WhiteLightnin83

well i spun a rod bearing on my mildly rebuilt 350 sbc and the whole top end has been redone already with bigger cam, intake, new carb and such. since i'm gonna be replacing the crank and a rod bearing or two anyways i was wondering if i would be able to buy a new set of pistons that would bump my compression to like 10:1? i need to know if i can do this with stock heads(since they are too expensive for my wallet at the time) and without replacing anything else besides the pistons. secondly, i'm wondering what set of pistons anybody would suggest i get and thirdly, i'm wondering what kind of power increase i could expect from this if its possible? the bottom of the motor is at the moment still stock. any help?

Damon

When you say a "stock" 350 I assume you mean an 87-up 350 TPI engine, right?

If so, your 350 TPI heads have 64cc chambers and it's pretty easy to get compresion up around 10:1. Regular old 350 4 valve relief flat tops and a GMPP .028" composite head gasket will get the job done for you. Yes, you can change them without changing anything else. Brand of piston is at your discretion and budget.

Power increase over stock (9.3:1) compression will be modest with no other changes- maybe 10 HP, but the bottom end torque increase will make it feel like a lot more than that. Raising compression is good for making a motor feel a lot more "snappy" in the lower-mid RPMs.

WhiteLightnin83

when i said stock i meant its a stock carburated 350(edelbrock intake, holly 650, bigger cam, headers, and minor dress up items), not tpi. i can't bump the compression to around 10-10.5:1 and still be ok? and thats all i'll get is around 10 hp out of it? also one more thing, what is the stock cc head size for this motor?

92RS305#2

i personally would look at getting a different set of heads than pistons, while getting smaller chambered heads and domed pistons can both boost compression if you get the right heads you can allow the engine to breathe alot better than those stock heads. correct me if i'm wrong guys

BOZS89IROC

If you want a little more power you could get longer conn. rods. Stock 350's run 5.700". Longer rods do 2 things they allow the rods to spend more time pushing the rod up instead of to the side, and they allow the piston to remain at TDC longer which makes for more efficient combustion. But they give up acceleration a little due to the rods being a little heavier. If you go with shorter rods it's just the opposite. You get faster acceleration but give up a little power. Heads would be a great improvement as would headers, high flow cat, and a cat back system.

Otherwise you can swap out the gasket like Damon said.

transxtreme

Retard!!!! longer rods + stock crank n pistons = boom. Get some domed pistons, mill the heads, or get the thin head gaskets.

WhiteLightnin83

well first of all, i already have headers and a hooker super comp muffler system so thats already done. secondly, i don't think i could offord heads... isn't a good set of heads gonna run me well over a grand? i want to keep my budget around like $400 on this rebuilld... i can't buy domed pistons and bump my compression to like 10.5:1 on stock heads and such? if so, what pistons would you suggest and what cc size do they need to be?

transxtreme

For what you are doing I strongly recomend having a machine shop mill your heads and get the thin gasket to get to your goal. A nice set of pistons will cost you 400 and well over that it itself. If you are set on getting pistons speed pro sells some for around 250 a set I believe. They give compression ratios depending on what size heads you have, which would be 64 cc's.

BOZS89IROC

I don't know who you are calling a retard. It's done all the time. You don't have to run forged internals to run longer rods. What would make them go "boom"? The compression? No. The same is going to happen when you run a thinner gasket. Not to mention the fact that he said he was replacing the crank anyway.

64cc comb. chambers on your heads is correct. But telling them you have chevy 350 heads will be good enough.

But be careful if it's a first gen. 350 then it won't handle compression ratios over 10.0:1 very well. Anything over that and they can start detonating and force the knock sensor (if equipped) to retard the timing. If it doesn't have a knock sensor then it will just detonate until the internals give up. LT1's have reverse cooling which cool the heads better allowing compression ratios of 10.5:1 and over to be reached fairly easy. First gens are any 350 built prior to the LT1's.

transxtreme

Dude go buy yourself a honda and get off this board. Who said anything about forged internals? Sounds like hes replacing the crank bearings not the entire crank son. Detonation from a thin gasket? NOT. Small block heads are not all 64 cc chambers either. GEN I blocks dont handle over 10.1 huh. Tell me I dont have 13.1's in my 388 . Knock sensor on his carb motor? Right.

DarthIROC

I didnt read this whole thread, but what I scanned through I didnt see much for an intelligible post.

