1300 twin carbs

[Standardthread]

This may have been answered before, if so, sorry.

I was recently told that BL produced a very small number of 1300SE's with twin carbs, does anyone have any information on this please?

I presume that if they did exist then they would have followed in the same line as the MkIV Spitfires which were fitted with twin HS2's.

My main reason for this information is that I have a pair of HS2's plus manifold ready to fit, but, if 1300SE's existed does anyone know if the needles fitted were the same as the Spit (AAN's) or were different needles fitted, if so which?

Thanks in anticipation.

[triumphdolomiteuk]

Close but no cigar. Triumph produced the Triumph 1300TC (front wheel drive) in reasonably large quantities, which had twin SU HS2 carbs, similar to the Spitfire mk3. The 1300SE which you refer to was actually a prototype Dolomite (rear wheel drive), of which we believe only three were made.

[TrustNo1]

The 1300TC, which as Andy said if the earlier front wheel drive did have HS2's but also had the bigger valved head.
Fitting twin SU's to a Dolomite 1300 won't give you any benefit if you're not going to change anything else. infact the single SU is a lot easier to set up and get running correctly

[Standardthread]

Thanks for the help and guidance.

To a large extent I’m trying to work with what I have and recreate the ‘silk purse’ and take my car back closer to ‘as built’ and designed, and away from the pigs ear the previous owner attempted to create.

I realise there are further steps to putting everything ‘in balance’. So far I have replaced the large bore SS exhaust (still for sale and open to offers – see my advert) with a complete 1500 version. The previous owner had changed the front pipe to a 1500, plus manifold etc. as well as using a pair of HS4’s from, I suspect, an 1850. So I have no single carb or exhaust manifold to fall back on, hence my choice of MkIV Spitfire HS2’s. The engine was over vented, probably virtually no back pressure for the engine/exhaust combination, and certainly too large a carb combination. That prompted my request for needle detail for the HS2’s I have (again their previous owner used the wrong needles).

The engine is now running better after the exhaust change, better still hopefully when I changed the carbs.

The next job, if I have to take the head off, is hardened seats, and air flowing the inlet and exhaust ports, done that on my Herald with great success.

At the end of the day I want the car to be economical on petrol etc. with no intention of me trying to get more power out of it.

Steve

[TrustNo1]

So back to the needles... I don't know of the top of my head. if you look up Burlen Carbs in Salisbury they were originally 'The SU carb Co' they should be able to advise you what needles go with what airfilter/ engine combo.

[GlenM]

It depends if you have the fixed, or biased (fitted with a spring at the top like the HS4s) needles in your HS2s. With a better exhaust manifold and air filters the fixed needles should be H6 and the biased ones AAU, or slightly leaner settings would be AN and AAT respectively.

If you are planning headwork as well it would probably be worth going with HS4s.

[GlenM]

It depends if you have the fixed, or biased (fitted with a spring at the top like the HS4s) needles in your HS2s. With a better exhaust manifold and air filters the fixed needles should be H6 and the biased ones AAU, or slightly leaner settings would be AN and AAT respectively.

If you are planning headwork as well it would probably worth going with HS4s.

[cleverusername]

Owners who think they know better than the company who built the car and don't understand that a bigger carb is not necessarily better. I suspect if you put most tuned cars on a rolling road, you would find that they make more noise and less power than a standard car.

Have you looked for a single carb manifold? I can't imagine they are too much money and I think twin carbs are more trouble than they are worth.

[TrustNo1]

Owners who think they know better than the company who built the car Have you looked for a single carb manifold? I can't imagine they are too much money and I think twin carbs are more trouble than they are worth.

Hence my comment 'Fitting twin SU's to a Dolomite 1300 won't give you any benefit if you're not going to change anything else. in fact the single SU is a lot easier to set up and get running correctly'
But as for owners thinking they know better sometimes that can be true as standard factory cars were about selling to the public masses and having a car that was cheap to run and maintain.

[cliftyhanger]

If you have the 1500 type exhaust manifold, it simply won't fit with a single carb inlet. I tried, a lot, and failed despite spending an afternoon butchering the inlet.
The downside of the "better"| exhaust manifold is that the downpipe gaskets have a nasty habit of blowing. This can be sorted, but involves getting the 2 mating faces flat with a file, and I ended up using M10 cap head setscrews (though I admit 3/8unc would have been better, but I didn't have a unc tap...)

The trouble with mods is that just "playing" at it is hopeless. It needs to be fully though out. So bigger carbs would help IF accompanied by a better cam, bigger valves and a bit of porting, higher CR, distributor matched and finally the needles selected using a rolling road or wideband sensor.

All that should get an economical car with about 75bhp. Better torque curve on the HS2 carbs over the HS4's.

Otherwise head for standard stuff. So on yours check the CR as it may well be lower than the mkIV spit. And be aware with the spit they did change cams, the early mkIV had the same profile as the mk3, probably the "best" cam for the engine. All a bit of a minefield...

