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Discussion Starter · #1 ·
A stock LS has around 9:1 compression correct? If I replaced them with type R pistons giving me a little over 11:1 compression ratio, how much power would I get from that over stock.

So basically comparing horsepower numbers from a stock 9:1 LS to a LS with 11:1 compression.

Thanks.
 

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i think the rule of thumb is ten hp per full point u go up......... or at least thats what some people say.............

so in theory it is a 20 hp gain from 9.1-11.1..................... (but i could be wrong.....but thats just what i heard)

but i dotn think ur compression will go up to 11.1 with type r pistons.........
 

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Discussion Starter · #5 ·
Why wouldn't it give me 11:1 compression?

I am not looking to keep it this way for long. I think my rings are going out so I figured I would get some higher CR pistons to replace my LS pistons. Then I plan to possibly put a VTEC head on there but for now I need the pistons and rings. The head can wait until the summer.
 

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Discussion Starter · #7 ·
Take a look at this:

http://www.bojangz.com/calculator/

With the P73-00 JDM Type R Pistons, a B18B block, a B18B head, a 81mm bore, and a 1 layer head gasket you get a compression ratio of: 11.3:1. Stock LS's have a CR of 9.2:1.

I think it would definetly help me over stock LS pistons.
 

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I would say you gain about 4% for each full point of compression you raise it. If you plan to go all motor, and a big all-motor set up, sounds like an ok idea. With an LS, bearing in mind the rod-stroke, its much better suited for a turbo set up. just a thought...
 

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yeah i was planning on jdm itr pistons into a b18a (my next project) from jdmhondaparts.com, maybe the spoon balanced set, not that it would make any difference.
anyways, an increased compression ratio would show you more power in it's self, but where it really starts to shine is when it's used in conjunction with a good set of cams. if you were running an 11.3:1 compression ratio with a set of crower 403's or 404's then you'd really see a nice increase in power. combine that with a mild to wild port and polish job and the power would really start to show. increaseing compression it's self show's minimal gains, when used in conjunction with other tricks it starts to shine.
 

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Discussion Starter · #10 ·
I was just going to throw a set of type r pistons in now to get my compression back up and then put a VTEC head on maybe this summer. I wouldn't run an all motor LS. I am aware of the rod-stroke ratio. I know that it is not suited for a high revving engine. I am not planning on revving up past 8000. I plan to get the type r pistons, a VTEC head this summer, and then soon after that get some beefier cams. This setup will give me all the power I need under 8000 RPM's.

It is just a project that I want to work on just to see what kind of results I can get. If I go through with it this summer I will fill everyone in on my results.
 

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USDM ITR: 10.6:1

JDM ITR: 11.0:1

LS: 9.2:1

I wouldn't recommend dropping just the pistons. Pistons should be put in built motors. That would be like dropping a turbo and boosting like 15lbs with no intercooler. Everything works together and installing one component will not be beneficial.

Also, the Type R pistons will fit, but the piston has to be cut to be installed onto the LS crank. And, not to mention the LS crank will be under tremendous stress with the new psitons. I wouldn't recommend this considering the crank runs about $1000.

-John
 

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Discussion Starter · #12 ·
It will work, the pistons are interchangable.
 

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mmmm..... consider the ls have a head cc's of 45 :) puting a set of p73 pistons in there wouldnt help much :) unless you also swap out for a gsr head :) dont you guys knows these thing? :)
 

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Discussion Starter · #14 ·
First of all you are telling me that putting a full 2 point higher compression pistons in a LS engine won't do anything? I find that hard to believe.

Second, I plan to put a VTEC head on this summer. My compression is low now and I have the money for new pistons so I was going to do the pistons now, and when I start working again this summer I plan to swap the head. I was just wondering what kind of power I would make out of a LS engine with type r pistons.
 

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hybridone said:
USDM ITR: 10.6:1

JDM ITR: 11.0:1

LS: 9.2:1

I wouldn't recommend dropping just the pistons. Pistons should be put in built motors. That would be like dropping a turbo and boosting like 15lbs with no intercooler. Everything works together and installing one component will not be beneficial.

