Go Back  Offshoreonly.com > Technical > General Q & A
Bowl Porting Heads on 500hp, worth it? >

Bowl Porting Heads on 500hp, worth it?

Notices

Bowl Porting Heads on 500hp, worth it?

Old 10-22-2005, 07:38 PM
  #1  
Registered
Thread Starter
 
BajaRunner's Avatar
 
Join Date: Nov 2001
Location: Austin
Posts: 3,622
Likes: 0
Received 0 Likes on 0 Posts
Default Bowl Porting Heads on 500hp, worth it?

Ive got my boat in getting the valve springs and headgaskets done. Is it worth it to get the heads bowl ported?? Its an extra $200 an engine. Id like to get some performance, just wondering if it was anything noticeable.
BajaRunner is offline  
Old 10-22-2005, 10:31 PM
  #2  
Registered
 
baja36ft's Avatar
 
Join Date: Oct 2004
Location: CHESAPEAKE,VA
Posts: 688
Likes: 0
Received 0 Likes on 0 Posts
Default Re: Bowl Porting Heads on 500hp, worth it?

I Would Do The Exhaust Ports And Mill The Heads
And Bring The Comp. Up To 9.1 0r 9.5 That Will Wake
Up That Motor.
baja36ft is offline  
Old 10-22-2005, 11:09 PM
  #3  
Platinum Member
Platinum Member
iTrader: (1)
 
KAAMA's Avatar
 
Join Date: Oct 2000
Location: Western Michigan
Posts: 4,349
Likes: 0
Received 0 Likes on 0 Posts
Default Re: Bowl Porting Heads on 500hp, worth it?

Yes, bowl/pocket porting--- remove/round out the rough edges, clean them up a bit and pay special attention to the short side radius's. You can do a little more to the exhaust ports as "baja36ft" has suggested because they are pretty crude as they come cast from GM. Take them to someone who has some familiararity with head porting. Might be worth 20hp or so. If they were mine, then I would have them done,---but that's just me. Every little bit helps. Have fun!
KAAMA is offline  
Old 10-23-2005, 07:07 AM
  #4  
Registered
Thread Starter
 
BajaRunner's Avatar
 
Join Date: Nov 2001
Location: Austin
Posts: 3,622
Likes: 0
Received 0 Likes on 0 Posts
Default Re: Bowl Porting Heads on 500hp, worth it?

Originally Posted by baja36ft
I Would Do The Exhaust Ports And Mill The Heads
And Bring The Comp. Up To 9.1 0r 9.5 That Will Wake
Up That Motor.
would a standard "milling" do that, or do i need to have the done a little more.

If I get that done, do i have to switch to super?

And what kind of gains would i see?
BajaRunner is offline  
Old 10-23-2005, 08:59 AM
  #5  
Registered
 
Join Date: Aug 2004
Location: Riverview, Michigan
Posts: 1,335
Likes: 0
Received 0 Likes on 0 Posts
Default Re: Bowl Porting Heads on 500hp, worth it?

Originally Posted by BajaRunner
Ive got my boat in getting the valve springs and headgaskets done. Is it worth it to get the heads bowl ported?? Its an extra $200 an engine. Id like to get some performance, just wondering if it was anything noticeable.
What GM heads do you have? Also, before you mill the heads, you should have the chambers measured for volume. My new heads right out of the box where not to spec (there is a tolerance level). Two heads where 116cc and second pair where 114cc. GM spec was 110cc. I had them all milled to achieve a 112cc volume across the board.
ROTAX454 is offline  
Old 10-23-2005, 02:59 PM
  #6  
Registered
 
Join Date: Apr 2005
Location: Castro Valley, California
Posts: 62
Likes: 0
Received 0 Likes on 0 Posts
Default Re: Bowl Porting Heads on 500hp, worth it?

BAJA Another thing you may want to check while you have the heads off is the "quench area". That is the space between the flat portion of the piston and the head surface, with the piston at TDC. Measure from the deck surface to the piston surface and add in the thickness of the head gasket, that will be your quench area. Ideal quench area is in the .038 to .040 range. This can altered somewhat without machine work by using head gaskets of different thicknesses. Cometic offers their BBC marine gaskets in a variety from about .027 to .060. Optomizing the quench will give you better combustion, and may increase your compression slightly also, depending on how far down the piston is in the bore.
Bubbletop409 is offline  
Old 10-24-2005, 12:33 PM
  #7  
Registered
 
baja36ft's Avatar
 
Join Date: Oct 2004
Location: CHESAPEAKE,VA
Posts: 688
Likes: 0
Received 0 Likes on 0 Posts
Default Re: Bowl Porting Heads on 500hp, worth it?

Originally Posted by BajaRunner
would a standard "milling" do that, or do i need to have the done a little more.

If I get that done, do i have to switch to super?

And what kind of gains would i see?
NO, STANDARD MILLING WILL NOT DO IT AND YES YOU WILL
NEED BETTER GAS I KNOW HP500 SHOULD BE 8.75 COMP.
BUT WHEN MINE WAS CHECKED IT WAS 8.4 WITH 75 HRS.
baja36ft is offline  
Old 10-24-2005, 12:46 PM
  #8  
Registered
Thread Starter
 
BajaRunner's Avatar
 
Join Date: Nov 2001
Location: Austin
Posts: 3,622
Likes: 0
Received 0 Likes on 0 Posts
Default Re: Bowl Porting Heads on 500hp, worth it?

Originally Posted by baja36ft
NO, STANDARD MILLING WILL NOT DO IT AND YES YOU WILL
NEED BETTER GAS I KNOW HP500 SHOULD BE 8.75 COMP.
BUT WHEN MINE WAS CHECKED IT WAS 8.4 WITH 75 HRS.
I talked with BobL whos doing the work. He said the same thing, they are usually a little low. Hes going to shave them .020 and bowl port the heads. Hopefully it will add a little. Mine have 370 hrs on them, so hes doing a valve job as well. Maybe with all that, Ill see a little gain.
BajaRunner is offline  
Old 10-24-2005, 01:03 PM
  #9  
Registered
 
baja36ft's Avatar
 
Join Date: Oct 2004
Location: CHESAPEAKE,VA
Posts: 688
Likes: 0
Received 0 Likes on 0 Posts
Default Re: Bowl Porting Heads on 500hp, worth it?

I Would Also Use The Cometic .027 Gaskets.
baja36ft is offline  
Old 10-24-2005, 02:51 PM
  #10  
Platinum Member
Platinum Member
 
Join Date: Dec 2002
Location: Dallas, TX
Posts: 2,196
Likes: 0
Received 0 Likes on 0 Posts
Default Re: Bowl Porting Heads on 500hp, worth it?

My opinion is you are probably wasting time and money. JimV frenquents this board and he is a VERY knowledgeable head porter and he builds marine engines. You should consider whatever he recommends.
BenPerfected is offline  

Quick Reply: Bowl Porting Heads on 500hp, worth it?


OSO Sponsor
OSO Advertiser
OSO Advertiser

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.

OSO Advertiser