Whos Clever On Compression?
 

if a compression test reads 7.3 (AVERAGE) at 500 rpm what will it read at 200 rpm.

CAN ANYONE ANSWER THIS QUESTION!!!

:wallbash: :wallbash: :wallbash:

7.08 i think

I was thinking in the 5s any more ideas remember its 150% more rpm than normal, what do you base that on mate, its a lttle bit precise, is there a conversion table?

I dont want an exact awnser i just want to know if my car is crap

Sounds like pretty low compression to me. What kind of vacuum does the car pull at idle?

There is a RPM/compression conversion chart in the FSM. My question is how the heck did you get it to crank at 500 RPM? You must have one hot battery. Are you having hot start problems?

/\ lol or not alot of compression to slow the starter down

It starts from hot and cold after 1 second on the starter fine, i dont know how the bloke did it to be honest, he said something about teh engine having to rotate one more time to read 200rpm????? its pure mystery to me?? i bought the car on the basis that this bloke was telling the truth, he had a ginger beard and he used a proper machine to do it. Wierd hey, my car goes like stink id just like decent awnser,

where can i get this conversion chart?

would hot starting problems signify a poor compression engine?
as this is the same hot and cold

.

compression VS cranking RPM & altitude
 

See page c-10 of 1994 FSM.

Sounds like the guy who conducted your test didn't know what he was doing. If you extrapolate 500 rpm from this chart, it looks like your 7.3 at 500rpm is akin to a 2.5 or 3 at 250 rpm, which is so low the car shouldn't want to start. Your results are probably inaccurate.
https://www.rx7club.com/attachment.p...hmentid=215655

dang big drop in just 300rpms

I was thinking in the low 5s,
But 2.5 is just awful isnt it, the car wouldnt start,
The oil pressure when hot at idle sits between the 2 markers with the large gap between then as i accelerate it goes to around 6,

what other signs are there of poor compression?

Thanks for the chart btw, my car flies and was supposed to have had a rebuild 1 year ago (dodgy hand written reciept)

Oil pressure has nothing to do with compression.

Other signs of poor compression? I asked you (twice) what your vacuum was at idle, and you never answered. Perhaps I had a reason for asking ;)

Idle? He cant start the car :)

From what I've read, if you have poor compression it will be more difficult to start the car once the engine is warm.

He says in post #8 the car starts fine :confused:

There is a difference between having low/poor compression verses having a blown engine. Typically a blown engine is the one that shakes (as you typically only have one rotor making any real power).

Low compression motors typically just don't have the same amount of power as a higher compression motor but they still run. However, that also depends on how low the compression is as obviously there is a point that the engine doesn't have enough compression to run.

ahh shaking stevens! i suppose the only real way to tell is if i get the compression done again.

How do you quantify shaking? i mean they all shake

Do you mean perhaps at idle a rocking of 1cm perhaps, makes sense to anyone?

my car is running .8 boost, fmic, and exhaust, intake mods, idles smooth at 900rpm and does 0-100 in 10/11 seconds 320/350 brake, the only signs of poor engine is it takes 1 too 2 secs to start the car from hot or cold, my last one was "on the button" so to speak

vacuum????? wheres the gauge????? sorry i didnt understand

Ideally yes. It sounds like the original compression test was somewhat flawed.

Have you ever seen the machines that mix gallon sized paint cannisters? If you engine shakes like that, you have a blown engine (not just low compression).


How are you reading your boost? Is your RX-7 a late enough model where it has the boost gauge in the dash?

ooops! :uh:

maybe you're just nosey! my vacuum is in the closet!

Dang, thats some serious shaking action!
On the flip side, I think you can take it to Mazda, they seem to do reliable compression tests. Though don't get anything fixed by them is what I hear.