Piston pin height

Discussion in 'Street/strip 400/430/455' started by 1969RIVI, May 24, 2020.

  1. 1969RIVI

    1969RIVI Well-Known Member

    Does anyone know the pin height on the TA 1621A forged pistons? I'm looking at different piston options for my build. I was thinking of going the autotec forged Custom pistons either flat tops ($639) or dished with valve reliefs ($649) and pin height of 1.980 to help get to zero deck. OR since I'll be doing a clean up cut of the block and heads anyways and I have a set of .20 steel shim head gaskets could I achieve the zero deck with the TA 1621A pistons ($430) and put the saved $200 towards something else for the build? This 70 455 bored .30 over engine is a street/strip build (90% street driven) going in a 69 Riv. I also have a 290-94H cam but not sure if I'm sticking with that one yet.
     
  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I don't see the TA1621A pistons in the catalog anymore, just on the website. In the catalog, I see the 1621B. They have a compression height of 1.985. Stock block deck height of the 455 block is 10.57. To figure out how far in the hole a piston will be, you take 1/2 the stroke + rod length + compression height. Then subtract that from the block deck height.

    3.9/2 + 6.6 + 1.980 = 10.53

    10.57 - 10.53 = .040

    The TA 1621B only has .005 more compression height, so .035 in the hole.

    The nice thing about the customizable pistons is you can manipulate CD and valve relief/dish volume to get 0 deck and the compression ratio you want.

    If you take .020 off the block deck, you'll need a CD of 2.00" to get to 0 deck.

    If you use flat top pistons, where will the valves go if you have 0 deck?
     
  3. Bigpig455

    Bigpig455 Fastest of the slow....

    I am using a set on a build I'm doing now - I did get the A's with 23cc dish, and am using stock rods. I cut the deck to 10.55, and that put the pistons .008 in the hole. now, with 70cc heads, and .038 gaskets, it comes out to exactly 10.0 :1 compression, and a quench of .046. Using a cam that closes at 64 ABDC, that should give me a DCR of 8.0. Hopefully that will be OK with pump gas, that's the idea anyway.
     
  4. 1969RIVI

    1969RIVI Well-Known Member

    This ^^^is what I'm after. Now if I use the .20 steel shim head gaskets and 69cc (I'll have to measure to confirm actuall cc) would that be cutting it too close and putting me into race gas and or detonation territory? I do have a few sets of felpro and some other black composite gaskets of some kind from TA that I think measure out to .38 that could be used to adjust quench distance. I'll probably use stick rods with ARP bolts.
     
  5. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    http://www.empirenet.com/pkelley2/DynamicCR.html
     
    Finbuick likes this.
  6. 1969RIVI

    1969RIVI Well-Known Member

    Time to play with Larry's calculator :)
     
  7. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    That's right, download it and keep it on your computer.
     
  8. 1969RIVI

    1969RIVI Well-Known Member

    Well there's a small problem, I need a computer to do that:rolleyes:. My old one crapped out on me.
     
  9. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    :D:D Get another, Puters are cheap.
     
  10. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Give me your numbers and I'll put them into the calculator.:)
     
  11. 1969RIVI

    1969RIVI Well-Known Member

    Ok I dont have definitive numbers as of yet but what I'm probably roughly looking at is a 70 455 block bored .30 over 68 430 69cc heads with clean up cut of probably. 002 on block and heads stock connecting rods with the TA 1621 B pistons with the valve reliefs. I can use .20 steel shim, .38 composite or .40 felpros (I have all of them) whichever one will keep me pump gas friendly (I don't mind 93 octane I run it now) out of detonation and close to zero deck and around 10:1 compression. TA se aluminum heads will be in the future
     
  12. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    OK, The .030 over TA1621B pistons are 4.3425. They have 25cc dish/valve notches.

    Cutting .020 off the deck comes to 10.55" block deck height. The pistons have a 1.985" CD.

    3.9/2 + 6.6 + 1.985 = 10.535"
    10.55 - 10.535 = .015 in the hole.

    With a .020 head gasket,

    1969RIVIA.JPG
     
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  13. 1969RIVI

    1969RIVI Well-Known Member

    Thanks Larry that's right where I want to be. I take it that 10.2:1 would be good for pump gas, no detonation and if I run the 290 94H cam I'll have enough vacuum to run power brakes? I assume the dynamic compression would be around 8.2?
     
  14. 70 GMuscle

    70 GMuscle Plan B

    You can put the flat tops in and go for maximum compression. Can you get E85 where you live?
    If so you can make max hp and torque. Have a bunch of friends doing it here on Long Island. Also helps engines run cooler. A great effect of the fuel.
    Go for max power. If I could do over I would have not listened to machine shop n got pistons myself .
     
  15. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    That cam will run the power brakes no problem. DCR is almost 7.6. Should be fine on pump gas.

    1969RIVIB.JPG
     
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  16. 1969RIVI

    1969RIVI Well-Known Member

    Thanks for doing those numbers for me Larry:). If I were to use the TA 1621A flattop pistons I would have to use a thicker gasket to gain clearance for the valves since there's no reliefs anymore right? What would be the thinnest gasket I could go before I had valve to piston contact?
     
  17. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Piston to valve contact has more to do with big duration. The TA290/94H is not a big cam. I can't answer your question for sure. Checking for valve interference is something that should be done anytime you modify an engine like this.
     
  18. 1969RIVI

    1969RIVI Well-Known Member

    In your opinion Larry is the 290 94H cam too small for the type of build I'm after? I like the heavy lump of the cam I have now but I think the current engine is over cammed. I don't want to make that mistake for my new engine. Will I get the the best of both worlds with this cam or should I be looking at something different. Keeping in mind this engine is for a big heavy Riv.
     
  19. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    No, it is not too small. It's 226*/235* on a 112* LSA. My cam is 230*/238* on a 112* LSA, yes it is a roller.:D. You want the best of both worlds? Get some aluminum heads with entry level porting and 10:1 SCR, and you'll make over 500 HP. Lump? What good is that if the car is a slug in real world driving?
     
  20. 1969RIVI

    1969RIVI Well-Known Member

    Aluminum heads with porting is in the not to distant future for sure:). If I stick to my current build plan I'll have the 10:1 SCR no problem. Big slug is what I'm trying to get away from, the trans rebuild and JW 9.5 converter got the Riv going quicker and out of the hole faster but the current engine there's tons of power left on the table. That's mostly the reason for a new engine build, I want to have an optimized engine that suits my driving style (plus a little extra for just in case:D) as well as have a nice lumpy sound to it without trading off the HP and turning it back into a slug. I do have dual 2.5" side dump exhaust, mufflers are unknown?
     

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