65mm or 70mm TB?

fox racer · Nov 6, 2005

ok, i have GT-40 turbo swirl heads, a cobra intake, 24lbs inj. waiting to go on, 1.7 RR, pullies, 14* timing, no smog and maybe in the future a custom cam. can i get away with a 70 mm TB for now? or will i just notice a power loss like others have?

vikingpower · Nov 6, 2005

75mm! why buy a 65 or 70 when a 75 is only like $20 more? And dont believe all the BS about "losing power" just look at the LS engines from GM they use even bigger TBs from the factory!

notchback · Nov 6, 2005

the opening on the intake is only 70mm.......and you don't need any more than that anyways. 65 is good til about 400 hp, but since the opening is 70, you don't wanna run into a wall

i'd go 70

Grn92LX · Nov 6, 2005

70mm at least. You may not feel much, but you should see a solid 8-10hp.

N8Miller · Nov 6, 2005

Grn92LX said:
70mm at least. You may not feel much, but you should see a solid 8-10hp.

im with him...

payupsucka · Nov 6, 2005

not to hijack the thread but, i have a 65 mm tb tw heads a cobra intake and an e cam and everyone told me that the tb and mass air was the restriction and that i should go bigger be cause my numbers were low i made 276 and 315 tq. a 65 is good to 400?

Grn92LX · Nov 6, 2005

payupsucka said:
not to hijack the thread but, i have a 65 mm tb tw heads a cobra intake and an e cam and everyone told me that the tb and mass air was the restriction and that i should go bigger be cause my numbers were low i made 276 and 315 tq. a 65 is good to 400?

That 65mm tb is holding you back a little as compared to the proper sized 75mm, But the 65mm isn't your problem for those low #'s. What was your timing at? How was the a/f? My old TW headed 302 liked 18* initial.

payupsucka · Nov 6, 2005

timing is at 14 and i cant remember the a/f i also heard that my cobra intake was the weak link but i dont buy it

Grn92LX · Nov 6, 2005

payupsucka said:
timing is at 14 and i cant remember the a/f i also heard that my cobra intake was the weak link but i dont buy it

The a/f is important to know. I gained 1.5 mph at the track on my old trickflow 302 combo going from 14* to 18* timing. The cobra manifold is ok for now, you're only running an E cam.

Repostyle · Nov 6, 2005

I had my cobra upper machined to a 75mm opening to get rid of the "wall" and a 75mm TB and have no problems.

90mustangGT · Nov 6, 2005

In long runner intakes, most of the velosity is made in the long runners, therefor the TB isn't where it is created. Really, I would do the 70mm because the inlet is 70mm, try to keep a smooth path. Having a large inlet and outlet, but small in the middle is called an orifice, and that is a restriction.

5spd GT · Nov 6, 2005

vikingpower said:
75mm! why buy a 65 or 70 when a 75 is only like $20 more? And dont believe all the BS about "losing power" just look at the LS engines from GM they use even bigger TBs from the factory!

There is alot more factors than just TB size...lol...to why they get the power they do.

I would go no bigger than a 70mm...

You will lose low rpm pickup and have a goosy feeling under part throttle conditions.

Michael Yount · Nov 6, 2005

Either a 65 or 70 should work fine -- there's no performance downside to going with the 65 and no performance upside to going with the 70. Neither will be a bottleneck with the HP/torque your combo is gonna make.

18mustangs · Nov 6, 2005

vikingpower said:
75mm! why buy a 65 or 70 when a 75 is only like $20 more? And dont believe all the BS about "losing power" just look at the LS engines from GM they use even bigger TBs from the factory!

GM is also providing a lot more cubes from the factory than the 302 has. Bigger is not always better, 65 should be good for him 70 max especially since he needs to port match his intake to the throttle body if he goes above 70 in most cases.

88_GT_5_oh · Nov 7, 2005

fyi alot of turbo guys run 70 mms on stock and cobra intakes. and alot of cars make 400+ rwhp

JimBowy · Nov 22, 2005

can the cobra intake be ported to accept the 75mm perfectly?

Grn92LX · Nov 23, 2005

JimBowy said:
can the cobra intake be ported to accept the 75mm perfectly?

Yes, guys on here have said they've done it.

Topdowncruise · Nov 23, 2005

65mm is lots for any 302/306 combo unless you supercharge.A 70mm would just soften your bottom end with no top end gain.Preserve your bottom end and enjoy driving your car for what you probably do the vast majority of the time - normal everyday driving.

CRASH7772 · Nov 23, 2005

I don't agree with anything smaller than a 70mm. I was making 260rwtq@2000 rpms with a 70mm....I don't think that's losing low end. Go with the biggest TB/EGR your intake is opened up to. Also I have seen dynos with TB/EGR's on mid 300hp engines and the 75mm didn't lose any down low and made a few more ponnies on top.

5spd GT · Nov 23, 2005

crash7772 - There are a lot more factors for the torque at 2000rpm than just the throttle body. Stroke/cam/heads/intake/maf/exhaust/etc. Not a valid point

65mm or 70mm TB?

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