305 H.o.???

Discussion in 'Engine Topic' started by racinman112, Mar 16, 2011.

  1. racinman112

    racinman112 New Member

    Nov 16, 2009
    powhatan point Ohio
    I have to run the 305 in my class due to c.i. restrictions,and I have a couple 305 H.O.s, can anyone tell me what makes them a High Output:confused: ? Is it the heads or a combo of things? Any help will be greatly appreciated. Thank You,:bowtie:
  2. nicks78camaro

    nicks78camaro Veteran Member

    Apr 3, 2010
    Probably the heads, cam, intake, carb/injection system, etc...not much else you could change?
  3. daustin

    daustin Veteran Member

    Jul 29, 2009
    Woodstock, GA
    I've had 2 of the 305 HO engines. From what i remember the heads were better, pistons were higher compression (double eyebrows i think) than the other 305's and they had factory aluminum Q-jet intakes - not a high rise though. I think the cam was slightly bigger, maybe .414 lift instead of the others .390.
  4. Air_Adam

    Air_Adam Veteran Member

    The 5.0 HO that came in the 3rdgens had 9.5:1 compression (as opposed to 8.5), bigger cam, higher flowing cat converter from the Corvette, bigger exhaust manifolds and pipes, electric rad fan (as opposed to mechanical), and more aggressive tuning of the CC Qjet and a more aggressive spark advance curve, and a very well breathing dual sporkel air cleaner.
  5. Todd80Z28

    Todd80Z28 Moderator Staff Member Lifetime Gold Member

    Jun 11, 2002
    Northern VA
    The L69 was the 5.0 Liter H.O, whereas the LG4 was the "regular" 305. Google L69 versus LG4, and you'll get a full answer.
  6. Damon

    Damon Veteran Member

    Nov 16, 2000
    Philly area
    The "HO" 305 (L69, computer controlled carbureted induction system) was, quite frankly, nothing super special. It differed from the lo-po LG4 305s only because it had higher compression, better cam and freeer flowing exhaust system (plus a higher flowing dual-snorkel air cleaner in 3rd gen F-body applications).

    It used the same block, crank, heads, intake, distributor and a zillion other common parts as the lower output LG4.

    Heads were cast iron -416 casting heads, same as the lo-po LG4 (58cc chambers, 1.84/1.50 valves).

    Pistons were 4 valve relief flattops that yielded 9.5:1 compression in the HO L69. Low output LG4 motors used dished pistons and had 8.5:1 compression ratios (except in 85-86 when the LG4 got the same flattops as the L69 and had the same higher compression ratio).

    Camshaft was the big difference. The LG4 and all over low output 305s of that vintage used a super-wimpy cam commonly referred to as the "peanut cam". The cam used in the HO L69 was much more aggressive and the basic specs on that cam were carried forward into the high output TPI engines of the 80s and even the LT1 engines of the 90s with few changes other than the fact that they were converted to roller-style cams. (All L69 HO cams were flat tappet.)

    L69 HO engines had better exhaust systems from the factory than their lower-output bretheren. This is expecially true of the Camaro versions that had bigger 2-1/4" outlet exhaust manifolds and 2-3/4" (sometimes referred to as 3") y-pipes, catalytic converters and cat-back systems right from the factory. Low output 305s had 2" outlet manifolds and the entire exhaust from the y-pipe back was only 2-1/4".

    So, if you have -416 heads on top of a 305 making it into a "high output" 305 isn't really all that difficult (flattop pistons, better cam, better exhaust). For racing purposes it really doesn't matter whether you start with an L69 or an LG4 since you will probably have wide latitude to change pistons, cam, intake and exhaust anyway (which already includes everything that makes a "high output" 305 better from the factory).
    Last edited: Mar 16, 2011
  7. rustbucket79

    rustbucket79 Veteran Member

    I always considered the 416 heads as the 4 bbl heads, and the 601 heads with their closed chambers as the HO heads. They are several cc's smaller than the 416's and the 2 bbl version 450 castings with their 1.72 valves.
  8. racinman112

    racinman112 New Member

    Nov 16, 2009
    powhatan point Ohio
    Thanks for the info guys

    Both of my motors have the 416 heads and the block casting numbers are 14010203. Thank Yáll again for the info. I have a 231@ .050 .480 cam. Is this gonna beat the snot out of my valvetrain? If so what upgrades do I need to do? I was told screw in studs and heavy springs and I'll be fine.
    Last edited: Mar 17, 2011
  9. z28rod

    z28rod Veteran Member

    Apr 30, 2009
    hopewell junction,ny
    305 ho = higher lift cam, 9-1 compression
  10. Damon

    Damon Veteran Member

    Nov 16, 2000
    Philly area
    The stock heads won't take that much lift without the retainers hitting the guide seals so a little machine work to cut down the guides would be needed in addition to the springs and (possibly) changing to screw-in studs.

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