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SBC Primer

Discussion in 'Gearheads' started by Dave70968, Apr 3, 2018.

  1. swampratt

    swampratt Sharpshooter

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    To confuse things even more is when picking a cam or intake the manufacturer posts an RPM range on them.

    Like this 1500-5500 RPM basic operating range.
    https://www.summitracing.com/parts/cca-cl12-210-2

    With all my cam swapping and testing I found that upper RPM is where the cam will make Max HP in the comp cams line of cams.
    I run that above 268H and 5700 RPM is where I make max HP with decent flowing heads. In a 350"
    Stock smogger heads you can be down 1000 RPM where the peaks come in.

    Now you normally shift 500-700RPM past Peak HP that puts the above 268H at a shift point of 6200rpm.
    But junk heads that do not move air well you may be shifting at 5200 or 5500 rpm. leaving power on the table.

    "Plugged up" exhaust system will hinder power also. or a carburetor that does not meter fuel well.
    There are ways to check those things.. Vacuum gauge is a great tuning tool to find things out.

    So many variables.
     
  2. Old Phart

    Old Phart Sharpshooter

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    I'm really enjoying this thread.

    @swampratt what are your thoughts on the small block 400 or the 383 stroker vs. the 350 for common street applications at 6000 rpm or so?
     
  3. swampratt

    swampratt Sharpshooter

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    I have built the 383 stroker and if you stick a bit more compression and a step larger cam into a 350 it will almost match it in a drag race.
    Say 76cc head on the 383 and 64cc on the 350 run a 214-224 on a 112 LSA on the 383 and the 224-224 On a 110 lsa for the 350 SBC and it will be almost dead even race. I know because I built just that for FIL and we raced often.

    Choke the 350 with exhaust manifolds and upper power does not seem to get hurt too much. do the same manifolds on the 383 and it totally kills the upper RPM capability.
    Those manifolds are just not built for flowing air.

    But 6000 rpm was not the limit.. the 350 shifted at 6900 and the 383 shifted at 6700.
    If you want max 6000 rpm then go big and try to make it hook up.

    My current 350 in the 57 chevy has had 76cc-72cc 64cc- 58cc and 54 cc heads on it it has had the 268H on a 110LSA the 270h 280H a herbert 235-245@ .050 solid flat tappet and a 268H on a 106LSA and 268H on a 112 LSA with same intake closing as the 106LSA cam.

    Stock Q jet iron intake, marine Q jet iron intake. Ported Iron Q jet intake. RPM intake, Strip dominator intake.
    And a dual 4 tunnel-ram intake.. all kinds of carbs and distributors.

    Test test test.
    Each time I stepped up in cam size with the "H" cams it went 1/2 second quicker. But it was optimized for the cam.

    268H 6500rpm shift. 270H 6900. 280H 7200rpm shift point was optimum.

    Some numbers for you to chew on.
    Best ET with 268H was 13.5. 270H was 12.9. 280H was 12.51.

    Solid flat tappet was set on kill and would run mid 11's in the 350" 3000 stall 370 gear with a spool. 295-65-15 hoosier dirt track tires. just about 30.5" tall.
    TH350 trans shift at 7500-7800rpm.

    I see a lot of 383 engines and many just are not spot on or the cars not dialed in.
    If you can't tune or something else is off in the build you could be down a full second or more from it's potential.


    What do you consider street application?
    Small 50,000 mile rated radial tires 3500lb vehicle?
    If yes the 383+ size will spend more time spinning than hooking up and winning. unless it has no snot.

    I pulled a 385" from my truck 3176 lb 280H comp cam tunnel-ram and lakester headers .
    anything below 45 mph and it would not hook to the street.
    My 350 was easier to make hook up.
    I run 235-75-15 good year wranglers on the street. They actually hook better on the street than MT drag radials 275-60-15.
     
    Old Phart likes this.
  4. swampratt

    swampratt Sharpshooter

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    Dave I have a book you can use until you are done with it.
    It is a Small block chevy interchange manual.
    It has a lot of good information in it.
    But like all books there are misprints ..one in there is for 307 rod length he put 3.7 instead of 5.7.
    He is biased in his opinion on some things and one is he does not like 305 heads. and he stated 60.5cc chambers as the smallest 305 head. I have measured my 601 castings at 53.5 cc chamber as it came from GM with no surfacing and no valve job.

    But all in all it will give you a lot of needed information.
    I also Have a bunch of old hot rods with builds and testing of parts I will let you use ..this should educate you into a place where you are comfortable in making a decision as to what kind of power plant you want to put together.
     
  5. swampratt

    swampratt Sharpshooter

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    Some reading for you on camshaft LSA (Lobe Separation Angle)
    Just trying to fill your heads with knowledge.

    Myself I like a tight LSA like 106 more than a wide 112 LSA for making power in these old school engines.
    The weaker the cylinder heads are at moving air the more benefit you will see from the tighter LSA camshafts.
    But MPG can suffer with the 106 LSA vs the 112

    The read.
    http://www.hotrod.com/articles/camshaft-shootout-lobe-separation-angle-tested-explained/
     
  6. Dave70968

    Dave70968 Sharpshooter

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    I just wanted to say thanks to Jeff for a fun afternoon talking about engines. I learned a lot and got a lot to think about. Jeff really knows his stuff and is a great guy to boot!
     
  7. swampratt

    swampratt Sharpshooter

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    Thanks Dave. I enjoyed it . sorry about talking your ear off :)
    I think I have a cracked head laying around you can use to practice porting on.
     

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