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Throttle body questions


Guest Anonymous

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Guest Anonymous

I have been interested in throttle bodies (individual), and was wondering about performance on them. I know the 2002 race cars had the injectors almost at the opening of the throttle body, and I know that would mean it was squirting the fuel at the butterfly. The TWM TB's have the injectors after the butterfly, so there is no interferance there. I was just wondering how the placement of the injectors affects performance, and how the plancement of the butterfly's affects performance. Like do you want the butterfly's close to the intake, or does it really matter.

I'm just a little curious and would like to hear what you know.

Thanks,

Bryan

red73

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Guest Anonymous

EFI ones like TWM put the injector after the TB for idle control

actually.. imagine a fuel injector spraying on the throttle plate...

the mechanical TB have the injector before the throttle

plate because they are more of a race setup and desire a better

"full on" atomization... some schnitzer slide throttle setups had

the injector suspended in the middle of the air horn... this is not

to say schnitzer and alpina units idle poorly but not as well as

after the TB.. I also have a video of a race m3 where the EFI

injectors are about 3" away from the air horn on the independant

TB setup of the m3.. they just spray through the air as it's stucked

down into the engine.. weird actually... then there are staged

injector setups for turbo cars where one set fires off boost and the

other comes on for mad crazy boost... etc etc..

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Guest Anonymous

from powerstation.org.uk. Maybe the one Kris saw?

Vid1

Vid2

From my brief experience with primary injectors out in front of the butterflies, the idle really stinks. Idle has to be pretty high, and still unstable. Staged appears to be a superior choice if you worried about low rpm and low throttle angle performance.

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Guest Anonymous

For a hot street setup, i'd want the injectors after the butterflies, and squirting the fuel at the valve stems to atomize the fuel.

I am just trying to figure stuff out because i'm thinking about designing an Individual TB set up, and I wasn't sure what the different locations did.

Thanks,

Bryan

red73

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Guest Anonymous

TBI sucks. My 89 truck had it, and it idled okay (for an 89 truck) but I've heard GM's switch from TBI to the newer forms brought about a 30% performance/economy increase...

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Guest Anonymous

The injectors are put right behind the throttle body plates in ITB's because the plates cause turbulence which enhances mixing of the fuel to the air.

In general, at higher rpm's ie race motors you need to inject farther away from the valve face. This is since the air and fuel have less time to mix before the piston sucks the mixture in. Real racecars that care about idle like the s14 from DTM are using 8 injectors (ie 2 per cylinder). The closer injectors are slowly phased out with rpm and throttle until the engine runs on only the far injectors.

If you look at formula one or indy car motor pictures they tend to run the pico style injectors way out in the CF airhorns. Yet I believe cart is at 14k rpm and f1 now nearing 20k rpm. For awhile actually indy car was running injectors that shoot a squirtgun pin stream to the back of the valve. The inlet valves were running so hot that the gas instantly atomized and cooled the intake charge.

I think the jenvey site has a fairly good writeup on how far the injector should be from the head. It's all based on rules of thumb unless you want to breakout some unsteady time varient CFD.

BTW, it is correct that the kuglefish and carbs in general atomize fuel better than conventional fuel injection. The real gains in efi are control, timing issues, infinite variability according to inputs etc. Also you can up fuel pressure in efi to increase atomiziation, but I'd talk to your fuel injector people first.

Goodluck with your ITB design. I gave up and bought some TWM's cheap. :) Eventually I'll build some roller throttle bodies with the correct taper and such but not now.

-Bernard

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Guest Anonymous

you will not enjoy street driving if your only injectors are infront of the butterlies. Teamed up with a big cam, injectors outside the butterflies makes for very poor street idleing.

At low revs, there is a lot of reversion of the intake charge during cam event overlap. You don't have very efficient cylinder filling. Combine that with the injectors smacking the back of the butterfly, and you wind up putting a lot of fuel in at idle to get the necessary amount of evaporated fuel into the cylinders. All that extra fuel winds up pooling infront of the throttle plates, and trickling in. That liquid fuel does no good for idle and transient response when it is sucked in, and since it does not burn some of it washes into the oil.

If you watched the video from the uk tuning shop, you saw what is called staged injection. The motor was a 4 cylinder, but with 8 injectors. 4 injectors in the normal after butterfly position, and 4 staged out in front. As shown in the video, the staged injectors are not always on. They turn on when the rpm is high engough that motor is efficient (cam has come on), reversion is much reduced. and a wide open throttle angle. Normally there is a blending between the 4 normal injectors fading out and the 4 staged being fully on as the rpms increase. This is a pretty sophisticated efi setup, and requires an extra amount to tune.

In short - stick with the norm, injectors after the throttle plates.

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Guest Anonymous

I'm in school right now (western washington university), and i'm in a program where I have CNC machines and other such neat toys at my disposal. Figured while i'm here, might as well take advantage and do some stuff for my car, while learning at the same time. We also have quite an extensive Carbon fiber knowledge base here, Wheeeeeeeeeeeeeeeeee =)

Plus I have ProE on my computer at home and yeah, it should be FUN!!!

Bryan

red73

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Guest Anonymous

This may be a bit of a stretch looking at the spray pattern from a movie, but the #3 cylinder may be adjusted richer.

1342 firing order makes the #3 cylinder have the cylinders adjacent to it have a firing event before and after #3 firing. The s14 being a siamesed bore block (water jacket does not surround the entire cylinder) may increase the likelihood of the #3 being tuned different because it is likely to run hotter.

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