SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: lupo1904 on October 19, 2010, 09:18:27 PM
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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
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EAST.
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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
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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!
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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
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Your 650 is just fine for a stock motor, with other mods a bigger would be better.
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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).
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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
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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
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Would say your pretty close...seen 63 64mph @ 4500
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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 %