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Old 05-21-2021, 06:34 PM
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Default Holley 800 Spreadbore Carb?

Anyone have any experience with an 800 CFM Holley Double pumper in the spreadbore configuration? Holley still makes the 650 version. Just wondering if the 800 w. mechanical secondaries might work on better on my 455 with a dual pattern intake that has a spreadbore shaped plenum flange. Ran across a nicely rebuilt unit and kind of like the small primary/big secondary layout that might give better fuel distribution with my intake.

I currently run a 750 QuickFuel w. vacuum secondaries with the intake block of plate and have an off idle I can't tune out. Tried additional idle air and also moved the pump cam to the top hole but still stumble on slow throttle tip-in off-idle.

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Last edited by NeighborsComplaint; 05-21-2021 at 06:51 PM.
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Old 05-21-2021, 06:48 PM
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I have played with a bunch of the 800 CFM Holley Spread Bore Carbs.
The majority of them being the Model: List # 6211.

They had smaller Fuel Bowls vs the normal #3310 type Square Bore Carbs.

When matched with a Holley Street Dominator Intake Manifold they were supposed to be 3% better on HP and torque vs a typical #3310 780 carb, per Holley advertising.
Holley build Emissions carbs and Street Performance Spread Bore Carbs, the #6211 being a good fit for a Pontiac engine size.

Tom V.

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Old 05-21-2021, 06:52 PM
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I had one on my 69 gto ram air IV back in the late 80’s it went 12.80@108 on the stock intake. I just got one a few months ago but have only used it on the test stand.

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Old 05-21-2021, 07:07 PM
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I had one years ago on a stock 68 Goat and it was for sure a tad too much as the Q jet ran better overall!
I have to say that with the 13% more cid of your motor and the way it’s built it should be a plus for you,

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Old 05-21-2021, 08:34 PM
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Many years ago, my friend put one on his '70 W30 Olds with the 328 deg cam. It was a pretty good match.

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Old 05-21-2021, 08:46 PM
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The one I had then and the one I just got are both dual feed double pumpers.

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Old 05-21-2021, 10:47 PM
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Had one on 462. It ran really good.

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Old 05-21-2021, 11:16 PM
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Quote:
Originally Posted by Tom Vaught View Post
I have played with a bunch of the 800 CFM Holley Spread Bore Carbs.
The majority of them being the Model: List # 6211.

They had smaller Fuel Bowls vs the normal #3310 type Square Bore Carbs.

When matched with a Holley Street Dominator Intake Manifold they were supposed to be 3% better on HP and torque vs a typical #3310 780 carb, per Holley advertising.
Holley build Emissions carbs and Street Performance Spread Bore Carbs, the #6211 being a good fit for a Pontiac engine size.

Tom V.
This one is a List-6212 with standard center hung float bowls.


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Old 05-22-2021, 06:52 AM
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They work really well! Ran one for years. Thing of beauty with a stick shift! Just know that the idle mixture screws are adjustable air bleeds vs. fuel control like most. So CCW means leaner. Also gotta be conservative when you tighten the mounting nuts (Which are a pain in the a$$). The secondaries will bind up very easily. I tightened the return spring on mine. Don't recall how. Re-bent the spring tail maybe.

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Old 05-22-2021, 07:19 AM
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I've got a decent pile of them under one of the work benches. They probably aren't much good as they hit the concrete floor pretty hard before I kicked them under the bench.

Not a fan of the smaller variety and never have been.

The 800cfm versions are a different story and work very well on a spread bore intake making more power than square flange carbs as they line up in the center of the plenum areas so the air entering the intake doesn't have to "bend" as much.....FWIW.....

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Old 05-22-2021, 10:52 AM
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Thanks for that info, Cliff. That was my impression of the 800 also. My squarebore carb alignment is a mismatch to the runners and I thought I might give this one a try.

