triumph 2500s twin carb engine in to gt6

[matt123]

As the title really, is the 2500 a biggerbore/stroke gt6 engine ? Would it go in to a gt6 mk 3 without massive fettling?

my engine could prob do with a rebuild and i could maybe get my hands on oone of these engines off a bloke from work as its larger i'd rather rebuild that and pop it in

matt

[Richard B]

Same block, marginally taller head for the combustion chamber. The bore is the same it's a stroked version (different Crank, pistons and a duplex timing chain).

The Induction system can take a little bit of work clearing the bonnet. As the capacity is larger you need to get more air / petrol in there vis-a-vi a 2000.

[Spitfire2500]

Unless the 2.5 lump come out of a Spitfire or GT6 you'll need to swap the engine front plate for the GT6 one (or modify it if you're good with that sort of stuff).

There may or may not be an issue with the G/B I/P shaft but I can't remember the details to be honest -- and this coming from someone who's a got a 2.5 lump in his Spit  :B

[Freebird]

I've got a 2.5 in my Vitesse and used the 2.5 sump which is deeper than the 2.0 to clear the longer throw crank. This fouled the steering rack, so I put 6mm spacers under the front engine mounts to lift it clear. The front 1 3/4" SU is very close to the bonnet - but a miss is as good as a mile!!

Some people have used a 2.0 sump and hammered a dent from the inside to clear the crank. I didn't have one, so opted for my solution.

Due to the longer stroke. the 2.5 is not as revvy as a 2.0, it's main advantage is torque. For this reason many people prefer to tune the 2.0.

Glen.

[matt123]

hmm, just been told i can prob have the whole car that the 2.5 is in for the princely sum of £150 . Its been garaged since 1985 so needs some work but its not a rust bucket.

i have access to large garage space and all tools for £120 a month , its tempting very tempting

[sbarc]

This does sound very tempting.  What sort of HP can you get from a mildly tuned  2.5 with carbs?

[Clive]

not a lot more than a 2litre, but lots more torque.
As an example I can use the notorious "retrocars" article that my 2.5 vitesse took part in. Done on a rolling road as a shootout.
My 2.5 vitesse, very mild road cam only, 110bhp@4900,125lb/ft@4200.
highly tuned carb 2.5, 130bhp@5500, 126lb/ft@4800
Mild tuned (k+N's, extractor manifold etc) 2000 91bhp@6200, 79lb/ft@5300
Higher tuned 2000 97bhp@5750, 90lb/ft@5500

These figures caused a lot of upset etc, but they are a fair comparison, all done the same day, same rolling road etc, so are fine to use to compare, even if people disagree with the figures. The 2.5 has about 30% more torque at 1000 lower rpm, 20% more power at again about 1000rpm less.
I think it provides a better usable engine, but if you want a screamer and driving at higher revs use the 2litre, but improve wisely!

Anyway, fitting the 2.5 is easy enough, same basic engine. Use the gt6 inlet and dolly sprint short dashpot carbs. Tall carbs don't fit! Gearbox, clutch/flywheel etc all from the GT6. But you will have to use the GT6 sump and dent it  (5 mins with a big hammer) Use the GT6 or better vitesse dizzy, Gt6 rad (needs to be good) and so on. All nuts and bolts, really worthwhile.
Of course if it has PI that can be fun!

Clive

[GT6boy]

Well said Clive- good post.
I would rebuild the 2.5 at your leisure whilst still using the 2 litre.
I've always fancied running a nicely sorted 2.5 set up. Not a 2.7 over-bore monster, just a mk2 Gt6 cam shaft and the HS6/dolly sprint dash pot carbies on a 2500S manifold. Smoooooooth! 8)

Oh, and it goes without saying, nice 6-3-1 exhaust manifold. Anyone know someone who could supply one (come on GT!)....

