windsway

Building for autocross. 1999 Miata.

dustinb

Hi there.

windsway

Hey.

Looking for a FFS or Rotrex SC. AXing in San Diego. Tried searching first so i wouldn't be the ultimate Noob. Just a runner up.

dustinb

Is there a reason you don't want to go with a turbo? And no, you can't site turbo lag as a reason.

windsway

Straighten me out, then. Why do people think there is turbo lag? Why do they say there is a "kick in" point?

What steps can i take to smooth it out? I am sure you know that what i do is a lot of second gear below 60 mph stuff.

Thanks for your help.

dustinb

Ok seriously, how often do you drive your car hard under lets say.... 2500rpm? Because power is basically based on what kind of rev you are running. Like do you go out in whatever race you do, hammer it till you hit 2500/3000pm, and then change gears? Or are you rather actually driving the car in its upper rpm range? Because I know when I shift down, and i'm at like 6500/6800rpm, the next gear drops it down to about 4500rpm. If you aren't going for maximum HP (lets say 300hp), and you don't need a massive turbo, you can have awesome spool at 2500/3000rpm, and make great power.

So lets compare. A supercharge can be making boost throughout the power range, and if you look at a typical supercharger dyno graph, it's just this very linear increase. A turbo on the other hand will usually come on much stronger because when it starts making power, the power rises dramatically upwards, much more then a supercharger would. If you actually compare a typical gt2554 turbo setup to a supercharger setup (dyno graph), you will notice that the turbo setup makes a bunch more power down low, in the middle, and up top, and it comes on much sooner. So really, it's more useable power. YES it is possible that lets say below 2500rpm you will be making more power with a supercharger, but seriously, I launch my car higher then that. My turbo is a t28 and slightly on the larger side, so if I'm cruising at 2000rpm on the highway, and I don't want to drop down a gear, if I punch it, the car will still accelerate. It's like having wide open throttle on an NA car, and in a second the boost builds up and i'm going ridiculous fast.

The whole "I don't want lag" thing is probably the worst argument you can make.

dustinb

For comparison, here is a 1999 miata with a jackson racing super charger (from flyin miata's site)

And then compare the power to my graph:


At 2500, I am about 40ish, and the super is 55. At 3500 RPM, I am making 105HP and the super is making about 90. 4000 i'm at 170, super about 105. 5000 I'm at just over 210, super is at 130, 6500 i'm at 260, super at about 170.

Like seriously, there's what, a 15 HP difference in a rev range you'll barely use. By 2700 RPM I've basically passed the super in power output. When the turbo really starts spooling it pulls like a train, and people with a supercharger might be like "oh man, look at that lag", but really, I'm faster even in my "low" power area. Even my torque is higher by 2600rpm. And it's not like my setup is some uncommon thing. There are tons of people here who have a better spooling turbo than mine that would put a supercharger setup to shame.

ThePass

iTrader: (3)

The upside that I see of a supercharger for autocross is the smoothness. There are time that my turbo is a little more abrupt than I would like when autocrossing. The other bonus is fewer components that could fail. For a street car that just gets occasional autocross use I would go supercharger, and that's coming from someone who has a turbo. If I ever boost my '99 street car it'll be a supercharger. For the track, I prefer turbo.

dustin - you're comparing a base JRSC kit which runs like 6 psi to your 14 psi turbo dyno graph. Pointless.

samnavy

iTrader: (7)

What autocross class? Adding a supercharger will bump you up to competing with cars that will hurt you bad without a crap-ton of other mods, and even then.

windsway

SU - Street Unlimited. A local class here in San Diego. Coming from SSM. 3 competitors in SSM have SCs (two FFSs) and two have turbos. Competitors in SU have SCs - FFS and Cosworth.

It's after digging out of a slow turn (where you can get a few feet of straight away) that I want the torque. I have a Torsen LSD to actually help get it to the ground.

I plan to film the speedo/tach at the next practice to see how far down I really care about the curve. No time to really look at the dash with 38 corners in 60 seconds.

Engine is naturally aspirated and pretty stock except for Cat back (now deleted) and cold air box and intake.

949 15 x 8s with Kuhmo V710s, 225s, going to 15 x 10s with 275/35/45 Hossiers or Goodyear Slicks. Also a set of Rota 13 x 8s with V710s.

Looking to add MS for 99, Rails, injectors, pump,

Just deleted interior, air con, cat back, antenna, interior.

Looking to delete windshield, cut fenders (blsphemy!), dash/radio and air bags (more blasphemy).

Suspension is shortened, revalved Konis and 600/350 lb. springs going to 700 to 800 lbs in the front and still investigated the spring rate in the rear.

Racing Beat big hollow with the stiffening bar in the front and no sway bar in the rear. Adjustable end links all around.

Nicley mismatched Hawk brake pads, Momo seat (passenger seat goes in for pratice sessions and fun runs), Auto Power roll bar.

I plan to learn about forced air through owning a reputable kit and programmable ECU that won't cause unreliablilty and then make any changes slowly and carefully from there. Been reading a lot of stickies with great info and misinfo straightened out.

Thanks for the resource and input.

AARP

As a guy with a stock 1.6 JR Supercharger, take my advice and go for a turbo. Unless it's just a street car with occasional track use, you'll be left wanting more power.

Joe Perez

iTrader: (8)

Just out of curiosity, how long have you been running at Qualcomm? I used to go down there from time to time with my red '92, back when it was called SM2, but it's been a while.

chicksdigmiatas

iTrader: (11)

BTw the ffs kit is garbage

windsway

Been going to Qualcomm for about 2.5 years. A few trips up to Fontana too. One to Laguna Seca so far.

The FFS is chosen by several here as the most HP to stay street legal (smog)

I won't be limiting myself.