EGT vs A/F?
03-15-2013, 03:05 AM
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Both are important in their own respect. The problem with tuning solely on EGT's, is that elevated EGT's may mean the engine is lean, or it may mean the engine is rich. If the engine is to rich, combustion will still be taking place in the exhaust pipe, which is where the EGT probe is located. This is where AFR's come in. There really is no discreptancy about lean or rich with AFRs. The tune of the engine will directly affect the AFR's.
EGT's can change with timing. When tuning an engine on the dyno, I will give it timing until it either stops making more power, or it gets on the knock sensor(efi engine) That, along with the combo itself, will pretty much determine what the EGT's are. Then you can tune in the AFR's. The EGT's are what they are at that point. Some engines will have 1300 EGT's and others will have 1500+. I use the EGT's as a tool, but rely more on AFR's for tuning. If I only had one to use, it would be AFR's.
This is a pretty simplified version but I hope it helps anyway.
Eddie
EGT's can change with timing. When tuning an engine on the dyno, I will give it timing until it either stops making more power, or it gets on the knock sensor(efi engine) That, along with the combo itself, will pretty much determine what the EGT's are. Then you can tune in the AFR's. The EGT's are what they are at that point. Some engines will have 1300 EGT's and others will have 1500+. I use the EGT's as a tool, but rely more on AFR's for tuning. If I only had one to use, it would be AFR's.
This is a pretty simplified version but I hope it helps anyway.
Eddie
We used to run a twin turbo 496 chev in our ski race boat, started out carbed and water cooled gentry turbo and manifold kit. We always relied on egt to monitor things and set up jetting etc. We then progressed to efi and dry headers and turbos. That's when relying on the egt's went out the window. We were pushing 22-24psi boost into her and as a result had to run well on the rich side to keep the pistons and valves cool. As a result the egt's went through the roof and no longer became a reliable gauge for what was going on. As Eddie said the fuel burning in the pipes and the fact they no longer where water cooled meant things got real hot in the pipes. I remember tuning it on the water late one afternoon, was a beautiful sight seeing the pipes and turbos glowing bright orange, they almost got white hot and translucent when pushed hard for extended periods.