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Old 05-22-2021, 10:56 AM
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Quote:
Originally Posted by JSchmitz View Post
They work really well! Ran one for years. Thing of beauty with a stick shift! Just know that the idle mixture screws are adjustable air bleeds vs. fuel control like most. So CCW means leaner. Also gotta be conservative when you tighten the mounting nuts (Which are a pain in the a$$). The secondaries will bind up very easily. I tightened the return spring on mine. Don't recall how. Re-bent the spring tail maybe.
Not all are reverse idle mixture. I have one that is set up with conventional idle mixture like a 4150.
It works great on a 455 with stock intake.

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Old 05-22-2021, 12:17 PM
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Quote:
Originally Posted by NeighborsComplaint View Post
This one is a List-6212 with standard center hung float bowls.

I have one of these 800's in my collection that I ran for awhile.
The bowl & block gaskets are per that design only unlike regular 4150 style.
They run fine

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Old 05-22-2021, 01:21 PM
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If you look at the Metering Block on the Primary Side (right side of the carb in the picture)
you will see that the Metering Block has the normal spread-bore "reverse idle" circuitry:
Fixed Idle Fuel Restriction and adjustable Idle Air Circuit. The rear block has the Normal fuel circuits (like a #3310-1 carb). (No adjustable 4 corner idle capability).

The idle of the engine will tend to vary somewhat (with the atmospheric conditions), but aside from that the carb will function in a normal manner.

Tom V.

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Old 05-22-2021, 01:31 PM
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Are you guys sure the 800's had the reverse idle systems? I have never seen an 800 with them and as far as I know all the 800's were considered a "performance application". Most 650's used the reverse idle system unless they were considered a "performance application" carburetor, then they used the standard adjustment idle screws.

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Old 05-22-2021, 02:10 PM
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[QUOTE=PAUL K;6252032]Are you guys sure the 800's had the reverse idle systems? I have never seen an 800 with them and as far as I know all the 800's were considered a "performance application". Most 650's used the reverse idle system unless they were considered a "performance application" carburetor, then they used the standard adjustment idle screws.[/QUOTE
Yes as Mr. V mention they do have reverse idle

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Old 05-22-2021, 02:12 PM
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Blabber Mouth, Paul LOL!

Guys have been playing with spread bore carbs on GM engines for many years.
Remove the Air Horn and you do not have a list number to go by.
The easiest way to tell if the carb is all ORIGINAL and a 800 cfm Spread bore carb
without reverse idle is to look at the pictures attached. You might still be wrong though.

The first picture is the Main Body Idle Circuit drilling.

The second picture is the Idle Circuit for the Reverse Idle Carbs.

So if you "modify" the appearance of the carb slightly you can make the 800 cfm carb into a 650 carb (in appearance). Look at the pictures and post how you would do that.

Tom V.
Attached Thumbnails
Click image for larger version

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ID:	567033   Click image for larger version

Name:	Reverse Idle -2.jpg
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ID:	567034  

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Old 05-22-2021, 05:18 PM
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OK, you all convinced me to give it a try. Carb was just rebuilt with a Holley HP kit. I'm thinking the manual choke might be worth keeping also instead of converting to electric.

I guess the ol' Holley sniper dream I had can wait. lol


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Last edited by NeighborsComplaint; 05-22-2021 at 05:37 PM.
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Old 05-22-2021, 06:25 PM
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quote: OK, you all convinced me to give it a try. Carb was just rebuilt with a Holley HP kit. I'm thinking the manual choke might be worth keeping also instead of converting to electric.

I guess the ol' Holley sniper dream I had can wait. lol Quote

(I saw no need to copy the oversize picture again.)
That 800 cfm carb should be very nice for you. Just use it with a spread bore manifold as was mentioned by other posters.

Tom V.

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Old 05-22-2021, 07:12 PM
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Quote:
Originally Posted by PAUL K View Post
Are you guys sure the 800's had the reverse idle systems? I have never seen an 800 with them and as far as I know all the 800's were considered a "performance application". Most 650's used the reverse idle system unless they were considered a "performance application" carburetor, then they used the standard adjustment idle screws.
I don't think they are sure. I have a 6212 just like the one in the photo. It does NOT have reverse idle circuits.

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