At what level do you upgrade throttle body?

[jjvites]

I was wondering at what level of either e.t. performance or turbo size or boost pressure does one go to a larger throttle body? When is the stock one a restriction in the path of boost.
There are Chevy's running in the low 10's amd 9's with a 58mm TB on V8's as seen in GM High Tech with superchargers.
When is it "better" to move up to say a 70mm for our GN's?

 

[KEVINS]

I have heard of some running 9's on the stock TB but 10's are typical with it.

ks

 

[madhat]

I have been told that it will make the car seem more responsive on the street, but not really make a huge difference in performance...but hey, I still have a stocker so I dotn know for sure

 

[bruce]

I was wondering at what level of either e.t. performance or turbo size or boost pressure does one go to a larger throttle body? When is the stock one a restriction in the path of boost.
There are Chevy's running in the low 10's amd 9's with a 58mm TB on V8's as seen in GM High Tech with superchargers.
When is it "better" to move up to say a 70mm for our GN's?

I've tried a 70, 62, and 58 on my car.
While mild, 206/206 cam, 60 PPH injectors, Cotton F/M, and alky control, for the best street manners, the 58 is the best. Unless you can really flow the air, the big stuff is only going to give the impression of being more responsive, since you get more air per amount of throttle opening. If you have AL heads, and are wanting a 10, don't do much street driving, then you might consider them, other then that IMO, you can better spend the money doing other things.

 

[John Wilde]

I agree with Bruce, unless you are building a 10 second car or faster I would not spend my money here.

 

[jjvites]

What about the Plenums with these TB's?

Thanks guys. I was feeling the same way about it. Will consentrate on cam and heads next and then will see. If anyone has any mile per hour differences at the track with the different TB's at lets say in the low 11's to mid 10's it would be interesting to know.
Also is there much to the PLENUMS at this power level , stock vs Precision vs Hemco etc. Assuming all had RJC Power Plates to balance flow.

 

[steve hughes]

I don't know at what point the tb becomes a restriction but i've been 9.40's with a 62mm.

 

[VadersV6]

The up-pipe is 2 1/2 inches, which is a little over 63mm. I think the 62 would be a better match all around, but yes, you can go pretty darn fast with the stock one. Going to a bigger TB definetely makes for much improved throttle response, and as far as ET gains or dyno gains, I havent seen any data with turbo buicks. They do make a difference in most cars though. I had the stock twin57mm TB on my cobra, and thats just an N/A 281 cube motor. It comes stock like that. I machined a spare TB I had, and bored it out to twin 59.5mm bores, and made my own blades and everything. Making a TB that doesnt bind takes ALOT of work and patience. Anyway, the throttle response was dramatically improved, and this is on a motor not pushing any boost. I had tried a twin 62mm TB from BBK, but the manufacturing process really sucked, and the end product was lame. They leave these extremely sharp edges at the TB bores. Alot of people would actually lose power with them. The one I made worked beautifully and it really woke the car up. I put the stock one back on and I couldnt believe what a dog the car became. Didnt seem possible given the size of the motor and the already massive flow potential of the stock TB. Even though you can go really quick with the stock one, I could easily see a TR gaining more than a few hp with one. A single 58mm TB seems like a joke to me with 23psi pushing through the motor. If I see a good price on a used 62mm TB for the buick, Ill snatch it up quick.

 

[Randy Greenoe]

I replaced my 58mm throttle body and stock plenum with a 62mm and a Hemco 65mm plenum. With no other changes it went from 12.0s to 11.78.
I know I am in the minority but the 62 and the Hemco works for me.

 

[jjvites]

Good stuff guys, thanks.

 

[Ormand]

A single 58mm TB seems like a joke to me with 23psi pushing through the motor

Remember, as you increase boost, the volume of air INTO the turbo increases, not the volume of air out of the turbo, and into the throttle body. The air gets compressed more as the boost goes up. Volume flow through the throttle body won't increase unless you turn up the rpms or increase the engine displacement. The 231 will have lower volume flow than the Cobra engine, even when the Buick is making much more power. A turbo engine makes power by increasing the lbs/hr, not the cfm, so there isn't as much need for big valves, big throttle body, etc.

 

[Marc87GN]

I don't know at what point the tb becomes a restriction but i've been 9.40's with a 62mm.

 

[Garycar]

I have asked this question to a number of venders over the years. The typical response has been that a larger throttlebody opening will not necessarlly increase performance. I have a ported stock throttle body with PTE's front mount and 3" tubing. Going from 3" inlet tubing to a 2 1/2 throttlebody might increase velocity but decrease volume. Don't know for sure how this affects performance. The answer is probably obtainable through back to back dyno pulls with different size throttle bodies.

