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Old 04-08-2012, 05:09 PM
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Chevy 383 750 or 650 carb @ 4200 ft

Need to get some opinions on a carb. for my car. Right now it has a Holley 750 w/vac. secondaries, main jets are 72. Right now its way to rich, I need to see if I should jet down quite a bit or if I need to step down to a 650 or something. Live in Utah @ 4200 feet. Motor 383 2-bolt chevy motor bored .030 over, forged TRW piston, rods 5.7 chevy, 286 comp cam. Heads are 76cc 202/160 valves, Victor JR. intake, MSD 6AL ignition. Lets hear some options, thanks.

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Old 04-08-2012, 07:46 PM
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My first opinion would be to get rid of the vic jr intake and go with a dual plane intake like the performer rpm. A single plane intake doesn't tolerate a larger carb the way a dual plan intake will. that vac sec 750 should be just fine. Not to mention that vic jr intake and those choking 76 cc heads make for a poorly atomized fuel combination.
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Old 04-09-2012, 10:18 AM
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Quote:
Originally Posted by my87Z
My first opinion would be to get rid of the vic jr intake and go with a dual plane intake like the performer rpm. A single plane intake doesn't tolerate a larger carb the way a dual plan intake will. that vac sec 750 should be just fine. Not to mention that vic jr intake and those choking 76 cc heads make for a poorly atomized fuel combination.
X2 on the post with the intake ur using...That manifold is designed for HIGH RPM's Like 7,000...Can u do that on the street at a stoplight? Go with a Edelbrock RPM intake, or an airgap, but RPM would be the choice for the street..

Now for some tricks...Shell out the money and get the Percy's adjust a jet...just look at the picture next to my name...cost from Summit is under $100.00 with shipping...15001, I think is the part number...Here is the cool part about this item....remove front float bowl and gasket, pull your jets out of the primary metering block... install new metering block in front of old metering block u just pulled the jets out of with both gaskets supplied to both sides of new block...Install float bowl again and tighten down with new supplied screws....look at the supplied sheet and gently turn out the adjust a jet screw in front of ur face the required amount on the sheet...
Holley states for every 2,000 ft in elevation drop down one jet size...I also have a 3310S carb that is a 750cfm with vacuum secondaries and it came with #70 jets, not 72's....So you might need to drop down to about a 68 jet to get it to run right, if you choose to buy jets instead of this cool metering block...Once this part is installed it is as easy as adjusting the idle mixture screws....
I also plan on installing a Wide Band O2 sensor at the header reducer and complete the whole build with a Air/fuel gauge from AEM, or Innovate....Then I will know what stoch is (14.7 fuel/air mixture) and hopefully will be about 12.5, or so at WOT....
Hope this helps and I think if you search this site, you will find other articles in reference to my idea here with these 2 products...My opinion is to keep it simple....These 2 products do just that, so you know where ur at with your carb fuel air mixture....Simple~!
P.S. You can buy the reducer with the bung for the O2 sensor already welded in...This is what I did, so it is ready to go in back of the header...Also, if u do this, make sure the O2 sensor is installed in the vertical position, so that any condensation drains out of the sensor, otherwise you may go through a lot of sensors and they cost 50 bucks plus a piece....Ground all your grounds close to the sensor and at the same place, otherwise this also will give you problems....

Last edited by Dannyringo; 04-09-2012 at 10:24 AM.
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Old 04-09-2012, 12:08 PM
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I think I will try a 68 jet and swap to an air gap manifold and see what that does. I agree the Vic Jr is prob. not the best for street use. Hopefully the airgap is worth it, found a polished one locally for $150.
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Old 04-09-2012, 01:49 PM
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Quote:
Originally Posted by slik
I think I will try a 68 jet and swap to an air gap manifold and see what that does. I agree the Vic Jr is prob. not the best for street use. Hopefully the airgap is worth it, found a polished one locally for $150.
this is what I am using and I bought the Pro-comp airgap after reading an article on a 305 build where they used PC roller lifters, PC HEI distributor, and PC airgap...They included the dyno results also, which I posted the link on this site...click on my name her and search the posts I did and you can read about it directly from the HP Magazines...I think you'll be ok with the jets your choosing and that is direct information from Holley....
Good luck~! N let us know what happens with your build~!
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Old 04-09-2012, 08:00 PM
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Quote:
Originally Posted by Dannyringo
this is what I am using and I bought the Pro-comp airgap after reading an article on a 305 build where they used PC roller lifters, PC HEI distributor, and PC airgap...They included the dyno results also, which I posted the link on this site...click on my name her and search the posts I did and you can read about it directly from the HP Magazines...I think you'll be ok with the jets your choosing and that is direct information from Holley....
Good luck~! N let us know what happens with your build~!
Hey danny you sound way to eager to sell something? glad it worked for you.
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Old 04-09-2012, 09:03 PM
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change the primary jets to a #69 or #70 for the high elevation.
Install a new 4.5" rated power valve.

Distributor curve for the comp 286H-10 Magnum cam.:

A stock default distributor curve will not work very well.

You can fix that.

Recurve the distributor mechanical advance to allow 22-24deg base initial at idle
and 34 to 36deg at max advance. (Limit the mechanical advance curve to 10-12deg)

Install new spark plugs gapped at .035"

The idle will be much cleaner and the throttle response much better.
The plugs will burn correctly now.

This cam needs a high stall converter. Especially with a Vic JR.
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