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Triumph TR6 - Need a quick answer

My Nov '73 (74 Model) has a head which is 3.550" thick - 7.5/1 CR. Have just spent serious dollars on bronze valve guides and hardenned seats and want it cut to 3.460" for a resonable 8.5/1 CR. IS THERE ENOUGH MATERIAL TO DO THIS SAFELY?? Have seen threads to this effect, but - is my head suitable for this modification ??
Much TIA Peter.
Peter G

I don't see why not. My '73 is machined down to 3.385" to give a calculated 9.75:1 compression. Kas' competition manual took the head thickness down to 3.375".
Brent B

Brent, at 9.75:1 do you get much pre-ignition? or do you have to add a supplement to the fuel to boost octane?

By changing the compression what was the biggest differences that you noticed? I assume you gained hp and torque but was it significantly better (ie to justify the costs and driveablity)?
Steven

Brent
Where did you have this work done. Thinking of wacking off my head also along with other machine work to the head. Were you satisfied with their work? You can email me if you want. Thanks
Steve H

Thank you for putting my mind at rest. Don't want a race car, just a good running beast, also did not want to break into water passages after all this money spent.Peter
Peter G

Steven - I get no preignition at all - of course that's with "premium" gas. The cost of the milling was cheap - under $100. Add in a valve job and it goes up a bit. Driveability is great as the power went up significantly. Only problem is that sometimes it wants to cough or try to diesel when shut off.
Brent B

The racers here in UK machine their heads down to around 12 to 1 CR, and standard UK cars had 9.5 to 1. As most production was exported the UK heads were simply machined down more then the exported ones. Machining for the highest compressions does cut into the squish platform (opposite the plug) which becomes broader. On a 9.5 head it appears that this platform is not machined down appreciably, as avery thin full-bore section remains. So you should be able to comfortably remove as much of the full-bore, cylindrical area of the head chamber (before the squish platform) to get the CR you want, without any worries.
The squish effect will become more vigorous as you raise the CR so the engine will be less likely to detonate on a given fuel, unless its real jungle juice.

Its a pity to hear you are all cutting down those nice thick heads- they are perfect for supercharging, and none too common over here.
Peter Cobbold

Peter - you're right! A supercharder these days IS intriguing. But I'm not convinced that the performance/run-time trade off is worth it...
Geez - you guys have the PI engines. Ya want more?
Brent B

A big Thankyou for all the response - I've learned a lot and am at ease as I pick uf my finished head tomorrow. This will be a fun weekend. Peter G
Peter G

Go for it. You won't run into water passage problems until you get around 16:1.
Mike Munson

Bent,
Well I had thought of keeping the PI and using the boost to operate the choke enrichment on the metering unit, but the attraction of just having a single SU ( albeit 2") won the day, that I can tune myself whereas the PI is another kettle of fish...
There was a kit made in USA by Vintage Induction Systems using an Eaton M90 blower that was really neat. And for a USA purchaser I should think an M90 is considerably cheaper than a set of triple Webers, and there's no need to gas-flow or mess with the insides of the motor at all, a stock cam is fine....
And if you want a TR6 that pulls a gear higher than normal with ease and has the feel of a torquey V8, supercharging is the way to go. I wish I had fitted mine with a blower 25 years ago.
And hey, you guys live in the original home of the blown street rod, or is that just California?
P H Cobbold

Mr. Cobbold,

Out of curiousity I have tried to find Vintage Induction Systems and have come up empty. Can you point me in the right direction?

Thanks,
SteveD

Steve DeLisle

Steve,
Google came up with this posting from 2001- it might help:

http://www.team.net/html_arc/6pack/0111/msg00007.html

The phone number for VIS is somewhere in a huge pile of paper in the loft, but I got his address from his US Patent ( no: 6,012,436):

Peter Boucher
24 Fern Road,
North Hampton,
NH 03862

The patent shows externals of the manifold, but the key to its operation will be how it is baffled internally to prevent biased mixture supply to the cylinders.
I also found a web page (now expired) that I printed showing photos of the kit fitted to a TR6. I got the blower model wrong- it uses an Eaton M62 not an M90. Can scan and send if absolutely essential ( 28,800bps connection speed)
Peter

P H Cobbold

This thread was discussed between 07/01/2003 and 23/01/2003

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