2bbl to offy dual port questions....

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74swingerlover

74swingerlover

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Will I be + or - for top rpm with this change?

It's just on a 318 stock (74) with headers.
I will be running a Holley 550cfm on top of the offy

And yes I know the dual port is a very bottom end intake
 
It will be an improvement over stock. Probably by a good margin.
 
That's a great intake for a stock 318 with headers. It will run nice and get good MPG. :thumleft:
 
Is the 550 enough to feed it?

What rpm do they usually top out at?
 
74swingerlover said:
Is the 550 enough to feed it?

What rpm do they usually top out at?
Click to expand...

With the stock cam, and even with a good exhaust, it's about done by 5000rpm's. Any vacuum secondary carb in the 500/600 range should be plenty for a really mild 318.
 
Since you're not doing anything to raise compression or open the valves longer, the 550 seems a good choice. If the car has an automatic, I recommend a vacuum/air valve secondary carburetor.

Hot Rod did a test of 18 manifolds on a 383. The Offy dual port produced 40 less hp than a Performer RPM (412 vs 451). IMO, the Edelbrock Performer will give better performance and will match up with the ports on the 318 cylinder head.
 
Of course a performer rpm would yield better results but the offy is sitting on a shelf in my garage. I like cheap power lol

Should I throw a carb spacer on too?
 
74swingerlover said:
Of course a performer rpm would yield better results but the offy is sitting on a shelf in my garage. I like cheap power lol

Should I throw a carb spacer on too?
Click to expand...

On an otherwise stock 318 I doubt the Performer RPM would be any better. Skip the spacer as well.

Holley 550? What is the list number on that carb? IIRC the 1849s were designed to be run as duals on tunnel rams. Also, the post title say 2bbl. What exactly do you plan to use?
 
I don't know the 550's model number of hand but I know it was running on top of a 360 with a torker 2 so I know it will run.

My 2 bbl is in the motor now and could use a rebuild so I figure now is the time to change it over to 4bbl (damn ethanol)

The offy has a dual plane already and the spacer I have also has the divider.

What would the pros and cons be if I used the spacer?
 
Get the list number off the choke tower. 550 is a strange CFM for a Holley.
 
Top rpm with that set up will be determined by your weakest valve spring, probably around the 5000 rpm range.
 
74swingerlover said:
Ok, just took a look...... It's a 1850-3 so 600cfm
Click to expand...

Throw an electric choke on it if you are going to drive it in cold weather. They work great when hooked up properly.


I would also put a lighter spring in the secondary pod.
 
Crazy idea..... Has anyone ever ground down the middle of the ports? More flow or would it hurt it?

And yes I have been smoking something.lol
 
74swingerlover said:
Crazy idea..... Has anyone ever ground down the middle of the ports? More flow or would it hurt it?

And yes I have been smoking something.lol
Click to expand...

It will hurt your performance.


They designed the intake so the primaries are on the bottom and insulate the secondaries on the top. The primaries are longer than the secondaries so they are tuned for the different RPM's.
 
I am going to try the bracket that the 1850 was using on the torker intake?

It's free!
 
Ended up using the 2 bbl throttle parts just one cut and weld a piece in to make it taller.

So she's in and running. Got to tune it and give it a test run..... Been raining here all weekend :(
 
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