I dont plan on building a compound boost car but just have a question. I know the supercharger helps reduce turbo lag because of its instant response, but at what point does the supercharger become more restrictive than helpful?
Compound boost
- Thread starter STERLING351
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ask Digital. 750ish? There are far cheaper ways to make the power.
I figured it was low because the flow of turbos are crazy compared to superchargers
Compound boost is a waste of either a supercharger or turbo(s). If u need more than one power adder go to nitrous. I compliments either nicely due too it's cooling properties. I'm not sure on when it becomes a restriction u would need to do a lot of testing to figure that out. even with different pullies on the eaton. however i still am of the opinion after seeing some of the parsitic drag numbers that the supercherger at more than a few pounds is a restriction
The supercharger works as pump at a certain point and just moves air from its inlet to its outlet. You'd need an extremely large amount of air to overload its ability to move the air before a restriction was encountered.
I suppose "helpful" is a relative term to each person. Depending on your application and goals a compound setup may fit what you want to do perfectly. It may not be the easiest or most cost effective, or efficient way of reaching that goal though.
Like any supercharged car you're essentially just adding the liters of the supercharger on top of the engines liters. You're just making the motor bigger. As far as its ability to consume air.
The nice thing about the supercharger is that it acts like a N/A motor as far as response and throttle control. If you have a 4.6L engine and strap a 3.2L blower on it you get the response and power of a 7.8L motor. But in the process you do leach some power from that motor to spin the blower.
When you're going turbo you release the motor of that strain and use the exhaust gasses to spin a turbine that eventually spins fast enough (at higher engine rpm) to give you power. This is much more efficient as far as straight power goes but there is a lag factor involved.
Now some people will claim that you can perfectly size a turbo kit to reduce the lag to almost nothing. This is completely true. But only to a certain power level.
If you have a 4.6L engine that makes ~300hp N/A you aren't going to make 1500hp with no lag. Maybe 500. Maybe 600. But at some point that motor is gonna run out of steam.
You also run into a PSI issue. Pump gas at 93 octane limiting you to ~18psi. So now you're limiting your power even further by not being able to use your power adder to its full potential of 25-30psi+
This would be where a compound setup would come in handy.
Lets pretend you had a regular cobra motor with a ported eaton on it. 500hp for this example. Now you have that 500hp at 2000rpm or whatever it is, pretty much instantly.
Now lets say you added two 76mm turbos to that same car. Now those two 76mm turbos would normally take forever to spin up. Maybe 5000rpm. But they make 1500hp. That's all fine and good if you're just running that car at the track or going for some high end runs. But that car would be a dog around town till it spooled up. It would be much more fun to have that 500hp instead of 300hp around town and help spool those turbos faster as well. That would be where the compound setup would shine.
Are there other ways to get low end power? Sure. Get a bigger motor. Use nitrous. Use two or more turbos of different sizes like in most big trucks and the supra. But ONE of those options is to use a supercharger.
Most of the compound cars you see are novelty cars. They are mostly made for the "wow" factor and "fun" factor. They are made to have fun with and drive around town. You can get better low end power with a huge blower and better high end power with straight big turbos. But if you wanted all around "driveability" then a compound kit might fit your goals. Especially if those goals are well north of 750hp and you plan on running high boost.
With enough boost you can produce a staggering amount of power with a compound setup that produces pull from the moment you put the hammer down to the moment you shift. Even at a stand still. Some will claim that it's a waste of PSI and can be done more efficiently. But it's the goal of the owner that really counts. Not how you achieve it. IMO.
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