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Horsepower Upgrades

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reidp View Drop Down
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    Posted: December-25-2003 at 4:19pm
If your Correct Craft's engine is getting tired and you'd like to step up the performance, it's not difficult or costly when doing a rebuild.

The main and least expensive areas of improvement are in the camshaft and pistons. Those items should always be replaced when doing a rebuild anyway. A higher lift marine cam is available thru several providers including SpeedPro and Crane and the cost with going with the upgrade is negligible. These are reverse rotation cams as well. An average increase of 20-30 horsepower can be expected with the right cam.

Marine engines in these boats are generally produced to run off regular fuel and thus have relatively low compression. Many owners fuel their boats with premium regardless. If that's your case or you don't mind using premium exclusively, then going with a compression increase will result in noticable power as well. This is obtained by a carefull match of piston to cylinder head which will result in a maximum compression ratio that doesn't need more than 92-93 octane fuel. Flat top or other higher compression pistons cost no more that the dished lower comp styles. Some early model marine engines from Holman Moody were based off high performance automotive engines and came with compression ratios similar to cars of the day, 9.5-10.5:1, which required premium fuel. Most all other marine engines were and are based off industrial and truck formats and lower compression has been the norm. An increase of 10-20 horsepower is not uncommon.

Depending on one's budget, cylinder head upgrades can be rewarding, by either having heads ported and polished (which can be expensive) or going with different heads altogther. The heads found on 351 (240-260 hp engines) from +/- '77 or so on, came with essentially 302 Ford heads with the smallest available valves, compared to those before and later GT-40 engines/heads. The heads and camshaft are the main ingredients for that original GT-40 increase to 285hp. Good, rebuilt early model 351 heads are available for +/-$500. High performance cast iron heads, such as GT-40 pieces are available thru several sources but expect to pay upwards of $800 for a set. Aluminum heads will be $900-1100 for a new set, but used ones of all types are out there.

In summation, if you're doing a rebuild, for maybe $200 more you can pick up 40-60 hp, and for about $1000 more, you can gain as much 80 or so hp. This could translate in to even more pulling power and 5+ mph depending on the boat model.
       

    
ReidP
1973 Mustang

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SS-201 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SS-201 Quote  Post ReplyReply Direct Link To This Post Posted: December-26-2003 at 9:03am
Crane stopped making reverese rotation cams four years ago. Unless someone has stocked one they are not aviable.
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tryan View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tryan Quote  Post ReplyReply Direct Link To This Post Posted: December-26-2003 at 12:06pm
comp made one for me about 4 years ago for a 351c , but that motor never was assembled.
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kenny g View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kenny g Quote  Post ReplyReply Direct Link To This Post Posted: December-26-2003 at 12:11pm
these older engines were produced to burn regular[leaded]fuel.the machine shop guy at don's crankshaft say's the lead in the fuel would cushion the blow on the valve seats.so he installed hardened valve seats.is this the same as haveing the heads ported?
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tryan View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tryan Quote  Post ReplyReply Direct Link To This Post Posted: December-26-2003 at 12:40pm
kenny, that is true on a cast head. you should install valve seats, but that is not the same as porting the heads.

a holman moody cam would be nice............


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reidp View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote reidp Quote  Post ReplyReply Direct Link To This Post Posted: December-26-2003 at 5:59pm
I work in Charlotte where Holman Moody's located, and tried to get them to grind me a camshaft, as they've still been doing that all along, but they didn't have the reverse rotation billet, plug, or whatever it is you start with, so I settled on another. It was a good 4 years ago that I got the last Crane cam, which I ordered thru PAW, and took about 3 weeks to get. So much for that source. And it was twice the cost+ of the SpeedPro. I've got the cam card spec's if anyone wants them. Both are fairly mild.

   
ReidP
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tryan View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tryan Quote  Post ReplyReply Direct Link To This Post Posted: January-04-2004 at 12:42pm
there are a couple of offenhauser ( offy ) heads available right now.

this one.



and this one.


i have some big valve 'L' jacket heads with a stock manifold on the waukesha. the top one looks like it would add a little juice.
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tryan View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tryan Quote  Post ReplyReply Direct Link To This Post Posted: January-06-2004 at 5:13pm
i have not purchased anything from these guys, but they have an assortment of early(big valve) and gt-40's. used heads and new gt-40's


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