aluminum head recommendations
10-28-2002, 10:29 AM
#31
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I knew this thread was going to develop into something. So here's my two cents worth. As usual everybody's right, but the problem is multi-faceted.
Dennis Moore is right, if you already have big intakes, the supercharger will be happy, but since much of the resistance to air flow occurs around the valve, I would think that close attention should be paid to porting in this area and the chamber.
JimV is right, if it can't get out, it ain't goin' in. The stock exhaust ports in an iron head are a problem. And if you reduce resistance in the heads, but don't change pulleys (on a positive displacement blower) the HP will stay the same, at a lower boost.
totalmp is right, increasing blower speed does increase air flow, but that also increases the temperature of the charge air and puts you closer to detonation and other bad things.
Every engine project has a power/reliablilty/$$$ goal. I could make 700 HP many ways with a blower:
- restrictive intake path and 11 psi boost
- lower resistance path and 8 psi boost
- best flowing intake path, 5 psi boost.
Changing pulleys is easy and has almost no additional cost, but for lower temperatures and reliability the high flow cylinder heads are the answer.
Of course, none of you guys would leave the high flow combination at only 5 psi boost, would you?
Dennis Moore is right, if you already have big intakes, the supercharger will be happy, but since much of the resistance to air flow occurs around the valve, I would think that close attention should be paid to porting in this area and the chamber.
JimV is right, if it can't get out, it ain't goin' in. The stock exhaust ports in an iron head are a problem. And if you reduce resistance in the heads, but don't change pulleys (on a positive displacement blower) the HP will stay the same, at a lower boost.
totalmp is right, increasing blower speed does increase air flow, but that also increases the temperature of the charge air and puts you closer to detonation and other bad things.
Every engine project has a power/reliablilty/$$$ goal. I could make 700 HP many ways with a blower:
- restrictive intake path and 11 psi boost
- lower resistance path and 8 psi boost
- best flowing intake path, 5 psi boost.
Changing pulleys is easy and has almost no additional cost, but for lower temperatures and reliability the high flow cylinder heads are the answer.
Of course, none of you guys would leave the high flow combination at only 5 psi boost, would you?
10-28-2002, 12:21 PM
#34
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Turbo2256- I would not queston your statment, I would guess there is more there after CNC'ed. The real question is at what cost of $, time, & frustration dealing with the head massuse.
10-28-2002, 01:14 PM
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29scarab, if you flush your motor out a lot, the aluminum heads will be fine. Many engine builders use the aluminum and in blower applications, are a major necessity.
Lowering the compression lowers your effective compression ratio and hence, can lower the engery/power of combustion. One thing you have to remember when looking at power, as many have touched on, power is directly related to the amount of airflow into the engine. Of course you need the proper fuel, timing, etc. to make power, but most never realize, boost is just a measurement of what is left outside the valves, thats' not telling you whats entering the cylinder or being combusted. So cam, head flow, head porting all matter. Just lowering the compression with flat tops in a 500 HP EFI is pretty much a waste of time for the cost vs. benefits. Running more boost on pump gas will blow the head gaskets because of detonation, you can run better grade gas and more boost, but it comes down to detonation. How much air and fuel you can fire in the cylinder before it detonates or pre-ignites. So when you get a chance to increase air flow while able to tolerate more air and fuel.
Thanks,
Dustin
Lowering the compression lowers your effective compression ratio and hence, can lower the engery/power of combustion. One thing you have to remember when looking at power, as many have touched on, power is directly related to the amount of airflow into the engine. Of course you need the proper fuel, timing, etc. to make power, but most never realize, boost is just a measurement of what is left outside the valves, thats' not telling you whats entering the cylinder or being combusted. So cam, head flow, head porting all matter. Just lowering the compression with flat tops in a 500 HP EFI is pretty much a waste of time for the cost vs. benefits. Running more boost on pump gas will blow the head gaskets because of detonation, you can run better grade gas and more boost, but it comes down to detonation. How much air and fuel you can fire in the cylinder before it detonates or pre-ignites. So when you get a chance to increase air flow while able to tolerate more air and fuel.
Thanks,
Dustin
10-28-2002, 08:31 PM
#36
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I think JimV would agree with me here but a set of fully CNC ed heads just wont out flow a hand massaged set.
