Null


carb

  • 10 Replies
  • 2407 Views

lupo1904

  • Join Date: Jun 2010
  • Location: santucky
  • *
  • Hero Member
  • *****
  • Posts: 1,184
  • Karma: +9/-0
  • jet boat life
    • View Profile
  • Liked:
  • Likes Given: 0
« on: October 19, 2010, 09:18:27 PM »
if i changed my carb to a bigger one would i gain horse power or just eat more gas? from wut i was told i have a stock 454 with a holley 750 carb and a roller valve train. i wanna go faster any suggestions? my boat runs great and i drive the dog shit out of it but i gps at 60 with 2 other people in there,is that good? can someone point me in the right direction


german1

  • Join Date: Aug 2010
  • Location: santuckey
  • *
  • Sr. Member
  • ****
  • Posts: 344
  • Karma: +0/-1
    • View Profile
  • Liked:
  • Likes Given: 0
« Reply #1 on: October 19, 2010, 09:24:19 PM »
EAST.

   WET FARTS

Nordie

  • Join Date: Dec 2007
  • Location: Las Vegas,NV
  • *
  • Team Member
  • Informative Member
  • *******
  • Posts: 4,132
  • Karma: +13/-0
  • never tattoo unlucky on your body, even if that is your luck it will come back ten fold!
    • View Profile
  • Liked:
  • Likes Given: 0
« Reply #2 on: October 19, 2010, 09:46:01 PM »
Sounds like your right about there, but if you wanna go faster there is bolt on and such...but if its reliable just leave it be...as far as going bigger carb i dont think it will do anything for you...your motor is going to use only so much air, and the 750 will be just fine


If im not posting..I'm pooping!

Taylor SJ

  • Join Date: Nov 2006
  • Location: Texas
  • *
  • Full Member
  • ***
  • Posts: 155
  • Karma: +6/-0
  • 79 Taylor SJ
    • View Profile
  • Liked:
  • Likes Given: 0
« Reply #3 on: October 19, 2010, 10:11:00 PM »
Great question. I am running a 650 on my BBF 460. Was told a 750 would add some mph. True or BS? All opinions appreciated!

GT Jets

  • Join Date: Jan 2007
  • Location: Morgan Hill CA
  • *
  • Informative Member
  • *******
  • Posts: 11,748
  • Karma: +192/-0
  • Team Evil Weiner
    • View Profile
  • Liked:
  • Likes Given: 138
« Reply #4 on: October 19, 2010, 11:44:13 PM »
You literally cannot "add MPH" without taking the entire set up into account.

The carburetor is a great place to start, but with some tuning and some data, there may be a "bigger bang for the buck" hidden in there somewhere...

Ignition, cam choice, heads, exhaust, pump specifics and hull design all make a major contribution to MPH, all will require the "right" carburetor to maximize their effect...

I have seen some instances where just changing the cam timing will buy you 200 RPM, so it would stand to reason that there may be bigger fish to fry.

The good news, is you have a built in dyno with a jet...Gains can be measured immediately... :thumbup:

GT
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
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

SS-201

  • Join Date: Apr 2010
  • Location: Orlando, Florida
  • *
  • Full Member
  • ***
  • Posts: 213
  • Karma: +0/-0
    • View Profile
  • Liked:
  • Likes Given: 3
« Reply #5 on: October 20, 2010, 02:14:56 AM »
Your 650 is just fine for a stock motor, with other mods a bigger would be better.

crewchief22

  • Join Date: Apr 2007
  • Location: Mentone Beach, CA
  • *
  • Team Member
  • Informative Member
  • *******
  • Posts: 5,396
  • Karma: +66/-0
    • View Profile
  • Liked:
  • Likes Given: 193
« Reply #6 on: October 20, 2010, 05:42:35 AM »
Try one before you buy one.   If you have access to an 850 for testing before you buy one, it could save you some money.  GT is correct that combinations make the best rpm/mph, but you should be able to tell right away if a bigger carb is going to make a difference (even without all of the fine tuning).
  • Boat #1: '77 Hondo Pantera GT Jet
"Racing is life!  Anything that happens before or after, is just waiting"    Steve McQueen

The problem with America is stupidity. I'm not saying there should be a capital punishment for stupidity, but why don't we just take the safety labels off of everything and let the problem solve itself?

