9krpmrx8's Boost Build Thread
01-20-2014, 11:04 PM
#3751
SARX Legend
Thread Starter
iTrader: (46)
Damn it I deleted a long post, grrr.
Anyway, about 6 months ago we bought the Rotary Diagnostics compression tester. I have tested my car a few times with mixed results showing less than stellar readings. And then after I installed the new S2 starter and battery my results jumped way up to 112psi or so average. I was always skeptical of the huge jump even though I knew a solid cranking RPM from the new starter would improve the results.
So, then carbon8 offered to ship me his new twisted rotors tester to compare it to ours since he had gotten some low numbers on his 3,000 Pettit built engine (104psi or so average on the front and 95psi average on the rear).
I received it and this past Saturday we used both testers on three different RX-8's. One high mileage, one low mileage, and my boosted engine with 20,000 miles on it. The short is that there was about a 15-20psi difference (rotary diagnostics was lower each time) between the Rotary Diagnostics tester and the twisted rotors tester. My car showed and average of 94psi across the board consistently with the Twisted Rotors tester at 268RPM or so each time. That was not good but I refused to think my engine was low on compression because it starts fine, idles fine, and there is no loss of power at all. So just to be sure, I called my buddy who is a Mazda tech, and I met up with him to do a proper test using the dealer equipment. Well, basically we did 5-6 straight tests and we determined that the Rotary diagnostic is crap (ours is anyway), and that the Twisted rotors tester is off by about 10psi on average compared to the Mazda tester.
So, out of the 5-6 tests that I took with the Mazda tester, I took the last one when my cranking RPM was coming down due to a discharging battery. For the first 4 or so I was right around 270RPM but the car has not been driven all week so the battery was probably not a full charge when we started. The engines were all warmed up when we did all of the tests.
Any here are my normalized results from the Mazda tester.
http://www.flickr.com/photos/9krpmrx8/12063809776/
So, we will contact Rotary Diagnostics tomorrow and see what they say. But I will probably try and buy a Mazda tester.
Anyway, about 6 months ago we bought the Rotary Diagnostics compression tester. I have tested my car a few times with mixed results showing less than stellar readings. And then after I installed the new S2 starter and battery my results jumped way up to 112psi or so average. I was always skeptical of the huge jump even though I knew a solid cranking RPM from the new starter would improve the results.
So, then carbon8 offered to ship me his new twisted rotors tester to compare it to ours since he had gotten some low numbers on his 3,000 Pettit built engine (104psi or so average on the front and 95psi average on the rear).
I received it and this past Saturday we used both testers on three different RX-8's. One high mileage, one low mileage, and my boosted engine with 20,000 miles on it. The short is that there was about a 15-20psi difference (rotary diagnostics was lower each time) between the Rotary Diagnostics tester and the twisted rotors tester. My car showed and average of 94psi across the board consistently with the Twisted Rotors tester at 268RPM or so each time. That was not good but I refused to think my engine was low on compression because it starts fine, idles fine, and there is no loss of power at all. So just to be sure, I called my buddy who is a Mazda tech, and I met up with him to do a proper test using the dealer equipment. Well, basically we did 5-6 straight tests and we determined that the Rotary diagnostic is crap (ours is anyway), and that the Twisted rotors tester is off by about 10psi on average compared to the Mazda tester.
So, out of the 5-6 tests that I took with the Mazda tester, I took the last one when my cranking RPM was coming down due to a discharging battery. For the first 4 or so I was right around 270RPM but the car has not been driven all week so the battery was probably not a full charge when we started. The engines were all warmed up when we did all of the tests.
Any here are my normalized results from the Mazda tester.
http://www.flickr.com/photos/9krpmrx8/12063809776/
So, we will contact Rotary Diagnostics tomorrow and see what they say. But I will probably try and buy a Mazda tester.
Last edited by 9krpmrx8; 01-20-2014 at 11:10 PM.
01-20-2014, 11:14 PM
#3752
They released a tech update about a year ago detailing how a warm or hot test probe would cause a high reading. I will look for it.
Otherwise it us generally accepted to be one of the best testers in the industry and used by many pro builders.
edit: this is for the Rotary Diagnostics tester
.
Otherwise it us generally accepted to be one of the best testers in the industry and used by many pro builders.
edit: this is for the Rotary Diagnostics tester
.
Last edited by TeamRX8; 01-23-2014 at 02:17 AM.
