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Username Post: Big Block Carb Recommendation        (Topic#230087)
Seon 
Valued Contributor
Posts: 4954

Loc: Lake Camanche, CA
Reg: 07-14-02
11-20-09 08:35 PM - Post#1809520    

I'm looking to swap out the stock carb on my 454 big block engine in my '84 MH. Will an Edelbrock 1406 600 cfm be enough that the motor won't be stumbling?



 
RODBUILDER 
Forum Newbie
Posts: 4

Loc: Mo.
Reg: 03-22-08
11-20-09 09:14 PM - Post#1809529    
    In response to Seon

I would go with a 750 cfm that would be the smallest I would use on a bbc 454. A 600 will not flow enough I think.

 
Jim.Biron 
"7th Year" Platinum Supporting Member
Posts: 2524
Jim.Biron
Age: 64
Loc: Saugerties, NY
Reg: 04-10-08
11-21-09 05:16 AM - Post#1809599    
    In response to Seon

  • Seon Said:
I'm looking to swap out the stock carb on my 454 big block engine in my '84 MH. Will an Edelbrock 1406 600 cfm be enough that the motor won't be stumbling?





Try this calculator... Its the one I like
http://www.gtsparkplugs.com/CarbCFMCalc.html

or Holley's
http://www.holley.com/applications/Carburet orSelec...

The Holley is not quite as good (too many suggestions in size) but will point you in the right Holley direction if you use the first calculator to get the size.

As you can see for a low RPM (5000 rpm or under) motor home a 600 would probably do it.
Jim
www.HudsonValleyCruise.com


 
Don57 
"9th Year" Silver Supporting Member
Posts: 1267
Don57
Age: 64
Loc: Illinois
Reg: 04-28-00
11-21-09 05:43 AM - Post#1809609    
    In response to Jim.Biron

Isn't that stock carb a quadrajet? If so, you need to consider the spreadbore pattern when buying a replacement. That limits your options. (or change the manifold)
Don


Happy Birthday to all the 1964 cars and trucks that are 50 years old this year. Get your car a present!


 
Jim.Biron 
"7th Year" Platinum Supporting Member
Posts: 2524
Jim.Biron
Age: 64
Loc: Saugerties, NY
Reg: 04-10-08
11-21-09 11:29 AM - Post#1809762    
    In response to Don57

  • Don57 Said:
Isn't that stock carb a quadrajet? If so, you need to consider the spreadbore pattern when buying a replacement. That limits your options. (or change the manifold)



If it is a Q-Jet you might want to consider...
http://www.smicarburetor.com/
Jim
www.HudsonValleyCruise.com


 
Seon 
Valued Contributor
Posts: 4954

Loc: Lake Camanche, CA
Reg: 07-14-02
11-21-09 05:50 PM - Post#1809972    
    In response to Jim.Biron

I believe it is a quadrajet. The reason why I want to swap is to get better gas mileage but if I have to change manifold plus buy a new Edelbrock carb, it'd probably be best to have the stock one rebuilt.
Thanks guys.

 
Don57 
"9th Year" Silver Supporting Member
Posts: 1267
Don57
Age: 64
Loc: Illinois
Reg: 04-28-00
11-21-09 07:41 PM - Post#1810074    
    In response to Seon

I'd try rebuilding it first. It's the cheapest way and it might help. Holley has a spreadbore carb that's a replacement for the quadrajet, so that's an option and you wouldn't have to change the manifold.
Don


Happy Birthday to all the 1964 cars and trucks that are 50 years old this year. Get your car a present!


 
Petroholic 
Contributor
Posts: 839
Petroholic
Loc: Moses Lake, Wa.
Reg: 08-12-05
11-21-09 09:53 PM - Post#1810145    
    In response to Don57

  • Don57 Said:
Isn't that stock carb a quadrajet? If so, you need to consider the spreadbore pattern when buying a replacement. That limits your options. (or change the manifold)



Don't they make adapter plates, so the stock manifold can support a square bore, for the big blocks?

They do for the small blocks.



 
Impala65SS 
Valued Contributor
Posts: 3758
Impala65SS
Loc: Sweden
Reg: 08-23-07
11-22-09 10:45 AM - Post#1810367    
    In response to Seon

  • Seon Said:
I believe it is a quadrajet. The reason why I want to swap is to get better gas mileage but if I have to change manifold plus buy a new Edelbrock carb, it'd probably be best to have the stock one rebuilt.
Thanks guys.



If economy is the case, then you are correct - rebuild the Rochester!

Any adapters will screw up the flow direction, hence slowing the mixture, and the gas droplets suspension collapse - you will need to enrich the mixture to compensate...
The square pattern is good for higher rpm torque, because the primaries are larger.
At economic highway cruising, you want to have the smallest primaries possible, so you can have the butterfly valve as open as possible to yeild just enough torque to keep your cruising speed.
If the air flow is as high as possible at the highest possible velocity, you get the most out of the gas for the particular rpm you cruise at.

