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What a 258 can handle (soon to turbo) |
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Wrestler1899 
AMC Fan 
Joined: Nov/06/2017 Location: USA Status: Offline Points: 5 |
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 Topic: What a 258 can handle (soon to turbo)Posted: Nov/06/2017 at 1:41pm |
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Hey everyone I have an 83 CJ7 with the 82 258 engine that has freshly been rebuilt and I'm looking to add more power to it, I've done a lot of research into turbo charging it and i have just about everything lined up and ready but i just don't know how much power and boost the stock engine can handle.(cams, crank, rods, ect.) If anyone out there knows much about how much it can handle please let me know, if you have any questions about the turbo set up or any in general please don't hesitate to ask!!
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jpnjim
AMC Addicted 
Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
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Posted: Nov/06/2017 at 3:20pm |
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I'm far from the expert here,
but I'd say the stock cast pistons would be your first weak link, followed closely by the cast rods/stock rod bolts. The pistons won't like detonation, or running too lean, the rod bolts and rods aren't fans of too much RPM with the nearly 4" stroke. All that said, 4.0L strokers use a 258 crank & most use the 258 rods, so they can handle power fairly well.
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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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jpnjim
AMC Addicted
Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
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Posted: Nov/06/2017 at 3:24pm |
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Random claimed stroker numbers from random thread:
Stroker Numbers: * JP Mags Golen 268 hp and 324 ft·lb * HESCO build * 269 hp and 340 ft·lb * CDP build ** 265 hp and 295 ft·lb |
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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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AMXRWB
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Joined: Apr/25/2013 Location: Midwest Status: Offline Points: 1153 |
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Posted: Nov/06/2017 at 4:21pm |
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If that is a small head bolt plastic valve cover style engine you have it will not handle a lot of boost.You need a early thicker block engine with the larger head bolts.
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Wrestler1899
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Joined: Nov/06/2017 Location: USA Status: Offline Points: 5 |
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Posted: Nov/06/2017 at 4:43pm |
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I knew the rods would be the weak link, but itll only be running around 5-8 psi boost amd i have a ignition timing control box to retard timing, also itll have a electric fuel pump with a fuel bypass regulator to help with fuel and an air/fuel ratio gauge.
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Wrestler1899
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Posted: Nov/06/2017 at 4:45pm |
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How can i tell about the valve cover? Mine is a so called "bulletproof" one
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farna
Supporter of TheAMCForum 
Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19676 |
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Posted: Nov/07/2017 at 6:50am |
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The main limiting factor to boost is going to be the compression ratio. Boost is similar to adding compression -- you can only run so much with pump gas, and will need premium fuel -- or better. Some are converting entirely to E-85 so they can run more boost (ethanol burns cooler and is more knock resistant).
82-86 258s in Jeeps run a 9.2:1 compression ratio stock. That means you're only going to be able to run 2-4 psi boost before you're at the premium gasoline limit of 10-11:1 final compression (stock compression + effect of boost). See http://www.xcceleration.com/cr-boost%20101.htm I don't think you will have any mechanical issues at all, just make sure all the parts are good and the engine is built to AMC specs. I wouldn't try running more than 3 psi unless the engine is rebuilt with forged or hypereutectic pistons and carb is modified to run E-85. Then you can run maybe 5-6 psi... Edited by farna - Nov/07/2017 at 6:53am |
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Frank Swygert
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Wrestler1899
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Joined: Nov/06/2017 Location: USA Status: Offline Points: 5 |
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Posted: Nov/09/2017 at 1:51pm |
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i read that there was a different compression between the 82 and the 83, 8:5:1 and 9:2:1, that's one thing i need to figure out, i will be getting a electric fuel pump with a bypass regulator, converting my carb to a blow through to handle boost, a knock box/ignition timing box with timing retard, and a t3 turbo running between 5-8psi depending on where i set it. it is a freshly rebuilt engine and carb around 3000 miles.
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DaemonForce
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Joined: Jul/05/2012 Location: Olympia, WA Status: Offline Points: 1070 |
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Posted: Nov/09/2017 at 4:37pm |
That's upsetting. When my 258 was factory it was already running 151psi on every cylinder. That doesn't look like 9.x:1 compression to me. I'm guessing boosting a 10.5:1 stroker is out of the question too. |
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1971 Javelin SST
American 304 2v | FMX | AM20-3.31 1983 American Limited Jeep 4(.7)L S-MPFI | 1982 NWC T-5M (4.03/.76) | Dana30IFS/35-2.72 |
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amc67rogue
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Joined: Nov/05/2008 Location: Phx. AZ. Status: Offline Points: 1578 |
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Posted: Nov/10/2017 at 9:24am |
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In the mid 70s Randall Rambler in mesa AZ. was putting turbos on 258 cu. in. Gremlins and Hornets. Buicks V6 turbos also have cast rods.
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Keith Coggins 67Rogue X code
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farna wrote: