Correlation between compression and remaining engine life

[daniel_esp]

Hello again,

I'm looking to buy an RX8 in Spain. Clean, non-dubious units with service history cost around 8000-9000 euros. These are usually original engines with 60.000 - 80.000 miles (not kms) on the clock.

I would like to know how many miles I could potentially get out of a properly maintained RX8, based on the results
of a compression test. So basically I'm trying to figure out how many miles I can get for my money's worth, so I can better evaluate my options.

I know this is not an easy estimation to give, but I'm just looking for ballpark numbers or even relative values, i.e., if an engine with 6.9 bar has X miles before a rebuild, what about an engine with 7.2 or 7.5?

Thank you.

[kopite72]

Tbh that's huge money to be paying for a S1 8,that's even more than what you'd expect to pay for an R3 in the UK.If its doable you'd be far better off buying an R3 in the UK.You're based in Spain so it's not a big deal buying one in the UK and driving it home but 8-9K for a S1 with 80K on an original engine is crazy.

Regarding your compression figures,I'd be amazed if an original engine on 80K plus has compression in the low 7's.I'm not saying it's not possible but IMO it would be very surprising.

Just as an example,my own car ( R3 ) was rebuilt at 65K miles and it's now on 136K miles and going strong but the compression is all high 5's except for one face which is 6.1 so you can see my point on an original engine on 80K plus with compression figures of low 7's.

As I said previously you'd be far better off trying to source a sweet R3 in the UK for circa 4500-5k

[daniel_esp]

Don't get me started on how crazy prices for cars are around here. It's not just the RX8 though, I keep seeing 30 year old MK3 Supras or 944s in the 9k - 10k euro range. And I'm talking NA versions, not turbo. Maybe people think all these are / will be collectibles, idk what's going on.

Thank you for the reality check though. Deep down I know that paying 8k for a 60k mile RX8 is a bad idea. I guess I'm hoping I can get 20k miles (~4 years) of care-free usage which is honestly all I need for this to be worth it. These cars aren't getting any younger and I believe they stopped selling them in Spain in 2010.

Going "JDM" is not an option, as this won't be a track-only car and I'm very uncomfortable being on the "wrong" side of the car.

[kopite72]

Check this out...

viewtopic.php?f=145&t=80566#p1232767

[warpc0il]

UK-spec cars would have the same issue as JDM for driving in Spain - right-hand-drive.

Having done nearly 200,000km in a left-hand-drive Alfa Romeo, in the UK, I can confirm that it's doable but a pain in the neck at times.

Even simple things like car park barriers can be a nightmare and some overtakes get tricky

Back to the original question, there is no direct relationship between compression and remaining life of the engine.

It would be like asking your Doctor, "When will I die?" after he checks your blood pressure.


Sent from my SM-G800F using Tapatalk

[New Duke]

I guess I'm hoping I can get 20k miles (~4 years) of care-free usage

Probably not going to happen. As with all sports cars RX8s need love and any of them can get unlucky. But approach this with the thinking that you can spend reasonable amounts on maintaining key components? Then you should be set for very happy ownership. I drove mine to visit a grave today and it still managed to put a smile on my face.

I'm going to be a bit more optimistic than the previous estimate and suggest that you should be able to find cars with 60-80,000 miles on the clock with compression in the 6s and 7s (like mine).

If you can, I would suggest buying an RX8 with high compression (high 6s or low 7s) on the original engine rather than looking for a car with a rebuilt engine. Rebuilds vary and so does how long they last. Better to get an original engine in good condition in my humble view.

I'd agree with Ian (kopite) that you should try to get an R3 if you can. Before Warpc0il details why they're inferior to the older model.

Happy shopping. I hope that you don't get too worried and just have fun looking

Back to the original question, there is no direct relationship between compression and remaining life of the engine.

Oh yeah, and...

[daniel_esp]

Everything right-hand drive is "JDM" as far as I'm concerned

How is it possible that there's no direct relationship between compression and the life of the engine? I don't mean life of the engine as in "wait till the engine explodes", but as in "hot starts and power loss are so unbearable that you need a rebuild".

And to clear things up, by "care-free ownership" I basically meant "rebuild-free ownership".

[kopite72]

No such thing really with a rotary, they all need rebuilding eventually. If they don't drop a seal or a bearing the compression will take a dive to such an extent they'll be a bugger to start and we all kno what happens after that.

There is a relationship between compression and engine life. The more the compression drops the closer you are to needing a rebuild, simples

[warpc0il]

Low compression isn't the only reason for rotary engines dying, these days it might not even be the most common reason.

Some engines have low compression because they've been driven wrong (too gently) and have a build-up of carbon.
They're bought by someone that treats them right and, after a while the compression increases.
Eventually the compression drops again but they're still starting and running strong for years.

Another engine may have perfectly good compression, and then a bearing or side seal breaks because of increased exhaust back pressure, after the cat collapsed because it's being driven around with one duff coil and a rusted HT lead....

[casey]

Talking of odd/random failures, this was the reason my engine failed at 80k (but that included over 60 trackdays, so I have no complaints!). Failed in style, down Paddock Hill bend at Brands Hatch. The car was still driveable, to get car off track safely, but sounded horrid!

Rear rotor gear, tooth extracted at a weak point:

Engine Rebuild 065a.jpg