I agree 100%
Another thing to consider the cnc head that their selling you is the same program their selling to the drag racers for their drag race motors. They are selling airflow numbers that work with camshafts at .800 lift. Write this down Mark so you can baffle someone else in your future posts. Most all the drag race ports are designed to flow air at higher lifts. To achieve this the venturi area or the throat of the port below the valve seat has to be enlarged and the short turn radius has to be laid back. When this done the numbers in the mid lift suffer. The result from this will decrease torque substantially at low rpms. 4000 rpms is low for a drag motor, it's where most of us boaters cruise and we need the torque. Also the back angle on the valve cannot be too wide or it will cause turbulance in the port at the higher lifts. The right back angle will gain 4-6 percent from .2 up to .6 lift. In a marine motor the ports need to be small and flow a lot of air. This port pictured has a volume of 318cc's and mates to a 572 twin turbo motor that made I believe 1300hp.
I agree 100%
Another thing to consider the cnc head that their selling you is the same program their selling to the drag racers for their drag race motors. They are selling airflow numbers that work with camshafts at .800 lift. Write this down Mark so you can baffle someone else in your future posts. Most all the drag race ports are designed to flow air at higher lifts. To achieve this the venturi area or the throat of the port below the valve seat has to be enlarged and the short turn radius has to be laid back. When this done the numbers in the mid lift suffer. The result from this will decrease torque substantially at low rpms. 4000 rpms is low for a drag motor, it's where most of us boaters cruise and we need the torque. Also the back angle on the valve cannot be too wide or it will cause turbulance in the port at the higher lifts. The right back angle will gain 4-6 percent from .2 up to .6 lift. In a marine motor the ports need to be small and flow a lot of air. This port pictured has a volume of 318cc's and mates to a 572 twin turbo motor that made I believe 1300hp.
Last edited by JimV; 10-28-2002 at 08:35 PM.
10-28-2002, 08:40 PM
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We had bad luck using standard CNC heads. This is the reason we use Canfields so much. They CNC chambers, and Valve seats, and Port match, then we can come in and full port the heads for optimum flow, while keeping wall thickness at a comfortable level. We're in salt water here, so we try not to thin the walls excessively. We can do all of this complete with the best Manley Valves for around $2500.00.
10-28-2002, 09:22 PM
#38
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Also I forgot to mention the valve seat widths. The out of the box Dart has a seat width of 30-40 thousands intake about 60 exhaust. For cooling and longevity a marine motor seat widths need to be 60 -70 intake 80-90 exhaust. One more thing is the seats are rarely square with the guide and need to be ground. If the guide clearance is .002 and there is .008 runout in the seat the stem can seize or wear prematurly.
10-29-2002, 09:48 AM
#39
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How much to correct that? Another $500 ???
Looking it from your consumers point of view, even at $500.00 dollars for a valve grind is cheaper than rebuilding a destroyed motor. I get consumers in my shop that will whine about how much money their spending and they cant offord my services but will show up three days later with a set of cool guy rocker arms with no needle bearings that cost $1,100.00 dollars when there was nothing wrong with his original rockers. Or the guy that we just completed his 700 hp 540 motor that wanted to change the cams because there was soot in the exhaust port. Meantime this guy has more aeroquip on his boat than the space shuttle and he is beating me up because he thinks I am charging him too much for my labor. Should I go on? Its impossible to deal with a customer that believes that what glitters is gold.
Oh yes if you reread my post the point was that marine ported heads are different than non marine ported heads. The volumes, seats, venturi area are different. A .650 lift cam doesn't care what a port is flowing at .800 lift. And yes the difference between a good combination and bad could be 50+ hp
Looking it from your consumers point of view, even at $500.00 dollars for a valve grind is cheaper than rebuilding a destroyed motor. I get consumers in my shop that will whine about how much money their spending and they cant offord my services but will show up three days later with a set of cool guy rocker arms with no needle bearings that cost $1,100.00 dollars when there was nothing wrong with his original rockers. Or the guy that we just completed his 700 hp 540 motor that wanted to change the cams because there was soot in the exhaust port. Meantime this guy has more aeroquip on his boat than the space shuttle and he is beating me up because he thinks I am charging him too much for my labor. Should I go on? Its impossible to deal with a customer that believes that what glitters is gold.
Oh yes if you reread my post the point was that marine ported heads are different than non marine ported heads. The volumes, seats, venturi area are different. A .650 lift cam doesn't care what a port is flowing at .800 lift. And yes the difference between a good combination and bad could be 50+ hp
Last edited by JimV; 10-29-2002 at 10:04 AM.
