What's my compression test telling me?

[brenno]

This afternoon I did a compression test on my newly acquired NA8 out of curiosity. The motor has done 220k, so I figure it's probably a wise thing to do.

I had a dyno run at IS motorsports yesterday and noticed a puff of white smoke when backing off. Indy tells me it is probably valve stem seals, but I wanted to eliminate the possibility of piston rings. The motor feels pretty flat when cold but fine when warm. I haven't dríven any other NA8's though, to compare.

It's the first time I've done a DIY comp test, so there is a possibility I might have done something wrong

Dry test;

1 - 190
2 - 195
3 - 202
4 - 203

Wet test;

1 - 215
2 - 227
3 - 227
4 - 230

Is it just me, or are those figures pretty high? Or are they indicative of a healthy motor?

[Babalouie]

Those look fine to me and pretty good really for a 200k+ motor.

The results are pretty even (w/in 10% variance) and the wet figures are only 15% above the dry, which is fine.

Mazda factory manual says comp when new is 190 and when buggered and in need of a rebuild is 130. That gap between dry and wet is greater than 10%, so what that shows is a little ring wear (but only a little), and overall the figures are quite high due to carbon buildup in the combustion chamber.

So all in all, a very healthy motor I would surmise, and in much better shape than I would have expected for the miles. What power did it produce?

[brenno]

Thanks Kevin. That's good to know. I figure that even if my guage is reading a bit high, the variances are OK.

I read in an old post that your motor once had around 130 psi. What was causing that?

Here's the dyno chat;



What do you reckon?

[Babalouie]

I read in an old post that your motor once had around 130 psi. What was causing that?

...the fact that it was rooted after years of motorsport and drift events

Your power seems perfectly normal for a stock NA8, so it seems in pretty good nick. Mine was reading 130~160psi dry (so miles more than a 10% variance) and wet results were 160~190psi (so about a 30% increase). It was all in the rings, the head was in fact, just reco'd.

[SuperMazdaKart]

ooo, my 1.6 is nearly matching that dyno figure, 65.1kw

[StanTheMan]

yea but he still probably got more torque
you'ver also got a CAI and extractors
mine came in at 74RWKw but in reality is probaly more like your engine in reality.
It would be interesting to put both all 3 engines on the same Dyno on the same day.

[SuperMazdaKart]

when it did that figure it only had the extractors, & was on BP Ultimate (no timing bump though).

2nd time did 63kw, with also that CAI & extractor wrapping, regular unleaded. no gain though, different dyno different day.

think i read a totally standard NA6 is meant to be 58kw & NA8 with 65kw?

[StanTheMan]

mine had 64.7 with timing bump & snorkel removed.
so mine wasn't really stock standard. but pretty close

on that day. standard NA6's were anything from 58 -65Kw.
I just can't recall figures from the NA8's it was in 2001