Unibody Mk4 Spitfire 6

[Mark]

Supprised these have not been more widely used. Must be a reason, thought this engine was developed by Leyland/Triumph, based on the Triumph straight six. I maybe wrong,  but thought they shared some triumph parts. On the face of it, a straight six crossflow OHC engine with similar dimentions would have been the obvious upgrade, so makes me wonder why they weren't used. 

[BiTurbo228]

@Escadrille Ecosse Yeah I thought they'd be much too tall as well. Bought one on a whim for £60 ages ago and was surprised at how compact they are height-wise. They don't look it really, but when you measure them they're pretty much bang on what the old OHV engine is.

Would definitely make an interesting project with a full MS setup. Helps get rid of the distributor which wouldn't help fitment in a Spitfire (although a Vitesse and a big saloon should be ok for that).

Just gone out and measured the length on the upper side of the engine. The OHV is 25" from the plane of the gearbox mounting plate to the top of the thermostat housing, and about 22" to the top of the cam cover. The 2600 is 25" to the top of the cam cover, and 28" to the top of the cam pulley so it is a little longer right at the top which isn't particularly conducive to clearing a GT6 bonnet. Would be fine in my car as I've moved the engine 3" further back so it can drop down a bit more level.

@Mark Yeah I'm surprised too when looking at it. Seems like a design with real legs.

I expect there's a number of things that didn't work in its favour. The only car it was fitted to is the SD1 (there were plans for a Triumph saloon version which presumably would use the 6, but they never came to fruition). In the SD1 it'd always play second fiddle to the bigger and more readily tunable V8. Add in that there were some typical BL teething problems with the engines when new, and the obvious detuning of the engine, and they got a bit of a reputation as being more trouble than they're worth. Also, a lot of the early (and continued) development work on Triumph racing engines came from the US where sports cars were very much still popular. The US never got the 2600-engined SD1 (and nor did Australia or South Africa either, where a decent amount of development also happens). That leaves it with pretty much just us which is a relatively small pool of people.

Seems that the main thing standing in the way of just good basic tuning is the camshaft. I've read about a hot cam being made by the aftermarket back in the day, but haven't found any information on who made it or the specs. If you can get something sorted for that (either a regrind of the stock cam or a blank for a new one) then it becomes quite a simple job to get quite a good OHC engine.

As for its history it is a Triumph-designed engine. It began life as a project to fit an OHC head to the old OHV 2.5l. Over the course of its development more and more got changed until it was finally decided that the basic block design itself was a severe limitation so that was changed for a brand new casting. At that point the only part it shared with any other BL car was the Dolly Sprint conrods it used, which were later changed for ones with bigger big ends. So started off as an OHC head upgrade and ended as a clean-sheet design!

[Nick Jones]

1 hour ago, Mark said:

Supprised these have not been more widely used. Must be a reason, thought this engine was developed by Leyland/Triumph, based on the Triumph straight six. I maybe wrong,  but thought they shared some triumph parts. On the face of it, a straight six crossflow OHC engine with similar dimentions would have been the obvious upgrade, so makes me wonder why they weren't used. 

Don’t reckon BL (or whatever it was called at the time) was doing much joined up thinking at the time.....

The general move towards FWD wouldn’t help either as straight 6s don’t package well in that context.

[Escadrille Ecosse]

3 hours ago, Mark said:

Supprised these have not been more widely used. Must be a reason, thought this engine was developed by Leyland/Triumph, based on the Triumph straight six. I maybe wrong,  but thought they shared some triumph parts. On the face of it, a straight six crossflow OHC engine with similar dimentions would have been the obvious upgrade, so makes me wonder why they weren't used. 

I read all about the background to these engines years ago. Can't remember all the details but basically Triumph were looking to update all their engines as part of their future development plan. Of which the TR7 was the first.

The 2.6 was essentially a development of the existing straight 6 block, getting rid of the siamesed cylinder bores, sorting out the oilways and filter, the crank thrust washer issue, etc and with a new crossflow head. Pretty sure they had a 2.3 version as well.

