Throttle Bodies... Come hither JT.

[Turbo Joe]

when i went with a gt35rr i removed the elbow from my 2 piece and fabbed up
a new mounting plate and i'm running a 60mm throttlebody cause i was leary of
the backpressure issues that may arrise using a 52mm.. I'm suprised trbovan didn't overheat his turbo with a throttlebody that small with that kind of whp..

[Shel-Game]

Quote:

Originally Posted by BadAssPerformance CFM is CFM. HP is a direct calculation of how much fuel you can burn efficiently. More air means you can burn more fuel. Larger T-Body, more CFM, more air...

That's only true as long as the TB is the main restriction in the engine. At a certain point, the valves, intake, etc. become the restriction. Ideally, that point should be at or just before WOT.

If the engine is only capable of flowing a maximum of, say 300CFM; then a 600CFM a throttle body is pretty useless.

[Shel-Game]

Quote:

Originally Posted by TrboVan Something to think about. Pretend you have 10 psi of boost at WOT. Now you have 10 psi of boost at 1/2 Throttle. Which car is quicker? Is there a difference of 10 psi through a 52mm hole vs a 26mm hole?

Yes, there is a difference. The difference is in the mass airflow through the throttle. At max load, any throttle should always be choked. That means the airflow through it equals the speed of sound. At this point, no change in pressure on either side of the throttle will cause an increase in mass airflow. So, at 1/2 throttle, you should flow 1/2 the mass of air of WOT. Regardless of the upstream pressure.

[B.A.P.]

Quote:

Originally Posted by Shel-Game That's only true as long as the TB is the main restriction in the engine. At a certain point, the valves, intake, etc. become the restriction. Ideally, that point should be at or just before WOT. If the engine is only capable of flowing a maximum of, say 300CFM; then a 600CFM a throttle body is pretty useless.

Its always down to the least restriction... the 'CFM is CFM' comment was not just about throttle bodies...

Your 300CFM vs. 600CFM comment is not true for forced induction applications. The ideal CFM of an N/A 2.2L engine is ~273CFM at 7000rpm. A Super 60 T3 turbo will flow ~600CFM at 27psi...

[russ jerome]

Remember the old argument about throttle response and going to
a 52mm TB? Have shot that down myself with 2 different vehicle's.
Exact same off idle pull on street and in the case of my old red van
exact same 1/4 speed/ET. Granted a 52mm is a small size jump.

Sooooo...my next experiment would be to see how large you could
go before helping/hindering street driving and track setup.
LonewolfPerformance is building my new intake and it looks
like they are going BIG on TB side, but this is a full race manifold
so dropping TB size would cause a nasty change in intake air speed.

[Ondonti]

Im building a log intake manifold for my 3.0 with mitsu parts............I guess I better go bigger then 58 on the TB. Probably need to make the throttle lever more progressive though.

[gasketmaster]

A good friend with a Buick GN changed from a 62mm TB to a 70mm TB on a V6 powered car that ran 10.20's.......he didn't pick up anything.No mph and not .001 of a second in the quarter.The only thing he got out of the swap was a bill for the new TB.......LOL

The car was making over 600 fwhp and didn't respond to a larger TB no matter how it looked on paper

[GLHNSLHT2]

Quote:

Originally Posted by Frank i dont know why everyone is so hesitant on this... frank

Because back in the day Gary D said it wasn't needed. There were also reports of MPG dropping off 3-4MPG when running a 52mm TB. I know of one car that this isn't true on. Anyone else? TD'ers are just afraid of change in general as well.

[Shel-Game]

Quote:

Originally Posted by BadAssPerformance Its always down to the least restriction... the 'CFM is CFM' comment was not just about throttle bodies... Your 300CFM vs. 600CFM comment is not true for forced induction applications. The ideal CFM of an N/A 2.2L engine is ~273CFM at 7000rpm. A Super 60 T3 turbo will flow ~600CFM at 27psi...

Right. But in that case, the engine (ie, engine + turbo) is capable of flowing 600CFM, so the throttle body should be as well.

A 46mm TB may flow ~300CFM at 10in vacuum. But it will flow a lot more than that at a larger pressure differential (up to the point that it chokes).

The only way a larger TB would help is if it is the restriction at WOT.

[Frank]

Quote:

Originally Posted by GLHNSLHT2 Because back in the day Gary D said it wasn't needed. There were also reports of MPG dropping off 3-4MPG when running a 52mm TB. I know of one car that this isn't true on. Anyone else? TD'ers are just afraid of change in general as well.

Quote:

Originally Posted by Shel-Game Right. But in that case, the engine (ie, engine + turbo) is capable of flowing 600CFM, so the throttle body should be as well. A 46mm TB may flow ~300CFM at 10in vacuum. But it will flow a lot more than that at a larger pressure differential (up to the point that it chokes). The only way a larger TB would help is if it is the restriction at WOT.

Yes sir! Exactly my point in both cases. We dont need a TB to run fast, but we can run way faster for a small expense.

The more a throttle body flows, the better power however the less streetability you have--dropped MPG once you go too big and hard to control throttle.


Frank

[Frank]

Quote:

Originally Posted by BadAssPerformance Sure, I'll test it out... whatcha want me to test?

Cutting off the elbow on your intake, weld a larger pipe on, and trying out a 65mm throttlebody.


Frank

[Shadow]

An interesting read, was wondering when a thread like this would come up. Based on the improvements we've seen from 46-52mm TB's on 250-380ishwhp cars it is my opinion that there are several cars out there that could benefit
from a larger TB. Although, as some have already stated, only if it's the biggest restriction. We're putting together a 2.4SRT 5-speed PT in my bro's 85 Shelby Charger and looking to make around 600whp. After thinking it through I came to the conclusion we needed a 75mm TB, anything less(while it would still work well) would be a restriction of sorts. The info contained in this thread seems to back this up 100%, only time will tell.

[DakotaKid]

Quote:

Originally Posted by Shadow The info contained in this thread seems to back this up 100%, only time will tell.

You mean where Terry (GasketMaker) mentions that a bigger TB did nothing for his buddies Grand National?

[DakotaKid]

Quote:

Originally Posted by gasketmaster A good friend with a Buick GN changed from a 62mm TB to a 70mm TB on a V6 powered car that ran 10.20's.......he didn't pick up anything.No mph and not .001 of a second in the quarter.The only thing he got out of the swap was a bill for the new TB.......LOL The car was making over 600 fwhp and didn't respond to a larger TB no matter how it looked on paper

I love Real World examples. Thanks Terry,.

[Shadow]

Quote:

Originally Posted by TrboVan You mean where Terry (GasketMaker) mentions that a bigger TB did nothing for his buddies Grand National?

I haven't seen his buddies GN so I can't speek to it's restrictions.