RX8Club.com - Help on compession test please

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Help on compession test please

Hi there recently in the process of buying a rx8.. Went to compression test and found out rotor 1 : 5.6 and rotor 2 : 5.0 ... Is that okay? Advisable to buy? Or need rebuilt??

Quote:

Originally Posted by thevan (Post 4246166)

Hi there recently in the process of buying a rx8.. Went to compression test and found out rotor 1 : 5.6 and rotor 2 : 5.0 ... Is that okay? Advisable to buy? Or need rebuilt??

They didn't do the test correctly or they are not providing you with all the data you need to make a proper assessment.

Basically you need 8 values

Rotor 1 you should have 3 compression values and one RPM value.
Same for Rotor 2.

A compression value for each face of the rotor and an measured RPM value.

That being said, Sorry but the numbers above are meaningless without the RPM value. Well they are meaningless for more than that but that is the most important one.

The average value of rotor 1 is 5.6 and rotor 2 is 5.0 ... Rpm i did nt see it.. But car start smooth

Quote:

Originally Posted by thevan (Post 4246320)

The average value of rotor 1 is 5.6 and rotor 2 is 5.0 ... Rpm i did nt see it.. But car start smooth

Doesn't matter in the slightest.
You need the rpm.

First of all ... what year is it?
The 2004 and 05's came with a slower weaker starter that would result in lower compression values during the test.
The 06 models and up had a faster improved starter that would yield higher results.

If those numbers are from an old starter turning the engine you "might ... MIGHT" be ok.

If its from a new starter, the engine has already failed.

For you mean value of 5.0 the engine would need to be turning at 175 rpm to achieve a normalized value at 250 rpm of 6.9 and that is just barely a pass.

Look at post #6 from this thread, actually you should read the entire first page
https://www.rx8club.com/new-member-forum-197/new-potential-owners-start-here-202454/

Other stuff on compression
https://www.rx8club.com/series-i-tech-garage-22/help-rotary-compression-math-231810/

https://www.rx8club.com/group-buy-center-85/tr-01-rotary-engine-compression-tester-official-group-buy-172238/

Quote:

Originally Posted by wcs (Post 4246328)

Doesn't matter in the slightest.
First of all ... what year is it?
The 2004 and 05's came with a slower weaker starter that would result in lower compression values during the test.

FYI: There is a TSB out to replace the slower starters on the early cars, so the year alone is not sufficient for these cars.

Unless the motor is turning REALLY slow...anything in the 5's is not good ;)

Its a 2004 year model

Rpm hw to see it? Its just a pressure gauge as in utube.. I can only see the compression pressure value

You need a specific rotary compression tester to get the most accurate readings.

Quote:

Originally Posted by dannobre (Post 4246414)

Unless the motor is turning REALLY slow...anything in the 5's is not good

+1 agreed

Quote:

Originally Posted by thevan (Post 4247110)

Rpm hw to see it? Its just a pressure gauge as in utube.. I can only see the compression pressure value

Wait? Huh?

Quote:

Originally Posted by shadycrew31 (Post 4247131)

You need a specific rotary compression tester to get the most accurate readings.

The OP's obviously not read any of the links I gave him.

Who's doing the compression test here?
Some pal that works at a piston Garage or a Mazda Tech?

PM from the OP with my response.

Quote:

Originally Posted by RIWWP

Quote:

Originally Posted by thevan

Engine compreSsion test please

Hi there, what hwppened is that i buying a rx8 and went for compression test to a mazdaspecialist. He uses analog pressure gauge and what reading it shows is that 5.6 front and 5.0 back... The reading is average of three readings.
Is the engine in gud condition. Many saying low compression engine might blow off need to rebuilt.. But the owner just rebuilt in 2010 and asking for ur advice dude.. I loved the car and ready to be a rotary guy

This is largely illegible, lacking proper spelling, punctuation, and grammar. It's rather disrespectful when you want help from someone but aren't willing to put in enough effort to actually communicate your question clearly and articulately.

From what I can decipher, you are wondering if your compression is good. Check out this thread: https://www.rx8club.com/showthread.php?t=202454

Specifically post number 6.

It answers your questions, as well as giving you 3 reasons why your numbers don't mean anything.

I'll give you 1 reason:
1) The chart text indicates that there is an acceptable limit in the difference of compression from one rotor face to the next. Without each of the face's individually, you can't determine this difference value to know if each of the 6 possible pairs are within bounds.

See if you can determine the other 2 reasons why your numbers don't tell you much.

2)
3)

Just as an FYI.

He clearly isn't willing to read at all, having only gotten through my thread far enough to see my name.

Didn't see this thread earlier.