what works best..high compression low boost or high boost lower compression? what arethe pros and cons of these two setups and which would see better gains, just want to get a plan together before i start my project...thanks in advance!

you have less tuning to do if you have a lower compression engine with boost.

that sounds like a plus to me...i was thinking about going with a 8.8:1 ratio but i was wanting to consider all possibilities...

Originally posted by white_eclipse97
what works best..high compression low boost or high boost lower compression? what arethe pros and cons of these two setups and which would see better gains, just want to get a plan together before i start my project...thanks in advance!

I agree with ^^^, lower CR and higher boost would be a lot easier to tune. It also saves the chance of "accidentally" over boosting on a higher CR. You ever seen a head get blown off the block??? Funny shit let me tell you. Glad it wasnt mine.

Higher CR with lower boost is not going to be super hard, it's just a question of how much attention you want to pay to the vitals in everyday driving. If you're cool with keeping your car tuned on a daily basis, then you can go with the stock or better CR. If you'd rather just turn up the boost and drive it like you stole it, drop the CR to 8.8 or so.

NOTE:
Just because you run a lower CR piston doesn't mean you don't have to tune. I would think you should have to tune just as much running 15psi on 8.8 as you would running 7psi on 9.6. Lowering the CR doesn't prevent the threat of detonation - it just backs you away from that edge a little bit. You turn up the boost enough and you'll be right in the same situation either way.

:thumbsup

Personnally, I am going the hi comp, lo boost route. Believe it or not, I want power with good mileage :).



-------jezreel
hrc stage 1, sfmu, ml, prokits, egt, boost gauge, apexi tt, turbo xs rfl, haydans tranny cooler, costum dp, dr. uber groundwires, dynotune fp gauge. gst muff, turbo spoiler

nothing like driving with the windows down and the music low: i love hearing the turbo spool, swwwhhhttt!!!!
thanks for www.kaptainmyke.com for the sig hosting :thumbsup

high compression w/ boost tuned real nice ownz you. non-experts like me and most everyone else go the low comp route though cause like everyone said... it's easier to tune.

I am only really looking to run 8-10 psi. I figure that will be a fun daily driver. Plus, once you get up to the 15-20 psi range, reliability becomes an issue.


-------jezreel
hrc stage 1, sfmu, ml, prokits, egt, boost gauge, apexi tt, turbo xs rfl, haydans tranny cooler, costum dp, dr. uber groundwires, dynotune fp gauge. gst muff, turbo spoiler

nothing like driving with the windows down and the music low: i love hearing the turbo spool, swwwhhhttt!!!!
thanks for www.kaptainmyke.com for the sig hosting :thumbsup

i just bought some je pistons which turned out to be 9.6 stock compression.... i was originally going to run 15-18 psi on 8.8 pistons, what would the equivalent be with 9.6...what kind of tuning are we talking about? help me out a little, im debating if i should keep them and go high compression, or sell them and get low compression... lets keep this thread going
doug

I've been juggling this idea too. My question is, does higher compression give you more torque too, and would lower comperssion lower that torque? Also what would you have to pay more attention to if you went with high comp. with low boost? EGT's be higher, increased chance of detonation i'm sure, would pulling and advancing timing be more critical?

Originally posted by sd240
I've been juggling this idea too. My question is, does higher compression give you more torque too, and would lower comperssion lower that torque? Also what would you have to pay more attention to if you went with high comp. with low boost? EGT's be higher, increased chance of detonation i'm sure, would pulling and advancing timing be more critical?

the difference between the two is power dropoff due to the atmosphere and spool time/powerband

For example we'll use two (arbitrary setups)

7lbs on 10.5:1

10lbs on 8.8:1

We'll say that the high compression (HC) makes about 250, while the Low compression makes 270 (LC)