IRRebel

  • Join Date: Dec 2008
  • Location: Casa Grande, Arizona
  • *
  • Informative Member
  • *******
  • Posts: 5,635
  • Karma: +16/-0
    • View Profile
  • Liked:
  • Likes Given: 12
« Reply #7 on: October 20, 2010, 10:19:30 AM »
In my humble opinion, I think a 650 is too dang small for even a stock marine 460. Std Cobrajet style cast iron intake and all, some pretty good hot rod stuff put in those things from the word go.

750's are what Ive seen come on every one I have or had, ( that's, wait 1,2....3....oh wait that one sank....ok 3,4,5, plus two from the Sleek.....yeah, 7 of them here right now..... :screwy: ) and only one did I try an 850 on that didn't seem to make a huge difference seat of the pants. It did pick up 100 rpm, if you want to split hairs. Granted this was on a 21' cruiser too.

The larger carb is not going to "burn up" more fuel, it's simply able to flow more air, to which you CAN and SHOULD jet up for if the engine is working well with the increased airflow, it's gonna run lean then.  Then, yeah, you're gonna burn more fuel..... ;)

You haven't mentioned at what rpm the boat tops out, and what your plugs are telling you. You might well be able to pick up some rpm, maybe a lot depending on where you're hitting 60 at, but it's not gonna be a huge MPH increase. What you will gain, however is better tuning, better cylinder to cylinder distribution on the lean/fat problems, and much crisper throttle response.

Sell the 650 to a small block user or get the other one for a Tunnel Ram...... >:D

Ray

"Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways totally worn out shouting 'Holy Shit what a ride!"---Crewcheif22 AKA Keith

lupo1904

  • Join Date: Jun 2010
  • Location: santucky
  • *
  • Hero Member
  • *****
  • Posts: 1,184
  • Karma: +9/-0
  • jet boat life
    • View Profile
  • Liked:
  • Likes Given: 0
« Reply #8 on: October 20, 2010, 04:46:39 PM »
well i have a 750 right now and i turn 4500 at 60 mphs and wont go no more and i got a fresh rebuild on my pump, i thought forsure that would have gave me some more rpms

Nordie

  • Join Date: Dec 2007
  • Location: Las Vegas,NV
  • *
  • Team Member
  • Informative Member
  • *******
  • Posts: 4,132
  • Karma: +13/-0
  • never tattoo unlucky on your body, even if that is your luck it will come back ten fold!
    • View Profile
  • Liked:
  • Likes Given: 0
« Reply #9 on: October 20, 2010, 08:54:41 PM »
Would say your pretty close...seen 63 64mph @ 4500


If im not posting..I'm pooping!

SS-201

  • Join Date: Apr 2010
  • Location: Orlando, Florida
  • *
  • Full Member
  • ***
  • Posts: 213
  • Karma: +0/-0
    • View Profile
  • Liked:
  • Likes Given: 3
« Reply #10 on: October 21, 2010, 03:38:54 AM »
To add more Carb or CFM depending on the modifications may add maybe 5 HP however you want to improve on the VE volemetric effeciently. Again the mods, heads,cam,intake manifold, comp, etc are necessary to increase the VE. The formula to figure CFM is pretty much a good indicator.
Remembering that at 5250 is where the hp and torque meet . EX. Given all the facts 750 to 850 CFM more carb can give raise the HP 5 hp and raise the VE from 88 to 90 %
« Last Edit: October 21, 2010, 03:48:56 AM by SS-201 »

 


Website Security Test
Powered by EzPortal

Website Security Test