Technical discussion: lower compression on front rotor vs. rear rotor
 

Results from the 10 compression tests done last weekend at the meet point to the fact that in all cases, the front rotor had lower compression values than the rear.

This certainly cannot be explained coincidence or whether the engine was built on a Monday or a Friday.

So why do you guys think this is happening? Let's discuss...

My front rotor actually scored higher than my rear, however this is the cars second engine. Not sure what to make of that if anything.

Maybe I got it reversed.... I don't remember exactly, but it was either all the fronts scored lower than the rear or vice versa...

WCS do you remember?

Footman we should try to get everyone to post their compression tests.

Now I've been thinking about this topic as I knew you had a bit of a thing for it.

I was trying to think if there was something that could induce this common ... result

All I can think of is that I always did the front rotor first as so that would make it a few degrees warmer then the rear when tested.

However it would also mean the rear had an cycle of "deflood" before getting tested

That all being said speaking with FazdaRX8 he recalls most engine failures to be on the front. There was another member present at the meet as well that says both his engines failed on the front.

I do think there is something to this but the analitical boyz will want their fill

i think most of the results from sunday were lower compression on the front rotor compared to the rear. Livelycorpse was the only exception i believe.


I can see flashwing is following this thread maybe he can give us some BHR knowledge :dunno:

IIRC the coolant from the radiator enters the rotor housing via the rear rotor on the cold side (driver side), exits out the front on the cold side and enters the hot side of the housing on the front of the motor (passenger side) and exits at the back of the hot side.

Consider hot exhaust gases travel away from the front...

I'm not sure about lubrication.

^ Can you post your numbers Ken?

How much psi difference are we talking?

I think you guys are over analyzing this waaaayyyy too much.

The fall outs on older series FC/FDs have lower compression in the rear rotor. It would be interesting to see and note the revisions made and maybe gather some correlation in between.

My results may be contrary to your hypothesis however I did find it odd that my front rotor results were all around 4 or 5 psi higher (3 or 4 when calculated to 250 rpm). Is this coincidence? Or perhaps something contrary was done during my test not done during others tests? I have no idea as I have a very VERY basic understanding of all this, just trying to examine with a critical eye.
Front 113 117 112 - 115.8 119.9 114.7
Rear 109 112 107 - 112.9 115.9 110.8

Per Mazda:

R1 6.6, 6.7, 6.5
R2 8.1, 7.9, 8.0

at 268 rpm

Not sure which rotor is which?

normalized to 250rpm:

Front rotor : 89.5 , 91.6 , 100.9

Rear rotor: 103.5, 103.5 , 102.5


Now that i look at it again i dont think my front compression is THAT BAD... its slighty below minimum i guess.

I guess no one has any ideas then... we're fucked....

this was done back when I was having misfiring issues with my car and found I had the incorrect ECU in my car. Had a Cali Spec ECU (Which I have laying around, WCS you have any use for it?)

http://i46.tinypic.com/21537o.jpg

welp.. compression was waaaayyyy lower in my second rotor then my first..... didn't matter though since the engine failed on all faces (spectacularly I might add).

I'm now going through the new break in period on the new engine/clutch.... can't wait or it to be over.

^ you already got your new engine ?!?! Man was that quick lol.

Did you go to scarboro ?

What dealership would you recommend to get the engine compression tested.
Any idea on the failure rate and resulting engine replacement?

Cheers...

Congrats on the new engine Rev... welcome to the 2nd engine club :)

.. and yes... it really does feel like getting a brand new car again!

i want my new engine but im scared they wont honor it cause i dont have maintenance records from the previous owner :|

well looks like i will be joining the new engine club too. mazda approved the replacement today. will post compression results when i get them.

Do ALL dealerships ask for ALL the maintenance records ? Cause i only have the records since i owned the car. I do not have the previous owners maintenance records. Will this be a big issue ?

IT shouldn't really matter. The compression test procedure, and all of the other steps are standardized and done through Mazda Canada.

Danka. It's hard having to roll around under 4k. I had a new clutch installed as well seeing as how the springs were pretty much dead in the OEM.

Nice... sorry for the added wait ;) Looks like we'll be on level ground soon then.

Yes, new clutch and new flywheel too. Since I still have manufacturer's warranty left on this engine, I didn't want to chance with a RB flywheel. Though once the warranty is out, that's what I'll be doing. The flywheel comes with the engine block.

I drove almost 2 months below 4000 rpm... it's tough!

Sorry for posting my results so late. But believe it or not this is the first time I noticed this post.

Front Rotor 114 119 121 Corr. Factor 118.5 123.6 125.7

Rear Rotor 118 118 122 Corr. Factor 122.6 122.6 126.8


Normalized to 250 rpm

Front Rotor 111.3 116.4 118.5

Rear Rotor 114.0 114.0 118.3