Does car hiccup when it detonates??
06-06-2003, 02:32 PM
#1
Drifting
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Does car hiccup when it detonates??
I had a problem with my car at the track afew weeks ago. it hiccuped on boost at certain times. I thought it was because the bottom latch on the distributor cap was loose. I have it on correctly and last night in 4th gear i passed some one and it hiccuped. I am going to turn the boost down before I get on it again to see if it goes away. I increased my boost a year ago to 18psi with some chips and a 3.0 bar fpr. I have been meaning to get to the dyno to make sure air/fuel is OK. Whena turbo detonates does it also loose power like a hiccup?
06-08-2003, 06:07 AM
#2
Racer
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It sounds like the KLR is pulling the timing back because it's detecting a knock. I would get your air/fuel ratios checked soon. Replacing a headgasket is not much fun.
06-08-2003, 08:10 AM
#3
Race Director
Yes, the car will feel stumbles and surging as the KLR dials back ignition. Part of the issue is that the amount of igntion-retard required is significant once detonation starts.
For example, let's say you're at the edge of detonation at 20-degrees BTDC. If you program in 21-degrees BTDC to try and squeeze out a little more power, the car will start to knock/detonate. In order to stop the detonation, the KLR will have to dial back ignition to 18-degrees BTDC, well past the point where it was working fine before. This amount is significant to cause stumbling, which feels similar to ignition misfires.
Also on some chipsets, the air-fuel ratio is way too rich in the mid-range when boost hits its maximum value (3500-4000rpm). This is partially due to the FPR which is boost-sensitive and increases fuel-pressure as boost builds. The chips must be programmed to account for this rising fuel-pressure.
If you have any intake-mods like port & polished head along with aftermarket cams, the mid-range exhaust reversion will be more than stock. On some of these cars, I've actually had to dial back mid-range fuel by -25% compared to stock to compensate; high-end really screams from 5000rpm+ though
!
For example, let's say you're at the edge of detonation at 20-degrees BTDC. If you program in 21-degrees BTDC to try and squeeze out a little more power, the car will start to knock/detonate. In order to stop the detonation, the KLR will have to dial back ignition to 18-degrees BTDC, well past the point where it was working fine before. This amount is significant to cause stumbling, which feels similar to ignition misfires.
Also on some chipsets, the air-fuel ratio is way too rich in the mid-range when boost hits its maximum value (3500-4000rpm). This is partially due to the FPR which is boost-sensitive and increases fuel-pressure as boost builds. The chips must be programmed to account for this rising fuel-pressure.
If you have any intake-mods like port & polished head along with aftermarket cams, the mid-range exhaust reversion will be more than stock. On some of these cars, I've actually had to dial back mid-range fuel by -25% compared to stock to compensate; high-end really screams from 5000rpm+ though
!