Why Spreadbore Holley's Don't Work? - Chevelle Tech
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post #1 of 27 (permalink) Old Feb 25th, 11, 11:47 AM Thread Starter
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Why Spreadbore Holley's Don't Work?

Its a question I have been thinking of this long winter here in the Great White North.
You have to think of their concept here, but it didn't catch on or work.
Quadrajets are great on gas cruising on the small primary's, so why shouldn't the Holley spreadbore, being the same.
Quadrajets have their huge secondary throttle blades for great secondary action with their huge cfm, same as the Holley spreadbore, they actually use a Dominator throttle plate for this.
So I am going to buy either a 6210 or a 6211 to do some experimenting on.
I am going to try to make it a great cruising carb with their small primary's and "TRY" to make it really hit hard with their huge secondary's.

I think it should work, or be a bogging piece of crap like most of them were?

Dave
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post #2 of 27 (permalink) Old Feb 25th, 11, 12:16 PM
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Re: Why Spreadbore Holley's Don't Work?

Always wondered about that always liked the idea of small primarys.

Doesnt Holley still make the spreadbore?

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post #3 of 27 (permalink) Old Feb 25th, 11, 12:31 PM
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Re: Why Spreadbore Holley's Don't Work?

those carbs are nothin but trouble stick with the Qjet.
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post #4 of 27 (permalink) Old Feb 25th, 11, 12:36 PM
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Re: Why Spreadbore Holley's Don't Work?

Dave,
I had one on the 355 in my Heavy Chevy for quite a few years. Ran 12.50's and still was very driveable on the street. I think that the main difference from the Q-jet is the fact that the Holley is a mechanical secondary carb. The Q-jet will not open the secondaries until the engine really needs the air flow, where the Holley is going to open them no matter what if you put your foot in it. I certainly was not concerned with fuel mileage back then, but I dont remember it being terrible. I used to drive back and forth to Boston a few times a year and I bet it got at least 16 - 18 mpg, maybe better.

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post #5 of 27 (permalink) Old Feb 25th, 11, 12:55 PM
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Re: Why Spreadbore Holley's Don't Work?

If you want to try I've got one I'll sell for 75.00...................

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post #6 of 27 (permalink) Old Feb 25th, 11, 1:19 PM
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Re: Why Spreadbore Holley's Don't Work?

Ran one of the 4165's back in the early 70's on a 400GP and it worked fairly well.
Was surprised it got better mileage than the QJ considering the mechanical secondaries.
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post #7 of 27 (permalink) Old Feb 25th, 11, 1:52 PM
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Re: Why Spreadbore Holley's Don't Work?

I've run both the 6210 and 6211 on various combos for the last 30 years or so.

It's always amusing to see people who have never had something, bashing on it.

Not sure where the "nothing but trouble" comment could possibly have come from; they're typical stock-ish Holleys, with side-hung bowls and a fuel transfer tube; just yerbasic street carb. The only significant difference between them and a square-bore side-hung 4-bbl like alot of the Frod and Xler stock ones in the 60s, is the bore dia.

Properly calibrated, they have no "bogging" problem in particular, any more than any other carb. Less than some others maybe even, given the small primaries. IMproperly calibrated (including out-of-the-box), who knows.

I ran a 6211 on a SBC 400 for many years. At various times it had a Comp 282S, XE274, and XR282HR in it. With a T-5 and 3.23 gears, it got just shy of 20 mpg on the highway, with all 3 cams.

The 6210 is still avaliable new; not sure about the 6211.

Raffman, excatly what carb do you have? (list #, approx age) I could be interested.
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post #8 of 27 (permalink) Old Feb 25th, 11, 2:00 PM Thread Starter
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Re: Why Spreadbore Holley's Don't Work?

Well good, a few people have had decent reviews with them.
I am just bored and I want throw something together to see if it works.
I want to see if I can make a double pumper Holley that performs well, but get good fuel mileage with small primaries.


Dave
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post #9 of 27 (permalink) Old Feb 25th, 11, 2:05 PM
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Re: Why Spreadbore Holley's Don't Work?

I ran an older 4165 800 on the 408bbc in the '67 for over 20 years and never a problem,
it did have a rich idle but never a bog.
I did put a kit in it once but never changed a thing.
A few years ago I rebuilt a '68 3310 780 and thats been on the car since and I like it.
Mileage seems close between to two.

Brett
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post #10 of 27 (permalink) Old Feb 25th, 11, 2:37 PM
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Re: Why Spreadbore Holley's Don't Work?

I might be doing the same thing out of boredom. I recently re-discovered a few carb bodies in a forgotten junkpile. Most either came from junkyard engines i pulled or were donations from other guys' scrap piles, usually when they either upgraded to DPs or gave up on Holley and went to Edelbrock.

One of these is a complete 4165, LIST-6710 800cfm spreadbore holley. I'd really like to mate it to an spreadbore RPM or Stealth, but I've got a stock alum QJ intake sitting on a rack. Now if I can only pry the main body off of the baseplate without tearing up the gasket between them, I could give it a nice thorough cleaning and put it back together without spending any money. Then I'm just a spread-to-square adapter (free) or set of intake gaskets (not free) away from testing it out. CFM is probably overkill for a Isky z-25 cammed, Sportman II headed, 9.7:1 355, but would be fun to try out.

Anybody know how to figure out the part number for JUST the gasket that goes between the mainbody and baseplate? The rest of the gaskets should be in my inventory of rebuild kit left-overs.

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post #11 of 27 (permalink) Old Feb 25th, 11, 2:56 PM
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Re: Why Spreadbore Holley's Don't Work?

Are they the "econo-masters"?

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post #12 of 27 (permalink) Old Feb 25th, 11, 4:05 PM
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Re: Why Spreadbore Holley's Don't Work?

Quote:
Originally Posted by job68327 View Post
Are they the "econo-masters"?
No.The Economaster is a tiny mechanical secondary spreadbore thats 450 cfm.All the throttle bores are the same size and there is no secondary accelerator pump.Work good on a 307 or a stock 350 that you don't rev high. I have used both the 650 (vacuum and mechanical secondaries) and 800 cfm spreadbore carbs. The 800 sure hits hard on a WOT powershift with a stick car The 650 works pretty decent on a 396-400 cubic inch motor...not bad with a 350 either,especially with a high stall convertor.Never had to jet one..they always ran great right out of the box.
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post #13 of 27 (permalink) Old Feb 25th, 11, 4:11 PM
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Re: Why Spreadbore Holley's Don't Work?

I ran one on a 327 from 1983-1985, never had a problem with it.
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post #14 of 27 (permalink) Old Feb 25th, 11, 4:12 PM
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Re: Why Spreadbore Holley's Don't Work?

The spread bore worked real well on the '70. It will go back on one of these days, but since I need to pull the engine out of the '71 the 3310 is staying on there for a while longer.

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post #15 of 27 (permalink) Old Feb 25th, 11, 4:40 PM
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Re: Why Spreadbore Holley's Don't Work?

Quote:
Originally Posted by Dave427 View Post
Quadrajets are great on gas cruising on the small primary's,
Dave
That's what they always said but I could never drive with just the primary's working. For some reason the secondary's seemed to always be open unless my foot was on the brake. Maybe that's why I got only 6 or 7 miles per gallon. Mom always wondered why I needed more gas money.
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