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Old 06-16-2008, 05:32 AM
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Advice on selecting proper Carb

Hello, just recently my Rochester Qjet let go, well we all know the common symptom, leakiness problem hehe, so i figured well time for an upgrade and edelbrock caught my eye on the ease of tune and keeping the tune as i don't want to have to tune the carb often.

My specs as is
93 S-10 Reg cab /short-bed
350 3970010 block bored.040 produced in St-Cathrine's Ont. 1975
3932442 crank
set of double humps 186 castings w/accessories holes 2.02/1.65 valves
torquer rpm manifold
Comp-cams 286H magnum
th350 w/shift-kit
ceramic coated headers 1 1/2 primaries 2 1/2 collectors
3.73 rear gears and 28 inch tall 15x 10 rear tires

now i was looking at the specs of a 600cfm witch will be more than adequate for street/strip and feed my mild motor but i came across the "will work up to 220 deg duration at .050" lift", where as my cam specs are,

Operating Range: 2200-6200 RPM
Duration Advertised: 286? Intake / 286? Exhaust
Duration @ .050'' Lift: 236? Intake / 236? Exhaust
Valve Lift w/1.5 Rockers: .490'' Intake / .490'' Exhaust
Lobe Separation Angle: 110?


now the question at hand is do i order a higher cfm carb capable of handling up to 250 degrees of duration ,setting me at around a 750-800cfm or will the 600 i had in mind be sufficient?

Thank you for your help in advance
Sick.

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Last edited by Sickpuppy22; 06-16-2008 at 05:38 AM.
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Old 06-16-2008, 06:01 AM
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Old 06-16-2008, 06:20 AM
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What usage will this see the majority of the time? If using for street I would not use the DP as it is not necessary. A vac sec carb should suit your needs just fine.
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"will work up to 220 deg duration at .050" lift"
A 1406 is a tad leaner than a 1405, in any case 600 or 650 should suffice, IMHO. If you are going to be getting it on more often than just cruising with occasional thrashing I'd use a DP or other in a 750 rating.
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Old 06-16-2008, 07:08 AM
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mostly street with weekend strip, with the Qjet it was running high 13's with an slow launch on street tires as it was not easy to get it to hook up on a hard launch out of the hole lol, but yes i would prefer to stay with a vac secondary. atm before the Qjet started acting up it was running rather rich, allot of fuel deposit and built up carbon on the plugs so the leaner bit of the 1406 doesn't bother me all to much might get a tad little more umph out of it.
only other thing im worried about is emptying the fuel bowl at the strip from wot, so might opt for a 750cfm 1407 or 650cfm 1805/1806 ( don't know what the difference in the tune of those 1805/1806 carb though)
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Old 06-16-2008, 09:35 AM
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Use a 750cfm carb. Keeping the fuel bowls full at WOT high rpm is a matter of fuel pump delvery volume capacity at the working pressure and carb inlet needle and seat diameter. Edelbrock carbs like 5.5 to 6 psi fuel pressure.

Your Qjet is a 795cfm carb. (when the sec air door is fully open).
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Old 06-16-2008, 10:07 AM
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Alrighty well thank you for the needed help in making the decision ill go forward with getting an Edelbrock 1407
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Old 06-16-2008, 10:27 AM
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The specs of "works with cams up to xxxx" refers to the fuel delivery curve, not the air volume = the necessity of rejetting/ rerodding the carb for proper fuel mixtures with the high overlap cam.

You still might have to "rejet" the 750.

Hoping for a perfect jetting "right out of the box" is wishful thinking for any brand of carb.

That is the reason folks like Barry Grant have a ready market. You can tell them what you have and they will send you something that is virtually perfect.

Last edited by ScoTFrenzel; 06-16-2008 at 10:33 AM.
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Old 06-16-2008, 11:34 AM
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thank you for the advice as for re-jetting, im not to worried about it,as jets are readily available at the speed shop close to me, (although he charges allot for the carbs he has in stock, and i mean allot compared to what you can find on the net)but he doesn't charge much for one off piece like a cam or jet's for this matter.

So i just finished ordering the Carb 1407 as mentioned before and as soon as it gets here 2-4 days or so ill let you guys know how it faired.

once again thanks for the helpful advice,

Sick
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Old 06-28-2008, 02:18 AM
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Well finally got the carb on Thursday, after such a long wait ( darn postal system hehe), got the sucker on and had a once over just in case there were any fuel leaks which there was not and all i can say is wow! im enjoying this carb quite allot nice and responsive and pretty smooth secondary engagement compared to my Qjet. although i still kept my Qjet so i can convert my 4.3blazer to carbed with my nifty find that one of my buddies had in his "spare/adopted" parts shed witch is a 4 barrel spread bore manifold for a 4.3L lol.

I'll take some pics later this morning-afternoon of the manifold for the blazer and the newly acquired edelbrock

Thanks again for the advice and suggestions i can smell the 12's coming with the slicks lol

Sickpuppy
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