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View Full Version : GT6 Higher compression GT-6 head - will it work?



davidk
04-02-2008, 10:49 PM
I'm hoping to buy a rebuilt head from another forum member for my 1974 TR-6 with a GT-6 engine. The rebuilt GT-6 head appears to be about 1/4 inch shorter than my head. My engine is stock with who knows how many miles. It does run strong. I think my compression ratio is 7.75. I think the new head is 9.25. I'm sure I'll need shorter push rods. Do you think this head will do any damage to my engine? Are there any other problems in making the switch? Thanks for your help!

DNK
04-02-2008, 11:06 PM
David- See Skikir Post

Not the piston 1

davidk
04-02-2008, 11:13 PM
It's Skikir I'm talking with about buying the head. My engine is a GT-6 engine.

DNK
04-02-2008, 11:16 PM
Funny , my GT6 head I thought was taller.

70herald
04-03-2008, 01:00 AM
9.25 should not be to high, there are others running similar comp ratio's however you should carefully measure the actual compression chamber volume to find out what the real compression will be. Oversized pistons will also increase the compression ratio.
Also many other factors will affect the results such as which cam you have (affects the dynamic comp ratio)

The real risk is if there is pinging. If it is minor, there are some methods of attempting to deal with it such as lower temperature thermostat, lower temp plugs, hi test gas, and if it is really a problem, thicker than normal head gaskets. Presumably, you will not want to change the pistons to dished types if the bottom end is in good condition.
As for the push rods, they are available in shorter lengths so that should not be a problem, take a look at the adjusters first however to see if there isn't by chance enough thread left to make it fit.

skikir
04-04-2008, 10:35 AM
Are you saying that you Actually have a stock GT6 Engine or a GT6 engine built to TR6 displacement like mine was? IF it is TR6 2.5 liter displacment then don't buy it! If is is a GT6 2 liter then it should be fine. If you have a 2.5 Liter engine then you would want a late model GT6 MK3 head with the larger combustion chamber which was used with domed pistons. The head I have is about 3.3 inches. The late GT6 head is about 3.46 inches. My '76 TR6 head I milled .1 inches off to about 3.4" which if I remember right I guestimated to about 9:1 or so up from the paltry 7.75:1. That made a huge difference in power in the lower end but with the '76 cam the upper end was gone. I bought the engine and trans and milled the head befor I put them in. I remember thinking that the gearing was different in the box then I realised that I was accelerating a lot quicker and was going through the gears faster. The real difference with the Six cylinder Triumph heads is in the thickness of the head. The head I have is a 517528.

Check the bottom of the page here.

https://www.triumphclub.co.nz/technical.html

davidk
04-04-2008, 12:45 PM
It is a stock GT-6 engine from a MK 2. My head is 3.53 inches tall.

I sent you a pm before I saw this post.

Brosky
04-04-2008, 01:46 PM
Or you can look here for more information on the heads:

https://www.goodparts.com/tech_docs/TR6_Compression_Ratio.html