What compression ratio are LS2165 flat type .030 pistons. I'm having trouble finding them on the internet.

 

There's a lot more to compression ratio than piston crown design. Deck clearance, head chamber volume, and head gasket thickness are also significant factors. My old Speed Pro catalog does not list net dish volume, but it's probably about the same as the OE cast pistons as used on base engines, so I doubt if you could get more than 9-9.5 true CR out of them.

I suggest you search for threads started by me and read the compression ratio article. Those forged pistons are pretty expensive, and a more economical choice would be the KB 156 or 157 depending on your target compression ratio, which is a function of available fuel octane and DCR. If you want to give more details on your configuration and available fuel octane I can probably offer advice on a "not to exceed" CR that will still allow an aggressive spark advance map.

Duke

 

I can't find your pistons either. In your other post you listed L2165, this post says LS2165.

 

For some reason we have to go through a science class every time this gets asked. And yes the info is true. But for brevities sake and assuming you don't have heads cut way down, with shim head gasket 9.8:1 with .040 head gaskets 9.2:1. Let the fun begin.

 

That was close to the same answer you gave in his other thread on pistons/compression ratio.

I think the OP maybe can't find a listing on his pistons? Or what is his real question?

 

Here it is. Note compression height.

https://www.summitracing.com/parts/s...make/chevrolet

 

I just did a quick calculation this morning. I was thinking I had answered something just like this at 8.5 and 9:1

670 CCs swept volume
64 CCs head
5 CCs valve reliefs plus 3 CCs for deck
4 CCs for thin gasket
9 CCs for thick.

670+64+8+4=746/76=9.8:1
670+64+8+9=751/81=9.3:1 rounded

I think before I was using cast Pistons with the extra deck height figured in. I'm assuming these L2165 are forged.



If the OP wants closer then he'll have to post specifics, deck, chamber volume,which head gasket he's going to use.

 

Like Mike mentioned Speed Pro (Federal Mogul) has a part number L-2165 which has 5.4cc valve reliefs (dish) and compression height of 1.671": https://www.summitracing.com/parts/slp-l2165f/.

Also as 8 piece set with rings also is Speed Pro number 8-KL2165F: https://www.summitracing.com/parts/slp-8kl2165f40.

Yes the Federal Mogul/Speed Pro/Sealed Power catalogs are difficult to navigate.

Like Robert shows you have several volumes to use to determine actual compression ratio. It takes more than just piston dish volume. And the more accurate the volumes you use the more accurate the compression ratio calculation will be.

If you need more help just ask.

 

Yes I need help to determine comp. ratio. Heads 1963 194 valves have been planned, block has been decked, and .030 over. I'm using GM steel gaskets. Will this help determine Comp. ratio??

 

Your question has been answered in your other thread.

 

Your question has been answered in both threads. You say your heads and block have been decked. How many keys do I have on my key ring? If you don't give exact numbers you don't get an exact answer. If your block was surfaced or cut to 9.005 makes a difference of about 1/2 point of compression. If someone in the last 60 years decided to cut your heads to 58cc that makes a difference. Realistically you have somewhere between 9.3-9.8. If you don't like that answer post real numbers and someone may give you an answer, myself I'm done and now know not to reply to your posts!

 

Well P6 we can see the frustration is spreading and I can assume you can't post accurate volume numbers because you didn't know what you needed to record when you had the chance. My approach would be to measure the volumes with liquid which isn't expensive at all but can be confusing and difficult and complicated if you haven't done it before. So having a machine shop do it or someone you know help can get you what you want.
I say this because determining the head volume after head work is just guessing as who knows how much the heads were milled/shaved and what the new valve size has done to the volume. You need to take a piece of 5"x5" plexiglass and drill a hole in it. Then you can seal it on a head with petro-jelly to add windshield washer fluid (or iso-alcohol with food coloring) using a graduated cylinder. Head needs to be held level - with a level of course. So that's for the head.
Same situation for guessing at the volume above the piston. You normally need deck height, piston to cylinder crevice volume, piston compressed height, head gasket compressed height, piston valve reliefs (dish volume) for this but again you probably didn't know what to record when you had the chance. A short cut for the piston volume which is not nearly as accurate as using liquid is to put the piston at TDC and use a straight edge to measure distance between piston crown and straight edge with a feeler gauge. You may need to take several measurements in different locations to get a reliable number. Then you can use algebra for a cylinder to calculate the piston volume and add the valve reliefs volume (5.4cc) and crevice volume estimate, and head gasket compressed height to get a final total for the volume above the piston. But the the piston has to be at TDC for this.

If do measure those volume let us know and we can get you an accurate compression ratio. Have fun.

 

Short of coming up with all the info asked for, I'd think it a safe bet that working with the info supplied, even if he doesn't know if the heads/block deck have been cut, he won't have any problem with too much compression.

 

Myself, I have been surprised several times how much compression changes with just a few cc difference. Maybe if you plan for nearly 12:1 compression you can relax your requirements. And it takes very little money to get it right - more patience than anything.

What I did notice in the OP's profile is he has at least 3 and maybe 4 small block corvettes and 5 corvettes total. IMHO he is overdue for evaluating compression ratio and the skills required. Not trying to be patronizing here but rather give some coaching. I think many get into denial to easily having overlooked what some key skills for engine rebuilding are and what it really takes. I don't read any retaliation by the OP but rather some frustration. But we can only help those that are willing to listen. For us hobbyist types it's gonna be one step at a time. Full time mechanics can digest a lot more a lot faster so we just have to see where the advice goes.

And yes I'm a little bored right now.

 

I've tried to point that out in both threads. He can make a fine motor with them but says he wants a 360hp. Hard to make the same power as a high compression motor with a low compression motor.

 

So I have a 1973 350 block bored 60 over, but it has a 307 crank with 327 pistons (L2165’s). I have the double hump heads with the smaller valves (I believe). What or how would I determine compression ratio? Running a 500 lift cam (.512”/.497”) with 1.5 roller rockers.

 

It's ALL been spelled out in post 12. We cannot do it for you.