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304 peformance mods?

Discussion in 'Intermediate CJ-5/6/7/8' started by godevil, Nov 29, 2011.

  1. Nov 29, 2011
    godevil

    godevil My Humor isnt appreciated

    Mt Pleasant SC
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    Aug 17, 2005
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    329
    We will be racing a CJ7 in the Everyman's Challenge stock class race at King of The Hammers this year.
    For you Pirate members, we are team Robby Bobby, I will spare my Early CJ friends with that thread, it's a little off color for these parts.
    We have a 304/turbo400/205 setup in the truck now.
    High performance upgrades for the 304 seem few and far between, what have you done? what worked? Didn't work?
    We will be running propane so compression will be our friend but looks like shaving 304 heads will be tricky?
    Dummy,
    Didn't you run a 304 at TTC one year?
    Any help will be appriciated,
    Donnie
     
  2. Nov 29, 2011
    '74Renegade

    '74Renegade Active Member

    Fair Oaks, CA
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    If you don't want to post the thread link here, could you PM it to me? I would like to read about it. Thanks!
     
  3. Nov 29, 2011
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    You have some reason to run a 304 and not a 360? A 304 is just a 360 with smaller bores, smaller pistons and inferior heads (smaller valves). The cheapest way to get more power is to swap in a 360. You can even go 401, but that's less cheap.

    I'd expect there are few 304-specific bits around for three reasons: 1) it's too easy to swap in a 360 or 401, 2) The 304 did not have as long a production life as the 360, so there are fewer of them around, and 3) most of the bits that fit a 360 also fit a 304 - except for the pistons and heads.

    If it has to say "304" on the block, you could sleeve it out to 4.08" bore (from 3.75") and run 360 pistons and heads. The 360/401 heads are said to be very good...
     
    Last edited: Nov 29, 2011
  4. Nov 29, 2011
    godevil

    godevil My Humor isnt appreciated

    Mt Pleasant SC
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    We are stuck with the 304, UNLESS there was a 360-401 CJ that I am not aware of?
    The 304 heads are the pits. We are leaning twards just an intake and some headers but wanted any help we could get.
    D
     
  5. Nov 29, 2011
    Corveeper

    Corveeper Member

    Chanute, Kansas
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    There was a guy over at Jeeps Unlimited that built his 304. Cam, intake, headers, dual 2.5" with glass packs exhaust, ignition, you know the bolt on goodys most will do. IIRC he got a little over 200 horses at the rear wheels on a chassis dyno, which I thought was fairly impressive.
    Thing about getting horses out of an engine, any engine, is you've got to spin some RPM's to do it and that's something I've just never heard of a 304 being any good at.
     
  6. Nov 29, 2011
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
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    The 360 heads are a great upgrade but typically have to clearance the block slightly for the larger valves. If you can get an early set they had smaller combustion chambers, screw in studs and guide plates, and a better rocker ratio. These may be hard to come by though. I'd say cam, lifters, free flowing exhaust, good induction system, etc. The usual things. Maybe boring and stroking as well depending on funds available and rule stipulations
     
  7. Nov 29, 2011
    godevil

    godevil My Humor isnt appreciated

    Mt Pleasant SC
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    Good info on the heads, I will poke around. I didn't think i could use the 360's because of the valve issue.
    D
     
  8. Nov 29, 2011
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    From what I've read, you can fit the 360 heads if you relieve the block, but the shrouding due to the close proximity of the bore defeats any gain you get from the bigger valves. Apparently fitting modified Chevy valves works pretty well.

    Take a look at Greg Taylor's build, a 304 with a 390 crank: http://www.ifsja.org/forums/vb/showthread.php?t=95564
     
  9. Nov 29, 2011
    aallison

    aallison 74 cj6, 76 cj5. Has anyone seen my screwdriver?

    Green Cove...
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    Did the rules state the factory had to put in the motor or could it be swapped in at the dealership as long as it was bought new as a dealer option?

    A few dealers did put in the bigger motors as a dealer installed option, IIRC that is what they called it.

