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Mopar Head Advice

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    Just Me snoc653's Avatar
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    Default Mopar Head Advice

    I have a stock set of 346 Mopar heads. I'm wondering if the steel 346 heads with porting and the bigger valves can flow enough to keep up with a 510 CU IN with a healthy cam. Not sure on the cam specs yet, but it is going in my 21' mini cruiser jet. I took the block down to have it cleaned up and the machinist said it had .005 taper and recommends taking it .030 over. I'm thinking 11.5:1 or something close to that and run it on 91 octane. I'd go all out and do 14:1 on E85 but I'm not sure that would be as reliable for the family truckster, and I don't really want to have to go to dual carbs to keep it fed. Any thoughts on making more power from my mopar?
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    gn7
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    Quote Originally Posted by snoc653 View Post
    I have a stock set of 346 Mopar heads. I'm wondering if the steel 346 heads with porting and the bigger valves can flow enough to keep up with a 510 CU IN with a healthy cam. Not sure on the cam specs yet, but it is going in my 21' mini cruiser jet. I took the block down to have it cleaned up and the machinist said it had .005 taper and recommends taking it .030 over. I'm thinking 11.5:1 or something close to that and run it on 91 octane. I'd go all out and do 14:1 on E85 but I'm not sure that would be as reliable for the family truckster, and I don't really want to have to go to dual carbs to keep it fed. Any thoughts on making more power from my mopar?
    You are never going to get close to 11.5 to 1 on pump gas with those heads. 10.0 to 1 would be pushing it, and even then you better be on top of your quench, and cooling.
    Stock they flow less a stock set of BBC oval ports. With mods, maybe close to the same. It's a head designed in the late 50s, and it shows on the flow bench.
    Don't think of heads an engine size frame of mind and think if them in a HP frame of mind. How much HP are you hoping to make at what RPM.
    Those heads can easily feed a 600 incher, if the RPM is only 3500 rpm, making 375 HP. Don't bother camming them much larger than about 550 lift. The heads fall down by that time with out some PROFESSIONAL help. Duration is the only thing that can help after that much lift, and duration is not your friend in a recreational cruiser.
    Keep in mind, its easier to hurt the flow of a set of heads than it is too make big increases in flow. Bigger valves and porting is no guarantee of improved flow if done by the wrong person. Small gains with a clean up are one thing, and are just that, SMALL GAINS. Larger gains require some knowledge of the heads, not some guy with a die grinder and hand full of cutters.



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    Just Me snoc653's Avatar
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    I was told they will flow close to 230 at .500 on the intake and close to 190 on the exhaust at .500. I don't plan to turn the motor over 6500 if it will spin that high. More likely it will be below 5700. If I can get 650 HP or over out of it, I'd be happy. The cruiser isn't a race boat, but I do want to beat the local whacker jon boats.

    I hope to wind up around 70 MPH when it's all said and done. I definitely need the boat to pull from the stop since it pulls tubers and skiers all day. 10.5:1 wouldn't be a bad deal as long as it stays pretty bullet proof.
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    gn7
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    Quote Originally Posted by snoc653 View Post
    I was told they will flow close to 230 at .500 on the intake and close to 190 on the exhaust at .500. I don't plan to turn the motor over 6500 if it will spin that high. More likely it will be below 5700. If I can get 650 HP or over out of it, I'd be happy. The cruiser isn't a race boat, but I do want to beat the local whacker jon boats.

    I hope to wind up around 70 MPH when it's all said and done. I definitely need the boat to pull from the stop since it pulls tubers and skiers all day. 10.5:1 wouldn't be a bad deal as long as it stays pretty bullet proof.
    I have the flow closer to 200 at .500 lift. As an example, Dr. Js has them listed at 215 @ .500 and .550 lift, and that's where the test data stops. Everything I have on the BBC oval port with stock valves, unported is around the 250 to 260 range. Steelcomp may have different numbers for them, it is more than the stock MoPar 346 or 906 heads. 50 cfm at that flow level is an ass whoop'n.


    I see you added .5 to 1 to what I said was about the max, and then added so long as its bullet proof. Good luck with that with a heavily loaded engine. I take it you feel pretty confident of your ability to control detonation with a 50 year old chamber design and reasonably short camshaft.
    10.5 to 1 + pump gas + old iron head + heavy loaded low RPM + stone reliability, does not add up using the math I know.
    That is not a BBF or even BBC chamber your dealing with



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    Last edited by gn7; 09-26-2013 at 11:39 PM.

