[Nyairguard]

picked up a 69 400 w/16 heads big valve ,,engine that was rebuilt with of course junk parts.... rebuilder cast pistons .040 in the hole. heads cc @ 75cc and going to use a felpro gasket set .040 crush thinking of .020 decking and run a forged .040 over piston and a 2802 or 060 cam of course arp rod bolts and resized there are hyper and speed pro forged I see so far??

[tom s]

Might be better to put a set of forged rods and not spend money on the cast rods.if you want to run pump gas figure how to keep your CR about 9.5.Tom

[chiphead]

In my last motor I built I used to set of Auto tech 4032 forged alloy. Nice thing about those is you can custom set all the parameters dish ring pack pin height pin diameter etc etc. If you do it right you don't even have to deck the block.

Choose target compression first then have the heads done and confirm chamber size before ordering pistons. I just put a 2802 cam in a 400 with 62 heads. I'll post an idle video when I get time

[25stevem]

You should take full advantage of the work you need to do and the parts you need to get to rebuild this 54 year old motor.

Common replacement SP Pistons are heavy and so are the wrist pins they ship with, as such you can gain performance by using lighter ones of a different brand and you should run a forged piston so forget the hypers.
Along with the light Pistons comes more performance from stepping up to modern narrower ring that have less frictional hp losses and can reduce oil temps due to that.
Once again if you go with a aftermarket rod your gaining the performance plus of a faster reving motor due to there lighter weight then a stock rod and your gaining stafty as you rev the motor higher.

I can not these days see any logic in rebuilding 54 year old connecting rods just because they still happen to work for the moment!u
I mean if you needed to replace the oil furnace in your home and you got your hands on one 54 years old , yet worked would you still use it?

[tom s]

X2 on the Autotec pistons,Paul K on this site can help you with them.Tom

[Vid]

Interesting thread. Just curious what is considered a heavy piston for a 400?

I’ve used those 8 eyebrow SP pistons in a previous low budget 400 build, I never weighed them but they seemed pretty chunky.


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[Nyairguard]

Not really sure, why can’t they just make pistons that were made like the originals that would make things easy


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[b-man]

The 400 was introduced in 1967 which happened to be a cylinder head design transition year.

Both the new big-valve 2.11”/1.77” heads with 14 degree valve inclination angle and the older design small valve 1.92”/1.66” 20 degree heads were offered on 400 engines depending on the horsepower rating.

So that’s the reason why those 8 valve relief 400 pistons were made by the aftermarket, to insure compatibility with either cylinder head design. The valve inclination angle determined where the valve reliefs needed to be. The set closest to the center are for the 20 degree heads and the outer set for the 14 degree heads.

Kinda sad that the lousy 20 degree heads that came on the low performance station wagon and big Pontiac engines are still driving the universal design of the cast 400 replacement pistons. Having a decent cast 4 relief replacement 400 piston geared towards the big valve 14 degree market would make sense, forged pistons aren’t necessary for most of the moderately built street 400 engines.

When 1968 400 engines were produced they used both big and small valve heads with the same 14 degree valve inclination. The 350 started production in 1968 and used the same type of 14 degree head as the 400. The 326 engines were last produced in 1967, all 326 engines had the early style 20 degree heads.

[25stevem]

Let’s look deeper into why a modern forged piston is a big advantage.

The tried and true old school TRW 2262 400 cid replacement .030” over piston weighs in at 589 grams and ships with a 250 gram wrist pin for a total of some 839 grams.

A common JE brand piston is 504 grams and if I recall right ships with a 194 gram wrist pin for a total of 698 grams, or a 20% savings in weight.

When you look at the fact that the loads seen by the crank, bearings and most importantly in terms of running stock rods increase with the square of the rpm you can hopefully see that even a 50 gram reduction in overall piston weight is a huge plus, and this is without even talking about reduced friction from thinner more modern rings!

When you square the loads from let’s say 2500 rpm to only 3500 rpm they have then doubled.

If you have the least concern about cast iron rod longevity then you need to take advantage of running lighter pistons fitted with lighter wrist pins.

In the least if your sticking with pistons that use a .980” heavy pin at least opt for replacing those with thinner wall lighter ones.

These pistons also only have 2 valve notches making getting up to a higher compression ratio a tad easier.

Oh, did I mention that the motor will rev up a good bunch faster also!

[unruhjonny]

Originally Posted by Nyairguard

Not really sure, why can’t they just make pistons that were made like the originals that would make things easy

To add to what has been said, I believe that the eight valve relief cast pistons showed up in the mid 1970’s as an OE part, and essentially replaced all the earlier different valve relief cast slugs;
So to answer your post, they do make cast pistons like originals/OEM - but as I have understood it, the last version of OEM cast piston was the eight valve relief slug.

Additionally, the TRW slug WAS the OEM RAIV slug, and you can still get it.

[Goatracer1]

If you are going to replace pistons and rods then go all the way and install a Butler stroker kit. You get everything new and end up with a bigger engine.

[Nyairguard]

Thought about that ..probably not way much going with a stroker


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