• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Bored TB on renix motors


NAXJA Forum User
Just wanted to know what increases were noticed if any boring to 58mm and or using a TB spacer. I already made a TB spacer out of Phenolic which is supposed to be heat resistant rater than alum but haven't installed it as of yet and I am about to bore my extra TB out to 58mm.


I bored my 88 throttle body to 60 mm and it helped noticibly throughout the rpm range, especially at higher rpms. My engine is bored over .030 also.
I bored mt 88 TB as well to 59.5mm. The bigger throttle plate was a pain to get right. I noticed most of my gain in cooling. runs a little cooler, little snappier at higher rpm's. My opinion is if you have to buy one its not worth it, if you can bore it out yourself, do it.
I used a bridgeport milling machine with a boring tool. I think people have done it differntly and works for them. Do a search its there. The throttle plate was a little tougher. I used 2.5" alluminum round stock, Put it in a adjustible dividing head for the mill, found the angles I needed and parted the peace from the round stock. polished it up and put it all back together. good luck!
four11outback said:
I used a computer CNC milling maching at school for the butterfly.
Can you make me one for $$$$ ???
I have a neighbor that has a mill to bore mine, but the plate would seem tobe a PIA !!!

George in Kentucky
georgemu said:
Can you make me one for $$$$ ???
I have a neighbor that has a mill to bore mine, but the plate would seem tobe a PIA !!!

George in Kentucky

You can buy just the plate from XJ Armor in CA.

You can also buy the whole TB from him.
Ok so I bored my throttle body at work. (a cnc mill) and made a new plate for the butterfly, opened up the shaft to accept the larger butterfly and I think it fits together better than the factory. The thing you have to realize is that the butterfly sits in the TB at an exact angle and has to be machined to fit the bore precisely while sitting at that angle(eliptical) or the motor will have too much air getting through and you will essentially have caused a huge vacuum leak. I went to 58mm to start and am now planning on going to 60mm to match the intake. I did notice a power increase at freeway speeds and a slight increase in fuel economy. I do not think this is worth the money people charge for this unless you have an engine requiring larger amounts of air where the real power gain will be noticed. I have also machined a TB spacer out of phenolic resin. Phenolic insulates against heat and keeps the throttle body cool to the touch even after a hard drive and thus aids in keeping the incomming air charge cooler(in theory). I think this would be aided by a coldair intake or snorkle. So thats what I came up with since I first started this post. Thanks for the replys