Infamous throttle body size question!!!

[84convertablegt]

OK, ive seen a million posts on this, but the throttle body issue is driving me crazy. Ive just finished my afr 165 head swap and ported 95 cobra intake. everything is done, i still have the stock 60mm tb. I hear 70mm can be too big and 65 is right? what will a 65 really do for me over the stock 60mm tb? this is driving me crazy, will the 200 dollar price tag be worth it, and if so with these mods (see sig) will a bigger one say 70mm be better or is 65 enough? Ive seen corvettes with 80mm tb's and honda civics with 75mm tb's, so it seems as size is relative here. If my 60mm will flow enough to support 300hp well than ok, but if not what should i get? this really is bothering me way to much, its like my last issue.

 

[a50sn95]

http://forums.stangnet.com/showthread.php?t=600561

 

[84convertablegt]

http://forums.stangnet.com/showthread.php?t=600561

Well, that helps, thanks for the link. basically what i take from it is that a million people still disagree on what a tb does. but one point does make sense, i suppose i only have a 65mm opening in my cobra intake so using anything bigger is pointless. but i can see a 60mm tb being a slight restriction, especially the stock tb. so i guess ill be using a 65mm tb, anyone else feel free to chime in with contrary advice

 

[Don 95Vert]

There are people running 8's and 9's with turbo Mustangs with 65mm TBs... On an NA car, naturally it won't flow that well, but it will NOT be a restriction on your setup.

There is another consideration for you and that's idle control and driveability. Ford manufactures their TBs with a special coating on the inside of the bore. It is a 'non-stick' coating and it's there so the throttle blade can be shut completely without sticking. Once it's shut, the IAC can control idel like it is designed to do. None of the aftermarket TB companies can afford to do this coating - they rely on keeping the throttle blade slightly open to prevent sticking. So IMHO, for an NA car like yours without a doubt, I wouldn't consider anything else but a Ford Racing 65mm TB...

Don

 

[YEAHLOH95]

i say if you are set on getting a throttle body get a 65mm and if you can find a ford one that will be your best bet also

 

[final5-0]

There are people running 8's and 9's with turbo Mustangs with 65mm TBs... On an NA car, naturally it won't flow that well, but it will NOT be a restriction on your setup.

There is another consideration for you and that's idle control and driveability. Ford manufactures their TBs with a special coating on the inside of the bore. It is a 'non-stick' coating and it's there so the throttle blade can be shut completely without sticking. Once it's shut, the IAC can control idel like it is designed to do. None of the aftermarket TB companies can afford to do this coating - they rely on keeping the throttle blade slightly open to prevent sticking. So IMHO, for an NA car like yours without a doubt, I wouldn't consider anything else but a Ford Racing 65mm TB...

Don

Don

I always find the stuff you share helpful and informative

For quite some time now, I have not been too active in tb size threads.

Simply Put and getting right to the point.

I'm unsure
and
I've not been able to make up my mind about this issue to this day

I can see what I think are valid points from both camps in those discussions.

The only hard data I have is ................
I put a FRPP 65mm tb on the sig combo and at 6K rpm, the 5mm larger tb pulled 25kghr more airflow as shown my dlog. An increase for sure but, I have no way of knowing more than that
or
what gain it might be, lol

btw ... nothing was changed other than taking off the 60 and putting on the 65

Your info you have now shared is making me think a bit more

Grady

 

[Grn92LX]

My old 302 combo was in the same ballpark as you. My cam grinder (ed curtis) recommended a 75mm tb, so I swapped from the tiny 65mm to the proper sized 75mm Do it once, do it right. And no, its NOT too big LOL

 

[VibrantRedGT]

Buy it once, go big out of the gate. Just make sure you intake opening matches.

 

[84convertablegt]

There are people running 8's and 9's with turbo Mustangs with 65mm TBs... On an NA car, naturally it won't flow that well, but it will NOT be a restriction on your setup.

There is another consideration for you and that's idle control and driveability. Ford manufactures their TBs with a special coating on the inside of the bore. It is a 'non-stick' coating and it's there so the throttle blade can be shut completely without sticking. Once it's shut, the IAC can control idel like it is designed to do. None of the aftermarket TB companies can afford to do this coating - they rely on keeping the throttle blade slightly open to prevent sticking. So IMHO, for an NA car like yours without a doubt, I wouldn't consider anything else but a Ford Racing 65mm TB...

Don

OK, I was planning on probably using the 65mm Ford TB. It is a little more expensive than other 65mm tb's, but in my experience I've never had problems with ford parts designed specifically by ford engineers. So just to justify this to me more Don, besides the included IAC and TPS parts with the ford unit, it has a coating on it that aftermarket ones do not? Ive heard of this teflon like coating that resists carbon and stuff and this is why they say dont clean the inside of the tb with any cleaners. Ive also heard that for some reason the 65mm ford tb doesnt flow as well as competetors 65mm tb's. anyone shed any light on this?

 

[18mustangs]

OK, I was planning on probably using the 65mm Ford TB. It is a little more expensive than other 65mm tb's, but in my experience I've never had problems with ford parts designed specifically by ford engineers. So just to justify this to me more Don, besides the included IAC and TPS parts with the ford unit, it has a coating on it that aftermarket ones do not? Ive heard of this teflon like coating that resists carbon and stuff and this is why they say dont clean the inside of the tb with any cleaners. Ive also heard that for some reason the 65mm ford tb doesnt flow as well as competetors 65mm tb's. anyone shed any light on this?

I used the FRPP 65mm on my car before I did the Fox TB conversion and loved it. I tried to get another 65mm, but lost the auction so the only reason I moved to 70mm is because I got a good deal. IMO, you'll be good to go with 65mm.
Tim

 

[bimmertech]

i personally feel t/b size should be chosen based on the runner length and plenum size of your intake.

for example: if you have a stock or cobra intake a stock size t/b will will be enough to keep the plenum full of air due to the fact the air takes longer to reach the head--see 3rd wave pulse tuning.

now compare that to a short runner intake like a vic jr. yes the intake is usually fitted on an engine that has very good breathing capabilities, but if the t/b is not able to keep the plenum full of air due to the fast movement of the charge--2nd wave pulse--then a larger t/b would be required.

this is just my WAG, but it sounds good.

 

[Don 95Vert]

OK, I was planning on probably using the 65mm Ford TB. It is a little more expensive than other 65mm tb's, but in my experience I've never had problems with ford parts designed specifically by ford engineers. So just to justify this to me more Don, besides the included IAC and TPS parts with the ford unit, it has a coating on it that aftermarket ones do not? Ive heard of this teflon like coating that resists carbon and stuff and this is why they say dont clean the inside of the tb with any cleaners. Ive also heard that for some reason the 65mm ford tb doesnt flow as well as competetors 65mm tb's. anyone shed any light on this?

Yep the Ford TB has the coating and if you clean it, DO NOT use carb cleaner - use the specially formulated TB cleaner that is 'coating safe'. I think it IS teflon, but I'm not sure so I really shouldn't say. Not sure on the flow data, but suffice to say, it won't make a hill of beans of difference.

 

[scarless]

The opening on my 94/95 Cobra upper is 70mm. 65mm is good, 70mm would be okay if you get a deal on one. I don't think the difference in the two will matter much at all. With AFR 165's and a ported intake, I think I'd lean more to the 70mm, but no bigger.