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?
65mm or 70mm TB?
- Thread starter fox racer
- Start date
vikingpower
New Member
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
Founding Member
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
i'd go 70
payupsucka
Member
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?
payupsucka said:
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
Member
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
Repostyle
Member
I had my cobra upper machined to a 75mm opening to get rid of the "wall" and a 75mm TB and have no problems.
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.
vikingpower said:
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
Mustang Master
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
New Member
vikingpower said:
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
Sportin' a turbo 5.0 in Canadistan
JimBowy
Member
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.
