will 360 j heads fit on my 273

Small Block Mopar Engine

  1. bill paynter

    bill paynter 67 Cuda

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    I have an opportunity to buy a pair of complete ready to run J heads already ported and polished for 100.00

    my question is: will they fit my 273, heads still have small 1.88 valves
    I'm worried that they may be too large and valve will hit the side of the bore or top of the piston, any thoughts???
     
  2. C130 Chief

    C130 Chief Mechanical Genius

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    Yes, they'll bolt right on. Your compression will take a serious dive due to the larger chambers. With a 273 you'd need a pretty hairy cam to see any gains from the larger ports.

    If you need heads and these are cheaper than rebuilding your current heads it may be a good deal. But if you were to slap them on an otherwise stock 273 and expect to go lot's faster, you may be disappointed.
     
  3. victory273

    victory273 Active Member

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    I just set a head on a 273 block, looked thru bore 1.60 ex is closer than intake. On standard bore block may have .o2o" clearance. You'll aso lose about a point in compresion or more cuz chambers are bigger.
     
  4. bill paynter

    bill paynter 67 Cuda

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    Not too famiair with J heads does this sound correct??? was told these were a closed chamber head 63-65 CC does it sound correct ???
    My worry is that it will hit the side of the cylinder wall or should I be worried about the top of the piston ????

    motor was boared .060 over
    .509 / 292 purple shaft cam any benifit
     
  5. C130 Chief

    C130 Chief Mechanical Genius

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    1.88/1.60 valves wont hit the cylinder on a 273, but 2.02's will. Valve-to-piston clearance is a function of lift, so if the valves didn't hit before you should be OK.

    If they are "J" heads they are most certainly not closed chamber.

    What is the casting number?

    With that cam you'll have no low end torque no matter what, so you may as well focus on upper RPM breathing. For this the bigger ports will help (so long as the rest of you intake and exhaust are adequate).

    What pistons are you running? What is your compression?
     
  6. bill paynter

    bill paynter 67 Cuda

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    Thanks for your comments guys I was getting a few mixed opinions weather or not these heads would work, they are 188/160 heads
    not sure what the casting numer is ,all I know is my friends dart runs 12.20's all day long with these heads, he decided to to an edelbrock head his car should go low 12's
    all stock compression the only reason I know it's .060 over is because I pulled the heads of to have them rebuilt

    What intake would work best performer ????
     
  7. fishy68

    fishy68 Tyr Fryr's Inc. FABO Gold Member

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    Another thing to note is that unless the J heads have been milled quite a bit and have aftermarket valves the chambers are close to 70 cc's.

    A 302 head from a 88-91 318 roller engine might be a good improvement for the 273. I believe they are closed chambers and in the low 60's for cc's. Too bad your not close. A buddy of mine has a set of 302's for sale for a good price.

    As far as the intake goes. It depends on what your doing with it. The performer is an ok choice but I believe the rpm is better. Definitely stick with a dual plane on a motor that small. Only problem is if you still have 273 heads the intake bolt pattern is different. The 273 head was an oddball because it was the only small block with a different intake bolt angle so a standard aftermarket intake that works on a 318-360 won't bolt up.
     
  8. damnimcooltom

    damnimcooltom Too Cool For School

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    For $100, if they are ready to bolt on, and have been ported by someone that knows what they're doing, you can pick them up and sell them for a profit. Now, if they were done by some hack that doesn't know what they're doing, they probably aren't worth dealing with. Since you've been told incorrect information about the chambers, I'd be leary.
     
  9. challenger57

    challenger57 cuda57

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    If you have not already bought the 360 heads DON'T. I have a 65 cuda that had a 273 with 360 j heads. No bottom end, even had them milled .080, still a dog. Removed the big .550 lift cam and replaced it with a stock 340 lift with 214 duration and still no power. Eventually replace motor with a crate spec 360. You would do better to rebuild the 273 heads and have them milled .020 to boost the compression. Good luck!
     
  10. rumblefish360

    rumblefish360 So close, yet so far away FABO Gold Member

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    Now theres some excellent advice AND it's a "Been there done that!" set of words.

    You should play around with the stock heads for the cheapest way and for some money well spent, as said above, the 318's late year casting , the 302 head is a good bet for power.
     
  11. 68 Sedan

    68 Sedan Well-Known Member

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    I've never understood why people think porting and polishing on a street head is a good idea. Going to a larger port will cause the velocities to drop quite a bit. Polishing will help with flow, but only in a motor capable of some deep breathing. Also, it can mess with the way the A/F mixture moves and atomizes through the port.

