RoachLIVEinLA

Whats the importance between these measurements? Im guessing these would be circumfrance of the opening, but whats the significance? Will a 75mm throttle body produce more HP than a 65? Or do you need to upgrade your intake manifolds or fuel injectors if you choose to go with a 75mm? Im hoping some can clear this up for me.

NotchAbove

The number (65,70,75) represents the opening of the throttle body. What you want to do is match the size that best suits your setup. Everyone you ask will have their own opinions on which is the best size, etc. Certain manifolds will require a larger TB to match the openings. Most guys with a 302 and mild upgrades run either a 65 or 70.

RoachLIVEinLA

Lets say I have plans to do some serious upgrading, however, I have the option of buying 75mm TB/egr spacer combo for cheap. Is it possible to run stock 302 with a 75mm tb/egr now until i have the heads/intake/fuel injs. upgraded or would it cause it to run lean?

NotchAbove

You can go with the 75mm on a stock engine. You will not run lean, as the TB does not affect the A/F ratio, it just allows air in. What it will do however is, since a 75 is larger than the engine needs you will lose some bottom end torque, as that larger of a TB will cause the air to move slowly. Keep in mind the stock is 55mm.

Joel5.0

Nope.... it doesn't affect torque due to changes in the speed of the air through the intake. The TB, as mentioned, is simply an air stream valve accounted for by the MAF, which starts the fuel metering calculations, you would only need to increase the accelerator pump function in the ECM to compensate for a better intake pulse...... easily done in a speed density system as I confirmed with two stock '86 setups I had to install an 80mm TB.

NotchAbove

I saw you talk about this before Joel. So, then, why do they make different sizes ? Why don't we just all run a 90mm and call it a day ? Just asking.

AdderMk2

because people still believe that there is no need for such a large TB.

I ran a 70mm on my stock manifold. any bigger and it wouldnt have been beneficial. the opening on my intake wasnt going to take advantage of anything larger.

my new manifold however has a 75mm opening... so, my new TB... is 75mm

Joel5.0

Same reason the 331 is an option...... marketing..... nah!, as everything in this vice, it all depends on the whole combo. IOW.... you could also have a 70mm or 65mm TB perform within your goals, if the rest of the combo IS compatible. Same goes with the other components. For example..... if a 75mm TB is "HUGE" for a 302 CID engine with some performance mods, why does a Lincoln LS comes with a 82mm bore/70mm blade TB on a 240 CID engine from the factory?