84_Carrera

Went from 203.5hp back in late '04 with the stock setup on everything (but poor ignition per graph), to 197/198 this afternoon. Indoor temps were a bit high (92 deg in the shop today), pulled with the cone K&N / cone removed, M&K 1-in / 1-out, Fabspeed Pre-muffler, newer tune w/ Magnacor 8.5mm(?) wires, new Bosch uhhhh 7DC??? plugs (whatever Pelican recommends for stock 3.2L '84), recent valve adjustment, too.

Awaiting graphs via email now.

My previous pulls back in June '05 were similar, with the Bursch muffler & the muffler bypass (again, summer temps), vs. November '04, needing tune-up, stock airbox, stock cat, stock muffler.

All runs done with the Weltmeister chip. Dyno today was for a Steve Wong baseline.

Quadcammer

that could easily be the result of a temperature difference.

Tire pressure, even how tight the car was strapped down could all make a difference.

I wouldn't worry about it.

g-50cab

or the quality of the gas for that matter

Loaded

should the correction factor keep that in account to bring the test to standard?

r911

is this an engine dyno?

84_Carrera

Chassis Dyno, Randy (Dynojet 248 from memory). Same unit I tested on the last 2x, FWIW.

Didn't know if this loss of power is attributable to something known mechanical, ie valve guides, ring wear, etc. at this age / mileage (1984 3.2L US, 75k miles). I should just get off my butt & do a leak rate on it, huh.

r911

variations that large on a chassis dyno are meaningless - they are not very accurate nor repeatable

don't worry about it --

take the dog for a walk instead

84_Carrera

Well, I got the data in, and I am concerned a bit about it. IMO, if the engine didn't have something going on, the charts would have been largely similar, just lower. Check the Air/Fuel...

Now, I did replace the O2 after the 1st set of runs, along with the Head Temp Sensor, & some basic other items, but nothing that's case-cracking. Anyone (like Steve Weiner, Pete, etc. who may have more history with stuff like this on these engines) have any input - look into something becoming amiss, or as perhaps wisely suggested by ubermod Randy, dismiss (can't walk the dog Randy, he's recovering from, ummm, becoming less of a man this evening... even I wouldn't be so mean as to walk him around with the cone on, nevermind the physical pain!)

fennlane

Interesting that the two torque and HP curves don't both cross at 5252rpm and this may be because the zero on the chassis dyno is not correctly set.

The differnce in power you are looking at is around 2.5% and I would be surprised to find a chassis dyno that was repeatable to this level over 3 years.

Have you looked at the torque calibration data from the dyno to see iof the torque measuring system has suffered from either a zero shift or has a small slope error?

If the dyno hasn't been calibrated during the time then the HP change is probably within the uncertainty of the measuring system.

I would be surprised that uncertainties would be within 1% even for a well calibrated chassis dyno.

If you are going to allow for environmental conditions you also need to measure atmospheric pressure and possibly humidity.

All in all not too worrying.

84_Carrera

Actually, it looks like they cross perfectly at 5250 to me.

It is the same equipment, but the shop was relocated about 18 months ago. I'd imagine that was the last time of a true re-cal. I can certainly ask them.

r911

chassis dynos just have too many sources of error -- for example - are the tires inflated exactly the same for each of the runs?

if want good date you need to pull the motor out and put it on an engine dyno - if done right then you should expect to get the same numbers +- 1 or 2 hp

Daniel Dudley

If everything else is good, as in timing , tuneup etc, you may want to SW chip it. It could be scavenging too well for the stock chip to compensate. [I don't care what anyone says, I have seen this to be true on some cars.]

BTW, a small vaccume leak could easily cost you a couple of ponies, assuming that you even lost them.

Daniel Dudley

Smoke machine is the best for finding intake leaks.

wdonovan

Are these (both runs) corrected torque and corrected HP? On all dynos I've seen, the y-axis says "corrected HP" and "corrected torque" if it is not raw numbers. If they are not corrected then you can't compare. Uncorrected numbers are actual values produced under current conditions. Your engine makes different HP every day with changing air density. The only way you can compare power gains (or losses) from modifiactions is to use corrected numbers. Correction also makes somewhat possible comparing runs from different dynos although there is usually enough difference between dynos to disqualify comparisons.

84_Carrera

Top Right Corner, both graphs are super-imposed on a clean slate, SAE corrected, Smoothing Factor 2 (there was a jump in tq curve on run 2, if you smooth it out, I mistakenly gain 10 lb-ft).

I have all of the actual run files I've done with the 911, & did a screen capture from the DynoJet WinPep RunViewer program. I should have John send me over the old SHO ones too. Would be pretty cool to superimpose my old blower car on top of the 911's. Hey, they're both 3.2L... :-D

Before I send the info & DME out to Steve W, I might see if I can find a set of intake runners to Extrude Hone. Anyone have an extra set?