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.

weber dcoe sp carbs as fitted to the lotus esprit turbo

or use the su as a sucker

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

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.

cheers chaps!

ed.

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.

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.

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.

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]

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.