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post #46 of 55 (permalink) Old 06-29-2013, 09:33 AM
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Re: Dyno run question

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Originally Posted by MauriSSio View Post
15% is too low for a c6. As an example, the 5th gen camaro rated at 400hp only produces 320rwhp or so and that car has a much more efficient transmission than the clunky old c6 we use. i think a c6 might be closer to %22+ in losses.

a new zr1 corvette typically sees %15-17 in losses through a more effient MANUAL transmission too. just for reference.

stock LS1 Fbodies typically see %16-18 drivetrain losses in their auto cars and maybe %14-15 in the manual versions.

everything i hear is that the C6 is probably the least efficient passenger car transmission ever created with some people even claiming %30 losses! (bull ****). %25 percent isnt out of the realm of possibility though i think.

Your probably right. I built a light weight or lightened internal parts C6 once and it was much quicker in the 1/4 than the stock tranny. I took every rotating part and put them on a lathe and made some kind of weight reduction in them . There is a lot of rotating mass in the C6 trans for sure.
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post #47 of 55 (permalink) Old 08-10-2013, 07:04 AM Thread Starter
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Re: Dyno run question

Still can't work out a new dyno run, but I have a new question.

On the dyno print out I posted you can see the engine starts misfiring around 5500 rpm. The shop supervisor said that it was the MSD dropping cylinders as a result of the rpm limiter. So, I pulled the MSD plug that limits rpm and it said 6000. Whats up with 5500 vs 6000.

I went ahead and replaced the 6000 plug with a 7000 but haven't taken it out to see what happens. I plan on putting the car in 2nd and see where it now starts dropping cylinders. If it still bangs out at 5500 what could it be.

Don
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post #48 of 55 (permalink) Old 08-10-2013, 09:27 AM
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Re: Dyno run question

Assuming all the parts are reasonably matched - high-RPM misfire is most commonly weak, wrong, broken, or improperly installed valve springs, weak coil, plug gap too small or too large, bad ignition trigger, bad AFRs, mis-adjusted lifters (hydro too much preload combined with marginal springs), or poor fuel distribution. In a used setup, it's anything related to those that's marginal (cap, rotor, degraded or cross-firing wires, carb bowl dirt, etc.).

I am leaning towards a valve spring or ignition issue, as your graph shows AFRs a bit rich but OK, then showing lean with misfire - but gradually. A rev-limiter cutoff is usually sharp, HP/TQ stops dead, AFRs go sharply lean, etc. Yours is similar, but is not so sharp, and stumbles rather than looking like you threw an off-switch. I didn't look to see if your system uses an increasing rolling misfire for rev-limit, or a cutoff. Most that use pills have a sharp cutoff.

I haven't included over-advance as I assume you've already zeroed-in on that with street pulls as described earlier.

David

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post #49 of 55 (permalink) Old 08-11-2013, 09:48 AM Thread Starter
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Re: Dyno run question

Damn David, can't you think of more items. This list will keep me busy for a couple of months.

Seriously, thanks for the list. I want to rule out ignition system, except plug gap, since it is all new MSD. I think I have the timing at 13 degrees advanced, tried to run it at 16 but it pinged to much.

It well could be the springs, the engine used to be bracket raced before I got it and I don't know how much abuse it has had.

I will keep plugging away at these items.

don

Don
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post #50 of 55 (permalink) Old 08-11-2013, 11:20 AM
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Re: Dyno run question

LOL... and that's not all of them. But - you don't have to drill to the bottom of each one at first. Give each a quick check for anything obvious. For example, do a highway run and check where it breaks-up. Is it higher RPM than before and the pill is working? Test your coil to verify spec's. Pull a valve cover and look closely for cracked or broken springs. Perhaps pull one set and do a quick check for installed height and pressure against factory recommendations for that cam. All stuff you can do in an afternoon, and if you find more clues or something odd, then you can chase that instead of everything.

