Scracho

Alright I need some help on this. I have been trying to get an idea as to what "normal compression" should be on a 13B Turbo II. I ask this because I have had some conflicting inputs. I know that I can take my TII to Mazda and have them use their funky tester and pay $75CAN for it, but I've heard that a conventional Compression Tester can be just as effective. I have read the Hayes Manual and they say to perform this test on a warm motor by inserting the tester into the Trailling plug hole with the throttle wide open; now disconnect the CAS and remove the fuse for the Fuel Pump; then turn over the motor using the starter. According to them normal or good compression should read 85-90PSI. I have tried this and I get several bounces over 90PSI on both rotors. But I started doing a little more research and I have read that it should be 125-150PSI. Which is true? I would like some input; maybe even your own compression tests results.

Erik

anything over 90 psi is good on a turbo2 motor

the 125-150 is what an n/a should be at (non turbo)

hope that helps

Scracho

Thanks I figured as much. 87 TII 8.5:1 Comp. N/A 9.5:1

black7

Anyone have the specs for the rest of the cars? Like 86-88 NA and 89-91 NA? What is good? What PSI means time for a rebuild?

Snufelupogus

iTrader: (2)

I recently got a rebuild on my 88 N/A and it was showing 45psi in the front and 70psi in the rear... I am told that the optimal for my car is like 125psi but with the rebuild it should be a bit lower because of used housings, but I dont think its supposed to be THAT low!
One guy (that I trust with my car) tells me that with that compression there is NO way that the engine will EVER start, and another guy tells me that it will run fine and the compression will be fine after I let it run for aboot 30minutes.
Is there any possible way to get the engine started with that low of compression? because Ive tried everything including push start in 2nd @ 30km/h! and NOTHING!

Thanks guys!

hypntyz7

Anything under 90 psi on any rotary is about dead. No matter what year or what compresison rating the rotor faces have.

Per teh FSM for s4 and s5 cars, there is no difference in compression numbers for turbo adn nonturbo rotaries...85psi is minimum acceptable for engines, and 125 is closer to new.

You guys are thinking about compression *ratio*...I dont know how to explain teh difference, and how they relate to each other, but one is like static compression and one is dynamic compression. ONe is a measure of how tight the combustion chamber is sealed, and that's the number youre interested in. The other is, well, (someone may correct me here) more of a measure of the rate of compression per the dish on teh rotor's face(or dish/dome on a piston engine).

You guys are right that these engines have different compression ratios...t2 8.5, na 9.4, s5 t2 9.0, s5 na 9.7:1 respectively. But the overall value of how tight the chamber is sealed by the seals(apex seal wear) is what you are looking at when you use a psi gage to check compression, and it should be between 125psi(like new) and 85psi(nearly dead).

They are right...a rebuild using old housings will be real low on compression to begin with. Especially if you test it dry...remember, the engine has to have run under load before the OMP injects any oil into the chambers, which is required for good compression. I'm not saying to dump any oil/atf in there and then test it, that is a way to get an excessively high reading form a worn rotary...this is why I dont trust jspec compression readouts.

The last one I rebuilt with decent housings gave me 60 adn 70 psi...after its first day of running at idle, both chambers showed 90psi. Last I checked, after 300 miles it went up to 100. After full breakin of 2-3000 miles, it will reach 115 or above depending on the quality of your used housings. That is really the key to how tight a motor will be.

Funklord

if you didnt get it done professionally then dont take the numbers too seriously. i compression checked my car in my friends garage with his cheap compression tester. i got about 70 psi on all rotor faces and my car runs like a champ. the biggest thing to look for when you do it yourself is even compression across all the faces.

Snufelupogus

iTrader: (2)

The engine was rebuilt by a respecable RX-7 shop, so... The HIGHEST compression in the front rotor was 45psi and the HIGHEST in the rear was 70psi.
I towed the car over to their shop last night and the guy said that he WILL get it to run... My guess is that he thinks Im an idiot and hooked a bunch of crap up wrong.

hypntyz7

I dont think there's much wrong with that endine other than the fact it hasnt run yet. All it probably needed was some help getting started and it would have doubled in compression. But, Im not there so I cant say for sure.

Oh, and for the guy who said compression numbers arent accurate, Ive figured out how to conduct the test and read the gage to rival teh factory compression tester.

Josh Blair

I just got my compression test results on Thurs. for my 88 10th AE TII with 110,323 miles on it at the time. I got it done at a Mazda dealership with one of their fancy rotary compression testers. It read:

1st rotor(psi)- 94-97-97 2nd rotor(psi)- 90-91-96
(kPa)- 6.5-6.7-6.7 (kPa)- 6.2-6.3-6.6
I wasn't sure about these so I called up AIM Tuning in Indianapolis. The guy told me that these are good and that a variance between them is normal. He said your car will run on compression as low as the 4 range in kPa. Basically he told me I should just rev the engine for a while and that should clean up some of that buildup. Or use ATF. I think I'm gonna stick with how it is for now, get another test in 6 months and if it's getting lower then use ATF.

