If anyone has been watching the SCCA Speed [Channel] World Challenge in the GT class, then you've probably seen the Realtime Racing (RTR) NSX running in the series. I've only see the last race in the series (at Mid-Ohio) and was disappointed to see the NSX do so poorly, especially in the last few laps of the race.

But, I was glad to see it staying up there with cars like the Porsche 911 GT3 Cup and the Saleen. With the NSX's rather low stock hp, I wasn't surprised to see that they were using FI... but I was surprised to see them using a Vortec supercharger.

From what I've read Vortec SCs (and centrifugal SCs in general) are supposed to be the worst of both FI worlds: the lag of a turbo with the ineffeciency of a SC. Positive displacement SCs (like the JRSC and Comptech's NSX SC), OTOH, have great gains across the rev range. So why would anyone want to use a centrifugal SC? I mean, if you're looking for high-end power, why not use a turbo (rules permitting)?

I started a discussion on this over at Team Integra (http://www.team-integra.net/forum/di...1&ThreadPage=1), which had some interesting points...

To see a bit more about the RTR NSX, their web site is useful:
http://www.realtimerl.com/indexRTR.html

And last, but not least, to see the SC I'm surprised they're not using, there's Comptech's web page:
http://solar.innercite.com/comptech/...hargernsx.html

So, can anyone explain it? Why use a Vortec SC instead of a Comptech SC (or something else), rules permitting?

 

Centrifical type
Higher peak hp with greater efficiency: less heat added to the intake charge less likely to detonate.
Who the hell drives at 2000 rpm on a racetrack? You want power at the top of the band, not the bottom.
Also, all of the listed superchargers are gear driven: there is no lag on any type of gear driven blower.

 

Then why use a SC at all? As I understand it, top-end specific power is better from a turbocharger than a comparable supercharger. That's what I'm getting at. The main purpose of a SC instead of a turbo is that the SC delivers better power increases across the whole rev range whereas a turbo is more focused at the top-end.

And to quote Comptech...

Unless the Vortec is a unique type of SC, what is this lag they're talking about? Spool up time? That's what I think it is...

 

Superchargers don't spool, they are gear driven.

By the way, Comptech makes a Centrifical Supercharger for the S2000 but they supply a Whipple type Supercharger for the NSX. Its all about the marketing hype if you are quoting the manufacturers. Check out http://www.howstuffworks.com for a quick break-down on Turbos. There is some information on Superchargers, but unfortunately there isn't much applied knowledge there. Its a start though.

With a close ratio six speed where you never dip below 6000rpm what good is power at 2000rpm? How many Realtime Prepped NSX's do you see at the corner grocery store avoiding shopping carts at 5mph?

The main reason why you try to aviod Turbos in road racing is the "spooling" or Turbo lag. Becuase a turbo is exhaust driven you need to have exhaust in the exhaust manifold to have boost. If you were just using the brakes, you were off the throttle and there is little or no exhaust pressure to drive the turbine.

On another note: Comptech, Basch, and K&N's Gruppe M are currently the only manufacturers of superchargers for the NSX. Comptech is no longer a Sponsor and/or Realtime is no longer using Comptech's service. The Vortech setup on the RealTime NSX's are a one off deal. Makes you go Hmmm. For at least the 96 and 97 seasons the Realtime NSX's were equipped with Comptech Wipple-based SC's. If they worked before I can only speculate why the are now using centrifical type superchargers.

 

That's not the application I was recommending for the SC...

BTW, I am familiar with the basics of SCs and turbos... As far as the "spooling" of the Vortec one: I was told (and since I know nothing about them it's all I have to go on) that the Vortec ones are similar to turbos in design except that they are driven off of the engine SC-style instead of exhaust gasses. They still have to spin up to be effective, hence little low-end hp like in a positive displacement SC. That's just what I was told. Still, you wouldn't have the turbo effect of lag, that's true.

As far as I know, Porsche 911 Turbos seem to cope with turbo lag pretty well. And the main problem with lag and turbos isn't braking but shifting (and the blow-off that goes with it).

Ah, now that's interesting. I didn't know that. Like I said, I just started watching this series and I was disappointed to see the NSX not doing better at Mid-Ohio (NSXs are great cars and I love 'em but sadly they're rare at races I've seen... in fact this is the only one I've seen; it's usually hard for them to keep up with a race-prepped 911, one of my other favorite cars). When I saw the Vortec SC on their web page and remembered what I was told about them, I began to wonder why they'd bother using one.

Someone on Team-Integra made the point that while Vortec/centrifugal SCs are terrible for small engine applications like the Civic or Integra, they work well with larger engines (such as the NSX or, more importantly, big American V-8s).


[Modified by RobertMcDonald, 6:13 AM 7/17/2002]

 

BTW, here's the type of stuff that's made me think the Vortecs are such ****:

http://www.team-integra.net/forum/di...2&TopicID=4214

Of course that's on only a 1.8L (Integra) engine, but it still makes you wonder about the quality of the Vortec engineering...


[Modified by RobertMcDonald, 7:58 AM 7/17/2002]

 

Vortech blowers from what Ive seen work better on larger motors. They usually boost up the HP of a mustang or Camaro by a descent amount.

They do have a weaker lowerend, but the reason that they do well on the bigger motors is because the V6s and 8s have torque. When you have the power down low already you dont need a whole lot more or it. The centrificals are a better street application of a FI. When you lack the torque to move it... The performance suffers. Hence the crappy numbers in the imports.

 

Part of the reason the NSX is not enjoying as much success as Realtime would like right now is that SCCA Pro has reduced the amount of boost they're allowed and added weight to the NSX in order to equalize competition. Same with the Audi S4.

 

8lbs and 2800lbs with driver respectively.

 

How much boost were they running before though?

 

The Audi seemed to be doing pretty good in the last race, though. I was hoping the Porsches would take that thing, but, sadly, they didn't. I don't know about you guys, but I'm not much of an Audi fan...

Obviously, BTW, the Vortec isn't working out too badly. Apparently, the NSX is in second place with 128 points (vs. the Audi S4 with 147). So what happened at Mid-Ohio, then? Just not Peter Cunningham's course? Seems odd that'd he'd be second in the whole series and take seventh this race...

OTOH, in the Touring Car class, RTR's two ITRs that are leading in points both didn't do as well as they could have... BTW, earlier on in the season I saw some cars that don't seem to be in the series now. Have the cars been changed around or something? The last race I saw it was one of the two ITRs (Pierre Kleinubing's) running against a BMW 3-series for first and the other (Peter Cunningham's) running against a New Jetta. This last race I couldn't tell about the BMW (there were too many!), but I didn't see that black Jetta anywhere...