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Anybody have any data on which SB dual plane GM intake manifold flows the best in road race application ie High RPM (5000-8000). And any idea how the GM would compare to Edelbrock Performer(non air gap). Jerry
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Re: C2 small block intake flow rates
I don't have any flow rate data, but the Z-28/LT-1 manifold is probably the best dual plane SB manifold ever built. I doubt if any "modern" designs will do any better, but if you are serious about a 5000-8000 rev operating range, the engine will probably make better average power over that range with a race type single plane manifold.
Duke -
Re: C2 small block intake flow rates
if you use a dual plane and try to run at higher RPMs you will need to cut down the divider about 1". edelbrock performer are only good to about 5000/5500 RPM. to get to 8000 you will need a single plane intakeComment
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Re: C2 small block intake flow rates
I wish I could use a single plane but Vintage racing rules are rules. I thought there might be some old racer tricks or insight that might help me on this. Any clever old cheater tricks .It's really 5000- 8000.Comment
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Re: C2 small block intake flow rates
You are kidding about the rules, right? I've seen vintage Vettes with the Victor Jr the manifold of choice in what seems like forever.
I've even seen them plumbed with Holley injections systems and such. Running the LT1 manifold on mine actually made me more period-accurate than the vintage cars even though I was running in a current class.
The LT1 manifold is about as good as you will get for stock small block of any size, at least on the single four. This was the manifold of choice through much of the '70s when running Prod rules where they still had to use stock parts.
You can hog it out considerably to match ports and to increase volume if needed.
A 1 inch carb spacer plate, especially if non-metallic, will help.
Drill the rear water passage block-off plates and plumb them with 3/8th to the thermostat housing (you are using a Moroso housing right?). This equalizes the temperatures on the heads.
Block the heat cross-over at the heads.Comment
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Re: C2 small block intake flow rates
Assuming you're running a 3.25" stroke, 8000 revs is a mean piston speed of 4333 ft/min. If they make you run stock heads, I don't see how the engine will rev useably beyond about 7000-7500 no matter what manifold and cam you use.
Consider the 302 T/A engine with heavily reworked "stock" heads made peak power at about 7500 and was tapped out at 8000. With only a 3" stroke, mean piston speed at 8000 is only 4000 ft/min, but that was it because the heads were choked.
If you want to build a competitive engine within the rules get the Engine Analyser simulation program and some accurate flow numbers for your heads. Pay particular attention to the inlet Mach index and its relation to mean piston speed. Unless you are allowed to used some very high flowing modern aftermarket heads you will find that the heads are choked at a Mach index of about 0.550 at 4000 ft/min, and power falls off the proverbial cliff.
Doesn't matter if you are building a max performance street or racing engine. The bottom line is HEADS, HEADS, HEADS!!! And despite all the naysayers, my research indicates that a reworked '63-'65 FI system will make more power than any carb and dual plane manifold. The FI system is essentially a single plane manifold with a very generous sized plenum and large, efficient runners. The Air Meter can be reworked to flow 750 CFM @ 1.5" Hg.
Beyond that, I don't see how the engine will live in the dynamic environment of road racing at 5000-8000 with a conventional wet sump oiling system.
DukeComment
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Re: C2 small block intake flow rates
SVRA requires period correct intakes that are dual plane. There are many santioning bodies . Many are formula Libre, run what ya brung. Your suggestions on the intakeare good and I've done them. They helped. Thanks JerryComment
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Re: Intake trick
Jerry, The "trick" is to send your legal intake to Wilson porting with a check for $1000 and let HIM do his magic......HNComment
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Re: C2 small block intake flow rates
They may tap out at 7,000-7,500 but Smokey Yunick was turning them past 9,000 in 1968 and making unbelievable power.Dick WhittingtonComment
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Re: C2 small block intake flow rates
Very true, and we did also, but not in '68. My machinist/crew chief had probably 100 hours in on the heads, and we initally shifted at 9500. Initially, because while I have driven Mazdas at over 10,000, 9500 on a small block just seemed insane.
I held it at 8500 with a decent lifespan.Comment
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Re: C2 small block intake flow rates
They've tightened up. I knew a lot of SVRA guys that ran Victor Jr manifolds and even a few that had aluminum heads. Some of them painted the intake and heads orange to look "original".
Did SVRA have them remove the fender flares or are they still running those? What is SVRA running as the cut-off year now? The flare never became legal until '72 and only if they copied the original profile when viewed from the side. That means round flares like these were not legal in SCCA in '72.Comment
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Re: C2 small block intake flow rates
The Grand American team that I was a gofer fer pitted beside Smokey at the Paul Revere 250 in 1968. The tell-tale on that car would always show 9,500+ every time they came back in. It came back in one time at 10,200, but then again all that was salvageable from that trip was the carbs, water pump, and front pulleys. Came apart coming down the front straightaway and TOTALLY destroyed the engine. Block looked like a piece of Swiss Cheese, cam broke, both heads destroyed, and the crank looked like someone beat on it with a four pound hammer and chisel for several hours.
Smokey did not care if he had a car that ever won a race, as long as it was on the pole and lead one lap.Dick WhittingtonComment
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Re: C2 small block intake flow rates
I also agree with the LT-1, Z-28 manifold. Although I wasn't road racing, I did autocross and drag race with my 383 corvette. I had the Holley Z-28 copy, which was extensively ported along with the aluminum heads by Slovers porting in Los Angeles. I kept the rev limit at 7,000 only due to the nodular iron crank, it wanted to keep on going, it actually had a surge in power above 6,000 RPMComment
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Re: C2 small block intake flow rates
BTW, the engines at that time ran the factory cross rams (then again who knows what Smokey really had). Seems like if you wanted any good "stuff" for the 302's, it came out of "The Best D..n Garage in Town" in Daytona Beach.Dick WhittingtonComment
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Re: C2 small block intake flow rates
I've been there a few times. Amazing some of the "junk" laying around.
A lot was highly modified, although mostly internally so you wouldn't know when assembled.
I asked him once about my car, telling him it was gold over black once upon a time from the paint and some old pictures I got with it. He immediately dropped talking to others at the table and began with me. A few got annoyed and tried to interrupt and he just shut them down, saying he was talking to me then.
The car didn't have any connection to him, so he assumes someone just painted it that way as flattery long ago.Comment
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