If all you are trying to do is get a "baseline" then use a piston engine compression tester. You get a number and you can watch that number go down over time. Much, Much cheaper.

 

This is 8club.com. We don't want to get bogged down with "accuracy" or "reality". Just numbers, damn it!

I would highly consider buying this product also.

 

Delmeister, thank you for your post. You've brought up some very good points and questions. I've been on the road all day and it's late, but I wanted to get this post out ASAP and then I will follow up with more detailed info as I look it up (or figure it out :-P).
Dead Volume - This is something I have ignored up to this point, as for me personally it doesn't make much difference. However, if I am to offer my tester for sale there is no way I can overlook something like that, especially seeing as how I can easily incorporate an automatic correction factor into the unit. It will be done.
Digitizing/Detecting - Datalogging my sensor in realtime with Hyperterminal gets me ~166 samples in .1 second. That number is while the micro and sensor are testing an actual compression pulse. Open air sampling (0 psi) gets ~280 samples. Readings are calculated to the closest whole PSI. My micro's ADC is 10bit, so spread across the voltage of my sensor I could theoretically get a display accuracy of .25 psi, but that's just overkill if you ask me, and would require a bigger (more expensive) LCD.

Jmc, I do want my tester to be as accurate as possible. What I'm trying to convey when I talk about comparing mine to the Mazda tester is that I will not be able to guarantee that my tester will match it. Not because my tester is inaccurate, but because of the inherent differences between the two units. When I finaly stop tweaking this thing then they will be tested side by side and we'll put this issue to rest. If they match perfectly then I'll be tickled pink.

Ash and Nemesis, thank you both for that info from Mazda, as you can see it's playing a direct part in helping me refine my design!

I hope I've worded everything right and gotten the math correct, the screen is getting quite fuzzy. If I messed up somewhere then I'll fix it tomorrow. Good night RX8Club!
-John

 

if it helps, I'd volunteer to be a beta tester and I still have the Mazda printout from my compression test i did 3 months ago -shrug-

...of course 3 month may or may not be a timetable that means something for comparing the two, but hell why not volunteer! lol

 

stupid question,

will altitude play a factor in the compression results?

 

Great news and margaritas tonight!
Finally I've got a video of the TR-01 testing a blown rotary. This was the test that I was waiting on to prove that the tester worked and it couldn't have gone better. My girlfriend and I spent the better part of the day rebuilding the rear rotor of a low compression 13B-REW. We "modified" one of the apex seals by cracking it in the middle and grinding off a corner. Here's a video of the results, exactly what I wanted to see:
http://www.youtube.com/watch?v=dZG28b05H9k
At this point I am working on implementing a correction factor to take into account the dead volume inside my sensor but that's just software. A panel of PCB's will be ordered in the next couple of days and I expect to begin organizing a group buy soon. On that note please keep this thread "technical", a group buy thread will be started when the time is right. Thank you all for your help and interest!
-John

P.S. - Texak, I am unsure how altitude will affect the reading, the sensor I use measures pressure relative to the ambient room pressure.

 

My interest in having your device compared to Mazdas has nothing to do with wanting the results to be exactly the same. When you do test it, I would like to see the results of both yours and mazdas on multiple engines. This way, if it is off, we could make a simple calculation to get an estimated mazda result. To make it easy to understand, we will say your test returns 100psi at 250rpm and Mazdas returns 110psi at 250rpm. If we can show a consistent difference in the two numbers, then we can very easily know that after getting the result from your tester(lets say its border line low compression) we can add X(in this case I made it 10psi) to it to find out if Mazda will find it to be low and authorize a new engine.

"And knowing is half the battle." -G.I. Joe


Nice job on the results of the blown motor. Time to mass produce?

 

Add me to the interested pool. If I forget to look when for sale pm me.

 

Sweet, good to know it works well on the blown! Can't wait for this to be in my hands.

 

Well hey folks, just a little update:
Dead volume has been calculated and the correction factors are listed below. I decided not to code in an automatic correction as the number varies slightly depending on the engine type. For reference the internal volume of the sensor (with adapter) is 2.85cc. To correct for the sensor dead volume just multiply your readings by the correction number appropriate for your engine.
Engine Year Ratio Correction
12A 76-82 9.4 1.042
12A 83-85 9.4 1.042
13B 74-78 9.2 1.035
13B 84-85 9.4 1.036
13B N/T 86-88 9.4 1.036
13B T 86-88 8.5 1.032
13B N/T 89-92 9.7 1.038
13B T 89-92 9.0 1.034
13B T/T 93-95 9.0 1.034
13B Ren 04-on 10.0 1.039

I have paid for a Group Buy subscription so hopefully my GB will be approved soon! :-)
-John

 

I'm subscribed to this thread, please post here when your group buy has been approved.

 

I got to see this thing in person last week and I have to say I want it! It's pretty cool. It does show you compression and engine rpm which is nice. He's done a great job of building these and it's even a nice looking little package. It definitely doesn't look like something that average Joe just made at home. It's very professional and people would expect it to be.

 

Well thanks RG, I'm glad you liked it. That was a great meet and it was really nice to finally get to meet you in person.

I will definately post here when the GB is approved...I'll be posting everywhere they'll let me!
-John

 

If it's still possible to modify the software, it would be nice if the final display showed the average of the pressures taken, say, between the first and fifth second of testing.

 

Averaging the results was an idea that I played with, but I decided against it. While using my tester it's elementary to average the results in your head while it's testing. The readings should only vary by 1-2 psi. If there are bigger variances then I don't want them averaged out, I want to see them.
-John

 

I didn't mean during cranking. Show the instantaneous pressures but display the averages after the instrument senses that cranking has stopped.

 

I want 2

 

I'd like to test it side by side with my OEM tester.

 

I want one now! Post Prices!

 

oooohh, ok, I see what you meant now. That's an interesting idea, but not one I could implement at this time. The code I'm running is solid and tested in real world conditions and I'm happy with the way it is.
-John

 

Yes, like teknics software Here

 

I've seen that, and I like it! I wonder if I can get it to run on my linux machine.....
-John

 

Woo hoo!! Group Buy has been approved and posted! Let's finally get this show on the road!

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

-John

 

Thats what I'm talking about!!! I want one too

YES! man I cant wait

 

Yea, I got mine ordered and paid for. I figure it's a must have tool.