LT1 Throttle body question.
 

Ok I have a question. Can you put too large of a TB onto a LT1? Right now I have the 48mm stock TB on my motor. When it was on the dyno last I was told that I could use a bigger one as my motor wanted more air. My question is what size to get, 52mm, 54mm, or 58mm? I can get the following.

BBK 1543 TWIN 52MM 750-CFM Throttle Body
EDELBROCK 3810 TWIN 58MM 94-97 LT1 Throttle Body
EDELBROCK 3809 TWIN 52MM 94-97 LT1 Throttle Body
BBK 58mm Throttle Body
The 54mm would be a stock TB sent out and bored out to 54mm

Also what’s better BBK or Edelbrock? Thanks for any info.

Well that was helpful.

I'm sure you will see different answers on this.

My opinion is an LT4 that revs to about 6400 uses a 48mm throttle body, so GM didn't think it needed a larger one.
Are you moving more air than an LT4 engine and what do you limit your rpms to?

If you still have 350 cubic inches and don't go past 6000, I seriously doubt that you need anything larger than 48mm.

In my testing, at WOT and 6K rpms, of my '92 A4 with 350 cubic inches, 48mm throttle body, AFR heads, and a Crane cam shows that the MAP sensor is indicating (kpa reading of atmospheric) I have no restriction that can be registered on the intake (this includes the air filter and throttle body).

So, in my case, it would be a waste of money.

For me:
Larger throttle body = same increase as air foil = nothing.


Tom Piper

OK Since no one else is answering I will give it my best shot. I have read where the 502 crate motor that gm sells only uses a 48mm TB. I have heard that the bigger ones dont actually help our cars. Probably the best evidence of this is on Nathans web page. The best I remember he posted no hp gains when going from stock to a 52mm holley unit.
However I wonder why Lingenfelter used 58mm on his 350-383 motors if they dont help.
This and aftermarket mufflers are two things that I wonder about in the back of my mind. Hate to invest in either and find no power increase. But sometime I probably will.
By the way, who does the 54mm stock unit? I have seen 52's but not 54's.

Edit oops, my post came 2 min. after Toms. We must have been typing at the same time.

I don't believe anyone has dyno proven that going to a larger TB will increase your horsepower. However, if you are doing heads, cam, headers, it only seems to make sense to go to a larger TB.

But then again, maybe these shops recommend a larger TB just to make more profit of their packages. Something to consider.

As for your question regarding too large TB on a LT1, let me tell you my experience. When I ordered my LT1 heads/cam package, I ordered a Holley 52mm TB. When it was time for the install, the shop couldn't get their hands on a 52mm, so they installed a 58mm!

My first reaction was "that TB is way to BIG". But the car pulls just fine. It makes great power and is very streetable. It got me thinking, 48, 52, 58? Probably doesn't make a stick of difference.

The morale of my story is, don't waste your money on a larger TB unless you are moving up to a 383/396 stroker package. And even then...

There is a book I had where they mod an LT1 camaro engine step by step and dyno each time. Their mods were the blue print for what I did to my car, I used the same cylinder heads guy.

The TB they did after the cylinder head porting, and it gained 12 hp and 3 ft-lb at the crank. Author says this gain would not be nearly as substantial w/o the ported LT1 heads.

What I think is that it may help as a last addition after you do the heads/cam/headers/exhaust package. It will not help the stock car.