By definition, a throttle bod is a restricter. By this i mean an engine withOUT one with want to accelorate untill i guess it blows up.

So you put one on and you control the engines speed. It really has nothing at all to do with hp theoretically. BUT when the throttle body does not flow enough to sustain the engines air needs, then a bigger throttle body is needed.

More hypothetical talk. if you car needs 1000cfm and you have a choice of 3 throttle bodys:
20mm 500 CFM
50mm 1000CFM
Garage door 10000000 CFM

Of course the 20mm will still restrict HP AND the other two will make THE SAME MAX horse power(WOT[duh])

But with thing like throttle respons, cruise control and space, the 50mm is best.


Now for the lt1, i think its just based on both personel preference an engine CFM needs.
I currenly use a 58mm body on my bolt on LT1. I do this for personel preference. The amount of time it takes to go from 1000 rpm to 6000 rpm is so much faster then the 48mm that its great for me for downshifting witch i like to do.

Now my new engine with IMO need the more CFM becuz with a huge cam, ported heads and 500 hp it will raise the CFMs my engine needs.




TO sum it up, Neglecting your PCM, there is no way a bigger TB would HURT HP just possible driveability

 

Dyno test - 48mm vs. 58mm TB on a fairly stock LT1

 

Its about time someone had some actual numbers.

 

Though you cant really accept that as proof as he states that he did the dyno runs almost 5 months apart, so conditions could defintaly change.

 

SAE corrected?

 

Ah ok.... helps if i didnt skim the thread. I saw his reply saying they were.

 

That's a damn fine looking TB there, Mr. Tamez! I still want to try a 4bbl TB on my car with a "conventional" intake, but the time required to make this happen just hasn't appeared yet.

Something to keep in mind when considering theoretical maximum TB flow - the engine does not consume air in a steady, consistant fashion. Those same pulses that seem to get everyone all riled up when discussing manifold design also affect the TB, and with the small plenum volume of the LT1 manifold I feel that this is somewhat significant. So, while you may have an engine that only consumes an average of 650 CFM, it may have instantanous demands that exceed this number. Of course, there's a ton of variables that will determine the relationship between instantanous and average airflow demands, such as, oh, just about anything that sits behind the TB and regulates airflow in the engine (intake, heads, cam, exhaust).

There's also the velocity element that someone mentioned early on. A gentleman in the Impala world did some flowbench testing and found that the TB size does indeed have an effect on intake port velocity, but I don't know the specifics of his data nor have I pursued this sort of testing on my own. When someone drops off a Superflow 600 in my barn, I'll be happy to work on this

So, to summarize, I think that TB selection is more than just a consideration of the theoretical average pressure drop across the bore diameter, and I think that TB selection needs to be done when considering a lot more than expected RWHP numbers, displacement, FI vs. NA, etc. Now, since we don't seem to have the info required to calculated optimum TB size, it would seem that duplicating known combos or testing various TBs on your particular combo would be the way to go.

 

Back to back track results coming in about 2 weeks

-Shannon

 

good idea Shannon. Which TBs are you going to dyno and on what car? What mods have been done to it??

 

i'll test one for ya

 

I had a 52mm throttle body and had the engine on a dyno engine.
I then put a monoblade on the engine. The engine made a bit more hp (like 5hp) but the interesting thing was that the back cylinders EGT's were greatly improved, even at idle which was surprising.

you can see my motor buy looking at my sig.

Rob

 

At idle, wasn't most of the air coming from the IAC system, or was that eliminated, or somehow altered by the design of the monoblade?

 

I know the IAC is different on the monoblade, it maybe that they somehow modified it, i know we were surprised when we saw the EGT's on the dyno.
I don't have any data from the egt's cause they don't normally record that data but i know it was significantly better at wide open throttle. I want to say 60 degrees better.

My 396 is pretty basic, GTP stage 2's with a cc306 cam.
11:1 compression. I think it made pretty good power.

 

Running one of my 52mm ones against a stock 48mm one. Car has long tubes, heavy cam, port/polish, elec water pump... On down the line. This car is very quick, so i'm hoping these gains seen on this will be detrimental to how we look at this whole subject

-Shannon

 

your site shows you're running the LT4 hotcam. Is that current?

Is there any chance that anybody around you might let you borrow a 58mm to compare?