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Small block RPM
I purchased a 29 non step fountain with twin 396 small blocks in it. Currently has 23 mirage plus on it. Previous owner claimed 48mph at 3200rpm. Gps 81mph. Rev limiters set at 6200. I only ran the boat on muffs and then winterized.
Reading other posts it seems everyone is spinning the stroker motors to 6k. This seems way too high to me. My main goal is midrange cruising. Would jumping to a 25 mirage plus be too much strain at 3200? My goal would be a 50mph cruise with best efficiency. I have the dyno sheets on the motors. Stevehttps://cimg1.ibsrv.net/gimg/www.off...3e7b1b145a.jpg |
If you have the dyno sheets, where is peak torque, would it make sense to drive it the way it is before making changes on assumptions.
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What is your max rpm at top speed. I run the dog sh.t out of a well built stroked 421 sbc and pulls over 7,400 but shift at 7,000 for years with a solid roller. No issues what so ever. As mentioned above I would try and get dyno sheets to prop appropriately but that rpm wouldn't scare me a bit with good internals/valvetrain, drives etc. worse thing you can do in my opinion is over prop and load the engines at WOT. Opinions vary in this however I've always like to prop for a couple hundred rpm under peak hp. Propping near peak torque not good. Free the engine up and roll. Usually 900 to 1,500 above peak torque. Varies on build. |
Btw nice looking set up. |
Here is the sheet from one of the engines. Lookinig at this, how would I determine where the best cruise rpm is at?
Thanks getrdunn, it was spotless till I winterized it. have to clean it up in the spring when I can get the hose in the engine compartment.https://cimg2.ibsrv.net/gimg/www.off...98dd768906.jpg |
Based on what getrdunn is saying I should be propping for closer to 5000.
The engines have Callies rotating assemblies, Inconel valves, stainless rockers, and dart pro 1 aluminum heads. |
That M+ 25 is a big wheel from the 23. I’d maybe try having the current props tweaked for a little more pitch. |
As of now it is screaming for AirGap RPM intakes. I'd love to see the build sheet,thanks.
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Based on the dyno sheet, you should prop it for around 5400rpms WOT with a rev limiter around 5600rpms.
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