GM Camel Hump Heads (492) & Chevy 355 With TRW L2252A Pistons De-Tuning Queston

Took way too long to look up suffix # ending HW so I didn’t breaking down the forwarding numbers. Casting number say’s either 1969 327 or 350. Suffix HW say’s factory 350 HP 350 cid 4 Barrel 4 Speed.

 

Wow, I would have never thought that what you mentioned above with regards to milling the piston domes down was even possible. Wouldn't that compromise the strength of the pistons. Of course that would only apply to the pistons if the domes are not solid, but then you would have to keep a very careful eye on what the actual weight of each piston after the machining to keep them all within an acceptable + or - finished weight.

Doesn't seem like a very practical approach unless you have your own lathe or access to one where the milling could be done very cheap.

I think in my case of having those KB pistons for a swap would be a more prudent approach.

I think I will look into the cylinder head swapping approach you mentioned by investigating the 76cc heads available which will make things a little complicated.

 

Johnny, I'm told this engine was the actual factory SBC 350 that was in the 1970 Chevelle my relative owned.

I believe he bought that car new from the dealer and it had the factory 4-speed transmission. I have the transmission, with the bell housing, a aftermarket Lakewood ****ter shield, Z-bar, pedals and Hurst shifter with the linkage.

Do you have any opinion on the bore scope picture showing the cylinder wall and the top part where theirs clearly an area where the piston isn't making it way up to the very top of the deck.

 

If you mean has the block been decked? You’ve been looking at the answer all along.

 

I used to mill the TRW forged pistons I ran in the race car. Never had a problem with a piston being weak.

 

Johnny pointed it out, so not decked, which works in your favor if you move forward to lower the static CR.

edit: I meant to add about you CR #’s you posted with the KB pistons, because I didn’t see it mentioned.
Some after market manufacturers post the numbers with the block zero decked.
So what you need to do is find out the piston volume, plug in .025 (should be close enough) for them down in the cylinder, then add the head gasket, and head chamber volume.
You also need to know the wrist pin height of those pistons, as many come .020? Different in height which moves the top of the piston further down into the cylinder.

 

Yes, I was aware that having the block decked usually means that the stamping on the block can get removed, but it's not always the case if the machine shop just skims the deck a few thousandths to just clean it up and remove any light warping.

But yes you verified what I was referencing.

 

Gotcha you.

I was just looking at some aftermarket heads to get a bigger combustion chamber size and I'm finding that a pair of complete heads are far more pricey than swapping out the pistons.

So to me, having the pistons sitting below the deck, as you pointed out, and roughly around .025 is a something that works in favor of doing a dished piston swap.

The pistons you are referring too being .020 wrist pin height are the TRW's in the holes or the Kieth Black 9002HC hypereutectic 2-valve relief flat top pistons that are 0.30 thousandths that I was talking about swapping into the block?

I know someone pointed out that the TRW pistons are forged while the KB pistons are cast and are a tighter fitting pistons.

 

The 350, 350 horse engine was only optional in Corvettes in 1969. There were two suffix codes for that engine, HW and HX, I have a HW short block in the garage. The HX code engines came in an air conditioned car.

 

Now you did it!

 

Forged pistons usually require about .005" piston to wall clearance. Those KB's will require only .0015" clearance. Your KB pistons would flop around in the loose bore terribly.
Won't work. Too bad though. I have KB's in a 355 for 10.31:1CR. It runs on 89 octane with no detonation. They are aluminum 64cc heads.

 

About time. This is killing me.

 

I used KB hypers once, never again for me, I know some people love them but they came apart on my Henry J's first engine. This engine had about 200 street miles and 4.5 1/8 miles p***es shifting at 5,000 rpm, next engine got forged pistons.

 

Ouch!......

 

Those 386 blocks were also used on 1969 Z/28s along with 4 other different block casting numbers which included the 010 block.... 1 er 2 different block casting numbers were made with more nickle (sp) for extra strength.....