01-21-2014, 12:41 AM
#3755
Registered
Good info to know. I know the owner of Twisted and I'll forward this information on to him as well. He's been asking me for updates on anyone that is using his product.
01-21-2014, 08:15 AM
#3758
Scott,
Of note all my test where done at operating temp, not sure what parameters your compared under.
I begin my testing when coolant hit 180-190 and by the time I finished coolant was still above 140. The TR maker instructed that all test be performed on a hot engine as you will get better numbers.
I never tested it cold though, so not sure how it compares exactly. I will have to normalize my numbers again and see where I'm at.
Thanks again for the comparison. Keep the tester as long as you need to finish up your work.
Of note all my test where done at operating temp, not sure what parameters your compared under.
I begin my testing when coolant hit 180-190 and by the time I finished coolant was still above 140. The TR maker instructed that all test be performed on a hot engine as you will get better numbers.
I never tested it cold though, so not sure how it compares exactly. I will have to normalize my numbers again and see where I'm at.
Thanks again for the comparison. Keep the tester as long as you need to finish up your work.
01-21-2014, 09:06 AM
#3759
Carbon, we did the test with a hot engine and we also tested both Leading and Trailing ports (there was no difference as expected).
Team, I assume you are talking about the Rotary Diagnostics....I received an update regarding the software installation but not anything technical
Team, I assume you are talking about the Rotary Diagnostics....I received an update regarding the software installation but not anything technical
01-21-2014, 09:31 AM
#3760
SARX Legend
Thread Starter
iTrader: (46)
Yeah we did these tests on hot engines. My coolant temps were 195F when we started and we even put the plugs back on mid way thru and let it warm up again. But at the end temps were about 170F, which according to my buddy is fine.
Last edited by 9krpmrx8; 01-21-2014 at 10:05 AM.
01-21-2014, 10:39 AM
#3761
SARX Legend
Thread Starter
iTrader: (46)
Okay, so I normalized the twisted rotors results from my engine. So that is an average of 96.92psi on the front and 95.88psi on the rear. So, that is a difference of 13.77psi on the front and 10.48psi on the rear when compared to the Mazda tester.
http://www.flickr.com/photos/9krpmrx8/12071493016/
Also here are the shots of the Mazda tester from the last 249RPM test. The screen on the twisted rotors device sucks ***** in the day light so I could not get a decent picture of the screen.
Front:
http://www.flickr.com/photos/9krpmrx8/12064260664/
Rear:
http://www.flickr.com/photos/9krpmrx8/12064174643/
http://www.flickr.com/photos/9krpmrx8/12071493016/
Also here are the shots of the Mazda tester from the last 249RPM test. The screen on the twisted rotors device sucks ***** in the day light so I could not get a decent picture of the screen.
Front:
http://www.flickr.com/photos/9krpmrx8/12064260664/
Rear:
http://www.flickr.com/photos/9krpmrx8/12064174643/
01-21-2014, 01:36 PM
#3763
SARX Legend
Thread Starter
iTrader: (46)
Yeah we have considered that idea but if we think like that then why test at all, 
. My buddy said they have tested a few that were in for oil changes and stuff just to see what a fresh engine does and that the couple of low mileage well running RX-8 they have done will see mid 8's tops.
. My buddy said they have tested a few that were in for oil changes and stuff just to see what a fresh engine does and that the couple of low mileage well running RX-8 they have done will see mid 8's tops.
01-21-2014, 01:45 PM
#3764
I am in communication with Rotary Diagnostics and one thing we did forget was to depress the gas pedal...ugh. I just did a test on the spare rx8 I have and the difference was only 3psi (no pedal vs 100% pedal). but this engine is only seeing 85psi so it may not be the best candidate. I will test my car this afternoon and see if a high compression engine yields different results.
01-23-2014, 02:11 AM
#3765
Operator error, should have known :-p
From July/2012:
From July/2012:
To all users of our compression tester systems (Rotary Diagnostics):
Recent testing has indicated a phenomenon that users of our systems should be aware of. It appears that if the Acquisition Units (i.e., pressure transducer/adapters) are connected to a thoroughly heat-soaked engine for say 15 minutes or more prior to a test, the resultant compression readings may be inflated by as much as 10-15 percent. Testing, therefore, should be conducted with the engine cold or slightly warmed up. That is, not operated extensively in an environment where high temperatures will be generated in engine components. Testing can be conducted with the engine cold, as long as it has been run within the previous few days and a normal thin film of oil remains on the internal housing surfaces. Testing conducted with our systems has shown that the compression readings do not differ between a recently-operated, cold engine and an engine warmed up slightly prior to the test.
