The year of the carb...

your just going to be running rich all of the time if you don't change the cam so stay away from a 4bbl carb if all your going to do is get a new carb.

if you want to change the cam and upgrade to a 4bbl that would be your best bet the heads are a wash you'll never tell a difference, without a cam change it's not going to gain anything been there done that when I was 17 big waste of cash.

Good reading! I have nothing to offer- just another fly on the wall soaking it all in.

if your going from a 500 2bl to a 450 4bl do you plan on runing on the secondaries all the time or just running lean all the time on the primaries?

the cam drives the air flow not the carb so there's no need to re-invert the engine unless your doing other major changes like the cam and rockers.

well you've taken comments out of context to combine them in to one, so if you look at the context, you'll maybe figure it out.


So we have engine that wants to see 500 cfm all the time and you are suggesting using a 450 cfm 4bl carb that is going to allow 225 cfm all of the time and then 450 cfm if you use the secondaries. Sure seems like your creating a restriction to me.

I just love a guy that has all the answers and takes stuff out of context but when it comes down to the show part they're look at the rear of the other boats ahead of them because his can't keep up, stay with them out of the hole for about 30 seconds then fades. HHHMMMMmm

use a 500cfm 2bbl carb and call it a day.

TRBenj wrote: The air and fuel needs of an engine vary across the RPM band. Neither scenario requires the max CFM until you get close to WOT. Explain to me why the cam (or the rest of the engine) would care whether a 500cfm 2bbl or the front 2 barrels of a 450cfm are feeding it air and fuel at 2500 rpm's. Its only going to need 175cfm of air at that speed. So long as the A/F ratio is correct, its going to run good. Explain to me why a 4bbl cant be dialed in to work.

so then if it only needs 175 cfm at 2500 why will the secondaries open with the throttle completely open and your only doing 3000 rpm? load is why and it doesn't care what rpm your at.

Far from the need for the max CFM rating and max RPM of WOT

you have a guy that has a carb problem that's not the sharpest tool in the box when it comes to carboration. He states he doesn't want to modify or change any part of the engine that is going to require a different CFM rating or style carborator. So since the compression ratio isn't changing, the stroke isn't change and the cam isn't changing, why ignore the orginal engine builders specs and change the carb, he only wants better starting and engine operation for the whole day instead of the continued issue's he's been fighting with the current carb. What You know more than Holman or Moody.... maybe... probaly not would be the better answer.

So instead of suggesting he gets a 2 BBL 500 CFM carb to replace a 500 CFM unit, lets change the intake to a 4bbl, use a smaller carb to boot and then expect the guy to figure out the jetting and mixture issue you created because he took your advice. Are you going to be there to rejet the carb, adjust the floats and all the other crap that will need to be done? I doubt it.

So I suggest getting a new 500 CFM 2 bbl carb, and save the head ack after all isn't that why he wants to change the carb in the first place because he can't figure it out and get it to work properly? What the F am I missing here?

BZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ The reading gets even better.

Vondy your correct.

about 500-800 bucks maybe a little more if you going all new, but for a used intake, new cam, new carb 500-600 depending on what carb you choose.

79nautique wrote: they are called vaccum secondaries for a reason not RPM secondaries. They open because of vaccum not because you just hit 4000 rpm.

I dont care what you call them. Yes, vaccuum is a key. So is RPM. I dont know exactly how they work, not having designed the circuit. I do know that if you try to pull up 10 skiers, the secondaries still wont open... they have to be close to the RPM they normally open (3500-4000) regardless of load for them to activate. And yes, they'll open at a very similar RPM even with minimal load (eg, a lightly loaded boat, slowly creeping up to speed).

Yes, he would have to check the float levels and verify the jetting on the 4bbl- he'll have to set the idle too. Youre saying he can just bolt a 2bbl on with no adjustment at all? I dont think so. He'll have to dial in either one.

Dont confuse the issue here- a 302 will not be choked by a 450cfm carb any more than a 500cfm, so calling the 4bbl a "smaller carb" and implying it will hurt performance and economy is not accurate. I would think both would be improved with the 4bbl- especially when he's only running on the primaries. No need to run on on larger jets and throat sized for WOT operation (like the 2bbl would have to be) when he's only cruising.

