New Compression Tester, handheld and digital!!
03-31-2009, 11:47 PM
#102
Compression Tester Guy
Thread Starter
Join Date: Nov 2006
Location: Houston, TX
Posts: 93
Likes: 0
Received 0 Likes
on
0 Posts
Still here guys, sorry, had some RL stuff to take care of. Still looking for a real job. :-/
Work on the tester continues: I have received the final version of the prototype boards and they work great. Bought some cheap-o LCD's, the blue one actually looked really good but it would require some hardware and software changes to get it to work right. I "may" look into that in the future, but for now I'm sticking with what I know will work. Also got some sample cable strain reliefs in the mail today.
I don't have any new pictures or videos, so nothing interesting to show.
As far as testing goes....well, I still need to find an engine that has 2 low faces and 1 high, like a cracked apex seal. But I did test an engine that had 0 psi on 2 faces....the results were what I expected. In that situation the tester is unable to distinguish the 3 different faces so the 1 face that is good is what is displayed for all 3 readings. The RPM reading is also extremely low due to it calculating RPM based on time between pulses.
-John
Work on the tester continues: I have received the final version of the prototype boards and they work great. Bought some cheap-o LCD's, the blue one actually looked really good but it would require some hardware and software changes to get it to work right. I "may" look into that in the future, but for now I'm sticking with what I know will work. Also got some sample cable strain reliefs in the mail today.
I don't have any new pictures or videos, so nothing interesting to show.
As far as testing goes....well, I still need to find an engine that has 2 low faces and 1 high, like a cracked apex seal. But I did test an engine that had 0 psi on 2 faces....the results were what I expected. In that situation the tester is unable to distinguish the 3 different faces so the 1 face that is good is what is displayed for all 3 readings. The RPM reading is also extremely low due to it calculating RPM based on time between pulses.
-John
04-03-2009, 09:49 PM
#107
Super Moderator
04-03-2009, 09:59 PM
#108
Don't Tase Me Bro!
Join Date: Jan 2005
Location: CO
Posts: 239
Likes: 0
Received 0 Likes
on
0 Posts
this will be my next investment if its accuracy relative to the mazda compression tester is verified. its absolutely worth it if it meant we don't have to rip out all my modifications before testing. i want one asap. if you have a preorder list, sign me up.
04-06-2009, 09:37 AM
#112
Registered
Join Date: Sep 2008
Posts: 921
Likes: 0
Received 0 Likes
on
0 Posts
TwistedRotors and Nemesis, you guys should figure out a way of testing the same car with both of your testers. This way we can see if the Mazda Compression Testers results are similar to or even x+- off of Twisteds testers results. Jsut a thought.
04-06-2009, 10:09 AM
#113
Registered
I don't think it's absolute accuracy against the Mazda tester is relevant in any way. Close is good enough. Look at dynos. They're all supposed to measure the same thing but none of them measure the same in relation to each other or potentially the correct number for that matter. People just 'pick" the highest number and use it as their reference. I'm sure the same thing would be true here too.
04-06-2009, 10:58 AM
#116
Registered
Join Date: Sep 2008
Posts: 921
Likes: 0
Received 0 Likes
on
0 Posts
RotaryGod, the only reason accuracy is important is for engine replacements. If twisteds compression tester shows under minimum compression(meaning new engine) and the mazda compression test shows slightly above minimum(no new engine) then when you bring it to the dealer, you will have to pay $200 or so for the compression test showing you are within the correct compression specs. Being able to know if your engine has lower then minimum compression(even according to Mazdas testing) would make this tool very worth while. Then, you could go to the dealer with confidence that your engine needs to be replaced. Thats the only reason why I would like to see the comparison between results.
I'm a little impatient
04-06-2009, 10:49 PM
#119
Compression Tester Guy
Thread Starter
Join Date: Nov 2006
Location: Houston, TX
Posts: 93
Likes: 0
Received 0 Likes
on
0 Posts
lol, sorry Texak.....the hardware and software are done..finalized....but there is one test left. I really want to test a blown engine. Something with a cracked or chipped apex seal. There are videos showing successful real world tests of high and low compression engines, but none of a blown engine. Honestly, I'm getting just as frustrated as you are!
As for my tester versus the Mazda one, I'm not sure a definative correction factor will be possible. There are quite a few real world factors that can affect the readings. If you check your engine with my tester and it's borderline, then you'll have to decide if you want to risk taking it to the dealership or not.
I feel that the best use of my tester is going to be to watch how your compression changes over a matter of time. You can monitor the break-in period of a new engine or just check it each time you change your oil. That might be a little overkill....but at least you won't be paying ~$200 each time! :-)
-John
As for my tester versus the Mazda one, I'm not sure a definative correction factor will be possible. There are quite a few real world factors that can affect the readings. If you check your engine with my tester and it's borderline, then you'll have to decide if you want to risk taking it to the dealership or not.
