'90 Mazdaspeed Miata Rallycross Project

My RX-7 is good at rallyx because it was cheap.

Winston wrote: What is it about the RX-7 that makes it so good at rallycross compared to other RWD options? Is it the combination of low torque (less wasted energy due to wheelspin), high redline (allowing you to stay in each gear longer), LSD (duh), and IRS (better contact over uneven terrain)? Clearly the Miata and E30 have the latter two features (or at least the potential to have them) as well, so is it the rotary engine that makes the difference?

It mostly comes down to the driver.

Other than that the RX-7 has more suspension travel than the Miata.

irish44j wrote: I expect my copyright royalty check to be in the mail pronto

Is that about 10% of what it cost me to do it? What is 10% of nothing?

There was only one BMW at Nationals, it got beat by a few Miatas.

In reply to EvanB: There were two BMWs in SR: 318ti and 325i.

Winston: The FB RX-7s have a solid rear axle which is not necessarily good or bad. I wouldn't say that rotaries have low torque either, especially when considering gearing. They definitely have enough to spin the tires on most rallycross surfaces. The torque 'curve' of many naturally aspirated rotaries is also very linear which is great for driveability. Wheelspin isn't all bad on dirt, assuming you're throwing some stuff behind you and not just floating on top of the surface.

The car is a tool and some tools are better than others, but ultimately the quality of the finished product (in our case timed laps) depends entirely on the one wielding the tool.

That said, Evan's Miata is getting pretty close to being about as good of a rallycross tool as is can be and while we aren't the best drivers ( yet ) it is really fun to drive in the dirt.

I appreciate the confirmation that the RX-7 isn't the end-all be-all in terms of RWD rallycross machinery (because it seems like the results everywhere usually have RX-7's in the top spots).

Also, I didn't realize that the FBs have a live axle. That gives me some hope that my live axle Spitfire will be fine, so thanks for that.

Keep fighting the good fight! The car looks like a blast and gives me extra motivation to keep plugging away at my project.

cghstang wrote: In reply to EvanB: There were two BMWs in SR: 318ti and 325i.

Oh yea, that's right.

The point is they were both beaten by a Miata.

Spotted.

Note that the 2.5RS has an oil filter zip-screwed into the end of the muffler to act as a silencer.

Also note the GRM Dork sticker on the back of the Miata.

Spotted again. 2:30 mark. Bye bye magnet

http://www.youtube.com/watch?v=4vEjNZm0iPs

EvanB wrote:

Winston wrote: What is it about the RX-7 that makes it so good at rallycross compared to other RWD options? Is it the combination of low torque (less wasted energy due to wheelspin), high redline (allowing you to stay in each gear longer), LSD (duh), and IRS (better contact over uneven terrain)? Clearly the Miata and E30 have the latter two features (or at least the potential to have them) as well, so is it the rotary engine that makes the difference?

It mostly comes down to the driver. Other than that the RX-7 has more suspension travel than the Miata.

especially with blown shocks!

I won't be able to make it down to Ohio rallyX until I fix the truck (aka frankenburban) but I will be sure to come when I can!

You mean you can't just drive the rx7?

EvanB wrote: You mean you can't just drive the rx7?

no :(

well probably, I used to do it for years, maybe I'm just getting old at my weary age of 25...

it is a bit scary driving it all loaded up with my rallyX gear on the blown out shocks.

I changed the fuel filter hoping it would solve the problem of the engine cutting out under full throttle that I have been battling constantly (also I had no idea when it was changed last so it was probably time anyway). I took it out on a short run on the highway to do a couple full throttle pulls and it is worse than ever.

Some ideas: Spark blow out? Plugs correct heat range and gap set appropriately? Obstruction in a fuel supply or return line? Section of soft fuel line collapsing? I don't really know what I'm talking about but these are some possibilities I hadn't thought of before.

I changed the plugs and gapped them tighter but it could still be spark blowout. I need to do some more data logs and see if I can figure out what is going on.

Hope you get it sorted soon. Any chance the TPS is going wonky? And I'm glad front and rear wheel drive are separate in modified class now

No tps, just map sensor.

What plugs and wires are you running?

What did you gap the plugs to?

Is anything in this thread relevant: miataturbo link ?

ngk copper gapped at .030, stock msm coils/wires.

Suppose it could be worn coils/wires, but now i don't really have any good input. I know we had issues with parts store wires above 14psi on my buddy's 1.6 car, but that's an entirely different ignition. (We swapped to NGK wires and it went away.) I don't know as much about the MSM limitations.

Could be worth throwing in a new set of ZFR6F11s to see what happens i suppose.

Chris, I looked through that link when we were having problems at nationals and didn't find anything.

it feels and sounds just like a fuel cut and the fact that it is worse with race fuel and after changing the filter is confusing, at least to me.

EvanB wrote: it feels and sounds just like a fuel cut and the fact that it is worse with race fuel and after changing the filter is confusing, at least to me.

I'm probably way off base, but if it feels like a fuel cutout at full throttle, is there a chance you're overworking the fuel pump? Is the cut out still there when you set a lower max boost?

eastsidemav wrote:

EvanB wrote: it feels and sounds just like a fuel cut and the fact that it is worse with race fuel and after changing the filter is confusing, at least to me.

I'm probably way off base, but if it feels like a fuel cutout at full throttle, is there a chance you're overworking the fuel pump? Is the cut out still there when you set a lower max boost?

I don't think there's any way possible that an MSM turbo will ever generate enough power to overwork the fuel pump.

Especially since I put in a walbro 190hp and it didn't improve anything. Still cuts out at the lowest boost (8psi).