throttle body theory??

[jetuomi]

I'm curious to see what you come up with.. as for the blower guy, in this case I would say the answer is to make sure your intake is all port matched so if the opening of your intake manifold is 75mm then get a 75mm t-body..

Now you know why the inatke valve starts to open before the exhaust is closed, even though the piston is still on the way UP in the cylinder... that is overlap. In a boosted car, you want to minimize this as the incoming air has more pressure than the exhaust so you will actually push your incoming air/fuel mixture right out the tail pipe if the overlap is too much.

As for the whole TB thing... I have to think about this some more...

 

[jruppert]

I will say this.. I have a 347 with AFR 185's and last year used a 70mm throttle. I contacted Anderson Motorsports and was told that I was choking the engine with this 'small' throttle. I purchase an Accufab 80mm race throttle which has a 90mm inlet. I also upgrade to long tube headers. Last year I could break the tires loose in 2nd with no sweat. I could even break them in 3rd if I tried. With this setup I cant break em loose in 2nd. It seems to pull decent at 4,000 but has dead up to 3500. Sounds like the throttle is too large eh? Maybe I will have to sell it and buy a 75mm non race throttle.

 

[bimmertech]

how about this to really screw with this thread, an engine running and running well with absolutely no throttle body? bmw has what is called valvetronic which is basically a variable valve lift unit which can reduce lift to like 2mm and increase it to somewhere around 120 mm which coupled with thier variable valve timing(vanos) and infinetly variable intake runner does not actualy require a t/b. a third wave pulse engine is affected mostly by when the intake valve closes(inertial supercharging factor) which is determined by port flow velocity in the cyl head, the intake including the throttle body aids in increasing that velocity but is normally not used when figuring your inertial supercharging factor. imo the throttle body should match the flow characteristics more to the head than the engine size(on a n/a engine) cuz the head can only flow a certain amount of cfm regardless. that's just the way i see it. oh yeah i've also read that the maf should always be bigger than the t/b to create a funnel effect, or venturi of sorts.

 

[WhiteDevil]

I wasn't talking about idle. I was talking about part throttle voltages. As the TPS sensor notes that the butterfly is open to 3/4 throttle, the MAF actually senses full throttle.

No the MAF does not sense full throttle. The TPS sensor is what senses that. A new Tbody should not effect driveability at all unless the IAC and TPS are not adjusted correctly. The TPS is used to see closed, part, and WOT. Then the MAF is used to meter the amount of air, and all those calculations are used to create a load number which is how the car chooses what values to use from the tables and scalars. Unless its in closed loop then it gets teh KAM values.
Anyway our long runner intake manifolds are what create the intake velocity, so with a larger Tbody you are just allowing the intake manifold to have all the air it needs. I love my 75mm tbody.

 

[Car Nut]

imo the throttle body should match the flow characteristics more to the head than the engine size(on a n/a engine) cuz the head can only flow a certain amount of cfm regardless. that's just the way i see it. oh yeah i've also read that the maf should always be bigger than the t/b to create a funnel effect, or venturi of sorts.

That makes sense to me. Plus, isn't the stock MAF bigger than the stock t/b which also creates the funnel effect you mentioned?

Edelbrock Performer and Performer II intakes have a 70mm t/b opening I believe, so wouldn't a 70mm t/b be optimal (even with edelbrock heads and a good exhaust). Not sure what size MAF would be used in this scenario, but probably something slightly larger to "funnel" the air into the intake.

Just throwing out a thought.

 

[WhiteDevil]

That makes sense to me. Plus, isn't the stock MAF bigger than the stock t/b which also creates the funnel effect you mentioned?

Edelbrock Performer and Performer II intakes have a 70mm t/b opening I believe, so wouldn't a 70mm t/b be optimal (even with edelbrock heads and a good exhaust). Not sure what size MAF would be used in this scenario, but probably something slightly larger to "funnel" the air into the intake.

Just throwing out a thought.

THis funnel effect, about 10 guys just got through explaining the high intake speeds that our long runner intakes help to create, and that the real intake velocity is created in the intake manifold runners. Also whats this Performer II ur talkin about? Is that the RPM II intake because that has a 75mm opening the performer and performer RPM has 70mm openings. I ported mine to match the 75mm throttle body i have.

 

[bimmertech]

THis funnel effect, about 10 guys just got through explaining the high intake speeds that our long runner intakes help to create, and that the real intake velocity is created in the intake manifold runners.

how about a engine without intake runners at all, is there no velocity made? individual t/b setups rely on inertial supercharging to maximize cylinder filling and any velocity is created in the intake port of the cylinder head due to a "funneling" of a larger t/b into a smaller intake port into a smaller valve. intake runners are tuned to deminish the effect of the intake pulse hitting the valve and reverting back into the intake reducing velocity(wave pulse theory). the longer runners take a longer time to reach the valve which aids in cylinder filling at lower rpm's, then at hgher rpm's the shorter runner prevails as the actual time between intake openings is lesser. so intake runners don't actually create velocity but rather regulate it to provide optimal cylinder filling in a certain rpm range.

