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tuning info needed,sbc 350 w/ 305 heads

Discussion in 'The Hokey Ass Message Board' started by MarkKoch, Feb 20, 2011.

  1. MarkKoch
    Joined: Jan 16, 2010
    Posts: 294

    MarkKoch
    Member
    from Maryland

    A month or two ago I posted that I have picked up a 350 w/ 305 heads and got some good responses on why this was done.Well the weather has gotn a bit better and I'm ready to tune this thing.So heres the info I need.Which plugs do I use?What should the gap be?What should the timing be set at? Its a early to m id 70`s 350 (3970010)with 305 heads(14022601 kb3).Stock intake,stock cam....I believe,600 cfm carb,stock exhaust manifolds 2.5 exhaust w/ flow masters.Thanks
     
  2. ANDEREGG TRIBUTE
    Joined: Jan 1, 2008
    Posts: 1,370

    ANDEREGG TRIBUTE
    Member
    from Bordertown

    whats it going in, what tranny and rear ratio and tires? I have run that basic same set up for years in my street cars and racecars. That set up really likes headers, the lower rpm range Lunati Voodoo hydraulic cams (they have extra exhaust duration for the small exhaust valves and ports). The way I tune mine is, remove 1 centrifugal weight spring, no vac advance, about 32-36 degrees total advance, a really good battery and starter, Auotlite 45 or 276 Accel plugs with HEI ignition. Oh, if ya got flat top pistons run mid grade or premium gas, to keep it from pinging, with dish pistons octane is probably not a concern Oops, gap the plugs at .045 for HEI.... Tune the carb for best vac and idle at probably 750 rpms with an auto trans.
     
    Last edited: Feb 21, 2011
  3. MarkKoch
    Joined: Jan 16, 2010
    Posts: 294

    MarkKoch
    Member
    from Maryland

    Thanks for the info!:)it came in a chevy nova I picked up,turbo 350 trans,stock gears....I think.245 60 tires.Sorry for my lack of knowledge but what and where is the weight spring?I understand the battery and starter part...doesn't like to start when hot.Run no vacuum advance at all?or just when adjusting the timing?
     
  4. MarkKoch
    Joined: Jan 16, 2010
    Posts: 294

    MarkKoch
    Member
    from Maryland


  5. 56sedandelivery
    Joined: Nov 21, 2006
    Posts: 6,566

    56sedandelivery
    ALLIANCE MEMBER

    The 601 heads are said to have 53cc combustion chambers; that's pretty small when your 350 probably came with 76cc chambered heads; there were some 70-72 cc chamber 350 heads around 70-71. IF your 350 has DISHED pistons, you may be alright, and have around 9.5-10:1 CR, BUT if the pistons are a true FLAT TOP, with 4 valve reliefs, 10.5-11:1 is going to be the concern, and will require 92-93 octane fuel. The 601's also usually have the small 1.72 intake valves, which are going to limit flow; some have 1.84 intakes; BUT, the ports are also small, so valve size really does'nt make a lot of difference. DETONATION is your major concern, so plan on retarding the timing. It will be a good torque motor, but probably won't rev much past 5K RPM. I have 601 heads on my stroker 305/334 CID motor (305 + .030, 400 cut down crank, forged, dished pistons, and it absolutely requires 92-93 octane fuel, and backing the timing off. 601's are a good replacement head for 265,283,307 motors, and start to get marginal on the 327 motors (lo-perf ones, not the factory domed ones; way too much CR there). It was the circle track, dirt track, roundy-rounders that started the 305 head on a 350 deal, for the most part; they were a cheap way to increase CR using stock heads, gave good low end torque, and were easy to find. For a street 350, with stock pistons and a mild cam, the 416 heads are probably a better choice with their 58cc chambers, but they too have small valves and ports. 601 and 416 heads can be ported, and worked over, for much improvement. There's a fella over on HotRodders.Com that swears by 416 reworked heads, FireBird88 I believe is his handle. Do a search on that site/engine forum for 305 heads on a 350; there are a ton of posts. Butch/56sedandelivery.

    Your hot start situation could be because of too much static advance, which causes the motor to run hotter. That makes the starter motor also get hot, and heat increases resistance in the field windings of the starter and solenoid. You might have to shield the starter from heat, particularly with headers. The "springs" mentioned are in the advance mechanism of the distributor; usually, lighter springs let the distributor advance come in quicker (advance sooner), but that can also cause more heat/hot start problems. You're really just going to have to play with things, and see what works best for your particular combination.
     