A half open butterfly is causing disruptive turbulence that is not what you want
- with 500hp 454 with a square pattern 850DP you have to moderate the butterfly of course, unless you want to cruise at 6000rpm and 140mph.
- Using a much smaller primary will help you draw use of the full venturi effect.
http://www.youtube.com/watch?v=SXn2QVipK2o&a mp;fea...


 
Don57 
"9th Year" Silver Supporting Member
Posts: 1267
Don57
Age: 64
Loc: Illinois
Reg: 04-28-00
11-22-09 04:02 PM - Post#1810512    
    In response to Impala65SS

I agree. The QJ is an economical carburetor if you stay out of the secondaries.

I had a 396 during the first gas crunch back in the 1970's and disconnected those big secondaries just so I could afford to drive it. It made a big difference.
Don


Happy Birthday to all the 1964 cars and trucks that are 50 years old this year. Get your car a present!


 
jetblue69 
Member
Posts: 157

Loc: Osteen, FL
Reg: 06-03-05
11-22-09 06:42 PM - Post#1810641    
    In response to Don57

The q-jet is probably one of the best carbs money can buy...IF you can get it tuned right.
The only substitution for cubic inches is more cubic inches.


 
BBC-454 
Senior Member
Posts: 1400
BBC-454
Loc: Edmonton, Alberta
Reg: 05-11-03
11-22-09 08:22 PM - Post#1810689    
    In response to jetblue69

Good luck trying to get better mileage from a big block in a motorhome. . . .

It takes alot of fuel to move a vehicle that big down the road at 50 mph, not really any way around it.
Josh R.L.
Licensed Automotive Mechanic
1966 Buick Special 2 door
1961 Chevrolet Apache 10 panel van
1995 GMC K2500
2011 VW Jetta TDI


 
Seon 
Valued Contributor
Posts: 4954

Loc: Lake Camanche, CA
Reg: 07-14-02
11-23-09 06:38 AM - Post#1810826    
    In response to BBC-454

Thanks to all for your suggestions. It's been years since I rebuilt a carb so thought that an Edelbrock would be the way to go to increase the mileage from 6mpg to 8-9 mpg. I'll give the MH a good tune-up and see if I can adjust the existing carb.
Again, thanks.

 
Johnny468 
"6th Year" Silver Supporting Member
Posts: 602
Johnny468
Loc: Richmond, Va.
Reg: 10-24-08
11-23-09 07:05 AM - Post#1810845    
    In response to Seon

What about your exhaust system? If it's fairly restrictive a more free flowing set-up should increase efficiency, especially on a big block.

Johnny
1965 Impala SS
505/4-speed/4.30


 
74camaro 
"4th Year" Silver Supporting Member
Posts: 401
74camaro
Age: 26
Loc: North Dakota
Reg: 03-27-07
12-02-09 07:08 PM - Post#1816781    
    In response to Seon

I have a 670 Holley on my 454 bored 30 over with a couple steps up from stock cam, headers, Edie Performer RPM intake. The throttle response is awesome and it produces plenty of bottom end torque, which is what you want. A good tune up would be good, along with opening up the air intake (open element air cleaner) and exhaust (headers, at least 2.25" pipes). I also agree with another poster- trying to get good mileage from a big block is like trying to get oil from a water spout- just aint gonna happen!
60 Bel Air, 283/ 3 spd on floor

65 GMC, getting a 327/ 4 spd winter of '14

70 C10, 350/ 350

74 Camaro, 355/ getting a 4 spd winter of '14

84 Monte Carlo SS, 305/ 700r4



 
Petroholic 
Contributor
Posts: 839
Petroholic
Loc: Moses Lake, Wa.
Reg: 08-12-05
12-02-09 08:42 PM - Post#1816845    
    In response to 74camaro

  • 74camaro Said:
I have a 670 Holley on my 454 bored 30 over with a couple steps up from stock cam, headers, Edie Performer RPM intake. The throttle response is awesome and it produces plenty of bottom end torque, which is what you want. A good tune up would be good, along with opening up the air intake (open element air cleaner) and exhaust (headers, at least 2.25" pipes). I also agree with another poster- trying to get good mileage from a big block is like trying to get oil from a water spout- just aint gonna happen!



There's a guy here somewhere that got in the high teens, with IIRC, a 3.08 rear, 700 tranny...in a truck!



 
phat rat 
Contributor
Posts: 324

Age: 70
Loc: muskegon mi
Reg: 09-02-09
12-03-09 04:10 AM - Post#1816920    
    In response to Petroholic

I have a 425hp/454 HO in my 41 cpe with 700R and 3.42 gears. I've gotten as high as 19.5 and 19.6 mpg. But yes with a motor home it's much more difficult, although you might consider U.S. Gear or Gear Vendor OD units

Edited by phat rat on 12-03-09 04:11 AM. Reason for edit: No reason given.

 
Nthefamily 
Contributor
Posts: 257
Nthefamily
Loc: North Ga.
Reg: 02-07-09
07-02-14 07:12 AM - Post#2466113    
    In response to phat rat

Phat rat, would you mind sharing what carb you are using?

