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Glenn,

I would advise against the Clutch Style LSD as well, I have a Shimmed RX7 Diff in my car now and it is fantastic on a road course with roughly 100 lbs of preload and it is sooo easy to keep the rear end sliding just a tad. But for AutoX it sucks, it has soo much mechanical grip that I have to really slow the car down and take a tighter line to get through corner so I can get back on the gas. This is why I'm now "this close" to purchasing a Guru LSD, a preload torsen would be the PERFECT rear end for what we do. Just enough preload to keep from lighting up the inside tire and still positive drive out the corners or in a mild slip angle.

 The RX7 Transmission is a LOT of work, once you have the backing plate fabricated you'd probably be into it for $1200-$1500. The quaife is the easiest way to go, but will cost more up front.

 Question on Suspension Mounting Points, I haven't sat down with a rule book yet, so please indulge me. Keith stated his setup required modifying the subframe to accomodate the new control arms. Now we're not allowed to do that in SM2, correct, but we can move the pickup points around in the stock subframe, such as moving the bolt hole up 1" on the lower control arm?

MNbiker:

I don't even use 1st gear on course - I launch in 2nd.  I can spin the wheels from a standing start all the way through 2nd gear, so 1st isn't necessary - even on a really tight course.  We just left the car in 3rd for the West course finish, and it worked fine.

-Steve

How did it work "fine"???  I was coming to the finish wanting another 150 hp!   And why were you 3rd to begin with?  We never even hit the limiter in 2nd gear, which is ~65 mph.

Father LeadFoot:

 Question on Suspension Mounting Points, I haven't sat down with a rule book yet, so please indulge me. Keith stated his setup required modifying the subframe to accomodate the new control arms. Now we're not allowed to do that in SM2, correct, but we can move the pickup points around in the stock subframe, such as moving the bolt hole up 1" on the lower control arm?

Outboard suspension points are open, inboard are off limits aside from SP, or ST allowances iirc.

Marshall Grice:

Father LeadFoot:

 Question on Suspension Mounting Points, I haven't sat down with a rule book yet, so please indulge me. Keith stated his setup required modifying the subframe to accomodate the new control arms. Now we're not allowed to do that in SM2, correct, but we can move the pickup points around in the stock subframe, such as moving the bolt hole up 1" on the lower control arm?

Outboard suspension points are open, inboard are off limits aside from SP, or ST allowances iirc.

Yup.  "Things that move" are basically open in SM2.  "Things that hold things that move" are not. 

Randy, if I were you I would go down to Tri Point and try and buy one of there used 2.3l motors out of the speed vision cars and stuff that in a 94-97 miata. Put a Quaife transmission in it,triple adjustable shocks, cage, and 15" wheels. That would be my approach if I built one.

CHRISFP78:

Randy, if I were you I would go down to Tri Point and try and buy one of there used 2.3l motors out of the speed vision cars and stuff that in a 94-97 miata. Put a Quaife transmission in it,triple adjustable shocks, cage, and 15" wheels. That would be my approach if I built one.

 

2060# all motor, 265bhp, maybe 225whp. A CSP car with about 50% more power. No need to ballast. Would be very interesting. CSP ran about 2 seconds slower than Andy's uber-time on the West course. I imagine the CSP cars were really suffering vs SM2 in the longish straights and very slow first left and finish on the West. I think the big question would be is the extra 200# worth it to add another ~130whp? The harder that question is to answer, the better the ruleset is.

129STS:

How did it work "fine"???  I was coming to the finish wanting another 150 hp!   And why were you 3rd to begin with?  We never even hit the limiter in 2nd gear, which is ~65 mph.

You missed the gist of my earlier post, which is that my gearing is set up to use 2nd & 3rd gears as 1st & 2nd.  This gives me a launch gear that's good for 51mph and a "course" gear that tops out at 73 mph.  This is pretty much perfect autocross gearing for the car IMHO.   Given the engine's almost totally flat torque curve between 2500-6000 rpm, I RARELY have to drop into 2nd on course.

rnoll98:

2060# all motor, 265bhp, maybe 225whp. A CSP car with about 50% more power. No need to ballast. Would be very interesting. CSP ran about 2 seconds slower than Andy's uber-time on the West course. I imagine the CSP cars were really suffering vs SM2 in the longish straights and very slow first left and finish on the West. I think the big question would be is the extra 200# worth it to add another ~130whp? The harder that question is to answer, the better the ruleset is.

I've seen the powerbands of those built Cosworth engines, and they're not exactly torquey.  Given ideal gearing, you could reduce the need to shift a bit, but IMHO you'd still be lagging well behind the rotary beasts.  Personally, I think the car would be fastest with a forced-induction engine and big tires.  Now that I think about it, the 2.0L engine might be a better choice than the 2.3 - since you'd get a lower weight minimum, lower CoG, and a more rev-friendly engine.

