Engine and Transmission Tech

While we won this past weekend we realize that we need more power in the GT2 RV8. Since we're forced to run a small restrictor plate under the carb, it seems that cam timing would't be all that helpfull, so looking at compression to bring the HP numbers up. What's the realistic limit on compression for the Rover V8 that the head bolts and gaskets will live with? We're running around 11:1 currently. How high can we go with out shrouding the valves with piston dome or blowing the head gaskets out routinely and still run no more than 112 octane racing gas.

IMHO, a more effective cam and valvetrain would "still" increase the dynamic compresson, being even more imprortant than static compression. To hold that pressure, Cometic MLS gaskets should work best, in lieu of "o-rings". You can't/woun't use five-six bolt configuration ? From my experiaence, the "fifth bolt" helps because that is the weakest side of head,(exhaust heat).What is the cc's of current head ? Should take maybe .125" pop up to make 13/1? 13/1 will burn faster than 11/1 = less end gas/detonation, with 112 octane. Using a restrictor plate, you need to increase the "fill window"/ flow under the curve. Faster intake lobe ramps,(roller) and duration should help. One of those trick "anti-reversion plates", under your restrictor, along with well designed stepped primaries on hedders, if allowed, should help. While your dual plane intake is helping low end torque, I suspect it's hurting the inlet fill, even more on top, because of the restrictor plate ? Without skilled dyno time, developement is difficult, at best. Good Luck, roverman.



Edited 2 time(s). Last edit at 05/07/2012 02:02PM by roverman.

Les Gonda admitted to about 13.5:1 (static) when I interviewed him.

His engines are reliable - he's invested a lot of development time and money into getting them that way! I'd suggest getting friendly with Les and with his engine builder, Abacus Racing in Virginia Beach. Understandably, they may be inclined to keep a few cards close to their chests although generally I've found them to be extremely helpful and generous with information.

Compression,Compression, Compression!
Run as much as you can. Restrictor plates tend to lean out the engine on the topend. This slows down the flame front letting you raise the compression much higher than an unrestricted engine. As a rough guess with aluminum heads and the right cam, 14.5 or 15 to one.
Helicoil the block and use head studs. "o" ring the head and the block making the head "o" ring circle slightly larger dia than the block one. This locks the gasket and head in one place.
Camshaft choice is going to become critical. You want lots of duration to fill the cylinders but you are rpm limited so you need to build the fattest torque plateau that you can. The small intake ports are actually an advantage here. I'm thinking 235/240 @ .050 or less. Some dyno time would be a huge asset.
Cold air to the carb and cooling the intake are important on a restricted engine. So is a really good ign to fire the lean mixtures.
Make sure your carb is set up to run with some vacuum at WOT (just like a blower engine) you don't want the power valve closing or the metering rods dropping and leaning out the engine.
Carb placement is going to matter as fuel distribution will be upset. No one said that the carb needs to be straight on the manifold.
Angle mill the heads if you are allowed, this will get you more quench area and unshroud the exhaust some.
The engine will become more sensitive to exhaust tuning and some experimentation will be needed.
Running a "hot" engine will get you some power as long as the intake is cold. 180 to 190' is a good target.
Divorce the thermostat housing from the intake and insulate the manifold from the heads. Either with a stack of gaskets or a spacer of some sort. Insulate the bolt holes with nylon tophats.
Thats all I got at the moment.

Cheers
Fred

With 8:1 static I was running 16+psi boost (roots, experimental intercooler) and at that level was having some compression related issues. The worst problem was that the head bolts were pulling out, even with double helicoils (stacked) and Olds heads. I'm sure studs would have helped, but how much I don't know. This was also a GM block and a Rover block may be stronger. So anyway, what's that work out to, about 16:1 or near thereabouts?

Jim

I like "Timeserts", a 1 piece, flanged thread insert. IMHO, the best. I suggest Dan Jones and his "Dynamation" for optimum cam selection. Good Luck, roverman.

Okay, here's more opinion than you've asked for:

For the time being, it probably makes sense to run the engine as-is while you develop the chassis. When you're really ready to spend money on the engine, do it once and do it right.

Compression ratio is one thing... but displacement is your real disadvantage!

At 3.5L, you're not going to be competitive at the runoffs in GT2. Period. Go, have fun, learn from the experience, but don't go with unrealistic expectations. Consider that SCCA GT2 racer Tom Patton's Sunbeam Tiger is allowed to run a 260cid/4260cc Ford V8, right? That's over twenty percent more displacement!

The 3.5L displacement limit SCCA has given you is unfair, and you have a very legitimate reason to petition SCCA to change it. Now that you're fully committed (actually running races) and now that other people are considering building GT2 RV8s, SCCA has reason to take your petition seriously.

Every single production MG RV8 came with a 3.9L engine. (Specifically: 3.702"/94.0mm bore by 2.800"/71.12mm stroke = 3947cc.) Logically, 3.9L should be the displacement for MG RV8 racecars!


Actually, you might even be able to justify an even larger displacement. Early in the RV8 production period, Rover introduced a 4.2L version of their aluminum V8 for U.S. market RangeRovers. (3.702/94.0mm bore by 3.03/77.00mm stroke = 4275cc.) Later in the production period, Rover introduced 4.0 and 4.6L engines. I don't know if you could make a case for SCCA allowing any of those displacements, but it's something to keep in mind.

Of course it would be a huge help of SCCA would remove or at least enlarge your restrictor plate...



Edited 1 time(s). Last edit at 05/09/2012 03:50PM by Moderator.

