Why Spreadbore Holley's Don't Work? [Archive] - Chevelle Tech

: Why Spreadbore Holley's Don't Work?


Dave427
Feb 25th, 11, 12:47 PM
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

cuisinartvette
Feb 25th, 11, 1:16 PM
Always wondered about that always liked the idea of small primarys.

Doesnt Holley still make the spreadbore?

jason dearduff
Feb 25th, 11, 1:31 PM
those carbs are nothin but trouble stick with the Qjet.

BillK
Feb 25th, 11, 1:36 PM
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.

Raffman
Feb 25th, 11, 1:55 PM
If you want to try I've got one I'll sell for 75.00...................

Mike
Feb 25th, 11, 2:19 PM
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.

RB69SS396Conv
Feb 25th, 11, 2:52 PM
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.

Dave427
Feb 25th, 11, 3:00 PM
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

bb67H-D
Feb 25th, 11, 3:05 PM
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.

Slowpoke70
Feb 25th, 11, 3:37 PM
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.

job68327
Feb 25th, 11, 3:56 PM
Are they the "econo-masters"?

mr 4 speed
Feb 25th, 11, 5:05 PM
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 :thumbsup: 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.

Raven1
Feb 25th, 11, 5:11 PM
I ran one on a 327 from 1983-1985, never had a problem with it.

MEJ1990TM
Feb 25th, 11, 5:12 PM
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.

Jerry Briggs
Feb 25th, 11, 5:40 PM
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.:D

thunderstruck507
Feb 25th, 11, 6:22 PM
I had one on my 355. (ported 882 heads, comp 268HE cam, headers, performer intake, hei, etc)

It worked great and got great mileage for the way I drove it.

I tried a 670 street avenger and it took a lot of work and the car never felt any faster, it bogged and ran like ass out of the box. So much for bolt on and go.

I had to up the front jets in it to 68s before it would run worth a crap.

Vintage Musclecar
Feb 25th, 11, 7:04 PM
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

Spreadbore Holleys "work" just fine provided they're on an appropriate installation--but they just don't compare to the more sophisticated and far more efficient primary booster design and primary metering rod system on a QJet. A well set-up QJet can deliver near FI-like throttle response and mileage if you spend enough time to dial it on.

Not too shabby for near 50 year old technology. :thumbsup: :beers:

langss
Feb 25th, 11, 8:29 PM
I ran one on a 4-speed 74 Corvette I had for a while. I took me a while playing with it,(jetting and pump cams),but once I got it where I wanted it, the mileage was great and if you put your foot in it on the freeway it was like passing gear in a powerglide.

Keith Tedford
Feb 25th, 11, 8:45 PM
I had one of those spreadbore 450 Holleys years ago. Every vehicle I put it on immediately lost better than 2 mph. Of course I didn't tune it at all. Other than that it worked fine. I had a 650 spreadbore Holley on a 4x4 in the late '70s. It was at least two mpg better that the Q'jet that it replaced. Playing with the jetting on the Q'jet could have gotten that 2 mpg back no doubt. Carbs that come from the factory on cars are dialed in for that particular application. Stuff from the speed shops is set up pretty generically. You have to set it up for your application. They were all designed to work for a certain application. You just have to figure out the combination that works best. A 4500 Dominator obviously isn't going to work on a 210 hp 327 no matter what you do.

hpsherlin
Feb 25th, 11, 11:07 PM
I ran a 650 double pumper spreadbore on my car from '85 to '92 or so. The same 454 in the car now but it was pure stock except for the carb back then. Drove it about 40,000 miles. Never had any problems with it.
Have a new 770SA on it now.
The spreadbore is out in the garage on a shelf. Probably be good again with a rebuild kit.

von
Feb 26th, 11, 6:55 AM
Do the spreadbore Holleys have primary metering rods controlled by vacuum or just the jets?

71454Chevelle
Feb 26th, 11, 7:42 AM
Do the spreadbore Holleys have primary metering rods controlled by vacuum or just the jets?

Jets

davewho1
Feb 26th, 11, 7:43 AM
Once we got it dialed in, my 6210-3 works great. Still needs some fine-tuning, but no complaints, other than it doesn't pass up many gas stations ... :D

I'm still going to go with my "correct" Q-Jet once I get it restored.

69-CHVL
Feb 26th, 11, 8:41 AM
Dave, just run whatever carb you had but focus on leaning out the primaries as best you can, and then open the PVCR's to compensate. Can be done pretty quickly if you get a wideband.

But really, a OD trans may give you the streetability you seek, like a 200r4 maybe. My pig got 15 mpg with a 4781 delivering a 12.8:1 AFR at cruise. Then EFI installed running 15:1 at cruise, mileage went only to 16:1. Evidently, my rpms are so low at cruise that AFR's dont do anything here. Admiittedly, the leaner setting will likely make a bigger difference for a motor running over 3000 rpms.

engineguy
Feb 26th, 11, 7:39 PM
Holley Spread-bore carburetors work very well on GM vehicles as Quadrajet replacements. This means a stock intake manifold, or one that is designed for Q-jet carb. Adapters do not work well at all. Have a vacuum secondary Holley spread bore carb on one of my trucks with 454 engine, RV cam, etc. Truck has more power and gets better mileage with the Holley than it did with the Q-jet, but it needed to be tuned. Proper jetting, powervalve, etc.

Jason Snyder
Feb 26th, 11, 7:49 PM
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=110649803504&viewitem=&sspagename=STRK%3AMEWNX%3AIT


HOW aboout this !! picked it up for 8.00 bucks shipped !!

1966_L78
Feb 26th, 11, 8:16 PM
Holley Spread-bore carburetors work very well on GM vehicles as Quadrajet replacements. This means a stock intake manifold, or one that is designed for Q-jet carb. Adapters do not work well at all. Have a vacuum secondary Holley spread bore carb on one of my trucks with 454 engine, RV cam, etc. Truck has more power and gets better mileage with the Holley than it did with the Q-jet, but it needed to be tuned. Proper jetting, powervalve, etc.

We swapped a 650 DP spreadbore for a tired Qjet ('68 Vette, 427, stock Q-jet low-rise alum intake, RV cam and headers). After we tuned it, he car definitely ran better than the Q-jet, but mileage was really poor (4.10 gears)... So we swapped to the Holley Spreadbore Vacuum secondaries ( also a 650 cfm)... After we tuned it, it "felt" slower (seat of the pants), but was actually quicker at the track ( 60-ft, 330 ft 660 ft 1000 ft, ALL quicker with VS vs DP). Of course, with street tires, the DP had to be tune to keep the tires from blowing off. The 650 was running out of breathe on the top end though. Much better driveability.

Swapped the 650 SB DP onto my stock 327 (stock '66 275 HP) with a Muncie and 4.10s in the 12-bolt... Lots of fun, and ran pretty good without bogging much, but buying gas and tries got old quickly...

But both version ran very nice. I think I still have the DP around somewhere...