Dyno day

[jlevie]

We spent several hours on a DynoJet yesterday tweaking a pair of Spec E30's. At the end both cars were making peak numbers of 162hp & 155 torque (in 100F temps). That is about as good gets for a stock M20B25. Both my car and and the other have blue printed engines with stock components. The Spec E30 rules impose pretty severe limits on what we can do, so the tuning was mostly a matter of finding a good DME (we had eight or so to play with) and tweaking the AFM to richen the mixture below 4500rpm.

I've learned over time that the choice of DME is pretty important. Several times now I've seen a change in the DME make a marked difference in the power output of the engine. You pretty much can't tell that there is anything wrong with the DME from driving the the car, but it sure is obvious on the dyno. Given that the DME's are 20'ish year old and that the analog portions of the DME do age, that isn't a surprising finding.

[Sagaris]

Wow, that is impressive! What fuel do you run? I find that my car feels the best with BP 93 octane. I would run 91 octane but I cannot find it here (I have a 91 octane chip).

[nando]

I'd love a dyno chart of these engines!

[blueapplesoda]

schweet. sounds exactly like what we are doing with the spec miatas. blue printing the motor is one part, but alot has to do with finding the right ecu. we've got stacks of them too, haha. On the dyno, each ecu puts out something a little bit different than the last one.

162hp/155tq is pretty impressive for a stock m20.

[E30Nova]

That's kind of disheartening to learn that even though you think your car is running optimally, there's a chance that a new(er) DME could free up some power.

Matt

[jlevie]

I'd love a dyno chart of these engines!

I'll try to remember to scan one of the plots tomorrow put it up as a jpeg.

That's kind of disheartening to learn that even though you think your car is running optimally, there's a chance that a new(er) DME could free up some power.

It is more a matter of finding a different DME that happens to work better. Of the three that I kept as usable, one is a 153 from an 87 325is, one is a 173 from who knows what, and one is a ProgRama 173 rebuild a few years old. That covers quite a range of age. Fortunately, DME's are cheap. We have a good relationship with a salvage yard and they'll let us pick up a half a dozen or so to try and only charge for the ones we don't return.

The real guts of the DME are purely digital, and thus not affected by aging. But the interfaces to the engine, specifically the AFM, IAT, and ECT, are analog and can drift with component aging. Finding a DME where those are working well is the reason to flip DME's.

Wow, that is impressive! What fuel do you run? I find that my car feels the best with BP 93 octane. I would run 91 octane but I cannot find it here (I have a 91 octane chip).

Once the ambient temp gets to the 90's I run 89 octane, which is what was in the tank at the time. I don't know what fuel was in the other car.

[kishg]

those are pretty good numbers jim. i'd be interested to see what my rebuilt motor makes. should schedule some dyno-time. i expect you and gress will be on the podium at RA next weekend with those numbers :)

[reelizmpro]

C'mon now Jim, you know those DME's were actually PnP Megasquirts in a Motronic box with dummy AFM's. Seriously though, those are great numbers. Just around 200HP or so.

[jlevie]

those are pretty good numbers jim. i'd be interested to see what my rebuilt motor makes. should schedule some dyno-time. i expect you and gress will be on the podium at RA next weekend with those numbers :)

My winding up on the podium in the crowd that will be at RA will happen at the same time that it is reliably determined that pigs can fly. At this point I'll consider the weekend a success if; a) nobody wrecks me, b) I don't finish last.

My focus since I've gotten the car running has been to get back to where I was at the time of the wreck. Being out of the car for 9 months really hurts one's skills and it takes a bunch of seat time to recover those skills. Right now I'm a good two-three seconds off of where I was last August. There's a fine line between the desired corner entry speed and the not to exceed speed. The judgment required is a very perishable skill, which you loose if you don't regularly use. You can get it back, but it doesn't instantly return.

[JGood]

That's awesome. My 270k mile m20b25 (stock everything, from airbox to muffler) with a real Dinan Chip made 145hp & 143tq.

[nando]

That's awesome. My 270k mile m20b25 (stock everything, from airbox to muffler) with a real Dinan Chip made 145hp & 143tq.

I have your chart, it's nice. I use it to convince people that slapping an 885 head onto an eta block without compression mods or a turbo is pointless. :p

jim, are these maximum factory overbore engines as well?

[jlevie]

Part of the power this engine makes is from the way it was built, and part comes from the exhaust. During the engine build the block was bored 50 over and all of the tolerances were brought to the ideal values, rotating parts were individually balanced and then everything from the harmonic balancer through the clutch (less the rods & pistons) was balanced as a unit. Rods, pistons, and position in the engine were juggled around to get the most uniform deck height possible. The real magic was in a meticulous head build. A matched set of springs, new guides, and new exhaust valves were used and we had the cam blue printed to bring it back to original shape. Naturally particular care was taken in fitting the valves to the seats.

The car has a Spec E30 exhaust, which is where the rest of the power come from. That is a two into one collector just before where the catalytic converters would be and a 2.25" (I think) pipe back to a single glass pack. The exhaust imposes no restrictions, though it is loud.

[jlevie]

Here is a representative plot from one of the final runs of the day. The roughness in the torque curve above 5k is probably caused by not quite enough timing advance.

[JGood]

Wow, that is a pretty wild jump at 5k. Is that something that can be corrected and still retain the majority of the usable powerband? This kind of stuff really interests me, I love seeing what can be done with a stock spec engine.

Here is my dyno, I'll just link to it so as not to clutter this thread, since it's not really relevant:

http://www.apexeta.com/img/87325isdyno.jpg

I'm just amazed at the top end of yours. It peaks at 160ish and stays there. Mine barely creeps over 140, with a chip. Image what yours could do with a custom tune. And that would still be on a factory spec engine...

[jlevie]

That dip is typical of a stock M20B25. My guess is that it is caused by intake flow dynamics. Given the rules I don't know of anything that can be done about it, though I wish I could.