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Block and Cyl Head ID help please


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OK here goes

My 1971 GT6 MKIII was/is fitted with a 2000TC engine (ML23396HE) which I believe to be around 85 bhp from the factory?
Possibly making my GT6 the most underpowered on the forum :B  (AFAIK It is standard apart from K+N's and a twin exit exhaust)

Am I right in thinking this engine will have domed type pistons as standard - is there any way to tell without taking the cylinder head off?

Now I also have in the garage a 2.5 Short engine that appears to have been decked as the engine number has been ground off in the process and pistons 3 & 4 appear to stand slightly higher than the top face of the block. The block casting number is 308758.

The cam was 308778 I belive a good one but the lobes are to pitted to use it again, is it worth getting it reprofiled? Or any suggestions for a goo fast road cam.

I also have a cylinder head that came with the engine. It has a casting number of 313248 and is stamped with 313248, This is supposed to have been skimmed to give a compression ratio of around 10 to 1 and has all new valves and guides that appear to be standard.

If this all appears a little long winded (sorry) I got this stuff off an old boy having a garage clear out, he got this stuff together to put in a vitesse 30 years ago and never got round to it. I am hoping to improve my GT6 with it in any number of ways.

If the 2000 engine has flat top pistons then can I use the head with it and get another cam or if not then I'll get the 2.5 stuff balanced,lightened etc and may need the piston tops machined as I reckon 3&4 stand proud by 10 to 15 thou. though I would need to check this properly and not just estimate it.

I am open to any suggestions to the best way forward, I'm not after an out and out racer but a strong road car and for the odd track day too ;)

Any thoughts gentlemen?

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can you not see the tops of the pistons with the plugs out and at tdc with a small torch?poke a length of stiff wire in and you should be able to feel any dome on the piston.
as for the engine bits you really need to burette the chambers to get the exact volume then dry build your engine either 2l or 2.5l to measure effective piston stroke etc.with a really wild cam it would not be unusual to have a static c/r of 12-13/1  even for a road car.you're aiming for a compression pressure around 180psi.
my advice would be choose your cam then do the above.

anyone else?

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Couple of thoughts;

If the head gasket has a tag sticking out the back then it will be recessed bores & dome pistons.

The 2500 head will fit this as the dome of the piston reduces the volume of the combustion chamber.

You need to decide what you want, a 2000 which revs to 5,500 - 6000 or a 2.5  which is fussy over 5000?

GT6 MkII cam is good or a TH5.

What carburettors do you have? If you go 2.5 you want 1-3/4" carbs.

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So a quick check would be to check for a tag protruding between the cyl head and block at the rear of the engine above the bellhousing?

I am hoping to keep it a 2000, I like a few revs :)  I was going to go 2500 but had a change of heart, maybe to much torque for the drveline.

Although if the combination of parts is going to add up to a good 2500 I'm not totally against it.

At the moment it's on stromberg cdse 150's but I have a pair of 1 3/4" dolly carbs (low dashpots for clearance)

I also picked up a 2500s inlet manifold but that is going to need a lot of work to make it fit, cutting and welding etc. (anybody here who can do it for me for a fair price?)

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Richard_B wrote:
If the head gasket has a tag sticking out the back then it will be recessed bores & dome pistons.

B*ll*cks!!!     That does appear to be the case.  There is indeed a large tab at the rear of the block.

As I understand it the flat top pistons are more desireable from a tuning point of view.

So I suppose with what I have it would be easier (cheaper) to build a 2500, send off my block to have crank, pistons lightened and balanced and get a th5 profile cam. build up the engine and swap it over. Also less time off the road ;)

Or start again with the right engine an early MKIII or a MKII GT6 that way I can build up a good 2000 engine to swap over as time allows.

So I suppose it boils down to do I want a good fast revving 2000 or a lazy torqmonster 2500...................AAARRRRGGGGGGHHHHHHHHHHHHH

Unfortunatly I really don't know but I think I still favour the 2000 option :B

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A bit of lateral thinking,

Would it be possible to put my 2000 crankshaft and corods into the 2500 block, using the flat top pistons?

I believe it can be done the other way round with a adapted sump ;)

Does that even make sense :-/ just that if I can make some form of good combiation with what I have I can then afford a good camshaft to get the best out of things.
Otherwise it's time to save a few more beer tokens towards doing things properly.

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2000 and 2500 pistons different. but the conrods the same.....

