TB max bore

[3100gagt]

Hey guys i have a 99GT-3400 and i want to get a spare TB and have my friend the works at a machine shope bore it out for me. I was wondering what the max you can bore these TB out to.
All the ones you can buy are like 62mm i didnt know if i could go 65mm or even 70mm. What is max?
I have intake, H-flow cat and SLP so i want more air in the engine.
Also planing on PCM very soon.
Thanks Lee

[99GrandAMSE]

... obviously, there would be a limit but you will also have to consider how large you can properly make a plate to suit it ... personally, mine is a custom job that is 61mm IIRC because it matched the stock bore of a 5.0L Mustang which there were plenty of plates around :)

[3100gagt]

yes all it is is a screw holding a brass plate and brass is verry easy to machine
i just dont want to hit the water jacket or idle air pocket. then waste the TB.

[99GrandAMSE]

... brass is certainly easy to machine but the edges are bevelled to a specific degree for proper closing ... as well, the plate and the bore have to be a perfect match of the amount of air flow will not be consistent ... good luck!

[3100gagt]

well he builds trans for nascar and doing this for over 20 years so we will see
Does any one know the max bore? Thanks

[kickarsgrdam01]

they sell a 65mm throttle body somewhere...most people go with the 62...but a 65 is possible. so probably 67-68 is my guess

[99GrandAMSE]

Originally posted by 3100gagt
well he builds trans for nascar and doing this for over 20 years so we will see ...

I didn't say it COULDN'T be done, what I told you was how to do it EASILY ... if you or someone else wants to take the time and effort to go above and beyond the norm and make a special matching plate and body, you can probably get away with 65 or thereabout like already mentioned (if you go that far, the person doing to milling can judge for themselves as they go along) ... in all honesty though, unless you match the upper and lower intake you won't see much difference ... hell, even if you did have them matched, I doubt there will be significant difference compared to a standard oversized 61/62mm unit unless you modify other engine components to warrant the little bit extra you'll get ... enjoy!

[3100gagt]

i allready Gasket matched the upper and lower manifolds and i planed to match it for the oversized TB i just didnt want to spend $210 on a 62mm when i could have one made for less.

[coupe]

No matter what it will be a waiste of time and money.

[voyager]

i'm with coupe. i wouldn't spend any more than $30 on a TB without forced induction. you don't even have headers or ported manifolds.. do you think a TB will give you more than 1hp?

[Pte Socks]

Well id have to say, save the money and invest the time elsewhere. As a nicer way of saying it than voyager, your not going to really need a larger TB until you really start upgrading yoru car because the stock one is already a decent size.

[ChevelleSSLS6]

going from a 650cfm holley on a 350 v8 with exhaust, intake, and other bolt ons to a 750 isn't going to do any good. The same applies to our GAs.

If it's a screamin demon 350, on the other hand, it probably has a dual=quad setup with 2 500cfm holleys.