I thinking about getting a throttle body for my 94 lt1. Looking to go with a 58mm. My question is what kind of power increase should I expect and how big of a drop in mpg? I do plan to go supercharged in about 3 years once i get out of college. My car is mostly stock: mid headers and ram air intake.
Thanks

 

There would be no point in putting one on now. You don't have any mods that would make it be of any benefit.

 

You will gain no additional performance with the mods you have using a 58mm tb. Stock is fine for now.

 

Well right now I am trying to build in stages when i have the $$$ and I looking at that or a rear end. planing to go 3.73. I'm in school right now though and don't have a lot of extra time so I figured that a TB would be faster then a rear end rebuild. Would I loose any mpg by going bigger with the TB?

 

Nothing would change. Unless you have an automatic trans. In that case, the revised air flow vs. throttle angle will screw up the shift tables, requiring a reprogram.

Additionally, the openings in the stock LT1 intake manifold are only 52mm, so you would be creating a "lip" due to the 58mm TB opening, that would cause pressure loss and disrupt air flow.

All-in-all, a bad idea, You will actually feel the change from a set of 3.73 gears.

Beside the mods you have now - cat-back exhaust, throttle body coolant bypass, mail-order PCM tune, 1.6X roller rockers and headers would all be more sensible choices than a 58mm TB.

What is your "ram air intake"?

 

Now im looking more at like 3.42's because I dont want to lose alot of mpgs and once I go supercharged I think those will be good for that. Right now i got about 16/20 city/hwy With those 3.42s what should I end up getting? What is the "best", if there is one, brand of gears?

The ram air intake is a hood to this one: 93-97 Firebird Ram Air Hood "Bolt On | WS6store.com
With this under it.

I hope that pic works.

 

I like Motive gears but if you're planning to supercharge the car at some point you might want to put the money towards a stronger rear end instead of gears for the 10 bolt. What gears are in the car now? If it's the 3.23 set then it wouldn't even be worth changing them to 3.42, IMO.

 

What trans do you have - T56 manual or 4L60E automatic? If auto, do you have 2.73 or 3.23 gears? Whether you have a manual or automatic will have a huge impact on choice of gears, and to some extent, modifications.

 

Well from what I have read as long as you rebuild the 10 bolt rear end with quality parts you can put a lot of power through them.
I have the a4. I believe they are 3.23s. The code for my rear end is gu5 I believe.

 

The 10-bolt upper limit for an automatic, with a huge investment in upgrades to the rear, is about 425rwHP. That is not to say 100% certainty of failure - people have taken the stock 10-bolt into the 10's. But as HP increases, the chances of failure increases exponentially. Your choice.

Read these articles.... they spent $1,700 on 10-bolt upgrades, and said exactly what I stated in the first sentence. Invest that money + some more in a Strange 60, a 12-bolt or a 9-inch.

Strengthening The Rearend From An LS1 Firebird Formula - High Performance Pontiac Magazine

Fourth-Gen 10-Bolt, Part 2 - High Performance Pontiac Magazine

 

There is more than one type of 10 bolt transmission. The one in your car is weak no matter what you do to it.

And if you have an A4 transmission, the pressures get all screwed up when you put a larger throttle body like a 58mm and don't know how to adjust the pressure tables in the programming. A 52mm might be OK just put on there. The problem is that 1/4 throttle of a 58 might be more like 1/2 in a 48 or something similar to that, so the pcm doesn't adjust for it - you are letting in more air and making more power at less throttle angle, so the transmission needs to make pressure sooner or the clutches might slip and burn up. It thinks you are motoring down the road when really you are getting on it if you get my drift.

 

An older 8.5" 10 bolt maybe. Th3 7.5" 10 bolt in these cars flexes and won't handle big power for long usually. You do get a few guys who run them low 10's or whatever but for every one of those you see there is a line of guys behind them who have blown up a 10 bolt or two or three.

GU5 is a 3.23 RPO code.

Honestly I'd leave the rear end alone and look at a good converter, shift kit and cooler instead of the gears. Maybe replace the 20 year old posi if it's dog leggin it.

 

follow what hes telling you theres no other way

 

Which of the above posts are you referencing?

 

I have considered doing a converter but they have a lot bigger price tag then gears. A converter wont do much as far as performance goes either will it? What do you guys say about used converters?
It will be a long time before I change rear ends all the ones I have found have a big price tag and im not exactly swimming in the dough right now. Lol.
I have considered doing a cam next winter but I have been told I need to do a rear end rebuild and a torque converter before I do that.