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Old 09-17-2004, 11:42 AM   #1
Honkey3k
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Default Bling Bling: Custom Port Matching

I am currently putting in a new shortblock and last night I port matched my heads by myself... with.... *moment of silence for suspence* a craftsman pocket tool. The blades in their cut the aluminum right up. I ended up taking about a 1/9th of an inch off. Its all smooth and pretty. However I doubt their will be much gain if any... Just thought I would share my boredum in the garage last night. Pics?
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Old 09-17-2004, 11:44 AM   #2
PARANOID56
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post the pics
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Old 09-17-2004, 12:34 PM   #3
Honkey3k
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Alright, im at school right now but I will post them up tonight. I talked to my friend brent who p&p's his own heads/turbos etc and he said it should be a noticeable difference.
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Old 09-17-2004, 02:32 PM   #4
Tim Sanderson
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One of the best things you can do besides cleaning up the ports is gasket matching the ports. Be sure to get all the shavings out or it could spell trouble later.
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Old 09-17-2004, 08:03 PM   #5
bugeyes
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In a normally aspirated motor it is NOT advisable to perfectly port match the intake manifold to the head port OR the head port to the header pipe (of course make sure the gasgets are not protruding).
WHY???
Because of flow reversion. Where the port joins to the head whether it be the inlet or exhaust it should be stepped in the direction of flow. This means on the inlet manifold it should be marginally smaller than the port and the exhaust header marginally bigger than the head port. There should be a definate 90 degree step.
Lets talk about intake port.
As the intake cam is designed to operate at a particular rpm range at low rpms it isnt as efficient as at its peak torque range. What happens at low rpm is the cylinder fills during the intake stroke and then because the inlet valve doesnt close till after bottom dead centre on the crank the piston starts to push intake charge back out before the intake valve shuts. This is why lumpy cams give low manifold vacuum. The step in the manifold will create a resistance to flow in the backwards direction and fight reversion.
The same applies to the exhaust port. If you ever get your heads modified you may find out that backcutting on the exhaust valves can be modified to also help with reversion.
Dont think that everything should be perfectly smooth, before you take to your heads/manifolds with a die grinder do your homework or you may be going backwards. Do a search on the internet you may find more info about this or talk to a helpfull race heads workshop.

Last edited by bugeyes; 09-17-2004 at 08:04 PM. Reason: wrong quote entered
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Old 09-17-2004, 08:30 PM   #6
Kevin Thomas
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Quote:
Originally Posted by bugeyes
As the intake cam is designed to operate at a particular rpm range at low rpms it isnt as efficient as at its peak torque range. What happens at low rpm is the cylinder fills during the intake stroke and then because the inlet valve doesnt close till after bottom dead centre on the crank the piston starts to push intake charge back out before the intake valve shuts. This is why lumpy cams give low manifold vacuum. The step in the manifold will create a resistance to flow in the backwards direction and fight reversion.
The same applies to the exhaust port. If you ever get your heads modified you may find out that backcutting on the exhaust valves can be modified to also help with reversion.
Dont think that everything should be perfectly smooth, before you take to your heads/manifolds with a die grinder do your homework or you may be going backwards. Do a search on the internet you may find more info about this or talk to a helpfull race heads workshop.
This is interesting info bugeyes. I better read up more on reversion.

If what you are as saying is true as far as reversion is concerned, it isn't all bad either. Yes, during low rpm operation, you'd lose some power from the extra air being allowed to 'revert' back out through the valves but during high rpm operation, there should be a significant gain since the flow is smooth and unobstructed. I would think it would all depend on how you drive and what you use your car for. For all out racing at high rpms, reversion shouldn't be an issue.

For our cars though, I'd think it would be of concern like you pointed out, especially during everyday driving. Ok, I'm off to reading.
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Old 09-21-2004, 10:25 PM   #7
Honkey3k
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I only did the Exhaust ports on the heads, and their is a small, yet noticeable lip still before the whole reaches the gasket. I didnt do the Intake because I know they had to be left rough and I didnt want to mess with that.
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Old 09-21-2004, 10:27 PM   #8
Honkey3k
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Quote:
Originally Posted by Kevin Thomas
This is interesting info bugeyes. I better read up more on reversion.

If what you are as saying is true as far as reversion is concerned, it isn't all bad either. Yes, during low rpm operation, you'd lose some power from the extra air being allowed to 'revert' back out through the valves but during high rpm operation, there should be a significant gain since the flow is smooth and unobstructed. I would think it would all depend on how you drive and what you use your car for. For all out racing at high rpms, reversion shouldn't be an issue.

For our cars though, I'd think it would be of concern like you pointed out, especially during everyday driving. Ok, I'm off to reading.
As you would notice on the Cobb Stage 3 Cylinder heads (and probably TWE also), they state low end power is LOST due to the sizeing of the intake ports. So, in a sence, bugeyes is right
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Old 09-21-2004, 11:29 PM   #9
redwagon
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Quote:
Originally Posted by Honkey3k
As you would notice on the Cobb Stage 3 Cylinder heads (and probably TWE also), they state low end power is LOST due to the sizeing of the intake ports. So, in a sence, bugeyes is right
Probably the intake are just large enough at stage 3 to lose some port velocity at low rpm. It comes with the territory.
I'm pretty sure the stock port is necked enough to avoid reversion and I don't recall the step at the port as being either necessary of beneficial here. I always match intake ports to the manifold but leave the exhaust alone, since the benefit of the step there is well documented.
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Old 09-22-2004, 03:09 AM   #10
Storm
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I did the same thing, tool wise. I cleaned up the intake side noticably, without altering the port shapes too much. Mainly just major-major polishing, except for the divider between the valves. I shaped that very sharp on all cylinders and smoothed the port floor to be a bit more uniform. On the exhaust side I only smoothed out the rough cast to a fine polish. I left the step intact....well, maybe opened up a little bit. I only hope I got all the ports even. On the intake plenum, I gasket matched and smoothed the rough cast as much as I could. Being a EJ20G manifold, it's already pretty big for my N/A application.

Hopefully it works well when I fire it up.........maybe this weekend!


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