tell me about pistons...

[Turbo6Smackdown]

Does anyone here, have measurements I would need, to go shopping for pistons?
I guess things like pin diameter, compression height, ring lands width, and bore. And what are the tolerances for these measurements? This would be for a mild build up in a stock 109.

 

[bison]

Does anyone here, have measurements I would need, to go shopping for pistons?
I guess things like pin diameter, compression height, ring lands width, and bore. And what are the tolerances for these measurements? This would be for a mild build up in a stock 109.

You would have to measure these things. No one can do it from behind a computer. You need to know you rod length and desired compression ratio. Plenty of off the shelf pistons will likely fit you application. If your doing a mild build up you should retain the stock pistons. Stock rods are 5.95", stock stroke is 3.4"

 

[Turbo6Smackdown]

I see. (I knew you'd chime in. and glad too) The reason I'm seeking extra's, is because I want to build at my own pace, while I learn. So that the buick isn't down while I'm tinkering. Her bullet's going to Mr. Diers for a real rebuild. These parts I seek, is at my own pace, when it's convenient. When I finally assemble the short block parts, I will begin my first journey into the lower half of engines. (hopefully, it'll be in school, which I've just signed up for)

 

[bison]

The deck height on untouched stock blocks has been measured by a couple members recently. Im not sure what it was. Id definitely measure it carefully before ordering pistons if your looking for exact numbers. If you want to have 9:1 compression with a piston that has 25-27cc dish you will need to be at or very close to zero deck on a 3.8 bore and have smaller than 50cc heads and thin head gaskets.

 

[49-blues]

What do you consider thin gaskets? .020",.030",.040"?

 

[bison]

what do you consider thin gaskets? .020",.030",.040"?

.040

 

[Turbo6Smackdown]

The deck height on untouched stock blocks has been measured by a couple members recently. Im not sure what it was. Id definitely measure it carefully before ordering pistons if your looking for exact numbers. If you want to have 9:1 compression with a piston that has 25-27cc dish you will need to be at or very close to zero deck on a 3.8 bore and have smaller than 50cc heads and thin head gaskets.

Uhh, do I want 9:1 compression? lol. Actually, bone stock would be fine with me. (which is...? i forgot lol)
And 50cc heads? Is that stock I'm taking it? :redface:

 

[bison]

Uhh, do I want 9:1 compression? lol. Actually, bone stock would be fine with me. (which is...? i forgot lol)
And 50cc heads? Is that stock I'm taking it? :redface:

More compression = better everything but will reduce the detonation tolerance a lot. If unsure about it then stay around 8:1Stock is a tick under 8:1. Stock heads are 49cc's i think. Not positve though could be 47. Maybe someone will CC a stock set. I would but all mine have different valves and combustion chamber mods so they arent stock cc.

 

[Turbo6Smackdown]

Yea, I hear that "better everything" thing on raising compression... Though, tell me this bison; Why is the phrase "NA, run high compression. forced induc, stay with ultra low compression." soooo prevalent? I read it everywhere.. and while talking to a guy at the car show a month ago, he was considering putting a turbo on his sbc 73 camaro, and he said the same thing. I said that I heard different. I remember reading someone on this board typing, "there is no down side to raising the compression". So now I'm confused. Though, I believe you, over most other people.
Can you explain to me exactly how raising the compresison on our engines, helps us benefit? Because I may want to take advantage of this as well. Plus I really want to step up my technical knowlege of engine internals and nuances. (if you have the time)

 

[bison]

Yea, I hear that "better everything" thing on raising compression... Though, tell me this bison; Why is the phrase "NA, run high compression. forced induc, stay with ultra low compression." soooo prevalent? I read it everywhere.. and while talking to a guy at the car show a month ago, he was considering putting a turbo on his sbc 73 camaro, and he said the same thing. I said that I heard different. I remember reading someone on this board typing, "there is no down side to raising the compression". So now I'm confused. Though, I believe you, over most other people.
Can you explain to me exactly how raising the compresison on our engines, helps us benefit? Because I may want to take advantage of this as well. Plus I really want to step up my technical knowlege of engine internals and nuances. (if you have the time)