I have put a 454 bored .30 in my 4x4 and have a 600 holley on it now.

I think it is a little small.

Thanks
65 C10
85 Silverado 4x4
92 S10


 
carbking 
Senior Member
Posts: 1210
carbking
Loc: Missouri
Reg: 06-14-03
07-05-14 09:20 AM - Post#2466788    
    In response to Seon

No recommendation, as each application is different, however will relate a similiar experience.

In 1979 my Dad bought a new 30 foot Winnebago built on a GM chassis with Chevrolet 454 CID engine AND a dual-fuel (propane) set-up.

I tried everything to talk him out of the dual fuel, but he wanted the extra tank for additional range (gasoline wasn't always easy to obtain at night in 1979).

The dual fuel turned out to be a horrible mistake! Driveability, power, and especially economy all suffered big-time when using the propane. Unloaded, Dad got about 9 MPG with the 800 CFM Q-jet; but NEVER better than 3 MPG on the propane (he never made 100 miles on a 40 gallon propane tank).

After he removed and gave away the $5,000 propane system and had some 30K on the motorhome; we started looking at alternative carburetion.

The problem: the factory cruise control could not open the secondaries on the Q-Jet without downshifting. As a result, the engine would overheat when loaded (we pulled my Ford Econoline full of carbs and parts) on the way to Hershey in the western PA mountains.

My solution: first I ordered a new Offenhauser square-bore intake manifold (the Q-Jet was a spread-bore, and while I love the spread-bore design on passenger vehicles and pickups, the primaries are TOO SMALL for a motorhome). Next I rebuilt a Carter 4760s (750 CFM) AFB. Dad was watching, and asked about the manual choke. So I married the choke and fast idle components (it requires some machine work) from a junk 9625s (electric choke) Carter AFB. Then I modified the original aircleaner for cold-air induction (the air temperature in that dog-house is HOT).

Put it all together, tried the power on a hill on the local interstate (from a stopsign on the on-ramp, for the first time we able to acquire merging speed on the ramp, an increase in some 12 MPH).

That fall, took the motorhome again to Hershey. Same route, same cruise-control setting .... TWO HOURS LESS DRIVING TIME!!! The cruise control would hold the specified speed in the mountains.

Fuel economy before the change:

Unloaded:

Propane - < 3 MPG
Gasoline - average about 9 MPG


Loaded (pulling my van)

Propane - not possible, it simply wouldn't!
Gasoline - 6.3 MPG

After the change (propane had been removed):

Unloaded as high as 11, generally about 10.4 MPG
Loaded 6.9 MPG

After I related this story to a friend at Carter, the Carter 9755s (750 CFM with choke and fast idle) appeared. It turns out he also had a GM motorhome with the same issues we had.

Again, my experience. NOT a recommendation.

Jon.
Good carburetion is fuelish hot air!

The most expensive carburetor you will ever buy.....is the incorrect one you attempt to modify!

If you truly believe "one size fits all", trying walking a mile in your spouse's shoes!


 
carbking 
Senior Member
Posts: 1210
carbking
Loc: Missouri
Reg: 06-14-03
07-05-14 09:29 AM - Post#2466792    
    In response to carbking

And a bit of food for thought:

The primary/secondary CFM splits:

800 CFM Q-Jet 200 / 600
750 CFM AFB 375 / 375
600 CFM AFB 250 / 375 (the 250 is NOT an error)!

Jon.
Good carburetion is fuelish hot air!

The most expensive carburetor you will ever buy.....is the incorrect one you attempt to modify!

If you truly believe "one size fits all", trying walking a mile in your spouse's shoes!


 
Nthefamily 
Contributor
Posts: 257
Nthefamily
Loc: North Ga.
Reg: 02-07-09
07-05-14 10:04 AM - Post#2466803    
    In response to carbking

Carbking,
Thanks for the information!

The cam I am running in my 454 bored .30 is a comp cam XR270HR part# 11-422-8.

Will this big of a cam require a larger carburetor than I am using now (600 cfm holley), or do I just need to do more adjusting on the carb and timing? As of now, the timing is set at around 12º BTDC.

The truck is just a weekend driver, occassional trailer puller, wood hauler.

Also, with this cam is my stock tourque convertor okay? The guy who built my engine said it was one just before needing a stall convertor.

Thanks.
65 C10
85 Silverado 4x4
92 S10


 
carbking 
Senior Member
Posts: 1210
carbking
Loc: Missouri
Reg: 06-14-03
07-05-14 10:28 AM - Post#2466806    
    In response to Nthefamily

Read my previous post on loaded vs unloaded (of course this was a motorhome application), and think about the weight of your 4x4 when either pulling the trailer or hauling wood.

Also check the second line in my "signature".

Jon.
Good carburetion is fuelish hot air!

The most expensive carburetor you will ever buy.....is the incorrect one you attempt to modify!

If you truly believe "one size fits all", trying walking a mile in your spouse's shoes!


 
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