LT4 Breakdown on LT4 Dyno numbers w/mods

[wx briefer]

Using dynojet for testing:

Corsa, hotcam, SLP claw intake-315.7 HP/303.2 torque

added Long Tube headers and random cats-330.7 HP/328.8 torque

changed to 52mm TB-340.8 HP/ 334.5 torque

notes:

unplugging little vacuum fuel pressure thingamagiggy at the manifold as per Gordon Killebrew hurt A/F ratio and lost HP.

52mm TB makes a very noticable sucking noise as intake air is increased. Also, 52mm effects a near perfect 13.5 A/F ratio through entire RPM range with stock programming but idle really suffers!

YMMV.

 

[Redmanf1]

Do you have any numbers when stock?
on your Mods

 

[wx briefer]

Redman, unfortunately I did not get a baseline before hot cam. However, 2 other LT4's on the same dyno had numbers right in the same ballpark. Although, one now has no exhaust, cnc'd heads, reprogrammed and is getting over 380HP.

 

[Redmanf1]

I was curious to what the mods did over stock.
Thanks

 

[Louis Bartay]

I have a 1996 LT4 Red Coupe, what size is the Stock Throttle body?

 

[lew]

I believe all factory LT1 and LT4 engines came with 48 mm throttle bodies. The intake manifold holes, however, are 52 mm. You can bolt on a 52 mm throttle body. Anything larger you have to machine the intake manifold.

Lew

 

[Louis Bartay]

If I change to the larger 52 mm throttle body will I get a check engine light error? And will it gain any more power?
Thanks
Louis

 

[lew]

There has been a lot of discussion about this on the Impala SS forums. Most have found that the Impala SS LT1 does not benefit from a 52 mm throttle body unless the engine is highly modified. An LT4 could be considered to be a highly modified LT1, so you might get some benefit. The idle problems are common with 52 mm throttle bodies. It is not because they are 52 mm. After all, the throttle is closed at idle. It is because the Idle Air Control (IAC) is a complex and sensitive device, and the aftermarket guys have not been able to get the design quite right. At least some aftermarket 52 mm throttle bodies have a hole drilled in one of the butterfly plates that is not in the stock 48 mm throttle body. That is there so at least some air can get into the engine in case the IAC closes up altogether, and the engine can still run (rough) and not stall out completely. If you are patient, the idle *may* improve with time, as your engine's computer learns the different IAC characteristics of the aftermarket 52 mm throttle body.

Lew

 

[all4c4lt4]

If I change to the larger 52 mm throttle body will I get a check engine light error? And will it gain any more power?
Thanks
Louis

You would need a modified LT4 to have any benefit IMO. As seen above, he already had a full exhaust and cam and then added the TB. I would think you would need at least the cam and exhaust before adding a 52mm tb.

As far as idle issues with the 52mm tb, send your factory 48 mm to LPE and they will port it to 52mm while retaining all the benefits of the stock unit. Check out LPE's website.

 

[Louis Bartay]

Thanks for the information. I will try to find LPE and see how much they charge and do I really need it as my LT4 just has a few bolt on mod`s with the stock exhaust.

 

[all4c4lt4]

Thanks for the information. I will try to find LPE and see how much they charge and do I really need it as my LT4 just has a few bolt on mod`s with the stock exhaust.

http://www.lingenfelter.com/lingenfelter/product.asp?dept_id=16&pf_id=49

Their website recentlt changed and the option of sending them your unit, and them returning it to you is no longer listed, but call them.

I wouldn't think you would need it right now considereing your mods. Rule of thumb most people use for mods is gears or exhaust first, then other things. The 48mm flows enough air on a mostly stock engine. But its your car, do what makes you happy!

 

[Shriker]

Hmm wx ..... your final numbers sound about right though your initial number with hot cam and corsas sounds WAY low. I have a feeling your car , for some reason or other, didnt dyno accurately on that pull(s).

Generally, LT4's are 290-300 stock at the wheels on a Dynojet 248. Add hot cam ~25, longtubes ~15, catback ~8, intake ~ 3+, cats ?, and TB is generally not much either until you really get up over 375 rwhp from what I have seen. I would say your car was probably in the low 290's rwhp stock (within the average) and you gained about 50 rwhp which is about right for those mods on an LT4.

FWIW I have seen a 380 rwhp heads/cam (hot cam) LT1 dyno back to back, changing only the TB from stock to 52mm and gained NOTHING over several pulls.

 

[wx briefer]

Shriker, if you check the other two LT4's on the Grandsportregistry.com page with same mods, you will find we are all 3 within 2 or 3 HP and torque of each other.

Not sure what you have 'seen'. But I generally like to refer to hard numbers.

 

[Shriker]

wx , what I have seen are dyno sheets and actual dynos of approx 35 LT4's with all types of mods down to stockers. Of the 15 stockers I have seen on the dyno or have seen dyno sheets they were ALL between 290 and 300 rwhp. Also , after researching on Vette forums like this and others for several years and owning my LT4 for almost 2 years and watching a good friend mod one as well .....all this has formed my opinions.

Just thought that info may help.......

 

[fastglass95]

48mm throttle bodies vs. 52mm!!!

My experience with a neighbors 96 LT1 Vette has been that the 48mm is plenty of airflow for most modifications other than heads / cam type stuff.

He installed a BBK 52mm and it caused nothing but trouble, and finally bought a new 48mm from GM and the car ran much better, with much better throttle response and idle qualities.

IMHO: The LT1 ran like crap with the 52mm throttle body, I'm guessing the stock or near stock LT4 would run much better with the stock 48mm as well. Stroke it out or port the heads and you MAY reap a benifit with a larger throttle body.

The LT4 is one strong running motor in stock form! It will dyno right with basically stock LS1's made in 2003!

 

[pettsir]

my baseline for my LT4 was 299.7 hp/299.4 tq at the wheels. i added a K$N filter, open air lid, relocated my IAT, bypassed my T-body coolant, and put in a foil. i re-dynoed and the power went to 306.7 hp/ and 307.9 tq at the wheels.

 

[LT4man]

Stock LT1 has 44mm TB. Stock LT4 has 48mm TB. I put on one of the original Edelbrock 52mm TB. Came polished. The ones sold today come very rough. The trick is to have PCM reprogrammed. If you don't, the computer learns what you did and compensates. I found that out thru trial & error. After the reprogramming was done, I could not believe the difference! I have not yet dynoed, but the car feels like someone installed a supercharger. I thought the car was fast before, but I was wrong.