which carb? - Impala Tech
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post #1 of 6 (permalink) Old 11-22-2018, 10:14 AM Thread Starter
 
 
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which carb?

I have 3 HOlleys to play with.

The car- 66 SS 396/425- 9.5 comp, 3400lbs, m22, 373 gears. crane energizer 282, 108lsa. 208 rec port heads
In Colorado at 5000'.

Current carb-4776- 4150/600cfm down jetted primary for altitude 63/76.
mech secondaries- Runs well. Crisp throttle response.

Possibillities- 4778-4150/700cfm- jets 66/76. mech secondaries- Rebuilt and
runs well. Crisp throttle response.

- 3310-12/ 750 vac sec. stock jets . quicker spring in diaphram.
GM had this on as original but a 780cfm.
a bit sluggish out of the hole. Going to try down jetting the
primary's for altitude and test.

Any insight would be appreciated.
So far I'm leaning towards the 600-4150. Have to look at the plugs a bit closer too.

Last edited by boyd66k20; 11-22-2018 at 10:15 AM. Reason: addition
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post #2 of 6 (permalink) Old 11-22-2018, 10:51 AM
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I would go for the 600cfm Holley (to be a 4150 it has a rear metering plate installed). Your intake won't support anything bigger.

The 780cfm was only installed on the High Rise intake with a solid cam rectangular port head that shifted at 7,800 RPM and went through the traps a 8,500 RPM.

If you are not willing to twist it that high (or your cam and heads won't support it) then a larger carb is useless. You would be better off with the better throttle response of the smaller carb.

Might add rectangular port heads on a motor smaller than a 500 cubic inches of displacement makes for a poor performing car. Racers learned that with a 396 the best head was an oval port head with larger valves installed (makes thirty horse more than the small valves). I think a head change would do more to improve performance than a carb change.

Big Dave
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post #3 of 6 (permalink) Old 11-22-2018, 12:25 PM Thread Starter
 
 
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Quote:
Originally Posted by Big Dave View Post
I would go for the 600cfm Holley (to be a 4150 it has a rear metering plate installed). Your intake won't support anything bigger.

The 780cfm was only installed on the High Rise intake with a solid cam rectangular port head that shifted at 7,800 RPM and went through the traps a 8,500 RPM.

If you are not willing to twist it that high (or your cam and heads won't support it) then a larger carb is useless. You would be better off with the better throttle response of the smaller carb.

Might add rectangular port heads on a motor smaller than a 500 cubic inches of displacement makes for a poor performing car. Racers learned that with a 396 the best head was an oval port head with larger valves installed (makes thirty horse more than the small valves). I think a head change would do more to improve performance than a carb change.

Big Dave
THink the plate is in the 3310. Both 4150's have 2 metering blocks.

Last edited by boyd66k20; 11-22-2018 at 12:45 PM. Reason: addition
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post #4 of 6 (permalink) Old 11-22-2018, 12:59 PM
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Correct that is the difference. If it is missing a rear metering block, it is a 4160. The 4160 has a metering plate that is missing the ability to change jet size or to have a power valve.

425 horsepower 396 was only available in 1965 in the Chevelle SS or the Corvette. Only the 427 SS Impala had rectangular port heads installed. Regular SS with a 427 was the 390 horse "Passenger" head (oval port).

In 1966 the 427 was introduced and the 425 horse 396 was down rated (same motor dynoed at a lower RPM at 375 horsepower and the 425 horsepower engine was the HiPerf 427 single four barrel using the same 780 cfm Dual feed vacuum secondary as used on the 375 horse 396).

Big Dave
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post #5 of 6 (permalink) Old 11-22-2018, 03:02 PM Thread Starter
 
 
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Quote:
Originally Posted by Big Dave View Post
Correct that is the difference. If it is missing a rear metering block, it is a 4160. The 4160 has a metering plate that is missing the ability to change jet size or to have a power valve.

425 horsepower 396 was only available in 1965 in the Chevelle SS or the Corvette. Only the 427 SS Impala had rectangular port heads installed. Regular SS with a 427 was the 390 horse "Passenger" head (oval port).

In 1966 the 427 was introduced and the 425 horse 396 was down rated (same motor dynoed at a lower RPM at 375 horsepower and the 425 horsepower engine was the HiPerf 427 single four barrel using the same 780 cfm Dual feed vacuum secondary as used on the 375 horse 396).

Big Dave
Yes, this engine is the 962 thick wall block that came from a 65 big bodied car. It is coded as an IE block, so not the corvette. Was the 425 in '65, and 375 then in 66 if I have my ducks in a row. Soon to be the 427. The corvette then got the only 425 designation. Has the 208 heads and the winters intake. This engine is all dated very close so I think it all came as an original package. Basically an L78. Think there were only about 1800 in the full size cars. It was a runner in its day. Sort of a transition between the 409 and 427 from what I deduce. I saw a brochure and I think you could get it in station wagons as well. heh heh. Whether it was ever installed in one might be debatable.
Thanks for your input and expertise Dave. It is what it is at this point, and am going to leave it as is. Would be worth something to a guy who wanted an era correct package for his '65 impala. It's never been bored. Maybe a Mark Jones engine is the answer for 500hp for the chevelle. I remember as a kid thinking wow, more hp than cubes with the 425. Never thought I'd own one.
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post #6 of 6 (permalink) Old 11-22-2018, 03:21 PM
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That block can be bored to 409 dimensions (4.3125" bore plus 0.060 over that) for a 481 cube Marl IV engine with the 396 crank.

It would be a lot cheaper to buy a 8 custom made pistons and run a Mark IV than to try that with a 72 degree 409 block. Or you could add a 4.25 inch stroke crank for 511 cubes. That way you can keep those over grown 320 cc rectangular port heads and run an 850 cfm Holley.

Only that block has the extra thick cylinder walls caused by GM's corporate board vacillating in their decision to continue building a 409 with modern Mark IV heads; or go for the high torque stroker engine with a 396. Since B-bodies kept getting heavier Chevy abandoned the oh so fine 409 for the added half inch of stroke with a 396. Longer the stroke the faster a motor builds torque so adding a half inch again to the 396 stroke of 3.76" makes for torque monster (with full inch longer stroke than the 409 only bored 0.060" over).

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