Port matching
03-13-2002, 03:29 AM
#1
Instructor
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Port matching
Ok i know the theory...but, what is the realistic benefits from this procedure (944&951)? I think i am going to pull the head to do a valve job and seals, should i port match the intake/exhast manifolds? Not just the hp gains but is it good practice? you know worth the work? also is it very difficult?
83 944
87 951
83 944
87 951
03-13-2002, 12:42 PM
#2
Done With Sidepatch
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Andrew, I think there is no denying the benefits of cleaning up a head. I have read alot about the only way to ensure an accurate port/polish is through bench flow testing and that is certainly true. Despite the lack of testing I believe positive results can be obtained by the DIYer at home. I'm going to try it but I have three heads to play with so if I screw one up I can move onto number 2. <a href="http://www.sa-motorsports.com/diyport.htm" target="_blank">Standard Abrasvies </a> descibes, in detail, how to DIY.
03-13-2002, 01:22 PM
#3
Drifting
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Andrew,
I have first-hand experience with DIY port matching. I matched the intake/gasket/head and then the turbo manifold/gasket/head on an Audi 5000 turbo motor I installed in a 4000 Quattro.
I bought a Bosch 4.6amp die-grinder and various
carbide burrs/bits. The tree-shaped and the straight ones that look like your pinky finger were the most useful. Unfortunetly it's hard to quantify the results, however the transitional throttle-response was was unlike any other turbo car I've driven. Very small throttle movements created lots of accelleration instantly. Be careful, that 4.6 amp grinder can get away from you if you catch the opposite edge of the burr(the edge you're not working with).
I have first-hand experience with DIY port matching. I matched the intake/gasket/head and then the turbo manifold/gasket/head on an Audi 5000 turbo motor I installed in a 4000 Quattro.
I bought a Bosch 4.6amp die-grinder and various
carbide burrs/bits. The tree-shaped and the straight ones that look like your pinky finger were the most useful. Unfortunetly it's hard to quantify the results, however the transitional throttle-response was was unlike any other turbo car I've driven. Very small throttle movements created lots of accelleration instantly. Be careful, that 4.6 amp grinder can get away from you if you catch the opposite edge of the burr(the edge you're not working with).
03-13-2002, 01:38 PM
#4
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When I rebuilt my '86 I found that the exaust manifold had a much smaller opening than the heads exaust port , which was evidenced by the deposition of carbon on the manifolds mating surface. I used this as a guide to remove some material from the exaust manifold. I was never able to quantify gains, if any, from doing this, but any sharp angles that exist in the intake or exaust streams( such as at the junctions of the intake and exaust manifolds) create turbulence and a resultant reduction in flow. I didn't find this a difficult procedure, but to really do it the right way you do need to put the head on the flow bench, then use the intake and exaust gaskets to serve as a guide to smooth the transitions between the head and manifolds. It is very important that enough material remain to handle the stresses that exist at the flanges, although this part is more of a judgement/experience call. Hope this helps, good luck... <img src="graemlins/c.gif" border="0" alt="[ouch]" />
03-13-2002, 02:51 PM
#5
Race Director
You have to be careful about the port-matching on the exhaust side! There's different techniques and shaped used depending upon whether you have an NA car or a Turbo.
On an NA car, flow is not straight in and straight out with the the largest ports winning. Since an NA car uses harmonic induction tuning with the exhaust pulses, volume and flow-rates of the ports determines best efficiencies at a particular RPM and its harmonics only (all others are compromised). Porting will typically shift the torque-peak higher but you'll lose low-RPM torque as well. And you DO NOT want to match the port on the head to the exhaust gasket and header. That's because of the reserve shock-wave pulse coming back up the exhaust. These travel backwards along the walls of the header and gets stopped by the ledge or lip created by an exhaust port that's smaller in diameter than the header.
If you remove this ledge, the reverse wave will have an easier time traveling right back into your combustion chamber and pushing the intake out the air filter! This is a pretty common problem with NA cars in the 2-3k RPM range and especially bad on carbureted cars because you end up with triple the fuel amount desired. It's metered once going in, once again as it pushed back out by the exhaust, and once again as it's sucked back in. With digital fuel-injection, you can compensate for this triple-carburetion by injecting fuel only once, but you still have the lack of flow due to the reversion. Reducing cam-overlap like on the 944NA cars (compared to other non-turbo cars), as well as using a 4-2-1 header helps reduce this loss of low-end torque due to exhaust reversion.
