod has a very heavy beam and top end and much less beef at the bottom.

Jim


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5830 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: 340 upgrade
Posted by: BlownMGB-V8
Date: September 16, 2008 02:32PM

Well the parts are on their way to Dale Spooner. Carl was gracious enough to help in transporting them, even going so far as to ride home from Townsend with an iron 340 block sitting in his passenger seat and other parts packed in around it. I'd say he had the weight of a passenger about my size riding with him. Hope it didn't slow you down too much getting over the ridge Carl.

Dale will take it from Carl's house up to his shop, where the rods will be narrowed and honed, the crank ground, and the block cleaned up where needed, probably including align hone, deck and hone, and cam bearings installed. Then I'll order the pistons from Venolia and Dale will balance the works. Maybe by spring the engine will be together and I can concentrate on the tranny.

In the meantime I need to complete the Jag IRS and get it installed. Of course, first is the 215 swap so I at least can drive it.

Plenty to do.

Jim


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5830 posts)

Registered:
10/23/2007 12:59PM

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

authors avatar
Re: 340 upgrade
Posted by: BlownMGB-V8
Date: September 17, 2008 12:07PM

So now, some more news on the blown up 215 Olds. The heads are off and there is only one place showing obvious damage.

MVC-783S.JPG

MVC-784S.JPG

The edge of one piston is missing above the top ring. I would attribute this to gradual erosion of the piston crown rather than breakage or melting based on the slight but similar damage seen at the same spot the last time the heads were off. At that time it wasn't considered severe enough to replace the piston, but clearly under the stress of repeated excursions into coolant temps around 220* the erosion has accelerated to the failure point. No doubt a combination of weakening due to elevated temperatures and mechanical separation from piston and ring reversals. It seems probable that cylinder damage will be slight or non-existant and with minimal wear just breaking the glaze should be enough to put the block back into service. Why this effect was localized to this one cylinder I do not know, as there are no indications that it was running hotter than any of the others. Why did this result in the crankcase explosion? The only explanation that comes to mind is that this cylinder fouled the plug (causing the miss noted by Dan) at which point blowby began filling the crankcase and was ultimately lit off by a backfire through the induction system and back down through the crankcase inlet vent tube which had no flame arrestor and was connected to the blower inlet. Bit of a design deficiency there it appears. That will be corrected.

But the head gaskets do tell the tale. Looking closely at the locations indicated by arrows it can be seen that there was indeed leakage of combustion gasses in a number of places, and the light areas which indicate the areas of maximum clamping force, clearly display an unbalance, with less pressure in the areas between the cylinders and even less at the ends. There are signs of obvious leakage, but no damage to heads, block or gaskets. Discoloration out into the area surrounding the cylinder bore clearly indicates a leakage pattern well out onto the deck. This type of gasket would benefit greatly from the use of o-rings, but the new MLS type gasket should suffice. Also, spot-facing the deck or heads at the two center rows of bolt holes would move the clamping force outwards and might yield a noticeable benefit, but this would not help the ends where the problem is the worst.

MVC-781S.JPG

MVC-782S.JPG

Overall, it would appear that with adequate sealing and the resultant proper control of coolant temperatures piston damage could be avoided. This, with 8.5:1 compression and 16+lbs of intercooled boost from the roots type blower is actually a very excellent result considering the pistons are cast low performance replacements. Much better than the gaping hole I was expecting to see.

Now if this experience can be extrapolated to the 340 build, there is reason to hope that the forged Venolia pistons will hold up much better. A little quick mental math might help. Assuming 100% volumetric efficiency, 16lbs of boost gives double the normal cylinder filling, therefore double the normal compression ratio of 8.5, or 17:1 in this case. Pretty darned good for a cast piston but if not for the restrictive intake and intercooling the motor would have been gone long ago. With the 340, at 8psi we have 1-1/2 times normal filling so working backwards, 17:1 divided by that gives about 11-1/3:1 compression. I'm shooting for10-1/2 to 11 and 6-8psi so I should be right in the zone, provided I scale up the intake system accordingly. I believe I have done that with the alloy 300 heads and stock valves on the 340 block. Cam selection is still up for grabs though. If I were to stay consistent I would use the stock cam, but if I can optimize that for economy I could end up with a potent package that gets very good mileage. I do not think that goal is inconsistent with good blower performance. Getting the redline up though may be another matter entirely.

What makes it difficult is that so far as I know there is nobody else pursuing this approach to blower use. It is unconventional and plays by different rules. It seeks to achieve goals outside the normal high performance envelope in that while I am seeking maximum performance under the curve, I am also seeking maximum economy just as aggressively and 8:1 compression just can't provide those results, no matter how good your blower is. So far the results have been encouraging, but I really need to find an open minded cam grinder to get the most from the combination.

Jim


Dan B
Dan Blackwood
South Charleston, WV
(972 posts)

Registered:
11/06/2007 01:55PM

Main British Car:
1966 TR4A, 1980 TR7 Multiport EFI MegaSquirt on the TR4A. Lexus V8 pl

authors avatar
Re: 340 upgrade
Posted by: Dan B
Date: September 17, 2008 03:53PM

Certainly not as bad as I expected.
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