243 milled 59cc...cr ? lq4
06-11-2010, 02:49 PM
#31
That's the problem, a lot of people don't do what they should. you should always check port alignment after milling a set of heads. You'd be surprised how much of a lip there is between where the intake manifold port and intake port of the head line up. This causes an obstruction of flow and turbulance. Next time one of you guys take your intake off your truck put some grease on your gaskets of your intake manifold then gently set it on your milled heads. Then remove the intake. You'll see the witness marks of the grease outlined around your intake ports. Now tell me how far it's off. Think of what you're missing out on by not having the intake side of your heads milled. That lip causes problems with smooth flow.
Actual pics, not something out of paintbrush. I get what you're explaining.
06-11-2010, 03:17 PM
#32
I'm sure someone on the board is going to be doing an intake swap soon, they could demonstrate. 
My heads aren't milled so even if I showed you, it's not going to be off that far. I could see potentially losing 10 CFM of flow or more by not checking this. Now compound that on top of milling the **** out of your heads, this shrouds the valves as well hindering the flow characteristics of the heads. You can lose flow quite a bit in the combustion chamber when you mill the heads too much. I can see losing 20cfm on a set of heads easily when milling them .040"-.050" and not having the intake aligned properly. Using Larry Meaux's head calc, you lose about 2HP for every 1 cfm loss. (or could gain as well). 20cfm head loss would equate to about 40 flywheel HP loss (mathemmatically). You will gain some back though just from the increase in compression. The compression gain won't nullify the loss in flow though. I could see losing 25HP at the flywheel easy for milling too much off and not having the port alignment dead on.
My heads aren't milled so even if I showed you, it's not going to be off that far. I could see potentially losing 10 CFM of flow or more by not checking this. Now compound that on top of milling the **** out of your heads, this shrouds the valves as well hindering the flow characteristics of the heads. You can lose flow quite a bit in the combustion chamber when you mill the heads too much. I can see losing 20cfm on a set of heads easily when milling them .040"-.050" and not having the intake aligned properly. Using Larry Meaux's head calc, you lose about 2HP for every 1 cfm loss. (or could gain as well). 20cfm head loss would equate to about 40 flywheel HP loss (mathemmatically). You will gain some back though just from the increase in compression. The compression gain won't nullify the loss in flow though. I could see losing 25HP at the flywheel easy for milling too much off and not having the port alignment dead on.
06-11-2010, 04:31 PM
#33
thats a pretty big guesstimation you got going on there. If there is indeed a lip that big to stop the airflow, theirs got to be a pretty decent size one on the stock heads imo, and of course milling will only exaggerate the issue. but as long as you keep the intake valve 2" or under i think the added flow and compression (with fixing any port miss match thats there) out weigh the slight valve shrouding that may be going on. I mean we are talking less than a 1/16", if theres valve shrouding going on, its going to be there before and after the mill imo..
06-11-2010, 05:40 PM
#35
That's the problem, a lot of people don't do what they should. you should always check port alignment after milling a set of heads. You'd be surprised how much of a lip there is between where the intake manifold port and intake port of the head line up. This causes an obstruction of flow and turbulance. Next time one of you guys take your intake off your truck put some grease on your gaskets of your intake manifold then gently set it on your milled heads. Then remove the intake. You'll see the witness marks of the grease outlined around your intake ports. Now tell me how far it's off. Think of what you're missing out on by not having the intake side of your heads milled. That lip causes problems with smooth flow.
Good Speed shops will port match the head/intake combo. A cheap alternative would be to mill the intake port openeings a bit, not the whole port itself but just the lip so that it's a bit bigger than the intake runners.
hirdlej is right on verifying that this isn't overlooked on milled heads.
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