Typical new engine compression #
 

this came thru my mind *suddenly*

I know it takes a bit of time to break-in, but lets say if the engine was new, ran for 1K miles, what kind of compression numbers should I expect ?

Peak compression should come much later around 20K right ?

Hardly scientific here, but from what I've seen on compression numbers posted on engines between ~1k and ~8k after reman replacement, the remans seem to hover in the mid to upper 7s at that mileage. Some outliers have had 8s, maybe 1 in 20(?) of the engines that are commented about on the forum.

No idea about beyond that, or original factory engines.

nobody compression tests a new engine...

i have a feeling the numbers you get depend on how many new parts you use, so if say you had an engine that was 100% new, it would test very well right away. if you had a used housings/rotors engine, that was in spec, with new seals, it would take a little while to test right.

all the engines i've built with new housings/rotors/etc have felt strong right away.

With a rotary specific tester a new engine should be around 120-130 psi.

I tested a recently rebuilt engine with new housing, new apex, new side seal spring. I think all other stuff was reused, ran for around 1.5k miles, I was just curious and did a compression test, numbers were around 7.1-7,0 on all faces on both rotors. just wondering if it would go up.

Yeah really it would depend on the build. I would assume a professionally built engine with mostly new hard parts would have quite a bit more compression than a rebuild with used housings, etc. But no one test new engines. Mine is mid 7's after 20,000 plus boosted miles, the engine I had rebuilt was a low mileage (8,000 miles IIRC) out of a 2008 RX-8.

well if the engine is 100% new, then the compression should reach the peak fairly soon, since on Renesis you don't even need to cut-to-fit the side seals.

Yeah, custom cut versus precut side seals is debatable I guess but most builders say they prefer custom cut. I priced out building an all new engine, it was $8,000.00 in parts alone I think the last time I added it up, :lol:

Q: What does that have to do with how long it takes all of the seals to fully seat to their maximum potential?

A: Nothing ....

It more than likely has to do with the quality of the build in both parts and assembly experience than anything else.


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true, I was mixing prior engines when I type I guess :lol:

I'm 700 miles into my new engine and she has felt more peppy and has been starting better than my old engine ever did by 400 miles into it. My builder said between 1k-3k I can expect max compression, but some engine take longer depending on the part replaced. I had plan on testing it every 1k miles till it maxes out.

I replaced the housings, bearings, and he custom cut the side seals. New oil injectors and rebuilt the omp lines and made me SS lines for the coolers.

Sucks I don't have a real Mazda comp tester though.. I have to do it the old school way which is not as accurate.

I'm on my second reman engine and it has about 5k miles? Just had it compression tested today. Results are in kPa.


Rotor 1: 808, 794, 814 @258rpm
Rotor 2: 799, 770, 797 @267rpm


Mazda's acceptable levels are:
830 "Standard"
680 "Minimum"
150 "Difference between chambers"
100 "Difference between rotor faces"


The car currently has 92k miles. I will recheck before it hits 100k.