65MM Throttle Body

[JPJP]

I am in the process of converting a 65MM (Explorer) throttle body and a matching EGR spacer to put on my '86 Mustang. The engine is stock and I have a 3.75 Dia. blower pulley on my SN Paxton. I have absolutely no dyno experience but would like to know an estimate from somebody who may have tried it/dynoed it. How much HP increase I should expect? Following are some things I have learned from published literature:

From Kenne Bell Ford Tech Tips: "A 65mm throttle body produces 3 additional horsepower on a stock 5.0 (220HP/330 cfm), yet there's 10HP on a Kenne Bell supercharged (300HP/450 cfm)."

From The Official Ford Mustang 5.0 Technical Reference & Performance Handbook:
Throttle body Dia. of 58 MM flows 541 CFM (only one value given)
Throttle body Dia. of 60 MM flows 580-600 CFM
Throttle body Dia. of 65 MM flows 625-650 CFM

I know the Paxton superchargers are not "draw thru" units like the Kenne Bell units so HP gains will be less. Also, I am going from 58MM to 65MM Dia. instead of from the usual 60MM found on the other years.

Pure flow area of the 65MM throttle body has 17.4% more flow area than the 60MM throttle body and 25.6% more flow area than the 58MM throttle body in round numbers (not considering the butterfly restriction in my math here).

Please provide what gains you may have experienced or any formulas (if available).

[speedytang]

If your still using the '86 Intake you will gain nothing. The '86 intake is so small that is why Ford used such a small throttle body. A larger stock intake(87-93) would be more important, then match a 70 mm throttle body to it. Then at least the intake and supercharger can handle the same cfm.

[JPJP]

I thought the only difference between the '86 and '87-'93 upper manifolds was the entry port (at least my technical handbook that I mentioned above says that) which I plan to match anyway with my die grinder.

Now I just went out to the garage and measured the opening: 56.4MM. Wowee that is small! I guess I would have a lot of material to remove.

Thanks for your answer I may just go get another upper!

[F=MA]

You want some real gains? Don't screw around too much with the TB. The lower intake on any EFI Mustang 5.0 is absolute dogshyyt beyond description. Whip out the die grinder and hog the shyyt out of it as much as you can and you'll see a meaningful improvement. Opening up the upper intake and TB is like trying to dump a bucket of water into a straw standing upright.

That goes for the 86 lower and the 87-93, which is identical.

F=MA

[JPJP]

Sorry about the delay. I listened to your advice and seached E-bay and bought a ported upper and lower intake manifold set for a great deal. Naturally the upper is from a '87-'93. I will refrain from tearing out the lower at this time and only use the ported upper I just got with the above mentioned 65MM (Explorer) throttle body.

F=MA: I knew you were probably going to talk about the lower since I know you have spoke about it in past posts. I will only use the upper as a bench mark since I only did the lower intake gaskets a short time ago and don't want to dive that deep presently. After a while I will add the lower for the added gains.

[F=MA]

As I said, the ONLY gain is in the lower. If your running stock heads the 87-93 stock, unported upper is plenty. The lower is where the problem lies. Get there as soon as you can and you'll be happier.

F=MA

[JPJP]

Thanks......I will try not to wait too many seasons.

[speedytang]

Spend the 30minutes and $20 on gaskets and switch over.

[JPJP]

Over the winter I rebuilt my SN89. I added a HO impeller while I was in there.

I went ahead and followed your advice and put the ported lower intake on and also a 1/4" phenolic intake spacer.

There is a definite increase in performance. I am assuming most of the improvement is from the HO impeller and the ported intake to be secondary.