On a turbo car, you still have to deal with the reverse pressure-wave in the header, perhaps not quite as significantly as an NA car. The way to increase exhaust port flow is to cut D-shaped constant-radius curves (flat-side of D on inside-curve) and to have square ports where it meets the headers. These allow you to have increased flow and yet still retain the ledge between the manifold and header to prevent the exhaust reverse-wave from re-entering your head.
P.S. You may notice that the flow-bench won't show these dynamic harmonic induction tuning effects... Flow-bench testing works great if you have an engine that only operates at a single RPM.
On an NA car, flow is not straight in and straight out with the the largest ports winning. Since an NA car uses harmonic induction tuning with the exhaust pulses, volume and flow-rates of the ports determines best efficiencies at a particular RPM and its harmonics only (all others are compromised). Porting will typically shift the torque-peak higher but you'll lose low-RPM torque as well. And you DO NOT want to match the port on the head to the exhaust gasket and header. That's because of the reserve shock-wave pulse coming back up the exhaust. These travel backwards along the walls of the header and gets stopped by the ledge or lip created by an exhaust port that's smaller in diameter than the header.
If you remove this ledge, the reverse wave will have an easier time traveling right back into your combustion chamber and pushing the intake out the air filter! This is a pretty common problem with NA cars in the 2-3k RPM range and especially bad on carbureted cars because you end up with triple the fuel amount desired. It's metered once going in, once again as it pushed back out by the exhaust, and once again as it's sucked back in. With digital fuel-injection, you can compensate for this triple-carburetion by injecting fuel only once, but you still have the lack of flow due to the reversion. Reducing cam-overlap like on the 944NA cars (compared to other non-turbo cars), as well as using a 4-2-1 header helps reduce this loss of low-end torque due to exhaust reversion.
On a turbo car, you still have to deal with the reverse pressure-wave in the header, perhaps not quite as significantly as an NA car. The way to increase exhaust port flow is to cut D-shaped constant-radius curves (flat-side of D on inside-curve) and to have square ports where it meets the headers. These allow you to have increased flow and yet still retain the ledge between the manifold and header to prevent the exhaust reverse-wave from re-entering your head.
P.S. You may notice that the flow-bench won't show these dynamic harmonic induction tuning effects... Flow-bench testing works great if you have an engine that only operates at a single RPM.
03-13-2002, 04:01 PM
#6
Three Wheelin'
The exhaust ports are also ceramic coated, so grinding away in that area may have an impact on the durability of the ceramic coat and subsequent heat transfer to the head.
I just port matched & polished my intakes though it wasnt particularly difficult.
Wayne.
I just port matched & polished my intakes though it wasnt particularly difficult.
Wayne.
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03-13-2002, 08:37 PM
#9
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Luke,
I got the motor from a guy named James Bell who I guess has a salvage yard in Idaho. $189.00 plus shipping. When it was all sorted out it was darn fast. 2500 lbs and probably 210 hp at 13 psi. The whole engine management and boost control (a wastegate spring with adjustable preload) was pretty crude but running with 951's at DE's was pretty easy. Not to bad for a four door.
I got the motor from a guy named James Bell who I guess has a salvage yard in Idaho. $189.00 plus shipping. When it was all sorted out it was darn fast. 2500 lbs and probably 210 hp at 13 psi. The whole engine management and boost control (a wastegate spring with adjustable preload) was pretty crude but running with 951's at DE's was pretty easy. Not to bad for a four door.
03-13-2002, 11:08 PM
#11
Race Director
Depends on how you ported the head. It can give you better results or even make things worse than stock. If you don't know how to distinguish between these two results or what types of grinding yields them, you shouldn't be attempting a head porting job.
Head-porting really should only be done as part of a complete high-flow head rebuild. This includes at a mininum slightly larger intake valves with a 5-angle valve job (you should also know the difference in flow between a 60-degree and 70-degree bottom cut). The port diameter should be xx% of the diameter of the valve. You want to back-cut the valves.. etc. etc.. blah, blah...
If you really want a high-performance head rebuild, check out the work that Scott Gomes or Garrity does, you won't be disappointed.
Head-porting really should only be done as part of a complete high-flow head rebuild. This includes at a mininum slightly larger intake valves with a 5-angle valve job (you should also know the difference in flow between a 60-degree and 70-degree bottom cut). The port diameter should be xx% of the diameter of the valve. You want to back-cut the valves.. etc. etc.. blah, blah...
If you really want a high-performance head rebuild, check out the work that Scott Gomes or Garrity does, you won't be disappointed.
