Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Vortec heads on a 75 350 (whats the cr ratio)

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by **DONOTDELETE**, Oct 19, 2001.

    I was wondering what the compresion ratio is for a stock 75 350?And also the combustion chamber cc's of the heads.
    I'm trying to determain what my cr ratio will be if I install these heads.Vortec's have 64cc chambers. Any info would be helpful,thanks.
     
  1. ftn96

    ftn96 1/2 ton status

    Joined:
    Sep 26, 2000
    Posts:
    3,238
    Likes Received:
    0
    Location:
    Nashville Tn
    10,000:1 and you'll have to run straight jet fuel. [​IMG]

    Surgeon General's Warning:
    Viagra and steroids may be harmful to your spouse![​IMG]
    <a target="_blank" href=http://www.nashvillek5.freeservers.com>www.nashvillek5.freeservers.com</a>
     
  2. LMAO Damn I can't even afford to keep 87 in it!
     
  3. chevyracing

    chevyracing 1/2 ton status

    Joined:
    Sep 8, 2001
    Posts:
    2,589
    Likes Received:
    0
    Location:
    Colorado
    I think stock was 8.3:1 (not much)

    John

    Like to go sloppin' 'round in da mud in a rapid fashion....=) [​IMG]
     
  4. Andreas

    Andreas 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    188
    Likes Received:
    0
    Location:
    Sweden
    Stock compression on a ´75 350 with 76cc heads was 8.5:1. If you slap on a set of 64cc Vortecs and no other modifications your compression will be around 9.6:1. A simple trick is to multiply your compression with 10 and there´s your required octane. You need 96 octane to sneak away from the evil ping-god. One option is to take advantage of this compression and install a Xtreme Energy 4x4 262H camshaft. It´ll bleed some of the pressure out as well as waking your 350 up real good.

    Andreas

    406cui of pure sh*t[​IMG]
     
  5. Blazer1970

    Blazer1970 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    1,600
    Likes Received:
    0
    Location:
    Old Mission, MI
    I have Vortecs on my Blazer with a stock bottom end (dished pistons). It is about 9.5:1 compression. Runs fine on 87 octane fuel. The Vortec heads have a "fast burn" type of combustion chamber which really controls the detonation problems you might otherwise have with that static compression ratio. You would never need to run 96 octane with only 9.5:1 compression though.

    Tim

    70 Blazer CST 4X4 350 SM465 NP205
    87 Burb 4X4 350
    01 GMC 2500HD 4X4 Duramax/Allison
     
  6. I was thinking more about the 254X.I'ld like to keep more bottom end power.It's power range is 1000-5200,thats about as big as I want to go with the stock converter,you loose to much off the line power without a stall.And as long as you don't get crazy with the timing 87 or 89 will be plenty.Thats the answer I was looking for though,I thought the heads were 76cc.9.5cr and a small rv cam will do wonders for a 350!

    ps
    Thanks for the replies and info.
     
  7. Blazer1970

    Blazer1970 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    1,600
    Likes Received:
    0
    Location:
    Old Mission, MI
    Yes, you are on the right track. That is pretty much how my motor is set up. Strong runner with a good idle and good low end torque.

    Tim

    70 Blazer CST 4X4 350 SM465 NP205
    87 Burb 4X4 350
    01 GMC 2500HD 4X4 Duramax/Allison
     
  8. xnoahx

    xnoahx 1/2 ton status

    Joined:
    Oct 12, 2000
    Posts:
    817
    Likes Received:
    0
    Location:
    Ventura, CA 93004
    I put some vortecs on my 73 and i dont have any problems with gas, i ran some 87 in it and driving it was fine, it would run on when i would shut it off so i like to run 91 now. I also used a thick head gasket

    My 73 K5 <a target="_blank" href=http://www.geocities.com/xk5blazerx/73k5.htm>http://www.geocities.com/xk5blazerx/73k5.htm</a> 350/TH350/NP203, Q-jet, Edelbrock intake, Vortec heads, 4" lift, and 36" TSL's
     
  9. '73 K5

    '73 K5 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    1,763
    Likes Received:
    0
    Location:
    Kansas
    I put Vortecs on my '73 and have minimal problems. It works with 89 octane on everything but the hottest days...then it pings a little, so in the summer I run 91. I also used the thicker head gaskets which I'm sure makes a small difference. I'm using the .447/.454 lift Comp Cams Xtreme Energy cam. Real nice combo. It will scream above 3,000 RPM and still has enough torque to pull my truck up my driveway in granny gear without touching the clutch or gas pedal...STEEP driveway too...the tach dips way under 500 RPM but the truck keeps going forward.

    '73 K5
    Chevy good...Ford bad
     
  10. Andreas

    Andreas 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    188
    Likes Received:
    0
    Location:
    Sweden
    I´m running a Xtreme Energy cam too. The 274 (230/236 @050 .487"/.490"). It´s in a 406 and all the Chevy Smallblock cams are specced for a 350, so the added strokelength of a 400 should make up for some lost torque. Desktop Dyno tells me 417 hp @ 5500 rpm and torque peaks at 3500 rpm with 470 ft.lbs. I run 10.14:1 compression with ironheads. No ping.

    /Andreas

    406cui of pure sh*t[​IMG]
     
  11. '73 K5

    '73 K5 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    1,763
    Likes Received:
    0
    Location:
    Kansas
    Hey Andreas. I have always wondered what the bigger Xtreme Energy cams were like. Does your truck have a lopey idle? And did that big of a cam affect the lower RPM torque alot? Thanks.

    '73 K5
    Chevy good...Ford bad
     
  12. Andreas

    Andreas 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    188
    Likes Received:
    0
    Location:
    Sweden
    Yes, it lopes a little. Sounds great [​IMG]. Before I built this engine I ran a severly worn 350 with almost non existing camlobes [​IMG] so I really can´t compare to anything. To clarify things - The 406 sits in a frame only for breaking it in. My Blazer, which will have this engine later on, is a million year project so I can´t say how it performs on the road. I might go one step up when it comes to stall, like 2200 rpm or so. I will not crawl any rocks, not tow anything, just floor it all day long[​IMG]

    /Andreas

    406cui of pure sh*t[​IMG]
     
  13. chevyboy24598

    chevyboy24598 1/2 ton status

    Joined:
    Jul 17, 2001
    Posts:
    212
    Likes Received:
    0
    Location:
    Va, USA
    Desktop Dyno shows 444hp@6500 and 421torque@4500 on my 350. I'm running a TCI 2400-2800 stall. I think I should of went with a 3500.

    Rust=Good
    <a target="_blank" href=http://www.bodatious.com> bodatious </a>
    <a target="_blank" href=http://www.mudboggingfun.homestead.com> my site </a>
     
  14. Andreas

    Andreas 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    188
    Likes Received:
    0
    Location:
    Sweden
    444 hp out of a 350 with a hydraulic cam?? What´s the specs on it? You must have really good heads !?

    Andreas

    406cui of pure sh*t[​IMG]
     
  15. chevyboy24598

    chevyboy24598 1/2 ton status

    Joined:
    Jul 17, 2001
    Posts:
    212
    Likes Received:
    0
    Location:
    Va, USA
    NO! I think its a solid. I don't know the specs.......It was put in by the previous owner.

    Rust=Good
    <a target="_blank" href=http://www.bodatious.com> bodatious </a>
    <a target="_blank" href=http://www.mudboggingfun.homestead.com> my site </a>
     

Share This Page