VI Cutty

Some of you may be following my adventures in engine swapping but for those who aren't, the short story is I'm removing a 260 from my '70 Cutlass and replacing it with a 1971 350.

The 350 has a standard two barrel but the 260 has a Dualjet. I'm thinking that if the Dualjet uses the same intake as a Quadrajet then it would make sense for me to swap intakes while the engine is out knowing that a Qjet will be installed later this year.

In the meantime, how would you expect the Dualjet to perform on the larger engine? Is the jetting and tune likely to be 260 specific to the point of needing too much attention to get decent performance on the 350?

I don't want to spend a lot of time/effort on the Dualjet and would otherwise stick with the 2 bbl currently installed. My primary objective at this point is to get the car streetworthy as soon as possible without getting pulled down multiple MAW rabbitholes...there are enough already!

svnt442

I'm guessing this is the Dualjet that looks like a Quadrajet? The later versions were completely different and wouldn't work for what you want to do.
As far as it working on the 350? I'm sure it would work, but the engine would just be down on power. All it is is the primary side of the Quadrajet with no secondary circuit. It's kinda like flooring a Quadrajet with the secondaries stuck shut.
The mixture might be way off though, so keep that in mind if you do attempt this.

VI Cutty

This is the Dualjet versus the two barrel on the 350 now. I'll have it off the engine tonight and will be able to compare the intake with my spare four barrel intake.

I have no expectations of better performance than the current setup, just planning ahead to avoid having to lift the intake while the engine's in the car.

shrimp

I had a 1979 chevy Malibu 2 door with a 262 V-8 and a Dualjet carb.
Worst gas milage I ever saw. I barely got 19 MPG on Interstate 90 with
a cruise control set to 55 MPH.

The only carb I ever had that was WORSE was the Ford VARI-Venturi carb in a 1984 Ford LTD Station Wagon. That carb stalled the motor every morning at the first stop sign and almost killed us several times until we replaced it with a Motorcraft standard 2100 carb. What a nightmare!

I would not expect much from the Dualjet. You car may run , but pretty badly on fuel economy.

VI Cutty

Thanks for the warning! The car's not a daily so mileage isn't a key factor, and replacing it with the rebuilt QJet will hopefully be within a few weeks at the most.

olds 307 and 403

My 260 has the regular Dualjet and disagree on the mileage part. My 260 gets very good mileage in town and got similar mileage to person above, 21 mpg Imperial on the highway. Yah it isn't great but the 260 was a big compromise motor all around. It has very good part throttle torque for what it is, sounds and looks like an Olds V8, the only good things about the 260. It is calibrated very lean but you could adjust the APT if you had to. I assume you are slapping it on a 350 intake?

midnightleadfoot

I'd think the dual jet set up for a 90 cid smaller engine would be lean,,
I'd put the q jet intake on.. and use an adapter to put the 2 barrel off the 350 on it until you are ready to install the q jet..

joe_padavano

Yes, that DualJet bolts to any Qjet intake. It will run the same as the primary barrels of the Qjet. As noted, I'd watch the plugs, as you might need to fatten the rods and jets.

shrimp

My experience is what it is. No changing that. I was a traveling salesmen in 1979 and I can tell you we were very aware of gas mileage . Remember we had gas Rationing. the gas was REAL gas, not Ethanol. The car was a 1979 Chevy Malibu 2 door. This was a company car.( No Towing! ). This was a car doing 1,000 miles per week. With synthetic oil. The speed limit was 55 MPH with big point violations for speeding in NY State. You would lose you license and be unemployed in the Jimmy Carter Recession. The car had just me in it. The transmission was a three speed automatic. Not an overdrive. The motor was a Chevy 262 "small block" V-8 but the gas mileage was very poor. I almost ALL interstate driving. I still do actually. I am still at 30K miles a year in my current car. I assume the Chevy motor and the three speed had a specific effect on the gas mileage, but as far as I could tell the Dualjet did not help any. I know the ignition was HEI at that time and I changed the plugs every 10 K miles but it did not have much effect. I will say that it did not "ping" like most cars then so I assume it was either rich or the EGR was working correctly.

Compared to my 96 Roadmaster ( which got 25 MPG Highway ) the Dualjet was a big disappointment. But maybe it was just the tranny and motor at fault.

midnightleadfoot

It was a combo of things.. A 79 malbu was a brick in the wind..
The 262 v8 didn't have any low end torque and g.m. put mighty high gears in the rear ends of many of them.. as high as 2.14


The 305 v8 cars got better real world mpg than the 262 v8 or the 229 v6

shiftbyear

As midnightleadfoot said, my big concern would be the lean factor, not only are you straining an emissions calibrated carb (dualjet) with almost 100 more cubic inches, but also the ethanol content in todays gas requires more fuel across curve. Without recalibrating the idle/transfer and main circuits, you may end up with holes in your pistons. Hope you get your cutlass running soon though, good luck.

VI Cutty

I run the Chevron 94 octane with no Ethanol, hopefully that helps a bit in that regard. All going well, it won't be running under the Dualjet for more than a few weeks and it's not my daily driver so the miles won't be excessive.