Tutorial: How to port and polish GT-40 heads (pics)
01-21-2008, 04:04 PM
#1
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Join Date: Jun 2007
Location: Roseville, CA
Posts: 444
Tutorial: How to port and polish GT-40 heads (pics)
Hey guys, since I recently ported and polished my gt-40's, I thought I would share how I did it! This is the first set of 2 valve Iron heads I have worked with. Hopefully this will help others looking to try it as well! ==>Note: I did not touch the intake ports since they already flow well and the rough texture promotes fuel suspension and atomization. The exhaust ports on the other hand need a lot of love!
Here we go:
As you can see in the above pic, the exhaust port is much smaller than the gasket opening, I used a combination of a dremel with sanding drums to polish,and a rotozip with with various dye grider bits to port. start working your way outwards and match the gasket opening, when you reach the desired shape you ca start polishing the entire port.
In this pic you can see how I have started to open up the exhaust ports to achieve the desired shape. Take you time and take care not to damage the gasket mating surfaces, valve guides and valve seats.
There is a nasty hump like obstruction in every exhaust port, which you can see i have started to grind away here(its to the right of the port in the center). take extreme care not to grind too far, or you may end up in a water jacket, thus ruining your head. Also start to grind the bowl area where it kinks just under the valve seat, taking care not to accidentally grind the seat itself.
here is a pic of the final product.
and an upclose, notice how close the port shape is to the gasket hole, and hw smooth the inside is. It looks like this all the way to the valve seat.
If you are unsure if you have GT-40 heads, there is a casting stamp saying GT all over the place on them, plus the 3 bars on the ends of the heads.
Anyways, I hope this was helpful!
Here we go:
As you can see in the above pic, the exhaust port is much smaller than the gasket opening, I used a combination of a dremel with sanding drums to polish,and a rotozip with with various dye grider bits to port. start working your way outwards and match the gasket opening, when you reach the desired shape you ca start polishing the entire port.
In this pic you can see how I have started to open up the exhaust ports to achieve the desired shape. Take you time and take care not to damage the gasket mating surfaces, valve guides and valve seats.
There is a nasty hump like obstruction in every exhaust port, which you can see i have started to grind away here(its to the right of the port in the center). take extreme care not to grind too far, or you may end up in a water jacket, thus ruining your head. Also start to grind the bowl area where it kinks just under the valve seat, taking care not to accidentally grind the seat itself.
here is a pic of the final product.
and an upclose, notice how close the port shape is to the gasket hole, and hw smooth the inside is. It looks like this all the way to the valve seat.
If you are unsure if you have GT-40 heads, there is a casting stamp saying GT all over the place on them, plus the 3 bars on the ends of the heads.
Anyways, I hope this was helpful!
01-21-2008, 04:37 PM
#3
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Join Date: Jun 2007
Location: Roseville, CA
Posts: 444
RE: Tutorial: How to port and polish GT-40 heads (pics)
It took me maybe around 6 hours of grind time, hard to say, I work on them over the course of a few days. gaskets are standard felpro's from summit. I should also note that once I was done I took them to the machine shop and got a 3 angle valve job done, had them hot tanked, reassembled with new seals. DO NOT do any grinding on your heads and reinstall them w/o hot tanking them and re building them with assembly lube and seals.
01-21-2008, 05:53 PM
#5
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Join Date: Jun 2007
Location: Roseville, CA
Posts: 444
RE: Tutorial: How to port and polish GT-40 heads (pics)
well, it was $30 per head to mill them, $10 per head to grind the valve stems down the same amount as the heads were milled, so I didnt need to get new pushrods, $100 for a 3 angle valve job, hot tank, shot peen, clean the valves, rebuild and paint.
01-21-2008, 07:19 PM
#6
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Join Date: May 2006
Location: Wisconsin
Posts: 718
RE: Tutorial: How to port and polish GT-40 heads (pics)
Wow that's a lot cheaper than I thought, I was wondering how you got it so clean. So if you do an engine rebuild you would want to hot tank just about everything too right?
01-21-2008, 07:23 PM
#7
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Join Date: Jun 2007
Location: Roseville, CA
Posts: 444
RE: Tutorial: How to port and polish GT-40 heads (pics)
yes, youll want to hot tank your parts, just make sure theyre properly lubed when reassembling. the shop i use is pretty inexpensive, but the one down the street from him charges twice as much for the same work, so shop around and dont let tweekers do the machine work.
