mx5cartalk.com

Hi guys thought this may be of some interest to some of you.
I love the idea of fabricating my own race car, was going down the track of the Sports Sedan, but a little too expensive. So I ended up tacking up some SHS so I'll end up with a clubman style race car.
I purchased a NB8A write off for the running gear. I'll be running the stock engine with ECU for now. Has a 4.44 subaru suretrac LSD. Using the MX5 uprights and brakes.
Most of the build diary is on the OzClubbies Forum.

Great project!

Subscribed.

Went to ozclubbies to have a further look but it appears you have to be a member.

yeah Ned Loh wasn't sure if you have to be a member of OzClubbies to view. sorry about that.

Thanks 93_Clubman, it is a great project. It makes it a lot less hassle if you build one for the track as opposed to a road registered version.

Indeed, especially in NSW of late!

Thanks for posting. It's looking good. I was going to ask about the 124 in your name. I used to have a 1600 BC - great car but fragile. Much of the time it looked like yours.

MB I am into Fiat 124s and Alfas I purchased the rust bucket Fiat in the photo for the clubbie running gear. But after a visit to Wakefield and talking to the Clubbie guys I scrapped that idea, went to the MX5 donk.
I've always had Fiat 124 CCs.

Book chassis, or presumably a little bigger?

After much deliberation I went with the book chassis dimensions. Talking to a few guys most of them said if its a race car keep it small you don't need the room. However I probably should have made it a bit higher to accommodate today's modern engine.

bit of an update. Currently fully welding the chassis and adding bracing.

Hoping to get some input into track preparation of the engine. I have a stock NB8A with 100,000km on it. At this time I want to keep it stock and get some time on the track before I start looking for more horses. What do I do to the unknown engine so it don't fall apart and keep it reliable. Don't want to spend a lot of coin on it yet.

My thoughts are
* timing belt and water pump kit would be the first thing.
* I have a concern about the harmonic balancer. It has some small pieces missing around the serpent pulley area, like some chipped bits. I believe this needs replacing?

your thoughts welcome

Build is coming along well - the NB8A motor is fairly bullet proof - so as you say replace timing belt & water pump, & anything else you'd normally do when recommissioning an unknown quantity motor that's been sitting for a while.
Re harmonic balancer, not having visibility of it, I'd probably replace it unless it was very minor chipping & I could establish it was not uncommon & could be run safely. The big forum (miata.net) <https://forum.miata.net/vb/> might have posts on this, or it might get a mention in the miata.net garage: <https://www.miata.net/garage/garageengine.html>

Thanks for your response 93 clubman. I like your comments that "the NB8A motor is fairly bullet proof" I figure If I keep it under the 7000 RPM mark I should be safe? with it being standard.
When I get to it I'll take a pic of the harmonic balancer so I can get some more informed opinions of whether it should be replaced or not. I may just purchase a new OE factory one as some reassurance.

Cheers

x2 on the bullet proof bit. If you end up going beyond around 7400 or with high lift cams then the cam buckets become a weak point - they throw the shim out - so you need to replace them with shim-under lightweight buckets.

If you're just after a tough dependable tractable N/A motor then the best performance gains come with a decent aftermarket ECU and a good 2 1/4" exhaust system. Minor porting helps too. Also lighter flywheel and lightweight wheels. Harmonic balancer failure is not particularly common - as long as the pulley runs true and there are no nicks to damage a belt then I wouldn't worry too much.

GR124 wrote:I figure If I keep it under the 7000 RPM mark I should be safe?

No probs as manga_blue says - if you're initially running factory ECU, then AFAIK, NB8A factory ECU is rev limited, although there might be differences in that limit between JDM & ADM MX5s as there has been in the past. Mention this as we don't know if your motor has come from a JDM or ADM MX5.
Re mods, in addition to manga's suggestions, 5x Racing & a few others in the US do a replacement timing wheel which allows advancement of timing: http://5xracing.com/i-6330020-5x-racing ... miata.html
Intake setup on a clubbie should be fairly free anyway, but if not then factor in so that it is. Again, if you're initially running factory ECU, then NB8A MAF isn't generally considered restrictive.