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Hey guys,

Im looking at buying a car thats basically a NA+T. But I've got a few questions. What is the "safe" limit of boost on an NA motor with an after market tune on a stand alone computer? The guy selling the car runs it on 11psi but said it was on 21psi when he bought it (which scares me). I spoke with the owner who built the car and he said he has never had it that high but that was due to the fact that he didn't have the stand alone. Everything else on the car is standard AFAIK and I doubt its engineered. Both owners have said the car runs well etc etc I'm just unsure as to weather or not this car is just a hand grenade or will actually last a while.

I have not dríven or seen the car yet, will be organised soon. If all else fails ill just buy an SE .

Any help is much appreciated! Thanks guys,

Ash.

I am out right now so cant type a proper response. If you need one now PM me and ill give you my number and ill give you the run down.

Dann

That's ok mate, when you get a chance is fine.

OK - while ND gets his crap together, i'll throw in my 2 cents.

The B6 is a strong engine, but as with anything you can't know how much abuse it's copped from previous owners. This is particularly true of modded cars like this one. 11psi, 21 psi, it's all just numbers as you have no real idea of the true history of the car.

In reality, you need to consider far more than just the engine. The gearbox and diff are just as fragile to excess power and ham-footed driving under boost.

Still, it could be a good thing and a well sorted turboed MX5 is a beautiful thing!

Get a cylinder leakdown test done on it. Check the plugs to get an idea of how it's tuned, whether it's detonating, and/or whether it's burning oil. Does it have a wideband gauge installed?

Make sure you see a cold start. By cold, I mean COLD. Don't let the guy start it before you get there at all, and feel the engine block to make sure. Watch for blue smoke on start-up (it will rattle a little, that's normal and should stop after a minute or two). When driving, cruise along in 4th or 5th for 30-45 secs and then plant the foot to the floor, keeping an eye on the rear-view for any puff of blue smoke (could indicate rings, valve guides or turbo seals).

Check the clutch by trying a hard rolling acceleration from low rpm in 2nd gear. It should hold the power and show no signs of slippage.

Gearbox should shift smoothly, especially the 3rd-to-2nd downshift. Listen for bearing noise in 2nd and 3rd under heavy acceleration.

There is lots you could do - if you can get it in a shop, you can pull it apart and check the turbo bearings and turbine condition, etc.

Depending on your knowledge, it may be a good idea to take someone along who knows aftermarket turbo systems. Spend the money on a skilled performance mechanic if you have to - it will be worth it.

As for the engineering side of things, I can't help you as I know SFA about South Australian requirements.

Good luck!!

open the intake and check for shaft movement in the turbo.

Thanks for the reply zossy. I am well aware of it having a standard driveline and the issues involved in that. I will check the gearbox bearings as you said, I didn't know about that. I don't know much about turbo systems since I've never owned a turbo car but I'll definatly have the car checked over by a decent garage if I feel the car isn't dodgy.

I recently bought a turbine inspired na6. And the guy had a well documented history on the car, and the thing oozed quality under the bonnet. I did alot of the checks zossy recommended, and it passed with flying colours!

I can't tell you how much I am in love with this car!!! After a few motorkhanas and a fair bit of daily driving duties, the car has been pushed hard and cruised and shows no sign of fatigue or pending doom. I guess if it look like a quality build, and it's a tested unit, these things inspire confidence. If it passes your condition tests you have got to get one!

I can't believe I used to think my skyline was fun....pffft taxi!

For pics of said car its on page 2 of for sales under eunos roadster turbo. On the iPad ATM so copy paste and such is too hard lol

Best of luck, I hope you do as well as I did scoring mine.

OK,

There is no safe limit of boost on any given engine, there is a safe limit of torque however.
A greddy kit will be able to be run at 18psi all day long and not be able to produce the torque needed to bend the stock rods, however a large frame turbo like a GT30 will smash rods to pieces at 8psi on a tubular manifold with a decent intercooler.

This is because the small exhaust wheel on the greddy kit is a HUGE restriction to flow through the head, and the tiny compressor on that turbo heats the air a hell of a lot, meaning that a lot of those PSI's are hot expanding air, not dense oxygen (and therefore power) rich air.

track_addict wrote:. I spoke with the owner who built the car and he said he has never had it that high but that was due to the fact that he didn't have the stand alone.

What was he using to control ignition timing and fueling?
Id definately be concerned for the condition of the insides of the engine.
Chris' advice is very sound, however keep in mind that you can buy pretty good condition na6 motors for a couple hundred dollars, so in the worst case scenario it has been abused in the past, a whole new engine gearbox and diff can be had for around 600 dollars if you can get your mates to help you swap them, which is really easy with regular handtools and an engine crane.

Of course if the damage was caused by a crappy tune, you would be up for a new tune too, which might cost 500 dollars.

Chris' advice is very good.

Id want to see a stone cold start (it has an aftermarket ecu, so if it takes 5 seconds thats fine), Id definately wet and dry compression test it, id check clutch slip, id listen for detonation, id check the plugs for detonation, id cut the motor off halfway through a power run in 2nd while still on the throttle and pull the plugs and make sure its running ok.

OR, take it to a dyno shop, and for around 150 they will check these things for you, and check the tune on a dyno run or 3.

Dann

Good info on torque. The car is running a t28 so I doubt it's rod bending on low psi. The builder (who owns an aftermarket parts store) said he ran it on 5psi on a standard computer cause "that's fine and works perfectly on these cars". So that is a worry I assume?

Damn, I didn't know b6's were that cheap! I'm not shy with tools, I work on aircraft so swapping a motor doesn't phase me.

So, a reasonable plan is to go look at the car, drive it, test of the mentioned weak points, if I'm happy get it checked by a reputable workshop especially engine health, if that checks out, buy it, get it engineered and enjoy?

Thanks for the advice guys.

Its NOT fine and dandy to just run 5psi...

NO WAY.

Anyways, yeah get a dyno run with an air fuel ratio readout and have them listen for detonation with det cans, if it has compression runs ok and that check out take it.

Dann

Oh that was what the guy who built it said to me saying it was fine. Rings alarm bells too me. Thanks again mate!

In regards to engineering, investigate the requirements upfront and budget for it, else you may be left out of pocket and a car that can't be registered in SA...

Thanks bark. The car is currently registered but I will talk to an engineer during the week and call service SA/Regency and have a chat. Do you have any experience with this?

Yes I do. I've been through the emissions testing process with regency, etc... and now have an engineered street registered turbo mx5 - which is fun! It cost me a pretty penny to go through the exercise, but well worth the effort and expense in my books.

How long did the whole process take and whats the rough cost? PM me if you like. This particular car is a stock na6 with a turbo kit slapped on so i'd say theres a fair bit to get it legal.