There is a detonation limit for every combo/ engine design based ont he type of fuel they are running. You can gain a decent amount (especially in heads up racing) bumping the CR. You cant run 12:1 and 20 psi on gasoline though. If you have 2 engines nearly identical the one with the higher CR up to a certain point will have the most potential. My stage 2 is 10:1. Its a high octane application though. Most likely a straight diet of C16 over 20psi. Dont let the NA thing full you either. They have a detonation limit too. They will tolerate a higher CR than a boosted engine but still require a lot of octane in high CR applications

 

[Turbo6Smackdown]

What about, if I plan on running 15 psi, on slightly bigger turbo than stock, with alky. What do you think I could get away with?

 

[bison]

What about, if I plan on running 15 psi, on slightly bigger turbo than stock, with alky. What do you think I could get away with?

You would be better staying around 8.5:1 for an alky 93 application and run more boost. 3 psi more boost will make a lot more power than a jump from 8:1 to 9:1. Big jumps in compression ratio is one of the last things you would do. You do it when you have exhausted other options. My 9.3:1 engine will detonate at 14-15psi on straight 93 even with aluminum heads and conservative timing.

 

[Turbo6Smackdown]

Right. Got it. Thank you very much sir

 

[1chance]

May i ask a ?? in this post. Im wanting to put together a stroker 4.1, but all the stroker kits i see are for 3.8, and i need a larger diamiter piston for the 4.1. What would the piston dimentions be for a 3.65 stoke crank? Also i was wondering if using a 4inch chevy piston would save on cost, and what over bore size would that be on a 4.1?

 

[bison]

May i ask a ?? in this post. Im wanting to put together a stroker 4.1, but all the stroker kits i see are for 3.8, and i need a larger diamiter piston for the 4.1. What would the piston dimentions be for a 3.65 stoke crank? Also i was wondering if using a 4inch chevy piston would save on cost, and what over bore size would that be on a 4.1?

Need a lot more info to answer the first question. Need to know desired comp ratio, deck height, and rod length. 4" equals .035 over on a 4.1. That is a common thin to do even though it doesnt really save on cost because you need a quality turbo piston. In reality you need 6 vs. 8 so that is savings in itself unless you want to 2 spares which is a good idea.

 

[Turbo6Smackdown]

how much would he actually gain, strokin a 4.1. is it worth it to you bison?

 

[bison]

how much would he actually gain, strokin a 4.1. is it worth it to you bison?

Depends on his goals. There is some considerable gain with the cubes. A waste on a production block though. Stage block or TA block id be stroking it. No pun intended.

 

[GNBRETT]

Stage block or TA block id be stroking it. No pun intended.

U mean pumping it....

 

[1chance]

Need a lot more info to answer the first question. Need to know desired comp ratio, deck height, and rod length. 4" equals .035 over on a 4.1. That is a common thin to do even though it doesnt really save on cost because you need a quality turbo piston. In reality you need 6 vs. 8 so that is savings in itself unless you want to 2 spares which is a good idea.

Ok, the comp ratio as long as i stay below 9;1, and the 3.65 stroker kit i see for 3.8 come with 6.35 rods. Any stroker kit they are sell for the 3.8, i just want to know what the piston would be for the 4.1, same comp ratio, same deck height, i hear the 4.1s deck is .025 taller than the 3.8. I have inexpensive pistons in the engine i have now. Was thinking all chevy stuff is chaep and plentyful.

 

[bison]

Ok, the comp ratio as long as i stay below 9;1, and the 3.65 stroker kit i see for 3.8 come with 6.35 rods. Any stroker kit they are sell for the 3.8, i just want to know what the piston would be for the 4.1, same comp ratio, same deck height, i hear the 4.1s deck is .025 taller than the 3.8. I have inexpensive pistons in the engine i have now. Was thinking all chevy stuff is chaep and plentyful.

Do you want the pistons in the hole, at zero deck or out? Without that info you cant aquire a compression height. The only short deck 3.8 is the 109 casting all others were taller production or stage blocks. Theres nothing cheap about building a 4.1