Ir intake manifolds and carbs

[dannobee]

I'd say the "OLD" school guys understood it pretty damned well, given their rules and technology constraints. If you look back several decades, the same calculations used to determine ideal intake tract length/volume sizes for each RPM are still great starting points for today. Those old guys knew a LOT about how an engine worked.
The IR vs plenum/carb decision was more about controlling costs than making peak power.

[David Redszus]

I'd say the "OLD" school guys understood it pretty damned well, given their rules and technology constraints. If you look back several decades, the same calculations used to determine ideal intake tract length/volume sizes for each RPM are still great starting points for today. Those old guys knew a LOT about how an engine worked.
The IR vs plenum/carb decision was more about controlling costs than making peak power.

I completely agree that the old guys knew a lot about the technology of their time. By that I mean prior to WW2.
I had some great mentors which I appreciated at a later point in time.

But that does not mean we understand what they understood.

[69427]

I you gentlemen don't mind me asking a simler question that I have been pondering for a while.

This would be in a drag car, automatic trans, BBC, say 500 cubes, 7500-8000 rpm, mechanical fuel injection on methanol.

With everything optimized, which of the following would make more power?

A tunnel ram with 2 throttle bodys on top or a Kinsler 8 stack injector.

Thanks
Tom

[rdwedge]

A tunnel ram with 2 throttle bodys on top or a Kinsler 8 stack injector.

I also would like to know which is more powerfull in say a bracket drag car.

[modok]

-Where- the throttles are located...makes zero difference, when the throttles are fully open. So of course it makes no difference to WOT power either way.

[modok]

Also one thing that throws off the comparison between a motorcycle and v8, is just the sheer scale.
The amount of wall area inside the manifold compared to what it flows just isn't comparable from small to large.

A briggs and stratton maybe should have a 20" long intake and a 40" exhaust, but it just won't work, the sheer amount of friction from running the gasses through such long skinny passages would be worse than any gain.

A little bug SWIMS through the air, because at that size, the air is thick like water.

TO a big V8 the air seems very thin and freely flowing, with or without bugs in it.

[digger]

-Where- the throttles are located...makes zero difference, when the throttles are fully open. So of course it makes no difference to WOT power either way.

not really, finite plenum vs open stacks is not the same, and the shafts etc are more of a restriction when they are in the runner closer to the head as the %age area blocked is higher.

[modok]

Is there drag froma throttle, yes, but It's fairly trivial, fraction of a %


ANd if the stacks could reach.... why would you have open stacks? put them all in a box

The big difference would be wet VS dry plenum

[jmarkaudio]

I would never consider carb going backwards, just depends on the application. A carb does an extremely good job of providing fuel and can be tailored to a wide variety of sizes and atomization/vaporization properties. As well it provide fuel in a more continuous homogenous mix. As an audio engineer for live sporting broadcasts computers and electronics are an every day part of my life. If I felt there was any advantage to FI I would have already been using it. On a 1500+ HP 650" money no object engine last year the builder tried the new Holley FI, only to be down over 50 HP against a large bore spread base carb. With a Grid capable of individual cylinder timing what advantage dose FI have? Street cars sure, meeting fuel economy and emission standards. Vehicles with high G changes, maybe. Drag or circle track the performance tends to be best with a carb. Tuning is easier and cost is generally less with a carb.

As far as sizes BLP make up to a 2.800" throttle blade, Braswell came out with one a couple areas ago just over 3"...

[digger]

Is there drag froma throttle, yes, but It's fairly trivial, fraction of a %


ANd if the stacks could reach.... why would you have open stacks? put them all in a box

The big difference would be wet VS dry plenum

often the shaft is 8 mm and streamlined to maybe 5 mm, so if its close to the head on a port say that is otherwise D50 mm its more than a fraction of a % in area

D50 mm = 1,963 mm^2
D50 mm with 5 mm shaft = 1,963 -5*50 = 1,713 mm^2

that's another choke point 13% smaller area, sometimes that matters, other times it doesn't obviously depends on the average air velocity in that area and the size of other chokes in the system and so on. The further from the head the less it matters as there is usually taper so the runner is bigger and the throttle is bigger but the shaft will probably be the same size.

you could connect them all to a common box but the Kinsler stuff is open for the eye candy

[Belgian1979]

My personal experience:
- top end difference : none but dependant on the cam (see below)
- mid range : a lot
- low rpm : a lot

Things also depend alot on the cam you're using.

Larger overlap, means more disrupted mid/low rpm mixture when using a common plenum (certainly with a carb) in which case an IR plays out its superiority. If using EFI, you can also negate some of the effects of the large overlap. The more overlap then leads to more rpm and more top end power...

So in drag racing or circle track racing (no experience) where you would run at full power all the time, I could see no real difference. Road racing or any other form of racing where you'll have varying rpm, cornering,... different animal altogether.
Street : completely different, but then again the maintenance also plays a role.

[David Redszus]

In days of old...when racing was not limited by rules...just by gold.

