Which Miata for ST2? 1.6 VLSD vs 1.8 open diff

[jaball77]

Thoughts?

Since only factory installed viscous coupler units are allowed in ST2, 94-97's with the Torsen are out... So it's the 1.6L with the Silly Putty diff vs the 1.8L with the one wheel peel.

I guess it comes down to more torque off the corners and bigger brakes vs the 15-25% locking from the vlsd... Assuming you can find a vlsd car and assuming it still works, heh.

Or is it all moot, and won't make a difference to a hamfisted galoot like myself? Feel free to say so. :D

[mofugga]

no replacement for displacement... even in a miata:lol:

[Loren]

The bigger brakes really don't matter for autocross. In fact, a lot of the CSP guys "backdate" to the smaller 1.6 brakes to save weight. In fact, they do EVERYTHING they legally can to save weight, often including the removal of factory chassis braces in addition to the usual A/C removal and such as that.

So, that leaves you with the torque... and how you can apply it. But, there may be other things to consider.

There was a short thread on Miata.Net (http://forum.miata.net/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=4;t=003295#000002) earlier this year raising the same question. And another thread (http://forum.miata.net/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=4;t=003324#000001) about "bench building" the perfect STS2 Miata.

STS2 allows you to change wheels. Personally, I'd go for the lightest possible 14" wheels and 205/60 Azenis at this time. OR... for better tire selection, maybe some ultra-light 15's with up to 225's. But weight matters, always keep that in mind.

STS2 only allows an OE VSLD, and there are those who will say that "any LSD is better than no LSD". I can't say, myself as my experience is mostly in my own car that has a Torsen. (and I sometimes run STS2 if I know my competition doesn't mind... it's that or get eaten by CSP)

The 1.6 cars are a little over 100 pounds lighter than the later cars. That can make a difference, too.

And the 1.6 cars are geared for better acceleration, which helps balance out their having less power. This is why a lot of people feel that the 1.6 cars feel "peppier" than the 1.8's.

Lots of stuff to consider, for sure. If I were starting from scratch with the intent of building a car for this class, I'd probably seek out a nice 1.6. Should be able to pick a really nice one up for under $3k... or a ratty one up for well under $2k... or a fixable wreck or terminal mechanical failure for well under $1000. Put a good suspension under it, good wheels and tires, fresh and functional VLSD, and go have some fun!

[jaball77]

Originally posted by Loren
And the 1.6 cars are geared for better acceleration, which helps balance out their having less power. This is why a lot of people feel that the 1.6 cars feel "peppier" than the 1.8's.

Interesting. I didn't know about the gearing!

It looks like you almost have to go with 15" wheels to get any respectable tires. There are a bunch of ~10 lb wheels in 15x7... I was poking around some Spec Miata info and found the Team Dynamics wheels they're all in love with. About 13 lbs, plus, they have that super wide +30 offset for extra track width. :D

Can you buy "new" vlsd's? It may even be worth it to find a beat-on '92 or '93 and add or replace the vlsd later on...

[Loren]

Originally posted by jaball77
It looks like you almost have to go with 15" wheels to get any respectable tires. There are a bunch of ~10 lb wheels in 15x7... I was poking around some Spec Miata info and found the Team Dynamics wheels they're all in love with. About 13 lbs, plus, they have that super wide +30 offset for extra track width. :D

Can you buy "new" vlsd's? It may even be worth it to find a beat-on '92 or '93 and add or replace the vlsd later on... [/B]

Spec Miata guys are not allowed to run a wheel that weighs less than 13 pounds, if I recall. That's why they run those wheels. Keeps the costs down. Right now, the best bang/buck is the Kosei K1-TS at 10.5 pounds. The lightest is um... I think SSR Comps at 8.5 pounds. For 15's that is... the lightest 14 is the 6.5 pound Volk CE28N that I have.

Not sure what your options for VLSD are. Having a Torsen, I've never really looked into it. I'm pretty sure you could get a new one or have the old one rebuilt... for a price.

With good tires and alignment and a beefy front swaybar you might get around okay without the VLSD. Good enough to have some local fun, anyway.

