Hey guys 70 or 65 mm tb?

astronut1885 · Jul 16, 2004

Guys- it's all about air velocity and air volume. Imagine a 2 liter bottle of coke. Pour it down a narrow hose. Not much gets through at once, but it moves fast because of the pressure behind it. That's a stock TB. Now go to a huge chunk of PVC. Pour it through. Yeah, it all gets through, but not as fast, and it's all over the place, very turbulent. That's a TB that's too big for the intake capacity. Now get a middle sized pipe. Pour it through. Now it moves fast, but it's also moving alot of quantity, which is the perfect situation. You want a throttle body that will supply enough air, but not too much so that it stalls and you loose all your torque. I say a 70mm is more than enough for a 302-306-308 N/A motor, unless it's really extreme, then a 75. I'll be getting a 70 for my combo.

86Cobra · Jul 16, 2004

Sigh. Ok, I'll explain this one more time.

The tb is a VERY small portion of the intake tract. Your whole pipe and hose analogy is totally meaningless in this case. You have a long (compared to the tb) intake track before the tb, then the intake itself after the tb. Any velocity gained or lost in the tb doesn't mean jack.

astronut1885 · Jul 16, 2004

Does the term bottleneck mean anything to you? that's what happens with a stock TB. And with a TB that's to big the air gets turbulent, killing air velocity and torque. The airpath needs to be smooth and consistent, just like the insides of an intake runner. Don't know what the hell you're talking about that a TB doesn't matter. They've only done dyno tests to prove it.

86Cobra · Jul 16, 2004

Wow, you totally missed my point. Obviously you didn't actually read the rest of this thread where I told him to get a 75.

My point was that a larger tb (up to the intake size, 75mm in this case) won't hurt. The air won't "stall and you loose all your torque."

Grn92LX · Jul 16, 2004

shttygtstang said:
not true i have a edelbrock victor 5.0 intake and its recomended from edelbrock to have a 75 and i have one no porting involved

My bad, I meant the normal edelbrock intakes- the performer and the rpm.

FaistyGTS · Jul 16, 2004

I used a 70mm on my 95 and it runs pretty awesome. If your choices are 65 or 70 I'd recommend the 70mm just my $.02

astronut1885 · Jul 16, 2004

His motor isn't pulling (or pushing with a blower) enough air to justify a 75mm, and odds are he will loose some air velocity with a larger than 70mm TB. It's just the same as telling him to get a 105mm TB they use in NMRA race cars. Everything has to be in proportion. He needs a 75mm TB like he needs full 3" exhaust. It's nothing but overkill and torque suicide. I've read the reports, I've spoken to many experienced stangers, and they all agree. I've done my homework on this, because I am in the same boat. I need a better TB than my stock POS. Also- get a slightly larger MAF. The MAF should be larger than the TB if possible, again to maintain air velocity. You don't want a bottleneck somewhere in the system. I am a big fan of the Pro-M 75mm chrome bullet meters, that's what I'll be getting.

93 teal terror · Jul 16, 2004

Wheres the guy who picked up about 10rwhp moving up from a 75mm to a 90mm tbody. It was an all motor 306 as well, but I dont remember the rest of the combo.

86Cobra · Jul 16, 2004

I've noticed that some people on this site have a serious reading comprehension problem.

As I said before, the throttle body shouldn't be larger than the intake inlet (75mm for TFS). So, your 105mm comment is meaningless.

The tb should match the intake. It can't hurt to run a 75 on an intake with a 75mm neck because the intake normalizes the velocity from the tb.

