My 350 build getting closer need some advice

Discussion in 'Small Block Tech' started by Storm1, Oct 4, 2019.

  1. Storm1

    Storm1 Silver Level contributor

    After my catastrophic failure which can be see here:

    I've been trying to keep track of what everyone is doing on their 350 builds. I'm looking at cams, and compression ratio, and could use some advice from the great knowledgeable people here!

    First I'll post my specs and info so far. Then a few questions.

    BORE / STROKE = 3.83 / 3.85
    STOCK IRON HEADS VOLUME = 60CC (full port and polish)
    FLOW = 267 @ .600 INTAKE / 197 @ .600 EXHAUST
    PISTON COMP. HGT. = 1.875
    DECK HGT. = 10.185
    DECK CLEARANCE = .005 (in the hole)
    TA 3/8 VALVES = 1.92 INTAKE / 1.55 EXHAUST
    HEAD GASKET = .02 COMP STL. - 3.818 DIA.
    MOLNAR RODS = 6.39
    STOCK CRANK (reconditioned)
    3.73 GEAR (275/60/15" TIRES 28"hgt.) = 3.54 ACTUAL
    STALL 3200 from JW
    2-1/2" TO FLOWMASTERS 3" OUT
    STOCK QJET 7041544 (rebuilt by JW)
    TA Billet Distributor (TA_724RP)
    MSD Ignition Box (6AL Part# 6425)
    Mallory Coil 40,000v (Part# 29219)
    Taylor 8mm Spiro-Pro wires

    My plans for this build are realistically 90% street 10% strip. But I don't mind sacrificing some drivabillity, don't care about mileage, and I'm open to adding a pump if I don't have enough vacuum. I want a mean street/strip build.

    I want to run pump gas, 93oct is fine for most everywhere I go. Possibly some highway driving but not much.

    When the heads are decked, I can pretty much choose whatever compression ration I want. I ran some calc's and got this:



    Looking for suggestions on compression, and any clearance issues I may have.

    Any suggestions will be most appreciated! Thanks
    Last edited: Jul 5, 2020
  2. hugger

    hugger Well-Known Member

    Aluminum heads?
  3. alec296

    alec296 i need another buick

    Thats some excellent flow on heads . That cam is decent. I would go 850 carb, square bore like holley. Quad doesn’t seem to be that streetable on the sp3. Your gonna want more converter (3000)and heavy duty sprag in trans. Plan on a trans rebuild. Alittle more compression will make more lower end.
    Go atleast 10.25 compression. Its gonna pull to 7000 from what ta dyno sheet shows. Atleast 420 hp and 420 torque but I imagine it will be much higher.
    Hope its not a b&m shift kit. That will break parts sooner
    MrSony likes this.
  4. UNDERDOG350

    UNDERDOG350 350 Buick purestock racer

    I've never seen a stock head at 61cc. Usually 55-58. They must have ground lots out of the chamber.
    With iron heads and 93 octane I would not go over 10/1.
    850 Holley or clone would be best as Andy said.
  5. Mart

    Mart Gold level member

    Yep, 58-59 cc on chambers, unless they ground the bump out.
    Yes, excellent flow numbers with stock big TA 3/8" stem valves! Plus they have not been relocated, that's great.
    I run 11.1-1 with irons, 38* timing, but cam is more radical with 35* overlap.
    The timing helps make the cam more streetable. Except for brake vacuum pump. Couple hundred miles on it so far.
    Last edited: Oct 4, 2019
  6. Storm1

    Storm1 Silver Level contributor

    Original iron heads.

    I already bought the TA single plane for Qjet. Buying a carb wasn't really in my budget. Why wouldn't a Qjet be streetable? Is there an adapter I can use on the single plane if I decide to go Holly?

    Would I need to ditch the ram air intake if I ran a Holly? I didn't really want to do that, but...
  7. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    On the 455, the Q-jet works great on the SP1 intake, but the 350 SP3 might not be the same. I know Mark Demko couldn't tune out some hesitation when going wide open. Maybe your build will be different. Mark ended up using an AED 850 DP Holley 4150 type carburetor.

