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I've got a few interesting cars coming tomorrow (Porsche turbo, E46 M3, 550 Maranello, Mini Cooper S and hopefully and Ellise) for an informal dyno session with Geoffrey Ring from EFI doing the runs and some training. Dyno is a 5000 model Dynapack. Please contact me at [email protected] if interested. I'm in Emerson NJ (approx 3 miles from RS Motorsport in Closter). Session starts around 9:30am. SteveD

 

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Discussion Starter #3 (Edited)




Funny torque curve these cars have but power was good at the wheels and back to back runs were extremely consistent. Wonder what kind of correction factor this car uses to go from wheel hp to flywheel hp?

I'll let the owner elaborate on the results and experience when he gets home. Steve

PS - here's the FULL DATA LOG behind the graphs at http://www.ultimategarage.com/lotusdatalog.htm . There are another 14 columns of data that I did not print (AFR, acceleration, etc).

This gives the tuner an idea of which rpm ranges he needs to focus on....the Dynapack will hold rpms indefinitely while timing. fuel and other parameters are varied to see if torque goes up or down. The dyno is very repeatable....there is a red plot and a green plot run approx 10 minutes apart...you can barely see the difference between the 2 runs (actually the 2nd run made more power). Make a small change like a different exhaust and you'll see right away if the mod hurt or helped....you can even see the effect of 2 different weights of oil on engine performance.
 

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The torque curve looks scary on the picture. But if you look at the axis, it's plotted in a range of around 90-115 ft-lbs. For example, what looks like a giant drop between 4300 to 6000 rpm is a drop from 107 to 97 ft-lbs. If you plotted this with a range starting at zero, it wouldn't appear nearly as dramatic.
 

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Hey Steve. Glad to see you on this forum now :-D Also glad to see your garage further along than the last time I was at your place. Had I known you were going to host this event, I would have showed up just to gawk at the other cars :)

Best regards,
Chester
 

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Discussion Starter #6


The beauty of the Dynapack is it's sensitivity to changes which are not masked by the inertia of a big roller like on other dynos. Lotus gives you a torque burst between 3200-4300 for low speed acceleration and then another burst between 6200-7000 rpms. The changes look rather dramatic because of the scale of the torque graph. You don't see this detail on the roller dyno plot below which I found elsewhere on your forum. The end results, however, are pretty close (ie, 1hp apart).


 

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By looking at the way the power is falling off before it goes onto the second set of cam lobes, it seems like there could be some power picked up by lowering the engagement point by 500 rpms or so.

Anyone else see this?
 

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damcgee said:
By looking at the way the power is falling off before it goes onto the second set of cam lobes, it seems like there could be some power picked up by lowering the engagement point by 500 rpms or so.

Anyone else see this?
In the screen shot of the torque curve shown in ultgar's post, follow the high-lift cam torque profile down the curve to 5700 RPM and you will see it will fall off the bottom of the screen. The power produced by doing that would be abysmal. That dip in the power curve would deepen considerably.
 

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ChrisB said:
In the screen shot of the torque curve shown in ultgar's post, follow the high-lift cam torque profile down the curve to 5700 RPM and you will see it will fall off the bottom of the screen. The power produced by doing that would be abysmal. That dip in the power curve would deepen considerably.
I thought perhaps that was just some sort of transition, and not actually the result of the hi lift cam profile.

I'm not saying either of is wrong or right (we're just speculating) but I have never seen a torque curve fall off that dramatically (or pick up that dramatically) on a naturally aspirated engine.

Anyone else wanna weigh in?
 

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Discussion Starter #10
You're looking at 2 different runs, back to back, so the results from this car were pretty consistent. If I ever dyno another Elise, we should be able to confirm whether the 10 ft lb dip in torque is due to cam or mapping. SD
 

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ultgar said:
You're looking at 2 different runs, back to back, so the results from this car were pretty consistent. If I ever dyno another Elise, we should be able to confirm whether the 10 ft lb dip in torque is due to cam or mapping. SD

The computer might back off timing as it prepares to switch cams? I'm just guessing.
 

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Also, this probably wouldn't be noticed by seat of the pants, because it looks like horsepower never actually goes down, it just ceases to climb for a few hundred RPM.
 

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damcgee said:
The computer might back off timing as it prepares to switch cams? I'm just guessing.
If the dyno can do it, it would be interesting to see the torque curve plotted from max RPM down instead of low RPM up to max. The Lotus ECU is supposed to hold the high cam active until 5800 RPM when coming down. That would show the high cam torque profile in that 5800-6200 range that can't be seen when plotting on the way up.
 

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ChrisB said:
If the dyno can do it, it would be interesting to see the torque curve plotted from max RPM down instead of low RPM up to max. The Lotus ECU is supposed to hold the high cam active until 5800 RPM when coming down. That would show the high cam torque profile in that 5800-6200 range that can't be seen when plotting on the way up.
Wow, very interesting proposition. I hadn't thought of that.
However, you won't be able to lose revs at full throttle, and you won't be able to get an accurate max torque reading at part throttle.
 
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