at the low engine speed, the overlap would allow the intake to back out the exhaust port. that would not allow enough air/fuel to compress, and giving low compression.

so yes a high overlap/agressive port motor would have lower readings

 

Hey Anthony,

cranking speed was around 260 rpm each time. motor was warm. when I was testing front rotor, both plugs were out of rear rotor, and vice versa.

I didnt use the conversion chart......need to check and see if it's on the back. Tester cost about half the cost of a new unit.


Swolbynos, that is good info, and intuitively I figured as much. The car runs friggin' great, and is most definitely not down on power .

 

My friend just ripped into me for my post. Let me rephrase.

MY MAZDA compression tester is quirky at times. We think there may be something that is wrong with the one I have but when we tested against his, his read perfect and gave no issues.

Sorry!



Anthony

 

I agree that the mazda tester seems less reliable to me than a standard gauge. I've had the thing refuse to give readings when it's in a bad mood, and other times it gives readings off by 50% then a simple reset and retest 30 seconds later yeilds believeable results.

Not to mention that it has torn up twice now for no aparent reason, powers up fine but won't read pulses no matter how long you crank. The first time I paid to have it repaired, took 3 months and cost $275. Now, it's down again with the same failure. The manufacturer wouldnt tell me the problem or how to prevent it last time, and were generally hard to work with.

I plan to sell it, either as is or once I repair it, because honestly I trust myself interpreting a piston tester more than I trust that 1600 mazda tester.

As for the rest of the discussion, I've built hundreds of engines from stockport to bridgeport, some low compression rotors, some high compression. Some 2mm, some 3mm, variety of seals. Porting doesnt significantly affect compression readings at all. Neither does compression ratio. I can get the same 120psi out of an 8.5:1 motor as I can a 9.7:1 NA motor.

My current halfbridgeport motor in the FD tested 115-118psi last week with about 600 HARD miles on breakin. Basically breakin consisted of a drive around the neighborhood and then let 'er rip. I'm running OEM 3mm seals (which are said to drop compression, ha), 9.0:1 rotors with some material removed from the bevelling process (drops compression ratio even more), solid cornerseals (said to lose a few psi compression due to no rubber insert), and JHB cermet resurfaced housings.

 

Same exact problems with mine and one other one around the area that I know of.

Anthony

 

Thats not good.. I've already bought one of these. Just waiting for it to get here.

Oh, and thanks for the info on cermet coating. I knew about ceramic coating but didn't know that was what it was called.

Anyone have hands on experience with these coating?? It quite costly.

 

I'm not following how a solid corner seal...can lower compression

the rubber insert is behind the "line" of the side seals...which seal to the side of the corner seals??

what is the reasoning behind wider apex seal lowering compression?? seems a wider seal shortens the compression face by 1mm (0.5mm on each side)

 

kevin landers. . . he just stated that his current motor is running them.

spring tension is spread across a wider surface area. . . therefore lessening the amount of pressure the seal presents to the housing. thats the idea, anyway.

 

I didnt say they do. People on this forum claim they do.




Again, as the people that go around spewing this crap on this forum. "Oh, 3mm seals are shitty, stay with OEM 2mm". Seriously, anytime a member mentions getting an engine built and possibly using 3mm seals, a bunch of forking idiots flood the thread with useless misinformation. "Oh, a buddy of mine is a racer in puerto rico and he runs 69 psi boost on stock 2mm seals, there is no place for 3mm seals in a rotary". "Yeah, 3mm seals make poor compression and don't seal well, and they chatter a lot at high rpms too".

I just thought I'd throw in a comment that I'm making better compression with that combination of parts that the all knowing members of this forum claim should offer low compression, than most of them are making with their "recommended" setup.

 

^gotcha...spewing something already spewed by forking idiots, LOL!

 

it sucks since you just bought it, but maybe the tester is off... have you done a test with a piston tester recently?

i've been meaning to ask you, rotaryresurrection, did you get NEW coated housings or get used ones and send in cores? how much did it end up costing in the end?

 

Opps.. I think I used to be that person.. sorry Kevin!

Paul, I guess I need to read little closer. I completely missed that.

 

The coating they do is not just a coating over top of whats there...they grind off original material and build back up with their stuff. Apparently it has to be this way to make a strong, stable coating hold up. If they just coated on top of what was already there, it'd be too thick, and the housing dimensions would change, and not be useable.

it'd be pretty dumb to fork over the money for new mazda housings and turn right around and start grinding the perfect coating that you paid for off just to put your own. So yes, you use old worn housings and work from those, because the end result will be a perfect like new surface regardless of how it started...though, there is definitely a limit to what they're able/willing to repair, and deep gouges from apex seal damage is beyond that limit.

 

that's what i had assumed, thank you. i agree with using used housings... it's also something like 2x the cost if you get it with new housings judging from the site. i guess the whole thing with new housings is there is no chance of cooling channel erosion and pinhole leaks, etc... but i'm sure used ones are inspected for that anyways... or i'd hope they do at least.

 

THE C/P Number affect by Port. Cranking speed this is two major thing.


The car still starable under 5KG. and drive able. but I think it will loose some HP at mid range due to the seal is not seal good.

MY 13BPP with 2mm Carbon seal. got about 5.9KG of compression. this is normal for this type of engine with this type of seal. Start up fine. rev it fine. tons of power, infact I just make 310HP at 8500RPM on engine dyno.

But your number seen a little be low.. but along as it start up fine. and got power who care

J

 

Thanks for the input. It's funny you mention midrange, because my car has killer power from 4500 to 7500. The car seems to explode forward in 2nd/3rd gear at 4500 or so. Some may disagree, but I feel 4500 can be considered 'midrange.'

Just for the hell of it, I may try the tester again this weekend and see how consistent it is. Having no p/s and a/c makes it a piece of cake to swap out my plugs.

 

hey this might be something you already know but you need to hold the throttle wide open when turning the motor over on the test....just thinking, I have seen low numbers with the throttle closed

 

If that is the case then I am an absolute friggin' retard, because my throttle was most definitely closed when I was cranking.

Time for round 2 on sunday

 

wow you're dad owns an FD?

 

Yup. 290 rwhp. He does more street racing than I do nowadays. My younger brother also just bought a bridgeported fb too

 

oh DAM... YEP you need to hold it wide open !!. and you know you need to do C/P at hot!!. because cold test will read higher noumber. Any way hope to see some better result

 

Yeah, the car was warmed up. Throttle plate was closed though. Maybe I'll get 7s or 8s now.....you learn something new every day

 

I definitely learned something new from this thead.
Since I'll be getting my tester in a week or two, I wondered about what is the correct procedure.

AnthonyNYC sent me this thread describing correct procedure when performing compression tests.

http://www.fd3s.net/compression_test.html

 

This is all good info. Thanks alot. Not shure if I had the throttle open when I did mine last year. Although that would not explain uneven bumps on the compresion tester, right?

 

No, I don't believe so. My readings were on the low side, but were nice and even.