Is the engine in the 2500 saloon basically similar to the GT6 6-banger? If so, will it slot into a 1500 Spitfire with miniumum effort?

What about the gearbox? Will it fit up to the existing 'box in my Spit (standard single-rail with O/D), which was re-con a couple of years ago? Or do I use the 'box from the 2500, in which case do I need a different gearstick etc?

Engine and gearbox mounts - does it bolt straight down to the same mounts?

What else would I need to complete the job? I assume:

• GT6 tacho (is it electronic or mechanical?)
  
• MkIII Bonnet - are these available in fibreglass, I can't really afford a new steel one, and s/h ones are hard to come by, particularly in Scotland
  
• Front springs, to cope with the heavier engine
  
• GT6 exhaust manifold, and presumably complete exhaust system (and I thought my stainless exhaust would last me forever...). Or is the 2500 manifold the same, in which case I'd just need the system from downstream of the manifold?
  

Anything else I would need? I'm happy keeping the existing swing-spring rear suspension, if Triumph reckoned it was good enough for the later GT6s then it's good enough for me. I don't have a bunch of money to spend on this, and the car is pretty shabby-looking (but mechanically sound), so I'm certainly not aiming to do a perfect job.

Thanks for any advice (inclding, if appropriate, give up now you're wasting your time!)

Richard & Daffy

For the benefit of anyone who is tempted, this is what I've found out in my research.

Engine block is basically the same. In the saloon application the monting bosses for the GT6 may not have been drilled, so that would need doing.

The extra capacity is achieved with extra stroke. This makes an engine that was already heavy to be sitting in the nose of a car as light as a Spit, even heavier, with corresponding effects on the handling.

Due to the extra stroke, no standard sump pan is applicable. The one normally fitted to a 2500 engine will not clear the front cross-member; the GT6 sump is too shallow for the extra stroke. Modifying a GT6 sump may work.

Neither the 2500 saloon gearbox nor the Spit box is right. The 2500 box has an output flange that is a bit higher, which would mean the driveline wasn't straight, leading to possible vibration problems. A GT6 'box probably would work.

GT6 suspension towers would be required to have the correct engine mounts. GT6 front suspension uprights are needed to hold the larger brakes, and also have a larger stub axle better able to cope with the heavier engine, so these are a good idea.

The GT6 also has larger rear drum brakes, which would be a good idea.

I have a habit of breaking driveshaft UJs - the extra output from the 2500 engine would probably make this worse. Changing the diff ratio would help with this, but would defeat the point - the 1500 already has a top speed which is faster than I feel comfortable travelling at, the benefit of a bigger engine for me would be more acceleration.

The GT6 engine has a lower rocker cover and lowered front carb to fit under the bonnet, relative to the 2500 engine. Even replacing the Spit bonnet with a stock GT6 bonnet would not fit, a larger bulge would have to be fabricated.

GT6 radiator would be required to get adequate cooling for the 2500 engine.

All in all, more work and more money than I want to get involved in.

Richard & Daffy (staying as a 1500 for the forseeable future!)

A GT6/Vitesse sump will fit, with a bit of metal bashing to clear bigends 1 & 2. In the originally six cylinder cars this leaves minimal but acceptable clearance with the steering rack. Leave a groove/ridge (depending of which side you look at) between the bulges
for the rack.

The 2.5 engine was canted slightly (7.5 degrees, I believe) for bonnet clearance, and the original inlet manifold was 'bent', to place the carbs horizontally. Mounting the engine upright, in a Spit/Vit/GT6 leaves the carbs sloping down into the engine, poking up through the bonnet. Moreover, the float chambers are not horizontal. I don't think this is enough to matter, but the HS6 carbs have bolt on float chambers, that can be fettled to fit horizontally if you must. A GT6 inlet manifold would be a bolt-on.

I hope that adds, if belatedly, to your list of desirable mods. But I agree - if you want a six cylinder Spitfire, buy a GT6!
John

PS is the said 2.5 engine still available?

Glad you got the info you were after, but sorry that nobody here replied in a timely manner.

I agree that it's probably much more hassle than it would be worth in terms to effort:performance.

Even Spit 6 conversions seem best when simply moving a Spitfire tub onto a GT6 chassis/bonnet/running gear.

Best wishes,

Jeff
San Diego, California
'68 Spitfire Mk3 aka "Mrs. Jones" FD 21032 L

Haavard Guttormsen
Norway