Posted by Brian in Oregon on Sunday, February 11, 2001 at 10:10PM :
In Reply to: turbo charging posted by Kevin on Sunday, February 11, 2001 at 8:30PM :
I haven't seen this kit, but there have been some successful turbo conversions done on older engines.
One of the biggest drawbacks is the amount of boost. These engines were designed for low compression, and on many the rings will have bad blow by with too much boost. Even worse, the cranks typically are not fully supported. Meaning the flatheads sixes have five main bearings, not seven. This limits the amount of power that can be applied. Going further, the L-heads are prone to detonation and pre-ignition with higher compression rations, effectively accomplished with a turbo. Remember the 202/217/230 engines have offset rods. Increased loading on them can cause a spun bearing. This is why the 251 & 265 can take higher RPMs than the 230 family. I would venture to guess the 351 et al can utilize this boost better than a 230.
Having said all that, if boost is kept reasonable, a turbo can provide a reasonable increase in power.
The blow through refers to how the air is inducted into the engine. The air outlet on the turbo is merely hooked up to the carb inlet.
The other kind is a suck through. The carb is ahead of the turbo air inlet, and the air/fuel is sucked into the turbo, then to the manifold.
Drawbacks of the suck through are slow throttle response, sometimes very slow. On the other hand, install is utter simplicity.
The blow through works the best for throttle response. It's major problem is that most carbs are made to run under vacuum, not pressurization. This means it is possible to blow fuel all over the place from gaskets, orifices, etc. The ideal solutionis to place the entire carb in a sealed box, and pressurize the box. Fuel will not be blown out of the carb. Also, you need to set the fuel pressure to be 5 lbs over whatever the boost pressure is. You use a high pressure fuel pump and a fuel regulator. The vent on the regulator is tapped so a fitting can take a hose, which you run to the air box. This tricks the vent into thinking the boosted air is normal atmospheric pressure, so it automatically regulates the fuel pressure at 5 lbs over boost pressure.
I would think a useful boost pressure would be about 5 lbs, and no more than 8 lbs, on an old engine. More than that and you're going to run into some serious engineering hurdles.
As far as which turbo to use, it's going to call for some research and careful thought as to requirements. Most turbos assume something like a 3000 rpm cruise and 5000+ rpm top end. A 230 flathead is not going to run much over 2800 rpm, and you don't need a lot of boost at that rpm. The typical charts and graphs that help you pick impeller and inlet/outlet size may not be of much help.
You also need a decent amount of oil pressure to keep the turbo from destroying itself. This means running an external line to the turbo and a return line.
I suggest getting one of the turbocharging books from HP Books and really reading up carefully.
One alternative that might be an easier solution is to use a Paxton style supercharger. These are belt driven, and you don't need an oil line, nor do you need to monkey with the exhaust. You'll still need a carb air box.
|
Follow Ups:
This board is powered by the Mr. Fong Device from Cyberarmy.com |