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stock compression ratio and rod ratio

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by solowookie, Sep 8, 2001.

  1. solowookie

    solowookie 1/2 ton status

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    ok guys... a couple questions...

    what compresion ratio can I run to be on the verge of not being able to run regular unleaded, but it wouldn't be mandatory unless I was towing???

    what rod ratio's give the best torque, and what kinda torque increase could I expect on a stock 350 with a higher compression ratio??? (and also optional increase in rod lenght...)

    <font color=blue> Jeff - may the force be with you</font color=blue>
    <a target="_blank" href=http://coloradok5.com/gallery/Jeffs-Stuff>link to k5's</a>
     
  2. DesertDueler

    DesertDueler 1/2 ton status

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    8.5-9.0 to 1 would be max on 87 octane. For torque the longer the rod, the more bottom end torque. Thats why pontiacs have alot of bottom end. They use 6.625 rods in all their motors(326,350,400,455). My pontiac 350 has close to 700 ft lbs of torque at 2500 rpms.

    86 Jimmy 4"lift 35"MTRs Other cars 69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  3. solowookie

    solowookie 1/2 ton status

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    ok, so other then rockers what would I have to change to be able to run the longer rods???

    <font color=blue> Jeff - may the force be with you</font color=blue>
    <a target="_blank" href=http://coloradok5.com/gallery/Jeffs-Stuff>link to k5's</a>
     
  4. DesertDueler

    DesertDueler 1/2 ton status

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    Are you talking about push rods, or piston rods, because I was talking about piston rods. For rockers you would want to use 1.6 rockers. You need to put pushrod guideplates in and have screw in rocker studs to use them if you dont already.

    86 Jimmy 4"lift 35"MTRs Other cars 69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  5. DesertDueler

    DesertDueler 1/2 ton status

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    Also need hardened pushrods. Stock length will work fine.

    86 Jimmy 4"lift 35"MTRs Other cars 69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  6. solowookie

    solowookie 1/2 ton status

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    ok, what kinda cost is involved in a kinda change like that, and would this require a new computer chip???

    <font color=blue> Jeff - may the force be with you</font color=blue>
    <a target="_blank" href=http://coloradok5.com/gallery/Jeffs-Stuff>link to k5's</a>
     
  7. DesertDueler

    DesertDueler 1/2 ton status

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    No new computer chip. The rocker arms are about 215, guide plates are about 60, studs are about 60, and hardened pushrods are about 60. Then you have to send the heads out to get machined and tapped for the studs. Thats about 75.

    86 Jimmy 4"lift 35"MTRs Other cars 69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  8. solowookie

    solowookie 1/2 ton status

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    what kinda performance gains am I going to get out of this??? (and evidently I don't have to change pistons???)

    <font color=blue> Jeff - may the force be with you</font color=blue>
    <a target="_blank" href=http://coloradok5.com/gallery/Jeffs-Stuff>link to k5's</a>
     
  9. DesertDueler

    DesertDueler 1/2 ton status

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    You get between 15 to 25 hp, and saves wear on your valve tips and valve springs. You do not have to change pistons with 1.6 rockers. If you go bigger (like 1.7 or 1.75) you have to have the tops of the pistons fly cut so they dont hit the valves.

    86 Jimmy 4"lift 35"MTRs Other cars 69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  10. solowookie

    solowookie 1/2 ton status

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    what about the torque???

    <font color=blue> Jeff - may the force be with you</font color=blue>
    <a target="_blank" href=http://coloradok5.com/gallery/Jeffs-Stuff>link to k5's</a>
     
  11. Neil

    Neil 1/2 ton status

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    It is like getting a cam with a little more lift and duration. With 1.6 rockers you might pick up 9-15 hp max as tested on dynos. You usually can hear some difference in idle too, but since you haven't cranked your motor yet...

    Neil H.. Alabama.. '78 K5 400ci 4x4 AT,AC,PW Cheyenne. '74 C10 3spd/floor 250ci 4x2
     
  12. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I don't mean to sound like an ass, but for a mild 350 running 1.6 rockers and all is really an un-necessary expense.
    Jeff could stick with the stock stamped 1.5 ratio rockers and still have a nice torquey 350. 9.0 to 1 is about the limit compression wise for pump gas (85-87 octane) unless aluminum heads are used.
    As for push rods, find a good flat surface and roll the pushrods on that. they should roll without any wobble. No wobble = a good re-usable push rod. Just clean em up really good.

    Rene

    <font color=green>Dyslexics of the world...UNTIE!</font color=green>
     
  13. DesertDueler

    DesertDueler 1/2 ton status

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    I belive the same. Not sure though. They rockers free up power though out the rpm band because they get rid of friction. Thats why roller cams make more power than flat tappet cams.