I think the view at the time was that properly designed the 4 bearing crank was perfectly adequate for the job in hand and 7 bearings were not really necessary for a road car. I suspect that watching how BL got on with their C series boat anchor may have contributed to that view as well.

They had planned it to go in a new saloon replacement for the 2000/2.5 as a direct competitor to Rover and their V8 saloon, existing and proposed.

Then of course the wheels came off the British car industry and so when Triumph and Rover were jammed together the Triumph saloon was dropped in favour of the SD1. Rover being the 'senior' partner.

However the Triumph engines were better and much further developed than Rover's replacement for it's 2L four so a modicum of common sense prevailed.

Edited August 19, 2020 by Escadrille Ecosse
spelling and grammar

[BiTurbo228]

@Nick Jones Yep they were in quite a mess at that time. Union action hobbling production efficiency, staunch tribalism from old competitors, a massive and overlapping portfolio of cars and engines, and the government breathing down their neck about their future plans. Could have all been very different if old Charles De Gaulle hadn't vetoed the UKs entry into the european free trade market.

Basically BMC had betted big on advanced and compact FWD cars in the early 60s like the ADO16 and Mini. At the time the UK market preferred stodgy unadventurous designs like the Escort and the Viva (they may be loved now due to the hot twincam versions, but apart from that they're a completely plain and uninspiring mechanica design). BMC's bid was to cash in from free trade when the agreement was due to be signed in 1965 (the British parliament thought it was a done deal). De Gaulle vetoed it, Britain's economy declined and BMC were left with a massive R&D bill and a too-small market to pay it. From that point they scrambled to produce domestic-oriented products like the Morris Marina to tide them over, but by the time we finally got accepted in 1973 the game had changed so much that the once-advanced BMC range was now looking obsolete and the new cars like the Allegro were so starved of development budget that they didn't look nearly as compelling to European customers.

You can see a similar trend in Triumph with the optimistic and advanced designs of the Triumph 2000 and FWD 1300 in the early 60s, which were either allowed to stagnate (the big saloon) or re-designed to a more traditional and cheaper mechanical specification (1300 FWD -> Dolomite/Toledo). Same with Rover going from the P6 with its DeDion rear and clever construction of panels hung off a central frame to the SD1 which was very traditionally designed.

So yeah, it's De Gaulle's fault

@Escadrille Ecosse Yeah the 4-bearing crank design is an interesting one. I know LJK Setright liked 4-bearing cranks for street I6s as they rarely need the additional stiffness of 7 and there's a lot less bearing drag impacting on power and economy. I expect both that and the C-Series issue was weighing heavily on their minds!

It's a real shame that things didn't pan out even slightly differently and let Triumph live on a little longer to see replacement of the big saloon, and the Michelotti-designed Dolomite replacement looked fantastic too (not the David Bache SD2 design that was chosen though...).

I'll have to settle for fitting a 2600 to a Triumph big saloon  

[Escadrille Ecosse]

2 minutes ago, BiTurbo228 said:

I'll have to settle for fitting a 2600 to a Triumph big saloon  

That would make a nice car

Yes, it's a real shame. All so 'nearly'. Rather like my other engineering love which is aeroplanes.

[BiTurbo228]

Ah I expect there's quite a lot of 'nearly' creations in the aeroplane world. Combination of high cost of development and flight being quite an inspirational thing! Whats the best/worst nearly one?

I've got a mate who works with planes (same one that gave me tons of leftover fuel tank sealant). I've been up there a couple of times when they've had planes in pieces and I've always liked how they're put together. Under this shiny sleek business jet the way they're built reminds me of old tanks and other military equipment. Quite basic, unfussy construction but made out of really really nice bits and meticulously put together. Quite different beasts to cars.

[Escadrille Ecosse]

In some ways yes, but mostly it's just the amount of paperwork!

