intake vs exhaust duration

[niswiz]

why would u use a camshaft with more intake duration than exhaust(272 intake,264 exhaust)

[Joe]

so you can get more air into the engine.

[DrifterProdigy85]

Id like to see tests done using a good flowing turbo and different variations of cams duration and lift. A test like this would give a good idea on how to manipulate the power for the rpm you want.

[Joe]

its not nearly as important on a turbo engine as a NA variant.

[95-S14]

But why not go with 272/272.

I dont know much about how cams work in terms of the lift/duration, but from what I have read, 264/264 would give good low/mid range power. Probably the best for a street car.

272/272 seems to be the way to go for all out power, such as those running a big turbo with lots of boost and not worried about low or mid range power.

So is going with a 272 on the intake and 264 exhaust kind of like the middle ground? Letting in more air than is going out?

[DrifterProdigy85]

A 272/264 setup should give large midrange gains and become restrictive at high rpm. This is because the 272 intake is letting alot of air in while the 264 exhaust wont be letting out enough air. I always look at duration and lift as the width and hieght of the cam lobe. The more duration and lift will allow for more air in and out of the cylinder but the larger duration and lift takes longer for the valve to open which is why there is usually a loss in low rpm tq. Ive used HKS 264 step 1 cams, BC 264 cams, and Tomei 270 cams with my SR20. The HKS step 1 cams were a 264/10.0mm lift i think. They allowed a good bit of low rpm tq during spool up and flowed decent to 7000rpm. The BC cams were a 264/12.0mm lift. They lost some low rpm tq during spool up but gained more tq at peak boost and carried tq better to 7000rpm over the HKS cams. The Tomei 270 cams was a total change. The only tq gains came at 5krpm and held tq quite solid to 8000rpm. For a street only car id use the Tomei Poncams with the RB. It should keep the engine very responsive and make well rounded power numbers (matching tq and hp). Cams always make a difference with any engine. They increase the effeciency of the head which is gonna make more power being NA and usually even bigger gains with F.I.

[niswiz]

thanks for ur help. i bought the cams off a friend and wanted to know the effect they'd have.i see everyone else use 264 intake and 272 exhaust so i was wondering what the difference was the other way round