Single carb or more ?

[blubayou]

I ran a single 1 3/4" on a modified log manifold for a few hundred miles on a Mk1V Spitfire.

This was on a small crank 1300 with Mk3 cam.

Worked fine but could have done with fine tuning.

Unfortunately it did not fit with the  factory cast 4-2-1 manifold I was using, so had to refit the stock MK1V manifold.

As a result I found no advantage over the stock setup.

 

[mpbarrett]

Re: Twin Carbs interesting articles in Triumph World on the Sabrina twin cam TRS engine.
Very interesting SU carbs on it, not seen SU like that. Are they 2 SU's joined together maybe with one float chamber I suppose it means you have one carb per cylinder?
mike

[Colin Lindsay]

I found this recently, elsewhere - someone has lost a pair!

That engine is impressive, nearly as much as the original 'Sabrina' too....  

 

 

 

[Nick Jones]

Those double SUs are rare for a reason. They weren’t nearly as good as their competitors - Weber and Dellorto. Look good though.

Nick

[mpbarrett]

so are they basically two separate carbs put together with a two separate but linked butterfly's and common float chamber? 
Never seen them before they do look very cool

mike

[AndyTV8]

DU6’s were also used on some Jaguars and (I think) a Coventry Climax variant.... they were either on or off and didn’t prove very popular. They do look nice though

........ Andy 

[Guest]

IIRC, SU DU carbs are the only twin choke carb made by SU - as Nick points out, light years out of touch compared to the Weber and Dellorto units.

Regards.

Richard. 

[Colin Lindsay]

On 19/11/2019 at 20:08, Casper said:

I think it was 39 to 49.  I don't know about the advert but the basic difference was the 'hot' cam as used on the 12/50 and the late Spit 4 and early Mk 2 in Nov 1964 with greater lift for better torque.  Note the 12/50 manifold only gave 3 bhp.

It was actually removing the mechanical engine fan and replacing it with an electric version - one of the first Herald / Triumph-related books I bought back in the early 1990s claimed that you could boost engine power, between 5 and 8hp and maybe even greater, by this simple mod; never tried it myself, but I'm wondering how much truth was in it?

[Pete Lewis]

removing any ancillary  improves output  there is some thoughts i have that at speed the ram of air helps offset it 

biggest change is no fan  less noise 

Pete 

[Guest]

Hello Colin,

It is certainly true the engine will recover some bhp by swapping from mechanical fan to electric, especially if the fan is metal. Not sure I would put it at 5-8, but certainly 3-4 may be more realistic. 

On some cars where the metal fan bolts to the water pump, it really does increase the water pumps longevity by not having that lump of metal hanging off it - this was certainly the case on Sunbeam Alpines which chewed through water pumps on a regular basis and likely to be the case with other classics of similar water pump set-up.

The Alpine fan is a 4x blade heavy metal affair and of significant weight, hence to good to replace it. 

Regards.

Richard.

[Clive]

9 hours ago, Colin Lindsay said:

It was actually removing the mechanical engine fan and replacing it with an electric version - one of the first Herald / Triumph-related books I bought back in the early 1990s claimed that you could boost engine power, between 5 and 8hp and maybe even greater, by this simple mod; never tried it myself, but I'm wondering how much truth was in it?

I think until the early 70's? a cars engine power was quoted without ANY ancillaries at all. So no water or fuel pump/fan/alternator etc etc. I suppose those functions were either calculated or externally supplied.

So when comparing the TR6, the early 150bhp model to later 125, the difference in reality is much less than the 25 BHP (probably 15?)

A fan may sap 5bhp. According to Davis Craig, the electric waterpump people (not to be confused with Craig Davies, the delightful artiste) a mechanical waterpump can sap a broadly similar amount. However, I doubt of a 40bhp engine you will be loosing 10bhp from those alone, it must have a relationship to the power output (fan and pump size?)