The issue here is he's dealing with a worn out Autolite automotive carb. Safety and reliability are the top 2 concerns, yes. I think either a new 4bbl or a new 2bbl would improve that. With no other changes (save for an intake manfold with the 4bbl), performance between the 2 wouldnt be very different. Economy might be a little better with the 4bbl. The real difference is if he ever wants to upgrade the cam and heads... he'll want a decent flowing intake to match them, and all the decent/cheap ones are 4bbl. Why buy a new 2bbl carb (expensive!)that wont support a future upgrade?

Vondy, no I wouldnt upgrade the cam unless youre doing the heads. Youre only looking at picking up 20hp or so at best- not worth the $250 and extra work. Do it all at once if youre going to bother.

It's pretty darn funny someone complaining about 302 heads not being good enough, but the same old fool is using 302 heads on there 351W that's all beefed up? where the hell's the logic in that? isn't that why the head bolt holes have to be opened up so that it fits on a 351W block that uses a larger bolt diameter. HHHHHHMMMMMMM maybe not so bright maybe the heads are better than one might think?

Vondy get a cam, used in take, a new carb and enjoy the added perfomance.

TRBenj wrote: All this coming from a guy that dropped in a longblock instead of building his own engine.

your correct it was a long block, was it the same long you can buy? NO it wasn't, as it was custom built to my specification's by the same engine builder my Buddy used to build his race engines for is top sportsman car and his super comp rail at his sponsor's facility and at his cost not retail. So penny earn penny saved smart buy maybe Very much so and a better engine than you brought to the show to boot.

It pays to invest wisely and get what you want in return, but then I was never looking at the back of your boat either or looking for you to pay the bill for the parts, pretty nice motor for 3K all in all and I could spin it at 5500k all day long with no worries, but that's why I could spin a bigger wheel too, because the stock wheel pegged the tach.

so you missed the piont where you state that vaccum and rpm drive the secondaries on a carb, but that's not really true it's true only for a holley or a carb with vaccum secondaies so they can open up but it's not a requirement to have vaccum secondaries now is it and if you had mechanical secondaries the engine would come up to speed faster pulling those ten skiers because it lets the engine breath more quicker than waiting for the vaccum to build and open the secondaries up?

So to say you can't get any horse power out of an engine unless the heads are changed along with the cam is horse dung. Might be in your book because you don't know of any other way to do it because thats how you've always done it, It doesn't mean everyone does or everyone should because there are many out there that can and do get around that issue ask a bracket racer where they spec out everything yet some are fast some are slow wonder why, maybe they way they massage the parts the engine the components that compliment all of the other parts so that they create the most HP given the rules and size limits?

Oh I'll never get a carb now...

never saw you get a length on me but oh well your story,

So maybe you should read up a little more since your suggesting using a 450 CFM carb BIG *************** Mistake going smaller and then if you want to upgrade your buying a new carb too.

So the question is what actuall heads are on it? what are the valve specs what? are the runner specs? then a good cam and carb can be selected to get the most bang for the buck without changing the heads.

But you better get atleast a 650 CFM carb if your going 4 BBL and want to up grade at a later date, much easier to restrict the flow than not have enough flow to start with, so Read up Tim, your a little off.

Come on Chris, try to keep up!

Like I said, the 450cfm that Vondy picked out is the stock 302 4bbl (220hp) carb. That wont be a limiting factor, even if he wants to wind it up to 5200rpm (and thats assuming 100% volumetric efficiency). Some have gotten a 600cfm carb to work great on a 302 (like Reid's baby blue), but others needed to finesse it more to get it to run right (like Doc's 331 stroker). The 600cfm carb isnt holding back my 351w from turning up to 5400, so I feel its overkill in this application... especially if Vondy is keeping the 2bbl heads and cam for now.

And dont try and pretend you hung with me out of the hole! Id tell you how many boat lengths I put on you, but it was hard to judge... how many boatlengths are there in a football field?

I feel the confusion here is due to misinterpretation. Tim, you just need to take the Chris course of spelling!!

TRBenj wrote: This makes no sense to me

79nautique wrote: doesn't make much since to me.