79CI13B

What should compression readings be for FD
I just checked my compression on my FD for the second time since the 2 years I have owned it and it read
105 p.s.i (front)
100 p.s.i (rear)
What is the minimum reading until I should really start getting ready for a rebuilt?

pistons

RX7 RAGE

iTrader: (22)

Those are excellent numbers. Mine read 90 psi on both front and rear 2 years ago and it still runs strong.

79CI13B

So I must be in good shape

RonKMiller

Your numbers don't mean a thing.

The only way to tell if you have good readings is to use a genuine Mazda compression tester. There are two models to my knowledge, analogue and digital
(sort of...). The analogue is the better of the two and is an extremely rare tool. It prints a readout of each cycle on graph paper - like an EKG.

books

iTrader: (8)

Besides the fact that you can get a printout, why is the analog tester better than the digital?

RX7 RAGE. how many miles have you put on your car in the last 2 years, and what is your compression now?

RonKMiller

Yep, the printout is the only real difference. It's nice to have for record keeping purposes and gives you an overall "snapshot" view of the health... a seasoned expert (of which I am most certainly not) can take a look at the printout and tell you exactly what's up with the innards. Just like a doc reading an EKG.

Saves alot of guesswork and unwarranted rebuilds.
$1,640.00 for the "new" one plus an hour of time to hook it up and read it. It still gives you a graph.

Any one who does a "compression check" without out it is just blowing "cold" air and if they are charging you for diagnostics - is ripping you off.

79CI13B

So why doesn't the manual mention anything like this?

books

iTrader: (8)

on pages c9 and c10 of the shop manual, you'll see the procedure for compression testing...it does mention on c10 the sst and has an illustration of the tester connected to the number...I believe your numbers do indicate the maximum compression on each rotor...the problem is you have three chambers per rotor...so while 100 psi is a good reading..you really don't know what the compression is for the other 2....if you hold down the relief valve on the compression gauge, you'll be able to see the all 3...although they bounce rather quickly...the peak of each bounce needs to be within spec

RonKMiller

Well, actually - it does. On pages C9& C10...

79CI13B

Thanx I see it now

RonKMiller

Sure, you can watch em' bounce, but I would not make a decision on $5K worth of new engine based on a guesstimate. The other problem you have with standard compression testers is that they are notoriously innaccurate. Unless you get into the $200 plus range they often miss the mark by 5 or 10% - and that's a lot. The certificated testers that I use are calibrated to 2% maximum error. The average tester you pick up at an auto parts store is fine for checking your lawn mower engine, but that's about it.

sevenup

iTrader: (1)

Ron, what would the "old style" digital Mazda compression tester cost in used condition? If you where to find one .Just curious

RonKMiller

The "old" style is analogue. I believe it was first manufactured in the 60's. I've only seen one, and to find one in working order would be rare. Kind of like finding MacIntosh tube amps if you are a stereo buff. I have absolutely no idea what it would be worth - but ya never know!

The "new" style is digital - if you can call it that - since it has led's and all, but it was probably designed 15 years ago. Any good rotary shop has one as part of their standard equipment. If they don't - find another shop 'cause they are amateurs.

They both work great, but there is the nostalgia factor for the old school stuff these days.

If you do find one for sale and don't want to buy it let me know. I'll buy it and throw in a compression check gratis. Of course you will have to drive to Tucson!

whitekingsnake

I'm probably going to regret saying this, but I will because I think this info is pertinent to the RX-7 community. ( I hope my engine doesn't blow).

I got a new engine about 2 1/2 years ago and had dave at KD put in Hurley seals along with the silicone coolant seals and the ecc shaft mod.

I started the new engine up and it sounded great right from the git go. Only prob was the EGR valve. I drove the car 240 miles from Alabama to my house in Alpharetta, Ga ( 40 mins above Atlanta).

Taking it easy no boost and 80 all the way on the interstate. Filled her up and was getting 24.5 MPG. Yeah C'mon. Drove it easy still w/no boost untill 500 total miles. Changed oil and started giving it little boost and getting the revs up to about 4k max under no boost untill 1000k total. Changed the oil again and its been ***** to the wall.

I drive it every day and redline it at least 5 or 6 times. I have been back and forth from Atlanta to Alabama(250-300 miles) once or twice every month, I've been to Fredericks, Va 3 times and drive it everywhere in Atlanta.

My MPG are 16-18 driving hard, 17-20 hard and city, 20 -25 on the interstate. my compression from day 1 and still to this day is front 125-125-128, rear 125-125-128....@ 52,000 miles.

Hope you can find this info helpful in any way and I hope my car starts now.

Later....Scottl