    86 Jimmy 4"lift 35"MTRs Other cars 69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  14. Neil

    Neil 1/2 ton status

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    I think he is also keeping in mind that Solowookie is on a budget. The 1.5s are to me not worth the gain for the $$ unless you have a built motor you are trying to get more out of. Solo(Jeff) is building this on a budget and has selected a cam already. I think the cost of studs,machine shop work, 1.6s, guideplates and p-rods will only frustrate
    his project even more than it already has for him.just my $.02.

    Neil H.. Alabama.. '78 K5 400ci 4x4 AT,AC,PW Cheyenne. '74 C10 3spd/floor 250ci 4x2
     
  15. solowookie

    solowookie 1/2 ton status

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    hey, Rene!!! good to hear from ya!!!

    actually I'm gonna rebuild Insane Ewok as soon as I finish up Jedi Mind Trick, but I don't really have the $$$ to go 383 short block... I'd like to do what I can for torque and really minimize my expenses doing it... was wondering if there are a few things I can do to the bottum end without spending much money...

    <font color=blue> Jeff - may the force be with you</font color=blue>
    <a target="_blank" href=http://coloradok5.com/gallery/Jeffs-Stuff>link to k5's</a>
     
  16. solowookie

    solowookie 1/2 ton status

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    you are right on neil, but wrong project... LOL (I know, this 2 k5's thing can be really confusing...) [​IMG]

    <font color=blue> Jeff - may the force be with you</font color=blue>
    <a target="_blank" href=http://coloradok5.com/gallery/Jeffs-Stuff>link to k5's</a>
     
  17. Neil

    Neil 1/2 ton status

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    I'll be over here under this rock if ya need me....

    Neil H.. Alabama.. '78 K5 400ci 4x4 AT,AC,PW Cheyenne. '74 C10 3spd/floor 250ci 4x2
     
  18. solowookie

    solowookie 1/2 ton status

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    oh, I need ya Neil... [​IMG] don't worry about the rock thing, you're quite aware I knee deep in @#$&amp; right now with Jedi Mind Trick...

    man I can tell ya what, there is no way in the world I be considering doing all that crap to the project I'm on...

    Insane Ewok has bad heads, and the bottum end compression is in real sorry shape. I gotta rebuild it as soon as I get Jedi Mind Trick out... I wanna do what I can to increase power, but I wanna really minimize my cost (Jedi Mind Trick project gone bad etc...)

    you seem to really know these engines real well...

    <font color=blue> Jeff - may the force be with you</font color=blue>
    <a target="_blank" href=http://coloradok5.com/gallery/Jeffs-Stuff>link to k5's</a>
     
  19. nyyef

    nyyef 1/2 ton status

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    you could try to install the roller tip rockers, they will add a little and they are not too expensive.
    a comment on the longer rods, you may have to change/modify the pistons if you used longer than stock rods and 1.6 rokers.

    "If it is breakable, IT will break. If it is indestructable, I will find a way to make it breakable, and I will break it."--Knife
     
  20. Twiz

    Twiz 1/2 ton status

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    I'm kinda confused with which ones which too. Up till now I thought;
    Jedi-mind tricks, the one with the wild paint and bad auto trans.
    Insane Ewok is the wheeler with the bad engine and is the current project. (with 8-lug 44 and FF14)

    Anyway, with our elivation, we can run a bit more timeing then our sea-level brathaz', due to lower dynamic compression (true compresion). So, playing off that, We could trade in a some timeing for a bit more compresion. Also, If you are running Vortec heads, with their high swirl intake and violent chambers, they should be less sensitive to detination, so even higher compresion can be used without getting detitantin.
    -But, I'd stick with 9.5:1 as a max, too give you room to play with.-

    Rod-ratio is dividing the (piston) rod length to the stroke length, giveing you a ratio of 1.63. (1.70 to 1.85 being ideal for ALL rpms IMOP)

    Higher rate rocker arms increase lift and valve-overlap, but NOT duration. With a higher rate rockers (1.5 vs 1.6) the vlave gets off the seat faster and reaches a higher amount of lift in the same amount of time. Unless you're running a radical cam with some mean ramps and high cam lobes, you -should- not run into a valve clearence problem. Also, from what i remember, the cam you selected is fairly mild. Keep in mind, the cam manufacture is ASSUMEING your going to use 1.5 rockers and recomend a cam with those specs in mind. (still that cam was mild and you should be able to play with it a bit with our low atmispheric (S/P?) pressure.)
    So....


    <font color=purple>Hi, I'm </font color=purple><font color=blue>Twiztid.</font color=blue><font color=purple> How do you like me so-far?</font color=purple>
     

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