Dual motorcraft 2 barrels vs holley 4 barrel ??? - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 05-13-2012, 10:42 PM
Augusto's Avatar
From the middle of the world
 
Last wiki edit: How to rebuild an engine Last photo:
Join Date: Mar 2006
Location: Ecuador, South America
Age: 51
Posts: 1,314
Wiki Edits: 6

Thanks: 4
Thanked 2 Times in 2 Posts
Dual motorcraft 2 barrels vs holley 4 barrel ???

ok, let's start this way, no, I can not just order a 750 from holley, it's expensive and hard from here.

so I was thinking of a way to feed the hunger of my supercharged 358 SBC, it's a 144 blower so a 750-800 CFM is perfect, all I have is a couple of 600 CFM 1850's

I have two Motorcraft 2 barrels, came out of stock 351W engines, what if I make an adaptor and run this two babies?

what are they... like 500 CFM each ? that'll be 1.000 CFM for the pair..!!!

anyone ever done this before?

thanks.

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 05-14-2012, 12:02 AM
4 Jaw Chuck's Avatar
Hotrodders.com Moderator
 
Last photo:
Join Date: Mar 2002
Location: Manitoba, Canada
Age: 46
Posts: 5,062
Wiki Edits: 0

Thanks: 2
Thanked 108 Times in 87 Posts
They are 350cfm each for the large venturi versions, the small venturi are 287 cfm. Don't forget two barrels are rated at a different level of vacuum drop so its not comparable.

My first suggestion is where are you going to get jets to make it work? I used to have a selection of MC jets that ranged from 47-62 that took a long time to collect from the boneyards, the largest (62) only came in the MC four barrels off a big block AMC.

Then of course there is the issue of dual accel pumps and nozzles that aren't replaceable, how are you going to tune that? Can't just block one off either because the original pump cavity is pretty small compared to a Holley 50cc Rio pump.

Anything is order-able via the internet these days, it will just cost you more...my guess is either your time is worthless to you and you have tons of it to burn so this project which might save you a few hundred dollars makes it a good idea, I don't know Augusto, anything is possible but have fun reinventing the wheel. My opinion is though, its a fire waiting to happen at the first cough when you whack open those twin carbs without dyno/flow testing it first.

If it were me, and I had unlimited time to burn I would do a triple setup, stage the outboards carbs to half throttle and custom cast/fabricate an AL manifold to make it all fit. At least this way you can run on the primary center carb to get it running and fool with the outboard carbs to find a tune that will work...you will likely have to custom make or silver solder/braze up some old jets and redrill to a custom size to make it run right...at least not impossible and it will run until half throttle at least.

Where are you going to get a manifold to fit all this? Weld it up out of pipe and some sheet-metal? Just so you don't too excited, every time I have seen some hair-brained scheme like this put into action the motor ended up making a lot less or only a few HP more than a stock setup and it ran like crap and was impossible to tune.

Other than those caveats, good luck on your project!

P.S. This is a SBC right? Why not just find a modern fuel injection and forget this idea, a lot less work and your at least guaranteed a performance/economy gain...it will be a lot easier.
__________________
Outlawed tunes from outlawed pipes
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 05-14-2012, 03:17 AM
cobalt327's Avatar
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 60
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 597 Times in 546 Posts
Quote:
Originally Posted by Augusto
ok, let's start this way, no, I can not just order a 750 from holley, it's expensive and hard from here.

so I was thinking of a way to feed the hunger of my supercharged 358 SBC, it's a 144 blower so a 750-800 CFM is perfect, all I have is a couple of 600 CFM 1850's

I have two Motorcraft 2 barrels, came out of stock 351W engines, what if I make an adaptor and run this two babies?

what are they... like 500 CFM each ? that'll be 1.000 CFM for the pair..!!!

anyone ever done this before?

