Rob Lay

OK, my question isn't quite that easy. The background…

I race a 2005 in SCCA Touring 3. My engine had been running strong, but I had 18 months of racing on it, so we rebuilt it right before the Runoffs. I show up to the Runoffs and my power is off enough to make a 1-2 second difference in lap times and 3-6 mph difference in trap speeds. Well, my mechanic and I started chasing everything but the engine, because we just rebuilt the engine and he's an "expert" rotary builder. We went through the fuel flow, air flow/port valves, and double checked electronics. In December we dynoed about 10 HP below where we should have been if everything was working right (use same dyno every time and it does atmosphere adjustments). This rebuilt motor showed a stronger pull up to high RPM's and then died out quicker with less power. Mechanic spent another month chasing electronics because of course it wasn't his engine that was "bad". One rotor getting a ton of misfires, so replaced all the coils, wires, and plugs. Had a double regional and car still felt off the power, so I took back to dyno yesterday and I was 12 HP down from December, so about 22 from where I should be. Car doesn't have a perfect idle, but not too bad like if a serious vacuum leak. Holding at 5k in neutral there is a steady miss you can hear every 5 seconds.

We still have to run cats and because we burn them up often I know how to identify that problem and know the symptoms. So I don't think it is cat.

We've replaced so many of the electronics, but at idle and 5k there are still symptoms of a miss.

So simply my question is how can you absolutely rule out a fuel, air, or electric problem and know the engine has gone bad? I know on 12A's you can't use an ordinary compression tester. My mechanic has a special one that he has used for the 12A's, but will that still work for the Renesis? Also from my experience I know that can mislead because I had a bad motor with carbon buildup that showed awesome compression numbers.

My mechanic is a rotary expert, but I'm asking on here for a second opinion without telling him because he's certain "my motor ain't bad!".

Thank you,
rob

corners

The special compression test for the 12A's should work. A rotary compression tester works by keeping track of which chamber it is measuring, since they all share the same spark plug hole. Since the 12A has the same # of chambers as a renesis it should work fine.

Rasputin

Reply to title : check top speed.

swoope

iTrader: (5)

rob,
some simple ?s

is the stock ecu used for scca? are you premixing?

if the stock ecu is used what flash are you on.... big changes into the amount of oil being injected into the motor... pm me if needed...

beers

Rob Lay

That might indicate engine down, but I think that would also indicate problems with fuel, air, or spark. I need to isolate the others and know whether the engine is good or not.

Rob Lay

Stock ECU as of now, we did reflash to get a little more oil and the little you can do with timing, then once Mazda this past year did the oil on their own, we updated the ECU to latest flash.

swoope

iTrader: (5)

that is good, but the damage might have been done with the old reflash... i dont know what your last flash was, but the s and t change all the rules about oil flow..

as to premix. have you done it at all?

beers

Rob Lay

not with this rebuilt engine, we did for awhile before until realized it eats cats.

car got to my mechanic and he confirmed poor compression. have race starting Friday, not enough time for him to overhaul, now we're in search for an engine to put in to just make it.

FlyLow

Does it just feel weak all the time or in certain RPM ranges?

swoope

iTrader: (5)

sounds like the damage was done.. you might be able to give us some insight on after a rebuild why you have low compression..

you can premix to help the problem.... as to premix killing cats. cut way back on the premix. as you have a omp working...

half an ounce per gal. plenty..

btw, where are you racing fri?

beers