So I performed a compression test on my Rx8 yesterday evening due to the fact I have been dealing with the dreaded "hot start" dilemma for a few months now. A little history on the car..


---Test was done with Steve Miracle's Rotary Compression Tester v5.2---


2005 Rx8 Grang Touring MT with approx. 85,500 miles on the original motor.
Coils, wires, plugs all have less than 10k on them.
Battery less than 18 months old and in excellent condition
Custom 6-cable high-stranded 6awg grounding kit, grounding points cleaned for minimal resistance


Test was done in my garage, I am located in Bakersfield, CA and approximate elevation above sea level is 400 ft.


Raw numbers are as follows:
77/72/70 @ 327rpm for the Front Rotor housing
76/81/66 @ 317rpm for the Rear Rotor housing


Corrected/normalized numbers are as follows:
64/60/59 psi Front Rotor
65/69/57 psi Rear Rotor




Talk about seriously failing numbers. That said, the car starts right up when cold, takes approximately 3-5 seconds to start hot, and once running drives just fine without any misfiring or other concerns. The only other issue is a very slowly leaking front main seal.


Curious to know if anyone has continued to drive their 8 with failing compression and approximately how much the got out of it before it either refused to start up again or blew up?

 

No one can really say, it could last a day or years. My first engine was driving okay when it "failed", it would just stall occasionally. My second was running fine and then all of the sudden it felt like I hit a wall and that was that.

But I have seen guys who thought their 8's "felt great" and then on dyno day they made 40WHP less than everyone else. This is why butt dynos (and most of the time real dynos) shouldn't be trusted.

 

I've been driving mine for about a year since I found out mine was failing.
Hot starts started taking a few extra seconds several months ago and have been getting gradually worse, especially since the weather started warming up.
I don't think I'll get through the summer without significant wait times, or until it won't start at all.

 

I don't want to count my chickens before they hatch, but I found a guy locally who bought an 8 with low compression that has plans to do a swap on it. There is potential he will sell me the shortblock for $100 (thankfully because I have a very tight budget ATM) and I am considering offering him more to get the motor nearly completely dressed. I could potentially rebuild that motor in preparation for installing into my 8 when the motor it currently has finally calls it quits or the replacement is done, whichever comes first.

 

Are you planning on doing the rebuild yourself?

 

I was considering it. If I take the time and pay attention to details during the build I'd like to believe its very much possible to do myself.

 

If you're doing it to save money, it may be a losing scenario unless you already have all of the tools to do so.

Minimum cost to do the rebuild is going to be $1300 just for the seals/springs/gaskets/bearings. This doesn't include rotors, eccentric shaft, housings, irons. An 85k mile engine is very likely to need housings at ~$850 each. Sure, you can re-use your housings, even if they are out of spec but do you really want an engine that only makes 90 psi @ 250 RPM?

Two new housings and a complete set of seals, etc is $3000. Then there's the tools. I'm assuming you have the basics (basic mechanics sockets/ratchets/wrenches/etc, jack, stands, air compressor makes life easier, 300+ lbft torque wrench, something to remove the flywheel nut), but how about micrometer(s), gauges, slide hammer, engine hoist, stuff to lap the irons flat...

If you're just doing it to do it, then by all means, have at it and document the process with many photos and words. But if you think you're going to save money, it's not guaranteed (especially with the apparent failure rate of first time rebuilds).

 

I'm pretty sure I'm going to do the Mazda reman, but I don't think it will be anytime soon.
Now that the weather has finally warmed up I want to test it, do a de-carb, and retest it.

I've been thinking about just letting it sit and do a little at a time at my convenience.
I want to rejuvenate it.
I won't say 'restore', cause that's too much money.
More like all the little details that require more time and effort than money.
Taking stuff apart and cleaning them, cleaning the engine bay and replacing all the old rusted, worn and brittle stuff.
Plus all the maintenance items that usually need to be done when you get into the +80k mile range.

 

The beauty of getting this "mystery" motor locally is it will be $140 as a nearly completely dressed engine. If need be i would be able to recover that investment parting out the good components from that block.

Local dealer would sell me a reman for $3,200. If the parts cost of rebuilding myself hits above 75%, then I will highly consider going reman. Too many unknown variables at the moment not entirely worth speculating over as until i have that mystery motor and tear it down, who knows what ill have to work with.

There is a good probability that I will need housings, finding replacements will be a bridge crossed when we get there should i go the rebuild route. I have all the tools minus micrometers and a way to resurface/lap the irons. That said I am in SoCal, and i could simply drive to one of many known places in the SoCal area to get irons inspected, lapped, and treated if needed along with whatever else need be if I decide to rebuild myself. I wouldnt need to invest in all the specialized equipment when i can pay the cost of those services for likely less than what the equipment would cost and have someone reputable be the individual to do it.

Again all this would be weighed "rebuild vs reman" upon recieving and breaking down the engine, but the option is at least there. Not to mention the experience and ability to have the expenses of the build over time is more manageable for myself than a large all at once expense.

Everything would be documented with pictures and the "do it right or do it twice" mentality for the most part. I dont drive a ton of miles annually, so a motor that lasts even only 50k i would be happy with for a first time build as dumb as that may sound to some since I may not even put 10k a year on the car. Besides this Rx8 i own a 2006 Ford Explorer so my annual use and mileage is split between the two vehicles to a degree.

 

On the bright side, Mazda don't appear to be too picky about the condition of the core if you purchase a reman. One of my friends thought the way you did until he got his engine apart. When the parts cost hit $3k, he threw in the towel and sort of reassembled everything finger tight and the dealer accepted it as a core.

 

I thought about keeping my old engine to rebuild just to see what it's like, but I realized I don't want to invest the time in it.

 

Should be picking up a fully dressed low compression engine and catalytic locally this weekend for $180. I will be tearing it apart to see what's the damage and prep it in advance for installing in my 8.


I plan on documenting the entire process and also documenting an "extreme budget rebuild". The extreme budget rebuild may be extremely cringe worthy, but we will get an idea of what to expect and what results in the areas of initial compression, drivability and long term lifespan.


Hell, I may even make a youtube channel specifically to share and document the rebuild process. Hopefully if I am able to monetize it to any degree I will be able to provide better content and a slightly better build. Its not my skills and abilities that are lacking in these circumstances, its my wallet