A 390 cfm. "resrictor carb" should be adequate restriction. SCCA is having serious trouble geting enough entries. They need to consider making it worthwhile to potential racers and spectators. More entries should produce more spectators. Good Luck, roverman.

I did a brief search on the SCCA rules and also saw a British V8 entry on your
build spec. I'm not sure if I got rules right or your build spec has changed
so correct me if I've made any erroneous assumptions.

> While we won this past weekend we realize that we need more power in the GT2
> RV8. Since we're forced to run a small restrictor plate under the carb, it
> seems that cam timing would't be all that helpful, so looking at compression
> to bring the HP numbers up.

What are your current cam specs? It appears:

"7. Any cam followers may be used, except that roller cam followers shall not
be used unless fitted as standard equipment."

Small port heads respond to steep ramp rates. The ramp rate is limited by
the diameter of lifter and unfortunately the Rover uses the GM lifter diameter
which is the smallest of the big three. You could bore the lifter bores to
accept either Ford or Mopar lifters but even better would be mushroom lifters
which do not appear to be excluded by the rules. For your engine, mushroom
lifters would likely outperform rollers as they accelerate off the seats more
quickly.

"8. Any rocker arms and rocker assembly supports may be used."

It would be worthwhile to experiment on a dyno with a shorter exhaust rocker
ratio. We've found better average power with about a point shorter exhaust
rocker ratio but it depends upon the head flow characteristics.

"Alternate induction: Holley P/N 0-80507-1 (390 CFM) on unrestricted manifold
with a mandatory plate between the carburetor and plenum of 0.060" flat steel
or aluminum plate with four (4) 1 1/16" holes. Spacer is unrestricted. The
restrictor plate shall be positioned within 4" of the throttle butterflies.
All inducted air shall pass through the specified restrictor plate."

Holley makes several 390 CFM carbs. The one pictured on your car has side
hung floats and appears to be a list number 8007. List number 80507 is a
very different carb. It's a 4150HP model meant for carb-restricted racing
applications. It does not have a choke tower and has a streamlined venturi
inlet, so flows more than a standard 8007 390. It also has progressive
mechanical secondaries, four-corner idle system, center hung (better for
cornering) dominator style fuel bowls with notched floats and jet extensions,
screw-in air bleeds and double 30cc accelerator pumps. Someone with experience
tweaking these carbs for use with restrictor plates like Bobby Oliver at
Competition Carburetor would be worth contacting. You'll want to duct cold
air to the carb, preferably from an area of high (dynamic) pressure. Vizard
has some very good information on barrier coating an intake manifold. Given
that your intake manifold is unrestricted, you'll want to run a Willpower,
Harcourt or Huffaker single plane intake manifold.

"9. Valve sizes are unrestricted except when limited by the GTCS for specific
automobiles. Centerlines shall not be altered."

It sounds like ported, large valve heads are permitted.

> We're running around 11:1 currently.

Was that calculated or did you infer from published specs for GM 215s?
The latter were somewhat inflated. I assume you currently have flat top
pistons, along with a zero decked block and/or milled heads?

> How high can we go with out shrouding the valves with piston dome

Shrouding the valves isn't typically a problem. The problem is the dome
impeding the combustion flame front. When the dome becomes large enough,
there's a trade-off where combustion efficiency drops off more quickly than
the gain from the increase in compression.

> 13/1 will burn faster than 11/1

Remember that higher octane fuel burns more slowly, as does a lean mixture.

The pictures of your headers show them to be shorty style which give up a
lot of area under the curve. The Pipemax exhaust design software can help
optimize a header design but you must feed it accurate information.

Dan Jones

Great information Dan, thanks. Didn't know about the optional Holly carb, but we removed the choke housing from this carb and did what we could to smooth out the air entrance. A cold air feed is in the works, just waiting on a new hood to be fabricated with a larger bulge to clear the carb adaptor, air will come through a oiled paper filter on the left side of the grill opening. Should be a positive pressure area. Can't say for sure what type of pistons we have or the head cut, got the 11:1 figure from Bill Davidson our engine man. Don't know how he calculated that, but he does seem to know what he's doing. This was basically a pretty stock "mule motor" we put together to sort out the chassis and now we need to start on a true race motor for later this year or next season. We still have so much to learn, just a bunch of real amatures at this point when it comes to really building a race car and engine, but we're learning as fast as we can. Having some experienced racers helping makes a lot of difference as well, We wouldn't be nearly as far along on the chassis without the help of Clancy Schmidt who has really helped fabricate the car and set it up for competition. We should be getting it on a chassis dyno later this month so I'll have some real numbers to pass on at that time.

Dan I hope your accessment of the rules hold up. Talking to Phil a while back about his next engine build, he had some real concerns about even the slighest variation to the heads still being legal. I suggested resleeving a 4 bolt main Rover to the smaller piston bore he would need to maintain in his class. This would give him some higher rpm capabilty wouldn't it? Can they juggle some stroke vs bore to their advantage? Could you predict potential hp for a fully optimized engine if the rule book stands as you read them? Phil and Bill are thinking they make around 200 hp now at fw I believe.

Of course there is all that gearing stuff!!!!

Guys let me know if I can help track down any parts for you.

dave bash mo faster

My GT-1 Huffaker TR 8 came with a 215 Buick block, built to 4L. Stock cast crank, Carrillo rods, 1" thick main girdle and "lived" at 8 grand,(not continuous).Joe Huffaker said this build dynoed at 350hp,(no dyno sheet). Ken Slagel ran a 3.1" billet crank and a 3.54" bore ? I suspect this was for more torque, off of the turns. SCCA needs to re-consider the " limit for this application. Onward, roverman.