My vitesse was a 2.5 on twin SU's. Great gobs of torque, no problems with 5500rpm (just ask TR5/6 drivers, they regard the 2500 as quite sporty ;) ) but depends on what you want. A screamer or something that goes better all the way through the rev range. It can hurt the box and diff if not treated with respect, but I know of several such cars that don't suffer. A nice 2.5, tr5 or th5 cam or whatever, 3.63 diff and away you go! Makes short work of most other cars....

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You can convert you dome-top engine to flat pistons; you then need to have the head skimmed to suit.

Hope that makes sense?

Take your 2.5 engine and yes change the crank & pistons if you want to build it up off-line. Still eed to source a head.  :-/

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So I suppose I have two realistic options,

Option 1
Build up the 2.5 with a decent cam and i'll end up with something very similar to engine wise to Clives Vitesse.


Option 2
Rebuild the 2.0 with new pistons and rings.  I believe it's possible to go as far as 2.3 with the correct pistons? Pop in a decent cam and I reckon that would make a good one.

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royboy66 wrote:
see you at Cadwell, you can have a go in both types,  screamer & wheezer !  ;)

might help you decide!

Roy 8)

Thanks for that Roy, I was hoping you were going to say that ;) :) 8)

But with a tired 2000tc which I belive only put out 85bhp factory fresh I think the title of "wheezer" may actually belong to my GT6 LOL

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Lots of threads about on 2.5's into GT6s. Some more research will add to the above advice.

TRs have the advantage of a higher final drive ratio.
For instance TR6 diff is 3.45:1 so they can cruise at high speed at lower engine revs. and reach higher speed without revving the nuts off it.  Sure, they are heavier than a GT6 - swings and roundabouts.

No one has taken up your mention of a decked block and pop-up pistons.   You need to be very careful indeed about skimming the head if you use that block.   Someone did mention a dry-build - check for interference of valves and pistons, as if the valve gear is closer to the block after a skim, they can collide, with devastating effects.  A blob of BluTack on the piston top will reveal the clearance if you cut it with a sharp knife across any valve mark.


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Thanks JohnD

I have looked at some of the info on 2.5 into GT6's but I was more after info ti ID the block and the head. (to see if they were any good as a starting point)
No good starting with an overly restrictive head for example, as usual I got sidetracked :-/

The Idea of a dry build is an excellent one (thanks Richard B) If I can find all the pushrods :o
I can Also check out the cc's of the chambers in the head once I get the stuff together to do it and then work out the compresion ratio to see if it's usable

Thanks all for the input so far.

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Oops got my numbers mixed up before the head casting number is 308351 & stamped 516816 which according to this site     http://www.triumphclub.co.nz/technical.html
makes it a MKI or early MKII PI head. Does anyone know if they are any good?

I think though I'm not sure that the six cylinder block is the same in all applications apart from weather or not it has recessed bores, and only the crank + piston type
makes the difference between 2 and 2.5 litres.

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The international man of mystery has a school of thought regarding performance improvements from the 6 cylinder engine, which could be surmised as: 'The shallower the head, the better the performance'.
Get yourself along to Cadwell Steve, me and Roy will let you have a 'contrast and compare' session in Team Wheezer's 2 litre and 2.5 litre cars.
Personally, I would stick with a 2 litre, whop the CR up and run a GT6 mk2 or TR5 cam and the HS6's you have and get that 2500S manifold done!
For all my limited experience, it just seems to be re-inforcing that Triumph got it right with their cam designs. They were after all, professionals at it, where-as I am a definite amateur in comparison!

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I can't wait for Cadwell now,

GT6DavidMK1 has PM'd me with an offer of a passeger ride in a very warm 2 litre too :) :) :)

All the best people seem to drive GT6's ;) (but I am biased)

Looks like I'll be able to dry build the 2.5 if I can find all of the bits, to see how it looks.
But I'll put off a final decision of what to do untill after a few rides in some wicked sounding GT6's 8)

Thanks for the offers of rides and suggestion everyone!!!

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peterhlewis wrote:
surely the TR5 Cam is for  fuel injected with shorter opening times   how will it improve a carburettor set up ??
and Ive seen a few Kent lobeless cams recently in Spitfires , made of chocolate   Peter

Dunno, but it does!  My Vit has one… bit lumpy down low, (but I don't think the 6-2-1 manifold helps), but goes like a train when it gets on cam.

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