GT-40 head porting, a compilation with a bunch of pics and measurements

[Guest]

[David Claflin]

First off, this is a thread to document porting GT40 heads. I am by no means any kind of expert, but have read on here the different threads about it, the info that Gerald has posted here and TNR, and what Tinman on corral did so that kind of made me get off my ass and see what mine would do. I finally got one port on these heads where I thought it was ready to be checked, so I took the head over to Ray (Coulter Racing) in Mississippi to have him check them on his flow bench. He pointed out some areas I could improve on, so I'll take that info and whatever else I learn from posting this and make the changes and then take them back over so he can redo it, to see what improvements the changes make.
The pics are what they looked like after he flowed them, and then I opened the throat up because that was where it was showing restriction. I also need to widen the short turn a little more, but am reluctant to for fear of hitting water. I really ought to get a sonic checker to measure wall thickness. At the end are some pics of the heads from my son's 94 cobra, they are untouched, I just ran them through the bead blaster to clean them up. The
 spreadsheet has measurements of the port of my head, and a stocker for comparison. The formula on the spreadsheet for calculating MCSA is what Gerald had posted on TNR so I just incorporated that into the calculations and have been using the spreadsheet since, as it is helpful when comparing all of the ports on a head to make sure they are the same.
First is all the other threads on here I've found about porting GT40 heads
http://sbftech.com/index.php/topic,31685.0.html
http://sbftech.com/index.php/topic,23855.0.html
http://sbftech.com/index.php/topic,4722.0.html
http://sbftech.com/index.php/topic,10879.0.html
http://sbftech.com/index.php/topic,31071.0.html
http://sbftech.com/index.php/topic,25443.0.html

Here are the numbers from the flow bench at Rays
Intake


Exhaust

[David Claflin]

Ray suggested that the throat should be 85-90% of the valve size, so I cut down an intake valve to 1.65, and an exhaust valve to 1.33 then dropped them in to see how they fit.

[David Claflin]

As the valves didn't drop in that indicated I needed to open the throat up some more to get them to the right size, I opened them up, and then used a marker in the throat, to see where the valves were hitting. I need to open them up even further, but am reluctant to go much further, again, still got my little girl panties on I guess, I don't want to make these into doorstops. LOL!!




measuring the throat

[David Claflin]

Here's some of the exhaust



measuring the exhaust throat

[David Claflin]

Stock stuff

[David Claflin]

[David Claflin]

This is a spreadsheet that I put together using info that Gerald and Chad Speir had talked about on TNR. I use it to make sure that all measurements on all ports are the same.

[jayh]

 
 just got me a few new burrs yesterday

[jayh]

http://www.yellowbullet.com/forum/showthread.php?t=437947&highlight=porting+burrs+shank

good find-(from your links)

[Outlaw Bill]

Looks good David.

[David Claflin]

 just got me a few new burrs yesterday

I did too last week. This place does the best, I think, and shipping is free in the US
http://www.carbidebur.com/

Looks good David.

Thank you!

One thing that I wonder if it's an issue or not, on the stock heads the pinch is where the MCSA is smallest at the 1" point. On my head it is at 1.5", just past the pushrod pinch. You can see in the one pic of the ported intake, where I got to happy opening it up, and had to put a copper tube into the pushrod tube. I think I should open it up at the 1.5" spot so that the smallest MCSA is at the pushrod pinch. Thoughts?

[coulterracn]

I think I should open it up at the 1.5" spot so that the smallest MCSA is at the pushrod pinch. Thoughts?

I would work the port wall to have the MSCA at the pinch. Looking at the cutaway pictures Rocky posted in one of the other threads shows the walls have some thickness but I'd take it slow.

Ray

[David Claflin]

I would work the port wall to have the MSCA at the pinch. Looking at the cutaway pictures Rocky posted in one of the other threads shows the walls have some thickness but I'd take it slow.

Ray

Thanks, hopefully having my sphincter all clenched up won't adversely affect my already bad hand/eye coordination.  

BTW, I cross posted over on TNR, because I'd gathered some info over there about porting as well.
http://www.toonutsracing.com/smf/index.php?topic=1421.0

[David Claflin]

Had some time to work on this tonight, opened up the port some past the pinch, and a little bit in the throat. I think I have the port pretty close, just need to work the throat a little more and then the recheck the measurements at the 2.5" point. I had apparently messed up when I measured last time. The pinch is now the smallest point in the port, would just like to open it a bit more at the 2.5" point if the measurement is correct.

[David Claflin]

Found this while searching for GT40 cutaways, I wanted to see where the water jacket is.