throttle body boring?

[88camaroproject]

hey i got a 400 ci with tpi and i was wondering about how much to bore it out for best gains and about how much it might cost? thanks, Tom

[Morley]

The largest you can open up a stock TB is 52mm (stock is 48mm)
I am currently getting set up to be able to bore TB's to 52mm, add larger throttle blades and bore the shaft holes to accept needle bearings (the stock TB has the steel throttle shaft running in the aluminum TB bores, unbushed, so the shaft wears out the TB holes).
If you look on E bay this service costs about $175 (you provide the throttle body)
I'm planning to charge $125-$150 and should be set up to start in about 2 weeks (hopefully) This will be for TPI and LT1 throttle bodies.

[92zcamaroperson]

bbk makes a 58 mm they are just really expensive.

[88camaroproject]

do you think boring my tb to 52mm will make a big difference? ill it help low rpm or high??? cause arent 400s not really for high rpms...thanks, and i might be interested in having you bore my throttle body. lemme know when you start, and how long would i be without my throttlebody?

[92zcamaroperson]

It all depends on how the motor was built up. Thats whats going to determine its rpm limits. Valvetrain weight and durability, balance or the rotating assembly. There may be some truth to a 400 engine not being a high rever but I would suspect that it will respond to any modifications just like any other engine. Thats why I say full tpi modification will give some extra power to the motor whether it revs high or not.

[Morley]

Originally Posted by 88camaroproject

do you think boring my tb to 52mm will make a big difference? ill it help low rpm or high?

With a 400cid you really need to either ditch the TPI and go with a superram or miniram, but those are expensive. If you are limited by $$$, you' want to port the stock base manifold as much as possible. Then look on E bay for a set of SLP's siameased runners (they can go cheaply) and port them out, then match the plenum to them and do a good porting on the front of the plenum, behind the throttle body bores.
Top it off with a 52mm TB and you'll be breathing about as well as you can. The TB won't make more hp in high RPM's or low RPM's...it will allow the engine to breathe better and make more power at the RPM's the throttle body was causing restriction...clear? The engine's air requirements are going to be different at the same RPM's depending on things like, temp, engine load....etc. So it is a matter of potential air flow for the 52mm throttle body, it has the potential to flow much more air than the stock 48mm, and will if the engine needs it.
If you have headers, good heads (even ported stock heads), mild to wild cam....Then you'd benifit from a larger TB. Unless you are into the 500hp range you'd want to steer away from the 58mm + throttle bodies. To use a larger TB like that you'd need the engine to be pumping gobs of air. The secret to TPI is velocity, the runners and manifold runners are around 22" long (combined) and the air must be kept moving at high velocity to ensure filling the cylinders. If the air slows down too much in the inlet tract, it can eddy and staginate, causing the cylinders to only fill partially and cause a loss of power.

And as for how long you'd be without a TB...That depends on the mail/UPS/Fedex. The way it works is I have some "spares" that are already bored & bearings installed & polished up. As soon as someone sends me a TB (& payment) and I get it, I send out the "spare". The exception to this is if you have a "wing" in your TB that you want to use. It would have to be bored up along with the TB bores. Then I'd have to wait for the TB to arrive and do all of the work to it...figure 2-3 days for the work (or less if over a weekend) then shipping it back.


One other thing. If you opt for a 58mm TB you'll have to have the throttle bores in the plenum brought up to 59mm (they are 52mm from the factory), otherwise you have effectivly turned a 58mm TB into a 52mm and provided a place for stagnation to occur.

[88camaroproject]

has anyone ever tried the holley stealth ram kit????? and if i went with short ram.....ummm feel dumb, but what would i be replacing, isnt short ram just like the little tube from the tb and then like a cone k&n or something. ima go take pics and get the camera to work.

[Link85x]

I heard the stealth ram is really good. I was gonna get it when i had plans one building up a 350 tpi. They say it can pull after 6000rpms with the right set-up, not bad.

[wrightz28]

Stealth ram is kinda like TPIs version of a high plane intake for a carb set up. tell ya what, I install it on mine and let ya know how it is, if you buy it and ship my way

Ya know tho, I've heard that unless you a cam with some bump and jump to it the bigger T/B really dosen't have much payoff, kinda like too big of an exhaust tube. Plus, don't you have to adjust the MAF tables?

[88camaroproject]

umm well i have a cam with like .500 lift or something, i will look it up tonight, but i got my camera to work so yeah go to the got my new car thread i started a while back if you want to see it.