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Discussion Starter · #1 ·
Has anyone had a chance to try out some higher compression pistons in the car yet?

Been thinking about when we do get around to replacing the pistions going with a bit more compression to help things a long.
 

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Discussion Starter · #3 ·
stowaway said:
higher compression means you can't run as much boost, kind of a tradeoff for more non-boosted power.

that was kinda the idea to a point, you wouldnt have to run as much boost. give more pwr out of the stock set up or people with stock turbos as well.
 

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Personally, I think raising compression and lowering boost pressure would be a waste on an engine like ours. Our turbo spools so quickly as it is, response and bottom end torque isnt an issue. Raising the compression would give you better throttle response and more torque on demand when not in the boost, but are these traits you feel the car lacks? I dont. The small bump in throttle tip in response and non-WOT torque from more compression would be in vain when you came into the boost...because there would have to be less of it.

my .02
 

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Tell Cox you can not run higher comp pistons on a turbo car...its all in the tune and how you set up the car. Though low compression IS safer it is not better.

You could get some JE's which I think are 8.8:1 or some thing close to that mark, either way they are higher than stock yet still a safe level :).
 

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MikeCandler said:
Tell Cox you can not run higher comp pistons on a turbo car...its all in the tune and how you set up the car. Though low compression IS safer it is not better.

You could get some JE's which I think are 8.8:1 or some thing close to that mark, either way they are higher than stock yet still a safe level :).
Sure you can run higher compression ratio...you can run anything you want, but like you said, it's all in the tune. Most high powered hondas run 9.5 cr. Higher compression ratio will provide a more efficent use of the amount of gasoline you use. Meaning 400hp on a high comp/low boost motor will require less fuel than 400hp on a low comp/high boost motor.

The negative is that a low comp/high boost motor will make more power based off of the specific octane you are running. If you are building a race car, or a car that will only see C16, this is not an issue, because the octane will take care of whatever boost pressure you want (too an extent) regardless of the higher compression. For someone building a street car that will rarely, if ever, see race gas. Low compression is usually the best choice because (to paraphrase) low comp/high boost will make more power on 93 octane than high comp/lower boost will.

If you run race gas exclusively, then high compression/high boost is the way to go ;)

One more thing - high compression means higher cylinder pressures at the same horsepower. No one on here is really pushing the limits of the engine cylinder pressure wise so it probably doesn't matter to you, but it is another thing to take into account.

HTH.

/Mark
 

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I will do 8.8:1 down the line sometime. Nothing wrong with this.
 

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Jakencub said:
Has anyone had a chance to try out some higher compression pistons in the car yet?

Been thinking about when we do get around to replacing the pistions going with a bit more compression to help things a long.
Shaun's drag car was 11.0:1 ratio with a T-72 (??) trim.
 

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How high are you talking? What engine management? Most high power built DSms run 9:1 compression. You can still get away with plenty on pump gas. I certainly don't recomend going any higher than that, especially if you have no way to take timing out of it. Higher cylinder pressure are a bad thing in my book. More liklely to detonate, harder on the hard parts..... the list goes on..
 

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you are addressing just swapping the pistons leaving the stock head alone? Id have some exhaust porting and a lot of cleanup done, that would take out a lot of potential detonation issues before i tore apart the bottom end as well. you can shave the head a bit while you are at it. more compression can help spool a bigger turbo if this is still a street driven car.
 

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drewsrt said:
higher compression pistons would be fine im my opinion. Something just a little bit higher. Also since when do most high powered hondas run 9.5 compression ratio? Anyway I've thought about this also but I dont think id do it if i was going to upgrade the turbo.....but id up the CR just a titty bit to get more power out of the stocker. I did read in a magazine (SCC i think) that the prototype srt motor had around 8.6- 8.7:1 or something like that. Made 15 more hp stock. It's in the article about the srt-4 vs boosted svt focus.
The 832whp 2.0 liter B18C1, 689whp B18C1, 522whp H22, 2 430ish whp D16s I've helped with or built...and future 600ish whp B16A, and 500whp K20 I'm building all do... :dunno:
 

