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Old 03-04-2002, 04:11 PM   #1
Patrick Olsen
NASIOC Supporter
Member#: 120
Join Date: Jul 1999
Chapter/Region: AKIC
Location: Where the Navy sends me...
1997 Legacy 2.5GT
1996 Impreza coupe

Default Dyno graph comparison - stock SOHC vs. stock DOHC

A little while back a group of us NESIC types got together for a dyno day at Adrenalin Motorsports in Massachusetts. I dyno'd my '97 Legacy 2.5GT 5-speed sedan in stock configuration (well, stock + K&N drop-in filter and synthetic fluids), and Marc Sawaya dyno'd his '00 2.5RS 5-speed also in stock configuration.

We all know that the SOHC is supposed to have better mid-range than the DOHC, and I wanted to see how true that was. So, I finally got around to reading the numbers off of my graph and off of Marc's graph to create a combined DOHC vs. SOHC graph. I did actually cheat a bit on my graph - the day that Marc dyno'd his car (and hit 104.x hp) my car dyno'd at 100.6hp or something like that. On a previous day, also in stock configuration, and on the same dyno, I had dyno'd at 104.x hp. Knowing that (theoretically) the peak power should be the same on the two engines, I used my graph from an earlier day so that the graphs would "match". Who knows, maybe in real life the SOHC cars actually do make a few more HP than the DOHC engines, as was indicated on the day we dyno'd at the same time. Or, perhaps the few extra HP that Marc's car laid to the rollers was due to the fact that my engine has twice (?) the mileage and hence is a bit tired? I dunno. I just figured for a "neater" comparison I'd use the graphs that had virtually matching peak power outputs.

So, here's the graph:

It's pretty clear to see that the SOHC has significantly better mid-range torque. You can also see that, at least in this case with these specific engines, the DOHC doesn't drop off as severely at high RPM. (Plus we DOHC-kids can actually rev to redline! )

Pretty cool, eh?

Edit: I apologize for the light blue SOHC Torque curve, which is kinda hard to see - you'll have to thank Microsoft Excel for that!

Also, the dyno used for both cars was a Dyno Dynamics Low Boy AWD eddy current type dyno.

Pat Olsen
'97 Legacy 2.5GT sedan
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Last edited by Patrick Olsen; 12-06-2006 at 01:23 PM.
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