I feel that the best use of my tester is going to be to watch how your compression changes over a matter of time. You can monitor the break-in period of a new engine or just check it each time you change your oil. That might be a little overkill....but at least you won't be paying ~$200 each time! :-)
-John
04-06-2009, 10:52 PM
#120
Compression Tester Guy
Thread Starter
Join Date: Nov 2006
Location: Houston, TX
Posts: 93
Likes: 0
Received 0 Likes
on
0 Posts
04-07-2009, 01:50 AM
#121
Super Moderator
lol, sorry Texak.....the hardware and software are done..finalized....but there is one test left. I really want to test a blown engine. Something with a cracked or chipped apex seal. There are videos showing successful real world tests of high and low compression engines, but none of a blown engine. Honestly, I'm getting just as frustrated as you are!
As for my tester versus the Mazda one, I'm not sure a definative correction factor will be possible. There are quite a few real world factors that can affect the readings. If you check your engine with my tester and it's borderline, then you'll have to decide if you want to risk taking it to the dealership or not.
I feel that the best use of my tester is going to be to watch how your compression changes over a matter of time. You can monitor the break-in period of a new engine or just check it each time you change your oil. That might be a little overkill....but at least you won't be paying ~$200 each time! :-)
-John
As for my tester versus the Mazda one, I'm not sure a definative correction factor will be possible. There are quite a few real world factors that can affect the readings. If you check your engine with my tester and it's borderline, then you'll have to decide if you want to risk taking it to the dealership or not.
I feel that the best use of my tester is going to be to watch how your compression changes over a matter of time. You can monitor the break-in period of a new engine or just check it each time you change your oil. That might be a little overkill....but at least you won't be paying ~$200 each time! :-)
-John
Ash
04-07-2009, 01:55 AM
#122
Registered
What is not important here is:
1. The accuracy of the device, that is the conversion of pressure into voltage. I believe these are 0.5% accuracy units which exceed our requirements (The Mazda manual talks about an overall accuracy of 2%).
2. Protecting the head. These are industrial units and capable of some pretty hard handling. They will be used infrequently, and, if they break, so what. Buy a replacement like you do for every other tool that breaks.
3. Comparison to the Mazda unit. What you need to know is what the Mazda unit does and what this unit does, which leads to
What is important:
1. The digitizing rate. If the time between individual measurements is too long, the peak will be missed. The result is a low measurement value. The Mazda manual talks about a measurement time of 0.5 ms. Is this supposed to mean a measurement frequency of 2000 samples/s? I have built my own unit using an analogue to digital converter with a laptop and use 1000 samples/s but a few hundred are probably OK.
2. The digitizing step. This gives you the resolving power of the instrument. In my setup, I detect a small fraction of a psi/step. From the You-tube video, it looks the resolving power of this instrument is about 1psi/step, which throws over 1% inaccuracy into the mix, but this is OK if that is what it really is.
3. Detecting pulses and keeping track of them so the numbers displayed always refer to their respective lobe. But this is just software and should not be a major show stopper. To test you don't really need a pressure input, you can input a repeating 3 pulse stream, each pulse of different amplitudes. This gives a lot more bench testing capability if you have the means to set it up.
4. Dead volume. This is important. If this is not properly accounted for, it can make all other references to inaccuracies moot. The air volume is compressed by a factor of 10 from about 650 cc down to about 65 cc. It is quite easy to get a dead volume of 6.5 cc. tied up in the instrument, which is about 10 % of the compressed volume. The indicated pressure is lower than what it would be if the instrument were not there. To get a more accurate indication of the true pressure under vehicle operation, we need to multiply our indicated pressure by about 10% in this example. My dead volume is more than that, but this instrument has reduced the dead volume to the absolute minimum. In comparing to Mazda, we need to know what corrections they make if any. It looks like they increase their pressure by 12.5% to compensate for the dead volume in their instrument, but the manual is difficult to interpret.
Twisted rotors: You've done some really nice and original work. It looks like you are probably going to get a lot of requests. How do you plan to get this thing into production, and, once you are satisfied with the instrument, how long do you think it would take to then get it into people's hands? Can you provide information on your digitizing frequency, and internal resolution?
Nemesis8: Thanks for that manual but it is not the easiest to understand. What do you make of the dead volume corrections if any?
1. The accuracy of the device, that is the conversion of pressure into voltage. I believe these are 0.5% accuracy units which exceed our requirements (The Mazda manual talks about an overall accuracy of 2%).
2. Protecting the head. These are industrial units and capable of some pretty hard handling. They will be used infrequently, and, if they break, so what. Buy a replacement like you do for every other tool that breaks.