If you think about it for a while, you *might* understand. Then again, maybe not. I'm done.

mob · Jul 16, 2004

the densecharger is a good cai for a 5.0l, it has a nice full length intake and comes with a pro-m 75mm maf for 290

astronut1885 · Jul 16, 2004

I can see what you're saying. I hadn't taken into account his intake opening. You are right, the intake will check the air up to it's diameter anyway. So in that case, the whole thing is kicking torque right in the face in order to make high end horsepower.

remat457 · Jul 16, 2004

astronut1885 said:
His motor isn't pulling (or pushing with a blower) enough air to justify a 75mm, and odds are he will loose some air velocity with a larger than 70mm TB. It's just the same as telling him to get a 105mm TB they use in NMRA race cars. Everything has to be in proportion. He needs a 75mm TB like he needs full 3" exhaust. It's nothing but overkill and torque suicide. I've read the reports, I've spoken to many experienced stangers, and they all agree. I've done my homework on this, because I am in the same boat. I need a better TB than my stock POS. Also- get a slightly larger MAF. The MAF should be larger than the TB if possible, again to maintain air velocity. You don't want a bottleneck somewhere in the system. I am a big fan of the Pro-M 75mm chrome bullet meters, that's what I'll be getting.

I agree....

I think that a 70mm TB is fine and you want your MAF to be slightly larger..

D347643 · Jul 16, 2004

does anyone have any dyno runs showing a comparison between the tb's?
i have the exact same setup as the guy who started this thread. i think i should go with a 75mm now,

NoSloCoupes · Jul 16, 2004

These threads are always gay. They always turn the same way....86 always gets his "internet racer" jab in. Its great!

Former 90mm tb user here. Yes and it was on a little bitty ol 306 too.

I know of a n/a 347 using a 110mm tb also...it only runs 10.20's and only dyno's 500rwhp.

remat457 · Jul 16, 2004

Here is what Edelbrock says about 75MM TB: "75mm is intended for more radical engine cominations and requires port matching to fit most manifolds.." They recommend a 70mm for their own H/C/I Performer Package...

The Official Mustang Tech Ref. book does say that using too large of a TB will result in power loss. Of course, what that is though will vary by engine

I still would personally go 70mm (in fact, that's what I have) but I think a 75mm would be fine...I think that it would depend on how much more are you going to do to the motor? (It's not a 306 or 347 yet..)

Here is a link to a very similar thread (I didn't read all of it since it is 4 pgs but maybe it will help): http://forums.stangnet.com/showthread.php?t=482132&highlight=afr+165

shttygtstang · Jul 16, 2004

are you say im not normal every one says that

70XR7ConvertCat · Jul 16, 2004

For a naturally aspirated engine, it defies logic (dyno could prove me wrong) there is a benefit to going with a larger MAF size, than the throttle body. Each cylinder's respective intake stroke is creating vacuum to draw air into the engine. There is going to be no velocity gain by using a larger MAF in this case. I'm in the process of building a balanced '93 5.0 HO (.020 over) for a '67 Cougar. The induction is based around an extensively ported '93 Cobra upper and lower intake. BTW, the inlet diameter on the Cobra upper is 71 mm. My Accufab 70 mm TB, and 70 mm Pro-M calibrated for 24 lb injectors is about right. With a 2 1/4" - 2 1/2" exhaust, I expect 300-325 hp at the rear wheels. This is not huge rwhp, but keeping the torque up is more important to a street machine. That's where the intake porting has me a bit worried.... If these rwhp goals seem out of reach to anyone (please let me know), the other part of the package is AFR 165 heads, Comp Cams Xtreme Energy Roller (ok, so it's sort of mild), and 1.6 rockers.

Steve C.

shttygtstang · Jul 17, 2004

its real simple i think and this what ive done pick a motor combo buy the stuff but dont install it till you have it all.whats the point of buying a 70mm tb when in 4 months youll need a 75 comon its not that hard theres plent of proven combos out there pick one

jaidedeye · Jul 17, 2004

mob said:
65 is stock man id be a waste of money,

stock is either 55 or 60..

id go with a 70mm

bmo37 · Jul 17, 2004

I like the 70mm t-body from experience compared to the 75mm, I lost lowend and the car actually reved slower imo with the 75mm. But thats prior to my stroker and boost, so I can't comment on a sc setup. Like stated the car has to be in proportion. I can't wait to be called an internet racer, here we go again.

Hey guys 70 or 65 mm tb?

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