DIY digital compression tester < $200
05-03-03, 11:34 PM
#1
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DIY digital compression tester < $200
The attached picture shows some test results using a digital compression tester that I assembled from readily available commercial parts. The total cost is way less than $200 USD. Almost anyone can do the same.
I have a write up but no way to post so if your interested send me a PM or e-mail and I'll send you a copy. The Word 2000 document is a little over one meg because of the pictures it contains. I'll post some other pictures here, too.
I have a write up but no way to post so if your interested send me a PM or e-mail and I'll send you a copy. The Word 2000 document is a little over one meg because of the pictures it contains. I'll post some other pictures here, too.
05-04-03, 12:00 AM
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Shopping list for this DIY tester:
1. Pressure transducer – www.grainger.com part number 1X742 @ $103.05 plus tax & shipping; total $117.04
2. Data acquisition unit – www.dataq.com part number DI-194RS @ $24.95 plus tax & shipping; total $30.02
3. Misc. – Radio Shack – 16-gauge 2-conductor wire with one red and one black jacket, battery clips, fuse holder & fuse, and shrink tubing assortment for about $30 +/-
4. Stolen flex hose from previous compression tester – free
1. Pressure transducer – www.grainger.com part number 1X742 @ $103.05 plus tax & shipping; total $117.04
2. Data acquisition unit – www.dataq.com part number DI-194RS @ $24.95 plus tax & shipping; total $30.02
3. Misc. – Radio Shack – 16-gauge 2-conductor wire with one red and one black jacket, battery clips, fuse holder & fuse, and shrink tubing assortment for about $30 +/-
4. Stolen flex hose from previous compression tester – free
05-04-03, 12:10 AM
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Last one. Picture of computer in the passenger's seat while testing. And for the computer savvy, yes that's a wireless NIC card and I could have been surfing the net at the same time.
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05-04-03, 10:24 AM
#8
Weird Cat Man
Very neat... good job.
This is what I was thinking of doing, but I was having a hard time finding a pressure transducer for under 150 that I thought would work. I ended up getting a steal of deal on a Mazda tester new in the box for 200 bucks so I just bought that
Brian
This is what I was thinking of doing, but I was having a hard time finding a pressure transducer for under 150 that I thought would work. I ended up getting a steal of deal on a Mazda tester new in the box for 200 bucks so I just bought that
Brian
05-04-03, 11:12 AM
#9
Very good! I won't be surprised if your readings are a little low, because of the length of the hose between the plug hole and the transducer. If you estimate that the volume of the hose will add about 0.5cc to the compressed volume, then your readings would be about 3.5% lower than actual. Not much, but visible.
05-05-03, 06:21 PM
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FormerPorscheGuy - Thanks for the positive feedback. I like doing things like this myself, too.
Wargasm - You're right that the key was in finding this transducer; and it has all its voltage supply electronics built-in.
Orange!FD - I hadn't even thought about the effects of that flex line. My decidedly un-calibrated numbers are looking way too low right now at 85-87 PSI, so a 3-4 PSI increase is important! At least they're balanced, though.
Wargasm - You're right that the key was in finding this transducer; and it has all its voltage supply electronics built-in.
Orange!FD - I hadn't even thought about the effects of that flex line. My decidedly un-calibrated numbers are looking way too low right now at 85-87 PSI, so a 3-4 PSI increase is important! At least they're balanced, though.
05-06-03, 05:51 PM
#11
I R SAD PANDA W/O BAW
Originally posted by Wargasm
Very neat... good job.
This is what I was thinking of doing, but I was having a hard time finding a pressure transducer for under 150 that I thought would work. I ended up getting a steal of deal on a Mazda tester new in the box for 200 bucks so I just bought that
Brian
Very neat... good job.
This is what I was thinking of doing, but I was having a hard time finding a pressure transducer for under 150 that I thought would work. I ended up getting a steal of deal on a Mazda tester new in the box for 200 bucks so I just bought that
Brian
05-10-03, 09:55 PM
#12
Weird Cat Man
There are at least two "official" testers that I know Mazda used.
The original one was set up with a spool of calculator-type thermal paper with little grids on it indicating the different PSI. When the hose received pressure waves, it moves an arm with a heated needle and draws a line.
The original is the one I have and I think it's better than the new one because it's CHEAP and it WORKS.
You can see some sample outputs from mine:
http://www.zeroglabs.com/rx7/compression.htm
http://www.zeroglabs.com/rx7/compression2.htm
The newer one is digital and MUCH more expensive. I've seen them on websites for 1800-2400 dollars... hahaha can you say, "Markup"?
Digital is WAY more expensive and what the heck are you getting?
Anyhow, I got mine from some sort of Rotary Recyler place and I think I paid around 200 + shipping.
Brian
The original one was set up with a spool of calculator-type thermal paper with little grids on it indicating the different PSI. When the hose received pressure waves, it moves an arm with a heated needle and draws a line.
The original is the one I have and I think it's better than the new one because it's CHEAP and it WORKS.
You can see some sample outputs from mine:
http://www.zeroglabs.com/rx7/compression.htm
http://www.zeroglabs.com/rx7/compression2.htm
The newer one is digital and MUCH more expensive. I've seen them on websites for 1800-2400 dollars... hahaha can you say, "Markup"?
Digital is WAY more expensive and what the heck are you getting?
Anyhow, I got mine from some sort of Rotary Recyler place and I think I paid around 200 + shipping.
Brian
good job!
05-11-03, 04:27 PM
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I'm really please with all the positive feedback. Here's a new question:
During one of my tests, and included in my write-up, I saw the minimum pressure within the rotor rise when the engine tried to fire. I thought this was due to backpressure from exhaust restriction, but could it also be a result of port timing? I was measuring compression from the leading plug at the time and apparently there was just enough fuel left in the injector to let the engine cough a little. As this happened the minimum pressure went up to about 20-25 PSI, and the maximum was around 155 PSI. What do you think? Backpressure or port timing effect, or???
Attached is the pressure trace.
During one of my tests, and included in my write-up, I saw the minimum pressure within the rotor rise when the engine tried to fire. I thought this was due to backpressure from exhaust restriction, but could it also be a result of port timing? I was measuring compression from the leading plug at the time and apparently there was just enough fuel left in the injector to let the engine cough a little. As this happened the minimum pressure went up to about 20-25 PSI, and the maximum was around 155 PSI. What do you think? Backpressure or port timing effect, or???
Attached is the pressure trace.