I don't claim to be an expert on forced induction, but I'll do my best
here.
My guess is that a blow through is the most fuel efficient, but probably
trades that for all out power. The reason being that the same volume of
air is passing through the carb (albeit preassurized); whereas with a
draw-through there is more air passing through the carb so more fuel will
be drawn. A higher volume of air will be passing on the intake side of the
turbo, while higher preassure air will be on the output side. Those
preassure numbers sound about right for mild factory turbo cars. In the
US one of the most popular turbos to use for projects such as this is the
stock GM turbo on thier 2.8L( I think) motors. One application that comes
to mind is on the GM minivans of the 80's and early 90's. The reason for
its popularity is partially because of the volume of them made, and the
ease of location in junk yards. Also they are a fairly mild turbo designed
for a fairly modest engine.
The rev range you are discussing does not lend itself well to turbos
however, turbos normally start to kick in at 3-4k RPM. The size of the
turbo, and thus the spoolup time etc is directly related to its size, so
the smaller the turbo the faster it spools up, but it will still take a
few krpm. The numbers you discuss are more akin to superchargers.
One method I have read about, but not tried, for simple supercharging is
very interesting. It is also simple to do. Basically find an air pump
from a large american V8 and use it to supercharge a small 4-cyl via a
preassurized airbox. It appears that this makes about 3-4# of boost,
and since it is supercharged it will make that at much lower rpm. I'd
send info but I don't remember where I read it.
--
James Nazarian Jr
71 MGB roadster
71 MGBGT-V8 in need of paint
01 Impreza 2.5RS
A complex system that does not work is invariably found to have
evolved from a simpler system that worked just fine.
On Tue, Jul 17, 2001 at 03:15:43PM -0500, S & M Barnes profoundly declared:
> Mayan I throw in a small additional question to try and acquire some of the
> vast spread of knowledge here?
>
> If I should happen to be considering adding a little power to a 1967 B
> engine and had decided a turbo may be the easiest way (also possibly the
> best $ to BHP ratio), without compromising drivability or reliability too
> much, what would your opinions be on these options?
>
> 1. Use a blow-through system using a sealed SU from a Maestro Turbo suitably
> re-jetted.
> 2. Use a draw-through system using a single 1 3/4" SU.
> 3. Use two small draw-through turbos using the existing twin 1 1/2" SUs.
>
> Assume I could make all necessary manifolds, adaptor plates etc. What size
> turbos would I need to give a reasonably smooth increase in power through
> the normal driving rev range - say, boost starting to come on at 1200rpm,
> max boost at 3000rpm or so? I have been told that I could use 5psi boost on
> a high compression engine safely and 6-7psi on a low compression without
> altering them - do you agree?
>
> Just for academic interest of course! :-)
>
> MikeB
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