How much of a gain does a bigger TB give on 3.1's?

[BillS]

so a 3.4 TB is 62mm? Will it bolt to my3.1 intake or will i need an adapter made?

No, a 3.4 is 52 mm. The 3400 may well be larger.

I question whether just adding a larger throttle body to a stock engine gets you anything. Certainly on the 2.8 I wouldn't think it would.

On a modified engine it probably is worthwhile. I have a 3.4 iron head engine, modified, in a British car and went for the 62 mm throttle body, which seems to work very well indeed, but then I never drove if with the small original version so can't assess what difference it might have made (one always HOPES there is a difference when one shells out bucks for something...)

[3.1cutlass]

ok so i need to get a 62mm TB somewhere and get my manifold bored to 62mm sounds good.

[JMo60]

I from experience saw no gains using a 3400 throttle body on a 3100. i did port the mounting flange to the diameter of the TB. i ran the car at the track 3 runs with a 3100 TB, and 3 runs with the 3400 TB in the same day. there were no gains to be seen with a stock engine.. maybe with some mods it may be useful.

[BillS]

ok so i need to get a 62mm TB somewhere and get my manifold bored to 62mm sounds good.

Be careful - it isn't always as easy as just boring it out.

We bored my Camaro plenum to match the 62 mm TB and broke through in a couple of places. It is a right swine to weld anything that thin (i.e. all the metal surrounding the area that broke through) so I use JB Weld, but there goes any thought of having a nice polished plenum!

You also have to taper the hole into the plenum with a die grinder - takes an hour or two.

[kflo 93 gt]

On a 3.1 mpfi I wouldn't worry about going 62mm without having that engine pretty much worked. Those intake manifolds just don't move that kind of air. I think with the mods you had listed on the grand prix you would be totally lucky to see a 2 - 3hp increase. About the only noticeable difference I got when I put a 59mm on my pretty much full bolt on 3.1mpfi engine was a neat whistle sound at certain rpms.

Now that I'm going 3x00 I'm sticking with a stock 56mm tb.

[strtrydr]

As said above...

Stock 3400 manifolds are 56mm at the plenum ... but they can be bored out to 65mm MAX. 62mm is the common one for a 3400 manifold though.

[torq455]

i felt a decent gain on a stock 3100 going from 52mm to 56mm. as far as an extensively worked 3.1, not really. i have mild mods and when i went to the 62mm TB, wow!