1972 402 bbc pistons

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springer
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1972 402 bbc pistons

Post by springer »

hello i just bought a 1972 402 and the pistons are stamped ,,1872 ,, and 030,, im just trying to see what the compression ratio is roughly.the heads are the stock 1972.6272292 castings.i want to freshing the motor up and replace the cam with a flat tappet and dont want to get the wrong cam based on the compression...thank you Eric
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Re: 1972 402 bbc pistons

Post by Baprace »

Springer, I will have to check on the compression ratio with the 402 , if I remember it is about 8.4 and that is with a dome piston , I will try and get back to you on Monday evening. That engine is basically a .030 over 396 ci.
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Re: 1972 402 bbc pistons

Post by BillK »

Eric,
I just looked through a couple of interchanges I have and cannot find a piston number 1872. Can you post a picture of the top of the piston ? Also, look inside and see if there are any numbers or symbols that might identify it.
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Re: 1972 402 bbc pistons

Post by rfoll »

I had one of these engines. The heads aren't too bad, I think the extra area around the exhaust valve helps keep it cool. I remember them being around 116 cc chamber. Factory advertised compression ratios were calculated using a steel shim head gasket. It takes a fairly large dome to get anywhere near 9:1.
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Re: 1972 402 bbc pistons

Post by PackardV8 »

The Silvolite number is 1445, with a .132" crown to keep up the compression.
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Re: 1972 402 bbc pistons

Post by 1972ho »

Lowest Price Guarantee
396ci Closed Chamber Head Stock-Type Pistons, .030'' Overbore
Piston Dia.: 4.124''
Piston Top: 21cc Dome
Pressed Pin
Comp Ratio: 9.59:1 w/100.9cc Heads, 8.23:1 w/119cc Heads
Ring Grooves: 5/64'', 5/64'', 3/16''
Set of 8
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Re: 1972 402 bbc pistons

Post by rfoll »

"Comp Ratio: 9.59:1 w/100.9cc Heads, 8.23:1 w/119cc Heads". Advertised, your results may vary.
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Re: 1972 402 bbc pistons

Post by PackardV8 »

BTW, last we quoted one of these, it was less expensive to build a 454".
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Re: 1972 402 bbc pistons

Post by springer »

piston.jpg
piston1.jpg
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Re: 1972 402 bbc pistons

Post by novadude »

Without knowing all the details about deck height, gasket, etc, I am thinking that compression ratio with 292 heads and such a small dome would likely be 8:1 at best. Probably lower if pistons are deep in the hole and a thick composition gasket is used. I'd plan on replacing the pistons with the 65-69 style with larger domes (21cc mentioned above).
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Re: 1972 402 bbc pistons

Post by mag2555 »

Here’s some info to guide you.

If you are shooting for any one of these four of compression ratios then these are the number of total CCs you need above the piston top.

8 to 1. 118.2

8.5 to 1. 110.3

9 to 1 103.4

9.5 to 1. 97.3

I have never been in love with the dome shape I have seen on 396/ 402 pistons to compensate for big chambers,and the 5/64” rings are extremely old school.

If it where me I would try and sell those heads and pick up a used set of smaller chamber aftermarket heads and freshen them up with a valve job and new seals if need be.

If you can get a 9.5 comp going by means of a aluminum head you will be far ahead of what you could have otherwise with dome pistons.
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Re: 1972 402 bbc pistons

Post by novadude »

If it were me I would try and sell those heads and pick up a used set of smaller chamber aftermarket heads and freshen them up with a valve job and new seals if need be.
That becomes tricky with a 396, as there are not a lot of ~100cc aftermarket head options that would work well on a 396. Early closed chamber 396 heads would be a good way to get away from big domes. I think 292 chambers start our around 110-112 cc, so by the time you add a gasket and deck height, you are easily down in the 8:1 range. Especially when you consider most common composition head gaskets are designed with ~4.35" (or larger) bores. Very few small bore head gasket options, since most people are using blocks with 4.25 or larger bores. I'd probably just swap pistons for the ones with the 21cc domes.
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Re: 1972 402 bbc pistons

Post by BillK »

Looks very much like the same dome on a L2383F TRW Thats a 13.9 cc dome .110" tall ?

With a 110cc chamber they are only 8.5 to 1

Of course that will vary depending on deck hgt, gasket etc
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