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Losing Compression On Dyno, Any Ideas?

Old 03-28-2004, 10:30 AM
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I have a street ported single turbo 3rd gen. I run it with a power FC and my fuel sys is 550cc pri 1680 cc sec with nippon fuel pump (supra TT). also SX FPR. My issue is i have had several motors fail with less then 1k miles on them. most are babied until i hit the dyno for tuning then the motor seems to lose vaccum at idle and compression on every pull under boost. slightly but it loses vaccum. say 4 inches in 10-15 pulls. The car starts to sound like a harley and once the motor is torn down the apex seals are damaged. The seals are rounded off and overheated. this seems to always be the front rotor seals severly and the rear rotor seals mildly damaged. The car is always tuned on a dyno by either Demitrious of reactive racing or Steve Kan of gotham racing (formerly Rotary performance mechanic). The same problem has arised from the last 3 motors. the motors were rebuilt not replaced. all the housings and rotors were inspected by my engine builder and all seals were replaced and the motor was reinstalled. The car generates decent compression under break in driving (no boost) but once it hit the dyno it will fail like clockwork. Also i run very conservative air fuels in the low to mid 10's have replaced my secondarie inj and had pri flow tested and cleaned by rc engineering. Also I have verified timing ing with a light intake temps get no higher then 40-50 degrees C coolant temps in the low 90's fuel pressure is verified by a gauge on the regulator. boost didnt even exceed 13.8 psi on the last dyno tuning session and it still failed. the fuel pressure was 52 lbs at 12.5 psi. the plugs are NGK9's platinums all around new before every tuning session. The tuner pulled the plugs after almost every pull! The front rotor plugs get more damage then the rears and the tuner adds fuel to the front but it doesnt seem to help much. even with Air /fuels in the 10'conservative timing and the apex seals get damaged by what looks like overheating. they warp or bend but never break. Stock mazda 2mm seals. We have tried the 2 and 3 piece with no difference. the car even has a new wiring harness. I am out of ideas. Please comment. Here is a list of my mods



JR's Rotary Large Streetport Race Spec'd 2mm mazda seals,(NEW), A-SPEC GT3540 Dual ball Bearing Single Turbo, Fluidyne radiator, 3 BAR MAP, Greddy2 Row R-spec core FMIC, Miata Battery, Supra FP, SX FPR, 1680cc Inj, HKS Twin Power Ign. Apexi Power FC w/ Commander, Defi Boost gauge and White Gauge faces, ACT 6 Puck unsprung clutch with ACT HD Pressure plate, Mazdatrix short shifter, Redline fuid, Blitz SBC-ID boost controller, Greddy Underdrive pully. Ceramic coated 4 inch custom DP, ATR SS Midpipe, Greddy SP catback, 18 inch Volk TE-37's with Bridgestone S-03's. Bilstein HD's with HKS Super sport springs. Strut tower brace, Rotor Sports Racing Urethane Engine mounts and sway bar bushings.
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Old 03-28-2004, 10:58 AM
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Good air/fuels, good fuel pressure, good temps, good timing...not a whole lot left after that point. What are your tuners and engine builders saying?
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Old 03-28-2004, 11:25 AM
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I have witnessed two of Mike's motors fail and want to add a few things that I think will be helpful when examining his problem



Before the last dyno tuning session the following was replaced

-main wiring harness -brand new harness installed

-secondary injectors and resistors

-primary injectors cleaned and flow tested

-ground strap to upper intake manifold

-negative connection to battery

-plugs





As Mike said after one pull on the dyno and some part throttle time we shut the car down and pulled the plugs to inspect. The front plugs were slightly white, but generally dark and the rears were dark. Steve added 5% more fuel to the front by adjusting the front primary injector. After another pull we re examined the plugs and found that we overcompensated. Eventually steve reduced the fuel increase to 2% and from this point on, for the rest of the day, both plugs looked even and were both damp after runs.



Steve knows the history of Mike's motors and for that reason was not tuning for power; timing and AFRs were very conservative. Knowing exactly the way Mike's previous two motors failed I checked idle vac after each run. Initially it was around 355 on the pfc. It started dropping when we got to around 11psi. From this point on we started losing about 10 points of vac after each run. At no point was there detonation of any kind.
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Old 03-28-2004, 11:26 AM
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Here is a pic of one of Mike's apex seals out of the 4th or 5th motor-which failed with the same symptoms.
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Old 03-28-2004, 11:28 AM
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How long had those cleaned injectors sat around for before they put into the car?
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Old 03-28-2004, 11:30 AM
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So is the edge that seats against the rotor housing rounded?
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Old 03-28-2004, 11:33 AM
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These are new rotors too? I guess if you've tried 2 and 3mm seals there isn't any play for them to move around.
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Old 03-28-2004, 11:35 AM
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Originally Posted by 94touring' date='Mar 28 2004, 08:58 AM
Good air/fuels, good fuel pressure, good temps, good timing...not a whole lot left after that point. What are your tuners and engine builders saying?
tuners dont know, basically grasping at straws, engine builder is one of the better builders and hasnt ever seen this either. The only other things may be internal due to the same problem arising from same reused housings. I need to consult the engine builder for specifics of the build. The tuner thought the rotor housing exhaust port could cause a seals to fail but i would know for sure if that was the issue unless i replaced the housings with new ones. Can an oil metering failure cause this type of damage/heat to plugs and seals? car does not break up. no detonation. its run rich into low 10's and as high as mid 11's on different rebuilds and all with same result. no more then 15-16 degrees of advance
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Old 03-28-2004, 11:38 AM
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JR's as in Ito built your motor?
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Old 03-28-2004, 11:38 AM
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burn outline
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