[Clive]

Ta!
Forgot to mention use the GT6 engine backplate with ethe GT6 gearbox. And the diff may want changing, ideally to 3.27 or easier a 3.63. I have broken 2 or 3 3.27 in the vitesse, so really should be more careful (but have been using a saloon gearbox, almost indestructable but very short first gear, gt6 box better ratios)

and I hope nobody is too disgusted at the power outputs. As I said, it was all back to back, and I am convinced most rolling roads will "tweek" the readings to flatter the owner./ Suspect the guy who tuned my spit did that by 10hp or so, still the reading is 150 so it is a nice round number.

Clive

[DoZ]

Have you done this swap Cliffy?  If so can you or anyone esle comment on what its like to drive?

I am in a simmiler position in that my engine needs a re-build.  So thinking I either re-build mine or maybe swap it out.  Then if I swap it do I go for a 2.5?

Everyone seems to say they don't rev so well and the 2.0L is more tuneable in some respects but the preformance figures above make you think its not worth starting with a 2.0L.

Anyone got a 2.5L they want rid of?

[Spitfire2500]

DoZ wrote:

Everyone seems to say they don't rev so well and the 2.0L is more tuneable in some respects but the preformance figures above make you think its not worth starting with a 2.0L.

I've only ever driven a standard GT6 to compare with my 2500 (midly+ tuned) Spit and personally I'd take the 2.5 every time. The 2.5 is just so effortless especially when you stick it in something as light as a Spit :)

I'm not sure what people mean by "don't rev so well" -- you certainly can't rev it as highly, but my 2.5 lump is no slouch and in terms of getting to 5.5k/6k it gets there every bit as fast as any 2l engine I've had experience of. Doubters are welcome to come see it action during the RBRR if you don't believe me  :D albeit I need another three people to drop out before I get in :P

OK my engine's had a fair bit of work done so the comment will be fair enough comparing standard lumps but no way I'd dismiss the 2.5 solely based on the "revs issue".

[Freebird]

Quote:

Use the GT6 or better vitesse dizzy

In my experience (limited admittedly) the Vitesse/GT6 dizzy gives too much vacuum advance resulting in pinking and running on.

Better to fit the vac advance unit from the doner 2.5 to the GT6 housing to retain the tacho drive.

[Richard B]

Freebird wrote:

Better to fit the vac advance unit from the doner 2.5 to the GT6 housing to retain the tacho drive.

Yep, but if you are fitting a 2.5PI under a GT6 bonnet the dizzy with a tacho drive will hit the bonnet. You have to go for an electronic tacho.

[Clive]

And the GT6 is delco, vitesse and 2.5 lucas, so won't swap.
I really think the over advance issue is down to stretched springs on the mechanical advance. Fitting stronger than std would reduce midrange advance, so may well be worthwhile.
Best of all a mappable 3d ignition like megajolt!

And yes agree with Bill above, when building my car I chose a 2.5 over a 2.o because of the relaxed torque which does make the car great for just leaving in 4th gear. Can't be too bad an engine, fitted to TR5+6 and nobody swaps those out for a 2.0! It doesn't rev quite as easily, but not that you would care as it will probably leave the 2litre behind anyway. Yes if you want a screamer do for the 2 litre, if you want a bit more relaxed, but still probably quicker and pulls much better, get a 2.5  All IMHO of course!

Clive

[rotoflex]

My GT6 Mk3 has had a Lucas 22D distributor in it as long as I can remember.
It has a cable drive for the taco meter.

[GT6boy]

rotoflex wrote:

My GT6 Mk3 has had a Lucas 22D distributor in it as long as I can remember.
It has a cable drive for the taco meter.

Me too!
Hi Clive. Why was the 'Retro Cars' article controversial? I had a copy but have mislaid it. I thought it was a poor article, with little relevent detail for the techno-hound. A missed opportunity. ::)
Was there a thread on here about it? :-/

[James]

Give us some details on such a setup GT...

I am considering 2 litre vs 2.5 litre at the moment...

I think because it's a big saloon it may need the 2.5 torque... but really I love the revvy smooth 2 litre and would take the drama of whizzing past people at 7k over the thumping 2.5s torque...

[JohnD]

Just for comparison, here is the Silverback's rollers report.
Flowed head, 6-3-1, Pi, TR6 cam.
125 at the wheels, Dennis' estimate 140 at flywheel.

