FrontEngineDragsters.Org Forum
Technical => Matt Shaff's Engine Shop => Topic started by: wideopen231 on March 03, 2019, 11:08:04 AM
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Ok I know this could open can of worms.
Using desktop dyno,which you may or may not believe is fairly good tool.
Every cam I run thru it shows that running more intake duration than exhaust makes best power.Usually some where around 8* less exhaust.Where as most BBC engine show that little more exhaust makes best power.
This is on my Hemi engine with BAE fuel heads, I know not norm around here and maybe out of realm of working knowledge. I figure some will have thoughts that may be helpful. For what its worth Chad Speirs Had similar results using his calculations a while back.
Opinion as to why?
I have my own thoughts,but figure other opinions are worth listening to.
Maybe helpful:Intake flow .100 85
.200 152
.300 214
.400 293
.500 364
.600 440
.700 494
.800 518
.900 526
exhaust flow.100 73
.200 138
.300 203
.400 270
.500 335
.600 387
.700 390
.800 398
.900 401
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I would say the program is compensating for an out of whack inlet to exhaust ratio. By increasing the inlet a more favourable ratio is achieved and therefore you see increased HP.
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Are those numbers for Fuel/Alc or gas???
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Alcohol. Like stated its come out same thru my program,one cam company and a head flow specialist. Not sure what qualifies as out of balance ratio wise.These are std BAE fuel style heads and flow about exact same as a friends AJPE 2 heads. I agree that treason Hemi head combo wants less duration exhaust and BBC wants few degrees more than intake is because ratio or that was my S.W.A.G.. Just figure getting opinions to see if other came to same conclusion wasn't bad thing.
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Had lunch with Isky today and tried to explain you situation, He laughed, said don't worry about the exhaust, its all about the intake. He's tried More than- same as -less than and found nothing
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Ok so now we are resorting to name dropping.LOL Have to say you have pretty good sources.
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He's 97 and has lunch at the same burger stand every day, sometimes its just me and other times, a group of us. I fear the day when he does not show up
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Had lunch with Isky today and tried to explain you situation, He laughed, said don't worry about the exhaust, its all about the intake. He's tried More than- same as -less than and found nothing
YUP.
That is my feeling too. When you think about it, the preponderance of the exhaust mass flow happens soon after exhaust valve starts opening, when cylinder pressures are still relatively high (on the order of 100 psi).
That is the "blow down" phase.
And the final purge of exhaust gasses comes at the end of the exhaust event.
That is the "pump-down" phase. Again, at low valve lifts.
So if you really want to help things out concentrate your exhaust side efforts on achieving the greatest possible exhaust flow at the low exhaust valve lifts.