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240/300 open chamber used intake

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old28racer
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240/300 open chamber used intake

Post #1 by old28racer » Thu Jul 25, 2019 11:31 pm

Does anyone out there have a used Offy C / Clifford / or other open chamber intake that I can mount a 4x2 adapter to so I can run my Holley 2300 or a Autolite 2100 1.08 carb. PM me if you have any, Thanks
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pmuller9
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Re: 240/300 open chamber used intake

Post #2 by pmuller9 » Sat Jul 27, 2019 9:43 am

If you have an Offy DP use a 1" or more spacer plate under the 4x2 adapter or
Cut out the plenum so it is open.

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Re: 240/300 open chamber used intake

Post #3 by old28racer » Sat Jul 27, 2019 5:20 pm

pmuller9 --- Ok Paul now I am lost. I have the Offy DP intake and a 1" 4 hole spacer as shown in the pictures. Are you saying that I could get a open 4V 1" spacer and run it between the intake & the 4x2 spacer without modifying the 4 hole DP intake? Would I have to take down all the intake port hole edges so there was a nice angle?

I am not set up to cut out the plenum area as I do not have a mill.

As I said before I feel a bit lost on this one. If the open 2V part of the 2x4 adapter sent air/fuel mixture down the Pri runner & some down the Sec runner would it be at different rates? I just don't understand how it can work without being an open chamber in the intake. Help please as if I can make this work it would save cost of another intake. Thanks Tom
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old28racer
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Re: 240/300 open chamber used intake

Post #4 by old28racer » Sat Jul 27, 2019 6:13 pm

Ok I just looked up some adapters & spacers for the DP intake. Am I correct that I can use a Mr Gasket #1933 2x4 adapter & a Mr Gasket 6005 open 1" thick spacer to make this work. I would place a 4V open gasket on the intake around the 4 holes, then the #6005 1" spacer, then another4V open gasket, then the #1933 4x2 adapter. I was not aware that you could bolt the adapter directly to the DP intake. Is this an OK cruise setup? What does the 1" open spacer do for the setup?
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Re: 240/300 open chamber used intake

Post #5 by pmuller9 » Sat Jul 27, 2019 7:16 pm

old28racer wrote:Ok I just looked up some adapters & spacers for the DP intake. Am I correct that I can use a Mr Gasket #1933 2x4 adapter & a Mr Gasket 6005 open 1" thick spacer to make this work. I would place a 4V open gasket on the intake around the 4 holes, then the #6005 1" spacer, then another4V open gasket, then the #1933 4x2 adapter. I was not aware that you could bolt the adapter directly to the DP intake. Is this an OK cruise setup? What does the 1" open spacer do for the setup?

That is what I was talking about. I should have said "open spacer" to be more clear.
The 1" open spacer adds a little more volume plus it the decreases the turn the air/fuel mixture has to make as it enters the DP manifold openings by raising the carb.
Last edited by pmuller9 on Wed Jul 31, 2019 8:36 am, edited 1 time in total.

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Re: 240/300 open chamber used intake

Post #6 by old28racer » Sat Jul 27, 2019 7:54 pm

Now that I know how to mount it I need to ask another question, are the pri & sec runners the same size inside the manifold? No problem with this setup? Is a C or Clifford another $250 better? I know it would flow better but at $350 bit out of my range at this time.
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Re: 240/300 open chamber used intake

Post #7 by pmuller9 » Sat Jul 27, 2019 8:33 pm

The primary and secondary manifold runners are different sizes but it doesn't matter in your case because you will be using both at the same time and since you are using a two barrel carb the total runner flow will be sufficient for what you are doing.

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Re: 240/300 open chamber used intake

Post #8 by old28racer » Sat Jul 27, 2019 10:59 pm

Just a couple of additional questions. Is the 1" spacer thick enough or does it need to be thicker? As I can see we are building a small open plenum on top of the 4 DP intake ports, correct? I only looked at Mr Gasket 1933 adapter & 6005 1" spacer, are there any others that might be better or higher quality?

Also do you think the air/fuel will stay in suspension and flow well with 20" manifold vacuum at idle and no less than 14 during cruising?
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Re: 240/300 open chamber used intake

Post #9 by THE FRENCHTOWN FLYER » Sun Jul 28, 2019 9:14 pm

I think it will work fine. If you want to improve the flow more and no longer desire the "benefits" of the dual plane design I would taper the entrance way of all four holes in the intake opening. I've even used a router for this.

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Re: 240/300 open chamber used intake

Post #10 by old28racer » Mon Jul 29, 2019 2:53 pm

The FrenchTown Flyer -- Greg I would like to taper the 4 inlet holes, I have a HD grinder for porting along with some smaller finish bits that I think would work for this project.

From the intake picture how far down inside would you run the taper? Would you try to round the center section to a point if I can?
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Re: 240/300 open chamber used intake

Post #11 by THE FRENCHTOWN FLYER » Mon Jul 29, 2019 3:21 pm

old28racer wrote:The FrenchTown Flyer -- Greg I would like to taper the 4 inlet holes, I have a HD grinder for porting along with some smaller finish bits that I think would work for this project.

From the intake picture how far down inside would you run the taper? Would you try to round the center section to a point if I can?

