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steele211

  • Karma: +0/-0
427 heads
« on: January 19, 2008, 08:11:54 AM »
can i get some of the pros and cons to running a 427 head on a 454 in a jet boat?
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HDriderTH

  • Karma: +12/-0
Re: 427 heads
« Reply #1 on: January 19, 2008, 09:12:48 AM »
smaller combustion chamber, higher compression

http://www.mortec.com/bbc.htm
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'82 Sanger Bubble deck, Blown 454....V-drive

hotrod56cars

  • Karma: +1/-8
Re: 427 heads
« Reply #2 on: January 19, 2008, 10:11:10 AM »
You have 4 basic Chevy head variables: open chamber, closed chamber, oval port, rectangular port.

Apparently open chamber is better than closed chamber but more difficult to get a lot of compression out of. Most race car builders prefer rectangular port. Boat engine builders don't seem to have a common opinion of which port to run, some prefer oval and others prefer rect.. On aftermarket aluminum heads the common opinion seems to be AFR's are the best.

You can physically mount any 396, 427, or 454 head on any 396, 427, or 454 block. Valve to piston clearences will need to be checked.
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NO REGRET$ ... Arguing on the internet is like competing in the Special Olympics / no matter how good you do you're still retarded!!!!!

                                                          1978  19' Mach 1 Tunnel jet

SLCKREG

  • Karma: +0/-0
Re: 427 heads
« Reply #3 on: January 19, 2008, 02:15:55 PM »
As a general rule rect. port perform better above 4500 r's and oval better  from 0 -4500 r's. For what it's worth I run rect. port and have no problems from low end power or at least I didn't with my 427 in my 18' tahiti the 21 hasn't been fired yet. :o
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Jetaholic

  • Karma: +3/-0
Re: 427 heads
« Reply #4 on: January 19, 2008, 05:59:46 PM »
Actually there are 3 different port configs: small oval (aka "peanut" ports), large oval and rect.

"Peanut" port heads are more for a truck that pulls in the low RPM band.

Large oval seem to be the best for the midrange powerband that jetboats run in. The most popular jet boat head seems to be the large oval port open chamber casting #353049.

Rect. performs best from 6,000RPM on up from what I've heard from several engine builders.

Where closed chamber has the advantage over open chamber...

With an open chamber head you have to run a dome piston to get a decent compression ratio whereas with a closed chamber you can get away with running flat top pistons for a decent CR. You get a much better flame front on a flat top piston than you do on a dome.
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To err is human, to forgive divine...except for running Fords ;D

F - Found
O - On
R - River
D - Dead

SLCKREG

  • Karma: +0/-0
Re: 427 heads
« Reply #5 on: January 19, 2008, 07:02:52 PM »
I'm going to "generalize" again. I'd say if your going to build a dual plane intake motor, then go oval port, if your going to go rect port(higher r's) single plane. Obviously cam and compression would have to match either.
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hotrod56cars

  • Karma: +1/-8
Re: 427 heads
« Reply #6 on: January 19, 2008, 07:18:48 PM »
I guess an oval is not an oval.  :D
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NO REGRET$ ... Arguing on the internet is like competing in the Special Olympics / no matter how good you do you're still retarded!!!!!

                                                          1978  19' Mach 1 Tunnel jet

speedymopars

  • Karma: +6/-0
Re: 427 heads
« Reply #7 on: January 19, 2008, 09:32:29 PM »
There is more to open chambers / closed chamber heads - The big difference is in the quench. With a closed chamber head and a .039 head gasket, you only need your piston .001 down the hole for perfect quench. With an open chamber, you may need to run your piston positive deck to get optimal quench - and that opens up a host of other problems.
YMMV
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21' 74 cheyenne 543 Mopar Berkeley Jet Place diverter

Jetaholic

  • Karma: +3/-0
Re: 427 heads
« Reply #8 on: January 21, 2008, 06:50:01 AM »
Quote from: hotrod56cars on January 19, 2008, 07:18:48 PM
I guess an oval is not an oval.  :D

But as long as it's not a blue oval you're good ;D
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To err is human, to forgive divine...except for running Fords ;D

F - Found
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R - River
D - Dead

hotrod56cars

  • Karma: +1/-8
Re: 427 heads
« Reply #9 on: January 21, 2008, 08:24:09 AM »
Quote from: Jetaholic on January 21, 2008, 06:50:01 AM
But as long as it's not a blue oval you're good ;D

 ;)   ;D
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NO REGRET$ ... Arguing on the internet is like competing in the Special Olympics / no matter how good you do you're still retarded!!!!!

                                                          1978  19' Mach 1 Tunnel jet

Marcsrollin

  • Karma: +33/-0
Re: 427 heads
« Reply #10 on: January 21, 2008, 08:25:40 AM »
Quote from: Jetaholic on January 21, 2008, 06:50:01 AM
But as long as it's not a blue oval you're good ;D

Good point you wouldent want to go too fast in your boat!
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  • Boat #1: 1978 TX-19 Youngblood
  • Boat #2: 1994 24 foot Sundancer Pontoon
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Taco'd "a person or people that show up with one lake lice and a family of 50 and cram 3 people at a time on it with no disregard to boating rules or ethics. Usualy crap in toilets and throw shit paper in trash cans. Hang out at the boat ramp like its a swimming hole. Have zero insurance on anything they own and dont give two shits less about your property."

Josh@JBP

  • Karma: +6/-0
Re: 427 heads
« Reply #11 on: January 21, 2008, 11:39:28 AM »
From what I understand the smaller chambers act more like a fast burn head because of the compact chambers.  Typically you can run less timing or a little more compression seeing as they are not as prone to detonation compared to a dome piston and an open chamber head with the same CR.   Like they said above the flat top will have a more efficient burn, however the closed chambers shroud the valve (made worse by installing larger than factory valves) so the open chamber tend to flow a bit better. 
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KonaCole

  • Karma: +1/-0
Re: 427 heads
« Reply #12 on: January 22, 2008, 02:02:34 PM »
Quote from: Marcsrollin on January 21, 2008, 08:25:40 AM
Good point you wouldent want to go too fast in your boat!

Here we go!  Get out your boots, it could deep!
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I didn't do it... ok, it was me.

hotrod56cars

  • Karma: +1/-8
Re: 427 heads
« Reply #13 on: January 22, 2008, 05:45:48 PM »
So correct me if I'm wrong, but it seems the best to run is flat topped pistons, coupled with open chambered heads, and a blower.   >:D
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NO REGRET$ ... Arguing on the internet is like competing in the Special Olympics / no matter how good you do you're still retarded!!!!!

                                                          1978  19' Mach 1 Tunnel jet

pw_Tony

  • Karma: +12/-0
Re: 427 heads
« Reply #14 on: January 22, 2008, 05:48:33 PM »
Quote from: hotrod56cars on January 22, 2008, 05:45:48 PM
So correct me if I'm wrong, but it seems the best to run is flat topped pistons, coupled with open chambered heads, and a blower.   >:D

Dished small chambers is where it's at. But flat top with closed chambers is bitchen as well
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