Porting the VW/Audi 8v head with port energy discussion

General engine tech -- Drag Racing to Circle Track

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peejay
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by peejay » Mon Nov 06, 2017 8:33 pm

Interestingly the period factory-backed competition heads I've seen pictures of had the guides just cut off flush with the top of the head. Of course that leaves you with a guide that is about a half inch long so lifespan is short.

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Re: Porting the VW/Audi 8v head with port energy discussion

Post by KnightEngines » Mon Nov 06, 2017 9:48 pm

There would be some real good gains to be had welding up those bathtub chambers & cutting a proper pressure recovery chamber into them.
I won't show much on the flow bench, but the engine will love it.

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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Carnut1 » Mon Nov 06, 2017 10:07 pm

KnightEngines wrote:
Mon Nov 06, 2017 9:48 pm
There would be some real good gains to be had welding up those bathtub chambers & cutting a proper pressure recovery chamber into them.
I won't show much on the flow bench, but the engine will love it.
This is actually on the program but I don't have a complete shop so some will need to be farmed out. Pop the seats, weld the chambers, install bigger seats, custom shaped chambers. I am thinking nearly a figure 8 shape. We will see how it developes. Thanks, Charlie

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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Carnut1 » Tue Nov 07, 2017 4:35 pm

1106171510a.jpg
1106171541.jpg
Different approaches to tiny bowls and guides in the way. Top photo is 8mm guide mowed down to see how much flow would be gained with a better bowl shape and no guide. Worth 7 cfm on a tiny port which is a big gain. I am thinking the bucket lifter arrangement has very little to no side loading to the guide so a shorter guide may still have a long life. Bottom pic popped guide reshaped bowl and reinstalled guide worth 9 cfm.
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Carnut1 » Tue Nov 07, 2017 8:52 pm

8v vw stock counter flow 7th cfm.jpg
vw 8v stock vs. 7th porting and flow tests.
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Carnut1 » Tue Nov 07, 2017 8:54 pm

8v vw stock counter flow 7th cfm sqin.jpg
vw 8v stock vs 7th porting flows cfm/sqin graph.
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Carnut1 » Tue Nov 07, 2017 8:55 pm

8v vw stock counter flow 7th velocity.jpg
vw 8v stock vs. 7th porting flows velocity graph
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Carnut1 » Tue Nov 07, 2017 8:58 pm

8v vw stock counter flow 7th port energy ft lbs.jpg
vw 8v stock vs 7th porting flows port energy graph
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Carnut1 » Tue Nov 07, 2017 9:01 pm

8v vw stock counter flow 7th port energy ft lbs sq in ft.jpg
vw 8v stock vs. 7th porting flows port energy density graph.
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by lewy-d » Wed Nov 08, 2017 8:17 am

since you are testing guides. bullet/cone shape one and test. also maybe shaped like a vane?

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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Carnut1 » Wed Nov 08, 2017 9:54 pm

1108171828_HDR.jpg
Not my best photo but I would like some input. My smallest exhaust pipe is 1 5/8" tube which does boost exhaust flow but I feel it is too big for an engine that will need a wide torque band. Thinking about a 1.3" pipe would be about right I looked through some scrap aluminum conduit I had and found 1.375" id which looks good but does not leave a huge anti reversion damn. Input welcome. Thanks, Charlie
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by cjperformance » Wed Nov 08, 2017 11:44 pm

The closer you get the port face and pipe size to being correct and the better the design and combo match the pipes are the less you need to worry about anti reversion dams. Ie- So if its all spot on then a match at the port is best but the worse it all gets the more anti reversion stuff will help.
In the case you show id be happier to run the smaller pipe and less mismatch.
Craig.

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Re: Porting the VW/Audi 8v head with port energy discussion

Post by digger » Thu Nov 09, 2017 6:51 am

cjperformance wrote:
Wed Nov 08, 2017 11:44 pm
The closer you get the port face and pipe size to being correct and the better the design and combo match the pipes are the less you need to worry about anti reversion dams. Ie- So if its all spot on then a match at the port is best but the worse it all gets the more anti reversion stuff will help.
In the case you show id be happier to run the smaller pipe and less mismatch.
Do you think that's really true in a street motor? The pipe size to make a certain hp at certain rpm like 7000 or whatever is always going to be too large at low to medium rpm why wouldn't AR things always work effectively ?

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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Carnut1 » Thu Nov 09, 2017 12:23 pm

I started using anti reversion techniques on my engines back in the 90's and have always had good luck. As in running a bigger cam than usually advised from cam coaches of the day with better than most street manners with come up on cam right now power. I think using AR on this build will really help. Thanks, Charlie

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Re: Porting the VW/Audi 8v head with port energy discussion

Post by cjperformance » Thu Nov 09, 2017 3:26 pm

digger wrote:
Thu Nov 09, 2017 6:51 am
cjperformance wrote:
Wed Nov 08, 2017 11:44 pm
The closer you get the port face and pipe size to being correct and the better the design and combo match the pipes are the less you need to worry about anti reversion dams. Ie- So if its all spot on then a match at the port is best but the worse it all gets the more anti reversion stuff will help.
In the case you show id be happier to run the smaller pipe and less mismatch.
Do you think that's really true in a street motor? The pipe size to make a certain hp at certain rpm like 7000 or whatever is always going to be too large at low to medium rpm why wouldn't AR things always work effectively ?
In a street motor,,, yes if getting that ar dam means going 'up' a pipe size! Why put a bigger lazier less responsive primary pipe on it just the get an ar dam?
Craig.

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