Fumanchu

I am buying a 94 FD touring with 83,000 miles on it. The turbos have been replaced recently but I was skeptical on the motor having that many miles. I had the owner do a compression test and it came back like this...
Rotor 1: 85.3, 85.0. 85.0
Rotor 2: 82.5, 81.5, 80.5

From what I have read on this forum, these are very good numbers especially for 83k. When, if I take good care of the car would my engine go out? What are the compression numbers stock? I know you can't say for sure but in ballpark firgures. Just so I know so I can start saving for a new motor.

Any answers would be appreciated.

BoOsTin FD

Those Are good numbers for that many miles on the engine. If you take good care of it and do reliability mods, and change oil, flush the radiator you should be fine. Just don't let it overheat and do a fan mod as well.

Nathan Kwok

Those numbers are a little borderline but since the differential is so small, I wouldn't worry. The differential is the more important number imho. The new spec is 120psi but I don't have a scan of that, here is the scan from the test procedure:

vosko

iTrader: (4)

that is a little low. 100psi is good although it can run fine with 85psi. it just means the motor is old.... it will need a rebuild soon

Fumanchu

Everywhere I read on these forums, 6 is bad, 7 is ok and anything over 7 is good. ****, now I dont know what to believe. I thought 9 was brand new.

Anybody else want to give me an opinion???

DaedelGT

different measurements

Fumanchu

Just read on a site that said stock specs and it should be from 9.0 to 1 from the factory.

Has anybody gotten there compression tested in the last year...what are the numbers????

DaedelGT

Steve Kan compression tested mine when I got it a few months ago and he told me I scored 8s on all 6 faces. I believe the max possible is 9 kg/cm or something like that? I can't remember the units.

Fumanchu

That sounds more on the money. Are there 2 different measures that people are using or is it all the same? I just found out that the reading I had done was using kgf/cm^2.

psi= pounds per square inch
kgf/cm^2= ???? Im a freakin Sociology major!

DaedelGT...is ur motor healthy?

Anybody else done the kgf/cm^2 test? Obviously the different tests would yield different results.

Nathan Kwok

kg/cm^2 = kilograms per square centimeter. Its just a unit of pressure like psi is.

Minimum spec is: 6.0kg/cm^2 = 85psi
New spec is: 8.5kg/cm^2 = 120psi
Compression ratio: 9.0:1 (unitless)

C/R does not change, you are measuring dynamic compression not compression ratio. JDM, the numbers you posted cannot be in kg/cm^2. Sure you have the decimal right? It looks like typical psi readings.

Fumanchu

Im a Sociology major...I dont get it. What does that mean for the numbers i got?

Rotor 1: 85.3, 85.0. 85.0
Rotor 2: 82.5, 81.5, 80.5

So the top number I could have is 90.0?

Freakin confusing...can u clarify it for me alittle more. Thanks

t-von

iTrader: (8)

Ive got 3 engines I want to check (91 vert,94fd,&20b) but, I'm to cheap to go to Mazda and spend 100.00 a pop for the testing. The 20b will have to wait until my install. Anyways could I use a regular compression tester and just watch the needle bounce and get a reading? If so, what psi should I be looking for on my gauge? I know the readings from the 91 NA will be differant from the Fd because of the differances in compression ratios.

DaedelGT

JDM, that looks like they were using PSI as their units in that compression check. They also look pretty decent. Having the numbers be very close to eachother is more important than them all being a little low (which they are). The motor will need a rebuild soon, as vosko said. Those numbers indicate how much pressure the seals on on each face of the rotor are able to hold.

y2kz3

I just bought an 89 GXL (non-turbo) with 57,000 miles from original owner with new tires and recent tune-up. Mazda did a compression test with my 60,000 mile maintenance at my request, and the numbers are:
Front rotor: 9.4, 9.8, 9.2
Rear rotor: 9.7, 9.3, 9.2

I'm not interpreting the numbers, just posting them for reference. A 14 year old car can score over 9.0, so factory must have been even higher than my numbers.

The test cost me $72.00, but gave me peace of mind with what I bought since they told me this was within factory spec. It looks beautiful, but I had to know if anything was lurking. This thing is MINT and I'm pretty happy with my purchase at $4,000. It's loaded, and looks new inside and out.

racer1

120psi is max from factory. 85psi = 6 which is bad so yes you'll need a rebuild soon

damian

iTrader: (2)

i tested mine and got all 8.0 on one rotor and and all 7.9 on the other...this was with the old analog tester...so ur telling my my motor needs a rebuild?, im confused... steve kan told me that was good readings, and my car runs strong (49k miles now).

vosko

iTrader: (4)

6 is the minimum acceptible... it is low but acceptible
7 is good
8 is better
9,10 is amazing

SPOautos

Ok, your readings apear to be in PSI. Remember in one of your posts you said this.....

"Everywhere I read on these forums, 6 is bad, 7 is ok and anything over 7 is good. ****, now I dont know what to believe. I thought 9 was brand new."

Well, your PSI numbers translate into a 6ish

STEPHEN

damian

iTrader: (2)

ahh yes, thanks for the clarification vosko

Fumanchu

SPOautos...they arent in PSI.

Damian...half the people on here dont know what they are talking about. Our compression numbers are fine. Lets prove em wrong and show em our motors will last another 40k. Plus I believe Steve Kan over anybody on here

Vosko... Thanks, your right.

SPOautos

Well if they arent psi what are they then???

they arent kg/cm^2


What does Steve Kan have to do with this??? He told Damian that his 8.0 was good...well it is but that has NOTHING to do with your 80's numbers. 8.0 and 83.0 are 2 totally different types of readings. Damians 8.0 would be about 113psi NOT 83.0 like yours

STEPHEN

Fumanchu

Why wouldn't they be SPOautos?

SPOautos

Cause kg/cm^2 would be just one number then a decimal then another number like this.... 8.0

HOWEVER

PSI would be 2 numbers then a decimal and another number like this..... 83.5


Where was it tested at???? More than likely the only place where you can get a kg/cm^2 reading is at a major rotary builder or at the Mazda Dealership.

Fumanchu

Dont know...the owner took it to a shop in LA somewhere. I am having me fax the actual paper right now to see.

Im gonna hold of on the arguing till I get the paper.

pluto

here're some clarification.

1bar = 14.7psi
1kg/cm^2 = 14.3 psi

so 1 bar = 1.02 kg/cm^2

depending on the units they used to measure your compression, you can get any of the following I mentioned above.

so 8kg/cm^2 will equate to 114.4 psi

If you're getting 85kg/cm^2, your compression will be 1215.5 psi. Even the pressure washer is only 1000psi so I agreed with SPO that your number is most likely psi instead of kg/cm^2