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Old 09-09-2011, 02:26 PM
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tuning holley blower carbs

Have a 420 Megablower blown 496 8.5 to 1 with dual 4777's. Qft blocks and 4 corner idle. Mild hyd. roller,114lc on 109icl 640 lift Lunati blower cam. msd6al and locked 32 timing. I have that trailer hitch jerking surge below 2200rpm in gear steady speed and when decelerating in gear. I tuned the idle for high 12's a/f and it cruises at 12.4 at 2000. Tip in throttle and it goes in to the 10's then stays in the high 11's once in the jets when I gun it. If I snap the throttle closed with clutch in it will lean in to the 15's nearly die then recover. Idle is always shaking not smooth. I run the idle screws at 1/2 turn out. I can go 3/4 and it drops in to 11's and smooths out some. Jerking still there but snap closed is better. Eye burning at 1 turn out and I have to turn up the idle to 1000 again but it really has great throttle response there. Sort of lazy if I whack it unloaded leaner that that but not any lag or stumble driving it. I tried for highest idle vacuum around 12" and it really jerks around at 14 afr. It is holding 10" idle but at cruising speed it is 14". Seems like it should be smoother. I tried with and without pcv with same results thinking the carb needed the air leak. Didn't change anything. I have to think my innovate wide band is okay. Any ideas?

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Old 09-09-2011, 07:58 PM
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Tuning a blown 496

Forget the wideband and tune it so it runs best. Let the engine tell you what it wants and listen to what it says. When I dynoed engines I always looked for the best TQ & HP.

Then again...I may be wrong.

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Old 09-09-2011, 08:41 PM
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I never used A/f meter in the last 45 years. Guess I'll try it your way. I put a Z28 pcv on and tuned it for best throttle response and will take it out tomorrow if it isn't raining. I tried a pcv in both carbs but it didn't seem to like that. The ifr's must be sized for that port expecting extra air. Never had Holley's with those pcv ports blocked before.
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