Father LeadFoot:

 Question on Suspension Mounting Points, I haven't sat down with a rule book yet, so please indulge me. Keith stated his setup required modifying the subframe to accomodate the new control arms. Now we're not allowed to do that in SM2, correct, but we can move the pickup points around in the stock subframe, such as moving the bolt hole up 1" on the lower control arm?

As others have said, you can't change the subframe suspension mounting points in SM/SM2.

A related note about the Brakke suspension used on Keith Brown's car.  Similar to SM/SM2, the Production road racing rules require stock inner suspension mounting points.  All geometry correction is done at the spindles/uprights.  Installing Brakke's control arms does require plates be welded in place where the stock eccentric washers used to reside.  However, the Production rules still consider this OK, as long as the holes though the subframes aren't moved.  Therefore, I believe the Brakke setup would be SM2 legal in it's standard configuration.  Worst case, you could simply weld the stock eccentric washers in place and use rod ends that fit the stock control arm bolts.  This configuration would undoubtedly be legal.

-Steve

p.s.  Please note - it's possible that Keith relocated the inner mounting points on his car, to obtain even more geometry correction than provided by the standard Brakke setup.  This, of course, would not be SM/SM2 legal.

MNbiker:

p.s.  Please note - it's possible that Keith relocated the inner mounting points on his car, to obtain even more geometry correction than provided by the standard Brakke setup.  This, of course, would not be SM/SM2 legal.

Since I run the small tires, it was not necessary to change the inner mount points.  If/when it becomes necessary to run the taller tires, I will have to break out the sawzall again anyway... 

MNbiker:

129STS:

How did it work "fine"???  I was coming to the finish wanting another 150 hp!   And why were you 3rd to begin with?  We never even hit the limiter in 2nd gear, which is ~65 mph.

You missed the gist of my earlier post, which is that my gearing is set up to use 2nd & 3rd gears as 1st & 2nd.  This gives me a launch gear that's good for 51mph and a "course" gear that tops out at 73 mph.  This is pretty much perfect autocross gearing for the car IMHO.   Given the engine's almost totally flat torque curve between 2500-6000 rpm, I RARELY have to drop into 2nd on course.

No, I got that gist.  But you weren't traction limited, and there was AMPLE time to go back down to 2nd gear in those two turns.  There's an easy couple tenths right there.  You'd probably go across the line right near the top of your 2nd gear. 

129STS:

No, I got that gist.  But you weren't traction limited, and there was AMPLE time to go back down to 2nd gear in those two turns.  There's an easy couple tenths right there.  You'd probably go across the line right near the top of your 2nd gear. 

Actually, we could get wheelspin in 3rd at full throttle in some areas of that section, so we were already traction-limited.   Keep in mind that the engine starts dumping boost above 6500 rpm, so the car pulls harder well below the rev limit, and the last 1000 rpm are there mainly to avoid shifting. I believe my co-driver tried downshifting once in that section, and found it a wash.  There may have been a little time to gain if executed properly, but given our mediocre performances, I'm sure we could identify several such areas on both days. 

A directly related factor is that the car currently gains way too much camber when the suspension is compressed - especially in back. As a result, it doesn't put power down as well as it should.  Correcting the suspension geometry is my top priority for this Winter,  so hopefully those downshifts to rocket out of slow corners will become more productive next year.

rnoll98:

CHRISFP78:

Randy, if I were you I would go down to Tri Point and try and buy one of there used 2.3l motors out of the speed vision cars and stuff that in a 94-97 miata. Put a Quaife transmission in it,triple adjustable shocks, cage, and 15" wheels. That would be my approach if I built one.

 

2060# all motor, 265bhp, maybe 225whp. A CSP car with about 50% more power. No need to ballast. Would be very interesting. CSP ran about 2 seconds slower than Andy's uber-time on the West course. I imagine the CSP cars were really suffering vs SM2 in the longish straights and very slow first left and finish on the West. I think the big question would be is the extra 200# worth it to add another ~130whp? The harder that question is to answer, the better the ruleset is.

Um more like 300hp with an inlet restrictor. S can the restrictor and I think you would have more than enough power.

CHRISFP78:

rnoll98:

CHRISFP78:

Randy, if I were you I would go down to Tri Point and try and buy one of there used 2.3l motors out of the speed vision cars and stuff that in a 94-97 miata. Put a Quaife transmission in it,triple adjustable shocks, cage, and 15" wheels. That would be my approach if I built one.