Also, the Type R pistons will fit, but the piston has to be cut to be installed onto the LS crank. And, not to mention the LS crank will be under tremendous stress with the new psitons. I wouldn't recommend this considering the crank runs about $1000.

-John
Huh??? I'm still trying to figure out what you're talking about.

First, pistons are in all cars, not just built engines. I dont understand how just replacing pistons will be the same as "dropping a turbo and boosting like 15 lbs. with no intercooler". Please enlighten me. If you mean that you need certain work done such as honing, or balancing before your pistons can be put on, then, yes, you are correct. But if you mean just replacing a different piston, then no sir, you are not correct.

Second, when did you have to cut a piston to fit directly onto a crank?? Hopefully, that was just a typing error ;) . Besides, I really doubt that changing a c/r of 2 points is really going to ruin your motor. If anything, I would think you would worry about your rods or your cylinder walls before your crank. Even if you did somehow "break a crank" or something, a new small block will run you considerably less than "$1000". I can find one for a few hundred or less.

First of all you are telling me that putting a full 2 point higher compression pistons in a LS engine won't do anything? I find that hard to believe.
What she probably means is that unless you have upgraded cams/valvetrain and a better flowing head, you probably wont see the full potential of that 2 points. It will obviously give you some horsepower, but it will be very limited to what it could be.
 

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who's a she?
and exactly what are you talking about cutting the pistons to match the crank or some shiz like that? the rods connect to the crank you dufus.... and if you're asking i'll be using the ls rods on the pistons, i honestly don't expect to be reving this motor past 7500 rpm.
 

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Discussion Starter · #17 ·
That is what I am saying. I am not planning on building a high revving motor. When I am finished I will let you all know how it turned out. Maybe this will make you believers.
 

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deMad10 said:
First of all you are telling me that putting a full 2 point higher compression pistons in a LS engine won't do anything? I find that hard to believe.

it doesnt matter what you believe :) jk , anyways dont you understand? just because the p73 have a cr of 11:1 in a b18c its doesnt mean that it have the same cr in your b18b :)
 

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NOSed_b18b said:

Huh??? I'm still trying to figure out what you're talking about.

First, pistons are in all cars, not just built engines. I dont understand how just replacing pistons will be the same as "dropping a turbo and boosting like 15 lbs. with no intercooler". Please enlighten me. If you mean that you need certain work done such as honing, or balancing before your pistons can be put on, then, yes, you are correct. But if you mean just replacing a different piston, then no sir, you are not correct.

Second, when did you have to cut a piston to fit directly onto a crank?? Hopefully, that was just a typing error . Besides, I really doubt that changing a c/r of 2 points is really going to ruin your motor. If anything, I would think you would worry about your rods or your cylinder walls before your crank. Even if you did somehow "break a crank" or something, a new small block will run you considerably less than "$1000". I can find one for a few hundred or less.
Yes, that's what I meant. My mind wasn't totally into the thread when I posted so sorry for the vagueness. Yes, all cars do have pistons, what I meant to say was that it would not benefit him to just drop higher compression pistons without having other work done to the motor. This is just my opinion, I never said it wasn't do-able. And I messed up when I said the piston had to be cut to fit the crank. When I called Pann Auto in San Diego about 2 years ago to inquire about the LS/VTEC swap, I told them I wanted to drop JDM ITR pistons and they said that I could do one of two things: 1) Cut/modify the piston to fit onto the LS conrods (sorry for the mistake again) or 2) Machine the crank and install the ITR pistons and conrods. They said that option 2 would compromise the life and performance of the crank. And if you call Acura, the price of a brand new crank is around $1000. I realize nobody would pay this and you would probably find it used, but it is still this price so I don't think I was wrong there.

-John
 

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ok that last reply made more sense thanks for clearing things up... and you're right it's when you combine higher compression with other things that it really starts to shine.
anyways, what exactly did they say you have to machine to get the itr pistons and ls rods to match up? this is kind of disturbing to me because i wanted to use the itr pistons for a "cheap thrill" so to speak but if there's a ton of machining to do i might as well get some good forged pistons...
 
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