thanks.
I believe you can make the Holley 600's work, providing you can mount them on that small of a blower case. I know they're usually used w/a single 4 barrel, but because the 600 carbs are vacuum secondary, you can still not be over carbureted using them- if you can mount them, that is.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 05-14-2012, 05:39 PM
Augusto's Avatar
From the middle of the world
 
Last wiki edit: How to rebuild an engine Last photo:
Join Date: Mar 2006
Location: Ecuador, South America
Age: 51
Posts: 1,314
Wiki Edits: 6

Thanks: 4
Thanked 2 Times in 2 Posts
Quote:
Originally Posted by cobalt327
I believe you can make the Holley 600's work, providing you can mount them on that small of a blower case. I know they're usually used w/a single 4 barrel, but because the 600 carbs are vacuum secondary, you can still not be over carbureted using them- if you can mount them, that is.
you mean mouting two 600CFM atop the blower?

since they are vaccum secondaries... makes a lot of sense to me.. I guess I should use the hardest springs in the vaccum pots to prevent over-carburation.? or maybe not?

fabricating a funnel adaptor would be pretty simple and would look even meaner than the two motorcraft 2 barrels..
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 05-14-2012, 05:47 PM
Augusto's Avatar
From the middle of the world
 
Last wiki edit: How to rebuild an engine Last photo:
Join Date: Mar 2006
Location: Ecuador, South America
Age: 51
Posts: 1,314
Wiki Edits: 6

Thanks: 4
Thanked 2 Times in 2 Posts
Quote:
Originally Posted by 4 Jaw Chuck
They are 350cfm each for the large venturi versions, the small venturi are 287 cfm. Don't forget two barrels are rated at a different level of vacuum drop so its not comparable.
are this figures the equivalent for the 4bbl rating at 1.5" ?

Quote:
Originally Posted by 4 Jaw Chuck
Where are you going to get a manifold to fit all this? Weld it up out of pipe and some sheet-metal? Just so you don't too excited, every time I have seen some hair-brained scheme like this put into action the motor ended up making a lot less or only a few HP more than a stock setup and it ran like crap and was impossible to tune.
atop the supercharger, only a sheetmetal funnel would be needed


Quote:
Originally Posted by 4 Jaw Chuck
P.S. This is a SBC right? Why not just find a modern fuel injection and forget this idea, a lot less work and your at least guaranteed a performance/economy gain...it will be a lot easier.
this is for a racing engine, a racing EFI would be quite expensive.

seems like it's not a very good idea, maybe the two 600 holleys seems a better idea, what do you think?
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 05-14-2012, 05:56 PM
cobalt327's Avatar
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 60
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 597 Times in 546 Posts
Quote:
Originally Posted by Augusto
you mean mouting two 600CFM atop the blower?

since they are vaccum secondaries... makes a lot of sense to me.. I guess I should use the hardest springs in the vaccum pots to prevent over-carburation.? or maybe not?

fabricating a funnel adaptor would be pretty simple and would look even meaner than the two motorcraft 2 barrels..
Yeah, two 600s on top of the blower.

The secondary springs would need to be experimented with until you found the right tension for them. This could mean cutting or shimming the stock springs as needed to get them to behave like they need to. You might want to use a secondary throttle stop to keep the secondaries from opening 100%- that might let you use a lighter secondary spring w/o over carb'ing it.

Same thing for the accelerator pump shooter size and cam; gonna take a fair amount of trial and error to dial it all in. But I don't see a reason you couldn't get satisfactory performance out of it.

