RX8 Engine decision

The engine in my RX8 has low compression. 5.8 kpa on rotor 1 and 6.8 on rotor 2. It runs well and doesn't seem to be down on power, but is a bit of a hard starter in cold weather. I really like the car and enjoy driving it. I would replace the engine but I'm a little surprised at the price from the dealer for a reman with a warranty ($7,000 Cdn installed). Advice from the collective would be much appreciated.

Replace coils/wires/plugs first. They miraculously gain compression in many cases.

flatlander937 wrote: Replace coils/wires/plugs first. They miraculously gain compression in many cases.

Yes. Do this first!

I've seen a 20psi gain in compression with new coils and plugs and some drive time.

(kpa? I hope you got the units wrong, or I'm thinking wrong, or something... 6-7kpa is closer to the atmospheric pressure on Mars than something an engine should make for compression. I don't think any of my rotaries could pull the intake manifold down to that low of a pressure)

If I had an RX-8, I'd add a little 2 stroke oil to the fuel. Not as much as if the metering pump were disabled, just a little bit, like maybe 200:1 ratio. Just enough to supplement, since Mazda really shortchanged the engines for oil in the name of catalyst life.

6.895 kPa is 1 psi, so the units must be wrong.

Copying from the printout . 5.9 kPa or 5.9 kgf/cm squared. No PSI readout but I think 120 is maximum and 98 minimum. Maybe my error in reading the print out? 8.5 kgf is standard and 6.9 minimum. I like the suggestions I usually ran premix in my other rotaries. New plugs but not coils and wires.

Some thinking and on line experimenting kilogram force per square centimeter yields around 83 psi so there is a print out error on the first section of my report. Thank you all,

That works :) I didn't want to assume that the number was supposed to be bar, or something else entirely. Best thing to do with questionable data is discard it until clarification.

Mainly I was curious as to what 20psi would indicate in the Mazda spec's metric equivalent and realized something was amiss Clearly if the spec is X units and the measured output is .8x units something isn't good. And with rotaries the only real compression spec you need to concern yourself with is "Does it start easily cold and hot?"... and you know the answer to that one.

Neat thing you can do if you're not afraid of teh Google:

https://www.google.com/?gws_rd=ssl#q=8.5+kgf-cm+%3D+%3F+psi

So, to belabor the point I made earlier, I've seen an increase of 1.4 kgf-cm just by replacing the coils and plugs and driving a bit...

Additionally, poor cold-weather starting can be caused by a weak battery or a worn starter. If you're cheap and not afraid of electric motors, you can pull your starter out, pop the end cap off, and hit the commutator with emery paper or fine sandpaper to cut the glaze, make it bright again. Make sure the brushes move freely. You may be amazed at how much a little starter tuneup helps with cranking speed, and cranking speed is life for a rotary.

This cropped up because it stalled and flooded in -30 degrees Celsius. The compression test was done with very little drive time so that might have a bearing as I'm sure the seals would have lost most of their lubrication. Starter and battery are less than a year old. Starting isn't that much of an issue except right around the freezing mark. I don't know the provenance of the engine and I didn't do a compression check even though I know better. I will try all of the above before I invest too many dollars.

To be honest, at -30, I'm somewhat amazed that it started and ran at all. Usually they crank far too slowly to build any compression, and the chamber shape means they can flood and starve for fuel at the same time when the fuel all condenses out to the walls.

Back when I used to drive them in the winter, I had carbureted cars. When it got below freezing, they would need so much choke that they would burble like a bridge port. Spark plug life was about a set per oil change if I wanted to ensure getting to to work in the morning. I'd imagine that EFI would be worse since injection has poorer atomization than carbs.

The fun part is, the carbs would ice over about a block away from home no matter how much I warmed the engine up. I kept a can of windshield de-icer at the ready. Open hood, pop air cleaner lid off, spray the de-icer directly at the venturis. This would melt the ice and prime the engine. No more problems for the rest of the drive.

Did they give you the rpm the compression was measured at? Normally the results are supposed to be normalized at 250 rpm. If the starter was cranking the engine slowly the normalized values might be higher, although I doubt they'll jump up to the minimum unless the dealer cranked the engine by hand...

I'd do coils and wires before doing anything else provided you want to keep the car, even if the engine is past it the next one will benefit.

Unfortunately the price for a replacement engine sounds about right if we're talking Mazda main dealer (assuming approximate price parity between US and Canadian prices). There have been various Internet rumours about the variable quality of Mazda reman engines, although recent reports suggests that the quality has improved. It might be worth it - although most likely even more expensive - to have your existing engine rebuilt by a reputable rotary specialist.

Thanks for all the above. I really appreciate this forum. The members respond like reasonable humans and I'm happy to be part of the community.

Opinions differ on whether one who has become a rotary expert can still be considered 'reasonable'.

<(scampers away)

Welcome aboard!

In reply to Vigo:

i warned you guys i was sick this weekend

I've owned an Austin Marina. I might not qualify as reasonable.

If you're up to it, you can rent an engine lift and replace the rotary yourself and save around 1-2 grand.

One could... but you can't condemn the engine until you put new coils in it.

FWIW, Mazdatrix sells Mazda reman engines for what our jobber cost from the dealer network is. No idea how this translates with shipping/duty to Canada.

They're so close to dealer cost that I'll use their website for making estimates if the need arises. Came up recently when someone let their RX-8 run out of oil and it bricked. Reman engine will be X, plus we'll need Y and Z. "What about if you rebuild? I've seen you rebuild one in an eight hour day."

Well... it'll need all the bearings, and the soft seal kit, and the gasket kit, and probably an eccentric shaft at a minimum. If there is no damage to the rotors and housings if the rotors rattled around in there. It would be bonkers to have an RX-8 engine apart and not replace the rotor seals, and oh look, with parts and rebuild labor we should just get a reman engine and let it be someone else's liability.

Sucks that way but that's the economics.

When you swapped the starter did you swap to the later starter? I'm just assuming it's a first gen RX-8.