My Dad was in the RAF so I was brought up around aeroplanes. When we lived at RAF Valley my bedroom window looked out across the lake to the end of the main runway.

Dad took me to the maintenance hanger one day where they were stripping down a Folland Gnat (same aircraft used by the Red Arrows at the time). When I asked the Engineering Officer how often they had to do this he said something along the lines of "in this case about twice in a fortnight. We log every component that comes off to make sure it all goes back in. Unfortunately in this case we are missing a tiny bolt so the entire cockpit has to come out until we find it". Oops

The Gnat was a tiny aeroplane!

Another day Dad came back one lunch time and told me and my pal to come with him in the car down to the Station although he didn't say why. He drove up to the Control tower and we all go out and went upstairs while he had a word with the Senior Controller. We then went back down and walked out across the grass at the front of the tower towards the runway. Something really out of the ordinary. We walked right up to the runway edge under strict instruction from Dad not to step onto the tarmac where he told us to wait and look out to the right where we could just see a landing light shining in the sky. It got bigger and bigger until finally one of these came into sight, did a touch down, applied full power and went straight back up again.

We were standing pretty much as close as the grass in the picture. The noise was so loud you couldn't actually hear it any more. You just felt it.

However my favourite was and still is the Lightning which is arguably the greatest jet interceptor ever built. Seeing these take off on a summer night from my bedroom window with full reheat shock cones was just amazing.

 

 

[BiTurbo228]

@Escadrille Ecosse Yeah that sounds like a good place to grow up! The sound of a fighter-jet engine at full chat is something else. Sort of like really angry ripping silk.

Missing bolts mean big problems in aviation maintenance! Partially because planes tend to be designed so much for weight that each bolt is crucial, but mainly because a stray bolt amongst all sorts of mechanical linkages and delicate electronics could be disastrous!

2600/PE166 stuff

Well, I've been doing a little more research on the 2600. First off I've been looking at some engineering practices around low rod ratios and gudgeon pin diameters to try and find out whether there's an accepted minimum pin diameter for short rod/long stroke engines. I've found a couple of other short-rod engines that aren't regarded as being junk, and compared bits and pieces.

All of these engines have as long or longer strokes than the Rover and higher redlines (aside from the 2.5 PI) so should have higher mean piston speeds, although none have as few main bearings compared to cylinders as the two trumph-designed engines. Interestingly, all of these low-ratio motors seem to be late developments of engines designed for smaller capacities that have had the stroke increased to try and eke a little more displacement from them (the Rover was initially designed as a 2300).

The standard rover engine stacks up pretty well in terms of having a meaty gudgeon pin compared to the others. Both the S54 and Honda B20 are quite low, which looks to me like a drive to use smaller pins to reduce reciprocating weight for high revving engines. The M54 is an interesting comparison as that has quite a small pin for its stroke and rod ratio, but it also has a really low compression height on the piston (28.32mm), which suggests they were really pushing the limits of the engine to try and get 3.0l out of it (similar to Triumph and the 2.5l 6!). That probably necessitated a smaller than ideal pin diameter.

Still, that's useful as a potential minimum, which is lucky as using the NA O-Series pistons with a 21mm pin is about the same. A 21mm pin is used a lot in various engines so a good selection available, and it's a minimal amount of boring on the O-Series pistons (20.683mm pin). Using the stock pin would still have a 32 in the comparison which is better than the B20 and S54, so if the O-Series pistons and pins (or another suitable pin) are of high quality then it should still be good.

Ideally, you'd want the O-Series turbo pistons, but it looks like the NA ones would still work.

Chat with the racer

Also, I managed to get in touch with the chap who had the Group 2 SD1 2600 on the previus page. He seemed quite chuffed to share some information!

Power-wise, it had a 6-2-1, triple Webers on a custom manifold, electronic contactless ignition and a standard camshaft reground to a similar spec to an Austin Healey 3000 race cam. If it's the same as the works AH race cam then that's around 300deg duration and similar valve lift to the stock Rover one (0.454" vs 0.444"). That made 192ps on a rolling road, which is really not that bad at all! If there wasn't any head work done then that's really rather good (M20B25s can just about get a streetable 185bhp with similar modifications). Just knowing there's enough metal on the standard cams to regrind them a bit wilder is useful!