David

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post #51 of 55 (permalink) Old 09-01-2013, 10:03 AM Thread Starter
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Re: Dyno run question

New report, I changed the MSD plug in (pill) from 6000 to 7000 and took it for a drive. I chickened out at 6500 RPM, with no break up. I guess this shows that the MSD was cutting it off at the 5500 RPM as shown on the Dyno chart, it also shows the valve springs are good up to at least 6500 RPM. I feel better now, but sure would like to get back on the dyno to see how the additional RPM and better flowing exhaust have affected the HP and TQ.

Don

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post #52 of 55 (permalink) Old 09-08-2013, 07:47 AM
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Re: Dyno run question

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New report, I changed the MSD plug in (pill) from 6000 to 7000 and took it for a drive. I chickened out at 6500 RPM, with no break up. I guess this shows that the MSD was cutting it off at the 5500 RPM as shown on the Dyno chart, it also shows the valve springs are good up to at least 6500 RPM. I feel better now, but sure would like to get back on the dyno to see how the additional RPM and better flowing exhaust have affected the HP and TQ.

Don
Several thoughts/comments for you:

- Put the 6000 chip back in. Your HP is peaking at 5000, so there is no need at all to ever go past 5500

- You are actually making more power than I would have guessed, with the parts that you have. That is more than enough to run 12's in the quarter mile.

- I recently tested a mild street motor with 2" pipes, then retested with 2.5". It picked up over 20hp at the rear wheels.

- You are too rich (see the A/F on the dyno charts) Before you change the jets, though, try adding some timing on your next dyno session.

- I would plan on making 2 dyno pulls without any changes, to make sure the motor is performing consistently. Then plan on probably 5 more pulls to zero in on the best timing setting. Then, 2 to 4 more pulls to test carb jetting.

- TAKE NOTES while you are tuning!!! It is easy to get excited and forget exactly what change you did on each pull.

I'm a bit southeast of Houston, and I have a chassis dyno (DynoJet), if you ever happen to be out this way :-)

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'69 Falcon Wagon, 427W, 4R70W, 483rwhp, pump gas Best 1/4: 11.180 @ 121.7 (7.14 1/8-mile, at 3970#); Best 1/8 7.03 @ 98 (Feb. 2010 issue of Popular HotRodding, pp.32-37)
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post #53 of 55 (permalink) Old 09-08-2013, 08:09 AM Thread Starter
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Re: Dyno run question

Thanks for your comments, I wish you were closer.

I am going to wait to change the plug back to 6000. Over the weekend I discovered the timing had slipped, hope it wasn't a timing chain issue, and it only had 10 degrees advance at 800 RPM idle without vacuum. I had been running it at 13/14 degrees.

Ever since I ran it up to 6500 RPM I had low end torque loss even though I could still get it to 125 MPH. I am thinking timing.

Don
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post #54 of 55 (permalink) Old 09-08-2013, 12:20 PM
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Re: Dyno run question

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Originally Posted by donwhis View Post
Thanks for your comments, I wish you were closer.

I am going to wait to change the plug back to 6000. Over the weekend I discovered the timing had slipped, hope it wasn't a timing chain issue, and it only had 10 degrees advance at 800 RPM idle without vacuum. I had been running it at 13/14 degrees.

Ever since I ran it up to 6500 RPM I had low end torque loss even though I could still get it to 125 MPH. I am thinking timing.
The higher rpm probably vibrated the distributor, which may not have been tight. If the timing chain jumped, both the cam and ignition timing would have changed... and changed a whole lot more than it did.

Good Luck!
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post #55 of 55 (permalink) Old 09-09-2013, 08:30 AM
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Re: Dyno run question

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Thanks for your comments, I wish you were closer.
Dang. That offer is very gracious. I wouldn't pass that up. Dyno time with someone that knows what they're doing? I'd tow my car to the next state for that. Like someone offering to play the piano at your party, it's even better when they know how to play the piano.

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