High Compression Head

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psprat496

New Member
Nov 22, 2009
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New Jersey
I've got a Starfire 66cc GT-4 engine. Has anyone put MM High Compression head onto this engine? I've heard the head is only for GT-5 engines but why is that? Would it not fit onto my engine?
 
Sep 20, 2008
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Clearwater, FL
web.tampabay.rr.com
I've got a Starfire 66cc GT-4 engine. Has anyone put MM High Compression head onto this engine? I've heard the head is only for GT-5 engines but why is that? Would it not fit onto my engine?
psprat496:

I saw your post in the other thread...I'm working on a graphic and a description that will give everyone the info needed to determine whether or not it will work...and better yet, whether or not it will be of any benefit for a given engine.

Jim
 

psprat496

New Member
Nov 22, 2009
159
0
0
New Jersey
psprat496:

I saw your post in the other thread...I'm working on a graphic and a description that will give everyone the info needed to determine whether or not it will work...and better yet, whether or not it will be of any benefit for a given engine.

Jim
Wow that would be great. Really clear up some confusion that people might be having. Have you ever tried to put the head onto a GT-4 or heard of anyone doing so?
 
Sep 20, 2008
1,668
13
0
Clearwater, FL
web.tampabay.rr.com
Wow that would be great. Really clear up some confusion that people might be having. Have you ever tried to put the head onto a GT-4 or heard of anyone doing so?
I have no idea what the differences are between the GT-5 and the GT-4.

The current cylinder head offering was designed for engines that are as shown in the graphics below. All three graphics are the same...It's just a progressive zoom for reference.

The PK-80 and the Grubee GT-5 have nearly identical deck heights and piston crowns.

The deck height should be nearly zero, and the piston must be crowned. If your piston is flat...forget it...you will get zero performance benefit from this part!

As a final check, simply lay something pliable on top of the piston and bolt the head on. Rock the engine by hand to TDC and back again. Remove the head and check the thickness of the material. .015"-.020" is good.

Yes...something pliable. Light a candle and drip the wax around the perimeter of the piston, building inward to about 1/4" from the edge.

Jim
 

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