Anyone have any performance numbers before and after having their heads ported and polished? I am wondering if it is worth doing and what else should be done while the motor is apart? Like polish the intake manifold and exhaust manifolds?
------------------ Purple 1988 GT NOS injected 3800 Series II V6 Best ET(75 shot)-13.21@102.13 mph w/o NOS 14.86@92.06mph
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11:58 PM
PFF
System Bot
Oct 31st, 2001
Fierowrecker Member
Posts: 1858 From: Lowell, MI. USA Registered: Mar 2001
Hey NOS! No, they don't work, so I will trade you my stock 3800 heads for your ported and polished heads... In reality, it depends on who does them... If it is done with a flow bench, all the better... What you are trying to acheve is the smooth, quick filling of the cylinders... Generally, polishing adds quite a bit of improvement, getting rid of parting lines and other turbulence creating crap in the port... It helps to a lesser degree in the exhaust ports, but it does add up when combined with intake polishing and headers... Just remember, the engine is a glorified air pump, and the more efficient it passes air, the better it runs...
polish all you want smoother is better leave the porting to a pro it is a art more is not all ways better and flow is tricky in twisted spaces. just clean up bad flaws and bumps then polish
------------------ Question wonder and be wierd
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12:19 AM
Joe Torma Member
Posts: 3485 From: Hillsborough, NJ USA Registered: Jul 2001
Extrude Hone the manifold. This is where a corse paste is shot through the manifld iunder high pressure. It polishes the entire inside and removes casting imperfections.
If the 3800 manifold is composite you can't do it.
JM
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01:15 AM
fieroX Member
Posts: 5234 From: wichita, Ks Registered: Oct 2001
Originally posted by Fierowrecker: It helps to a lesser degree in the exhaust ports, but it does add up when combined with intake polishing and headers...
partially true, really depends on the exact application. In your case porting and polishing the intake and exhaust ports will add a sufficient gain. I have seen on thrashers website gains of 36-38 horsepower by porting heads with the L36 NA 3800. With a concentration of work on the intake side for better flow. Now when you get the air in there, you need to expel it, so you need to port the exhausts, but some people dont find exhaust porting to be so necessary. Now lets take the L67 supercharged 3800 for example. I concentrate a majority of my work on the exhaust side, first because the supercharger is an air pump, and it is going to fill the engine with the most air it can, because it is under pressure. this requires less porting work on the intake side heres why. 2 reasons #1 if you port out the intake side a bunch it will increase flow, but lower the port velocity of the air moving from the blower through the intake and heads and into the cylinders. This actually can decrease your low end torque band to an upper range, taking your horsepower band even higher into a range that is unattainable because of computer constraints. #2 so if you just leave the intake ports alone, just a slight touchup to fix the casting flash, and maybe a port match, you can keep the existing power band, with added torque. How you ask, ok I concentrate most of my work on the exhaust side so when you add a smaller pulley, port the blower and such to allow the blower to pump more air, well the boost pressure is going to force the air through the intake runners and into the cylinders, but the piston travel and exhaust scavenging is going to have to expel the gasses. so the more work you can do to the exhaust side the better off you are. (see next section called boost stacking for a better explination why) Thats also why im building my own headers and port matching the header flange to the ported heads, before i weld the tubes to the flange. so it is a custom perfect fit. Ok on to one more area of discussion called boost stacking. when you raise your boost level by adding a smaller pulley you could be creating a condition called boost stacking. this is when there is so much boost but not so much room for air to travel, so boost will back up into the intake, and blower and wait to be forced into the cylinders because of pressure within the exhaust system holding it back. people have seen gains of 40-45 horse by porting exhausts and stock manifolds to match. this allows the use of all the available boost, by relieving the pressure. Just imagine what kind of gains can be seen with ported exhausts port matched to custom 1 3/4 to 2 1/2 headers and 3" single exhaust system! oh yeah! Ok thats all I can really think of now and it is becoming increasingly difficult for me to think, it is getting very late and this message is getting very long. goodnite.
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02:42 AM
Nashco Member
Posts: 4144 From: Portland, OR Registered: Dec 2000
Originally posted by Slammed Fiero: Extrude Hone the manifold. This is where a corse paste is shot through the manifld iunder high pressure. It polishes the entire inside and removes casting imperfections.
If the 3800 manifold is composite you can't do it.
JM
I'm with him. Extrude honing is the best "port" you can get for your dollar. Problem with many "port" jobs is that they actually just widen the ends of the ports, but the center section remains the same diameter. The sludge takes away any flashing that may come loose easily, and sharp edges that create air disturbances and stress risers. I have been under the impression that it leaves a smooth surface, but rough under magnification. This is the ideal situation with intake flow, because fuel in the airflow deposits inside all of the tiny crevices. The fuel following deflects off the fuel sitting in the tiny crevice, rather than hitting any edge; fuel bouncing of fuel is supposed to have less friction that fuel bouncing off polished metal, thus allowing higher air velocities through the intake.
In theory, you want just slightly rough intakes, and smooth exhausts. The fuel builds an artificial liquid wall on the intakes, and the exhaust air flows with minimal restrictions this way. Again, this is theory, some applications differ with many variables, but in general, this is all true.
Originally posted by fieroX: Ok on to one more area of discussion called boost stacking. when you raise your boost level by adding a smaller pulley you could be creating a condition called boost stacking. this is when there is so much boost but not so much room for air to travel, so boost will back up into the intake, and blower and wait to be forced into the cylinders because of pressure within the exhaust system holding it back. people have seen gains of 40-45 horse by porting exhausts and stock manifolds to match. this allows the use of all the available boost, by relieving the pressure. Just imagine what kind of gains can be seen with ported exhausts port matched to custom 1 3/4 to 2 1/2 headers and 3" single exhaust system! oh yeah!
FieroX, what you said is correct but I want to expound for those unfamiliar with forced induction... 1) pressurizing on the intake pushes more air/fuel mass into the combustion chamber creating more work (expelling of expanded gases) for the exhaust stroke to purge it. 2) if an exhaust restriction exists anywhere in the the exhaust, then the pressure on the exhaust side will build and back up into the cylinder. 3) the duration of the exhaust valve opening is finite, so if not all of the exhaust gases are expelled (minus the combustion chamber) then that leftover gas will displace air/fuel on the next intake stroke. As FieroX said in order to take advantage of the pressurization effect on the intake side, you want to remove as much exhaust gas as possible on a forced induction engine or the stacking effect will reduce the efficiency/power of your engine.
[This message has been edited by 87GTZ34 (edited 10-31-2001).]
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10:31 AM
fieroX Member
Posts: 5234 From: wichita, Ks Registered: Oct 2001
Originally posted by Nashco: I'm with him. Extrude honing is the best "port" you can get for your dollar.
I agree that an extrude honing is an excellent port job, but not for your dollar. Have you ever paid for an extrude hone job? A friend of mine had one done on his upper and lower intake for a 5.0 mustang engine, and it cost $700. It was very smooth, perfect to be exact, but not everyone has that kind of cash to put into an intake manifold.
