OldschoolV6
Member
- Joined
- Jul 16, 2013
Some of the v8 guys that are 88 turbo can make 1250 hp with a 80 mm tb. Some have made 2500 plus with a 90mm and twins . Just thinking the stock TB should make say 600-650. Can you run 10.20s on a stock TB?
Anybody done any tesing on larger TBs?
- Thread starter OldschoolV6
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OldschoolV6
Member
- Joined
- Jul 16, 2013
On your car how much did the larger TB pick you up? What size are you running?
psycho6cyl
Ponies Are For Lil Girls
- Joined
- Feb 11, 2005
from the research I did the larger tbs are good for 9 sec or better unless you like the bling. 
delcowizzid
newzealand turbo 3.8
- Joined
- Mar 3, 2010
i have a 90mm TB on a later buick 3800 with turbo and at low boost theres no difference in grunt from half throttle to full throttle its way tooooo big LOL
Larger throttle bodies give a false sense of extra power with the butt dyno. It's some pretty complex math but the basics are that when cracking the throttle, the rate of opening area is far far greater. The result of that is that when you're used to giving 3/16" of gas pedal to pull off from a stop, that same pedal travel with a larger TB will be like pushing the pedal 1/2". It makes the car jumpy and twitchy off the line.
Now the above comparison is comparing two mechanically sound throttle bodies. In real life when we get a larger TB from someone like Steve, we're going from a small TB with shaft leaks, to a larger unit with a sealed shaft. Since that's more than one factor changed at once, it's not a valid comparison. much like comparing the cooling capabilities of a clogged 25yo radiator to a new Fbody unit)
Another thing to keep in mind is that air under boost is MUCH MUCH smaller than air at atmospheric pressure. That 600CFMs of air you're moving under boost is WAAAAAAAAAAAAAYYYYYYYY bigger when decompressed. That's why turbo engines don't have to have porting and perfect big ass cams as much as N/A units.
Turbos are a great way to get around a bunch of nit picky stuff and still have great results in the end.
Now the above comparison is comparing two mechanically sound throttle bodies. In real life when we get a larger TB from someone like Steve, we're going from a small TB with shaft leaks, to a larger unit with a sealed shaft. Since that's more than one factor changed at once, it's not a valid comparison. much like comparing the cooling capabilities of a clogged 25yo radiator to a new Fbody unit)
Another thing to keep in mind is that air under boost is MUCH MUCH smaller than air at atmospheric pressure. That 600CFMs of air you're moving under boost is WAAAAAAAAAAAAAYYYYYYYY bigger when decompressed. That's why turbo engines don't have to have porting and perfect big ass cams as much as N/A units.
Turbos are a great way to get around a bunch of nit picky stuff and still have great results in the end.
My reply was meant to say I ran 10.20's with a stock TB.
Think of it this way - the engine takes in 231 cubic inches of air every 2 revolutions. Low boost, high boost, vacuum, whatever - 231 cubic inches. The volume air flow is always the same. Mass air flow changes depending on the manifold pressure, but volume air flow does not. Since volume air flow stays the same, velocity through the throttle body stays the same. So if the throttle body is well sized for a stockish type car, it will still be well sized for a big hp car. Now velocity does go up with rpm - that 231 cid of air flow does happen faster and faster as the revs come faster. So the situations I can think of where a bigger throttle body might help would be a) when your rpms are lot higher than stock (and so velocities end up being higher). Hitting 7000+ rpm? Maybe a bigger tb will help. b) more cubes. I can see how a 4.1 or larger might like a bigger tb than a 3.8. Or a V-8 car. Because more cubes will have more cfm of air flowing through it, so it needs a throttle body with a little more cross sectional area.
Final case for a bigger throttle body is when it is on the inlet side of the turbo. While the cfm of air entering the engine stays the same no matter the boost level on an intercooled car, the cfm of air going through the air filter and into the turbo varies greatly. A high hp hot air car will see a LOT more cfm through the throttle body than a low hp hot air car. In that case a bigger tb ought to make a big difference.
I did ignore volumetric efficiency effects in the above discussion, but I think for the purposes of this discussion that is ok. Hopefully you can see why most guys still run stockish sized throttle bodies.
John
Final case for a bigger throttle body is when it is on the inlet side of the turbo. While the cfm of air entering the engine stays the same no matter the boost level on an intercooled car, the cfm of air going through the air filter and into the turbo varies greatly. A high hp hot air car will see a LOT more cfm through the throttle body than a low hp hot air car. In that case a bigger tb ought to make a big difference.
I did ignore volumetric efficiency effects in the above discussion, but I think for the purposes of this discussion that is ok. Hopefully you can see why most guys still run stockish sized throttle bodies.
John
And to expand on Johns stuff above.... Keep in mind airfow is limited to the smallest choke area in the entire intake tract. If the total square inches of the intercooler core, the MAF, the piping, etc... is the limit, you can put a 500mm throttle body on there and you won't go any faster.
(and to expand on my stuff way above, that 500mm throttlebody will give you damn near full power with 2* of blade rotation).
(and to expand on my stuff way above, that 500mm throttlebody will give you damn near full power with 2* of blade rotation).
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