 

[VadersV6]

Remember, as you increase boost, the volume of air INTO the turbo increases, not the volume of air out of the turbo, and into the throttle body. The air gets compressed more as the boost goes up. Volume flow through the throttle body won't increase unless you turn up the rpms or increase the engine displacement. The 231 will have lower volume flow than the Cobra engine, even when the Buick is making much more power. A turbo engine makes power by increasing the lbs/hr, not the cfm, so there isn't as much need for big valves, big throttle body, etc.

Huh???? WTF......
Once again, (seems like I go through this every week) All engines make more power by increasing flow through the motor. More in/more out. No idea what you're talking about with lbs/hr vs. CFM. They are intertwined.
As far as not needing a bigger TB...why do we bother with reducing the pressure drop caused by a small restrictive intercooler? The small TB creates a pressure drop just like the small necked stock IC.
So you're saying more air goes into the turbo, but no out. Where is that air going? The 5th dimension?

 

[simple]

just like too add, that those chevy's with the 58mm TB's are using twin (side by side) 58mm openings, not just one

 

[CTX-SLPR]

Its a concept of mass flow. Since both water and air under around 270mph is incompressable you can use a water hose as an example, at constant water pressure, ie constant mass per time, your open hose flow velocity is low, stick your thumb over it and you decrease the area for same amount of water to go through, your velocity goes up. If you need to see if volumetricaly think about it this way with the hose end open you get a fix volume of water in a cylinder the diameter of the hose, its relatively wide and short. When you stick your thumb over it the cylinder becomes the same diameter as the hole left, its thin and tall. Roughly speaking the height of the cylinders is your velocity.
A street car will like the smaller opening for higher velocities off idle and such, a race car will like the bigger throttle body since you don't want the air too fast to hit the back of plenum and bottle neck into the rear cylinders like a stock plenum makes it do. A prostock car uses a pair of 1050 dominators, they do this so they get as little pressure drop across the carb as possible a WOT, you put something like that on a street car and it will make good WOT power but you won't be able to get it to idle or run worth crap below WOT. I'd really like to see some flow bench work on a throttle body at different throttle angles or percents.

 

[VadersV6]

Yeah, fluids arent a new concept for me. Been at this for 23 years. I developed an intake manifold for the cobras that pulled off something no one has been able to acheive. I gained 60rwhp at redline on my bolt on/ NA stock heads and cams car, and lost only 3 lb. ft of torque across the curve. No one has to this day been able to figure out how I did it because conventional wisdom says it cant happen. My sometimes unconventional approaches to this stuff are the answer.
BTW, the acceleration (velocity) of the piston which is a result of the rod/stroke ratio creates alot of the velocity you get with the intake charge. Its not all about cross sectional area. Timing and ramp angles with the cam, rod/stroke ratios, runner length, cross sectional area of the runners, plenum volume etc have alot to do with the velocity. You can create an intake manifold that wont mind a huge throttle body. You can actually run a huge throttle blade/blades and still retain velocity down low if things are correctly designed. If you run twin 1150 dominators, you will have a problem creating enough of a pressure drop for the venturi to do its job and draw fuel and properly atomize it at lower rpm's. With fuel injection, where the injectors are aimed right at the intake vales, this isnt as much of an issue. Most late model intake manifolds are designed to deliver a uniform turbulence (laminar is rarely the way to go), in order to get better atomization. Proper atomization is executed through other means, and doesnt require a small throttle body to get it done.

 

[FBSideoiler427]

Remember, as you increase boost, the volume of air INTO the turbo increases, not the volume of air out of the turbo, and into the throttle body. The air gets compressed more as the boost goes up. Volume flow through the throttle body won't increase unless you turn up the rpms or increase the engine displacement. The 231 will have lower volume flow than the Cobra engine, even when the Buick is making much more power. A turbo engine makes power by increasing the lbs/hr, not the cfm, so there isn't as much need for big valves, big throttle body, etc.

Good ole fundamental PV = nRT: The Ideal Gas Law

 

[bruce]

A street car will like the smaller opening for higher velocities off idle and such, a race car will like the bigger throttle body since you don't want the air too fast to hit the back of plenum and bottle neck into the rear cylinders like a stock plenum makes it do.

The velocity that matters is the one the works best. Not always will the bigger is better concept work at WOT.

In addition the velocity issue, is *plenum* volume*. While on a N/A engine it's what's below the butterflies, but on a S/C engine, you get into Mean Manifold Pressure, and the post turbo colum of air needs to be considered. If you look at Lingenfelters Cavalier, the whole intake tract design reflects a consideration of this.

While the velocity in the plenum may be part of the problem, the actual problem is the manifold design. The Mini-Ram, and GN manifold both have the rear runner floors, and back wall being shared with the plenum, and have the some inherit rear cylinders leanness. A basic Heating and A/C book shows how the last duct in a column should have a *dead* area behind it.
Using a .5" can make a difference in releiving this proble some, as well as the Power Plate. Both work to keep the air from stacking up against the back wall/ floor.
I *dropped* the floor on my stock manifold, and had to add 8% more fuel to get the same AFR. And yes, there was an increase in power.