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Hey guys,

I posted a few questions in other posts, but I thought this forum could provide a few more answers.

I've been thinking of building a road/race car that offers me a fair bit of flexibility in terms of what I can do with it. I love my NA, but I do miss the extra power that I had in my STi road/race car. I've thought of turboing the NA, but it would fit into any CAMS recognised category.

I could just build a 2B SP replica but I couldn't realistically keep it registered and I'd need deep pockets which I don't have

So the other option could be an NB SP replica, which could be registered and still fit into the CAMS 2F category. To make it compliant with the 2F regs, I'd need to run 34mm restrictor on the engine, and I have no real idea on how this would affect the power and torque curves.

The current crop of competitive 2F cars run about 150-160hp at the rear wheels and weigh in at around 930-950kg. I reckon I could get a stripped out NB with roll cage and hardtop down to about 1080kg, so you would need about 180hp at the rear wheels to have a similar power to weight ratio.

Given that the standard SP setup supposedly provides about 210hp at the flywheel (160hp at the wheels??) and I can use a different intake, exhaust and increase boost. I wouldn't have thought it'd be too hard to get 180hp at the rear wheels even with the restrictor in place?

Anyone had any experience with this sort of thing?

I'd imagine running 10-12psi on a fairly standard engine wouldn't be much of an issue would it?

Comments or thoughts?

Could be a very expensive experiment.
Don't forget to paint it unicorn blue.

Hey Paul,

As you know we ran a couple of SE’s here in NSW for about 18 months. They were both road registered, Aust delivered cars. The engines remained std and we ran no more than 9 pound boost and never had any engine issues. The drivetrains were std (inc clutch) but we did replace the diff centres. We ran aftermarket radiator, intercooler but std turbo, manifold etc. They were good for about 120 kW at the wheels and would run all day. Then to be competitive with the quick 2F cars, we decided we needed more power!! We ran an aftermarket ecu (Adaptronic), big injectors, high pressure fuel pump, fuel return pipe and regulator. With no engine mods (and still 9 pound boost) we ran them at 154 rwkw all day, every day. This is around the limit for the std SE turbo as it is quite small.

As with all turbos, the A/F ratio is the most important thing and running it lean (for whatever reason) for a very short time can do catastrophic damage. This is the same for buzzing the engine, due to the strain the internals are under and fault, even a minor one, usually develops very quickly into a more serious one.

We ran them a couple of times (on dynos) with the restrictor (home made one) and found they topped out at around 130 kw. With some more development you could get this up a bit higher but at that stage we had no need.

In the end our cars were too quick to compete with anyone in 2F and to slow for 2B. Also by this stage most of the 2B guys and girls were stepping into SP replicas so the evolution of racing MX5's was changing. I couldn’t justify spending the $$ needed to upgrade them so went to the NC’s.

On a side note, I was lucky enough to drive a heap of cars at Oran Park over the years and without a shadow of a doubt the most exciting one I ever drove from turn 3 to the last corner was a turbo MX5!! Out of Sutton’s to the dogleg I thought the thing would take off!! Somewhere I have a pic of it with just one wheel touching the ground across the top!!

Whatever you decide I’m looking forward to racing with you again soon.

Id love to see that photo

Awesome info Chris, thanks.

So 130kw(175bhp) at the rear wheels with the restrictor in place, would give you roughly the same power to weight ratio as most of the competitive naturally aspirated 2F cars. Given that you were only running 9psi, they should've been fairly reliable as well, more so than a naturally aspirated "race" engine producing similar power.

I'd imagine you should be able to get a bit more out of an SP setup as well?

From what I've read the internals of the SE and SP engines are the same as the standard NB models, is that right?

I'm at that point now where I either spend 6-7K on a race engine for my NA or look at other alternatives. I'd like something that was fairly "standard", reliable and road registerable, so it's either an NC which will cost at least 30K if I buy an Australian delivered car to start with, or go down this path by building an NB SP replica using a standard NB road car as the base.

Look forward to catching up soon. You guys going to Bathurst at Easter?

Paul.

Cheers, Paul.

bruce wrote:Could be a very expensive experiment.
Don't forget to paint it unicorn blue.

