Switching to 1970 500 pistons in a 1973 500 engine?
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500, 472, 425, 368 Discussion, Switching to 1970 500 pistons in a 1973 500 engine? in Cadillac Engine Technical Discussion; Ok so I am a recreational mechanic, IE I have rebuilt a few engines and so forth but have no ...
  1. #1
    jschlote is offline Cadillac Owners Member
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    Switching to 1970 500 pistons in a 1973 500 engine?

    Ok so I am a recreational mechanic, IE I have rebuilt a few engines and so forth but have no formal schooling in mechanicry. I have basically learned as I have gone along.

    But anyways here's my question, which could be a dumb one but I'mma ask anyways.

    I just found a 73 500 v8 from an eldorado that I am considering putting in my 68 deville convertible. However before I put it in and since I already have the engine completely broken down I looked into the specs on the 70 eldo 500 and all the numbers match up: bore, stroke and the case/head/crank #'s so my question is can I just switch the pistons to the 70 eldo 500 pistons for the higher compression ratio and get the higher torque and hp?

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    jschlote is offline Cadillac Owners Member
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    Re: Switching to 1970 500 pistons in a 1973 500 engine?

    as in would it really be just that simple, the rod lengths are listed as the same length in the websites I have found so I am assuming it is, however I thought I should check before I go blow 320 bucks on a set of new pistons since I have never really "tinkered" on an engine and played frankenstien with one to get more horse power.

    Please for the love of G_d tell me if this won't work lol

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    steelybill is offline Cadillac Owners Enthusiast
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    Re: Switching to 1970 500 pistons in a 1973 500 engine?

    If you go on the site www.cad500parts.com, their catalog has a description of the pistons and cylinder heads used in the 472/500 engines. That may help you figure it out.
    If I recall, the '73 had 120 CC heads, and the early engines had 76 CC heads, so the pistons were not the only thing determining compression ratio. Like most engines of that era, compression was dropped to 8.5:1 around 1971. This was done with heads mostly, from what I can figure out.

    That company has pistons to bring the compression up with the 120 CC heads. I used those in my engine, and ended up with around 9.2:1.
    Hope this helps.......

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    jschlote is offline Cadillac Owners Member
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    Re: Switching to 1970 500 pistons in a 1973 500 engine?

    Well the cc's on the heads are 76 for the 1973 500 thats double confirmed from my shop manuals and the cad500 web page so the heads shouldnt be a problem, so I guess i can just swap out the pistons and be golden.....right?

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    steelybill is offline Cadillac Owners Enthusiast
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    Re: Switching to 1970 500 pistons in a 1973 500 engine?

    That may depend on the top of the pistons. There were several types of dish etc during those years. The '70 Eldo had piston tops with two dishes, that looked like binoculars in their (so-called) 400 HP engine. Those would likely work for you. Are you going with a +.030 over-bore to clean up the bores for new pistons?? It may be necessary in order to fit the piston clearance to spec.

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    jschlote is offline Cadillac Owners Member
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    Re: Switching to 1970 500 pistons in a 1973 500 engine?

    The current pistons are "soap dish" tops, but i found a dealer that can get me new "peanut" top pistons. I am not sure if I will need to over bore them both the 73
    and the 70 use a 4.3 bore piston and the current chambers are smooth and solid I'll probably just hone them and put in the new pistons. but if you think its a better idea to overbore them I can probably get that done, I'll just have to take the short block to a machine shop

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    steelybill is offline Cadillac Owners Enthusiast
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    Re: Switching to 1970 500 pistons in a 1973 500 engine?

    You can check piston fit with a feeler gauge along side the piston, in the bore. The book calls out .0006 to .0010, which is actually a quite close fit. Some feeler gauges would tell you, but if you buy .030 oversized pistons you are home-free, with a new bore and proper fit. New stock bore pistons may or may not be the right fit. Around here, an over-bore is about 98 bucks for a V8. Good time to have the block boiled out and new cam bearings and soft/freeze plugs installed while it's at the machine shop. If you go that route, bring the new pistons to the the shop with the block, so they can fit the bore to the pistons.

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    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: Switching to 1970 500 pistons in a 1973 500 engine?

    I think you have too many 0's Bill. A Piston should be more like .006 clearance than .0006. Cheers.

  10. #9
    steelybill is offline Cadillac Owners Enthusiast
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    Re: Switching to 1970 500 pistons in a 1973 500 engine?

    Those figures do seem "tight", but that's what my Chiltons manual called out
    My '76 factory manual doesn't give clearance, just the piston size (10 of'em !!) and bore sizes to match.
    If the factory lists 10 sizes of piston, I would think an after market piston may not fit right in a standard bore.

    ( I could be wrong. I was once, in 1947)

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