Guest Anonymous Posted November 28, 2001 Share Posted November 28, 2001 I've heard that SU's dont handle forced induction very well and was wondering if anyone here has had experience with a forced SU set up and could share their experience with me. I am looking at a cowl induction set up but dont want to waste my time if it will mess up my carbs. Seems to me that the higher air volume would just require tuning the carbs. Thanks All. Quote Link to comment Share on other sites More sharing options...
fl327 Posted November 28, 2001 Share Posted November 28, 2001 ive heard that a single su works pretty good, or a single four barrell, su's can do the do pretty good i think, just jetting Quote Link to comment Share on other sites More sharing options...
DCZ Posted November 28, 2001 Share Posted November 28, 2001 I'm far from an expert but here's my take on it: SU's work by creating a vacuum at the jet tube. As air is sucked through the carb, a low pressure area is formed in the venturi area of the carb - where the jet and needle are located. Fuel is pulled up past the needle by this low pressure (which is "low" relative to the air pressure at the float bowl vents). If you try to force air through the carb by creating a higher pressure than atmospheric in your air box then you reduce the pressure gradient that pulls the fuel. However, it seems there must be a way to overcome this, because there was a single SU turbo system that used to be sold for the 240z. It may be as simple as having your float bowl vents pressurized to the level of your forced air. Anyone have experience with the SU turbo system? Is the air injected before or after the needle/jet? Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted November 28, 2001 Share Posted November 28, 2001 Thanks, that makes sense but would presurizing the float bowls cause problems for example if you were going fast enough or had a weak enough fuel pump that air pressure was equal to the fuel pressure causing the floats to run dry. Not sure if this is a valid concern or not. Quote Link to comment Share on other sites More sharing options...
fl327 Posted November 28, 2001 Share Posted November 28, 2001 if the su system is hard to boost with, why not go with a four barrel holley or a 500cfm two barrell, youll love it. Quote Link to comment Share on other sites More sharing options...
Guest John Adkins Posted November 29, 2001 Share Posted November 29, 2001 I've seen a turbo system using a single SU but the it was a draw-through system; the carb wasn't pressurized. The turbo drew air and fuel through the carb.... quote: Originally posted by DCZ: [QB] However, it seems there must be a way to overcome this, because there was a single SU turbo system that used to be sold for the 240z. [QB] Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted November 29, 2001 Share Posted November 29, 2001 In Corky Bell's book he mentions the easiest blow-through carbs as being Mikuni's, then webers as they require the least amount of work. A holley will need nitryl floats and a mod to the throttle shaft bores so they get pressurized and don't try to spit gas out of the throttle shafts. Also it would need to be mechanical secondary unless you did like Macinnes did in his book and used boost to open the secondaries and a check valve to close them when you let off the gas. He also mentions a Autolite two barrel which might work ok for a L6 if it flows enough air but probably would need the above mentioned float and throttle shaft mods. You can do just the floats on Holleys and put the whole carb in an enclosure which gets pressurized, but it gets expensive fabricating everything and sealing everything in the box (linkage, fuel line etc). FWIW. Regards, Lone Quote Link to comment Share on other sites More sharing options...
Guest jens Posted November 29, 2001 Share Posted November 29, 2001 The mg montego and metro turbo used a 1.75" su with succes as a blow through setup. I have owned a 150 hp montego 2.0. It has a bit of lag but it works fine to 200-250 hp. As far as i remember it had a fuelregulator that raised the fuelpressure under boost. The float bowls ( i think its called that ) must be changed to one made in basalt wood in a weber or else the raised pressure would flatten the bowls. Rover v8 used 2 2" su carburetors. I would prefer a k-jetronic injection instead. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted November 29, 2001 Share Posted November 29, 2001 Yeah, another couple of cars that ran successful blow through systems was the Maserati Bi-Turbo (which had problems, but it wasn't due to its blow through turbo system), and one of the Lotus's. The floats as Jen said are a big concern, thats why they tend to use Nitryl in Holleys otherwise it'll squash the float. A rising rate fuel regulator also mentioned is needed to overcome the boost pressure in the float bowl. Regards, Lone Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.