1300 twin carbs

[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.

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.

I am well aware that it was engineering tolerances that were the main issue with the Sprint engine, I didn't say that it was specifically down to the carburettors being set up badly (although I am certain that would have probably been a factor too), it was merely an indication of the standards of BLs engineering generally. Your opinions of BL are obviously quite different to mine, so let's leave it at that.

[Jod Clark]

If you're solely after better fuel economy the first step would be to increase the pitifully low compression ratio of the 1300. Some / many / not necessarily all OHV engines have the same head casting for both the 1300 and 1500 variants and the only difference is the height - thickness if you like - of the head and the only difference is the amount of skim at the face. Valve sizes differ over the years of course, so try to find one with larger valves as these will improve your pumping efficiency. Have the head skimmed heavily when you send it off for hardened valve exhaust valve seat inserts. While the head is off, reach in and withdraw the cam followers. If you find one that's concave and pitted then your camshaft is screwed too so change it and the followers if there's any doubt whatsoever. I'll bet you find at least one pitted follower and a matching cam lobe that looks like its for the fuel pump instead of a valve. Time / money spent here will save ages and ages of fruitless messing about later on.

If you really want the very best efficiency you can possibly achieve with standard parts, then the 1500 exhaust manifold has to be used. This will necessitate the use of twin carbs. The only way I found to make the 1500 manifold seal reliably is to install short stub pipes into the downpipe that 'socket' the downpipe, gasket and manifold together. You will need to do this with the manifold and downpipe off the car. Then replace the silly little studs and nuts with something bigger and stronger. I think I used OHV big end bolts and spring washers for this. The standard stainless studs and brass nuts make it easier to change the gasket of course, but the gasket usually only needs changing because the standard hardware doesn't hold everything in place well enough. Don't miss out the bracket that holds the cold end of the front pipe to the gearbox. Ideally make this yourself with a degree of adjustability so you can hold the front pipe in the position is which it naturally falls, if you try to force it into a position it doesn't want to be in then it will break at the gasket joint every time.

Consider finding a 3.89:1 ratio differential. The 1300 will pull it easily and will reduce the frantic revving at cruising speed without making it unable to climb hills. 3.63:1 may suit too, depending on your application / intended use but 3.89 would be a good first stage. Diffs are interchangeable quite easily once you have done it a few times. An overdrive gearbox is both expensive and quite a lot heavier. A well-chosen final drive ratio is almost as good as an overdrive gearbox, without the weight penalty.

Keep the standard airbox. Use some free-flowing filters in it if you like but keep the standard airbox and its cold air feed tubes. Advance the timing as much as you can without causing pinking. Make sure both springs in the distributor are present, unstretched and that the weights move freely. Fit electronic ignition and a high-output coil of reputable make. Widen the plug gaps as much as you dare. Remove the engine driven fan and fit an electric one. It quietens the engine by a huge amount and only moves air (saps power) when actually needed. Use a 10W/40 synthetic oil if you have no oil consumption issues. The more modern oil will work just as well and will reduce internal drag significantly. If you're burning or leaking oil you need to repair / rebuild it, not use a thicker oil to try and hide it.

Use good quality tyres, correctly inflated. I won't discuss pressures here because that always ends up in a fight, but the factory recommended pressures are way too low for modern tyres in my opinion. Correctly inflated tyres can save up to 10% on fuel. Keep the vehicle as light as possible.

All carb needle profiles are a compromise and setting mixture at idle is stupid. Read John Tilson's SU carb tuning guide and get each carb set exactly the same for airflow, synchronisation and jet height. Use fixed, not waxstat jets and plain butterflies. Adjust mixture by driving, adjusting, driving, adjusting, driving, adjusting until you're happy with the consumption : performance ratio. When it drives right it will likely be an MOT pass with no adjustment. Never let anyone else touch your carbs, least of all an MOT tester. If they need adjusting to meet emissions then adjust them yourself. If your friendly local garage will let you use their gas tester for basic setting-up even better.

Of course the greatest factor in economical motoring is the big nut behind the steering wheel....

I hope some of this is useful in your quest.
Jod

[cleverusername]

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.