At the end of the day if it didn't work out then I guess I'd have to decide to run it as either:

1) a 2F naturally aspirated car
2) a 2B unrestricted turbo car
3) an unrestricted turbo car in the AASA events.

Either way, I'd still have options but it just wouldn't be quite as flexible as I'd hoped

Or....buy a cheap NB roadie and buy my SE race car( which has a genuine SE gearbox) and swap all the bits over...

Boyracer wrote:Or....buy a cheap NB roadie and buy my SE race car( which has a genuine SE gearbox) and swap all the bits over...

Not really ready to do anything right now, just looking ahead. Besides I barely have space to work on one car let alone two at once.

Talk to Pat/Greg (Turbogirl/Pilsener here) and/or Russell (Russell) about Turbogirl and Turboboy. TG is road registered (or was), both are SP replicas. Both go very hard. Both are for sale (still - I think)

They have learned a few expensive lessons along the way, and should be able to give you a good steer about the issues in developing them and racing them in Prod Sports.

You guys going to Bathurst at Easter?

Yep - at this point we'll be there with at least a couple of NC's and a couple of BMW's as well!!

For what it's worth I would forget about the road rego'd bit on a turbo car. The amount of mods you have to get them fast and reliable (stripping all the weighty bits like airbags, heaters, blowers, etc) would make one not eligible for road rego anyway. You will save 10 - 12k on a "non registerable" car but it will still be eligible for Targa and unreg permits. I know the towing bit can be a pain but I can assure you it's a much better way of doing things. A couple of DNF's or damaged cars requiring tows and it pays for itself in no time!! Also you can fit a FULL rollcage - I won't race a car without one .

To do the reliable turbo route on an Aussie car will get you no change from mid $30's and you will be JUST ahead of the NA 2F cars.

Plenty for you to think about!!

mx5racing wrote:

You guys going to Bathurst at Easter?

Yep - at this point we'll be there with at least a couple of NC's and a couple of BMW's as well!!

For what it's worth I would forget about the road rego'd bit on a turbo car. The amount of mods you have to get them fast and reliable (stripping all the weighty bits like airbags, heaters, blowers, etc) would make one not eligible for road rego anyway. You will save 10 - 12k on a "non registerable" car but it will still be eligible for Targa and unreg permits. I know the towing bit can be a pain but I can assure you it's a much better way of doing things. A couple of DNF's or damaged cars requiring tows and it pays for itself in no time!! Also you can fit a FULL rollcage - I won't race a car without one .

To do the reliable turbo route on an Aussie car will get you no change from mid $30's and you will be JUST ahead of the NA 2F cars.

Plenty for you to think about!!

I know they will always be heavier than a stripped out car, Cal and I have that problem now, but it does allow for a lot more flexability and they're a lot more attractive to potential buyers come resale time.

I've always had full cages in my cars including my current one. Getting them mod plated in a road registered car up here in QLD doesn't seem to be a real issue.

It's not so much the towing, as most of the time I tow it to the track anyway.

At this stage though, the simpliest solution for a road registered, reliable, and resonably competitve 2F car would seem to be an NC.

Thanks for the info though, see you at Bathurst

Paul.

Paul talk to some of the IPRA guys about restrictors.

I know its one big headache for a lot of them.

They are breaking bits all the time. Especially gearbox's in the later model heavier cars.

The restrictor doesn't give you a very broad rev range. With the 36mm restrictor the IPRA guys are using i think it's all over at about 5000 rpm.

I am no expert on restrictors. Better off speaking to someone who has been there and done it. They also spend a lot of money on restrictor design.

Cheers
Brett

Thanks Brett.

At one stage I was looking to get my STi logbooked as an IP car, but after reading about the restrictor issues most of the IP were having with the late model cars I decided against it.

You're right though, the 36mm restrictor seemed to limit them to about 350hp but they had quite a lot of torque. Problem is, that torque was quite high up in the rev range and came on like a switch, which tended to break a lot of gearboxes.

As much as I miss the extra power, I think if I ever go down the path of FI with an MX5, it'd probably be a 2B car.

For now though, I'm tending to lean towards an NC 2F car.