THSCC Forums

I picked up a 1991 Miata today with some body damage (but nothing major...needs drivers door skin and rear quarter panel). Has 115k miles and does run (probably needs a clutch if it were to be driven and the ABS light is on).

I originally bought it with the intent of parting it out and keeping a lot of it as spares for my Spec Miata. But then I got this crazy SM2 idea. But I *thought* motor swaps were more open than they appear to be...am I right in that you can only build a 1.6L up but you can *not* put a 1.8L in there? It seems to say that the block had to be standard or an option on your model year or update/backdate swaps are allowed per SP rules. But according to SP rules I can't put a 1.8L in there because those aren't on the same line.

Is there a way to legally go to a 1.8L with a supercharger or turbocharger that I'm not seeing?

Also, am I reading right that a turbo or supercharged Miata would have to be 2100 pounds? Seems annoyingly high.


--Donnie

Donnie,

My understanding is that in the case of the Miata, the block must be from any other Mazda (MX-5 or otherwise). It could even be from a non-NA market model. Also there is the weight/displacement rules to look at as well (if you wanted to stuff in the largest Mazda made motor). I think you could even do rotary swaps as well.

I would also think that SM/SM2 is between SP and Mod. So you go one step beyond the "SP line" updated/backdate and just lump all engines from the manufacture (and partner is some case) together and you can pick and choose as well as go pretty crazy once you pick a block.

For the Honda folks, this is how they do all of the crazy Civic engine swaps. Engin swaps from other Honda's that might never have been in a Civic.

Richard

_________________
Richard Casto
1972 Porsche 914
2013 Honda Fit Sport
2015 Honda Fit EX
http://motorsport.zyyz.com
Money can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.

Under SM2 rules, you can swap *any* motor Mazda makes in there.

My old yellow turbo car was a 1990 with a '94 1.8L, '96 tranny and a '97 torsen rear end. All of that would have been legal under SP rules as well (without the turbo of course) as the only listing under CSP is MX-5. AFAIK, the top CSP Miata guys use the 99+ motors since they have the most stock hp.

The 2100lb limit is correct for a turbo/supercharged car with that displacement. You will actually have a hard time getting a turbo/supercharged Miata to that weight anyway. Mine weighed in at 2300lbs but it certainly wasn't maxed out or anything. I could have gone to much lighter seats, exhaust and a few other knick-knacks but it wasn't worth it to me at the time. I've heard some of those CSP guys get their cars close to 1900lbs but they can do a couple of thing that you can't in SM(2), namely losing the convertible top. And all the turbo/supercharger stuff is surprisingly heavy.

The biggest issue will be finding tires to put the power down. The "standard" 225-45-15's won't get it done and it becomes a chore to squeeze anything larger under there.

If you do build one, you'll have to let me drive it sometime since Les won't let me near his car!

Jim

Ah, okay. Rereading it, I get it now. It says it must be badged the same as the original model, not that it has to *be* the same or the same as any model *year*.

So, the easy thing would be a 1.8L with a turbo or supercharger, since that'll bolt right in.
Hmm. I think with a 1991 and all the stuff you can do to lighten one, I should be able to leave the AC and still get down to minimum weight. Interesting....

(Well, I say 1.8L, but I really mean start with a 1.8L and build it up as much as you safely can.)

Being that brakes are open, are there any add-on ABS systems worth looking at?

How crazy can you go with engine management? Looks like with SP rules you can pretty much use any computer module out there, though I don't really understand the wording about turbos. The SM rules don't say anything about computers that I see.

Looks like you'd want to go to basically a CSP suspension and wheel setup. Hmm....


--Donnie

A SM2 Miata should always be able to be lighter than a CSP Miata. The SM rulest builds off of SP, but with more liber engine, suspension and weight reduciton allowances. There is NOTHING in the SP ruleset that is illegal in the SM rules.

Scott

Yeah, I remember Pomblad's car had some wacky front/rear wheel combination for that reason. Is there no available rear end gear that would let you go with 13's all the way around like CSP cars? Seems like doing that with the lowering it gives you and the fact that they can stick way the hell out and not rub since they are so small in diameter would make sense. But then again, I'm no expert on this kind of thing (obviously).

Well, this is all based on what might be an incorrect assumption on my part that gearing is the reason people with high HP Miatas *don't* go with the small tires.



