I am mystified by this. Why does a turbocharged Maxima engine with a pressure ratio less than a supercharged Maxima engine make more power? The only thing I can think of is better air density ratio, i.e. the intercooler the tc folks are using is doing a great job of keeping the air mass density up, resulting in more total air mass to the engine than a non-intercooled supercharger can provide.

 

SC takes power to make power via drive belt... turbo uses waste (exhaust gas).

 

That certainly is a factor, but a supercharger pumping 500 cfm at 10 psi is only using around 25-30 hp, and the power difference between sc and tc seems to be very much larger than that.

By the way, there is a certain amount of parasitic loss caused by the back-pressure a tc produces in the exhaust. The net power to loss ratio is certainly better than with a sc, however.

 

I think i'll disagree with the S/C being less parasitic than the Turbo... the backpressure restriction cost is much less than that of turning the S/C with the belt.

Keep in mind that since the turbo is not "mechanically" linked to the engine (rpm), it can/does spool up to full boost much faster (and stay at full boost longer) than the centrifugal S/C like the Vortech. More power under the dyno curve...

 

You know there are many varibles that control how much air is pumped via turbo or SC. In this case the Vortech features the same type of compressor side design(turboish) But due to the many choices in ar ratios, size and design of turbos vs the pulley, rpm, and compressor size/ar ratio on the SC, it's difficult just to say xxxx creates more power than xxx. Now add all the heat/parasidic lose characteristics of each.

 

why does a t78 @5psi give more hp than a t3 @5psi? (if you could spool it granted haha)

cfm.

 

I'm not sure who you're disagreeing with. I said net power to parasitic loss is better for a turbo than a supercharger.

Spooling speed and area under the torque curve doesn't enter into the picture. We're talking peak hp of a turbocharger at full boost versus peak power of a supercharger at full boost. The question remains, why does a turbo at x psi boost produce more power than a supercharger at the same amount of boost? Parasitic loss in turning the impellor of a sc does not fully explain the large difference. I think the presence of an intercooler must be making a big difference, since air mass is dependent on charge temperature.

Another difference maybe is thermal efficiency of the blowers. It could be that the V1 and V2 blowers (developed for over 300 cu in v8 engines) are too big for the 3 liter Maxima engine, so thermal efficiency suffers compared to a more favorably matched turbo unit being used by Nigel and Harold.

 

Their has never been an apple to apple comparisson of SC & TC Maxima's. For instance, most SC Max's have 2.5" exhaust and Nigel and Harold both have 3", this makes a big difference! The altitude correction factors used for SAE calculations are not aplicable to turbo boosted motors, they add some power that actually isnt their on turbo cars, so the dyno's you have seen are not a exactlly fair comparisson. As mentioned above and inter cooler is also a factor, only a hand full of SC Max's have intercoolers, and none of them are runnign over ~9psi. Its not apples to apples, never will be. The big issue we should all be concerned with is how to get more traction.

 

I was wondering about that. What was the uncorrected peak hp Nigel achieved at 4 psi? (Coincidence - I'm listening to Radio Paradise right now, they're playing an old XTC song, "Making Plans for Nigel" )

 

I am still quite new to boost but as mardi said there has never been a comparison based on dynos at sae corrected numbers at proven psi levels to create a comparison. I have talked to a man Geoff Knight in Florida on numerous occasions who has turboed and supercharged everything from his riding lawnmower, a three wheeler, multiple motorcycles, to his ford probe gt and builds hundreds of custom kits . He has been doing this for 20 year as he is very knowledgeable on the matters of boost and intercooling. His conscensus is that pound for pound with the same efficiency of intercooler a turbo and supercharger setup will be withing 5% of power output. The main reason is at any given psi the mass of air could be quite different but when the air charges are brought down to the same level the playing field is somewhat equal. A supercharger will create a parasitic loss that will increase like a bell curve yet the turbo backpressure is double what the exhaust would be otherwise. What will never be equal is spool up on a centrifugal charger and maximum boost.