Offy SB intake…. Any good??

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dadodgekid said:
Just a street car. Maybe go to the track rarely, but something fun i can take my kids out in to do burnouts and such
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Clean it up, may be blast it, and see what you have. It's pretty easy to measure the ports to see if they are right for your 340 heads. Is it an open plenum or a dual plane? The dual planes work better at lower rpm and with mildly built engines.
 
340six said:
I was looking for a # 5884 to restore but the ones I found were rough where the Termostat were always eatten up.
Was also looking for a LD340 but same thing. junk I gave up looking, looks like after a nice blast you have a good one. If so run it. Most want good money for junk ones.
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it's only aluminum, nothing a good welder can't fix :thumbsup:
neil.
 
dadodgekid said:
Just a street car. Maybe go to the track rarely, but something fun i can take my kids out in to do burnouts and such
Click to expand...
So in the big picture there are dual plane manifolds and single plane manifolds. The manifold that you have tries to be both - there is a reason that there is no current manifold on the market that uses that design. A dual plane manifold has 2 plenums under the carb - one feeds every other cylinder in your firing order, and the other side feeds the other half. A single plane manifold feed all the cylinders from one big plenum under the carb. Your manifold feeds the driver side cylinders from one plenum and the passenger side cylinders from the other side. It would take quite a bit of time and writing to describe the advantages of each (reversion pulses, separation of draws on air fuel mixture, la la la la), but generally single plane manifolds show their strength at higher rpms, and dual planes have real advantages at low and mid range rpms. That means that for a street car, hot rodding around, wanting to punch it from low rpms and feel seat of the pants acceleration the dual plane is best, at the expense of quarter mile time slips if you are willing to really wind that motor up. Your Offy manifold is a cool piece to hang on the garage wall, but I think that the factory iron 4bbl manifold (which was a dual plane) would do as well or better. You can identify a dual plane because the manifold under the carb is split in two, and each pair of runners at the heads has one runner that goes high and one that goes low - all the low runners end up in the deeper of the two plenums under the carb, and all the high runners go to the shallower plenum.

There are lots of dual plane manifolds out there. The best vintage one is an Edelbrock LD340, but Weiand make a nice Stealth, The newer Edelbrock efforts are the RPM and some of their Air-gap manifolds. You should be able to get a real name brand used dual plane in nice condition for less than a new knock off. For a street car I wouldn't pay extra money for an airGap version.
 
str12-340 said:
So in the big picture there are dual plane manifolds and single plane manifolds. The manifold that you have tries to be both - there is a reason that there is no current manifold on the market that uses that design. A dual plane manifold has 2 plenums under the carb - one feeds every other cylinder in your firing order, and the other side feeds the other half. A single plane manifold feed all the cylinders from one big plenum under the carb. Your manifold feeds the driver side cylinders from one plenum and the passenger side cylinders from the other side. It would take quite a bit of time and writing to describe the advantages of each (reversion pulses, separation of draws on air fuel mixture, la la la la), but generally single plane manifolds show their strength at higher rpms, and dual planes have real advantages at low and mid range rpms. That means that for a street car, hot rodding around, wanting to punch it from low rpms and feel seat of the pants acceleration the dual plane is best, at the expense of quarter mile time slips if you are willing to really wind that motor up. Your Offy manifold is a cool piece to hang on the garage wall, but I think that the factory iron 4bbl manifold (which was a dual plane) would do as well or better. You can identify a dual plane because the manifold under the carb is split in two, and each pair of runners at the heads has one runner that goes high and one that goes low - all the low runners end up in the deeper of the two plenums under the carb, and all the high runners go to the shallower plenum.

There are lots of dual plane manifolds out there. The best vintage one is an Edelbrock LD340, but Weiand make a nice Stealth, The newer Edelbrock efforts are the RPM and some of their Air-gap manifolds. You should be able to get a real name brand used dual plane in nice condition for less than a new knock off. For a street car I wouldn't pay extra money for an airGap version.
Click to expand...
Speaking of Stealth. Here's one for sale. A bargain too. [FOR SALE] - 4 Speed & Engine Parts
 
