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GT6 cylinder head


Mike T
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Hi

 

A quick question. Is there any difference between a TR6 head and a GT6 MkIII cylinder head. From what I can see reading the two manuals I can't see any but wanted to check if there was some difference that would prevent me fitting a TR6 head to my GT6

 

Thanks

Mike

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I don't think there is, but I'm glad to be corrected.

 

John Thomason, in his Originality book (£12 to £194 on Amazon!) says that from KC10001, Triumph rationalised their head range for six cylinders, to fit the T2000 head that had bigger chambers and a lower CR than the GT6, but fitting domed pistons to the latter to raise the compression towards, but not to, the earlier level.     It detuned the GT6.

 

  How did T2000s have "bigger chambers?  By being taller, like a TR6 head.    With no evidence, I think that those T2000 heads were TR6 heads, in which the longer stroke and larger displacement would have delivered a higher CR than in a 2L engine.

 

Why did they do this? To reduce production costs.  The head castings were ground down to a flat block-facing surface, from blanks that were identical for all their six cylinder engines.    More time, more complexity of parts ID and more cost if their were two or three types of head.

 

The stud patterns are identical, as are the ports.    But your engine must have domed pistons of you will end up with a CR of about 7:1.      Even if your GT6 MkIII is after KC10001, check that an earlier engine has not been fitted.   But even if you don't have domes, you can get the head skimmed back to GT6 spec. and it will become a GT6 head, 40 years later!

 

JOhn

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Don't know about the TR6 head but I've been told, during my recent head gasket tribulations, that the GT6 mk3 head is shallower than the mk2. This is because of the mk3's domed pistons. Clive (I think it was)  advised me to change to flat top pistons, stick with the shallow head, change to a mk2 cam and my engine will be much improved!  

 

For those on the edge of their seats following my progress with my head gasket, the head goes on today! Rain allowing. :(

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"the GT6 mk3 head is shallower than the mk2 (GT6?) because of the mk3's domed pistons"

Shurely shome mishtake?

 

Think about it, just for a moment.  

 Shallower head = smaller chambers

Smaller chambers = higher CR

PLUS

domed pistons = higher CR

Fit the smaller head AND domes and your CR will be about 14:1.  Fine, if you run on pure alcohol (not even 10% in petrol), but it will pink a bit otherwise.

 

It's the other way about, as I said above.   GT6 Mk2 and early Mk3 = shallow head.

 

John

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confusion rules! Domed piston GT6 use the same head as later GT6, the 225 IIRC.

The earlier, flat topped pistoned GT6 (rotoflex, more or less, from the factory) use the shallower 2 litre head.

 

Too much stuff to remember! I am sure memories are like a tube of smarties. Push some new info in, and another bit of info drops out the other end into oblivion. That is my excuse.

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My books say from Jan 72 the Triumph 2000 cylinder head was fitted to the GT6 - from engine KE10001. The domed pistons were introduced to make up some of the difference caused by the deeper combustion chambers, but the compression ratio still dropped from 9.25:1 to 9.0:1. The milder camshaft introduced at the same time to improve emissions didn't help performance either.

 

The GT6 Mk3 parts book suggests a further change at KE20000.

 

Gully

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Smarties are not what they were. They were redone to get rid of the noxious colorants used to appeal to kids. For a long time there weren't any blue ones and the rest are now dull and pale versions of their former selves. They still taste alright though.

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My books say from Jan 72 the Triumph 2000 cylinder head was fitted to the GT6 - from engine KE10001. The domed pistons were introduced to make up some of the difference caused by the deeper combustion chambers, but the compression ratio still dropped from 9.25:1 to 9.0:1. The milder camshaft introduced at the same time to improve emissions didn't help performance either.

The GT6 Mk3 parts book suggests a further change at KE20000.

Gully

There's an echo in here!

See post 2

 

John

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Hi 

 

Thanks for all the comments. My engine number is KE10489HE, this is not the original engine from what I can tell as the chassis number is KE4390. From what has been said above it looks like I might have the head with the larger combustion chamber. Are there any markings on the head itself that would identify it?

 

As I am relatively new to these engines am I correct that the GT6 and the TR5/6 have the same valve sizes? This would suggest that the limitation on power output on the GT6 engine is not the head design as this was capable of flowing enough to give the power outputs seen in the TR range - is this correct?

 

Mike 

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I think that the largest inlet valves were on the 2.5Pi saloons, and that their later heads had a better throat profile

 

This chart from Chris Witor's website may help head ID: http://www.chriswitor.com/cw_technical/head_applications_chart.pdf

See Chris' site also for throat profiles.

 

You can use larger inlet valves by recutting the seat, when you should have steel seat inserts fitted, else lead-less valve recession may occur.

 

JOhn

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Come on, keep up!

 

The domed pistons on a GT6 meant that a head, unmodified from a TR6, with larger chambers, would achieve a suitable CR, because the domes take up space in the chamber and make it in effect smaller.

I think that a TR6 head will slot right onto your GT6.

BUT, you should measure the chambers, and do the sums, not forgetting to subtract the dome volume.

 

JOhn

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Heads.....

 

Early heads, big exhaust valves. Two types of head, thin on Vitesse, GT6, 2000. Thick on 2500 and TR6

 

Later heads, smaller exhaust valves to stop the cracking between the seats that afflicts the big vlave heads.

I have two cracked heads on the shelf.

Just the one head model that's common across any GT6, 2000, 2500 or TR6

 

Lots of claims about the latter heads being 'better' flowing, but the later heads can also suffer from epic core shift and can have major misalignments in the ports.

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  • 2 weeks later...

Why do you want to fit a TR6 head?  Dependent of the year of the donor car it will either be effectively the same as what you already have with  same chamber volume and same valve sizes, or possibly even have the smaller exhaust valve.

 

Flow wise, as mentioned above, apart from random manufacturing variations between heads due to the way the cast-in areas of the ports match up to the machined areas, the only heads that are different are the 219016 stamped ones from the 2500S saloon, which is meant to give the best flow in standard form (according to Chris Witor).  The 219016 has small exhaust valves (not convinced this makes a huge performance difference and they certainly crack less often) and also a deeper chamber so would need a skim to get you back to the compression ratio you have now.

 

Nick

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I have acquired a TR6 head with the larger exhaust valves. The head I currently have does not have hardened seats and I know I have low compression on 2 cylinders which appears to be head related rather than worn bores. I was planning to recondition the TR6 head with hardened inserts and then just swap them over. The other option was to take the current head off and recondition that.

 

Mike

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Ok, fair enough.  Was the stamped number you gave earlier from the GT6 head?  If so what is the number on the TR6 head?

 

Bottom line - if your 2L engine has domed pistons, which you should be able to see if you turn the engine to TDC, take no.1 plug out and shine a decent torch in the plug hole, you can fit the TR6 head.

 

This link has head numbers and some related details though not sure it adds much to that given on Chris Witors site.

http://www.triumphclub.co.nz/?page_id=653

 

Nick

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