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TahitiTiger76

  • Karma: +0/-0
Olds 455 - need new carb what to get?
« on: June 08, 2008, 05:13:27 pm »
First off, hello all, new here...   Have a 76 Tahiti Tiger, 455 Olds bored to 468, balanced, Torker intake, Rewarder Twisties, Flamethrower HEI, Milodon big pan, Hydraulic Comp Cam 280dur/.490 lift

Currently the boat has a Holley 4175 Spreadbore 650CFM carb.  It is leaking, yes shockingly so.   :banghead:  It did however run great with this setup minus the Rewarders, it had logs.  Would turn 5200 rpm with A impeller Berk GPS'd at 64mph. 

So now with the Rewarders I am wondering what carb to get.  I am thinking somewhere through 750 - 850 CFM Holley or Demon. 


Whaddayall think? 

Mighty Marine Demon  me like  O0
http://www.barrygrant.com/demon/default.aspx?page=21a

According to what they are saying it seems I should pick a 825 or 850.  What diff will the Annular Boosters give me?  Any loss of bottom end with either choice? 

Looking for all around performance, still a decent idle, good out of the hole for skiing, and decent top speed.  Also planning on getting a diverter at some point...finally!

THANKS!

Mark

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'76 Tahiti Tiger, 468 Olds, Berk JC
'78 K5 1 Ton'd Dual Cased Caged Rock crusher

GT Jets

  • Karma: +192/-0
Re: Olds 455 - need new carb what to get?
« Reply #1 on: June 08, 2008, 05:39:05 pm »
Welcome aboard! I would like to throw out that 800+cfm seems a little large, someone else will pipe in I'm sure but if it really is turning 5200 RPM You're really close now, otherwise your tach is off or the pump is undercut or worn out, 750 CFM mechanical secondary seems to be stuck in my head, should give good all around performance and be pretty consistant even with a "pretty close" tune.

But don't take my word for it I may not be taking everything into consideration, not knowing your boat.

  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

GT Jets

  • Karma: +192/-0
Re: Olds 455 - need new carb what to get?
« Reply #2 on: June 08, 2008, 05:43:50 pm »
BTW also should take into consideration how the boat would be driven, (like a rental, or like it belongs to someone bigger than you ;D)

The one good thing about a jet is acceleration is based on water velocity, not engine RPM (so the engine gets into its powerband without a huge load).

Hope this is helpful.
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

TahitiTiger76

  • Karma: +0/-0
Re: Olds 455 - need new carb what to get?
« Reply #3 on: June 08, 2008, 09:53:55 pm »
Thanks!  So I have totally been wondering this myself, I also did some CFM calculator thing on the internet that prescribed much smaller, not to mention the boat runs pretty good with a 650 CFM (wondering if it is a limiting factor).  I know that I could screw my bottom end for sure going to large, or at least lose throttle response.  Just mainly curious if the headers will make a big difference, they look like they would flow a hell of a lot better than those guardian logs I had. 


My pump could well be worn also, it hasn't been rebuilt....yet.   ;D
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'76 Tahiti Tiger, 468 Olds, Berk JC
'78 K5 1 Ton'd Dual Cased Caged Rock crusher

GT Jets

  • Karma: +192/-0
Re: Olds 455 - need new carb what to get?
« Reply #4 on: June 08, 2008, 10:04:53 pm »
Headers will flow better than logs everytime but I don't believe it will make an enormous difference, that being said, they could cause a leaner burn do to the exhaust gasses being more efficiently evacuated.

You should get better throttle response, a little more RPM, but the "Assanometer" won't see a lot of difference, but they do look cool!

You would see more gain with a tight pump.
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
  • Like
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

TahitiTiger76

  • Karma: +0/-0
Re: Olds 455 - need new carb what to get?
« Reply #5 on: July 03, 2008, 08:33:05 am »
Ordered a Proform 750 Race Series, should be here today.  :)

Went with a 750 because I don't think my engine needs an 850 with my setup.  I don't plan to run it past 5000 rpm either, cause I don't want another blown bottom end!  Hopefully be on the water testing this weekend.

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'76 Tahiti Tiger, 468 Olds, Berk JC
'78 K5 1 Ton'd Dual Cased Caged Rock crusher

KonaCole

  • Karma: +1/-0
Re: Olds 455 - need new carb what to get?
« Reply #6 on: July 03, 2008, 09:26:56 am »
Ordered a Proform 750 Race Series, should be here today.  :)

Went with a 750 because I don't think my engine needs an 850 with my setup.  I don't plan to run it past 5000 rpm either, cause I don't want another blown bottom end!  Hopefully be on the water testing this weekend.



I am running a Holley 4150 750 DP on a 468 olds 10:1, comp 280H cam, pocket ported G heads, comp magnum roller rockers, glenwood logs in an 18 ft Kona.  Engine turns 4850 with an A2 in a Berkley 12 JC @ ~ 61.5 mph.  I am still playing with jet sizes, but so far the 750 is doing a great job.
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TahitiTiger76

  • Karma: +0/-0
Re: Olds 455 - need new carb what to get?
« Reply #7 on: July 03, 2008, 11:39:08 am »
cool, I have the same cam, but stock K heads and and stock rockers.   ;D
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'76 Tahiti Tiger, 468 Olds, Berk JC
'78 K5 1 Ton'd Dual Cased Caged Rock crusher

KonaCole

  • Karma: +1/-0
Re: Olds 455 - need new carb what to get?
« Reply #8 on: July 03, 2008, 12:15:08 pm »
cool, I have the same cam, but stock K heads and and stock rockers.   ;D
I think that you will be happy with the carb choice
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