ed_crouch
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| posted on 29/10/03 at 08:57 AM |
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carbs for turbo application
Does anyone know what is involved to convert an SU (say) carb to run as a blown carb with a turbo??
OR, are there any carbs out there that will run pressurised??
Thanks
Ed.
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timf
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| posted on 29/10/03 at 09:05 AM |
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weber dcoe sp carbs as fitted to the lotus esprit turbo
or use the su as a sucker
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Simon
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| posted on 29/10/03 at 09:57 AM |
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Ed,
IIRC the SU used on the Metro turbo didn't appear any different to a normal SU except that the dashpot lit had a clamp around it.
An alternative is to have the carb mounted inside a small airbox and pressurize that.
Also IIRC Steve Gusterson (on here) had a Metro Turbo so may remember/know a bit more than me.
ATB
Simon
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Noodle
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| posted on 29/10/03 at 10:18 AM |
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The MG Metro Turbo used a blow-through 1.75" SU. To make the blow through carb boost sensitive, run a line of boost pressure from the
pressurised plenum to the float chamber.
"By having some sort of restriction at the carb mouth, the air pressure in the float bowl increases faster than the air pressure in the carb
barrel. This will cause a greater pressure differential across the main jet and as a result, more fuel will flow. Becuase of the limited restriction
to flow offered by the carb ring (or whatever else is use) at low rpm little fuel enrichment will occur, even if boost pressures are relatively high.
This restriction technique for boost oriented enrichment works best in the higher rpm ranges. The greater the restriction in the carb mouth, the
greater the density oriented enrichment achieved" David Vizard
The Turbo Esprit used a blow-through Dellorto that waas also used on Janspeeds contemporary Metro Turbo installation back in 198x. That ran around
14psi.
There are issues with carbs too such as the spindles have to be sealed as normally, the suck from the engine draws mixture in and they prefer vacuums,
not boost.
Or, in English, just use a Metro Turbo setup! 
Cheers,
Neil.
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ed_crouch
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| posted on 29/10/03 at 11:58 AM |
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cheers chaps!
ed.
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Peteff
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| posted on 29/10/03 at 07:17 PM |
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Turbos suck through the carb using exhaust gas speed to run the turbo fan. A blown setup is a supercharger which is usually belt driven from the
crank. Turbo is usually associated with some lag problems caused by the turbo spinning up to speed whereas the supercharger is instant power. Also
turbos create a lot of heat and are more efficient if used with an intercooler.
yours, Pete.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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The Shootist
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 posted on 29/10/03 at 10:20 PM |
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Box the whole carb..
Here in the US Paxton Superchargers markets a kit with a box the encloses the whole carb, thereby fixing the problem with leaky shaft seals, and
applying pressure to the float bowl.
If you higher pressure fuel pump, with the regulator mounted inside the carb box, the fuel pressure will modulate up and down with boost pressure and
the carb will never even know it is turboed.
If you do pressurize the carb, an intercooler is advised. Of couse with all this trouble, a motor with factory turbo may be the way to go.
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Stu16v
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| posted on 31/10/03 at 06:16 PM |
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Peteff, not strictly correct mate. A blow through or suck through system depends on which side of the carb the turbo is mounted-hence blow or suck.
'Blower' is a common expression used to describe superchargers, but they to can be mounted either side of the carb.
With a blow through system you need to be careful that the float will withstand the pressure that it may be subjected too. Too much pressure and it
will collapse if it isnt designed to do the job.
Dont just build it.....make it!
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Peteff
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| posted on 31/10/03 at 08:37 PM |
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The MG one sucks (big time)
The carburettor can be mounted in two positions on a turbo-charged engine, and a great deal of controversy exists as to which is better. The
carburettor can me mounted such that it feeds air into the turbo then the turbo feeds it to the engine. This is known as a Draw-Through system.Under
these conditions the carburettor operates more or less as it would on a naturally asperated engine. Another school of thought says that the
carburettor should be mounted between the turbocharger and the intake manifold. This means that the turbocharger draws fresh air and pumps it into the
carburettor, which then feeds the fuel/air mixture to the engine. The claimed advantages of this method are that the turbocharger is always operating
with its intake at atmospheric pressure for quicker response. The principle snag with the blow-through system is that the carburettor calibration
becomes difficult. The carburettor is a velocity-sensitive device; it does not know about pressure changes. This means that although the engine may
receive vastly increased quantities of air, the fuels supplied to the engine may not go up in proportion. The result is that the engine runs weak and
is in danger of detonating and melting pistons, unless some often itricate and complex carburettor modifications are made.
The carb needs to be in a pressure box and fuel supplied at a pressure higher than turbo boost.
I don't actually know of any blown turbo applications but I am happy to learn. found this on a Datsun 1200 website.
The turbo is directly after the carb. They do mention a Dellorto sidedraught being developed especially for this application, sounds very
expensive.
yours, Pete.
[Edited on 31/10/03 by Peteff]
[Edited on 31/10/03 by Peteff]
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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Peteff
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| posted on 31/10/03 at 09:13 PM |
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http://datsun1200.com/modules/nsections/index.php?op=viewarticle&artid=35
Here's the site for you to read through. Sounds interesting if you like that kind of stuff. I don't see them as locost though, sounds like
one for the Yahoo theory group .
yours, Pete.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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