Don Terrill’s Speed-Talk

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.

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.

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

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.

vw 8v stock vs. 7th porting and flow tests.

vw 8v stock vs 7th porting flows cfm/sqin graph.

vw 8v stock vs. 7th porting flows velocity graph

vw 8v stock vs 7th porting flows port energy graph

vw 8v stock vs. 7th porting flows port energy density graph.

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

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

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.

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 ?

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

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?