Go Back  Offshoreonly.com > Technical > Restorations & Upgrades
Upgrading a 260hp 350 >

Upgrading a 260hp 350

Notices

Upgrading a 260hp 350

Thread Tools
 
Old 10-23-2014, 08:21 AM
  #1  
Registered
Thread Starter
 
Join Date: May 2014
Location: Buffalo, NY
Posts: 1,053
Likes: 0
Received 0 Likes on 0 Posts
Default Upgrading a 260hp 350

I know it's been beaten to death, but here's something I stumbled upon. I can pick up a set a 14096217 cylinder heads locally for cheap. They came off a running 270hp 350 Mag. I know these heads are the predecessor to the Vortec head. They are easily capable of making 285 to 300 horsepower, as they were on the 300 hp GM crate motors of the era. I know I need a new intake manifold with 27* center bolts and am wondering which intake to buy. Mind you, this is a budget build....because while the engine is out I will have to replace my wet transom.

Any recommendations on cam and intake would be great.

Thanks!!
Jonesyfxr is offline  
Old 10-23-2014, 08:53 AM
  #2  
Registered
Thread Starter
 
Join Date: May 2014
Location: Buffalo, NY
Posts: 1,053
Likes: 0
Received 0 Likes on 0 Posts
Default

Here's a cam I'm looking at.....

http://www.summitracing.com/parts/cc...make/chevrolet

I have to do more digging on the cam specs of that GM crate engine.
Jonesyfxr is offline  
Old 10-23-2014, 09:07 AM
  #3  
Registered
Thread Starter
 
Join Date: May 2014
Location: Buffalo, NY
Posts: 1,053
Likes: 0
Received 0 Likes on 0 Posts
Default

The 285hp engine had a cam lift of 447/447 with a 8.8-1 comp ratio

The 300hp engine had a cam lift of 435/460 with a 9.1-1 comp ratio

I really have no idea what pistons are in my engine and really won't know until I pull the heads. I'd be happy with 8.8-1, but of course the 9.1-1 would be best.
Jonesyfxr is offline  
Old 10-23-2014, 10:23 AM
  #4  
BUP
Banned
 
Join Date: Jul 2011
Location: Ft. Worth TX
Posts: 9,594
Likes: 0
Received 43 Likes on 37 Posts
Default

Buy that AFR composite intake manifold for the SB Chevy. It has been dynode by David Vizard and he swears by it. It made better HP and Torque # s right out of the box than any other intake manifold including the worked over intake manifolds. Plus you never ever have to worry about that intake manifold producing corrosion problems or dissimilar metals joining together.(dissimilar metals together produce corrosion over time especially in marine apps)

I would also look into bore & stroking the 350 into a 383.

Last edited by BUP; 10-23-2014 at 10:26 AM.
BUP is offline  
Old 10-23-2014, 11:09 AM
  #5  
SB
Registered
 
Join Date: Nov 2004
Location: On A Dirt Floor
Posts: 13,619
Received 3,166 Likes on 1,430 Posts
Default

The GM cast Iron Bowtie highrise intake was discontinued a few years ago. No stock left anywhere. I had sold 100's. GM's 86-95 part# is #14097494

So, a real good 86-95 application high rise Aluminum intake is Weiand's Speed Warrior:
http://www.summitracing.com/parts/wn...et?prefilter=1
SB is online now  
Old 10-23-2014, 11:24 AM
  #6  
Registered
 
Join Date: May 2012
Posts: 1,465
Received 9 Likes on 7 Posts
Default

the pre '86 260hp 350 heads are the same as the 270 horse 350mag post '86 except for the angle of the middle 2 intake bolt holes. You won't see any difference just switching those heads. They are the predecessor to the vortecs in that they came before them, but that is where the similarities end.
Mr Maine is offline  
Old 10-23-2014, 12:49 PM
  #7  
Registered
Thread Starter
 
Join Date: May 2014
Location: Buffalo, NY
Posts: 1,053
Likes: 0
Received 0 Likes on 0 Posts
Default

I think my heads are 76cc heads, not 64cc heads like the ones I'm looking at. I will pull a valve cover to be sure, but I'm 85% sure I have 76cc chambers on my engine.
Jonesyfxr is offline  
Old 10-23-2014, 01:42 PM
  #8  
Registered
 
Join Date: May 2012
Posts: 1,465
Received 9 Likes on 7 Posts
Default

Okay, the carbed '87-'95 350mag (and also the 5.7 260) had 76cc heads with center bolt valve covers and the more vertical center intake bolts. They were of the same performance as the pre 86 heads with perimeter valve covers and traditional intake pattern.

In '95 they had a TBI 350 mag, I assume these had the 64cc TBI heads, are these the ones you have? Aside from the compression bump I don't think you will gain much.
Mr Maine is offline  
Old 10-23-2014, 01:47 PM
  #9  
Registered
Thread Starter
 
Join Date: May 2014
Location: Buffalo, NY
Posts: 1,053
Likes: 0
Received 0 Likes on 0 Posts
Default

^^ The 64cc combustion chamber heads are what I will be picking up^^

They are an iron copy of the L-98 TPI heads that came on the Vettes and some Irocs.

http://www.gmpartsdirect.com/perform...CATID=671.html

Last edited by Jonesyfxr; 10-23-2014 at 01:49 PM.
Jonesyfxr is offline  
Old 10-23-2014, 01:56 PM
  #10  
Registered
 
Join Date: May 2012
Posts: 1,465
Received 9 Likes on 7 Posts
Default

Sorry wasn't trying to make it confusing.

If you don't have heads or an intake right now, go with 64cc VORTEC heads with a vortec style intake gm marine intake (or edelbrock rpm or rpm air gap). You will be much happier with the performance.
Mr Maine is offline  


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.