I am well aware that it was engineering tolerances that were the main issue with the Sprint engine, I didn't say that it was specifically down to the carburettors being set up badly (although I am certain that would have probably been a factor too), it was merely an indication of the standards of BLs engineering generally. Your opinions of BL are obviously quite different to mine, so let's leave it at that.

My point is if the problem is down to problems with production tooling for things like blocks and castings. Owner bolting a different set of carbs or fiddling with the needles is unlikely to liberate more power.

[soe8m]

My point is if the problem is down to problems with production tooling for things like blocks and castings. Owner bolting a different set of carbs or fiddling with the needles is unlikely to liberate more power.

That is correct. On my friends dyno the average std sprint has around 105hp at the rearwheels. A very decent sprint 110. When I blueprint a sprint engine, using std cam, pistons, manifolds and carbs etc, no fan and a good exhaust it's around 135hp at the wheels and one had 139 max.

My daily 1850 on LPG had 110HP on LPG at the rearwheels.

Balancing, flowing, raise compression ratio and fit a good exhaust and time the cam exact will give a powerfull and free revving engine mostly only work involved and no exotic parts needed.

Jeroen

[tony g]

What compression would you use on a sprint engine running petrol Jeroen?

Tony

[Carledo]

Wasn't going to get involved in this one, but Jeroen is right. there is not that much wrong with the Sprint engine DESIGN. Blueprinting is basically eradicating the tolerances that poor production machining quality introduced. It makes the engine as good as it can be, but is (or was) too expensive for the factories of the time to implement.

Blueprinting also improves economy by increasing efficiency and longevity because the engine is no longer fighting itself.

So blueprint your motor, balance it and then do the other thing that guarantees extra go for very little money, shave as much weight as possible from rotating part and the car in general. Then sit back and enjoy the benefits.

We are all, I hope, far too old and cynical to be fooled by the "Carlos Fandango" school of tuning!

Steve

[GrahamFountain]

Surely, if you want twin SUs on any Triumph 1300 engine, the solution is to fit or convert to a Spitfire engine. That's what a PO did to my 13/60 Herald, along with the Spitfire overdrive gearbox. That goes rather well as a result.

Be a bit wary about quoted HP values for the late and early Spit IV engines. It seems that there's the change from SAE to DIN measurement to factor in. So the late IV head with bigger inlet valves should have more capacity for improving power, given appropriate improvements in the rest of the breathing.

There were some issues in re-using the Herald dizzy in that, but I don't know what the Dolomite 1300 uses.

Graham

[GlenM]

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.

I am well aware that it was engineering tolerances that were the main issue with the Sprint engine, I didn't say that it was specifically down to the carburettors being set up badly (although I am certain that would have probably been a factor too), it was merely an indication of the standards of BLs engineering generally. Your opinions of BL are obviously quite different to mine, so let's leave it at that.

My point is if the problem is down to problems with production tooling for things like blocks and castings. Owner bolting a different set of carbs or fiddling with the needles is unlikely to liberate more power.

I did say 'well rebuilt with some improved components'!! Jod is the expert on the OHV engines. That's me done on this one.

[TrustNo1]

why not fit a Turbonator vortex fan, extra BHP for little cost?

https://www.ebay.co.uk/itm/UNIVERSAL-RE ... SwUjpak4Hr

[GrahamFountain]

why not fit a Turbonator vortex fan, extra BHP for little cost?

https://www.ebay.co.uk/itm/UNIVERSAL-RE ... SwUjpak4Hr

That is humor, isn't it?

Graham

[Standardthread]

Thanks Jod and everyone.

I think we're on the same wavelength Jod, I'm basically after efficiency not increased power. I tend to drive with a light foot anyway. I agree with your thoughts on exhaust flanges, they are basically crap, and I will follow your advice about an internal pipe to protect the gasket, I've already fitted bigger SS studs etc. I have a Gunson gas analyser if I have issues, my Herald was way below maximum emission values the last time it was tested, the tester got a shock. To resolve the issue of exhaust gaskets blowing on my 13/60 Herald (MkIV Spitfire block, D type overdrive etc.etc.) I got a 1500 SS Spitfire manifold, yet to fit to the Herald, and thought of fitting it to the Dolomite instead but was told it wouldn't fit so I won't even try. I do have a couple of spare D type overdrives (one brand new) and half a dozen 3 rail gearboxes spare so that may also happen in the future.

Thanks again everyone.

Steve