Induction Wars

[Joe C.]

IF: The 1963 L76 and L84 were identical in every way, EXCEPT the induction system.

AND: The 1964-65 L76 and L84 were identical in every way EXCEPT the induction system.

THEN: Why is there a 20hp diff between the '63 L76 & L84, and a 20hp diff between the 64-65 L76 & L84?

To suggest an answer to my own question, the diff must lie in the designs of the respective carb/intake manifold sets used in 63 vs. 64-65, assuming that there were no differences in the FI units used in 63 vs 64-65.
Am I on the right track? Were there differences in the FI units(other than possible recalibration for 30-30 vs Duntov sticks), as well as the Carter vs Holley setup, and the different intakes used with the carburetted engines?

[Joe C.]

Correction

make that 10hp not 20hp diff for 1964-65

[William C.]

Re: Correction

You are overlooking the improved flow capability of the Holley carb used in '64-65 on the 365 hp engines as compared to the afb in '63. The Holley got the carbureted engine a lot closer to the FI as compared to the AFB.

[Joe C.]

Re: Correction

Bill:

Thanks for the response. Yes, I know that the diff lies primarily in the Holley vs the AFB. But what is the DESIGN diff that causes this. Were the Holley bores larger to allow more flow? The Holley (7818) was rated @ 550 CFM--what was the Carter rated at? Was the intake manifold a complete redesign, or just a matter of adjusting the bolt pattern, etc to accomodate the Holley?

Joe

[William C.]

Re: Correction

Manifold design is very similar, primarily limited by the hood height available on the Corvette. Holley is a 585 CFM carb, as I remember the AFB is about a 500CFM unit. I know you can feel the difference in the seat of the pants if you replace the AFB with a Holley, been there done that circa 1967 or so...

[Duke W.]

Re: Correction

Keep in mind that there was as much marketing input into advertised HP ratings back then as technical input.

On paper FI should make more power due to a more efficient manifold, no manifold heating, better fuel distribution, and cold air induction. AFB is rated at 550 CFM at 1.5" Hg. versus 585 for the Holley, eventhough the Holley has less throttle bore area. I think the FI air meter flows about 600 CFM, but have never seen actual test data or specs.

From my own experience with rolling start runoffs - my L-76 SWC against FI cars - we were always about dead even.

Duke

[Mike M.]

Re: Correction

duke: had long talk with frank scibica a couple of years before his demise concerning air flow of rochester fi airmeters. frank related that they all flowed 585 cfm. if one were to space the cone out about 1/8" (as i recall) frank said they got close to 600 cfm during r + d during his years with Rochester. i tried the cone spacing on my 57 fi(the cheating one) and i couldn't tell much, if any difference in ets. mike

[Duke W.]

More air meter questions

Thanks for the info, Mike. I believe the design changes over the years improved air flow. I recall that the Dolza, et al. SAE paper mentioned "24 pounds per minute", but without a pressure drop, a quoted flow rate has no meaning.

If you or anyone else who has some air meters laying around, could you measure the throttle bore outlet. I believe it's about three inches, but I'm not sure if it increased over the years.

If you have one you could measure, be sure to mention the vintage.

Duke

[Joe C.]

Re: More air meter questions

Duke:

Far as I am concerned, much of this HP rating game is a marketing scheme. My gut tells me that there is little, if any difference between the FI/Holley/AFB induction systems. This is all moot unless someone can produce actual flowrates vs pressure drop graphs, as well as peak horsepower vs RPM graphs.
My feeling has always been KISS (keep it simple stupid), so that is why I prefer a carburetted engine over a fuel injected model, circa 1957-1965. The Rochester unit, far as I understand it, was just too finicky----if it got out of whack, then you need(ed) a guru to fix it. Carbs, on the other hand, are much simpler, and more reliable.
Bottom line: the tradeoff between marginal (at best) power gains, vs. reliability and simplicity, was just NOT THERE according to 1950-60's technology. Don't misunderstand me, THIS ABSOLUTELY DOES NOT APPLY TO MODERN, ELECTRONICALLY CONTROLLED ENGINES.
So......the next question is, why does NASCAR still cling to old fashioned induction technology. When will they go with modern PCM systems. This would eliminate the need for restrictor plates, as engines could then be electronically, dialed in to each track.

Joe

[Clem Z.]

the reason for FI and why it went away

the early FI,one piece doghouse, we split them down the center on do-all saw and ported them for more air flow and then welded them back together . the later ones,with the removable top,gulf research had some with 2 air meters on top for more air flow. i think bill thomas used this type on some of his cheetas. i think the FI was more for road racing "G" forces that HP. once holley came out with the "le mans",developed for fords le mans program, center pivot float bowls in 1964 the cornering problem with carbs was solved. i obtained a set from holley back in 64 and used them on my 64 365 HP and never had fuel starvation/flooding problems in the corners after that.also i never had a FI car beat me at the drag strip.those float bowls had the needle/seat installed horizonal in the front of the bowls making them very long and causing carb mounting problems and they were later made into the "cathedral" type with the needle/seat in the vertical position that you see now. playing with the shape of the holley float made even more difference in the cornering performance.

[Dick W.]

Re: More air meter questions

Joe, I think that the reason NASCAR stays with the carb is control. They can basically control what a carb is, but with a PCM and injectors, the world is wide open. They are having enough trouble with traction control devices today. Sure, they are outlawed, but there are systems out there that are almost undetectible. Wonder why some cars do not do a burnout after winning? It is a dead giveaway to the teams using a traction control system if they try to do a burnout.

Can you imagine what an inovative engineer could do with a PCM?

[Mike M.]

Re: the reason for FI and why it went away

agree with clem in that bill thomas was famous for adding an extra air meter to the rochester FI's. For the c-1 plenums, at least the ones i've seen, he'd remove the stock air meter, weld the large hole in the drivers side shut, then machine two new large holes on the driver's side of the plenum.Of course with the potential of 2 times 585cfm, he had to richen the mix by using larger discs in the nozzles.They would typically make a circumferential cut of the plenum, remove the top, shorten the runners, then re-weld the top to the bottom 2/3s of the plenum. would sure like to find one of those puppies. My 57 has been down the Duntov road and its starving for more air(and hence fuel). mike

[Mike M.]

Re: More air meter questions

Papa Smurf: are you insinuating that the Rainbow gayboy, who has trouble doing figure 8's after he wins, might be cheating a tad? MIKIE

[mike cobine]

the reason for FI and why it went away

I've seen some where they cut the top and side of the plenum, then rotated it so that the air meter sat out through a hole in the hood for getting more air.

If only they were so cheap people were using them for door stops again.

[Joe C.]

Re: More air meter questions

Dick:

Ya mean like Jeff Gordon tried last Monday in Atlanta. Is that why Tony Stewart couldn't catch him for the last 8-10 laps of the race, even though the #20 was faster than the #24??

Interesting point about the PCM being too complex, and therefore too hard to "police". But don'tcha think that if they put a PCM controlled car on an analyzer, that the tech inspectors could read every parameter on the readout. I have never been involved in tech inspection of race cars, but it seems to me that just reading the printout would be much easier than physically measuring each variable. They use electronic rev limiters now, so why not electronic flow limiters--the possibilities are endless. I am not advocating such a system. I for one approve of the "quaintness" of NASCAR for retaining the good old carburetors, and wallowing mid size behemouths. This is, in my opinion, what makes it "The American Brand Of Auto Racing". I just was thinking, what with all the sponsors' money pouring into the sport lately, that there would be a move to more hi-tech in the racecars.
I wish that they would go back to using REAL stock car bodies, without the generic profile and the decal headlights and taillights.

Joe