 

2060# all motor, 265bhp, maybe 225whp. A CSP car with about 50% more power. No need to ballast. Would be very interesting. CSP ran about 2 seconds slower than Andy's uber-time on the West course. I imagine the CSP cars were really suffering vs SM2 in the longish straights and very slow first left and finish on the West. I think the big question would be is the extra 200# worth it to add another ~130whp? The harder that question is to answer, the better the ruleset is.

Um more like 300hp with an inlet restrictor. S can the restrictor and I think you would have more than enough power.

 Yeah this is true, I pitcrew on and off for the Tindol Motorsports Mazda 6 Touring Car team. While I can't release our WHP numbers publicly I can tell you that without the restrictor we are forced to run, that 2.3L could probably make 330-340 Flywheel HP. But those Sunbelt engines cost some where around +/- $20,000 a pop. Plus the $10,000 Motec Engine Harness. It'd be a $70,000 SM2 Miata.

Father LeadFoot:

CHRISFP78:

rnoll98:

CHRISFP78:

Randy, if I were you I would go down to Tri Point and try and buy one of there used 2.3l motors out of the speed vision cars and stuff that in a 94-97 miata. Put a Quaife transmission in it,triple adjustable shocks, cage, and 15" wheels. That would be my approach if I built one.

 

2060# all motor, 265bhp, maybe 225whp. A CSP car with about 50% more power. No need to ballast. Would be very interesting. CSP ran about 2 seconds slower than Andy's uber-time on the West course. I imagine the CSP cars were really suffering vs SM2 in the longish straights and very slow first left and finish on the West. I think the big question would be is the extra 200# worth it to add another ~130whp? The harder that question is to answer, the better the ruleset is.

Um more like 300hp with an inlet restrictor. S can the restrictor and I think you would have more than enough power.

 Yeah this is true, I pitcrew on and off for the Tindol Motorsports Mazda 6 Touring Car team. While I can't release our WHP numbers publicly I can tell you that without the restrictor we are forced to run, that 2.3L could probably make 330-340 Flywheel HP. But those Sunbelt engines cost some where around +/- $20,000 a pop. Plus the $10,000 Motec Engine Harness. It'd be a $70,000 SM2 Miata.

So for $10k could you get a 300 fwhp engine and strap a $2k standalone on it? It seems to be the case with engines that the last 10% or so of the power costs 10x more than the first 90%.

Because those guys road race those motors , I am sure they have a lot of spare used parts. I bet you could buy enough used parts to put together a strong motor for less than 12 grand. Also replace the Motec with an elecromotive for 3 grand to save a little green. Thinking about it a little further, they have very restrictive rules on those motors. You could bump up the compression and change the valves to make even more power. That should cover the 10% 10x more problem.

All this talk about the SM2  Miata makes me want to take a shot a building one. It would be a lot of fun to build a NA car with the HP of my old FP car and the weight of an EP car. And....better tires and wheels than either car. I guess Pilar would be stuck driving the GT3.

CHRISFP78:

Because those guys road race those motors , I am sure they have a lot of spare used parts. I bet you could buy enough used parts to put together a strong motor for less than 12 grand. Also replace the Motec with an elecromotive for 3 grand to save a little green. Thinking about it a little further, they have very restrictive rules on those motors. You could bump up the compression and change the valves to make even more power. That should cover the 10% 10x more problem.

All this talk about the SM2  Miata makes me want to take a shot a building one. It would be a lot of fun to build a NA car with the HP of my old FP car and the weight of an EP car. And....better tires and wheels than either car. I guess Pilar would be stuck driving the GT3.

 

This is where it gets fun. You've now gotten to a point where you're on a similar budget that Logan outlined for us, but have gotten their via a completely different direction. His car is gonna decidedly have more grunt, but will also be carrying more weight. the 2.3NA won't have to ballast, but probably won't come off a corner as hard or pull quite as much on the straight, but will be able to carry more speed through the corner because it'll be lighter. I think we've just built the Sias v Tunnell matchup using Miatas. One car has the all motor NA setup, while the other runs the smaller motor with the blower. Too cool.

Engine = 20B or Renesis

 Why not a turbo rotary of some sort?

bruceman:

Engine = 20B or Renesis

 Why not a turbo rotary of some sort?

You can't easily fit the rotary into a miata without significantly modifying the subframe. 

sm2dan:

bruceman:

Engine = 20B or Renesis

 Why not a turbo rotary of some sort?

You can't easily fit the rotary into a miata without significantly modifying the subframe. 

And firewall, in the case of the 20B.  And if you go the rotary route with higher weight minimums, it's a LOT simpler just to go with an RX 7 chassis that doesn't require crazy fabrication to fit the engine and can support monster 335/315 tires.  Seems that formula has worked rather well in SM2 to date.