3. Comparison to the Mazda unit. What you need to know is what the Mazda unit does and what this unit does, which leads to
What is important:
1. The digitizing rate. If the time between individual measurements is too long, the peak will be missed. The result is a low measurement value. The Mazda manual talks about a measurement time of 0.5 ms. Is this supposed to mean a measurement frequency of 2000 samples/s? I have built my own unit using an analogue to digital converter with a laptop and use 1000 samples/s but a few hundred are probably OK.
2. The digitizing step. This gives you the resolving power of the instrument. In my setup, I detect a small fraction of a psi/step. From the You-tube video, it looks the resolving power of this instrument is about 1psi/step, which throws over 1% inaccuracy into the mix, but this is OK if that is what it really is.
3. Detecting pulses and keeping track of them so the numbers displayed always refer to their respective lobe. But this is just software and should not be a major show stopper. To test you don't really need a pressure input, you can input a repeating 3 pulse stream, each pulse of different amplitudes. This gives a lot more bench testing capability if you have the means to set it up.
4. Dead volume. This is important. If this is not properly accounted for, it can make all other references to inaccuracies moot. The air volume is compressed by a factor of 10 from about 650 cc down to about 65 cc. It is quite easy to get a dead volume of 6.5 cc. tied up in the instrument, which is about 10 % of the compressed volume. The indicated pressure is lower than what it would be if the instrument were not there. To get a more accurate indication of the true pressure under vehicle operation, we need to multiply our indicated pressure by about 10% in this example. My dead volume is more than that, but this instrument has reduced the dead volume to the absolute minimum. In comparing to Mazda, we need to know what corrections they make if any. It looks like they increase their pressure by 12.5% to compensate for the dead volume in their instrument, but the manual is difficult to interpret.
Twisted rotors: You've done some really nice and original work. It looks like you are probably going to get a lot of requests. How do you plan to get this thing into production, and, once you are satisfied with the instrument, how long do you think it would take to then get it into people's hands? Can you provide information on your digitizing frequency, and internal resolution?
Nemesis8: Thanks for that manual but it is not the easiest to understand. What do you make of the dead volume corrections if any?
04-07-2009, 02:12 AM
#123
Super Moderator
Mazda RX-8 WS Manual on Compression Testing
TwistedRotors
Here is what is in the 2009 RX-8 Workshop Manual on Compression Testing...
Thought some of the 'figures' may help..
Ash
Here is what is in the 2009 RX-8 Workshop Manual on Compression Testing...
Thought some of the 'figures' may help..
Ash
04-07-2009, 08:29 AM
#124
Registered
Join Date: Sep 2008
Posts: 921
Likes: 0
Received 0 Likes
on
0 Posts
See, I feel that knowing how accurate this tool is would be beneficial. One would assume that the Mazda tools are the most accurate or atleast the numbers that we should base our results off of. If this device gives us a completly different number then Mazda's tools, it would be pointless and you might as well be doing a compression test with a piston engine tester. Even with a piston engine compression tester, you can watch how the compression changes over time(just not the standard numbers you should be receiving). Just because one claims it is the most accurate, how do we know? Where is the comparison? If one does not know how Mazda calculates compression for the roatary engine, how do you definitavely calculate the correct compression for the rotary engine?
Mazda has been working with the rotary engine for 40 years. Comparing these two devices is a must. It would be very beneficial to know if you are eligable/non-eligable for a new engine instead of using this device, getting a low number, bringing it to Mazda, then being chaged $200 for a test that passed. It really boggles my mind why you WOULD NOT want to compare these devices. Do you not want to spend the time/money to get the most accurate numbers possible? I appreciate everything your doing, but if it cannot give a result that Mazda can replicate, its pointless.
Mazda has been working with the rotary engine for 40 years. Comparing these two devices is a must. It would be very beneficial to know if you are eligable/non-eligable for a new engine instead of using this device, getting a low number, bringing it to Mazda, then being chaged $200 for a test that passed. It really boggles my mind why you WOULD NOT want to compare these devices. Do you not want to spend the time/money to get the most accurate numbers possible? I appreciate everything your doing, but if it cannot give a result that Mazda can replicate, its pointless.
04-07-2009, 11:46 AM
#125
Delmeister, I have read it several times, and it is very confusing at best. I have no comment on the dead volume issue. All I have is a baseline compression test at 75K on my motor with this Mazda tester. I have been attempting to bring my compression back up with LC FP+, BG44K, and Seafoam. I will test again this weekend to see where I am.
I think anyone who purchases the digital unit for their car, and achieves a baseline, will then be able to at least keep a track record of the health of their engine, as compared to the baseline. The difference in the values is what I guess is all you need to monitor.