Incidentally, John Thomason did some proper research on his absolutely standard 1500 spitfire. He experimented with using a single HS4 on a dolly 1300 manifold (he did have a 4 branch, about the only mod on the car) and set both twin and single SU up on the same rolling road, same day etc. in practical tests, with huge mileages covered, he fond the difference between the 2 setups was negligible. Twins a tiny bit more power, the single a tiny bit more economical. He was surprised at how small the difference was.

[Standardthread]

Thanks everyone, I'm a bit clearer as to a course now. As I said previously, I'm trying to correct mistakes made by the previous owner who tried to make the car something it could never be, and without me throwing everything in the bin to start again, and spending a small fortune to have a usable car.

I had to draw file the manifold and front pipe on the Dolomite to get them flat (half a day gone) but I prefer the 1500 manifold to the triangular fit Herald 13/60 version (same as on the 1300 Dolomite I think) because over the decades I have found that to be the weak point in the exhaust and there is (to me) less potential for the exhaust to twist with a 1500 because of the greater mating area. I also fit twin Stromberg 125's on my Herald decades ago (and getting 40+ mpg from it) so setting up isn't really a problem, I intend to fit a 4 branch 1500 SS Spitfire manifold to on the Herald to overcome gasket failure. I've had to re-set the HS4's currently on the Dolomite, I think the previous owner just got it to start and run.

Thanks for the pointers on the needles, they are biased on the HS2's I have and currently fitted with ABT's (could be ABL, part of the last letter is missing) SU say if they are ABL they fit a TR7! The correct fit, according to SU for a MkIV are AAN but I wondered if there could be a difference for the few 1300 twin carb Dolomites built, hence the post.

Any head work will be as and when, it isn't a priority.

Thanks again.

[GlenM]

Owners who think they know better than the company who built the car and don't understand that a bigger carb is not necessarily better. I suspect if you put most tuned cars on a rolling road, you would find that they make more noise and less power than a standard car.

Have you looked for a single carb manifold? I can't imagine they are too much money and I think twin carbs are more trouble than they are worth.

I am sure that this is probably true with a lot of home tuned cars. However, BL were hardly good at setting the cars up properly themselves (look at the variation in Sprint engine outputs) and their choice of components would, nine times out of ten, have been to minimise cost rather than achieve performance or reliability. A classic from the 1960s, or 1970s, well re-built by an enthusiast with some improved components has the potential to be far superior to anything churned out by the manufacturer.

[GTS290N]

Jod is your 1300 tuning expert, maybe he'll catch sight of this thread, he doesn't visit here often these days.

[cleverusername]

Owners who think they know better than the company who built the car and don't understand that a bigger carb is not necessarily better. I suspect if you put most tuned cars on a rolling road, you would find that they make more noise and less power than a standard car.

Have you looked for a single carb manifold? I can't imagine they are too much money and I think twin carbs are more trouble than they are worth.

I am sure that this is probably true with a lot of home tuned cars. However, BL were hardly good at setting the cars up properly themselves (look at the variation in Sprint engine outputs) and their choice of components would, nine times out of ten, have been to minimise cost rather than achieve performance or reliability. A classic from the 1960s, or 1970s, well re-built by an enthusiast with some improved components has the potential to be far superior to anything churned out by the manufacturer.

As far I understand it the Sprint was suppose to be 135bhp but the output of production engines was downgraded because they couldn't achieve the tolerances to guarantee that output. I don't think it had anything to do with the fact Triumph couldn't set up twin carbs properly.

In fact I find it highly unlikely that a company with decades of experience would have struggled with something so basic. Also which parts bolted to a Sprint engine are cheap? SU carbs are SU carbs. OK it has cast manifolds but so do most production cars.

i am not saying that cars can't be tuned, I am saying I am doubtful of the results unless they are checked on a dyno. They did an experiment, I think it was with TR6s and they found the majority of tuned cars produced less power than a standard car.

[cliftyhanger]

Spot on.
The problem is the typified by the idea fitting a dolly 1300 with the twin SU's off a 1500 along with the exhaust manifold will give more power. That sort of thing is rife across the classic car community, and it is extremely rare for anybody to give any measured power figures.

My old vitesse was involve in a mag article about 22 years ago. 6 modified Triumphs on a rolling road. Mine was a pretty std 2.5 engine, and made 115bhp and loads or torque. Another 2.5, in a spitfire, had triple carbs (strombergs, not webers), a hot cam, stage 3 head, 6 branch manifold, all supplied/build by the puzzled specialist. 3bhp more, and a tad less torque than my car. The owner was fuming.... As would I be.

So indeed, NEVER believe "expected" bhp figures, and having used a few rolling roads, I an sceptical about their final numbers, as they are easy to rig (my one above was same rolling road, same day, so a fair comparison, plus they are ideal for setting up) A more useful comparison is a proper 1/4 mile time, you can't fudge that.