A half inch or so. Lay the open spacer over it and scribe a line just like you'd do matching a combustion chamber to a cylinder. Yes, You can Point the center; in fact one of the intake manufacturers [forgot which] sold an insert for their single plane intake that did just that. I think it was called 'ram sonic' or some such.
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old28racer
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Re: 240/300 open chamber used intake

Post #12 by old28racer » Mon Jul 29, 2019 7:01 pm

The FrenchTown Flyer and pmuller9 -- Greg & Paul, If I luck in and find someone with a mill can I lay the 1" spacer on the studs and mark the inside on the 4 port intake face?

I see that the two ports are at different depths so is it safe to mill all the material in the 4 port area down to the highest port then take the top off the lower 2 ports and angle & smooth between the two areas?

With the intake 4 port area cleared out would I need to run the 1" spacer below the 4x2 adapter that in it's self is 1" thick?

Will the new milled out intake plenum be two much volume for my Holley 2300 350cfm or a Autolite 2150 1.08 284cfm carb? What if I add the open 1" spacer?

Thanks Guys
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Re: 240/300 open chamber used intake

Post #13 by MechRick » Mon Jul 29, 2019 8:28 pm

old28racer wrote:If the open 2V part of the 2x4 adapter sent air/fuel mixture down the Pri runner & some down the Sec runner would it be at different rates?


Yes. Probably dependent on RPM and intake runner resonance.

I would be concerned with mixture distribution. I think less plenum actually helps in this regard.

I've been told that cutting the runner divider back a bit at the head mounting surface helps with top end on the DP.
1994 F150, 4.9L/ZF 5 speed, C-Vic police driveshaft
EFI head w/mild port work, 3 angle valve job
1996 long block, stock pistons, ARP rod bolts
Stock cam, aluminum cam gear
Hedman header, full mandrel bent duals, crossover, super turbos
http://fordsix.com/forum/viewtopic.php?f=2&t=73244
Bronco II with a 2.3L swap http://fordsix.com/forum/viewtopic.php?f=13&t=72863
1988 F250 2x4, 460 ZF 5 speed.

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Re: 240/300 open chamber used intake

Post #14 by jroach » Tue Jul 30, 2019 12:22 am

for what it's worth i'm running a c series with a 4 barrel and the torque is still very much like that of a tractor. it's basically impossible to give a 300 too much air.

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Re: 240/300 open chamber used intake

Post #15 by old28racer » Tue Jul 30, 2019 6:57 pm

MechRick & jroach -- Thanks guys for the additional information. I am only going with the modified DP intake because I have one, if I did not I would use a Offy C. This setup will be for my Holley 2v 2300 350cfm carb or a 2100/2150 unit both with a 4x2 adapter. Not going to a 4v at this time, trying for better mileage more than performance. I am getting 15.2 highway that is fine but my 7 city is real poor.
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Re: 240/300 open chamber used intake

Post #16 by MechRick » Tue Jul 30, 2019 8:23 pm

I did that on my '81 years ago. Ran a 2bbl and then a VV on an Edelbrock 4-2bbl adapter, lined up over the fatter side of the intake runners as a temporary solution while I saved money for a 4bbl. I got 19 mpg with the VV. An open spacer should be a better solution.

It's similar to the carb adapter available for the lower half of a 2300 EFI intake that the roundy-round guys like to run...

https://www.speed-talk.com/forum/viewtopic.php?t=44391

Managed 16.6 mpg with my Offy DP-equipped Bronco with a Holley 390.
1994 F150, 4.9L/ZF 5 speed, C-Vic police driveshaft
EFI head w/mild port work, 3 angle valve job
1996 long block, stock pistons, ARP rod bolts
Stock cam, aluminum cam gear
Hedman header, full mandrel bent duals, crossover, super turbos
http://fordsix.com/forum/viewtopic.php?f=2&t=73244
Bronco II with a 2.3L swap http://fordsix.com/forum/viewtopic.php?f=13&t=72863
1988 F250 2x4, 460 ZF 5 speed.

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Re: 240/300 open chamber used intake

Post #17 by old28racer » Wed Jul 31, 2019 1:11 am

MechRick -- Thanks for the picture, I know Modification is not on a DP intake but it sure shows what a 4 hole DP would look like when done.

Was the 19 & 16.6 mpg combined city & highway? Is the Holley 390 a 4bbl or a 2 bbl?

As I am going to run my existing Holley 2300 350cfm 2bbl on a Mr Gasket 4x2 carb adapter that has a 1" inside space & a 1" open spacer between the modified DP intake & the adapter.

Like I said before my 15.2 highway is not bad, but sure would like to get the city to 10-12 mpg.
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Re: 240/300 open chamber used intake

Post #18 by MechRick » Wed Jul 31, 2019 12:12 pm

Both were 80% highway, 20% city. The 19 mpg was in Ohio when the speed limit was still 55 mph.

The Bronco would drop off to 13-14 mpg with heavy city use.

The 390 Holley was a 4bbl...

https://www.holley.com/products/fuel_sy ... rts/0-8007

I highly recommend them. The Bronco was the closest carbed vehicle to EFI I've ever built. Ran it out of the box, with no changes, although I probably should have ran a lighter spring in the secondary.
1994 F150, 4.9L/ZF 5 speed, C-Vic police driveshaft
EFI head w/mild port work, 3 angle valve job
1996 long block, stock pistons, ARP rod bolts
Stock cam, aluminum cam gear
Hedman header, full mandrel bent duals, crossover, super turbos
http://fordsix.com/forum/viewtopic.php?f=2&t=73244
Bronco II with a 2.3L swap http://fordsix.com/forum/viewtopic.php?f=13&t=72863
1988 F250 2x4, 460 ZF 5 speed.

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