Confused after dyno - Chevelle Tech
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post #1 of 29 (permalink) Old Oct 23rd, 16, 2:08 PM Thread Starter
 
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Confused after dyno

First post with this account since I can't get logged into my former one anyway...
Went and put my car on the dyno just to see what it was doing not expecting a whole lot. My current engine set up is a 402bbc, comp xe274 230/236,eddy rpm dual plane, oval port heads, 2500 stall converter turbo 350 with 3.7x rear gear. Trying to figure out why torque and power curve come in so late and have such a small window. I didn't have them hook up a wideband. I was just trying to get a base to see what the motor was doing before I put my fitech on. I will try to attach the dyno sheet.
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post #2 of 29 (permalink) Old Oct 23rd, 16, 2:11 PM Thread Starter
 
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It has a Holley 750 vac secondary carb.
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post #3 of 29 (permalink) Old Oct 23rd, 16, 2:27 PM
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Re: Confused after dyno

You're really not getting a good picture without the O2 reading. That will help you (or the tuner) determine if you're starving the engine and where in the power band. Right now all you have is half the data. Not a whole lot you can do with it other than mess with the timing.

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post #4 of 29 (permalink) Old Oct 23rd, 16, 4:38 PM Thread Starter
 
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I understand that and I wish I would have but I didn't. Just for the sake of argument say the AFR is close. Timing is set at 21 initial and close to 38 total all in by 3000rpm. What else would cause the torque to come in that late and then be all done by 5100rpm.
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post #5 of 29 (permalink) Old Oct 23rd, 16, 4:55 PM
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Re: Confused after dyno

Valve springs? What's on it?

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post #6 of 29 (permalink) Old Oct 23rd, 16, 5:06 PM
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Re: Confused after dyno

Torque converter looser then you think?
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post #7 of 29 (permalink) Old Oct 23rd, 16, 8:07 PM
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Re: Confused after dyno

I'm going to assume a few things. The image is a little difficult to read. Looks like your torque starts to hit a flat line after 3500 rpm? Top line on your graph. So what's the cam rated at? 2500-5500? I don't know the cam but how much farther past 5000 is it expected to make power? Knock the simple things out first. Fuel, air, spark. Carb is in good working order, fuel system is good. Doesn't have a tiny little air cleaner on (or did you dyno without it). Ignition system is in good shape. Ya gotta put the O2 in sometime. Might as well go back for another spin and see what the data tells you.

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post #8 of 29 (permalink) Old Oct 23rd, 16, 8:10 PM
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Re: Confused after dyno

I'm thinking valve train instability.

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post #9 of 29 (permalink) Old Oct 23rd, 16, 8:50 PM
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Re: Confused after dyno

Something isn't right. I'm running the XE-268 (224/230) in my 402 and I'm certain that power is still building at it's 5600 shift point.
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post #10 of 29 (permalink) Old Oct 23rd, 16, 11:37 PM
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Re: Confused after dyno

What do you mean small window? you're at 90% or more of peak over a 3000RPM range.

Can you feel the engine running bad at 5000? still pulling hard? that choppy looking stuff could be the dyno itself or the tires on the roller or whatever.

I wouldn't get too weirded out but those results. They're better than you think.

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post #11 of 29 (permalink) Old Oct 23rd, 16, 11:41 PM
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Re: Confused after dyno

Best reason to do that is to get a graph of the WBO2 across the range. Run it again someday with the WB. 3310s typically do pretty well unless some ham-fisted "Holley expert" has worked on it.

Get two pulls in a row, often the second or later is a better indicator.

I'd bet your car runs pretty good.

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post #12 of 29 (permalink) Old Oct 24th, 16, 12:15 AM
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Re: Confused after dyno

They look like decent results to me. That's probably high 400s at the crank and a flat torque curve.

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post #13 of 29 (permalink) Old Oct 24th, 16, 12:50 AM Thread Starter
 
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Not sure what springs are in it. This was the motor that was in the car when I bought it. Same with the torque converter. It did have the air cleaner in it while on the dyno but it's not a small one. Operating range of that cam is 1800-6000. What I meant by small window is torque doesn't come in until around 3400rpm. I'm not complaining about what it made I was actually really surprised. I just thought the torque would come in earlier you can just feel that it doesn't pull hard on the low end.
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post #14 of 29 (permalink) Old Oct 24th, 16, 12:54 AM Thread Starter
 
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Here it is on the dyno.
https://youtu.be/XCs9nIjYUXU
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post #15 of 29 (permalink) Old Oct 24th, 16, 1:16 AM
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Re: Confused after dyno

its the dyno operator getting into the test. Don't worry about the power figures below 3400 rpm. You are for sure making more than 150 rwtq at those rpm's.

It's above 5000 that is a little more goofy to me.
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