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de-stroking the 258

Swaping 258 to 4.0, 4.0 parts to 258 etc!
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akadeutsch
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de-stroking the 258

Post by akadeutsch » March 30th, 2018, 7:32 am

I am considering a CJ7 build. Id like to use the original 258 but I’ve got to add a twist. I am wondering, if stroking an engine adds torque as we see it do, then does de-stroking an engine mean potential horsepower gains? By way of spinning what will be a smaller mass around a tighter orbit and reducing its rotating mass as much as possible (lighter weight hyper pistons and as few counter weights as possible)?
I'd like to see if I could build a horse power engine by de-stroking the 258 with a 242 crank. Did they ever produce a light weight low number of counter weights 242 crank? Ide use the 258 rods. I could punch it .060 over. Balance the rotating assembly to the .0000, advance the juice out of it and see how fast she might spin.

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SkylinesSuck
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Re: de-stroking the 258

Post by SkylinesSuck » March 30th, 2018, 11:19 am

I think you need to consider what the limit to horsepower is currently. I believe it's head flow (or lack of) and maybe engine harmonics. I think you would waste time and make less power. Maybe somebody will disagree.

akadeutsch
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Re: de-stroking the 258

Post by akadeutsch » March 30th, 2018, 9:35 pm

Valid point. I was reading an article about a Chevy straight 6 and thought....we could do that.
http://www.enginelabs.com/news/dyno-vid ... orsepower/
The article brings up similar concerns to yours with the Chevy engine. But they pulled 320 hp so I might still build it. I've had the doors open to my own shop now for a little bit and ive already collected nearly enough parts to put this together. By the time that I can afford the cj7 I'll have all the parts. I think all I'm missing now is a head at this point. It'll take doing the math to see if it's worth it. Or if it'll even compress. My estimate is that it will end up around a 3.8. Custom piston pin height? And who knows how fast it'll spin? I've heard that there is a harmonic imballance around 5grand. I wonder how it'll spin at 6+. I don't think I've ever spun my 4.6 over 5k.
I see this as a fun challenge with only Mall Crawling intentions. I'm.just curious to see what a straight 6 sounds like spinning that fast. Heehaw

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Re: de-stroking the 258

Post by IH 392 » March 31st, 2018, 11:28 am

The Chivy has a bigger bore letting it use bigger valve and less shrouding, getting the air in, the AMC engines have smaller bores and valves.
You can get more power out of ANY engine!!!
ASE Master certified engine machinist, gas and diesel

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