Quote:
Originally Posted by Allch Chcar
This has merit as it is done on Diesels and Direct Injection Gasoline engnes and is not done for power necessarily. It's a little bit beyond my scope of understanding but it seems like the idea isn't to increase manifold pressure past 30HG but to get almost barometric air pressure and essentially is just to decrease pumping losses. It should mean you can run higher loads than you normally would but the octane requirements would probably go up. This would work under cruise if you changed your gearing to be taller and should still be good for MPG until you start getting positive manifold pressure. But really this is a very advanced topic and I'm not so sure it can be done DIY without a lot of turbo knowledge and also the tuning of the engine for such conditions that it doesn't run pig rich into boost land.
A small enough turbo can start generating some pressure below 1500RPM but even Factory built turbo cars don't usually generate "positive" air pressure until at least 1500-2000rpm and they're usually designed to be pretty small and quick. The Ford Taurus SHO is advertised as having full torque from 1500RPM and the Cobalt SS when it switched to turbo from the supercharger was getting full torque at 2000rpm. The Ford Taurus uses a pair of GT1548(I think the last two numbers are correct). It's essentially the Turbo of choice for a low output single turbo Geo Metro sized engine like a 1.0l or 1.3l, but runs out of efficiency past 12lbs of "Boost" and bigger engines. If you use one in a bigger 4 cylinder like a 1.6L it'll work for what you're proposing but no one in the "Tuning" community will take you seriously  . A small enough turbo could do the scavenging job that you're talking about. But it's a serious undertaking. |
hi - thanks for the input there is a lot of good advice there.
i appreciate it would be quite a tuning undertaking.........would be a good exercise to learn from which I might try........need to secure a budget first though and of course time!
I see what you are saying about the technique to reduce pumping losses at cruise. It would be tricky and time consuming to tune.
In terms of the cam profile idea the aim is simply to prevent fuel going down the exhaust unless it is a result of incomplete combustion. As long as I could get it to idle and rev ok I would be happly. If the cam profile is used then I was thinking of having the turbo there to help control the airflow as required to compensate.