Hi,
Just received results from compression test done at Mazda dealership. The car is a 1994 with 57,000 miles and I'm about to purchase it. Here are the results

8.6, 8.8, 8.5
8.5, 8.9, 8.5

These numbers sound awfully high for a motor with 57,000 miles don't they? I thought 8.5 was the spec for a new motor. Think test was performed properly?

What are your thoughts guys?

Thanks

 

They are fine I'm sure. Different testers give a little bit different results. Depending on if they had the newer digital type or the older all mechanical type... they could have had the 0 calibration a bit off too. Looks like those results are good to me.

Brian

 

those results are very great if they are accurate.

 

Even if the absolute numbers are slightly high due to a calibration error, they are pretty consistent from chamber to chamber and indicate healthy apexes.

Things like crank speed, humidity, engine temp (warmed up), and air temp can also affect compression results. Crank speed should have been adjusted for, and the other variables shouldn't have a major effect.

Dave

 

It's impossible to have that compression on a engine with 57,000 miles, engine has either been rebuilt, equipment is off, or the car was not warmed up properly.

rgd

 

Yoy say it's *Impossible*. Why is that?

Thanks

 

Impossible? I doubt it.

That is very good compression. I've had compression numbers that are similar for a 37K mile motor. Mine were in the high 8s with a 9.0 thrown in there.

New motors typically have lower compression until they are broken in for a few 1000 miles.

 

Those numbers aren't impossible, but I would guess they were done cold instead of hot, which results in higher numbers. A list member tested his car hot and cold and returned almost exactly 1.0 kg/cm^2 higher in every chamber in the cold test. Even if done cold, those numbers are still very good and you have nothing to worry about. If you are curious you can call the dealer and confirm 1. unit of measurement (believe it or not someone reported a dealer that converted the readout to a 1-10 scale), 2. cranking speed, 3. cold/hot.

 

Motor probably is new. Mine had about the same compression with 20k on the new engine.

 

Let me dig up my original compression numbers. They were from 50,034 miles.

9.5 9.6 9.3 244RPM
8.7 9.0 9.0 243RPM

That's from Mazda, although I think new engines can only hold 9.0kg/cm^3.

Now Steve Kan did a compression check as well, but gave me some funky 8:1 ratio on all rotors or something like that.

 

if the engine was cold it'll be higher, and if it was cranking at like 300+ rpm it would be higher too

 

9.6 ??? and with 50k??? defintely not possible


rgds

 

That's what I said

 

In relation to those #'s, what would do you guys think he would see with a qauge needle type tester(psi)?

 

Thats real good. If i recall correctly the compression is supposed ot be like 9 or 9.5 to 1 but they are never that high. Like others said, many factors will affect compression. If the car feels strong, then appreciate it.

 

Those are great! Mine were 6-7 across...Now I got a new motor

 

Double post.

 

You are thinking of two different things. The compression ratio (#:1) and compression (# psi, or # of other unit of pressure) are two different things.

 

Hey oneptthree,

Have you decided to buy it yet? I will probably take a look at it in a few days if it hasn't been sold yet. How does it look? Any noticable dings or scratches that you picked up on? Any wear on the interior?

Thanks!

 

yea there is nothing wrong with those numbers. Go for it and have fun with the FD.