Intake stacks

[flat6rs]

What are the advantages of building an engine with racing stacks for the intake as oppose to a plastic intake manifold or a varioram manifold. From my knowledge the varioram manifold would provide better torque because of the multi stage intake length.

I have observed many race engines use the intake stacks instead of using a manifold. What are the advantages of using them?

[Bill Verburg]

Individual throttle body type intakes like TWM will give improved throttle response but are tuned to a specific rpm range.

The v-ram type intake improves mid range while still giving decent top end by varying the length of the intake tract.

Which is better depends on lots of things.

For street use w/ relatively tall, widely spaced gearing the v-ram will likely be the better choice

For track use w/ lower, closer gearing and relatively little part throttle use, the individuals will likely be better.

[flat6rs]

thanks alot Bill

[petevb]

I'd add that a single throttle body manifold requires a relatively mild cam in order to maintain any kind of idle. Individual throttle body intakes work well with much more aggressive, race-only type cams. These cams would never pass smog, but using one allows a properly set up race motor to make much more peak power than the milder cam options available with a stock intake manifold. The power difference between the these cams can be more than 30 hp, with the gains mostly coming at very high rpms- another big reason you'll see these intakes on race cars.

[RWebb]

hmmm, well, in general, but BMW has/does use[d] ITB's on some production cars...

[Grady Clay]

flat6rs,

The important fact is your application.

Carburetors are great period.

Same with MFI but greater performance.

CIS is period correct with some performance compromise.

DME improved performance while better emissions and economy.


If I were to build a performance engine today, it would still be MFI. A close second is an aftermarket EFI. I suspect the order will change in the next few years.

Best,
Grady

[flat6rs]

I am very sorry but I do not know much technical terms. I know that EFI is electronic fuel injection which you can setup with aftermarket ECUs like motec, etc. But what is MFI and DME and also CIS? And why are carburetors good? Aren't that for older cars?

Thanks in advance

[Bill Verburg]

Originally Posted by flat6rs

I am very sorry but I do not know much technical terms. I know that EFI is electronic fuel injection which you can setup with aftermarket ECUs like motec, etc. But what is MFI and DME and also CIS? And why are carburetors good? Aren't that for older cars?

Thanks in advance

Motec and DTA et al are aftermarket EFI setups

Carburators were the original throttle bodies, as used on Porsche they were ITB, 1 throttle/ cylinder, very crude metering and control but not sensitive to intake fluctuations from happy cams

MFI is mechanical fuel injection, an archaic 60s and 70s diesel system adapted for gas engines, very crude control but not sensitive to intake fluctuations from happy cams


DME is digital motor electroncs, the control unit used by the Porsche factory in it's Motronic systems, used on 911 form '84 to today, very precise control, drawback is the single throttle body and sensitivity to intake pulsations w/ happy cams

CIS is continuous injection system, another archaic FI system that let a continous stream of gas dribble into the intake ports, used for "73 to '83 on 911s, drawback is single throttle body and sensitivity to intake pulsations w/ happy cams

[flat6rs]

Thanks again for your prompt reply, Bill

Cheers!