twin turbo vs. supercharger

[dswartz]

SpeedDemon,

Have you run your car a the drag strip? If so, what is your time and trap speed?

Anyone,

I'm confused about something. A high lift long duration cam provides better breathing at high rpm and therefore develops more power. The cam profile on VTEC is essentially a high lift, long duration cam. However, my personal experience with turbo cars, albeit not an NSX, tells me that a turbo doesn't like such a cam because cylinder pressure is lost under forced induction. Wouldn't a forced induction NSX perform better with a different cam?

 

[mdoan300]

Originally posted by dswartz:
I'm confused about something. A high lift long duration cam provides better breathing at high rpm and therefore develops more power. The cam profile on VTEC is essentially a high lift, long duration cam. However, my personal experience with turbo cars, albeit not an NSX, tells me that a turbo doesn't like such a cam because cylinder pressure is lost under forced induction. Wouldn't a forced induction NSX perform better with a different cam?

If I'm not mistaken, you're not compressing air in the engine cylinder, but rather in the scroll area of the turbo compressor side and then "flowing" the denser air-charge to the engine. So having a "high lift, high duration" cam profile should actually help even more (if given the appropriate fuel supply).

Cheers!

Michael.

 

[Lud]

dswartz - What forced induction cars do not do well with is excessive valve overlap. It's hard to achieve compression when there is a leak...

 

[David]

The best forced induction cams are long duration but low/no overlap. High lift does not really make a big difference. Overlap will rob power on a forced induction car. If you think about why cars have overlap and what happens with high positive manifold pressure, this will make sense.

On NA motors, at higher rpm, you want high lift and a bit of overlap like the VTEC profile on the NSX.

As soon as I have some $, I will probably get new cams for my car with a VTEC profile designed for boost - moderate lift and max duration without overlap.

 

[SpeedDemon]

Originally posted by dswartz:
SpeedDemon,

Have you run your car a the drag strip? If so, what is your time and trap speed?

Not yet with the TT system. The TT system was added just a few weeks ago, and I still haven't set the boost to the normal level (I've been running at 3-4psi). Once it gets set to around 6psi and "seat of the pants dialed in" I'll take it to a drag strip & see what I can do. After that, I plan to find a good dyno tuner & get the car dialed in via dyno.. Then off to the track again!..

I'm not purposely going to the track before & after dyno'ing actually, I just know it's gonna take a while to find a dyno place, get an appointment, etc, and I don't know if I can wait that long to get to a drag strip

By the way, I want to publicly thank Bruce Nomura and Mark Basch for their help during the TT install. I spoke to Bruce several times during and after the install, he was extremely helpful with advice & brainstorming specific to the TT setup.

Mark Basch has been similarly invaluable over the past few months. Among other things Mark aided with determining EGT probe location, walking me through how to quickly tear down the NSX interior to get at all the wiring, and other assorted help with understanding the NSX.

There are very few tuners out there with the knowledge, integrity, and desire to help (without compensation, for cryin' out loud!) that these guys have. I only wish either of 'em lived in So. CA

.

Thanks again,

Marc


[This message has been edited by SpeedDemon (edited 07 June 2001).]

 

[dswartz]

I think the one feature everybody overlooks in the Turbo vs Supercharger argument is the sound. A turbo acts like a muffler and you lose the exhaust note we all know and love. In fact, at the drag strip they now specify on certain events "muffled or turbo cars only". What they mean is that a turbo car doesn't even need a muffler because it won't exceed the maximum noise ordinance.