Advice on SE Engine Block

[aussiecossie]

A good friend of mine, not very computer savvy so not on the forum, has a gorgeous MX5 SE. We were up in the Victorian high country at the weekend and unfortunately he had a major engine failure with a con-rod punching through the block

He wants to keep the car so is now looking for another block for the engine rebuild, but we're not sure what to look for - does anyone know if the SE blocks were anything special or were they just the same as a standard NB??

Cheers

[ManiacLachy]

The SE block have oil and water ports in them that the normal 99+ NB blocks do not have. And I think lower compression pistons to prevent detonation under boost.

A normal NB block could be used, but new oil and water lines will need to be fabricated. There are plenty of NBs running turbos that didn't from the factory, so clearly this isn't hard, and a search will reveal various options.

As for the pistons, well I guess it depends on the your friend's car and use. Do you know if the car is modified or if he's running a standalone ECU? The pistons should be perfectly fine on the stock tune, or even mildly modified, if using 98 octane fuel. If he has a standalone ECU then a re-tune to ensure safe timing should also ensure the pistons are safe from detonation - again plenty of normal NB blocks are running turbos these days.

He could keep an eye out for an SE block, but I'm not sure how often they come up. Personally I would not have an issue running a non-turbo NB block on my SE if I had a catastrophic failure like that.

[greenMachine]

Not surprised to read of another one. Unless an SE block lands in his lap, just follow ML's advice above on the block.

If he wants to rebuild, the formula is (in priority order):

New block (in this case), and possibly a new crank, I'm guessing having seen another SE that did just this that the crank is scrap.
New aftermarket ECU including wide band O2 sensor and electronic boost control .
New forged rods (ebay specials will suffice, unless he is going to chase big power).
New pistons for safety's sake, preferably lower compression, preferably forged.

That will produce a nice reliable car, with good safety margins. It should show a healthy increase in power, but not insane or impractical levels. Ideally it would also involve a new bigger intercooler, the OEM one is too small to work properly.

He can get away with plain rods and pistons, but plain rods almost mandate the replacement ECU as the stock ECU programming is considered by some to induce bent rods in certain conditions, and sometimes catastrophic failure (who knew!?!). A new ECU with WBO2, properly (but safely) tuned will be a big improvement as well as insurance against a repetition. Stock rods mean that the tuner shouldn't get carried away chasing power as they have the same weakness that brought this question on!

A second hand short block would be the way to go, it would need to be stripped and checked to ensure suitability and that the crank is in good shape. That should not be too difficult to find. He should be aware that all NBs use the same rods, and have the same weakness, and if he wants to reuse the rods (very inadvisable IMHO) they should be checked for straight and twist.

[aussiecossie]

Many thanks for the great answers, I'll pass them on to my mate. FWIW, the car was modified to produce about 170 RWKW but I'm not sure of details. Sounds like this isn't the first SE block to do this??

[StanTheMan]

well the hp isnt the problem here its the torque . and how its achieved in the tune.

thats only 230 whp....stock engine should normally be able to cope with that . especially the block

https://bofiracing.co.uk/how-to-keep-yo ... ata-alive/

[aussiecossie]

I know I said it was a con-rod through the block but we're not exactly sure what happened. TBH it looked like the con-rod was pretty much intact when seen through the hole so maybe it was a crank?? Can't imagine much else making a hole the size of a large orange other than rod or crank but I guess we'll know more once it's all out & stripped down.

[greenMachine]

Stan is right, tune makes all the difference. A good tuner, who knows both the engines and the gearboxes, can give you a a strong engine and a safe one, that won't bend/break rods etc nor gearboxes, and that engine (stock) will handle 200rwkw safely, with only bigger injectors to feed it.

That site Stan linked to has some really dodgy info. For example, the commonly accepted limit for 6-speeders is 250rwkw/350rwhp, and most tuners would prefer to stop a safe tune at around 240rwkw, to leave a margin. It is possible to get more, but you have to accept that you are pushing the limits. You'd do that in a track car perhaps, but probably not a road car. Although we have someone on here with so many killerwasps that he has replaced everything from the block back to the rear hubs with stronger, including a BMW gearbox, at a cost that I don't even want to think about (Daffy, thinking of you ).

Another is the reference to 'melting pistons'. What kills pistons is not heat, it is detonation. Detonation can be exacerbated by high EGTs, but mostly it is too much advance, too lean a mixture/poor quality fuel, etc. I could go on. However the list is useful in that it does identify critical items (in addition to items mentioned in posts above others include the crank damper and oil pump), but the information needs to be crosschecked with a local MX5 turbo expert.

If the car was pushing out 170rwkw, it had to have an aftermarket ECU and at least bigger injectors. If so, are there data logs in the ECU, that could point to the cause (academic now, but helpful going forward)? If not, there is the problem, I don't think the stock ECU is up to handling that level of power.

Hope that helps.



PS To answer you question, holed blocks are rare, but bent rods are way common and not just (but most often) on turbo engines. Sometimes you can hear them ticking at idle, as the rod touches the bottom of the cylinder bore

[ManiacLachy]

I would like to know what's been modified and with what parts/brands, but I agree with 170rwkw it would need to be running a standalone ECU, possibly a tune issue, or possibly a failure somewhere along the line?

With all that in mind, I would suggest getting a new block 1.8 NB block, running oil and water lines as needed. And refreshing the engine as much as the budget allows, but at least put in forged rods and maybe an upgraded oil pump. Also, stick an ATI Damper or Fluiddamper on the front of the crank. If you can go further, pistons etc then I would do it while you're in there. Also, consider ARP head and main studs. It's all insurance for the future.

Then re-tune, if he's happy at 170rwkw then a refreshed engine will handle that very easily. Or, he can push as much as the turbo will handle... which probably won't be much more than 170 on the stock IHI

[aussiecossie]

Again many thanks for the replies - all most helpful and I've passed them on to my mate. It's up to him now I guess ...

[Nevyn72]

One other thing, if the old engine is the original from the car, whether he plans on keeping it or not, he must salvage the sump!

The SE sump is so rare they're considered to be made of unobtainium and probably worth more than the car!*
No real reason other than it's uniqueness....

* Estimates of value are purely speculative and may not be realised on the open marketplace.

[StanTheMan]

whats different about an SE sump ?

[Nevyn72]

whats different about an SE sump ?

It's got an oil drain inlet opening for a catch-can (on the wrong side).