MAC 70 mm- Does it really hurt torque?
 

I'm still trying to pick a TB for my combo. I had pretty much settled on a 65 but then I ran across the MAC 70mm that is cheap and has a plate.
I've heard that 70 & up can hurt low end. I autocross alot and don't want to lose any of that grunt coming out of the corners. Since I will have much more hp I'm thinking that I wouldn't notice it too much.
I also think I'm on the edge of moving up from a 65 anyway.

Anybody have an opinion on the MAC, 70mm size, or what your car did when you changed?

Thanks,
Dan

Technically a 65mm TB can hold up to 400hp, but a 70mm would not be too bad a good intake/cam/heads combo.

My GT with only mild mods has a 70mm Edelbrock Throttle body and EGR plate and the stock intake was ported to match. From what i've noticed it's really not bad, but then again with the 3.55 gears it's not often i'm below 2,000rpm. Power really picks up around 2500 and i suppose it helps that my car has the stock MAF sensor to increase velocity (stiffle air flow), which will soon be removed for a larger unit. But I haven't noticed any negative effects like low rpm sputtering or anything else. Unlike a carbureted vehicle, you don't need a strong vacuum signal through the throttle body to help pull fuel... a nice man in a silver box does that for you (the ECU).

The 70 mm will probably be just fine. I doubt that you would really lose that much low-end torque. Plus, when autocrossing, how often are you under say 2500-3000 rpms? Probably not that much, right?

Sounds like you're putting together a a solid combo. Keep us posted on the install and results.

Good luck,
E

Remember, when naturally aspirated, more air is better, A 70mm will not lose you torque, what size mas do you have, that is a consideration as well, i work for Skip Barber Racing School here in Sebring, Florida. Want some insider rracer tips from Juan Montoya, just a little lunch at Wendy's to pick his brain back when he dominated the Pro Series.

i am currently an instructor, and would love to instruct you on-line, there are some things you can learn on paper as well as the track.

i'm bored.

Stock MAF

When I can afford it I will go with 24lb injectors and a calibrated 73mm.

Who knows, if this baby runs good enough I may forgo the injectors/MAF and concentrate on paying off this growing pile of engine upgrade debt that the wife doesn't know about yet....!

Dan

sounds like 24's will be plenty for you, whew!, GOOD LUCK.

stick with the 65mm. its all you need and throttle response will be much better, which you will want for autocrossing.

Ive had both, a 70mm BBK and a 65mm Ford motorsport, and I speak from personal experience.

the difference in power between a 65 and 70mm on a combo like yours is non-existent, but again, throttle response is much better

I had posted a similar question a while back and EVERYONE said go for a 65 mm. Sounds like he still has a stock TB and is wondering if he should get a 65 or 70MM unit.

Mac only sells a 70mm unit, they claim it makes somewhat more power than a 65 mm with no real torque loss therefore they felt the 65 mm was not necessary. Of course that is their opinion, many other mfr's make 65 mm units.

I was pretty sold on a 65 for my car till now, this is interesting.

I have a set of cobra 24# injectors, and need new headers and h pipe. Still have original fuel pump, TB, MAF etc So..

I was figuring on going long tube 1 5/8 headers with cat H pipe, 155 LPH pump Adjustable FPR, the 24# injectors, a 76 MM C&L MAF calib for 24# with the alum connector pipe, and a new TB. Now I am thinking a 70MM unit again ARRGH

Also have a pulley set and a 130 amp alt to install too, too dam cold for now!

I searched the past posts and came up with the same 65mm majority opinion.

Then I ran into the MAC thing. You can get TB & Plate for $170-180 but will pay $225 & up for the 65mm by the time you pay extra for the Plate too. Seems like the polished surface also appeals to people.

So the size vs performance traits is my last issue. My understanding is that after you do heads, intake, and exhaust the stock TB & MAF are next culprits.

Appreciate the advice so far....

Dan

Take this for what it's worth....

When MM&FF was putting together their stone pony project car, they tested a 65mm (ford racing) and 70mm TB (edelbrock/bbk) on the dyno. The mods on the car were edelbock performer Heads/cam/intake plus all the bolt-ons. I think the car was making 270-280 rwhp at the time. Anyways, they claim that the dyno runs between the 2 TBs were identical, and you could lay one graph on top of the other and not notice a single difference.
IMO, go with the 65mm.