Hey, if Les is gonna be *that* way about it, I'd have no problem letting you drive it (and not him).


--Donnie

Sure there is. I'm pretty sure the MINIMUM WEIGHTS section of the SM rules takes precedence over Stock, ST, and SP rules (since none of those categories *have* minimum weights anyway). See Appendix A (page 166) of the 2005 rulebook for the table of weights.


--Donnie

Yeah, those pesky minimum weights...

Let me revise... A SM2 Miata should requre special ballast to make minimum weight.

Just cut the fenders to fit wider tires (at the expense of a wider car). It works for SP cars.

Drivetrain is unrestricted, so you can run any gear set that you can get, even if it is a one-off that you pay a whole lot for.

The only real limitation in SM is the size of the budget. There are some that are screaming aobut the sky falling as soon as someone picks the right obscure light weight chassis and starts throwing exponential dollars at it.

Scott

You are correct about the rule set. I was thinking about the softtop which at the time I first got my car, you couldn't remove. After they released the club sport, that went away.

However, I would say an SM2 Miata may or may not be lighter than a CSP car. If you are building an N/A SM2 Miata sure, but with forced induction, it would be very hard (read: uber expensive). Considering the average forced induction kit weighs ~50lbs, you would be hard pressed to find places to remove that weight elsewhere (that you can't remove under the SP allowances).

Jim

That is the big problem-- the 13"'ers provide too much gearing that you really don't need (besides being not wide enough). The only way to get more rubber is to run 16" or 17" wheels but it hurts the handling and there is definitely sheet metal abuse required. The front can be a big problem as you can only go so wide without using big spacers (which kill the wheel bearings and do other nasty things to your handling) or you wind up hitting the control arms and other various suspension bits.

I couldn't put down more than ~220whp with 225-50-15's but that may have changed a bit with the V710's. And that was on concrete....





Jim

Ah, I was thinking you could get those 13's in some hella-wide sizes, but that appears to just be a misconception of mine.

Sounds to me like build 250whp and don't use more than the tires can handle.

Still not sure I'm gonna do it, but it's getting interesting. I gotta think a 2100 pound Miata with that much power and a well setup suspension can run with about anything. Well, given a decent driver. Damn, that rules me out!


--Donnie

I think it is a given that it will happen eventually at the national level. Someone is just going to have to figure out the right combo and dump the money and time into the project. I think the one example I saw mentioned was something like a Toyota Starlet (low weight, RWD) with some type of extreme built motor, single speed transmission (why shift gears?), etc.

But we probably all would agree that for playing around at the local level you could have fun with a car that would not do well nationally. Or might do well outside of local events until someone builds the SM/SM2 monsters. I am planning on building a SM2 car and I am not worried at all as it is going to be a "fun" car and not something targeted at anothing other than local level autocross and HPDE.

_________________
Richard Casto
1972 Porsche 914
2013 Honda Fit Sport
2015 Honda Fit EX
http://motorsport.zyyz.com
Money can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.

VERY interesting project. Do you need an engineer?

A few comments/questions:

1 - Weight reduction. IIRC, non-metal panels are allowed. That should add up if there are fiberglass fenders, doors, and trunklid available.

2 - Wheel size. Besides other problems mentioned with too-short gearing on 13" wheels, I'd also worry about the *length* of the contact patch with a small overall diameter setup. Not enough rubber in the "go" direction to handle power. Better to find a 245 on a 16 or 17" wheel min.

3 - Big tire clearance - with all the suspension pickup point allowances, is there anything that can be done to reloate the front suspension to avoid the need for big spacers to run a 245 or larger?

Mmmm, SM2 Miata. I've been dreaming about this for years....

_________________
Mike Whitney
whit32@gmail.com, 919-454-5445
V10, V8, V8t, I6, I6, V6, F4t, I4, I4, I4, I4, I2, 1, 1

Donnie, why you don't go all out and built a DM car with it. If I will have time and money that's what I will be building.
A Miata with a Honda S2000 engine/ tranny and diff. ( make sure you get one of the under 2L engine ). Car strip to the max. with fiberglass part should be close to min. weight. Racing slick should give you enough tire and suspension is free. That should be a hell of a car.

Patrice

Why would an increase in wheel diameter hurt handling if weight is kept in check?

_________________
Rich
http://www.v8mongrel.com/