Hi All,

I just bought a new 58MM TPI throttle body off fleabay last night. I'm doing a Speed Density TPI retrofit on my 1982 Corvette and liked this because the price was right and it looks 10x better than the dingy stock throttle body I currently had. I'm no speed freak so anything is better than the carburator thats on my engine right now.

Having said that:

Will bolting this straight to my stock plenum cause any side effects or problems? Maybe performance or whistling noises going past the holes in the plenum that will be 10mm smaller than the bore in the throttle body?

I thought about enlarging or beveling the holes in the front of the plenum myself ....any tips or pics?


I know I can get my plenum professionally reworked and buy larger runners to enhance the new TB, but that will cost me at least $500 and I'm already upside down in my swap and it's not even on the engine yet...so really that wouldn't be an option for me at the moment.

Thanks for any and all advice......I hope I can just bolt up the new throttle body and drive

 

You can bolt it up and drive it. Like you said the problem will be the lip on the plenum compared to the throttle body. It won't do anything for the air flow. Might make some noise. It's not hard to open up the plenum your self.

 

Thanks for the response!

I figure that it would make some sort of noise as the air rushes against the plenum lip, I think I'm either going to take a router and bevel the lip a little more or open it completly up to match the trottle body.

I know it sounds weird To attach a larger than stock throttle body to my stock set-up, but I like the fact that it's new and I may try to build a bigger motor (383 stroker) this winter, and then I would open the plenum, add larger runners etc. Crawl before I walk.......the TPI swap is eating my funds as it is.

I'm more concerned that it would hurt the performance of the car, kind of like a carburator with a cfm rating thats to big for a engine.

 

I don't think it will hurt the performance of the car if you bevel the plenum openings. This is a fuel injection system not a carburetor where you need a vacuum signal.

 

Ive been on the board for quite a while and Ive heard many people say that a 58mm tb on a stock engine can cause driveability issues since its letting more air flow sooner.
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Mods. GMPP Vortec heads, Comp Cams XR269HR, Crane Gold Rockers, Hooker headers, SDPC intake manifold, free flow exhaust, Air Foil, De-screened MAF, TB Bypass, K&N filter, MSD Coil. To be installed, Edelbrock runners, BBK AFPR, SFC.

 

 

Too big for stock intake and motor. Stick with the factory 48mm.

 

yeah , you in noway need that ....not even a 52 mm. You will probably notice less tip in response and it will maybe be a bit lagy in response across the board But thats just an assumption so take it as you will . But you DON'T want to put that on .

 

Thanks for the input everyone, I'll most likely sell this when it gets here tuesday.

It'll def be worth using on something hopped up but since my engine is pretty much stock I don't want to affect the performance.

If anyone is looking for a brand new 58mm polished throttle body let me know.

 

Jimmy,

If you wanted to do anything, get an airfoil and a k and n filter. Get a free flowing exhaust when you get some cash going. Then the usual like good oil (mobil 1) and clean plugs will make a difference.

Take care,

Rabi C.

 

Maybe i'll trade you for my newly polished 48mm TB.

 

PM me a picture of it and let me think about it. I have a 48 mm that I started polishing and it doesn't look too bad. If yours looks pretty good I may do that.

I should get my 58mm in today, If I decide to sell it I'll be asking $200 + shipping. I'll try the forums for about a week then I'll list it on fleabay.

Honestly I'd rather sell it outright and put that money back on my card




Here are pics, I'll take better one's when it comes in this afternoon.

Thanks again

Dennis

 

Actually I just ran the numbers for the cfm flow on my engine through DD2K and only gained 9 hp. True it puts me over that 500hp mark but I think i'll stick with what I have for now. Since you want the money and I don't need it.....

 

i have a 58mm TB on my L98. it was on there when i bought it. didnt notice any real difference at all. (ive driven enough L98s to know what a healthy stock one feels like) then i ported the plenum to match and it really came to life.

id say put it on but make sure you port your plenum to match. mine works great even with stock heads, intake, and cam. (though i do have aftrmkt exhaust, AFPR, ignition goodies, etc).