Larger throttle body discussion...pros and cons

DonnieShort

Who's Next?
Joined
May 27, 2001
I've done alot of searching about larger throttle bodies and larger plenums and have found that most say it's a waste of time and money but doesn't state why only just don't do it. But I also see that some say that it doesn't hurt and helps on a faster car. So with that being out there, what are some facts that says bigger is not better. And what makes bigger not better? It seems to me that a bigger intake opening can flow more air than the stocker, even if the gain is small it's still a gain right? What would be the results of a 70mm and plenum ( namely Precision's ) on an 11.70ish car still using stock unported heads? I don't want to start a war, just a fact filled discussion on the subject. And to start it off, I've had 2 very reputable people tell me in my case ( et wise ) that it would be benificial and a gain would be noticed. Let the discussion begin....
 
I run a JJ modified throttle body, and I dont have any statistics or dyno numbers, but the butt dyno says it was a smart move. Really seemed to wake the car up, but obviously its going to depend on the setup your running. I plan on getting a powerplate soon, I think that will be a nice little combo...striker
 
I have done track testing between a 62 mm stock t-body and a 70mm t-body/upp plenum.
I also did testing on a stock upper plenum/kb,accufab/and hemco.

Results:::: 70mm t-body/upper plenum will give you better throttle responce at half throttle but at wide open there is no difference.
During track testing i picked up nothing when i put on the 70mm/upper plenum verses the stock t-body(bored to 62mm)/upper plenum.

Now i did pick up 1.5mph in the 1/4 mile when i added a 62mm hemco to my combination.
Conclusion--- Sold the 70mm t-body/upper plenum.
Added the hemco to my stock t/body and it works!!

This was with real world track testing.

Note: From what i hear,chip programmers have a harder time programming chips to idle properly with a 70mm t-body.

Above tests where done 4 years ago on my consistent 11.1
unopened motor!

Mike.
 
One uneducated opinion

Probably the best way to determine if the throttle body upgrade would help is to see if it is causing a restriction in the airflow. The only way I can think to do that is to measure your boost pressure both before and after the throttle body and see if there is a pressure drop across it at full throttle. Who knows how you could do that measurement.

I have read varying opinions on the topic, but what I have read would suggest that a bigger throttle body would help in most situations. The concensus seems to be that the only real downside to a large single throttle body is that idle and low- to mid- throttle performance is diminished somewhat because it is harder to meter a small amount of air through a large throttle. That's why you will see those 4-barrel looking units with multiple smaller throttles on most v8 injection conversions instead of one mammoth throttle to feed the whole thing.

Even on lower performance motors, the extra throttle area seems to help performance. I remember reading a comparison between an EFI system and a carbureted one using the same manifold and comparing the results. The engine's needs topped out with a 650CFM carb, but performance was helped on the FI side by stepping up from a 900CFM to 1000CFM and then to even a 1300CFM throttle body unit.

In an extreme example of this, the 2.0 liter engine that powered the AWD Nissan Pulsar GTIr had 4 individual throttle bodies on the intake manifold. Each cylinder got its own throttle that way, and that throttle was pushed as close to the head as they could get it. The net result was a really short post-throttle intake tract giving phenomenal throttle response. This great response let them run a much bigger turbo on the motor without having to worry as much about lag.

If it were me, I'd upgrade. I can't see it hurting things at all.

- Freed
 
FREEDSTER Is exactly right. If you can flow enough air from the turbo, through the intercooler to where the up pipe and TB are causing a blockage, it can increase hp. I think its a combo of both the up pipe and TB since they are usually the same size. The reason why the turboi outlet into the intercooler can be smaller than the up pipe is because in the intercooler the air becomes denser because it is now cooler, so it needs more room to flow. I would say it would take a big turbo and a very efficient intercooler to warrant going to a bigger (70mm) tb.
 
You do not need a larger t-body,it will do nothing for you at all!
There is cars running well in the 9s with the stock t-body!
How ever if you like the looks and money is burning a hole in your pocket then buy one.

Mike.
 
One problem I can see with a very large throttle body is trying to hold steady partial boost.

If your wastegate is set at 18 psi and you want to accellerate at part throttle at say 10 psi, the larger TB will be open only a little, while the smaller TB would be open at a greater angle.