A decent electric fan will consume maybe 150watts. That is about 1/5 or 1 bhp. Allowing for losses in generation  it will not sap more than 1/3 bhp. So a big saving on a small engine at speed. (and at speed you really do not need a fan at all, but then again mechanical fans have an advantage in working constantly which can suit some cars, especially GT6's it seems)

Another source of power sapping is an overdrive. I think the J type is the most efficient, but D and A types less so (certainly when OD is out)? Which is why racers tend to shy away from overdrives. 

But in reality, the biggest factor in economy is driving style. And all the talk of power is irrelevant to 95% of owners, who rarely if ever use prolonged full throttle. I reckon 90% of driving is done at under 20% throttle opening when driving on the road. (I can get readings of my throttle opening on my car, and if I were clever could log it over a journey, but my observations are from driving with the wife mapping the car fuelling on a long journey)

Colin, try driving the car with the fan removed. And to test if there is a difference you will need to do some sort of timed run, maybe 1/4 mile or suchlike? Power gain will be mostly at higher rpm. And best to avoid roads likely to have traffic jams, but when the electric fan seized (it was over 25 years old, off an old golf)on my spitfire, I completed a long european trip with no overheating. I got good at heat management on motorways when i could see a jam looming, but never overheated. Spal fan now fitted, a thing of beauty!)

[Anglefire]

My previous car, a BMW 530D M sport, had a "Sport" display as one of the many toys and it showed a dial of both torque and power - occasionally I looked at it and it was surprising how little around either dial either went in normal driving - yes I could get the power around to dial to 250+ bhp but it was very short lived and was a proper holigan! driving at 70mph and it was 50 or 60 bhp from memory. 

[Bfg]

Interesting conversation, cheers..

The tropical fan on my TR4 engine (x6 short aluminium blades on a steel hub) weighs approximately 0.9kg.  And the whole pulley + fan extension + centre bolt + this fan weighs in around about 3kg.  To rotationally accelerate that mass certainly takes some force,  but it would be relatively little compared to the 11kg of flywheel + the 4kg of diaphragm clutch ..especial as unlike those items ; the mass of the fan + extension assembly is very close to its rotationally axis.  

Once a constant RPM is achieved, anything above 40mph, then as Pete Lewis says  "at speed the ram of air helps offset it"  and Clive experienced with his Spitfire, the cooling effect of the fan is minimal compared to the vehicle's through flow of air.  Then the fan blade's chord angle / angle of attack presents, at best, a deflecting sweep across that airflow ..so the energy used to maintain its rotation would be very small indeed. 

Conversely, I would think the tension on the fan belt, with its  2" lever arm (radius of the pulley) from the crank, which pulls the dynamo and water pump around, would have absorbed much greater power both to accelerate and at that constant speed.  Of course (re)charging a battery which monitors cooling needs and drives an electric fan is not free  energy.

Then at high vehicle speeds, combined with tall gearing ; the through airflow would try to turn the mechanical fan ..so although highly inefficient - that force would be conveyed to help turn the crankshaft !  

Pete

[Mjit]

On 19/11/2019 at 09:37, Bfg said:

Sounds interesting - would you happen to have any photos of (the TriumphTune cross-over manufold) ?

 

Still available - https://www.moss-europe.co.uk/manifold-inlet-cross-over-tt10549.html

[PeteH]

Intrigued by this?.

My understanding and experience with (Just) using larger Carbs, is that it is mostly a waste of time and effort Unless you make the whole intake system compatible?. This may take the form of Simply gas flowing the manifolds, Or indeed "improving" the complete induction/Exhaust system. Just upping the size of the Carb, will only likely increase fuel consumption and because of the poor conditions increase the proportion of UN-burnt gasses in the exhaust system.

Surely the better way is to make the gas flow more efficient throughout the cycle?. If necessary by altering the valve timing / Opening periods, larger valves, where conditions permit etc:. AND a more efficient Exhaust manifold system?. The object should be to get the most efficient "Burn" to release the power in the fuel, and to clear the used gasses as quickly as possible ready for the next cycle?.

Pete