Thoughts on annular vs down leg for street truck

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Thoughts on annular vs down leg for street truck

Post  somethingclever on December 8th 2018, 11:28 am

Need to buy a carb for my new build.

472
9.5:1
Edel heads
Performer and jomar powercone
218/224 HFT 112 Lsa 108 ICL
1 3/4” headers

Street truck, 79 F250 4x4, 3.55’s, 35” tires, wide ratio c6, 5500lbs with driver

90% 500lbs in bed or less, 5% 500-3000, 5% towing 6k

Would like vacuum secondaries, electric choke, good street manners in transient.

Seems like a lot of ppl like annular on the street for low rpm torque?

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Re: Thoughts on annular vs down leg for street truck

Post  Carl on December 8th 2018, 12:40 pm

I prefer annular boosters in most applications, especially street. Not sure if anyone makes them in a carb like you described though.

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Re: Thoughts on annular vs down leg for street truck

Post  Dave De on December 8th 2018, 1:39 pm

Downlegs are less costly to manufacture. Small CFM carbs are best suited for downlegs due to size of the opening some what to say that the space is not practical for a tiny annular.
Keeping that in mind... any carb over 750 CFM will like an annular over a downleg. Then also if a carb is modified from downleg to annular there is a CFM reduction because the booster occupies more space.

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Re: Thoughts on annular vs down leg for street truck

Post  rmk57 on December 8th 2018, 3:09 pm

I have Quick fuel 750 q series with annular boosters on a mild 502 and absolutely love it. It's probably a little small, but on the street it's super crisp and responsive.

I recently picked up a Holley 950 hp for it and look forward to a back to back drag test on both carbs.

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Re: Thoughts on annular vs down leg for street truck

Post  Price5113 on December 8th 2018, 3:24 pm

I have used a List #9380 850 on many different combos for everyday street use and it works great. Very responsive & very "tractable"................

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Re: Thoughts on annular vs down leg for street truck

Post  rmcomprandy on December 8th 2018, 5:17 pm

Annular booster provide more booster signal at lower venturi airspeed however, give up some signal at higher venturi airspeed along with some cfm of airflow.
Most every combination of engine and carburetor size will require different things to be optimum; venturi boosters included.

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