    Last edited: Feb 21, 2011
  6. MarkKoch
    Joined: Jan 16, 2010
    Posts: 294

    MarkKoch
    Member
    from Maryland

    56 sedan thanks for your input:).It does seem to run hot.Im going to do what ya said and see how things go...........Now why did it have to start snowing today.Keep you all posted on how thing work out
     
  7. Dyce
    Joined: Sep 12, 2006
    Posts: 1,894

    Dyce
    Member

    You need the autolite 85 plugs not the 45. The 45 has the washer, and you need the taper seat. The 85 is a set colder then the 86 you would need with 350 heads. You might want to narrow the gap a little from the .045 spec as well. With the higher compression I'd drop it to .035-.040
     
  8. ANDEREGG TRIBUTE
    Joined: Jan 1, 2008
    Posts: 1,370

    ANDEREGG TRIBUTE
    Member
    from Bordertown

    Sorry bout the plugs.... I run autolite 26 gapped at .045
     
  9. Dyce
    Joined: Sep 12, 2006
    Posts: 1,894

    Dyce
    Member

    I go the plug number wrong too:eek:.
     
  10. MarkKoch
    Joined: Jan 16, 2010
    Posts: 294

    MarkKoch
    Member
    from Maryland

    I have been making great progress,running a/c delco R44t plugs,gapped at 35.Medium and light spring in the distrubutor,accel adjustable vacuum advance.Base timing is 8 degrees.I have no hesitation anywhere in the throttle range.I am getting some spark nock after the motor gets nice and warm(195-200) at idle,goes away with a bit of throttle.Sometimes rite after I back of the throttle/lite cruising throttle.Could I be pulling a bit of extra timing from the vacuum advance at I idle after motor get up to temp.Its hooked up to ported vacuum.If I put the car in drive knock goes away,even if I foot brake and bring rpm`s up the where knock is in park...its not there.Idle in park is 1000,650 in drive
     
    Last edited: Mar 29, 2011
  11. MarkKoch
    Joined: Jan 16, 2010
    Posts: 294

    MarkKoch
    Member
    from Maryland

    Im having trouble understanding the graph that came with my advance kit and vacuum advance kit.Does mechanical come in at 500 rpm with the light and medium spring?And vacuum comes in with about 6 inches mercury(vacuum)?Im 3 turns in.Im new to all this.Just trying to make sense of it all.
     
  12. MarkKoch
    Joined: Jan 16, 2010
    Posts: 294

    MarkKoch
    Member
    from Maryland

  13. 70caminoman
    Joined: Mar 29, 2010
    Posts: 38

    70caminoman
    Member

    What happens with the mechanical advance is the lighter the springs the faster the full mechanical advance comes in. Both light springs in an HEI should come in around 1200RPM or so while both heavy would come in around 3500 or so I usually use both medium to fall in there at about the middle of the road. and as far a the vacuum advance that only comes in at about part throttle and goes away by 3000 rpm or so and it improves drivability gas mileage, ect. Keep your full advance timing conservative at no more than 38 preferably around 36 or 34. as far as your spark knock goes try to get your temperature down below 200 at full warm up shoot for around 180 fully hot after driving it around. Check things like your thermostat use a 180* one, always use a mechanical fan especially if you have a stock radiator, don't use under drive pulleys I.E make sure your crank pulley is larger than your water pump pulley, and please dont use an electric water pump on the street.
     
  14. 70caminoman
    Joined: Mar 29, 2010
    Posts: 38

    70caminoman
    Member

    also remember to get a buddy and tune your idle circuit on the car with the car in drive with your foot on the brake. Always tune it for highest vacuum level reading. and make sure that the knock you are detecting isnt mistaken for misadjusted rockers or anything. Give them a once over with the car running (1/4 of preload). and a good hint if you have a set of trashed valve covers cut the tops off and bolt them on to adjust the rockers while running, it saves the oil mess.
     
  15. MarkKoch
    Joined: Jan 16, 2010
    Posts: 294

    MarkKoch
    Member
    from Maryland

    70caminoman,thanks for the info man ........nice tattoo :)
     

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