hello
why mopar intakes are made with the spread bore carb mount instead of square bore, is there any performance from this?
thanks

No.

The intake are made for use with the TQ carb. This is ether for class racing requiring the use of the TQ,
OR, for use of the TQ in the street, street strip adventure. The reusing of a TQ keeps costs down and is a very good street, street/strip carb.

More power can be found with welding, cutting, grinding the intake into a square bore. Follow MoPars recommendations and use the pop sticks in the intake as shown in the engines book.

They're made with the spreadbore pattern because that's the type of carb Chrysler Corp was using that year.

The spreadbore 360 intakes are quite good. They're pretty tall for a stock intake. If it's an EGR intake and you don't want EGR just stick a valve on the pad and don't plumb up any vacuum to it.

I believe the reason Chrysler went to spreadbore intakes was that the Thermoquad was much more tunable and easier with which to get legal emissions readings.
GM and Ford had been using spreadbore carbs since 1967. Chrysler started in 1971, IIRC.

One benefit of the TQ is that even the smaller carb was 750cfm, which was as large or larger than the AFB or AVS that it replaced.

UNLESS you are in a racing class that requires stock intakes, it is far easier to just buy a decent intake than to attempt to modify a cast iron intake.

R.

Pretty sure Duspan is referring to the still currently available aluminum intakes from Mopar Performance...like the M1 single planes for small or big blocks, which are spread bore pattern.

Not sure why they do it. No one runs a spread bore in a performance application unless they have to for class reasons. There are a few Thermoquad loyalists, but they are few and far between. There's no performance benefit from it, just makes it easier to bolt on and run a POS carb. Mopar Performance has sold crap for a long time and been pretty disassociated w/ what Mopar racers need and want.

so now that the MP manifolds have been mentioned.
I have an NOS single plane low deck manifold, I only plan to run holley carbs, should I have a buddy weld up the flange so I can make it a square bore, or is it minimal gains for the work??

the intake is the m-1 that i used, but i bought the adapter to use the holley carb? would have like to try a tapered 4 hole spacer to see if they helped in the performance?

I've never used an adapter to bolt a normal square bore carb onto one of those manifolds.
Only way to know if a spacer works is to try it. They're very combo specific.

What makes even less sense is the MP duel plane M1 is square flange. Azz backward if you ask me.

The dual plane is just an Eddy RPM with “Mopar” cast into it instead of Edelbrock. I believe it is made by Eddy under contract from Mopar, so Mopar had nothing to do with designing that manifold.

That would be for the big block only. If you watch carefully, they can be had for cheaper then an Edelbrock sometimes.