Something else you can look into is boost referencing the power valves.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 05-14-2012, 09:42 PM
Augusto's Avatar
From the middle of the world
 
Last wiki edit: How to rebuild an engine Last photo:
Join Date: Mar 2006
Location: Ecuador, South America
Age: 51
Posts: 1,314
Wiki Edits: 6

Thanks: 4
Thanked 2 Times in 2 Posts
you make me wish I had bought a 6-71 instead...

the two 4 bbl would look just awsome, instead of limiting the secondaries travel, how about plugging the secondaries of the second carb? (nobody would know about that)

that would be a 6 barrel setup, good for maybe 900 CFM ?

what do you think?
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 05-15-2012, 06:37 AM
cobalt327's Avatar
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 60
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 597 Times in 546 Posts
Quote:
Originally Posted by Augusto
you make me wish I had bought a 6-71 instead...

the two 4 bbl would look just awsome, instead of limiting the secondaries travel, how about plugging the secondaries of the second carb? (nobody would know about that)

that would be a 6 barrel setup, good for maybe 900 CFM ?

what do you think?
The only possible downside I could think of is air/fuel distribution possibly being a bit upset by the difference in the distance between the "primary" carb's (the one using just the front bores) throttle bores to the secondary carb's primary throttle bores. But I'd bet that won't amount to enough to matter one way or the other, especially if the primary carb sits behind the secondary carb so the primary carb's throttle bores are more centered. This will matter even less if the engine will be running wide open most of the time.

If it wasn't for the throttle linkage, putting the carbs facing primary-to-primary on top of the blower would center both of the primaries. In other words, the rear (primary) carb mounted normally, the front (secondary) carb turned around "backwards".

BTW, what kind of competition is this for?
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 05-15-2012, 08:48 AM
Augusto's Avatar
From the middle of the world
 
Last wiki edit: How to rebuild an engine Last photo:
Join Date: Mar 2006
Location: Ecuador, South America
Age: 51
Posts: 1,314
Wiki Edits: 6

Thanks: 4
Thanked 2 Times in 2 Posts
is for drag racing, so most of the time it will be at WOT

I'm thinking of making a funnel type adaptor, not very flat, this will help with the airflow, but I'm not worried much because above the blower this does not matter too much, even fuel distribution takes place in the manifold under the blower and this won't be disturbed.

maybe the large plenum under the carbs may induce some little lag and may requiere a large fuel shot, but since there will be two squirters maybe it won't happen, only way to really know is making it.

I just saw that weiand, for their tunnel ram manifold reccomends for a hot natural aspirated street engine up to two 600 cfm carbs, and for racing up to two 750's so I guess for a supercharged 358 two 600's won't be overkill.

the visual impact alone I think is enough reason to make it
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 05-15-2012, 10:09 AM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,211
Wiki Edits: 0

Thanks: 5
Thanked 389 Times in 383 Posts
You can feed a supercharged motor a lot more carb cfm than you think.
The normal carb size rules do not apply. if you want power.
( The normal rules are too conservative for max power anyways)

A Qjet is 750 cfm (pre 1974) or 795 cfm (post 1974) depending on the model
A Qjet with a few mods makes a great carb for that lil blower.

Some factory oem carter AFB's / AVS carbs are quite big too.
A carter thermo quad is like 900cfm.

A edelbrock 750 will work very well too.

ALL these OEM carbs will work and make big power when set up right.

A external power piston boost vac control can be made from a 4 hole carb spacer.
Power piston boost referenceing is nessessessary if using high blower boost
as the blower will pull hard on the carb at Max boost and may shift the pri metering rods to lean @ WOT .

If only using moderate blower boost this can be delt with by the power piston spring choice. You determine this by measuring the vacuum producted under the carb ( above the blower) when at WOT high rpm MAx boost when the blower is pulling the hardest on the carb. A small carb and or a higher blower drive ratio will make the vacuum pulled @WOT increase.

B&M used to sell a optional dual 4 bbl carb top for that blower.
(info only these are no longer available)

Surely you have Qjets there. The Qjet is you go to factory OEM carb to use for this.