Some other points about fitting a 2.5 in a GT6:
The 2500 inlet manifold may be difficult, as it is for a canted engine and so sticks up when that is mounted vertically.  I'm amazed that a 2.5 engine lifted to clear the GT6 steering rack also clears the bonnet.
A 2500 gear box needs some chassis work, but it has been done.  See Binman's site: http://www.supersix.50megs.com/
If you go for the GT6 box, then you will need the GT6 flywheel, AND the GT6 spigot bearing.

John

[James]

Is that a late TR6 cam then?

I thought you would have gone for more of a race cam in the Silverback? What that a purposeful decision?

[Tim Bancroft]

I personally think a 2.0litre engine for a sports car and a 2.5 for a saloon.

My GT6 2.0l engine is +60 and the torque is very good-I think it equates to something like 2080cc.

My concern about Pi engined GT6s is always where to stick the fuel pump, I hate the thought of lobbing it under the rear-seems so vunerable?

As for Nigel Gair's car-its superb, nice revvy 2.0L in a mk 2 shell-terrific stuff-genuinely exciting car!!!!

James: I'd go for a 2.5 in yours though-you will have a sports car when you finish the Spitfire.

[ncoll]

[quote=JohnD]Just for comparison, here is the Silverback's rollers report.
Flowed head, 6-3-1, Pi, TR6 cam.
125 at the wheels, Dennis' estimate 140 at flywheel.




The graph/powerplot you show from dennis vessey is brake horse power at the flywheel and not at the wheels. :o
The difference between the 125bhp and the 140bhp is a percentage dennis adds to the figure because he says his rollers read low, (normally 10%) ;D

ncoll

[JohnD]

I KNEW you'd say that GT!
And you're right if that were an absolute figure.
Rolling roads differ, of course.

If more were obtainable, I'd say cam timing.
But which way to go? It was timed using lift on overlap.

John

[Clive]

My figures were entirely real worrld, back to back. Don't think it is fair to compare figures from different rolling roads at different times.
It was contravesial because none of the cars performed as expected, even mine was a tad daown as I was really hoping for 120bhp, but he did comment that my dizzy was tired and the fuelling not ideal. It hadn't been set up properly.....
However the real disappointment was from the guys who had spent SERIOUS money on engines etc and were doing little better than mine.
I think that is a fair comparison.
Of course it is possible to get large power from a 2 litre, but maintain that as an everyday motor the 2.5 is miles better. For me at least. Maybe I am a tad mellow  :P
And as a std engine or light mods the 2.5 will always be ahead. Spending LOTS of money may change things of course.
Guess the best ideal is a Zetec  :D

Clive

[James]

I think the difference is that a 2 litre in a Spit/GT6 gives the true sportscar experience - it's just that not all Spit/GT6 owners want to drive it like a sportscar. My Spit is not for every day driving... (well it's not for any driving at the moment) it's for ragging senseless and getting my adrenalin flowing :)

Tim-nice revvy 2 litre in a mk1 makes even more sense... it's lighter!

[JohnD]

[quote=ncoll]

JohnD wrote:

Just for comparison, here is the Silverback's rollers report.
Flowed head, 6-3-1, Pi, TR6 cam.
125 at the wheels, Dennis' estimate 140 at flywheel.

The graph/powerplot you show from dennis vessey is brake horse power at the flywheel and not at the wheels. :o
The difference between the 125bhp and the 140bhp is a percentage dennis adds to the figure because he says his rollers read low, (normally 10%) ;D

ncoll

ncoll,
It HAS to be power at the wheels, unless the engine is on an engine dyno, and Dennis's is a rolling road.  So, 125 at the wheels NOT the flywheel.
    Operators usually add something for "at the flywheel".  It can be an estimate based on the run-down with power off to see how much power lost in transmission, or on their experience, or often, I think, to make the owner feel better.  In this case, I had so much negative camber (corrected later) that the apprentice and I had to ride on the back of the car to make the wheels grip the rollers!

Anyway, power 'at the flywheel' is useless - it can't make the wheels go around without a transmission!
John