Tuning question egt temps?

[bonesfab]

I have a Camaro that has a blown 406 with a fast unit. The problem is the egt's go to 1400+ just cruisin down the road. High vacuum conditons and advanced the timing to 40 deg. You can fatten it up till it blubbers and still gets warm. a/f is 13.5 Anybody have any sugestions besides cover the the guage....

[Blown353]

40 degrees is actually pretty low for light load cruise timing... 48-56 degrees is more common.

13.5:1 is pretty rich also for light throttle cruise. I have my car running 15.4-15.5:1 with 50 degrees of timing going down the freeway.

Throw more timing at it and I bet the EGT's drop and you'll also be able to cruise it leaner. Get better mileage, too.

[RSX302]

Yes putting as much timing in as the motor allows during cruise will reduce egt's. As soon as I increased my compression ratio, egt went up from approx 1000 deg to 1300-1400 in cruise mode. (same cam) I checked around to find that at 14.7:1 (stoichiometric) this will net the highest egt's. The more fuel you add or less fuel you add from this point will reduce egt. Here's something I got off the net...Hope this helps...

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A Narrow band oxygen sensor is really only accurate at 14.7:1 air-fuel ratio. This is because that's the stoichiometric air-fuel ratio where all three major components of emissions--hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx)--are at their combined lowest point. This is where the new-car companies need their engines to run at part-throttle both for emission and fuel mileage reasons. That's why these narrow-band sensors were built this way.

When it comes to fuel mileage and increased fuel efficiency, this ratio changes again. All new cars run at 14.7:1 air-fuel ratio at part throttle because this is the lowest emission point. But depending upon the engine, it's possible to run an engine at leaner mixtures like 16:1 or more at part throttle to gain mileage. The difficulty with this is that driveability and throttle response suffers at these ratios. Engine response is lazy and stumbles are commonplace. Each engine will be different, but there is fuel mileage to be gained by fine-tuning your carburetor. Don't be intimidated by these lean mixtures at part throttle. You won't burn the engine up since it is making very little horsepower at part throttle cruise--often less than 30 hp.

[RSX302]

bonesfab: Hey Jim, I didn't catch the first time that it was you.

I had played around with this for a bit to try and find the best solution. I moved both the timimg and A/F around and the best I could do is around 1300 on mine. I raised timing up as far as the motor likes (before stumble) and ended up putting the A/F to around 15.5-16. I couldn't go past 40-43deg under cruise before it starts to buck. If I remember right, yours can go to 48. Overall I didn't see an egt reduction from 13.5-14 to 15.5-16 a/f. Just fuel econo. Timing was the only real reduction.

Also everyone I seem to ask or read about says that this temp is not an issue during cruise, other then cooking your nice ceramic headers.

I like your new website