LT4 throttle body question
Thread Starter
Drifting
Joined: Nov 2000
Posts: 1,276
Likes: 0
From: Ft. Worth Texas
St. Jude Donor '11
LT4 throttle body question
Im in the process of installing ported heads/intake on the GS. I already have the hot cam/LT headers/Hi-flow cats/PE exhaust.
My question is, what size TB do i need? Is a 52mm about right? If I went with a 58mm would I be wasting $$ and HP :confused: :confused: :confused: :confused: :cry
thanks,
jeff
My question is, what size TB do i need? Is a 52mm about right? If I went with a 58mm would I be wasting $$ and HP :confused: :confused: :confused: :confused: :cry
thanks,
jeff
Le Mans Master
Joined: Apr 2002
Posts: 7,281
Likes: 5
From: Boston
Re: LT4 throttle body question (GS345)
The word out is that the 58mm flows a little too much and will decrease intake velocity compared to the 52mm. I woudlnt know if it really looses hp over the 52mm but if you are going to keep your setup as is, the 52mm would be enough, but if your planning on a strocker, forced induction, or any other mod then you have a good part.
Paul :cheers:
Paul :cheers:
Race Director
Joined: Apr 2000
Posts: 15,344
Likes: 4,008
From: Texas
Re: LT4 throttle body question (GS345)
52 is sufficient. 58 is best left to stroker motors. Some will claim you don't need the 52 either and from a peak hp perspective that's probably true. I found it moved my peak hp up in the rpm range giving higher average readings. Before the HOT Cam but with the throttle body, my hp peak moved from just over 5800 to right at 6000. The HOT Cam pushed that peak even higher...As my engine currently exists, breathing through stock cylinder heads, my hp peak (342rwhp) occurs at 6400rpm
Another data point...Dan Parker found through testing that the 48mm was a restriction. At WOT with the 48mm, his MAP readings were in the 93-95kPa range. Once he switched to a 52, his readings were 98-100kPa, which are the same as mine. His car is a '96 LT1 with stock LT4 heads and the HOT Cam.
FWIW, YMMV, etc, etc
Another data point...Dan Parker found through testing that the 48mm was a restriction. At WOT with the 48mm, his MAP readings were in the 93-95kPa range. Once he switched to a 52, his readings were 98-100kPa, which are the same as mine. His car is a '96 LT1 with stock LT4 heads and the HOT Cam.
FWIW, YMMV, etc, etc
Le Mans Master
Joined: Apr 2002
Posts: 7,281
Likes: 5
From: Boston
Re: LT4 throttle body question (GS345)
If you have the 58mm already then just let it sit. Also once you go to a 58mm you need to port the TB hole on the intake, cause they're smaller than 58mm.
:cheers:
:cheers:
