first of all i need a misconception on my part to be cleared up.

now i know its possible to run a little higher comp piston with boost(10:1) but it is preferred to run lower comp

well i see after looking around they make 9:1 comp pistons but im not sure how much of a difference that will make.

now what i hear is the more the compression the more the power with boost and that is why the vtec engines are so great stock when boosted and blah blah...but i also hear that the lower the comp the better the hp result and the easier it is to tune...well what is the truth?!?!?! but in either case im looking for 8:1 comp pistons or EVEN 7:1...are they around? ive looked top to bottom to find them but it seems impossible to me....

 

OH my bad i also have a stock ls engine that im rebuilding to go big time turbo but also a dd...

 

https://honda-tech.com/zerothread?id=2044253
https://honda-tech.com/zerothread?id=2048569
https://honda-tech.com/zerothread?id=1765694
https://honda-tech.com/zerothread?id=1636494
http://www.evans-tuning.com/comp2.html

basically you want to be in the 9-10:1 area. lower compression will reduce cylinder pressures making it "safer" but 8:1 is way to low and 7:1 is just ridiculous.

 

yea but the 10:1 area is around stock for gsr and other vtec engines while the 9:1 is around what the b18 is and other D series engine...

 

most guys are staying in that 9:1 range because they can make safe power on it, but that limits the amount of power you can safely make on pump gas.

The lower the compression, the more boost you can shove into the engine w/o detonation (generally) but your off boost response is terrible....if you're not going to build an insane 800hp car, stay around the 9-9.5:1 area and you'll be fine

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VTEC_PRODUCTION &raquo;</TD></TR><TR><TD CLASS="quote">yea but the 10:1 area is around stock for gsr and other vtec engines while the 9:1 is around what the b18 is and other D series engine...</TD></TR></TABLE>

are you asking a question? did you check out the links? its gonna come down to personal preference, high comp will be slightly more responsive down low. you dont need to go lower than 9:1 and a good tune can make safe power at 10:1 as well.

 

i agree....there is almost never (if ever) a need to go lower than 9:1.

When i build my engine eventually, i'm going to run a 9.5:1 or somewhere in that range...i dont need 600whp and i want the low end response

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dpetro1 &raquo;</TD></TR><TR><TD CLASS="quote">

are you asking a question? did you check out the links? its gonna come down to personal preference, high comp will be slightly more responsive down low. you dont need to go lower than 9:1 and a good tune can make safe power at 10:1 as well. </TD></TR></TABLE>

ok thanks dude...just one question...i cant read the charts from evens tuning for some reason can you give me a quick rundown of what they say??? i think my monitor or eyes are bad...

 

basically the 10:1 makes more power at the same psi. also its noted that the 9:1 needed much more timing.

 

Cool thanks.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VTEC_PRODUCTION &raquo;</TD></TR><TR><TD CLASS="quote">yea but the 10:1 area is around stock for gsr and other vtec engines while the 9:1 is around what the b18 is and other D series engine...</TD></TR></TABLE>

yes that is true but that does not mean you have to go lower to be safe. STOCK LS compression is what MOST turbo vehicles run. i am around 10:1 on my setup. i like the low end gain. and a good tuner can work with it.

as stated above if your not goin for real high power 10ish:1 is acceptable.

hell there are guys boostin 11ish:1 and im sure higher. its in the tune.

lower compression gives more room for error in the tune and or a situation such as bad gas/lower octane than rated. for whatever reason

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by agrn93ls &raquo;</TD></TR><TR><TD CLASS="quote">

lower compression gives more room for error in the tune \</TD></TR></TABLE>

i agree that higher compression engines need to be more careful, but i really hate this statement. i hope whoever you are trusting/paying to tuner you car isnt making any "errors". higher compression will need to have less timing and more precise tuning of timing. i think almost anybody could dial in afr's, timing on the dyno is a dofferent story.

 

If an engine is going to detonate because of too much compression for the fuel being used, the tuner can only band aid the problem, not fix the problem. High compression and pump gas is not the way to go for turbocharged applications, low compression is MUCH more reliable.

Things happen in the real world, no matter how perfect the tune is, things are going to change. If your setup doesn't allow for any change without detonating (high compression turbo), then you're likely to have problems.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by agrn93ls &raquo;</TD></TR><TR><TD CLASS="quote">

as stated above if your not goin for real high power 10ish:1 is acceptable.

hell there are guys boostin 11ish:1 and im sure higher. its in the tune.

lower compression gives more room for error in the tune and or a situation such as bad gas/lower octane than rated. for whatever reason</TD></TR></TABLE>

i know guys who are some serious engine builders that run 13 or 14:1 and running supercharged, but this is in the donmestic carburated world...i dont really know how it works but the comp is so high and the blower is so huge oil is just getting spit out of the engine...

ever hear of a rap contest? no i dont mean hip hop...

 

just get some wiseco -18cc shelf pistons and call it a day.

 

go with at least 9:1 CR. anything less is going to be miserable to drive on out of boost.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VTEC_PRODUCTION &raquo;</TD></TR><TR><TD CLASS="quote">

i know guys who are some serious engine builders that run 13 or 14:1 and running supercharged, but this is in the donmestic carburated world...i dont really know how it works but the comp is so high and the blower is so huge oil is just getting spit out of the engine...

ever hear of a rap contest? no i dont mean hip hop...</TD></TR></TABLE>

this is usually done with alcohol.
even us t type guys back in the day ran 8, 8.25, 8.5 : 1 compression. but we also have 6 cylinders getting the car moving too.

8:1 pistons on an engine that makes relatively no torque down low would be even more of a slug in normal street driving.

 

Does anyone know how the quench compares on the two sets of pistons? Does going to 9:1 remove most of the effectiveness of the quench pads?

 

lots of us run vitaras that put us at 8.5:1 depending on the motor there used it, allows you a "wider tuning window" that will be more tolerant for boost and timing

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by CoreyR &raquo;</TD></TR><TR><TD CLASS="quote">go with at least 9:1 CR. anything less is going to be miserable to drive on out of boost.</TD></TR></TABLE>

I've done a ton of 8.5:1 B series motors that drive great and are super reliable at big power on pump gas.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by CoreyR &raquo;</TD></TR><TR><TD CLASS="quote">go with at least 9:1 CR. anything less is going to be miserable to drive on out of boost.</TD></TR></TABLE>

sure thing buddy.....

 

JDogg, funny how the tuners recommend low compression and the "tuners" recommend high compression, huh?

 

Hey Tony, in your experience, what is the pump gas limit on most 9:1 compression street driven turbo Hondas? I'm not building for a while, but i want to get an idea of what i'm doing before jumping into it.

The turbo i will be using will be approximately the size of the STC Silver Surfer or Borg Warner S258. I dont want anything crazy on pump gas because i still want streetability. Just wondering what you think is the limit on 93 octane w/ that setup...idk if there is enough info there for you but just wanted to know what you thought. Thanks

 

There are way too many other variables to put a number on the safe limit, but if the turbo setup is right, 350-400whp should be very reliable.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tony1 &raquo;</TD></TR><TR><TD CLASS="quote">350-400whp should be very reliable. </TD></TR></TABLE>

im sure we have all made more, but if you keep it in the 350-400 range they seem to run forever and you dont have to cross your fingers every time you go into boost.

ive done a few cars that make power so easily that we will run a "high boost" setting closer to 450....but its typically not driven at that boost level all the time.

race gas is cheaper than a new motor