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Thank for that sight but they show the LS1 heads, not the LS6 heads. I appreciate your help. :cheers:
My reason for this is to find out wether or not ported ls1 heads 2.02 in 1.57 ex milled to .035 flowing over 300 cfm with a 10.8:1 compression ratio will make a big difference over stock ls6 heads without headers.
Its hard to say how much better the heads are alone because they only came on the Z06s with bigger cam and better exhaust. But I estimate that they would be worth 20hp over stock LS1 heads, so you could geuss they maybe flow 10cfm more.
That Chevy HP article says the 990's (which were LS--6 service heads I believe) will flow Intake@300 183cfm --@400 233cfm -- @500 264cfm and 292@.600 Exhaust with ppipe is 140,176 198,and 204 cfm at those respective lifts..
The 291 head (the real LS6 head) has a raised intake floor so that it is superior to any previous head. I can't comment on the 990 I have never had any on a flow bench. The exhaust on iron heads is pretty much the same.