HAVE ANYONE EVERY TRIED 1.5RR ON THE EXHAUST SIDE? IF SO, WHAT WAS YOUR RESULTS?

 

I have heard of putting bigger on the exhast not smaller I take it you want 1.6RR on the intake and 1.5 on the exhast. but This more for power adder cars that try to cheat the cam to flow the exhast better, say to get rid of the forced or N20 gasses.

 

Most of what you gain form going to 1.6 rockers is on the exhaust side. There is little to no gain if you do just the intake side. The stock intake ports level off at about .380-.390 lift where as the exhaust slowly increases to about .450. Do all 16 valves or just the exhaust, dont do just the intake.

 

I have seen SBC dyno test on the same motor have more tq under the curve from 1.6/1.5 than 1.6/1.6. My guess would be that the heads port stall faster on the exhaust side than on the intake.

 

unless you are regulated by some wierd bracket rules or something- can I ask why?

lift is a good thing.

 

I've seen it the other way around, you gain more on the intake side and less on the exhaust side. This is on very low restiction exhaust systems though. A high restiction system might need more here, especially with a single pattern cam or a stock cam.

A good example is the Engine Masters winner last year built by Joe Sherman. He ran a 234/234 cam with 1.6 on the intake and 1.5's on the exhaust. Making 600+hp out of a 365 HR motor @ 6500rpm on pump gas to boot.

That along with alot of other examples shows that tendency for SBC based motors (and LT1's).

On the exhaust port there are alot of interesting things too, a head that has good low lift exhaust flow will not need as much lift, because the highest pressure that the exhaust valve sees is as it opens, the only time after that you really need the exhaust valve open is for the overlap period. So duration on the exhaust valve is much more important the lift on the exhaust valve.


Bret

 

It's not that simple.