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    Already miss the 310/562 2manymustangs's Avatar
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    Here is a butt load of info on these and the other mopar bb castings as well as figures for the Mopar Performance P4120437 porting templates and results... The templates have been around for a LONG time...

    Cylinder Heads Part I - Tech Articles - Mopar Muscle Magazine
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    There's no way those heads are going to move enough air for a 500" engine other than a very low rpm application. The amount of stroke you need is going to swallow up that port volume real fast more than anything. It's all about piston speed. GN's also right about the cam. It would have to be crazy, although duration isn't necessarily a bad thing. Long duration, short lift is a lot easier on parts than short duration and high lift.
    Last edited by scott foxwell; 09-27-2013 at 01:22 PM.
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    Quote Originally Posted by 2manymustangs View Post
    Here is a butt load of info on these and the other mopar bb castings as well as figures for the Mopar Performance P4120437 porting templates and results... The templates have been around for a LONG time...

    Cylinder Heads Part I - Tech Articles - Mopar Muscle Magazine
    Part two of that series says they got 240 at .500 lift and 249 at .600. From what I'm hearing that isn't enough air yet. I can go with the 440 source AL heads that flow 290 at .500 stock and they claim they'll move over 330 with porting.

    Quote Originally Posted by steelcomp View Post
    There's no way those heads are going to move enough air for a 500" engine other than a very low rpm application. The amount of stroke you need is going to swallow up that port volume real fast more than anything. It's all about piston speed. GN's also right about the cam. It would have to be crazy, although duration isn't necessarily a bad thing. Long duration, short lift is a lot easier on parts than short duration and high lift.
    Thanks. In case you didn't know,in my opinion this is one area that your opinion carries a lot of weight. What would you put on it within a reasonable budget? I need it to move from a stop and pull up skiers and the tube with 3 on it. And since it's a jet, there is no way it will go past 6000 if it can even hit that with an A impeller. I'll save the 346 heads for a 440 build for one of the project boats or the 51 pick up my mother-n-law has sitting at the old home place.
    So many projects, so little time

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    Quote Originally Posted by snoc653 View Post
    Part two of that series says they got 240 at .500 lift and 249 at .600. From what I'm hearing that isn't enough air yet. I can go with the 440 source AL heads that flow 290 at .500 stock and they claim they'll move over 330 with porting.



    Thanks. In case you didn't know,in my opinion this is one area that your opinion carries a lot of weight. What would you put on it within a reasonable budget? I need it to move from a stop and pull up skiers and the tube with 3 on it. And since it's a jet, there is no way it will go past 6000 if it can even hit that with an A impeller. I'll save the 346 heads for a 440 build for one of the project boats or the 51 pick up my mother-n-law has sitting at the old home place.
    I'm tooooo far into my aussie 351C 2v heads now to turn back, I'm going to have to drop a BUNCH more into them to get where I wanna be (close to 230CFM intakes AND maintain good velocity) for a 347" SBF... Might have to pack up all of my parts and make a trip to see Steele and Chris Straub in TN...

    Think about it long and hard Glen, by the time I finish with these factory iron heads I could have purchased a brand new set of aluminum heads that would have even more potential than my factory iron AFTER being tricked out...
    Last edited by 2manymustangs; 09-27-2013 at 05:37 PM.
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    Quote Originally Posted by snoc653 View Post



    Thanks. In case you didn't know,in my opinion this is one area that your opinion carries a lot of weight. What would you put on it within a reasonable budget? I need it to move from a stop and pull up skiers and the tube with 3 on it. And since it's a jet, there is no way it will go past 6000 if it can even hit that with an A impeller. I'll save the 346 heads for a 440 build for one of the project boats or the 51 pick up my mother-n-law has sitting at the old home place.
    I appreciate that and I don't mind helping. I have very little experience with what's available in the Mopar camp other than the hard core stuff, but I can do a little checking around. What block, what bore & stroke, what intake (if you have one) and what's the budget?
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    Quote Originally Posted by steelcomp View Post
    I appreciate that and I don't mind helping. I have very little experience with what's available in the Mopar camp other than the hard core stuff, but I can do a little checking around. What block, what bore & stroke, what intake (if you have one) and what's the budget?
    Dropped the main caps off today so he could start work on the block. I won't know exactly what I'll end up with until he gets the block bored. He says .020 over is possible but doubts I'll get there. Most likely it will be .030 over with a 4.25 stroke crank and 7.1" rods. That would net a 1.67 rod ratio. It will have the 2.200 Chevy rod journals so a minimum amount of clearancing will be required. It will have a main stud girdle on it, and I'm thinking a roller cam with roller rockers are probably a must for a decent cam profile.