    And if the block needs to say 304, I agree with Tim, bore it. As a matter of fact, if you can get 360 pistions, you might be able to turn it into a 360 stroker motor. Go to IFSJA for that information. http://www.ifsja.org/forums/vb/forumdisplay.php?f=97 and you can fine a good bit of motor information.
     
  10. Nov 29, 2011
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
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    401's were installed by some dealers. Brian Chuchua comes to mind but may have been others
     
  11. Nov 30, 2011
    LarryD

    LarryD Member

    Gallup NM/ 4 Corners
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    I went the 360 route last year. The 360s were pretty easy to find and I found a set of early heads with the smaller combustion chamber. There are a few aftermarket bolt ons available for the 304. You mentioned headers, I believe Edelbrock makes an aluminum dual plane intake and both Summit and Crane offer performance cams. If you have the factory intake you will need an adapter for most aftermarket cabs. There are GM HEI distributors available. The advantage of these are the 1 wire hookup. I have heard you can get quite a bit of performance gain by gasket matching the intakes and heads to each other.
     
    Last edited: Nov 30, 2011
  12. Nov 30, 2011
    Corveeper

    Corveeper Member

    Chanute, Kansas
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    That's debatable.
    In a race engine that's going to live bouncing off the rev limiter you're right that "port matching, or smoothing the transition from intake manifold to cyclinder head, helps smooth the air flow increasing volumetric efficiency, but in a street engine that also needs to operate at idle to mid-range RPM's it can lead to "reversion". Keeping a slight step between the intake and cylinder head helps prevent that.

    http://www.circletrack.com/enginetech/ctrp_1008_intake_reversion/index.html
     
    Last edited: Nov 30, 2011
  13. Dec 2, 2011
    w3srl

    w3srl All-around swell dude Staff Member

    Port Orange, FL
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    Aside from all of the usual bolt- on goodies, one way of getting more oomph out of a given cam is to use rocker arms with a higher ratio. 1.7 ratio rockers in place of 1.5 will give a noticeable. difference, but you have to make sure the springs/retainers will handle it and you also have to be sure the valves will clear the pistons.
     
  14. Dec 2, 2011
    godevil

    godevil My Humor isnt appreciated

    Mt Pleasant SC
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    Unfortunatly it has to be a production motor. Wish we could up the cubic inches but no go.
    D
     
  15. Dec 6, 2011
    brianmurphy

    brianmurphy 866

    Whitmell, Va.
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    I'm a newb to JEEPS and know even less about racing a jeep but I do have +20 yrs experience racing dirt bikes off road (hare scrambles, cross country, enduro,ect.). Any engine performance mods that are gonna cause your engine to run hotter (typical with 304's) is bad news! You have to finish to win! Spend that money on suspension (shocks) and brakes. Good Luck!
     
  16. Dec 6, 2011
    godevil

    godevil My Humor isnt appreciated

    Mt Pleasant SC
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    That is great advice! I can't agree more, you gotta finish to win.
    We have upgraded to adjustable valving 14" resivor shocks but have to keep the leaves.
    Brakes?!? We want to go fast!!!!lol
    D
     
  17. Dec 6, 2011
    Corveeper

    Corveeper Member

    Chanute, Kansas
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    Converting roller legal? Pretty damned expensive for an AMC mill but opens up a whole new world of cam lift and duration.
     
  18. Jan 14, 2012
    Dummy

    Dummy I kick hippies

    Escondido, CA
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    Cappa had a 304 in his J-truck on Rockwells at TTC. It had an Edelbrock Performer cam and intake and a 2-barrel Holley EFI. He may have had some long-tube headers and dual Flowmasters. It's all about the gearing, although the truck was never a slouch and did pretty well in the pulling portion of the contest even with 49s. He probably wouldn't come close to finishing at the top of the tank trap if he didn't flop it on its side. Engine counts for a lot, but it's not everything in those competitions.

    I ran the factory 304/2bbl in my Commando for Jp's Sh!%box Derby and won that.

    My opinion: don't try to rethink the wheel. Just stab in an Edelbrock 2132 or Summit K8600 (better) and a Performer manifold and then focus your attention on more important stuff that'll increase the Jeep's capability and survivability. That event is a marathon - not a sprint.
     
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