[jaball77]

Spec Miata guys are not allowed to run a wheel that weighs less than 13 pounds, if I recall. That's why they run those wheels. Keeps the costs down. Right now, the best bang/buck is the Kosei K1-TS at 10.5 pounds. The lightest is um... I think SSR Comps at 8.5 pounds. For 15's that is... the lightest 14 is the 6.5 pound Volk CE28N that I have.

Yeah, I saw the TS. Nice wheels. And I'd LOVE to get them in that neon orange color they have, haha...

Do you think the extra 8-10mm of offset for a +30 wheel would be noticeable for autox use over something like the K1-TS?

[Loren]

Originally posted by jaball77
Yeah, I saw the TS. Nice wheels. And I'd LOVE to get them in that neon orange color they have, haha...

Do you think the extra 8-10mm of offset for a +30 wheel would be noticeable for autox use over something like the K1-TS?

Not something I've experimented with. I don't think it would make a a night and day difference, though. Stock offset is 45 for the 14's, and I think 40 for the 15's and 16's. I ran 38 offset 15x6.5 Rotas for a couple years. I really don't think the offset affected much. Maybe going as far as 30 would make more of a difference?

Miata.Net is your friend. :D Lots of good info out there in the forum if you search.

[PseudoRealityX]

just a point of reference...being that I haven't driven any open diff 1.5G miatas that I know of...

if the wheelspin isn't bad, then a diff isn't helping all that much. You can always tune out wheelspin with setup, and STS2 allows a lot of setup.

Loren, where does the 100 lbs lighter for the 1.6 cars come from? other than the engine of course.

I'd sorta lean towards the 1.8L cars....



-driver of a 2550 lb car with ~170 CRANK lb-ft of torque and VERY LITTLE wheelspin using R compounds (which would increase wheelspin) and stock class rules.

[Loren]

Originally posted by PseudoRealityX
Loren, where does the 100 lbs lighter for the 1.6 cars come from? other than the engine of course.

I'd sorta lean towards the 1.8L cars....

1.8 could very well be the way to go, I'm not sure. I'm not willing to give up my Torsen to find out. ;)

The early 1.6 cars had none of the bracing that started apearing in 1992. The 1994 cars (first year of the 1.8) had all of the bracing installed. It doesn't add up to much, but that's part of it. The 1.6 diff is also something like 15 pounds lighter from what I've heard, in addition to the engine block/head being a bit ligher. The quote I read today from Andy Hollis (a knowledgable Miata autocrosser) said the difference was about 125 pounds total.

[jaball77]

Originally posted by PseudoRealityX
I'd sorta lean towards the 1.8L cars....

Yeah, that was my initial gut feeling, too.

Originally posted by Loren
The early 1.6 cars had none of the bracing that started apearing in 1992. The 1994 cars (first year of the 1. had all of the bracing installed. It doesn't add up to much, but that's part of it. The 1.6 diff is also something like 15 pounds lighter from what I've heard, in addition to the engine block/head being a bit ligher.

Man, I wasn't even considering the 90-91's because of the crankshaft problems.... 92-93's are still probably a little lighter and have the shorter gearing... Plus, they're cheaper...


Curiouser and curiouser. :-)

[PseudoRealityX]

Originally posted by Loren
The early 1.6 cars had none of the bracing that started apearing in 1992. The 1994 cars (first year of the 1.8) had all of the bracing installed. It doesn't add up to much, but that's part of it. The 1.6 diff is also something like 15 pounds lighter from what I've heard, in addition to the engine block/head being a bit ligher. The quote I read today from Andy Hollis (a knowledgable Miata autocrosser) said the difference was about 125 pounds total.

That's in stock trim I'm assuming? Or was Andy talking about ST prep?

Andy knows his stuff....too bad he's Andy. ;)

[Loren]

Originally posted by PseudoRealityX
That's in stock trim I'm assuming? Or was Andy talking about ST prep?

Andy knows his stuff....too bad he's Andy. ;)

I'm sure he was talking stock. How much bracing are you allowed to add/remove in ST? It's been too long since I studied the rules. (btw, jaball, that's the first thing you should do is get completely familiar with the rules of the class you're looking to get into... if you're going to get "serious" about it, anyway)

I think I've heard that about Andy before. :) I'm just glad that he shares that knowledge with us from time to time.

[jaball77]

Originally posted by Loren
I'm sure he was talking stock. How much bracing are you allowed to add/remove in ST? It's been too long since I studied the rules.

There's no update/backdate any more... So if it wasn't available, you can't add it, and if it WAS there you can't remove it. Especially to save weight, heh.



Jason

[Matt Vassallo]

you guys have never thought about rebuilding your vlsd and adding the wrong type of viscous fluid have you?

[Loren]

Originally posted by Ostrich
you guys have never thought about rebuilding your vlsd and adding the wrong type of viscous fluid have you?

I've seen that question raised on Miata.net. Someone has probably done it, they're just not talking much. I mean, the only people who are seriously using the VSLD are doing so because their rules (like this STS2 class) don't allow them to use something better. So, if they're doing something "sneaky", they're going to keep it hush so as to not give away their advantage.

Outside of a restrictive rule set like this, the Torsen is a much better option, and there are also aftermarket clutch-types available for the Miata.

[PseudoRealityX]

Originally posted by Ostrich
you guys have never thought about rebuilding your vlsd and adding the wrong type of viscous fluid have you?

a) anyone serious enough would just use a Torsen.

b) why would anyone talk about something illegal for the class they're playing in.

[jaball77]

Originally posted by PseudoRealityX
a) anyone serious enough would just use a Torsen.

b) why would anyone talk about something illegal for the class they're playing in.

No kidding. What's the fun of winning if you know you had to cheat to do it?

[mofugga]

Originally posted by PseudoRealityX
b) why would anyone talk about something illegal for the class they're playing in.
exactly why you never talk about the cams you've put in the MR2:lol:

[Loren]

Would it be illegal to put different oil in a diff? I'm not so sure about that. It would just be a "competitive advantage" that you might not want to share.

Now, if you had to physically modify the diff to change the oil, like drilling a drain hole or something... that would be illegal modification. But if you could change the oil without altering the parts, why not?

What next, are they going to start checking oil viscosity? "It's 85 degrees today, your owners manual specifies..." I don't think so. :)

[nunyo]

Jason, mid way through the '91 model year they switched the crank style from the earlier setup that everyone seems so concerned about. You can tell based on whether the VIN is after xxxx209446. My '91 has the '92 and up style crank.

So if you wanted to consider a '91 for the weight savings due to lack of bracing lack of bracing, you could. I have no idea however if the bracing is something that is really better to have despite it's weight.

I too was unaware of the different gearing, if the 1.8 is actually 125 lbs heavier than a 1.6 equipped car, I'd say that the reduced weight and ability to run the viscous diff make the 1.6 a better starting point.

It doesn't hurt that by being slightly older it should be a little bit cheaper to purchase one as well.

[Loren]

Apparently, the CSP guys take weight over all else. They remove bracing, don't run shock tower braces or roll bars, convert to the smaller 1.6 brakes, etc.

Probably not healthy for the car's unibody to run that way with a stiff suspension and R tires... but it must be the fast way or they wouldn't do it.

The Honda guys are the same way. Shave as much weight as is allowed and get as much power as is allowed.

[jaball77]

Originally posted by nunyo
Jason, mid way through the '91 model year they switched the crank style from the earlier setup that everyone seems so concerned about. You can tell based on whether the VIN is after xxxx209446. My '91 has the '92 and up style crank.


Sweet. I didn't know that. MORE years I can include in my search. :-)


I too was unaware of the different gearing, if the 1.8 is actually 125 lbs heavier than a 1.6 equipped car, I'd say that the reduced weight and ability to run the viscous diff make the 1.6 a better starting point.

It doesn't hurt that by being slightly older it should be a little bit cheaper to purchase one as well.


Yeah, the more I think about it, the better a 1.6 sounds. :-)