Alright, you dont ahve a TPI motor, Im guessing you probaly have a 350 out of some random 70s vehicle. You more than likely have 76cc chambered heads, that not only destory your compression but they flow like a smokers lungs.

While you could boost compression with just pistons, and or milling the heads I dont reccomend it. I dont like domed pistons they can sometimes lead to problems. You can get all the compression you need out of a flat top.

I reccomend buying a different set of heads, as soley boosting the compression will show some gains, but if you have those huge chambered heads anyway you have to mill the hell out of them. You want them around 64 CCs should net you around 10.1 which is fine for the street. And like I said those heads are gonna flow horribly anyway, just invest a little cash in a better set of heads taht come with smaller chambers. I see people all the time showing great results with vortechs, and they are very reasonably priced.

As for the longer rod argument. You can run a longer rod on the stock crank no problem. I think most gen I blocks can handle 6.0"s, maybe a little clearancing on some blocks. However when you buy pistons (and dont re-use the stock pistons) buy pistons made for the rod length you have.

WhiteLightnin83

ok.... sooo can we come to a conclusion as to what size heads i have? lol, some say 64 cc and some say 76 cc and i don't have a clue... how can i find this out for sure? i don't know exactly what year the motor is... the car is and 83 so maybe they put a newer 350 in it, i don't know. i know its not the original motor though, originally a 305 was in the car. mainly i need to know which heads i have. i don't think i could offord to have them milled right yet, atleast not till summer when i work full time. exactly how much does it cost to have them milled? well i've been looking at a kit in summit for a little while and its a "sealed power engine rebuild kit" by speed pro and it pretty much just consists of a set of pistons with a all the gaskets i'd need for a rebuild. providing i have 64 cc heads i can get hyperreutectic pistons with a compression ratio of 10.72(this is based on a .030 bore though, does it really matter?) and you can buy the kit in standard bore as well as various oversizes. this package is only $310 so thats within my price range and it seems like a pretty good deal. now i just need to know what size heads i have and can i bump my compression this substantially and still be ok? what kind of power increase can i expect out of something like this?

gun4hire

I think that is exactly what was left out of BOZS89IROC's post.

To get the size/type of head, you need to get the casting # off them. NEVER make any changes until you know what you are working with. Depending on how badly damaged the crank was, you may be able to have it machined and use the appropriate oversized bearings. Again, you have to know what you are starting with before making any decisions. Personally I would not use longer rods - just rebuild the bottom end and use the right combo of head/gasket to get the desired comp ratio.



P.S. There are several cast iron performance heads that cost less than $1000.

BOZS89IROC

Well if you don't have a stock cast crank than what do you have?

Maybe you should read the posts before you reply.
Again Not reading the post. I didn't say you would get detonation from a athin gasket. I said SBC's (stock) typically don't do well with compression ratios over 10.0:1. Anything over could cause detonation. I asked what would cause the engine to go boom...a higher compression? No. You will get a higher compression ratio using a thinner gasket as well as longer rods. So if the "boom" you talked about was from the higher compression ratio than you would get it either way.



Once again not reading. I didn't say all small blocks heads are 64cc's. I said his heads are 64cc heads. But telling a good machine shop they are stock chevy 350 heads would be good enough. Any good machine shop will automatically know the comb. chamber size, int. and exh. valve sizes, etc.

Is you 388 stock? I doubt it. Do you have stock internals, ignition, cooling system, and heads? Or do you just believe detonation is just an unexplained occurance inside an engine.
I have a 84 Z28 H.O. Does that mean anything to you? No? How about L69? Still nothing? O.K. let me spell this out for you. 305 cu.in., Rochester Quadrajet (that's the carburator), and the best part of this message...it came stock with a knock sensor.

Now I came here to give information I've learned from: 1. experience and 2. reading tech books and manuals. None of my understanding of engines comes second hand from friends or occasional people b.s.ing about engines. If I have given info that is just plain wrong I think there is a more intelligent, mature way to let me know. As for you, I don't know were you get your info from but I know what worked for me in the past. This is my fourth camaro I've had to mess around with and try different things. So the least you could do is extend me a little courtesy as I would extend to you. Or just keep your mouth shut.

WhiteLightnin83

ok so i have to look at the i.d. numbers on the heads to find what size chamber i have... there is no other easier way to do this? where are the numbers found? any other answers to all the questions i asked in my last post? thanks for everything so far guys... i dont' mean to start an arguement though...