if i dont find a twin turbo kit for my l98 i am going to add a procharger. what type of gain will it give my stock motor at 10 or 12 psi?? has anyone added a procharger? if so how much hp did you get?

 

Supercharger manufactures claim about 6% increase for every pound of boost. When my 92Z was stock, it made 350 rwhp and 416rwtq with 12psi. Hope this helps.

 

now running 12lbs of boost did you damage your engine at all?? what other mods have you done to your z. because i am torn between adding a supercharger, or just yanking the whole motor and dropping in a carbed crated motor. what is your rwhp now?? thanks for the help.

 

i gained about 2 seconds and almost 19mph

but i knew what i was doing

no offense, blowers need a lot of tuning

 

Ran for about two years with no problems. Went lean, broke two pistons. Now the engine has TPIS Miniram, ZZ9-X cam, ported heads, SLP headers, 5lbs. boost. Makes 375 to the rear wheels with 406 torque. Runs crappy E.T.'s (12.7's) with good MPH (112) with Drag Radials. Getting ready to go back to 12 lbs. boost.

 

Here is the technical answer... aka bench racing.

Boost is more or less a measure of the added atmosphere you are adding to you motor. If you have a theoreticly impossible 100% compressor, 14.7 lbs of boost will double your horse power. You also have to consider higher a/f ratios and less timing in the tune, mechanical losses to drive the unit and the inefficancy of the compressor(the ammount it heats the air therefore making the air charge less dense).

So... you have 10 or 12 lbs of boost... thats a 68% or 81% gain without the losses. I'll assume a intercooled setup with 80% efficancy 54% or 64% increase. Thats about 377 hp or 401 hp on a 245 hp stock L98. Consider 20-40 hp lost through powering the unit and the conservitave tune and you are in the 335 - 355 or 360 - 380 range.

I've done a procharger install on a mustang... My advice is if you still have an option get the self contained model. The extra cash spent is well worth not having to poke a hole in the oil pan for the return line.

 

GRRR, I hate rules of thumb worse then guesses, because you end up with people running around with no idea why something works or doesn’t work because the ‘numbers’ that they got don’t add up to what they’re seeing. With guesses at least people aren’t expecting to know exactly what will happen.

You get less gain for each additional amount of boost (in other words, you’ll gain more from the first # then the second, and more from that one then the 3rd).

To figure out just about everything in a boosted application, you need to figure out the pressure ratio, which is just the ratio between what the engine is seeing under boost to what the engine would see at atmospheric pressure (14.7psia under the conditions that you normally correct to). So in your case, you’re talking about 12psig over that, or 26.7psia, which when divided by the atmospheric pressure you get a pressure ratio of 1.816.

Engines are just a mechanism for combining air with fuel, burning it and collecting the energy. So the amount of air molecules that you can force into an engine and mix with the correct amount of fuel will be proportionate to the power output. Using the pressure ratio, and some estimated values for the conditions and the compressor adiabatic efficiency (I used about 65%, I don’t know what it is for a procharger, but that is a medium to low value for a modern turbocharger and centrifugal superchargers are basically turbo compressors hooked up to a gear box. All this # really represents is how much extra heat the compressor adds to the charge when compressing it besides the temperature rise from compressing the air), you can calculate the density ratio of the compressed air charge (assuming that the normal na air charge would have a value of 1), and in this case it comes out to about 1.44 (I won’t go through the math, but I think there are some charts that allow you to look up approximate values online somewhere).

A density ratio of 1.44 means that you have 1.44x the air being forced into the engine at that pressure then you would NA. So for a rough estimate you can multiply the hp the engine was making NA by this # to get some idea of what it would make at 12psi boost.

On street engines that are not completely optimized, you usually have some losses due to not having the optimum camshaft, heads, exhaust for the application, and forced induction can cover these sins up somewhat so usually the estimated power using these #’s ends up a little conservative compared to what you actually get.

Also, remember that this is power at the crank, and before it even gets to the transmission, some of that power is used by the supercharger to compress the air

So, assuming that the car was making 200hp at the wheels and you had about a 20% loss through the drive train (240 at the crank) and added that procharger that used say 30hp (just guessing here) to give you 12psig. You end up with (240*1.44)-30 = 315hp, or 252 hp at the wheels (again, in a non optimized street car situation you’ll probably see a little more).

 

BTW, if the #'s seem low, that should be enough to run mid to high 12's on an otherwise stock L98.

and, anything that would help flow through the engine (ex, headers, heads...) would increase HP at about the same ratio to what they would NA, which is why engines that are close to stock with mild mods seem to show a lot more HP then what you expect based on that # for a totally stock motor.