The combination of the large throttle blade and small opening angle can lead to compressor slam with a smaller quick spooling turbo.
 
Originally posted by MIKE10SECV6
I have done track testing between a 62 mm stock t-body and a 70mm t-body/upp plenum.
......Results:::: 70mm t-body/upper plenum will give you better throttle responce at half throttle but at wide open there is no difference.
During track testing i picked up nothing when i put on the 70mm/upper plenum verses the stock t-body(bored to 62mm)/upper plenum..................
......Above tests were done 4 years ago on my consistent 11.1
unopened motor! Mike.

Mike's results are identical to mine although I did NOT see better half-throttle response.

Have seen some high-11 sec. cars slow down and have lousy drivability with a 70mm. Contrary to what Freed said, know of more than one case it did hurt. Real world and what SEEMS logical are often different!

Sold my 70mm also.:)
 
Jay Jackson modified 62/65mm TB $80 vs. $250+ for a 70mm TB.

Ryan Guy went 9.99@136mph with a 62mm TB in a full weight GN. Enuf said.

I run one also and plan to with a T-70BB turbo, ported iron heads, ported lower and big cam.

-GNX7
 
I've only seen two magazines do a back to back t.b. test. The test where the car gained h.p. was a Kenne Bell bolt-on test and used a K-B 70 mm t.b./upper on a stock engine with bolt-ons and gained @ 20 h.p. The other test was in GM High-Tech and used a stock engine with bolt-ons and a 65mm unit and actually lost 13 rear wheel h.p. I'm looking into a JJ modded one myself, but am waiting for someone to do an actual back to back dyno test to see exactly what benefits it gives.
 
A Kenne-Bell test on a Kenne-Bell part in a magazine report where Kenne-Bell advertises and gains 20 HP on a Stock motor, and real world test show that doesn't happen......................??:D
 
That's some very good feedback and info. So is the general feeling is a Jay Jackson unit is about as big as you would want to go? And I'll ask this again, do you need a chip tweak when going to a larger tb? Keep it coming.
 
no chip change needed

you will start outflowing the stock TB at about 700+ HP

I use a stock (62mm) TB
 
well I want a 70 mm can someone sell me one real cheap since they are no good ..;)

how about on a 9 second car looking to run upper 130's trap :confused:
 
Misinformation..

There's some misleading stuff in this thread. For example, cooler, denser air coming out of the IC actuall needs LESS flow area, because it is cooler and denser. By definition, if it is denser, it takes up less room, and needs less flow area for a given velocity. Bottom line is this. The Buick 3.8 is only a 3.8. It will only flow as much air volume as a 3.8, NOT EVER as much as 5.0, etc, etc. You can more MASS of air through it by increasing the boost, but this increases DENSITY, not VOLUME. The volume is not going to be great enough to need the large flow areas that big engines use. You get the car to run faster, up to a point, by increasing boost and air density, not the volume of flow. IF you put a big cam in it, and turn it to really high rpm, you might up the volume enough to need a bigger throttle plate, but probably not 70mm. Comparisons to carburetors don't work, either, because the carb uses the throttle and venturi to meter the fuel, while on the EFI engine the throttle is used only to control air flow- it doesn't do any metering. Smoothing up the flow through a stock or near-stock sized TB would cut the WOT pressure drop, and add some "free" power, for minimal cost, and more bang for the buck.
 
And, of course, the biggest reason our cars don't need the really big throttle bodies like LS1's and Mustangs is that we blow through ours with boost, while they suck through theirs at atmospheric pressure. All else being equal (which in real life it never is but this is only a semiquantitative example :)), you need half the throttle body area (so 70% the diameter) at 15 psi boost as you do normally aspirated for the same restriction.
 
Originally posted by ijames
And, of course, the biggest reason our cars don't need the really big throttle bodies like LS1's and Mustangs is that we blow through ours with boost, while they suck through theirs at atmospheric pressure. All else being equal (which in real life it never is but this is only a semiquantitative example :)), you need half the throttle body area (so 70% the diameter) at 15 psi boost as you do normally aspirated for the same restriction.


Yes, all that and what Ormand said. One thing that is also forgotten is the mention of stock or near stock heads at the beginning of the thread. They're only going to flow so much, and adding that 70mm throttle body isn't going to do a thing (but probably slow you down and add drivability issues).
 
Top