“Awesome” and “epic” are two badly over-used words. But the 1966-1974 Canadian-American
Challenge Cup series of open cockpit, over-powered road racing, can’t be described in any
other terms. As close to unlimited as sports car racing ever got, the Can-Am years redefined
what was possible in speed and brute power. The rulebook allowed any engine and almost
any chassis configuration.

New cars from McLaren, Lola, and other chassis builders, were stuffed with a high-revving
variant of Chevy’s iconic 427 Big Block hot rod motor. Heavily developed to pump to a reliable
750 horsepower and nearly 7000 RPM’s of fury, the Can-Am contenders were now the fastest
and most powerful road racers in the world, even faster than the Formula One cars of the time.

Money was good, rules were loose, and the fans were excited. Horsepower was off the charts.
Even Ferrari couldn’t ignore the distant rumble, shaking North America. Conjuring up their
biggest engine ever, a 7-liter V-12, they crossed the ocean to try and bring some fight to the Chevy V-8’s.

McLaren offered their M8 to private team buyers, boasting that their advanced aluminum and
composite monocoque tub weighed a scant 98lbs. Bodies and suspension and engine/trans
brought the weight up to just shy of 2000lbs.

And what an engine it was. First 495, then 509 cubic inches of pistons and fire. Aluminum
blocks and long fuel injection trumpets reaching for the sky, staggered, to smooth out the
bumpy power delivery. A racing derivative of Chevy’s 427 ZL-1 motor, the Big Block was
strengthened and developed to deliver a stunning 750, then 800, then 840 hp.

Incredible for what was at heart, a regular single cam pushrod V-8.

It was only 54 years ago that Chevy switched from carbs to IR fuel injection to increase
power and response for road racing in the CanAm series.
Making almost two hp per cu in, it still ran a mean piston speed of only 22.28 m/s at 3300g.

Does anyone have actual, on track, Lambda data logged for a big bore, carbed race car?
Can it be shared?

[frnkeore]

In days of old...when racing was not limited by rules...just by gold.

“Awesome” and “epic” are two badly over-used words. But the 1966-1974 Canadian-American
Challenge Cup series of open cockpit, over-powered road racing, can’t be described in any
other terms. As close to unlimited as sports car racing ever got, the Can-Am years redefined
what was possible in speed and brute power. The rulebook allowed any engine and almost
any chassis configuration.

New cars from McLaren, Lola, and other chassis builders, were stuffed with a high-revving
variant of Chevy’s iconic 427 Big Block hot rod motor. Heavily developed to pump to a reliable
750 horsepower and nearly 7000 RPM’s of fury, the Can-Am contenders were now the fastest
and most powerful road racers in the world, even faster than the Formula One cars of the time.

Money was good, rules were loose, and the fans were excited. Horsepower was off the charts.
Even Ferrari couldn’t ignore the distant rumble, shaking North America. Conjuring up their
biggest engine ever, a 7-liter V-12, they crossed the ocean to try and bring some fight to the Chevy V-8’s.

McLaren offered their M8 to private team buyers, boasting that their advanced aluminum and
composite monocoque tub weighed a scant 98lbs. Bodies and suspension and engine/trans
brought the weight up to just shy of 2000lbs.

And what an engine it was. First 495, then 509 cubic inches of pistons and fire. Aluminum
blocks and long fuel injection trumpets reaching for the sky, staggered, to smooth out the
bumpy power delivery. A racing derivative of Chevy’s 427 ZL-1 motor, the Big Block was
strengthened and developed to deliver a stunning 750, then 800, then 840 hp.

Incredible for what was at heart, a regular single cam pushrod V-8.

It was only 54 years ago that Chevy switched from carbs to IR fuel injection to increase
power and response for road racing in the CanAm series.
Making almost two hp per cu in, it still ran a mean piston speed of only 22.28 m/s at 3300g.

Does anyone have actual, on track, Lambda data logged for a big bore, carbed race car?
Can it be shared?

But alas, no one could compete with the Penske/Porsche, 917 with it's much smaller, turbocharged engine and unlimited budget. It then became a 917 parade and that's what killed the Can Am! It might have survived as a 7 liter, non turbo formula if Ford and Mopar would have offered factory support and the BB tech, would have sky rocketed.

Ford made a feeble attempt with a high rise aluminum block, H&M entry, called the "Hooker" but, even Mario could get it the chassis working in the corners.

[David Redszus]

But alas, no one could compete with the Penske/Porsche, 917 with it's much smaller, turbocharged engine and unlimited budget. It then became a 917 parade and that's what killed the Can Am!

That was a popular myth but totally incorrect.

McLaren dominated the CanAm from 1967 to 1971, with the Bruce and Denny show, and no one complained about the lopsided finishes. Porsche entered the series with the 908, small displacement and underpowered. From 1972 till 1974, Porsche turbos dominated the series. Subsequently, rules changes to limit Porsche performance were implemented, combined with the fuel embargo and a poor economy, the series died. It was revived a few times later but it was simply not the same Formula Libre (unlimited) series.

[MadBill]

....Ford made a feeble attempt with a high rise aluminum block, H&M entry, called the "Hooker" but, even Mario could get it the chassis working in the corners.

Close; it was actually The Honker: https://www.hemmings.com/blog/article/the-honker-ii/