    I could tell a story about the 346s I had on my Bee, but you would all think me nutz
     
  12. BobsDart

    BobsDart Well-Known Member

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    Bill,
    Buy the 360 heads as a investment, not for the 273...Few things the 64-65 heads had the different bolt angles. The 292 cam is way too big. I had the 280/474 in my 273, sounded cool, but even less bottom end than before! I'd recommend cleaning up your stock heads, gasket match the ports intake/exhaust. Performer intake with a spacer or just the RPM. As far as the cam, I'd stay below 280 duration. I think comp makes a 268-270 solid that would work great with the high revving 273. That will easily spin 6500+.
    I upgraded my Dart to a 360, mild rebuild, for what it would cost to do the 273.
    Just my 2cts...
    Bob
     
  13. grimreaper

    grimreaper Cross Member

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    I've got a 273 with J heads that have had 2.02 intakes installed. The pistons are 10.5 compression. Cylinders are fly cut for clearance. With these heads the compression is pretty low and decent power doesn't happen until 4000 RPM. NO low end. Fortunately the 273 holds up to high rpm but the thing is a real pain for street driving. I'd recommend a good overhaul on stock heads for a 273 or put some 1.86 intakes in the original heads to retain decent compression.
     
  14. 66dartgt

    66dartgt Well-Known Member

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    If I were doing my 318 over, I'd opt for redoing my 273 heads with 1.88/1.60 valves instead of the 302's I used - the early 273 heads are closed chamber (at least my '66 273 heads are) and you don't have the problem with the 302's pushrod bulge impinging on the intake port. That bulge is a huge lump in the port that needs to be massaged pretty extensively. Put some hard seats in the exhausts and be happy.

    GO ahead and buy the 360 heads for another engine project and shelve them. Its highly likely you''ll end up with a bigger motor in the car at some point anyway.

    Your cam is way out of whack, use something about 3-4 steps smaller, as someone else mentioned - under 280 degrees would be a good bet. My thought would be a stock 340 grind.
     
  15. krazykuda

    krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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    68 Sedan has a good point. The bigger ports will have less velocity. As Rick Mudge once told me "velocity is torque". Rick ported heads and flow tested them for a living. Higher velocity also means more manifold vacuum. The port diameter needs to be increased with engine volume to get the same velocity, which means bigger engines need slightly larger ports than the smaller ones to have the same velocity.

    The J heads have 70 cc chambers. If your 273 is a 67 from your Barracuda the stock heads are 57 cc's. If you bolt them on to a stock 10.5 4-bbl engine your compression will drop to 8.79, and for a stock 9.0 2-bbl engine it will drop to 7.57. You would need a 11.0 compression piston to give you close to 9.0 final compression with J heads to run on pump gas.

    If you are going to use the 292 duration cam, you should put around 12.5:1 pistons in and use a single plane manifold with the J heads. It would not be a "daily driver".

    If you want something "streetable", I agree to stay under 280 duration, use the 273 head with some mild clean up porting - 1.88 intakes and 1.6 exhaust with hardened seats, and dual plane (performer is ok, I used a Wiand Stealth on a 360 in a 78 Warlock 4x4 stepside and was happy with it - It has a power band from idle - 5500 RPM). The Stealth has nice low end and still keeps high RPM power. The best dual plane for the 318 273 heads is the Edelbrock LD4B. It is the LD340 manifold made for the smaller ports. We just put one on my son's 318 Valiant with a stock cam and a new Edelbrock 625 carb and it has great low end pull on a stock 318 with a 4 bbl and dual exhaust - no bog off the line and good throttle response.
     
  16. djwhog

    djwhog Well-Known Member

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    Yes some good points.. Stick with the 273 heads, put in bigger valves. Compression and burn flow in cylinder will be better, you can even go smaller guides and find a taller and smaller stemed valve like a Chevy uses, then get your installed height set were you needit, go short duration on the 273 to save the bottom end torque, and you can go up to low 500s on lift. This is similar to how the D Dart was built. That should get you close to 250-270 HP with 10.5 pistons and good ignition and exhaust.
     
  17. rumblefish360

    rumblefish360 So close, yet so far away FABO Gold Member

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    KrazyKuda;
    Mistakes made. I think your fingers got confused.
    The LD4B hs the smaller ports, the LD340 has the larger ports.
    The Weiand Stealth has a RPM range of 1500 - 6500
    Weiands Action plus is idle to 5500 i think.
     
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