The year of the carb... |
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79nautique
Grand Poobah Joined: January-27-2004 Location: United States Status: Offline Points: 7872 |
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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. |
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TRBenj
Grand Poobah Joined: June-29-2005 Location: NWCT Status: Offline Points: 21169 |
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Chris, I dont know if I agree with this. You realize the engine in question is a 210hp 2bbl Holman Moody, right? That came with a 500cfm 2bbl... Its a different animal than the 165hp 2bbl Interceptor (which came witha 350cfm 2bbl?). I dont see why a 450cfm 4bbl would cause it to run rich. I agree a cam swap would optimize its performance though.
With a new carb (which has a vacuum port for the PCV) he can eliminate the spacer if need be, so height should be a non-issue. The RPM is ~1" taller than the regular performer, but it may not be an issue at all with his big wood motorbox. |
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Keeganino
Grand Poobah Joined: October-27-2009 Location: North Carolina Status: Offline Points: 2063 |
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Good reading! I have nothing to offer- just another fly on the wall soaking it all in.
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"working on these old boats may not be cost effective but as it shows its what it brings into your life that matters" -Roger
1973 Skier |
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hotboat
Gold Member Joined: March-28-2009 Location: Conn Lake Pa Status: Offline Points: 814 |
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Doesnt a carb meter the fuel depending on air flow/velocity? If there are further upgrades in the future you will already have some of the pieces
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Brian
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79nautique
Grand Poobah Joined: January-27-2004 Location: United States Status: Offline Points: 7872 |
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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. |
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TRBenj
Grand Poobah Joined: June-29-2005 Location: NWCT Status: Offline Points: 21169 |
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Wait, which is it? I agree that the carb wont likely be the limiting factor- the cam will be the most likely culprit... though everything from the carb to the exhaust (intake, heads and cam in the middle) will have an affect on the amount of airflow (and thus, the A/F ratio). The carb is the only thing metering fuel though, yes? Youre saying it will be impossible to dial in a 4bbl on a motor spec'd as a 2bbl, even though the carbs have similar CFM's? Seems like it wouldnt be too tall of an order. Really, how different can the longblocks be between a 210hp 450cfm 4bbl Interceptor vs. the 210hp 500cfm 2bbl H-M? |
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79nautique
Grand Poobah Joined: January-27-2004 Location: United States Status: Offline Points: 7872 |
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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. |
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TRBenj
Grand Poobah Joined: June-29-2005 Location: NWCT Status: Offline Points: 21169 |
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This makes no sense to me whatsoever. 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. Youre right, when we lined up at GL07, I only held you off out of the hole for 30 seconds. Pretty poor performance on my part. I would have been to the end of my home lake and back in that time! Bring any inboard ski boat you want to GL10 and we'll see if you can keep up... I promise you that you wont. |
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79nautique
Grand Poobah Joined: January-27-2004 Location: United States Status: Offline Points: 7872 |
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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 |
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TRBenj
Grand Poobah Joined: June-29-2005 Location: NWCT Status: Offline Points: 21169 |
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Yes, the secondaries are controlled by a circuit that is affected by both vaccuum and RPM. Yes, they will open well before youre at max RPM. Clearly there is a crossover point on a 4bbl application where the carb needs to open the back 2 barrels. That doesnt mean it cant run well on the primaries at lower RPM's with low to medium load... and that would just as easily apply to an engine that originally shipped with a 2bbl carb. The heads and cam that came on a H-M 2bbl cant be that radically different from an Interceptor 4bbl since its rated the same exact 210hp. If he wants to upgrade the top end in the future, he'll have a heck of a time finding a performance 2bbl manifold to match the 2bbl carb youre proposing he buy.
Am I way off base here? |
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79nautique
Grand Poobah Joined: January-27-2004 Location: United States Status: Offline Points: 7872 |
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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? |
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79nautique
Grand Poobah Joined: January-27-2004 Location: United States Status: Offline Points: 7872 |
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they are called vaccum secondaries for a reason not RPM secondaries. They open because of vaccum not because you just hit 4000 rpm. |
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Keeganino
Grand Poobah Joined: October-27-2009 Location: North Carolina Status: Offline Points: 2063 |
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BZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ The reading gets even better.
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"working on these old boats may not be cost effective but as it shows its what it brings into your life that matters" -Roger
1973 Skier |
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vondy
Platinum Member Joined: November-29-2007 Location: Dallas, Texas Status: Offline Points: 1116 |
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OK now I'm really confused...
According to Chris it seems like I could update my carb, intake and cam to 4bbl and be good. No heads needed. If I'm reading correctly, and I may not be. If that's the case, whats a good cam usually run? Is it a simple enough swap or terribly involved? If it's not a huge deal I could update the carb and intake to 4bbl this year and do the cam next. One thing I don't want is to get a 4bbl and waste a bunch of fuel and not get anything extra out of it. So basically if I have to change the heads down the line to see any advantage to a 4bbl I might just stick with a 2bbl cus I'm not planning on spending that kind of money any time soon. But, if it's not going to hurt anything, fuel economy, performance, reliability, etc., to have just a 4bbl intake and carb for a year until I get a cam then I might go that way. |
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79nautique
Grand Poobah Joined: January-27-2004 Location: United States Status: Offline Points: 7872 |
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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. |
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vondy
Platinum Member Joined: November-29-2007 Location: Dallas, Texas Status: Offline Points: 1116 |
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Wow, look what I started...
