im just looking for little input from whom ever.....

i got a 97 blazer that after descovering a leaky head gasket between the oil and coolant, i was just gonna replace the gaskets and be done with it. but of course like any person with a little extra money starts getting ideas...so i ordered up comp cams cam kit (p.n. K18-119-4) and roller tipped rockers and push rods kit (p.n. RP1412-12) also got a hypertech programmer..wich i am still waiting on the programmer and cam kit..i should get them next week...anyways...today has been a good day..my transmission desides to start slipping on the 3-4 clutch..and being the person i am..i hate rebuilding trannies with the same junk that failed..so in a couple weeks when my taxes come back im ordering up a 700-E Raptor Junior transmission from transmissioncenter.net another $1800. so i figured since im going to have most of it all apart why not replace the pistons...even though its only got 130,000+ on it i might as well get it done so im not ripping it all out in 20,000 or so..as i am hard on my vehicles....im going .030 over weather it needs it or not. i was thinking of putting stock pistons, but for the cost of some chevy 350 speed pro piston 10.68:1 at 64cc..and i think 4.3L has 65cc. correct me if im wrong...why not go with those for a little more grunt....any suggestions would be great...or if anyone knows where i can find piston directly made for the 4.3L vortec also any ideas on the cost to have the block bored and honed...i havnt had the chance to call any places around here.......

 

I believe that the stock compression ratio is something like 8.5:1 (ha, that's what my Bonneville is without the blower). It's low for sure, but 10.68 might be alittle much. If you are going that high, you may need to get a custom PCM rather than just an off the shelf hypertech. The hypertech only modifies the pcm given stock internals. Your fuel and spark curves will be way off with a cam, rockers, and high compression pistons. Not to mention that the high compression pistons will cause MAJOR detonation if you don't 1) retard the timing at higher RPMs (requires a custom pcm - not the hypertech which actually advances the timing at higher rpm - VERY BAD!) or 2) dump more fuel in to cool the combustion temps (again custom pcm for modified fuel curves).

I would go with a more street friendly 9.5:1 pistons and do your 0.030 over bore. Also, while you're down there, get your crank polished and deburred and get your block align honed on the mains. Have your pistons/rods balanced out so they are all the same weight and have your crank balanced to the weight of the pistons/rods. If you really want a stout bottom end, have your cylinders torque bored. They put a torque plate and tighten it down to mimic the clamping distortions when your head gets torqued down. All of this is commonly referred to as blue-printing a bottom end.

Another thing is to have your pistons coated (or buy them coated). Putting an antifriction coating on the piston skirts really helps out for both the life of the engine and it's efficiency.

One last thing would be to have the heads ported and possibly install larger valves. Awhile back I remember reading about a buildup of a 4.3L v6 in Hotrod Magazine (Article HERE). They got some MUCH better flow numbers with a port/polish on the heads and by installing larger valves. Nothing impressive by means of flow numbers from heads, but an impressive increase in flow over the VERY restrictive stock heads.

 

i thought the stock compression was 9.?:1...but you do have a good point about the piston....but i thought 10.5:1 was the "street" pistons...and like you said with the hypertech and the igntion. advancing the timing.....as much as i would like to do all the port/polish ect this is still a daily driver. and just want it to be a reliable engine with a little kick. so after reading all the information you gave i think stock pistons will be my choice given what i already have...thanx swartlkk....

 

Well, just for a point of reference, on my Chevelle, I'm running 10.25:1 pistons with double hump 2.02"intake heads. The heads are pretty much stock, but port matched to my intake and my headers. When I'm just driving it, I retard the timing and run lower octane gas. When I want to play, I advance the timing (I've got 2 marks on the firewall) and run premium and get a much added kick in the pants with this setup. But 10mpg on premium sucks! Much better to handle 10mpg on the cheap stuff and deal with the power loss.

 

Stock IS 9.2 or better, up to 9.5. Varies some by year, injection, heads used. Yes the bottom end will need some serious attention, how much is up to your wallet. I dont actually like overbore to 30 right away. Your motor might not require it. Have the machine shop do the lowest possible for a good job, perhaps saving yourself one more trip before 30 over is reached. Your block could possibly last for 400, 000 or more miles if not too much is taken out all at once. leave it to the machine shop as to what you need. Getting lighter pistons and rods is nice, but a higher compression will leave you in trouble at the gas pump. Getting the correct size is listening to the machine shop also. Checking end gap on those rings is very important here. Buying quality rings pays a huge dividend at the end. Be sure to break them in correctly.

Getting the rpm range up and fully functional is your goal. You may find your injection lacking somewhat with all those changes. Be sure when you get her going that you dont run too lean on the top end. Check those plugs, soon.