[Escadrille Ecosse]

Well, well, well. Very interesting!

[BiTurbo228]

Very little to report on the Spitfire front I'm afraid as it's been full steam ahead on the Jag, but I have done a thorough measure of the Rover 2600 engine to try and capture the dimensions a bit better. Here's what I've come up with:

I'll do something similar for the Triumph OHV as well seeing as I know have two knocking around, one in the Spitfire and the other in the 2000. Can't seem to find a decent technical drawing of those to work around though so if anyone's got one (or knows of one in a manual that can be scanned) that would be brilliant!

[Nick Jones]

This any use?

[BiTurbo228]

I'll have to dust off my 3d drawing skills (or lack thereof), but I'll see what I can do

[Escadrille Ecosse]

Excellent drawing there. Deserve a medal for Services to Sideways.

Got any @Nick Jones?

[Nick Jones]

I've given him the winners cup....... does that count? 

[Escadrille Ecosse]

[BiTurbo228]

Haha thanks guys 

[BiTurbo228]

No luck on the engine measurement front as yet, but I have been doing some more research on the Rover 2600 and come up with another cunning plan between the 2000 and the Spitfire for once the Jag's done.

First off the 2600 research part 1. I managed to pick up a dead head for not a great deal of money.

From a cursory glance I can tell that the inlet ports are indeed very nicely shaped, if a little on the small side at 31.5mm diameter (although that's good for velocity):

There is, however, significant improvement that could be made on the exhaust port.

The guide boss is unnecessarily substantial and cuts down the port diameter to a real half-moon shape as it goes past the guide. There's plenty of metal above the port to support the guide so (at least to my untrained eye) it seems completely superfluous.

The short-side radius might be difficult to improve much as it's quite a sharp angle and there isn't much metal supporting the seat right at the shortest bit. Would be wary of cracking there. You might be able to make a higher/less angled port by building the floor up a bit, but that's more advanced than I want to tackle just yet.

I've also got a set of new inlet and exhaust valves, and a spark plug out of one of the other engines so I could cc the chambers:

Interesting that the inlet valve pokes down slightly into the chamber. The chamber itself is pretty much bang on 29cc. If the headgasket gets compressed to 1mm then that should add another 5.15cc, which would make the dish in the piston 12.64cc to get the 9.25:1 compression ratio they're supposed to have.

I'd previously mentioned that O-Series Turbo pistons might be a good fit for a bigbore version (same piston pin diameter, bore is pretty much what the factory manual recommends boring out the 2600 to when fitting repair cylinder liners, pin height is 0.15mm lower than the 2600 pistons so there should be ever-so-slight poke out of the top of the block, and they have a decent sized dish). I've actually managed to snag two O-Turbo short blocks, although not measured the piston dish yet. However, I have calculated a size for the dish based on the )-Series NA pistons I have measured and they come to 12.09cc,

With the slightly bigger gasket area and the 0.15mm poke, using the 84.5mm O-Turbo pistons should give an engine of 2823cc and 10.26:1 compression. Pretty much perfect! The compression ratio will be dropped a little by cutouts for the valves, but this combo might stand a chance of working.

Nothing like modifying an already rare engine with parts that are like rocking horse poo!

I've also measured the narrowest points on the head between the existing bore and the coolant galleries. They vary around a bit, but provided the block walls are about where the head walls are then you should be able to fit an 86mm piston in there. 

I did manage to find an option for fitting Rover T16 pistons using Datsun L24 rods and a 0.5mm offset-ground crank. You can get T16 pistons all the way up to 86mm diameter. If you can get to an 86mm bore, with an 85mm stroke that would just about nudge you into 3.0l territory at 2962cc.