Bambam7

I just checked mine... I get about 102 on the back rotor, and just 108 on the front.
This is a 1 year old rebuilt engine, with 3mm seals. I was told my compression would be slightly lower with the 3mm's....

rxseven

The max compression I get with a regular tester is 105 and 100 psi. This is on a GSL-SE motor with 3mm seals and 180,000 miles. I am beginning to think most of these rebuilds with old housings are not worth the money in terms of power output. Seems like you would get the same result from a cheap do-it-yourself kinda deal with the bare minimum package that atkins offers.

Scracho

Thanks again guys for the input!

The Ace

Just to add Europe's version: my own '92 TII is supposed to have 9:1 CR when brand spanking new. Thats 9bars all around, or 130psi. Right now I have 8,1/8,0/8,0 front, and 8,0/7,8/7,9 rear, which is between 115 and 120psi.

Anyway, these are the numbers for the Euro spec TIIs. Same thing goes for JSpec I suppose....

EDIT: And something that my mechanic told me. Anything below 7,5bar (110 psi) is considered low. Anything below 7bar (100 psi) is considered dangerously low. If you drop below 90psi, its time to call it quits

Scracho

Well now I'm really confused. Why would Hayes claim in their book that 85-90 is normal on a warm motor? I have read all of your posts (which BTW thank you) and I'm not sure whats accurate. I think that I should really take it to Mazda, but I'm affriad that they might tell me I need a rebuild. Anyways the car runs really good and pulls really hard. So on that note I'll just drive it till the day it won't start!

88TurboII

I would really be surprised that an engine with 40/70 compression front/back rotor would even start! I tried rebuilding my 13B without success a couple of years ago. Could start the car with a push, but it ran bad, made the pre cat glow bright red, and didn't want to idle. I messed around with it for several days, and couldn't get it to run right. Took a compression test by pulling the pulling the valve on a normal compression tester and got approx. 60 psi on all three faces each rotor. Enough to run poorly with a push start, not enough to start on its own. I finally bought a jspec motor that's been runing like a champ. I got so disgusted about not really knowing what my compression was I bought used Mazda tester off ebay for over $500. I tested it with an air hose to see if it worked, but have never used it in the Turbo II because my motor starts, runs, doesn't flood so there hasn't been any need so far.

jreynish

iTrader: (2)

how do you modify a cheap compression tester to work on the rotary?

rxseven

Haynes alos tells you to use the cheapo tester. If you just hold down the release button and get 3 bounces of 85-90 psi, you are in good shape. if you don't hold down the button you will get a max reading after 3 bounces. When people talk about 125-130 psi with a regular tester, it is this max reading. As an example, my GSL-SE motor gives me 70 psi even bounces and has a maximum reading of 105-110psi. It starts in a couple of seconds and runs like a champ.
Also, try testing in the leading plug hole rather than trailing as suggested by haynes. You should have a higher, more accurate reading but still not the same as the Mazda tester.

TurboHead

I to am concerned about my compression. Mazda says it is low AND strange! Strange because of the huge difference in pressures. Anyway, all here have made good points BUT I have not seen anyone mention ALTITUDE!!! That seems to be a big player when checking compression!! I don't know the specs, but you subtract x-amount of compression (in your reading) per one thousand ft ASL in altitude. Mine will read MUCH higher (I am in Colorado at 6,000 ft.) in, say Texas than it will HERE! Something to think about! Don't be like me and worry about it all the time though cause face it, when it's dead, it's dead!

Scracho

I was thinking of using the Leading hole as apose to the Trailling. I couldn't understand why they suggested the Trailling. Anyways I'll try that but I still think it's going to be around 100-110 maybe.

I was thinking of doing the ATF treatment, but I had heard that this is only a temporary fix and dosen't revive my motor; just gives it temporary compression.

Bambam7

You won't get an accurate reading by just HOLDING down the check valve release.... unless you can seal up the release output.

You need a compression tester with a check valve you can completely remove.
It's easy enough to do anyways... on most cheap ones, the valve is attached to the hose (not the gauge), if it's not removable from the hose, just CUT IT OFF! Seriously, and just use some standard NPT fittings (for air compresors, gas lines, whatever) and a couple hose clamps to make it removable.
This is the ONLY way to get an accurate reading with a standard gauge.

ViperDude152

the above is just like saying..."overheating a rotary means death, time for a rebuild" WRONG!!!!



Why are people saying this? this is not true at all.

80-100psi is where you will see a good running motor. below 80 you can still have a running motor. maybe not as much power. but it will still run. I have 85psi in my motor. it runs likes its brand new. S4 n/a should be around 80-90psi (roughly) s5s should be around 90-100psi. I have never seen a rotary at 125+ psi. altough im sure it has happend

on a BRAND NEW rebuild with all nwe housings.. after the breakin period they will get 100+psi on a s5 motor. on a s4 they get aroun 90+ some actually do get 100psi.

ViperDude152

holy crap. old thread... lol.

opps. sory for bring it back. look what happensd when you get into sometine. hmm