Which Tw 170's 61 Or 58cc

Discussion in '1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-' started by 90lxwhite, Mar 7, 2014.


  1. 90lxwhite

    90lxwhite Mustang Master

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    So which do I want? The smaller will raise compression right? Right now I believe I have 9:1 or maybe its 9.5:1 I'll have to check the build sheet. But more compression equals more power right? What problems would/could one run into using the lower cc heads? I'm working on a 95 gt mild street car n/a

    Mike
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  2. gearheadboy

    gearheadboy Mod Dude

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    Are you planning on boost at some point? Nitrous? It is truthfully not that much difference in cc.
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  3. rbohm

    rbohm Founding Member

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    smaller is better, unless you are running a supercharger.
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  4. 90lxwhite

    90lxwhite Mustang Master

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    No no N20. As for boost, well I doubt it, don't think $ will ever allow.
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  5. NIKwoaC

    NIKwoaC 中國製造

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    Play around with this compression calculator:

    http://www.summitracing.com/expertadviceandnews/calcsandtools/compression-calculator

    There is about a .35 difference in compression between the two, so the difference is not huge.

    Pros:
    -Compression is free power.

    Cons:
    -Boost won't be impossible, but more caution should be taken if going with the 58cc head.
    -The 58cc head will make getting pump-gas-friendly compression ratios slightly more difficult, but not impossible, should you choose to stroke it in the future. This is even more exasperated if you go to a stroked Windsor.

    Life choices here.
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  6. 90lxwhite

    90lxwhite Mustang Master

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    Eh I think I'll stick w the 61's.
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  7. FastDriver

    FastDriver Mod Dude

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    They say that on average a point of compression is worth about 3-4% in power. So if that rule of thumb is right, and the difference in compression ratio is only .35, that sounds like a 1% difference, or so. If I knew I was sticking to n/a or preferred nitrous in the future instead of boost, I'd go with the smaller chambers. If I wanted to leave myself a little more flexibility, I'd go with the bigger ones.
    Last edited: Mar 7, 2014
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    A5literMan likes this.
  8. 84Ttop

    84Ttop They make new pistons every day, so why worry? SN Certified Technician Mod Dude

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    Agreed and x2!!!
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  9. 90lxwhite

    90lxwhite Mustang Master

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    Damn it... Still a tough choice. The smaller ones say they use 1/2" bolts. So does that mean I gotta drill and tap? 1% difference, prob noticeable huh?
    Last edited: Mar 7, 2014
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  10. 2000xp8

    2000xp8 Mustang Master

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    You are probably talking about the bolts that hold the head down to the block.
    Either way you are buying a set or ARP bolts (at $150), just buy the right set.

    They will probably take a 1/2 bolt stepped to 7/16 (if i remember correctly).
    Last edited: Mar 7, 2014
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  11. 90lxwhite

    90lxwhite Mustang Master

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    Ok thanks man
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  12. Gearbanger 101

    Gearbanger 101 we love us some gays up here Super Mod

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    Yeah, you'll need to buy stepped washers for your heads if bolting them to a 302. Trick Flow sells them too. I think they're about $60?
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  13. 2000xp8

    2000xp8 Mustang Master

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    I don't think you need the stepped washers with the stepped bolts.
    http://www.summitracing.com/parts/ARP-254-3708/
    #13
  14. Bullitt347

    Bullitt347 man bewbs please...

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    One other point to consider, an aluminum head sheds combustion heat a lot faster, so the aluminum head is more tolerant to higher compression. 10.0:1 compression with an aluminum head on (premium) pump gas is not an issue. Another way to look at it is this: Everything else being equal, a engine with a cast iron head will make more power than an engine with aluminum heads. Heat is power, and a iron head will hold more heat in the combustion process than an aluminum head will.
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  15. FastDriver

    FastDriver Mod Dude

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    That comment confuses me, bullitt. Pretty much all the baddest heads on the market are Aluminum.
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  16. FastDriver

    FastDriver Mod Dude

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    Well, 1% of 300rwhp would be 3 rwhp. That's probably hard to consistently notice even on a dyno.
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  17. Gearbanger 101

    Gearbanger 101 we love us some gays up here Super Mod

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    Didn't notice those, but for the price, it would be just as const effective, or more so to buy standard bolts, with the stepped washers. Six in one, half a dozen in the other I suppose?


    Not necessarily true. Heat = power for certain....but heat can also equal detonation unless you're got a high enough octane content in your fuel to keep pre-ignition at bay. If not, timing needs to be pulled and down too goes the power levels as a result. Aluminum heads are more resistant to detonation, which will allow the use of more ignition timing.

    I suppose if ALL things were equal, an iron head "could" produce more power. But that would only be in the case that the aluminum heads are not being utilized to their fullest potential. Aluminum heads will handle more heat, more compression and more timing than an equal iron head and will therefore make more power.
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  18. Bullitt347

    Bullitt347 man bewbs please...

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    If you built two 10.0:1 compression engines and everything between the 2 was exactly the same, except for one had cast iron heads, and one had aluminum heads (both sets of heads flow exactly the same) the cast iron headed engine will always make more power. Period. The thing is you can never find cast iron heads that are worth a crap. And in a car the loss of 50 lbs off of the nose of the car and the better architecture/design of the aluminum head (as opposed to commercially available cast iron heads) is a better head anyway. But from an engineering point of view when looking only at HP production, the cast iron head is "better".
    Last edited: Mar 9, 2014
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  19. Gearbanger 101

    Gearbanger 101 we love us some gays up here Super Mod

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    Negative. The aluminum headed engine will allow for more ignition timing. Whatever additional power gained with the hotter running iron head, would be surpassed by the power gained by the additional ignition timing the aluminum head would be capable of running.....Period!

    Case in point. Early GT40 aluminum heads (pre GT40Y GT40X) was merely an aluminum version of the more popular GT40 iron head, yet the alumium casting is good for another 10-15hp over the iron head. Same porting, same combustion chambers, same valve size.
    Last edited: Mar 9, 2014
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  20. Bullitt347

    Bullitt347 man bewbs please...

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    Believe what you want dude, I have seen it happen. Many times.
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