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Bigger Carb?

General engine tech -- Drag Racing to Circle Track

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Krooser
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Bigger Carb?

Post by Krooser » Sun Sep 22, 2019 7:46 pm

Getting my bare block back from the machine shop soon. Might be a bit early but I'm thinking of going bigger on my carb...getting anxious for next year's racing season.

SBM...388 ci.... ported W-2 heads... 310/160 @ 28"...13-1 compression... solid flat tappet cam from Mike Jones (don't have it yet)... trying to keep it under 7200 rpm for durability's sake. Running a dirt late model mostly on a 1/2 mile track.

I have an early 750 Barry Grant methanol carb that was run on this engine but the PO never ran it over 6K. I'm thinking of an 830-850 whatever I can find on a deal. Likely will be a used carb that I will go thru or send out to be freshened.

The engine produced 575 HP in it's first life.

Thoughts?
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mag2555
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Re: Bigger Carb?

Post by mag2555 » Mon Sep 23, 2019 6:29 am

Hook up a vacuum gauge to full Manifold vacuum and extend the hose so you can set it somewhere where you can see it with the motor under load and reving from the bottom of the motors on the track rpms to peak rev's.

If at some point in doing that the HG reading gets up to or above .75 then yes you could make good use of a larger Carb, the 830 sounds about right to me if that's the case.

Elroy
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Re: Bigger Carb?

Post by Elroy » Mon Sep 23, 2019 9:40 am

Should be in the ball park.

swampbuggy
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Re: Bigger Carb?

Post by swampbuggy » Mon Sep 23, 2019 11:00 pm

I am betting that an 850 with skirted annular boosters would work well ?? Mark H.

Krooser
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Re: Bigger Carb?

Post by Krooser » Tue Sep 24, 2019 11:19 am

Never had any carbs with annular boosters. Read somewhere that downlegs were better suited for oval track applications but I don't know.

I'm asking this because the cfm chart I have always used seems to be out of date. Now dry flow/ wet flow numbers seem to favor the larger carbs.

The guys I know SAY they are using 750's on their spec 360 SBC motors.... but none of my buddies are front runners so it may be true.

It's not in my budget to buy a new boutique carb for $1000+... and the used 750's seem to be what everybody is SELLING.

I have an old friend in the carb bidness but he does not do alky carbs. Has hundreds of gas jobs out there on everything from NASCAR pavement mods to no prep drag guys to schmoes like me with no budget operations. Kinda wish he'd make an exception considering all the beer I bought him when we were both 10' tall and bullet proof.
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jmarkaudio
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Re: Bigger Carb?

Post by jmarkaudio » Mon Sep 30, 2019 1:17 pm

Do you have any restrictions on what carb you can use? There are options with sizes using a billet body, I would look at something in the 1.40-1.45 Venturi range with a 1.75 throttle blade. If you are looking to go cheaper than new either a QF 850 or 950 will get you there, the 850 is 1.40 Venturi, the 950 1.45.
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Krooser
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Re: Bigger Carb?

Post by Krooser » Mon Sep 30, 2019 6:57 pm

Mark....no restrictions on the carb. But the open motors over 362 ci need a restrictor plate. I can sneek in under the IMCA modified engine catagory.

We can run almost any engine combo with the weight adjusted for the lower HP stuff like mine.

The 410 open's kick everyone's ass....but no wide bores allowed IIRC.,
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Krooser
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Re: Bigger Carb?

Post by Krooser » Wed Oct 02, 2019 9:46 pm

Pulled the trigger on a good, used 850 alky Holley yesterday. At $200.00 I don't think I can go wrong. May just keep the 750 for a spare in case the big one does not do the job.
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