 

[5spd GT]

For a h/c/i car (as many people know from me) I see no need to go any bigger than 70mm TB.

Some use the "lower intake ports" as where velocity is reached...but why would people that swap a Performer upper with a RPM upper report a loss of low end torque? (They have the same lowers). Guess what is right in line with the upper intake trac...yep the throttle body It can be used as a point of velocity.

Many (even in this thread) show their experience when they swap to these bigger throttle bodies how they lose the response down low...

 

[Muy_Pyro]

Wow, that's a ton of speculation (and way over my head) ... I really wish someone could just start testing out different TB's on Different application and post up some dyno numbers and really see what's going on.

 

[broken_joke]

yesterday i went to a local speed shop and what i found out was interesting. mainly about throttle bodies. this shop has a 2400 hp race car and they use a 90mm throttle body on their car. they said they didn't jump to 90mm until they had made about 1400hp until that point they were running a 80mm. they had made the comment that no n/a motor should go above 75mm. the reasoning is that the velocity is much slower with a larger tb and that is needed on a n/a car. anyways it is easy to get caught up in the bigger is better theroy. i made that mistake.

 

[Grn92LX]

they had made the comment that no n/a motor should go above 75mm. the reasoning is that the velocity is much slower with a larger tb and that is needed on a n/a car. anyways it is easy to get caught up in the bigger is better theroy. i made that mistake.

Tell that to GM. The zo6 vette uses a 90mm TB from the FACTORY.

I've seen a bunch of 302's pick up power putting a 75mm or even an 80mm on their cars. Rick 91GT made 5 MORE rwhp across putting a 75mm race tb on his car over a std 75mm tb. The race tb has a 90mm opening

 

[tmoss]

What you stand to loose with too big a TB is throttle response for street driving - not an issue with a track car that runs WOT most of the time is it?

 

[Grn92LX]

Tom, so a zo6 vette has poor throttle response with the 90mm tb?

My 302 has awesome response and driveability with the 65 and the 75mm.

 

[jruppert]

I changed my 80mm throttle with an old pos 58mm throttle and surprisingly enough the 58mm accelerates as good or a hair better then the 80mm. The 80mm does have a little better throttle response at part throttle though. imagine that..

 

[WhiteDevil]

I changed my 80mm throttle with an old pos 58mm throttle and surprisingly enough the 58mm accelerates as good or a hair better then the 80mm. The 80mm does have a little better throttle response at part throttle though. imagine that..

Thats just your ****ty SOTP meter. I went from a 65mm back to the stock 60mm for a while on my car, which is just a mild H/C/I i lots 8rwhp and 10rwtq from that alone.

 

[5spd GT]

Tom, so a zo6 vette has poor throttle response with the 90mm tb?

My 302 has awesome response and driveability with the 65 and the 75mm.

An ls6 has much more factors on it's throttle response then just the throttle body...much more.

 

[Green Machine]

I've got a Eldelbrock Perfomer intake, C&L 76mm MAF, and a 65mm FMS tbody (see signature). Making 281 / 308 at the rear wheels. After that last dyno I took the Pro Chamber off and put my O/R X-pipe back on and set the timing to 12 degrees then put new NGK FR5 plugs in. I'm think I'm close to 285-288 range now.

Ordered a Eldelbrock 70mm tbody. I'm saving up for a Pro Charger, and I'm starting with the tbody upgrade. I'm not counting on much increase with the current setup, but with the SC application it will be nice.

Have to wait on the dyno to get the real numbers. It's already 90 degrees and high humidity. Thanks again for all the info in the thread.

 

[zenboy99]

What speed shop? What car? I hate it when people just throw out random numbers without specifics. Anyone on this board can do that.

NO N/A motor over 75mm? Maybe your "local speedshop" could teach GM a thing or two.

yesterday i went to a local speed shop and what i found out was interesting. mainly about throttle bodies. this shop has a 2400 hp race car and they use a 90mm throttle body on their car. they said they didn't jump to 90mm until they had made about 1400hp until that point they were running a 80mm. they had made the comment that no n/a motor should go above 75mm. the reasoning is that the velocity is much slower with a larger tb and that is needed on a n/a car. anyways it is easy to get caught up in the bigger is better theroy. i made that mistake.

 

[zenboy99]

Does anyone here have specific dyno numbers they can post? N/A car, different throttle bodies being the only variable?

 

[GTJake]

I think JP's results are very convincing. kg/hr is the mass (kg) of air flowing through the MAF. An engine is a glorified air pump. The more air pumped through it, the more power it is making.

Jake