Possible Cure for SBC running hot at highway speed - Hot Rod Forum : Hotrodders Bulletin Board
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Old 01-30-2011, 08:33 PM
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Possible Cure for SBC running hot at highway speed

A couple of weeks ago I added an Innovate AFR gauge and wideband O2 sensor to my truck, and found some interesting readings. At idle I was running about 12.5 (too rich) and at Wide Open Throttle I was about 12.2 (rich, but not too bad for WOT). However at highway cruising speed I was running about 20 AFR, which is way too lean.

I have an Edelbrock 1406 and the tuning kit, and so far I have been able to get lean cruise to about 15.5-16 AFR by using the jets and rods for Ref #19. This may be okay for now, but I'll continue to play with it.

My engine is the GMPP 350/290 HP, and I'm running an Edelbrock Performer EPS manifold and stock iron exhaust manifolds with duals. I run initial timing of 16, with 20 degrees mechanical and about 18 vacuum advance. I can't hear a ping at light throttle, but the truck is noisy and I might be missing it.

My truck is a Camper Special with the factory HD cooling system, and I could never figure out why it ran quite a bit hotter at highway speeds. I may have found the problem (very lean cruise mixture). The AFR gauge will give me something to play with and figure out my tune over the winter.

Bruce

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Old 01-30-2011, 09:34 PM
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Richen up the cruise and power stage at least one more step. When you get the cruise set to about 14.5 or so try WOT. My guess is that you'll be around the 12.5 range which will be pretty close. If you find the WOT a bit rich just drop the secondaries one step.
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Old 01-31-2011, 05:45 AM
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Quote:
Originally Posted by 75gmck25
.... The AFR gauge will give me something to play with and figure out my tune over the winter.

Bruce
Better get on it then----we may only have 3 weeks of witner left
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Old 01-31-2011, 05:57 AM
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Try a 2 step leaner (on the cruise) set of metering rods. That should do it...
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Old 01-31-2011, 06:45 AM
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Quote:
Originally Posted by 345 desoto
Try a 2 step leaner (on the cruise) set of metering rods. That should do it...
NO! Too lean already. This can cause some fatal engine damage.
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Old 01-31-2011, 07:03 AM
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That SHOULD have been SMALLER not leaner...
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