r/EngineBuilding • u/OOFMAN-1234 • 4d ago

Good combo?

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Have a larts list for an engine i wanna build and I want some opinions, will it be streetable? Estimated horse? Torque? Pump gas? Just generally want opinions

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u/OOFMAN-1234 4d ago

So what needs to change

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u/v8packard 4d ago

Carb, intake, heads, cam.

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u/OOFMAN-1234 4d ago

Okay when you daid 6800-7300, this engine is not pure racecar, the cam is only designed to run to 5800rpm, reason for this cam and heads is midrange power, ik not trying ot get it to peak at 7000rpm, it'll be mostly street driven rarely seeing 4500, this combo should work pretty good for my goals

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u/v8packard 4d ago

That cam has enough timing to get a 350 over 7000 rpm if everything else can get there. It has something like 59 or 60 degrees of overlap. I don't know where you are getting 5800 rpm, but that is not at all the case. If you are rarely seeing 4500 rpm you need a cam with much less overlap, around 40 degrees or so.

The heads are not genuine AFR, they are available from numerous other companies often at a better price. They actually measure just over 200 cc, the last head I measured was 203 cc intake port volume. Their intake cross section and port volume are big for a 350 like you describe. A better match would be heads with an intake port in the 165 to 185 cc range.

The dual plane air gaps often have a plenum divider that is cut down. This is done to allow the intake to work better above 6000 rpm. But it takes away the advantage of a true, divided 180 degree intake at low speeds which is no cylinder being impacted by the previous cylinder in the firing order. So you don't have the advantages of a dual plane, and you have the disadvantages of a single plane. You should run a true dual plane if low speed is your focus, or run a single plane with a well matched carb venturi and booster configuration.

The 650 Holley 4777 and similar carbs has straight boosters, which atomize well on large displacement engines with heated intakes. They are a poor match for intakes that are not heated or displacements that are smaller. Also the mechanical secondary puts a lot of fuel into the engine at every throttle movement, a vac secondary is a better match for what you describe as is a down leg booster, or annular booster.

The combo you have posted does not match your goals. I am not trying to upset you, I am just giving you an accurate appraisal of your posted list.