Help!!! Detonation on the dyno...
Thread Starter
TECH Resident
Joined: Jan 2002
Posts: 865
Likes: 1
From: central TX
Help!!! Detonation on the dyno... Went to the dyno on Saturday, and experienced serious detonation. I'm trying to figure out: 1) what is causing it, and 2) how to fix it.
Previous dyno best was 309/322 - before headers. At the time I did that dyno, I was also experiencing some detonation. The MAFT was set at +15%base/+2%WOT.
After adding the headers, I set the MAFT back down to +5%/+2%, expecting that I'd be running a lot richer. Ltrims were still around +10%, but WOT O2s were averaging right around .90. Knock/detonation did not seem to be present in any ATAP runs...until this dyno on Sat:
1st pull:
323.6hp/330.9 lbft
2nd pull:
324.2hp/329.2 lbft
Pinging was *clearly* audible on both runs...
Anyway, I had expected the addition of longtubes to cause me to run much richer, but it seems that it only made me run a little richer. The car only gets 93 octane (Chevron), so I don't think it's the gas causing the detonation. Are the MAF ends the most likely cause, and if so, is there a fix *other* than going back to stock? What else could be causing it?
Thanks in advance...
frustrated,
Shane
Previous dyno best was 309/322 - before headers. At the time I did that dyno, I was also experiencing some detonation. The MAFT was set at +15%base/+2%WOT.
After adding the headers, I set the MAFT back down to +5%/+2%, expecting that I'd be running a lot richer. Ltrims were still around +10%, but WOT O2s were averaging right around .90. Knock/detonation did not seem to be present in any ATAP runs...until this dyno on Sat:
1st pull:
323.6hp/330.9 lbft
2nd pull:
324.2hp/329.2 lbft
Pinging was *clearly* audible on both runs...
Anyway, I had expected the addition of longtubes to cause me to run much richer, but it seems that it only made me run a little richer. The car only gets 93 octane (Chevron), so I don't think it's the gas causing the detonation. Are the MAF ends the most likely cause, and if so, is there a fix *other* than going back to stock? What else could be causing it?
Thanks in advance...
frustrated,
Shane
Re: Help!!! Detonation on the dyno... What were your engine temps? I don't see a 160F thermostat listed in your signature. Coolant temps above 185F tend to cause some detonation on our motors.
Do you have the FLP catalytics on the car? Cats can keep heat inside the headers and cause some pinging under load.
You really should readjust that MAF-T so that your Ltrims are closer to 0. Adjust the base setting first to get that value (+/- 2 is good) and then tweak the WOT setting to get .890-.900 O2 readings.
Tony
Do you have the FLP catalytics on the car? Cats can keep heat inside the headers and cause some pinging under load.
You really should readjust that MAF-T so that your Ltrims are closer to 0. Adjust the base setting first to get that value (+/- 2 is good) and then tweak the WOT setting to get .890-.900 O2 readings.
Tony
Re: Help!!! Detonation on the dyno... I'd definitely try out a set of stock MAF ends. You should still be able to adjust for the MAF ends with the MAFT. I'd go a little richer with it. It wouldn't hurt to get it on a dyno w/ a wideband O2 sensor so you can see exactly where your a/f ratio stands.
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Thread Starter
TECH Resident
Joined: Jan 2002
Posts: 865
Likes: 1
From: central TX
Re: Help!!! Detonation on the dyno... Thanks for the replies guys. I have not had a chance to look at the ATAP data from the dyno run, so I'm not sure what the engine temps were - I do not, however, have a 160 thermo. Also, I do not have the cats in right now.
I just bumped the MAFT back up - no new data yet to help tune it in. I'll shoot for Ltrims in the +/-2 range and see how it goes.
Trevor, I'm going to try to fix it with the MAFT first, and if I still have issues, I'll try going back to the stock MAF ends. In any case, I'll be hooked up to the wideband sensor on my next dyno...
Worst case, I've never tried the GM Top Engine Cleaner, and I may need to try that.
I'm hoping to have it fixed, or at least minimized by Friday...
RCR here I come... <img src="gr_stretch.gif" border="0">
Thanks again,
Shane
I just bumped the MAFT back up - no new data yet to help tune it in. I'll shoot for Ltrims in the +/-2 range and see how it goes.
Trevor, I'm going to try to fix it with the MAFT first, and if I still have issues, I'll try going back to the stock MAF ends. In any case, I'll be hooked up to the wideband sensor on my next dyno...
Worst case, I've never tried the GM Top Engine Cleaner, and I may need to try that.
I'm hoping to have it fixed, or at least minimized by Friday...
RCR here I come... <img src="gr_stretch.gif" border="0">
Thanks again,
Shane
