Help me interpret dyno results from my 81 ROW SC

SpeedracerIndy · 01:38 PM

I wanted to asses the health of my car, and get a baseline for future modifications I make to the car. 3.2 SS???

-Car is a 1981 RoW SC (204 hp stock)
-930/10 motor with about 99k miles.
-SSI heat exchangers
-M&K 2in/2out muffler
-93 octane gas
-last time I checked timing is was ~34 BTDC @ 6,000, and ~5 BTDC at idle
-otherwise it is 100% stock
-Dynojet - average of 3 runs
-The runs start at around 3900 RPM because I messed up! The guy told me to drive like I were on the street. I didn't realize I was supposed to shift to 4th sooner than normal. I didn't want to pay for another hour, so I'll have to make do with these results.

Average of 3 runs: max rear wheel HP = 182.77, max rear wheel torque = 176.69

Assuming 15% drive train loss, that would be about 210 hp, and 203 ft-lbs correct? To be honest, I'm a bit disappointed considering the cost of SSIs and muffler I just added. I expected a bit more of a bump from the SSIs.

See image below for results.

My concern is that around 5500 rpm, the HP begins to waver. The operator said that it looks like there could be detonation occurring. That has always been a concern of mine since this is a 9.8:1 motor. Also, the AFR is not very consistent. Do these results indicate any malfunction of any components of the engine? I appreciate any input.

Jeff Higgins · 10-22-2009, 02:37 PM

Timing spec on the Euro SC is 24 to 31 degrees advance at 6,000 rpm. You are well over that so, yes, it may very well be detonating. An erratic curve on the dyno sheet can, in fact, be an indication of that. I would back it off to under 30 degrees total and check again.

186 rwhp in a 3.0 with stock internals is about as good as it gets. SSI's and a free flowing muffler are not magic; any really serious power gains will require a good deal more work, along the lines of freeing up flow on the induction side. The CIS and CIS friendly cams will hold it back until they are replaced; they are the limiting factor on your motor. Webers (or PMO's) and 964 or WebCam 20/21 cams will get you well over 200 rwhp.

SpeedracerIndy · 10-22-2009, 06:22 PM

Guess need to verify the timing again. I had a local Porsche mechanic check it for me and he said it was good. I thought he said it was at 33-34 BTDC, but maybe I remembered it wrong. Or maybe he didn't realize it was a euro.

I guess I have to decide where I want to go with this car from here before I do anything else.

How about my AFR? I seemed odd to me that it is not very consistent.

Thanks.

Jeff Higgins · 10-23-2009, 05:16 AM

Yeah, a point and a half of variation in the A/F over the rev range is not normal for CIS. It should pretty much "flatline" accross the chart. My son's '79 does, not varying by more than 1/4 point or so. His, by the way, has SSI's and a single out Dansk, and makes almost identical power to yours.

As far as what to do about that variation, I have nary a clue. I don't know all that much about CIS; I'm an MFI guy. My son's car has never needed much work on its CIS, so we have never had to learn. Maybe one of our resident CIS gurus can help you out.

beepbeep · 10-23-2009, 05:55 AM

Dyno sheet looks OK, HP-curve jaggies are nothing to worry about. Dyno-wise, it's spot-on (stock ROW SC 3.0 has 204hp) New fancy headers can help, but you need hotter cams for that.

middle-range AFR's are not good. You are almost at 14:1 AFR where it matters the most: torque peak. BMEP and knock-sensitivity is greatest at torque peak and your CIS is running lean there.