1978 MCM 260 Vortec upgrade

[TomSawyer]

Hello,

I have a 1978 Sea Ray srv240 weekender that has a worn out MCM 260 in it. I am planning to go with either a 400 or 383 SBC. I have many questions as this is my first time upgrading from old 1978 to newer equipment. The stock exhaust manifolds are the rear dump type. I found some center dump manifolds and y pipe for a 2001 5.7 sbc. Will these work? Will the transom plate and coupler off the 2001 work on my 1978 stuff? I rebuilt the outdrive last year with SDI upper and lower so I don't want to change to a Bravo at this time. Thank you in advance for any info on this.

 

[harleyman1975]

Just one note. the 383/400 are balanced differently than the 305/350 and hence require engine specific flywheel and balancer. you cannot use the ones of your 350 on the 400/383.

 

[Bondo]

I am planning to go with either a 400 or 383 SBC.

Ayuh,..... Are ya buildin', or buyin',..??

I found some center dump manifolds and y pipe for a 2001 5.7 sbc. Will these work? Will the transom plate and coupler off the 2001 work on my 1978 stuff?

Ayuh,.... The manifolds will work,... the y-pipe might work, there's a few bolt patterns,...

Unless ya swap the entire transom assembly, the transom inner plate, 'n coupler are of no use to ya,....
You'd also need the late model flywheel cover to use the coupler,...

 

[thumpar]

Just make sure you are easy on the right hand with the added power.

 

[TomSawyer]

Good info! Thank you.

Just one note. the 383/400 are balanced differently than the 305/350 and hence require engine specific flywheel and balancer. you cannot use the ones of your 350 on the 400/383.

 

[TomSawyer]

If I change to center dumps do I need a different y pipe?

Ayuh,..... Are ya buildin', or buyin',..??


Ayuh,.... The manifolds will work,... the y-pipe might work, there's a few bolt patterns,...

Unless ya swap the entire transom assembly, the transom inner plate, 'n coupler are of no use to ya,....
You'd also need the late model flywheel cover to use the coupler,...

 

[Bondo]

If I change to center dumps do I need a different y pipe?

Ayuh,.... Donno,.... Center riser manifolds can use various risers bolted to the top,... 3", 4", 'n in several degrees of drop,.....

Then there's the metal elbows that connect the risers to the y-pipe,....
They also come is various sizes, lengths, 'n degrees of turn,... as well as oval or round,.....

Here's a few examples of risers that bolt onto center-riser manifolds,.....

 

[TomSawyer]

No Title

Ayuh,.... Donno,.... Center riser manifolds can use various risers bolted to the top,... 3", 4", 'n in several degrees of drop,.....

Then there's the metal elbows that connect the risers to the y-pipe,....
They also come is various sizes, lengths, 'n degrees of turn,... as well as oval or round,.....

Here's a few examples of risers that bolt onto center-riser manifolds,.....

Here are some pictures of what I was thinking of upgrading to. Is it worth getting the center dumps? I am going to have to replace 1 of the existing "log" manifolds already. Will this bolt up to my pre alpha stuff?

 

[Bondo]

Ayuh,.... Do you have the outer section of the transom assembly to go with the pile of parts in yer 3rd picture,..??

 

[TomSawyer]

Ayuh,.... Do you have the outer section of the transom assembly to go with the pile of parts in yer 3rd picture,..??

I am not sure, I will have to check. Is the outer transom assembly different? Craigslist wants $300 for what is in the pics.
from the ad:
"Came off my boat and are in great shape. They were on 2001 galaxy that had a merc, Alpha 1 out drive set up with 350 SBC. These have the y pipe and boots as well."