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  1. #1
    FEP Member 86MustangGtRob's Avatar
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    Default Gt40x heads with a stock cam

    Hi guys, I have a 85 Gt with a 1990 fuel injected motor with mass air. Are the ports to big for a stock cam? I like the torque right away with the ho cam.

  2. #2

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    Nope, should work great for you. But it's nice if you have the smaller chamber to get that compression up at least a half point.

  3. #3
    FEP Member 86MustangGtRob's Avatar
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    Thanks for the advice Online, no one ever talks about the gt40x heads for low rpm torque.

  4. #4

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    I'm working on a set right now actually, and opening up the ports and cleaning them up for a 347.

  5. #5

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    I'd love to know what a properly ported set is capable of.
    1984.5 G.T.350 had since 16y/o
    95 Cobra, Crystal White

  6. #6
    FEP Super Member erratic50's Avatar
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    Default

    Should work like a champ.

    How one slow is slow though? An E6 swirl head will better most of the others down low because of the swirl bumps. The don't tolerate quite as much timing advance but they do have their merits at slow engine speeds.

    I agree - more compression will help. And actually you can increase dynamic pressure from the combined A/F by switching to E85. It takes 35% more liquid fuel and liquid does not compress.... It's also higher octane but requires larger injectors and a custom tune to run it. EV6's with adapters will be better for atomization.

    You will benefit from a long runner style intake that's port matched too. Stock5.0HO or Explorer are good cheap options for this project. Just be careful not to open ports up too much as that will hurt low R port velocity.

    You will likely get an improvement mixing 1.6 and 1.7 rockers on intake and exhaust depending upon where your cam is.

    You could also benefit from higher oil pressure or even modded lifters to increase low RPM lift if the motor likes it. Don't go crazy though, sometimes they like less lift due to reduction in overlap- haven't measure the behavior of a 302 here before for sure.

    I do know SBF motors love more when looking for power up top but you have to be carful not to wash out bearings, etc. A loosely build bottom end will tolerate more pressure than a tight one. The stock cars we ran were always max loose spec and carried about 90 lbs at idle and went up from there and would run all season on one 351W build.

    speaking of cam fine tuning, I would consider about 4 degrees of advance on the stock 5.0 cam. Check multiple cyl as the factory bumpsticks were made very quickly. You will reduce high RPM capability but add to the low end substantially.

    Also some factory stock cams will help your cause more than others. It varies by year and application as do the MAF computers. I've heard the 89-90 5.0HO cam mixed with an A9L MAF computer is a good combo for this right out of the box.

    Ive also heard Explorer cam but don't trust that source as much and I haven't played with one myself and don't know the specs off hand. You might look into E series van 351 roller cam specs too to see their specs as far as that goes. Overlap is the enemy of low speed torque to a point, FYI.

    Another consideration is throttle body size. You need great port velocity and that comes at low speed with smaller ports. I suspect an 86 55MM throttle body willl be better paired with an 89-93 55MM MAF than the newer 60-65+ with an aftermarket or Cobra MAF in your case if only by a few foot-pounds.

    You will also want to explore advancing your base timing but don't trust factory marks unless you confirm them for this use. I would advance the distributor until the motor just starts speeding up. Check where this is on your marks with a light. Now start by taking out 1-2 degrees and see if you have avoided hard starting where the motor hitting stops the starter. If not take out another degree and repeat until you avoid this. This is a relative timing old hotrodder trick so leaving in the advance snub in is preferred. Don't care where it was, don't care where it is - just as long as the motor likes it.... Definitely run premium if you go near the limit because you could be at the ragged edge once you get on it at higher than 2500 R's. See if less timing helps low end torque and also watch your temps as an advanced motor can run hotter.

    A stroker kit would also help your cause greatly in terms of compression, displacement, and longer rod length.

    just things to think about. Make the build your own and have fun with your high torque low R motor!

  7. #7

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    Do you already have the heads? If not the 58cc combustion chamber heads will give you a slight bump in compression. The GT-40X heads are a pretty good quality head - order them through Summit Racing for the best price if you don't already have them. I've ordered plenty of heads via mail-order and have received some with shipping damage and Summit would immediately ship another head, no questions asked. You should consider running good quality 1.72:1 ratio roller rocker arms since those heads utilize a pedestal mount (don't buy junky, china made rockers) on both the intake and exhaust if you want to stick with the stock cam. You can also retard the stock cam by a couple degrees and gain a little more top end, you'll lose a tad on the low end, but it may not be noticeable depending upon your rear-end gear ratio.
    Mark

    1986 GT Hatchback (2R): 5spd, TFS FAC 170s, TFS Stage 2 Cam, Vortech SQ S-Trim, MM Suspension, SN95 5-lug conversion w/Fox 5-lug rear axles, 3.73's, 13" / 11.65" brakes, Moates QuarterHorse
    '88 LX 5.0
    '22 GT500

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