Got a free LT1... It's spun out

Discussion in 'Engine Topic' started by Da_Raabi, Oct 19, 2020.

  1. Da_Raabi

    Da_Raabi Veteran Member

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    Ok, I think that answers my question. Thanks guys. I expected to see markings indicating 1,2,3,etc., and was surprised when I did not. I guess it actually does not matter.

    I have been having trouble getting a hold of the shop I got the kit from. They had shipped the wrong pistons (.030 instead of std) so I was also trying to figure out what they were going to do about it. I did finally get through and they shipped out replacement pistons yesterday, so that's good.

    So at this point my next step (once I get the pistons) is to get the block back over to the machinist to get it line honed and decked so the new pistons will be .014 in the hole. With a .026 shim head gasket this will give me the ideal .040 quench, although with a rather mighty static compression of 11.29:1 and a dynamic compression of 9.29:1. I have been assured that this will be fine on the LT1 due to the reverse coolant flow but wow that is high. Definitely going to be a 93+ guzzler.

    Should be fun...
     
  2. 1320feet

    1320feet Veteran Member

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    Weigh the new pistons and make sure they weigh the same as the .030 ones.
     
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  3. Da_Raabi

    Da_Raabi Veteran Member

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    Thanks for all the info guys!

    I thought I would update with some final info I have put together. These are the final specs of what this engine will be using a couple of online calculators:

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  4. G72Zed

    G72Zed Veteran Member

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    Must be installing a late closing big duration cam if your @ 11.4 SCR with only a 172 psi cranking pressure.

    What does the cam manufacturer ask for a min or max CR ? any input from them?

    I can fool that RSR Dynamic calculator by 30-50 psi....
     
  5. Bandit723

    Bandit723 Veteran Member

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    no offense. I have no idea what you just said.
     
  6. G72Zed

    G72Zed Veteran Member

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    I just looked at the OP's post # 103, 4.000 bore with a 4.010 HG, that's tight with only .005 bore edge clearance, and to run 11.4 compression with only 172 cranking pressure, that shows there's something going on there.

    Sometimes engines don't listen to online calculators and formulas like that, it may be a rattler....you do not want that. But, unless it's got nice chambers, and upgraded head cooling, or reverse cooling, then it very well may be in the sweet spot, good tq I bet.
     
    Last edited: May 19, 2021
  7. sooner

    sooner Veteran Member Lifetime Gold Member

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    I agree with G72, cylinder pressure should be well above 200 psi with the cam on a 108 and over 11:1 static. To be only 172 id expect the cam to be on like a 120+ LSA or installed way slow.

    The actual bore size of that head gasket should be 4.1 not 4.01...significant digits :)
     
  8. Da_Raabi

    Da_Raabi Veteran Member

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    My mistake on the head gasket. 4.1 bore for the gasket is correct. Mr Gasket 5716G. Updated calcs below. New compression of 11.36 static.

    Remember, this is a reverse flow LT1, so high compression should be ok.

    The cam ended up getting changed out with a Comp 08-443-8 with a intake closing at 73 deg ABDC at .006 lift. This is where I appear to have made a mistake. The dynamic comp calculator needed this at .050 lift. I have since updated the dynamic calculation and the result is a rather unusable 10.17 with a cp of 216psi.

    However, and this is where this gets annoying, another calculator (GoFastMath, third pic below) puts me right at 9.29 dynamic, which is on the high side of acceptable for the LT1 (I've read 9.5 max, with 9.0 the goal on pump gas). So who to trust?

    So... That's a problem. This seems to be related to the fact that I plan to mill the block to get that .040 quench, but the chambers in the heads are just too dang small. 54cc is a way tiny chamber. I'm on a budget here so I'm not totally sure what to do. Open up the quench to lower compression? But that could lead to detonation...Grind out 4cc of each chamber? (Just kidding, even though that would get me right where I need to be)

    Hmm... Now I'm a little stuck.


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    Last edited: May 20, 2021
  9. G72Zed

    G72Zed Veteran Member

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    Personally, I like small efficient chambers and rather get the cc's from an inverted dome and min. safe piston to head clearance to hit the target CR.

    That Comp Cam you picked out, 08-443-8 calls for 9.5+ CR, the next one down is the 08-444-8, and that askes for 10:1+.

    I never used/ported an LT1 reverse flow head, but from the Comp recommendations of 9.5:1 and landing @ 11.36:1 is a big jump, unless Comp advised you will be OK.
     
  10. need-for-speed

    need-for-speed Veteran Member

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