Whether you can get a big enough valve and port in place to let that breathe I have no idea, but it has potential!

[RedRooster]

and i thought i was on the spectrum...

[Escadrille Ecosse]

1 hour ago, BiTurbo228 said:

I did manage to find an option for fitting Rover T16 pistons using Datsun L24 rods and a 0.5mm offset-ground crank. You can get T16 pistons all the way up to 86mm diameter. If you can get to an 86mm bore, with an 85mm stroke that would just about nudge you into 3.0l territory at 2962cc.

blimey!

[BiTurbo228]

3 hours ago, RedRooster said:

and i thought i was on the spectrum...

Haha I'm convinced all the best people are to some degree  

2 hours ago, Escadrille Ecosse said:

blimey!

Yeah it's nice to have an engine that's not stretched to the ragged edge in standard form! I'm quite interested to see what it will do in standard 2600 form with DIY head porting, injection and a better cam. Then I can start building another to a bit wilder spec

[Nick Jones]

16 hours ago, RedRooster said:

and i thought i was on the spectrum...

Comes with the territory. Some cases are more advanced than others…..

What car are you thinking of putting this in Simon?

There is at least one BL Mk2 saloon prototype in existence and in running order. Dave Pearson at Canleys owns it. Has a bonnet bulge iirc.

[Nick Jones]

1 hour ago, Nick Jones said:

Comes with the territory. Some cases are more advanced than others…..

Have to say, as regards research skills, effort expended and sheer attention to detail, this definitely merits special recognition! 

[BiTurbo228]

Haha thanks Nick! There's plenty more to come in terms of anal attention to detail 

I think these engines would have gone brilliantly in a 2000. It's a shame they didn't do what Jag did with the AJ6 in releasing it early in the XJS which (at the time) was thought to be approaching the end of its production run. That way they could sort out the teething problems in a car whose reputation isn't going to be forged in the first few years of production. Although from what I gather the 2600 wasn't too bad, only really being let down by poor maintenance causing oil flow issues with the head. The police rather liked them and they did galactic mileages.

Plus, it would have made a hell of a car in the big Triumph.

I've come up with a cunning plan regards engine swaps...

So, I've got a T2000 with a 2500S engine in that's running but the car needs work.

I've got a Spit6 with a 2.5PI engine that's had lots of work but needs all sorts of things fabricating to get it to run.

I've got 2x Rover/Triumph 2600 engines, one of which is seized.

I've got 2x Jaguar AJ6 4.0l engines, one of which has blown a headgasket.

Previously, the plan was fit the 2.5PI engine into the T2000 so I can bed it in while I finish the Spit6, sell the 2500S engine, swap the Jaguar AJ6 into the big Triumph, and then develop one of the Rover engines to go in the Spit6 sometime after it's been running on the 2.5PI.

1. 2.5PI->T2000
2. Finish Spit6 bodyshell
3. AJ6->T2000
4. 2.5PI->Spit6
5. Drive around for a bit
6. 2600->Spit6

However, I've come up with a plan that will get things going a bit sooner.

1. Cut short development on the 2.5PI and sell it to bankroll other bits of the process
2. 2500S->Spit6
3. Finish Spit6 bodyshell, now that's driveable sooner as it's already got a running engine
4. AJ6->T2000
5. 2600->Spit6

It'll mean I've put a lot of money into making a hot 2.5 OHC engine that I won't get to use, but I will get to use the Spitfire sooner and it's probably the most valuable engine I have so could be sold on for the most amount of money, which helps the other things progress faster too.

It also breaks the most new ground soonest, which I've found to be one of the main motivators for my car projects. I just like the idea of doing something that no-one's done before (but is also good and keeps things 'in the family' so to speak)!

So that's the plan  for now at least

Edited October 2, 2021 by BiTurbo228

[Escadrille Ecosse]

A plan so cunning you could pin a tail on it and call it a fox...

I am like Nick enormously impressed at the level of detail and research gone into all that - quite aside from the cunning plan.