str12-340 said:
So in the big picture there are dual plane manifolds and single plane manifolds. The manifold that you have tries to be both - there is a reason that there is no current manifold on the market that uses that design. A dual plane manifold has 2 plenums under the carb - one feeds every other cylinder in your firing order, and the other side feeds the other half. A single plane manifold feed all the cylinders from one big plenum under the carb. Your manifold feeds the driver side cylinders from one plenum and the passenger side cylinders from the other side. It would take quite a bit of time and writing to describe the advantages of each (reversion pulses, separation of draws on air fuel mixture, la la la la), but generally single plane manifolds show their strength at higher rpms, and dual planes have real advantages at low and mid range rpms. That means that for a street car, hot rodding around, wanting to punch it from low rpms and feel seat of the pants acceleration the dual plane is best, at the expense of quarter mile time slips if you are willing to really wind that motor up. Your Offy manifold is a cool piece to hang on the garage wall, but I think that the factory iron 4bbl manifold (which was a dual plane) would do as well or better. You can identify a dual plane because the manifold under the carb is split in two, and each pair of runners at the heads has one runner that goes high and one that goes low - all the low runners end up in the deeper of the two plenums under the carb, and all the high runners go to the shallower plenum.

There are lots of dual plane manifolds out there. The best vintage one is an Edelbrock LD340, but Weiand make a nice Stealth, The newer Edelbrock efforts are the RPM and some of their Air-gap manifolds. You should be able to get a real name brand used dual plane in nice condition for less than a new knock off. For a street car I wouldn't pay extra money for an airGap version.
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There is never an advantage to putting a corner in a manifold or port. Ever.
 
Newbomb Turk said:
There is never an advantage to putting a corner in a manifold or port. Ever.
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I believe that you have confirmed the location that you listed. I wish that all engineering calculations were that simple, but alas, they are not.
 
i love how these always devolve into esoteric debates about fluid dynamics, the arguments of cross sectional area and taper of runners and modifications of the center divider in order to gain that one-tenth of a second and half a mile an hour in a race.

the dude wants something fun to go out and do burnouts in and maybe take the track.

this will easily accomplish that.

it may not have good street manners, it may not have great racing numbers, it might not even be the best fit for what camshaft he has. but it's going on top of a 340 with a 4spd and 3.90's so who cares about good manners and numbers at the strip-- snap a double pumper on there, side step the clutch and listen to the roar of the motor while you annihilate a set of rear meats and grin from ear to ear.
 
junkyardhero said:
i love how these always devolve into esoteric debates about fluid dynamics, the arguments of cross sectional area and taper of runners and modifications of the center divider in order to gain that one-tenth of a second and half a mile an hour in a race.

the dude wants something fun to go out and do burnouts in and maybe take the track.

this will easily accomplish that.

it may not have good street manners, it may not have great racing numbers, it might not even be the best fit for what camshaft he has. but it's going on top of a 340 with a 4spd and 3.90's so who cares about good manners and numbers at the strip-- snap a double pumper on there, side step the clutch and listen to the roar of the motor while you annihilate a set of rear meats and grin from ear to ear.
Click to expand...
Very easily and totally unmodified. I'd not even modify the divider. In any way shape form or fashion. Unless you have a flow bench in your pocket, you don't know what you've done has helped, or destroyed a perfectly good intake manifold. I would clean that thing up, do any necessary repairs like bolt holes and run the snot out of it.
 
Removing the divider section below the carb pad does NOT convert the intake into a Torker. The divider runs the full length of the intake front to rear; design is totally different to a Torker or Holley SD.
 
To my knowledge Offy never built a dual plane. The 360* is the designation for a single plane. IIRC all of their V8 intakes were marked 360*.

I have one sitting on the top of my 360 in my work van. It has the 318 sized ports as the manifold I wanted was 340/360 specific. It ran fine with a Comp RV cam and pulled my 6200lb van hard to 5200RPM single exhaust, iron manifolds, and 850cfm Thermoquad.

It is an Offy 318 360* Dual Port. 2 sets of runners to each cylinder. 2 separate plenums. One for the primaries, and a bigger one for the secondaries.
 
Rug_Trucker said:
To my knowledge Offy never built a dual plane. The 360* is the designation for a single plane. IIRC all of their V8 intakes were marked 360*.

I have one sitting on the top of my 360 in my work van. It has the 318 sized ports as the manifold I wanted was 340/360 specific. It ran fine with a Comp RV cam and pulled my 6200lb van hard to 5200RPM single exhaust, iron manifolds, and 850cfm Thermoquad.

It is an Offy 318 360* Dual Port. 2 sets of runners to each cylinder. 2 separate plenums. One for the primaries, and a bigger one for the secondaries.
Click to expand...
OP's manifold is not a Dual Port, however. Dual Ports are plainly marked as such. The Offy 360s are a different series.
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