What kind of pistons do I have? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 08-01-2008, 05:26 PM
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What kind of pistons do I have?

I have what I believe is a stock SBC 400 (330817 block) and 882 heads. I have already tore the motor down and put it back together with new gaskets, intake, oil pump, etc because I always wanted to do it. I know someone worked on it before because the rods and main bearings were not standard. Also, the rods had the cylinder number stamped into the side to keep the halves matched up.

She ran fine and I was happy it did not explode When I went to check the valve adjustments I noticed the previous owner of the motor replaced the stock rocker arm nuts with polys (on stock press in studs). Well, one of the studs was broken right off, not horizontally, but vertically at an angle.

To make a long story short, I want to build a strong street/strip motor with new crank, rod, etc, but due to money that will have to wait. Since I could either pay to fix these smog heads or purchase new heads, I have chosen to spend a little $$$ on new heads and probably throw a little larger cam in to enjoy the car a little now. I was hoping to purchase heads that I could use on what I will call my future motor (probably a little m block). Is there a way to tell what these pistons will do with a new set of heads in terms of comression ratio? If these pistons are stock (sorry, I know nothing about piston lingo, flat top, valve relief, etc), it would appear the CR was probably around 8:1 with the 76cc 882 heads. If I purchased say AFR 195s or 215s and went with a larger cam, would the CR make it a complete dog? I have a 2500 rpm converter and 3:73 gears in the rear. If I went with the AFRs but went for a 65cc head would it make it much better?

I guess after all my rambling the question is how do I determine my CR with these particular pistons? Are there part numbers on pistons? I will also have to measure my head gasket and check to see if the block was decked (not really sure how to do this either).

Sorry for being such a newb, but I am learning.......very slowly.

Here are the pictures of my pistons.


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Old 08-01-2008, 05:56 PM
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The runner size of the heads has no effect on compression ratio, the combustion chamber size does, if you used 67cc heads with those pistons you should come out fine with around 9.5:1 compression. Add a decent sized cam around 224 duration @ .050, a set of headers and you`ll have a nice runner. Don`t go too big on the port runner sizes, or it`ll get soggy on the low end. me, for a basic street engine even so it is a 400, I wouldn`t go any bigger than 180 or 190 max. 400`s swallow up bigger cams, so the idle should remain good even with the bigger cam. 400`s make a lot of low end power which they are loved for. but since they have short rods, I wouldn`t rev it over 5500, and I would only rev it that high on occasion. Tune it up with the best components you can buy, use spiral core plug wires, tune it in, and you`ll have a low end stump puller as well as something that makes explosive mid range. Remember to break in the cam using oil with the needed additives, if not the cam will go flat in a rather short time. Regular off the shelf oil won`t cut it. If I`m not mistaken, Valvoline racing oil will work.
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Old 08-01-2008, 07:27 PM
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Thanks!

Right now I have a lot of good mid-high end parts for the combo. MSD Digital 6 ignition box and distributor, Aeromotive A1000 fuel pump and filter, 1-7/8" headers, Holley 750 carb, Edelbrock Performer RPM air gap intake and CSR electric water pump. No problem keeping the rpms down, like I said I want to have a little fun with the car now while I save to do the motor the right way.

Since I know nothing about pistons, what exactly does it look like I have? When I hear someone say flat top piston, I think a completely flat top without any valve indentation at all. Or do all pistons need some sort of valve indent which would mean what I have are flat top pistons?

Thanks again
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Old 08-01-2008, 07:30 PM
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You have concave dish top pistons. "flat top" pistons are referred to as a flat top with 4 valve reliefs being the most common, also they come in 2 valve relief types.
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Old 08-01-2008, 07:31 PM
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Got it, thanks.

I also assume you are suggesting using a cam up to roughly 224 at 0.050 since larger cams will move the power curve up past 5500 which will be useless for the current motor? I think I am starting to understand
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Old 08-01-2008, 07:33 PM
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is this piston make a good engine with vortec head ,3/4 cam, air gap intake ,header
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Old 08-01-2008, 07:48 PM
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Cool, thanks. Thought about vortecs but did not want to go for the new intake and rockers since I would not be able to use them down the road.
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Old 08-02-2008, 01:30 PM
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how to tell the difference between cast and ford pistons

How do you tell the differences between cast, hyper, and forged pistons by looking at them?
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