GM Electronic throttle body help

Hi Guys,

I have seen a nice intake manifold on the HPA 1UZ powered Toyota 86 and have decided to get one for my own 1Uz project. By accident, I bought the 105mm Holly plenum top (https://www.holley.com/products/intakes/cast/parts/300-246BK) and I am having a hard time finding a reasonably priced electronic throttle body. I guess I need a 102mm throttle body now to fit the plenum? Shockingly, the only proper units I can find cost 700$. I started investigating cheaper ones on eBay that obviously come from China for about 150$. I am concerned that these China units may be a waste of time and money, normally things like this from China always disappoint, does anyone have experience with this? Because I am not very keen on forking over 700 bucks. Furthermore, could a bad electronic throttle damage my management system? I am also located in Europe and GM does not sell any spare parts like TB's over here anymore.

Any advice would be much appreciated.

Best regards, Christiaan

As with a lot of US sourced parts, there is a regretable lack of information provided for that intake - it's not difficult, HOLLEY, to give the bolt pattern, height, etc. It appears to be intended for the OEM Corvette TB, so you may need to chase one down from a US source - new or S/H?

It is preferable, as you say, to use one that's sized to be a bolt on part, but there's enough material there to re-drill for a different brand of 'body, or an adaptor can be used. Matching the bore would be best, but a little smaller won't make too much difference and if larger it can be bored out to suit, if there's enough wall material.

Depending on your engine management, might be worth looking at it from EFI bodies the software/hardware supports and looking for something to match? I had a quick look, but didn't find anything of real use.

Hello Gord, Thank you for your reply.

I agree, they could supply more information of those parts and dimensions.

I learned that the gen 4 LS 90mm TB has the same bolt pattern as the 102mm TB and will fit onto my 105mm plenum, not ideal but I can not justify the 250% increase in price. So I bought an original 90mm unit after I learned that the China units give issues.

There are still a couple of things you may be able to do.

You may be able to fit a larger diameter (they're actually slightly oval) throttle butterfly on a machined out throttle body - the percent increase is the square of the diameter, so even 5 mm, if there is enough material in the 'body, will be ~10% more throttle area. You should be able to have one machined locally, to the same closed angle.

The second thing is there may be some potential for some blending/tapering of the transitions to, and from the butterfly seal area to the flanges. Again, might only be a couple of precentage points, but it all helps. similarly, small gains can be made by CAREFULLY 'knife edging' the throttle butterfly's leading and trailing edges - the important thing is to avaoid damage to the 'sealig' edge - some leakage is fine but too much will make it impossible to keep idle rpm down. If you mark the shaft where it abuts the housing' bore, you can also remove one side of the shaft to those points - NOT the threaded side - and smoothe the other for another small gain. Modern manufacturing is damn good, but check the butterfly blade is actually open 90 degrees - some may be a little less and some a little more - you may be able to adjust to correct this.

However, when all's said and done, you may not notice much difference, if any, as it may not be a significant restriction - and there are also trade-offs to be aware of. True, with an oversized TB you don't have the metering/signal problems you can get when over-carbying, but many other issues apply to both. The engine is going to be more responsive/twitchy at small throttle opening as the same throttle blade angle will allow more air through, and the engine will be less sensitive to the throttle when close to, or at, full open as the pressure drop across the blade as it moves will be reduces as the engine can only draw in a fixed amount of air per cycle.

Not quite apples and apples, but watch this https://www.youtube.com/watch?v=7hPYXz-V6Xc