Stuck between cylinder heads

Discussion in 'High Performance Modifications' started by Justin79maro, Sep 11, 2019.

  1. Justin79maro

    Justin79maro Veteran Member

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    So I guess the question now is do I get my darts worked on or go with afr 195s
     
  2. G72Zed

    G72Zed Veteran Member

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    I think if you had a "Pro Head Porter" go through and measure up those Dart heads for your cubic/RPM and overall car combo, he could tell you if he could get you more out of them, and in fact hit your ET and HP goals.

    Ask the "head porter" what he would do to them, how much work and estimate of the costs, he may in fact tell you your starting with the wrong head, and should go with the AFR's after everything is said and done.
     
    Last edited: Oct 28, 2019
  3. Justin79maro

    Justin79maro Veteran Member

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    Sounds like a good idea to me, I got some buddies that are big into drag racing I’ll ask them who they get their head work done by and see. I will let you know what he says
     
  4. G72Zed

    G72Zed Veteran Member

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    Keep us in the loop, asking the "top performers" in the racing circle your interested in will narrow it down quite a bit, see who runs the best and who does there work.
     
  5. Justin79maro

    Justin79maro Veteran Member

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    Told by a head builder that bow tie vortec small port 185cc heads and a edelbrock performer dual plane would work best with my combo. What do you think?
     
  6. G72Zed

    G72Zed Veteran Member

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    Well, looking at you combo in your sig, you may in fact benefit from the good velocity ports of the Vortec's, Iron material and efficient chambers requiring less timing(negative work) and the dual plane will give you better ave. TQ below peak and may work better under shift recovery.

    Many different ways to look at it.
     
  7. Justin79maro

    Justin79maro Veteran Member

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    I’ve seen where people were making 500ish hp with roughly the same cam and compression but the never stated at what rpm the hp and tq were at, they used 195-210cc intake runners on their combos as well, in the 1/8th mile I’m starting to think it’s a tq game instead of so much hp. But as always I could be wrong
     
  8. G72Zed

    G72Zed Veteran Member

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    Well, I was on the dyno last week with an engine very similar to yours, SBC 400ci (4.125x3.75) and the same HR cam as you, 10.5 ish CR, Super Vic intake/750 Holley with 200cc Dart Pro1 "platinum" heads. Peak HP was 530hp at 6,400rpm, peak TQ at 510 @ 4,700rpm, a nice 1,700 rpm peak spread. customer still "needs" more, but that's another story.

    I think you might be looking at this the right way. It's sometimes not "how much you have" but "how much of it you are using" , on the dyno big carbs generally make more peak HP, but more often than not, are slower on the track, and big heads flow more, and generally make higher HP at a higher rpm, but if you can't get there, or don't gear for it, and can't use it, you actually slow down with "more carb and head" than what you can use.

    Most well built engines have a peak tq to peak hp rpm spread of 1,500, some real nice combo's hit 1,700/1,800, top ones or FI's hit 2,000.

    Your using a TH350, that's a 39.7% drop into 2nd gear (2.52- 1.52). You stated your max rpm of being 6,000, if you shift at 6k, assuming now that's close to your peak HP, your TQ will be around 4,500 +/- 100 rpm or so, looking at the gear spread and % drop of 39.7%, this brings you down to 3,620 rpm at a 6k shift, way below your peak TQ. The Motown intake is a very good intake, but more in the upper RPM's.

    Going to a bigger runner head, you will make more HP, but it will be at a higher RPM everything being equal, your TQ peak will move up accordingly, and without the right converter/stall and gearing for it, you may in fact loose 60ft and ET/mph.

    Do not get stuck on head flow cfm #'s, yes, it's the way they all advertise, because it's the easiest way to compare the same style head in the market from one to the other. A well thought cylinder head will flow the right amount of air for your HP/TQ goals & requirements and be sized right for the cubic inch and RPM needed for the combo.

    To simplify it, looking at a nice, well thought out pump gas SBC street engine in the 330-400 inch range, you can make about 2.06 HP per available CFM. A 500hp goal only requires 243 CFM, perhaps your heads in the right hands can get you there, and if your not changing converter/gears, a nice big dual plane may help.
     
    Last edited: Nov 4, 2019
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  9. Justin79maro

    Justin79maro Veteran Member

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    Wow lots of good information there! And yes I plan on going to a dual plane anyway, I don’t like the hood clearance of the big single plane, so I’ll probably sell it. So if I had peak tq in a flat curve from say 3500-5000 it will recover from shifts fast and pull me back up to peak hp at around 6000, keeping me in that range, which in theory if I have a flat tq curve from preferably 3,000-5000ish my car will 60’ better giving me a better overall et and mph. I think I’m leaning towards selling the darts and losing some weight with aluminum heads 180-190cc and possibly jumping up in compression a little bit too to around 10.3:1 without causing any problems with clearance, which more compression means more torque correct? I’m thinking that the faster you can move more cfm in a smaller port head (185) the more power you will make across the bored vs a lower velocity head with a big say 220cc runner with 2.05-2.08 valves but still flows the same cfm right? Or will it move the powerband just up higher Bc the motor must turn faster in order to create enough velocity to use that much cylinder head?
     
  10. G72Zed

    G72Zed Veteran Member

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    I would keep the open plenum if you can, you never know, you may go back to it in the future to test it out, and your combo may change in the future, nothing beats on track testing as you don't race flow benches or dyno's.

    Looking at the tq/hp "averages" within a given RPM band that your spending the most amount of time is a good way of looking at it.

    And yes, everything being the same, If you have 10:1 with a good iron head without issues, and stay 10:1 with "better flowing" Aluminum heads, it may be a wash with no gains, you need to raise the CR with the alloy change. Chamber shape/size has a big impact on this.

    Your correct, it's all about port velocity and air speed to fill that hole based on CI/RPM, but, if a port is too fast for the combo, you can hit a wall so to speak. Valve size is closely chosen on bore size. Work with the head porter/manufacturer of your choice to make sure you get what you need for your performance goals.
     

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