Chris is right that I'm looking for an easy way to get her "running right". Any gains in HP were secondary thoughts. That being said, I do not want to limit myself for future upgrades. But if it's going to be a PITA to get running right in the meantime, I would rather keep it simple and just bight the bullet years form now when I decide to really upgrade. |
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TRBenj
Grand Poobah Joined: June-29-2005 Location: NWCT Status: Offline Points: 21169 |
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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. |
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79nautique
Grand Poobah Joined: January-27-2004 Location: United States Status: Offline Points: 7872 |
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Tim your so wrong the heads are not the limiting factor so changing the cam is going to get you way more than 20 hp.
Also explain where your engine's vaccum and RPM comes into play on a four barrel carb with mechanical secondaries? if the secondaries only work based upon the engines rpm and vaccum needs as you want to argue? Step on the gas peddle and the secondaries open up the engine is allowed to breath in more air and the RPM takes off. Keep reading your websits and books maybe one day it'll sink in. Good old teachings from a master tech don't mean *************** I guess that's why I'm so lost. |
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79nautique
Grand Poobah Joined: January-27-2004 Location: United States Status: Offline Points: 7872 |
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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. |
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TRBenj
Grand Poobah Joined: June-29-2005 Location: NWCT Status: Offline Points: 21169 |
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All this coming from a guy that dropped in a longblock instead of building his own engine.
Yes, the stock 302 heads suck. They put similarly awful heads on stock 351w's. Thats why the GT40 and GT40p heads are an upgrade. Yes, both of those heads were designed for and originally installed on 302's. Theyre not in the same league as the stock marine heads though- we're talking a 30-40 bolt on hp difference. Yes, they work well on a 351w that doesnt see much over 5k RPM's. If the stock 302 heads were so good, why were the 4bbl's only rated at 220-235hp? You think you can get a 2bbl to perform significantly above that level with a cam and intake change? That would surprise me, but hey, youre the Master Tech! Would a cam upgrade alone help? Yes. Would a head upgrade alone help? Yes. Would I do the cam without the heads? No- add the heads later and you'll probably want to change the cam again to take advantage of them. Would I do heads alone? Not in this 2bbl application- but others, maybe. All for the same reason Im recommending he go 4bbl now- support future growth, prevent buying the same part twice. Im not following you on a your mechanical secondary reference. I thought we were talking vaccuum secondaries, which 95% of people here are running. The 450cfm that Vondy is proposing to use (the stock 4bbl 302 carb) falls into that category. Even with vaccuum secondaries, theyre not going to open based purely on load- theyre RPM dependant as well. Like I said, attempt to pull 10 skiers out of the water- youre only going to get 2500-3000 RPM's with a 1:1 (at best) and no matter how much the engine struggles, the secondaries wont kick in. |
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79nautique
Grand Poobah Joined: January-27-2004 Location: United States Status: Offline Points: 7872 |
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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? |
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Keeganino
Grand Poobah Joined: October-27-2009 Location: North Carolina Status: Offline Points: 2063 |
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bbbzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
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"working on these old boats may not be cost effective but as it shows its what it brings into your life that matters" -Roger
1973 Skier |
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vondy
Platinum Member Joined: November-29-2007 Location: Dallas, Texas Status: Offline Points: 1116 |
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Oh I'll never get a carb now...
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TRBenj
Grand Poobah Joined: June-29-2005 Location: NWCT Status: Offline Points: 21169 |
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Chris, just poking at you about the Jasper longblock!
My comments regarding the vacuum secondaries and the need to upgrade both the cam and heads together were specific to Vondy's predicament. In case you forgot, he's trying to improve safety and reliability of the 2bbl 302 H-M in his Mustang with a new carb, while still allowing for future growth (without re-purchasing parts). All of my advice is good! Yes, I know you dont always have to upgrade heads to see an improvement. Im going through this right now on our BFN... we're picking up 90hp with a cam change alone- but thats only because it was the ONLY bottleneck in the system. I just dont see how upgrading either the cam or heads alone on a 2bbl 302 is going to make a big enough difference to justify the cost. Theyre BOTH bottlenecks. Vondy, long story short: Like Ive been saying from the beginning, Id upgrade to a new 4bbl carb. Grab a cheap/free 4bbl intake and go skiing. This will improve safety and reliability, and should improve performance over the worn out Autolite. If and when you ever decide to upgrade to upgrade the top end, pony up for a new set of heads, a cam upgrade, and a performance manifold. Spec the cam last to match your other components. Reuse the 4bbl carb that youve previously purchased. Chris, let me know if this is bad advice!!! Oh, and yes you did see the back of my boat- for the first 30 seconds of that race! If you want to line up again, bring a fast one- the BFN will be running 60 this summer. |
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79nautique
Grand Poobah Joined: January-27-2004 Location: United States Status: Offline Points: 7872 |
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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. |
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Air206
Grand Poobah Joined: September-28-2008 Location: Roanoke, VA Status: Offline Points: 3000 |
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I hope you 2 don't have day jobs!............... How can you get a day's work done posting so much? Well , you guys are certainly multi-taskers.......... Too funny!
No matter how old you get, it still comes down to comparing whose long block is bigger and better. Ha! |
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TRBenj
Grand Poobah Joined: June-29-2005 Location: NWCT Status: Offline Points: 21169 |
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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? |
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vondy
Platinum Member Joined: November-29-2007 Location: Dallas, Texas Status: Offline Points: 1116 |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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I feel the confusion here is due to misinterpretation. Tim, you just need to take the Chris course of spelling!!
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Gary S
Grand Poobah Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096 |
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The only thing I could add is, I doubt this piece of junk could be anywhere near 500cfm
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