    You bought the right intake with the Q-jet opening. It makes the intake much more versatile as all it takes to run a Holley is a simple thin plate adapter to square off the bore. I do it all the time at the track.

    Not sure if the Ram Air intake will line up on the SP3 intake, or you have the hood clearance with the taller intake manifold.
  8. Storm1

    Storm1 Silver Level contributor

    That's another concern I have. I'll use some clay on top of the air cleaner and slowly shut the hood and see what happens.

    Thanks for the link to the adapter plate. Much appreciated!

    I guess I'll see how it runs with the Qjet first. If I 'have' to go Holly, then I will.
  9. alec296

    alec296 i need another buick

    You will want an air fuel meter to tune the carb, so you can see where the fuel curve may give you problems. You will probably need a better then stock type fuel pump also. Its gonna rev quickly.
    MrSony likes this.
  10. Storm1

    Storm1 Silver Level contributor

    Steve, Why not over 10:1? If I go higher will there be an issue running pump gas? Or some other issues I'm not aware of?

    Andy is saying at least 10.25:1
  11. Storm1

    Storm1 Silver Level contributor

    Like an electric pump?
  12. alec296

    alec296 i need another buick

    Robbmc does a mechanical pump but it’s probably more then an electric.
    But you will see once engine is together whether it feeds enough fuel or falls flat.
    As far as compression, if you polish chambers you should be able to push more compression without detonation.
  13. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Depends on the cam you choose. Read this,
  14. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    With iron heads, I would stick as close to 7.50 DCR. From the info in your original post, I get 9.72 SCR, and 7.50 DCR with a 106* ICL.

    Storm1A.JPG Storm1B.JPG Storm1C.JPG Storm1D.JPG
  15. UNDERDOG350

    UNDERDOG350 350 Buick purestock racer

    Unless you have a really radical cam 10:1 is marginal with pump gas. All you need is some clown dumping 87 octane in the 93 octane tank to boost their profits and you lose an engine. I've worked at gas stations.
    Mart likes this.
  16. Storm1

    Storm1 Silver Level contributor

    I downloaded Pat Kelly's DCR calculator but It wont let me type in any numbers. Anyone have a fix? I downloaded/installed the big file.

    Correction, it lets me type in everything except the top 2 boxes (advertised intake dur)(intake closing angle)

    NVM I see those are resultants of what is input in the calc below.

    I need to run some numbers, as it seems like I'm at the fork in the road.
    Last edited: Oct 6, 2019
  17. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    You need to go in order. First fill in the compression ratio calculator and calculate the SCR. Then go to Cam Timing and Overlap Calculator, fill that in and hit calculate. Then the Dynamic stroke Calculator, fill it in and hit calculate. Then go back to the Compression calculator, check the white box next to stroke, and hit calculate to see the DCR.
  18. Storm1

    Storm1 Silver Level contributor

    Thanks Larry its working now.

    So the options available to me at this point are:

    I can have the heads decked to lower CC and boost compression, but if I do that it increases my DCR above 7.50.
    A SCR of 9.72 is not what I was expecting for all the money I've dumped into this build. I think my expectations and reality might be conflicting though.

    I can have the custom cam ground to whatever I want. What I want is a good power band in the 2000-6000 rpm range and moderately streetable.

    What I need to figure out is a cam with the right duration, paired with the right compression ratio, to let me get the max performance possible on pump gas.

    I'm not sure the cam card I posted above fits that or not.
  19. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    You can also run the cam straight up. Advancing the cam increases DCR by closing the intake valve sooner, retarding the cam decreases DCR by closing the intake valve later. What's wrong with the results in post 14?
  20. Storm1

    Storm1 Silver Level contributor

    The SCR just seems lower than what I was expecting. I'm still learning, so I'm not really sure why I thought it should be in the 10:1 + zone

    Running that cam straight up, I could get the 10:1 compression and stay at 7.56 DCR with no advance.

    Why advance?

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