brand new factory engine - compression numbers
 

Since I haven't found anything like that on the forum yet and maybe somebody is interested here are compression numbers of a brand new Japan factory engine N3H3-02-200 (no US-reman!).
Numbers are normalised to sea level 250 rpm, average of 3 tests per rotor on a cold engine after fitted into the car:

Front: 145,15 149,48 152,62 PSI
Rear: 122,87 128,51 131,73

Pretty high on the front, but I like it :-D
Will post new numbers after 600 miles.

there are several issues, likely because warm engine numbers are required for an accurate assessment

rather than get into all that, you may want to rerun the test under the correct condition to help provide an accurate assessment later

or not, your choice

Unlike piston engines, Rotary engines are tight when are cold hence higher compression number.
As they warm up they become loose since thermal expansion is always outward.
Sorry to say numbers are no valid and must do other test when engine baked hot.

So here are the numbers for the hot engine with now 70 miles on the clock:
Front: 126,18 128,73 127,97 PSI
Rear: 109,76 118,28 117,13

Excellent :icon_tup: may I ask how much cost you ?

That's not too bad but that's quite the delta between the front and rear rotor.

Factory spec says that the front and rear shouldn't have more than 14.5 PSI difference. Taking the mean average of your front and rear numbers, I got a 12.6 PSI delta between rotors. So it meets the specs but it's pretty close to the edge.

yeah, it was way worse in the first test

It’s not excellent, but ok. Those differences cause a dynamic imbalance under load. That’s why the limits exist. The problem in general is they don’t hand fit the side seals to exacting end clearance tolerances like a pro race engine builder would. They just use the pre-cut seals based on the letter classification system in the factory rebuild manual.

Engine was about 3.900 GBP

Excellent for being above 8.0 all factory engines were built by pre-cuted side seals. tolerance is range of turbo piston ring.
I have seen lots of "pro race engine builder " failed to get 8.5 after overhaul even those they had "street port" which could influenced static/ dynamic compression number.

Actually, now that I think of it, maybe 70 miles is too early?

Technically you can still be breaking in. Maybe at 1000 miles you could have better numbers?

Definitely still breaking in. Will probably be a good engine for you. That F/R balance should come into line.

well there are many opinions on that, mine is that anything over 600 miles (as stated in the owner manual) is just depriving yourself, but ok

it’s more for bearings, rotor gears, and such than for compression sealing. This is pretty much the accepted way to break in a rotary race engine, which you think if anything they’d be more concerned about it than for a street engine


On road or dyno after warm up with new bearings:
RPM MILES
5000 60
6000 60
7000 60
8000 60
8500 60

On road or dyno after warm up with old bearings:
RPM MILES
6000 25
7000 25
8000 25
8500 25

Is that info from Mr.D?

Mazda Motorsports is where I originally saw it 25+ years ago, still applies to this day ...

thanks.

I prefer faster break-in. When I rebuilt 4 stroke piston engines, I would assemble the piston skirts, rings, and cylinders dry, (everything else was oiled) and would freak people out, including the other mechanics.

Those engines always showed signs of excellent break-in. Low oil consumption, good power, excellent compression within the first couple of starts.No callbacks ever, even on commercial tractor engines that would run hard from the day they left the shop. I have done it since to all my own engines.

i felt 2 strokes were a different story, though. Those seem to like some "seed oil".

UPDATE: So here are the numbers for the engine with now 735 miles on the clock:
Front: 125,11 129,48 126,94 PSI
Rear: 116,57 122,06 120,60

Interestingly, not much did happen on the front rotor, but rear rotor is now more what one could expect for a new engine. Starting to go over 4500 rpm now.

Pardon my ignorance but what is the second number showing here? The 11,48,94 and so on? The 125, 129, and 126 look like PSI but what are the others? Are these numbers just not rounded or something?

The comma means decimal in many european countries. Those are just decimals.

2nd UPDATE: here are the numbers for the engine with 3580 miles on the clock:
Front: 120.78 121.08 115.88 PSI
Rear: 117.67 121.98 122.33

The high numbers on the front rotor have come down to normal levels now, while the rear rotor has stabilized.

One of my friends use to do break-in with WOT on the road. All of his cars were better in comparison with others.
Note that those areas would receive oil few seconds or under a min from other parts ( oil jet or leaks from connecting rod bearings)
Problem with engines which run unloaded aka idle a lot is mirroring of the cylinder wall, there is interesting design about Engine with rotating cylinder wall

Back to rotaries, they are different animals. apex seals only drag along the housing, unlike piston rings which have rotational movement too.
IMO the major problem is the material of the housing which is aluminum and it has much more heat expansion in comparison with rotors, hence increasing in clearance and compression reduction whereas in piston engines the piston will expand and reduce clearance. ( there is an exception on a few engines which has silic-alu block aka non-steel liner engine)
Another issue is the rotors as they are cast. Forge material has a higher thermal expansion rate, the same reason forge pistons need more clearance...

3nd UPDATE:
6360 miles
Front: 120.62 121.65 117.52 PSI
Rear: 110.08 116.50 118.91

13000 miles
Front: 113.01 117.21 110.91 PSI
Rear: 107.05 110.57 110.94

Started premixing after 6000 miles, so wondering about the benefit since numbers have come down significantly after that.