Odd Dyno Graph

#3

These motors have a harmonic where the motor goes lean at a certain rpm. There is always a horsepower drop associated with the motor going lean. Looking at your dyno report, I strongly suspect operator error…it just does not look like a M20 motor dyno plot. You need to scan the printed version and post…make sure hp/tq/and fuel air ratio are shown.

BTW, the motor is dangerously lean at 14.5 to one.

If you have a broken valve spring I doubt the motor would make 160hp. It is easy enough to check just by pulling the valve cover and moving each rocker arm to check for play. Chuck

#4

I don’t know enough to say yes or no to operator error, but I doubt it. PFM has done a few pulls in their day and Fowler’s no slouch either.

Below is a HP/TQ plot. I don’t have air-fuel plotted on this one. The scale is rather large, which makes the changes in the curve seem very dramatic, but even so it seems like a wierd torque curve.

Anybody got any suggestions other than “it’s not an M20?” :laugh:

Steve D.

#5

160 is probably right at Carter’s HP cap so you should be fine. I’d just run it as is.

#6

IndyJim wrote:

The post of a very threatened man. :stuck_out_tongue:

Again, I am more than happy with that peak number, but I gotta work on the curve…

Steve D.

PS - IndyJim - I am just doing this for Nationals. Afterwards, I will crank it back to “mediocre” so you and Geegar have a shot.

#7

Yeah for nationals you’ll want at least 180hp and a flat 175-185 or trq.

You can probably work a deal to borrow Craig’s motor.

#8

Steve,

It looks like your VANOs is installed backwards. :silly:

#9

Are you sure you were getting a good tach signal for that whole run? Something is very wrong about that dyno plot. You don’t just lose 70 ft/lbs in 1000 RPM.

#10

The dyno plot is screwed up. It is a mathematical formula between hp and tq…the plot lines MUST cross at 5250 because this is the constant. Find someone else to dyno your motor…that plot is useless. Chuck

#11

Oh, yea, Scott. If you feel like removing the small bumpers and hardware to attach I will buy them from you. Chuck

#12

i think they DO cross at 5250, the scales are just different. look at hp at 5250 and torque at 5250, seems like the same value to me.

#13

Steve - you did check fuel pressure? My lean problem, similar to yours, turned out to be a clogged fuel filter.
Ed

#14

edavidson wrote:

[quote]Steve - you did check fuel pressure? My lean problem, similar to yours, turned out to be a clogged fuel filter.
Ed[/quote]

Ed -

Thanks. We will check that out. The strange thing is that it goes from one relatively steady state to another. It seems like a clogged filter would cause an increasingly lean condition as revs rise. But as you can tell I am learning here.

Steve D.

#15

cwbaader wrote:

Chuck -

As OriginalSterm pointed out, the plot is correct. The scales for HP & TQ are different.

I appreciate everyone’s input, but telling me that the dyno operator is incompetent isn’t accurate - or helpful. PFM’s resume is pretty strong. Plenty of Runoffs podiums, Spec Miata national wins, etc.

Is there something peculiar about dyno’ing an M20 engine? I could have posted a dyno plot on a 20-200 scale and it would look like I had a little dip in TQ, but I think the plots I posted illustrate the big dip in torque. Also, the lack of a nice horsepower “hump” is puzzling.

Steve D.

#16

Ok, y’all…this is what a good Spec E30 dyno graph should look like. Note it still has the harmonic rich point at 5K. Chuck Am trying to upload the dyno sheet. [file name=scan0003.jpg size=0]http://spece30.com/media/kunena/attachments/legacy/files/scan0003.jpg[/file]

#17

Here is one of my old graphs for reference:

Click Here

#18

Your dyno plot looks ok until around 4300RPM. Then, it goes crazy.

Here is Mr. Junky’s plot.

#19

cwbaader wrote:

Here’s Chuck’s dyno plot. I am going to try to compile some of the publicly-posted graphs on a matched-scale basis for comparison.

Thanks everyone for the data and input. And thanks to IndyJim for the protest fodder.:woohoo:

Steve D.

#20

Check the Throttle Position Sensor. It needs to know you’re at WOT or it will try to adjust to stoich (run lean). Tests are in the Bentley.

#21

BTW Steve welcome to how you become Jim Levie.

Each one of these cars has a “weird dyno dip”, Fuel starve, electrical gremlin…, before you know it you possess invaluable information like excatly what torx sockets and in what order is quickest to remove the transmission.

And it starts with helpful stuff like Skeen posted - check everything in the car, then check it again, then replace it with new sh!t.

#22

A couple of notes for those of you who are not familiar with a good dyno plot:

  1. Fuel/air ratio…this needs to be as flat as possible just under 13 to 1 for best power. Wild swings in F/A ratio are not acceptable.

  2. This motor makes max torque at about 4000rpm. That is where the motor will start pulling really hard. Max power is at 6000rpm, so the power band on this motor is 2000rpm which is really wide. A wide power band will make the car much easier to drive given the lack of rear gear.

  3. This motor was dynoed with a fresh head, old bottom end. This is the best the motor is going to do…as it is raced, the seal on the valves deteriorates and the motor looses power. I have seen a motor such as this go from 166hp to 145hp (without freshening the head) in two years of frequent racing. Chuck