Last edited by F-BIRD'88; 05-15-2012 at 10:20 AM.
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 05-15-2012, 10:22 AM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,211
Wiki Edits: 0

Thanks: 5
Thanked 389 Times in 383 Posts
What is the blower drive ratio you will be using?
(pulley diameters)
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 05-15-2012, 11:58 AM
Augusto's Avatar
From the middle of the world
 
Last wiki edit: How to rebuild an engine Last photo:
Join Date: Mar 2006
Location: Ecuador, South America
Age: 51
Posts: 1,314
Wiki Edits: 6

Thanks: 4
Thanked 2 Times in 2 Posts
sure I was thinking of using boost referenced power valves, I know how important they are,

the pulley ratio is 2.4 6in drive, 2.5in driven.

I have a q-jet from a 454 that's supposed to be 850 cfm

but I kinda felt in love with the idea of twin carbs atop the blower
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 05-15-2012, 02:11 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,211
Wiki Edits: 0

Thanks: 5
Thanked 389 Times in 383 Posts
If you are using it for 1/4 mile racing only you can eliminate the primary metering rods and power piston and spring. Increase the primary jetting accordingly.

From there most of the jetting and tuning is done by the sec metering rods and hanger choice. start rich
The stock Qjet needle seat is .125" you want the larger .135" or .149" (edelbrock part) needle seat assembly.
The secondary air door is controlled by the spring tension adjustment combined with the vacuum diaphram brake on the side of the carb. The orifice size of the vacuum brake sets its delay timing. They both work together. and are tied into the choke and fast idle linkage.

you need lots of fuel flow volume but not much fuel pressure. 6psi

the 2.4:1 drive ratio will require high octane gas 110 or more.
I would start with less boost and sneak up on the tune.

The accelerator pump shot will need to be maximized.

Only a few of the Buick and Pontiac BB motors came with the 850cfm Qjet.
A Qjet from a 454 is likely 795 cfm. The difference is the primary booster design.

Here is a sweet cam for the blower on a SBC Lunati #401a3LUN

Last edited by F-BIRD'88; 05-15-2012 at 02:23 PM.
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 05-15-2012, 06:54 PM
Augusto's Avatar
From the middle of the world
 
Last wiki edit: How to rebuild an engine Last photo:
Join Date: Mar 2006
Location: Ecuador, South America
Age: 51
Posts: 1,314
Wiki Edits: 6

Thanks: 4
Thanked 2 Times in 2 Posts
finding parts to tune a q-jet here is near mission impossible, there are plenty for the holleys, I better use them.

I like the idea of removing the primary piston and rods, but maybe I'll try that in other engine.

what do you think of this cam?:

http://www.lunatipower.com/Product.aspx?id=1998
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 05-16-2012, 10:47 AM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,211
Wiki Edits: 0

Thanks: 5
Thanked 389 Times in 383 Posts
You can make your own sec metering rods by grinding a flat on the side of the
metering point, of spare stock metering rods. . You can make your own custom hanger just by bending the arm on a stock spare hanger. Making the rods sit higher make the fuel curve richer and sooner as the air door opens.

You can drill a stock primary jet as required to rejet using a numbered drill bit set.

Edelbrock sells lots of tuning parts for a Qjet.
So does http://www.thecarburetorshop.com/
GM dealers parts counters can order QJET service parts if you have current
part numbers.
Lots of people have spare parts and Qjet carbs in their collections.
The first turbo Buick V6 used a Qjet and had very rich sec metering rods.
SStock bread and butter Qjets from stock motors are set up lean and will need re
jetting richer for the blower. Start rich on the tune.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
motorcraft by holley? cutthroatkid Hotrodding Basics 3 08-14-2010 03:28 PM
56 corvette dual four barrel intake adam meagher Engine 0 07-04-2006 04:11 PM
Motorcraft 4300 4 barrel carb.... onebadmerc Engine 1 10-26-2004 11:19 AM
Motorcraft 2 barrel carb Levi Engine 4 12-01-2002 01:43 PM
Offenhauser 4 barrel dual-port? oly Hotrodders' Lounge 4 11-14-2002 03:41 PM


All times are GMT -6. The time now is 11:49 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.