    Mamma has ok'd $5,000 to rebuild which means I might get a bump to $6500 if I do it right. $2,000 goes to the Stroker kit, (pistons, rods, crank, bearings and rings) which leaves not enough for a great set of heads and big carb if I plan on going all out, so I'll have to be a little conservative. I have a dual 4bbl Weiand Tunnel ram (well the cops have it after they recovered it, not sure when I get it back) but I'm thinking more along the lines of a Dual plane with a 950cfm would be better suited for it. I'm fairly flexible when it comes to what intake and carb(s) to put on it.
    So many projects, so little time

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    Living in a cage of fear thatguy's Avatar
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    I like the sound of this build, but those RPM, HP, and MPH goals MAY be a bit optimistic considering the hull and propulsion?

    it's always a balancing act building a PERFORMANCE Jet truckster with solid reliability.
    (Unless your name is sleeper CP!)

    Maybe I am off base, lord knows I'm no expert!

    But I do know what it takes to make our 19' ski jet to run in the 80's.

    a couple hundred RPM either way takes significant changes in either power or pitch, or both.
    Fuel consumption in a MDC with a jet and those sort of parameters you mention will be a sobering reality too!!

    I've spent two seasons trying to optimize the carbs I built just so I can go most of a day without draining the 20 gallon tank capacity.

    Good luck and keep posted!
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    Quote Originally Posted by thatguy View Post
    I like the sound of this build, but those RPM, HP, and MPH goals MAY be a bit optimistic considering the hull and propulsion?

    it's always a balancing act building a PERFORMANCE Jet truckster with solid reliability.
    (Unless your name is sleeper CP!)

    Maybe I am off base, lord knows I'm no expert!

    But I do know what it takes to make our 19' ski jet to run in the 80's.

    a couple hundred RPM either way takes significant changes in either power or pitch, or both.
    Fuel consumption in a MDC with a jet and those sort of parameters you mention will be a sobering reality too!!
    I've spent two seasons trying to optimize the carbs I built just so I can go most of a day without draining the 20 gallon tank capacity.

    Good luck and keep posted!
    ^^^ what he said
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    Quote Originally Posted by thatguy View Post

    I've spent two seasons trying to optimize the carbs I built just so I can go most of a day without draining the 20 gallon tank capacity.

    Good luck and keep posted!
    That's not too bad. I spent 2 years getting a set of Domins to run 30 mintues on 50 gals



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    Quote Originally Posted by thatguy View Post
    I like the sound of this build, but those RPM, HP, and MPH goals MAY be a bit optimistic considering the hull and propulsion?

    it's always a balancing act building a PERFORMANCE Jet truckster with solid reliability.
    (Unless your name is sleeper CP!)

    Maybe I am off base, lord knows I'm no expert!

    But I do know what it takes to make our 19' ski jet to run in the 80's.

    a couple hundred RPM either way takes significant changes in either power or pitch, or both.
    Fuel consumption in a MDC with a jet and those sort of parameters you mention will be a sobering reality too!!

    I've spent two seasons trying to optimize the carbs I built just so I can go most of a day without draining the 20 gallon tank capacity.

    Good luck and keep posted!
    Thanks. I can get 52 to 55 MPH on GPS at 4600 rpm out of the HM 454 that was in it. The impeller chart shows I should be right around 5600 with 650 HP. At the current rpm to speed ratio I'd be in the mid 60s. I can live with that. If the build tops 650 HP I'll be getting close. Again I can live with that, but I don't need the tune set to the edge. Reliability within a budget is very important. Top speed, not so much so. But don't we all hope for as much as possible?

    The boat is a Riviera mini-day. It runs pretty well for a 21 footer. It does have a place diverter.
    So many projects, so little time

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