If it is critical that a compression test be conducted on a very hot, heat-soaked engine, the user should take into consideration the likely inflated readings mentioned above.
If you have questions, reply to this message. Thank you for your business.
Recent testing has indicated a phenomenon that users of our systems should be aware of. It appears that if the Acquisition Units (i.e., pressure transducer/adapters) are connected to a thoroughly heat-soaked engine for say 15 minutes or more prior to a test, the resultant compression readings may be inflated by as much as 10-15 percent. Testing, therefore, should be conducted with the engine cold or slightly warmed up. That is, not operated extensively in an environment where high temperatures will be generated in engine components. Testing can be conducted with the engine cold, as long as it has been run within the previous few days and a normal thin film of oil remains on the internal housing surfaces. Testing conducted with our systems has shown that the compression readings do not differ between a recently-operated, cold engine and an engine warmed up slightly prior to the test.
If it is critical that a compression test be conducted on a very hot, heat-soaked engine, the user should take into consideration the likely inflated readings mentioned above.
If you have questions, reply to this message. Thank you for your business.
Last edited by TeamRX8; 01-23-2014 at 02:16 AM.
01-23-2014, 07:42 AM
#3767
wow....that would be good info to put in the manual... that was just before we bought it too. I think I will respectfully let Larry know its not part of my manual. I will say the tool is great but I would recommend to anyone buying it....GET 2 TRANSDUCERS 
Posted From RX8Club.com Android App
that was just before we bought it too. I think I will respectfully let Larry know its not part of my manual. I will say the tool is great but I would recommend to anyone buying it....GET 2 TRANSDUCERS Posted From RX8Club.com Android App
01-23-2014, 10:35 AM
#3769
Half of what you posted makes little sense. Now that I reread the OP for the 3rd time you are saying the RD tester is crap without detailing the actual numbers and providing any logical explanation to support your 'evaluation' of it.
The RD tester requires some effort to setup initially, understand how to use it, and evaluate the results. It is a bit of a pain, but in return you get detailed curves of the entire compression cycle for all three rotor faces. This is good for evaluating issues, internal modifications, and the broader overall compression condition. You can purchase additional sensors to test 2, 3, and 4 rotors all at the same time rather than do each rotor individually.
The other testers just spit out a simple peak number that is only a go/no-go indicator. You can use a standard reciprocating engine compression tool with the schraeder/check valve removed for this purpose, which is the lowest cost option. A new OEM tester is the highest cost option, $1800+
as with any tool, it just depends on what you are trying to accomplish. If all you want is a go/no-go indicator then why drop $350+ for one?
The RD tester requires some effort to setup initially, understand how to use it, and evaluate the results. It is a bit of a pain, but in return you get detailed curves of the entire compression cycle for all three rotor faces. This is good for evaluating issues, internal modifications, and the broader overall compression condition. You can purchase additional sensors to test 2, 3, and 4 rotors all at the same time rather than do each rotor individually.
The other testers just spit out a simple peak number that is only a go/no-go indicator. You can use a standard reciprocating engine compression tool with the schraeder/check valve removed for this purpose, which is the lowest cost option. A new OEM tester is the highest cost option, $1800+
as with any tool, it just depends on what you are trying to accomplish. If all you want is a go/no-go indicator then why drop $350+ for one?
01-23-2014, 10:39 AM
#3770
01-27-2014, 02:58 PM
#3771
Driving my unreliable rx8
Did you consider the size of the sensor probe? compare it to a spark plug in length and internal volume. Then compare them across the different testers.
02-22-2014, 09:01 PM
#3774
SARX Legend
Thread Starter
iTrader: (46)
So the car is down for the turbo rebuild, oil feed upgrade, and S2 trans and ACT clutch install and we pulled the trans today and ran into a weird issue. One of the trans PPF nuts was super tight, like two of us cranking on it tight. Well then all of the sudden it broke loose, So we had to remove it with the PPF attached.
http://www.flickr.com/photos/9krpmrx8/12709544505/
http://www.flickr.com/photos/9krpmrx8/12709609015/
So we had to remove it with the PPF attached.http://www.flickr.com/photos/9krpmrx8/12709544505/
http://www.flickr.com/photos/9krpmrx8/12709609015/
Last edited by 9krpmrx8; 02-23-2014 at 01:25 AM.