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Author Topic: Porting and Flow testing GT40 heads  (Read 105929 times)
Outlaw Bill
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Posts: 4760

Location: Canton, Michigan

« Reply #135 on: April 02, 2013, 06:51:00 pm »

The exhaust ports are tough. They like to sign off early at .500 lift. The short turn is the 100%  key to the exhaust port to work. My exhaust port only flows 160cfm(no pipe) at .500 lift then rolls over after that, its all in the short turn.
On the one I did the exhaust went to 180 @ .400 and then tapered off to 168 @ .700. I was hoping there was more to be had there because the bowl looks like it should be a little bigger on the one side, but I don't want to hit water with it.
Yeah I need to widen and lay back the short turn more. No time to mess with them though.


TeamZmotorsports 25.2 outlaw drag radial stock suspension 1991 Mustang
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David Claflin
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Location: Redneck Riviera (Ft Walton Beach Florida)

« Reply #136 on: April 02, 2013, 09:42:34 pm »

Yeah I need to widen and lay back the short turn more. No time to mess with them though.
Same here, but I really need one of those electronic things that measures the port wall, that way I can know how much material is left there.

1990 Red LX, 306, 80MM, ported gt40's, ported explorer upper accufab longtubes, 3" exhaust, 4.30's, 336/331
1985 LTD LX 347, 205 11R's, TFS-R, 90MMTB, MAC 1 3/4" longtubes, 4R70W, mach 1 brakes
1988 GT long term project
6 Banger
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Location: Pascagoula, MS (Gulf Coast)

« Reply #137 on: April 05, 2013, 04:59:22 pm »

It's been awhile since I've read the entire thread and can't remember if anyone talked about port velocities. While we had David's head on the bench I checked port speed at the center of short side radius, it was in the 500+ range. Is there enough material in the port walls to widen this area to help reduce port velocity?

I think overall the head has good potential. Would have liked to enlarge the exhaust bowl and reground the exhaust valve seat. My fault this didn't happen, I got distracted.

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