How to Switch to Antifreeze Cooled Engine

[Lou C]

The bottom line is that boats that size if still running a small block should have a 383 stroker; the extra displacement makes a big difference. MPI on a boat like this where you are adding it on is a lot of extra cost and complexity for very little gain. It’s not the same thing as if you bought a complete MPI engine with everything that goes with it. An aftermarket EFI system even if marine certified may need expert tweaking to get it to run right.

 

[scatgo]

OK got it. I am going to go with a 4 barrel carb. Any suggestions on CFM? What about vacuum or mechanical secondary?

 

[achris]

OK got it. I am going to go with a 4 barrel carb. Any suggestions on CFM? What about vacuum or mechanical secondary?

Edelbrock 1409. It's a 600CFM mechanical carb.

 

[Scott Danforth]

I recommend 650 cfm

 

[scatgo]

Any opinions on spread bore VS square bore for marine use?

 

[Lou C]

Well your only options for a spread bore (which is the pattern for the original GM cast iron intakes) is a Quadrajet which has not been made in many years and good ones are very hard to find (but is an excellent carb) and the Holley 4175 which was intended as a Quadrajet replacement). Everything else is a square bore either the Edelbrock 1409 or any of the Holley 4150 or 4160 marine carbs. If you use a GM cast iron intake you can use a spread to square adapter plate if you want to use the Edelbrock 1409, or you can use a square bore Edelbrock intake with brass inserts so it won't corrode and then you don't need an adapter plate.

 

[Lou C]

The 4175 is a spread bore carb, the 4160 a square bore.
Right now I think the Edelbrock 1409 is still on back order. Keep checking to see when it will be available, some of the Holley carbs are available, some you have to order & wait.

PS looks like you can order the 1409 now....

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as far as what's better, you'll get 10 different answers from 10 different people. remember that any carb can need tweaking to get the engine to really run right, all come with more or less generic set ups that might not work in your application.
I was lucky I had a good Quadrajet original carb and all it needed was a good cleaning, rebuilding with new gaskets, needle & seat and accel pump.

 

[Scott Danforth]

4150 is also a square bore.

VP used many 4150 carbs and a few 4175 and even a 4160 over the years.

My 1988 Volvo Penta 271C ( 275hp ) had a 715 CFM 4150 vac secondary on it from the factory and I used the same carb when I went to a hotter cam and vortec heads. the same carb was on the 310A and B engines (310hp) and I had it on my 468 for a year.

a spread-bore is fine if the manifold is designed correctly.

agreed, currently the 1409 is on back order.

 

[scatgo]

What should would be max rpm on this engine as is?

 

[achris]

What should would be max rpm on this engine as is?

In it's factory format, 5.7 with a 4bbl was usually 4400-4800rpm.