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oooooooh thoooooose....wouldnt it be called a b20c1? lol anyway most of the ones ive seen are running around 9 or a little less. You said "most" and well that's what ive seen...then again im not around honda's too much except for a few buddies so i could be wrong. Anyway what's up with the low k20 number? If you can get 430 out of a d16 im sure u could pump more out of that thing if u really tried ;)
 

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Heres an excerpt from this site. It has very good info that eveyone can learn from.
*EDIT*I would post more pertaining to the topic at hand, but I might get in trouble, so just go to the link if you want to read more.

http://www.matt3t4.20m.com/photo5.html


EFFECTIVE COMPRESSION & CHOOSING A MOTOR!!!

what is "effective compression?"

Effective compression is the sum of the static compression, plus the additional compression added to the cylinder via some kind of forced induction tool. Static compression is the amount of air inside the cylinder that is compressed. In order to find what the static compression is, e.g. 12.5:1, one must find the ratio of cylinder volume at BDC, and TDC. An equation for effective compression is as follows:

((boost psi / 14.7) + 1) x motor compression = effective compression


The next argument that people usually bring up is that a higher compression is bad for turbocharging. Well, if you understand the concept of effective compression, then you should understand that this statement is entirely incorrect. A higher compression engine makes more power in NA form. So, why do you turbo guys think that a lower compression turbo motor makes more power? Does that make any sense when you really think about it? A turbocharger is a power adder? So why deplete power that was there to begin with? The answer I usually get to that is "So I can run more boost!" Well, sorry to rain on your parade, but more boost does not always equal more power. Check out this mathematical example of effective compression:

A motor with a 10.0:1 static CR boosting 10psi
10psi/14.7psi = .68
.68 + 1 = 1.68
1.68 x 10 = 16.8 effective CR

A motor with an 8.5:1 static CR boosting 10psi
10psi/14.7psi = .68
.68 + 1 = 1.68
1.68 x 8.5 = 14.28 effective CR

Now tell me who is going to make more power? The higher CR motor, or the lower CR motor?

So, maybe add more boost to the lower CR motor, right? Wrong...

A motor with an 8.5:1 static CR boosting 13psi
13psi/14.7psi = .88
.88 + 1 = 1.88
1.88 x 8.5 = 15.98 effective CR

Now you see, even adding 3psi of boost, still does not equal the effective CR of the higher compression, lower boost motor.
 

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drewsrt said:
oooooooh thoooooose....wouldnt it be called a b20c1? lol anyway most of the ones ive seen are running around 9 or a little less. You said "most" and well that's what ive seen...then again im not around honda's too much except for a few buddies so i could be wrong. Anyway what's up with the low k20 number? If you can get 430 out of a d16 im sure u could pump more out of that thing if u really tried ;)
B20 is already an engine (out of a CRV) Thin cylinder walls, doesn't take to power too well. The motor I'm speaking of is a sleeved b18 big bore. Technically you can call it a b20, but then there is confusion.

About the K20 number...I make what numbers the customer tells me to make :) Also I don't know if anyone has made 500whp out of a K20 yet...then again I haven't looked into it either.
 

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hemidakota said:
Shaun's drag car was 11.0:1 ratio with a T-72 (??) trim.
They also run 50 lbs of boost and nitrous. I don't see any of us doing that anytime soon.

Darrell uses a turbo on his car that is worth way more than a new SRT-4.
 

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Discussion Starter · #19 ·
was thinking a port and polish clean up of the head, intake larger tb, psi-fi gts61, water injection as well then replace stock pistons with like 9:1 since the pistons always seem to be the first engine part to go up.

all running the psi-fi PP unit for now. that is the long term plan just to see how it would all go.
 

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Ok, chew on this.
Stock piston compression in the SRT is 8.1:1.
The new Wiseco's I'm going with are 8.6:1. For those of you worried about detonation, I'm also having Nemo port & polish the head & intake manifold, Iceman 60mm tb, water injection, and the Mopar Stage 3 turbo, plus some high-performance coatings on parts from Swaintech.
I'm reeeeeeeeally interested in seeing what this will put down.
 
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