I'd prefer the HC which would most likely be the faster car because it has to spool less to make a similar amount of power, but it would spool it's 250 before the LC motor made it's 250 (before spooling the extra boost to make the rest of the 270). the LC motor would have peakier curve, but still quite useable at only 10lbs. It's earlier power would give it a broader HP/TQ to play with with more "on tap" while driving, imagine your 420a now plus 80 ponies, it's pretty quick compared to dropping the compression and having to build the extra pounds of boost to play catch up, besides proffesional turbo'd cars are using high compression. With this idea in mind the phenomenon increases with hgher boost so 20lbs on 8.8 won't be as tough as 16lbs on 9.6

Something else worth talking about is that at higher elevations the HC motor would acquire less power dropoff as compared to the LC because it's heating less air and running higher compression. The raised compression would make it stronger NA plus the fact that it's pressurizing less air. In higher elevation they HP levels would actually be close to the same but the HC motor would develope it sooner/longer.

High compression turbos motors are always the way to go but the draw back is the gas octane limitation. I'm in cali so I opt'd for the lower compression because my engine was big enough to compensate for the compression loss and to run low octane under low boost as well as being able to spool more pressure quicker than a 2L at similar compression

Originally posted by Skrilla
besides proffesional turbo'd cars are using high compression

um, skrilla? wrx's are 8.0:1, thats low, not high. 911 turbos are 9.4:1 if i remember right. you must mean full race like f1 cars or something. all of this is relative to what size turbo you have, yes...high compression will make more power at a said boost pressure on the same turbo with lower compression, i think you lose what...5% per every point lost off the CR? cant remember off my head right now, i'm probly way off. the point of low comp is to dodge detonation at higher boost pressures. i'd love to see, say 30psi pumped into a motor with reasonably high comp 9.5-10+ without the hammers of hell knocking on its doorstep, especially in CA



_________
96 talon esi-t
san clemente, ca


as needles of ice
are the ill winds' talons
the coldest of shadows
they seep unto the bone

silent souls leave .308 holes

how do i tune a car with high compression (9.6:1), what do i have to look out for, whats the worst case scenario that happens with high compression detonation....pretty much, how do i avoid detonation...i have 93 and 94 octane around here...thanks
doug

Originally posted by lickscissors
how do i tune a car with high compression (9.6:1), what do i have to look out for, whats the worst case scenario that happens with high compression detonation....pretty much, how do i avoid detonation...i have 93 and 94 octane around here...thanks doug

do you know what detonation is? if not i can summarize for ya. basically..... the air and fuel mixture inside the combustion chamber ignites in a in a controlled situation. the a/f charge is ignited by the spark from the plug after the initial spark, what occurs is known as a 'flame front', it moves from the spark towards the outside of the cylinder. Detonation happens when the air and fuel that is ahead of the flame front ignites before the flame front arrives because it becomes overheated. thats why water injection is helpful because in esscence, it keeps the intake temps of the combustion chamber low enough to avoid detonation (pre-ignition, knock, etc etc) you have to think here, gas is explosive obviously...and the heat in there is enough to want to rile things up a bit, even the glowing hot tip of the plug can induce knock. under knock, the combustion becomes out of control and normally produces a pinging noise, or a "knock" noise when the conditions get worse. theres a reason they call knock the 'hammers of hell' theres not really anything that can withstand it for a length of time.

so basically theres two factors here...keeping the intake charge COOL (water/alcohol injection) and running higher octane gas. higher octane gas has a lower tendency to pre-ignite (thats the reason it suppresses knock, its harder to get lit in other words)

so 93 octane would probably be ok, but with a 14b at 18psi thats going to be heating up the charged air substantially, look into a homemade h20 kit to spray at a set boost pressure, its really easy....very safe, been around for a long ass time, and will give you some peice of mind as to the 'hammers of hell' owning your precious motor

:thumbsup



_________
96 talon esi-t
san clemente, ca


as needles of ice
are the ill winds' talons
the coldest of shadows
they seep unto the bone

silent souls leave .308 holes

thanks alot turbo8u....i always looked at h20 injection as dangerous, which i guess it could be if you dont do it right....i always knew water couldnt be compressed, so if you shoot too much in there at the wrong time, you could do some serious damage....but it looks like im going to try that.....with high compression (9.6) i wasnt planning on 18psi...maybe more like 12-15max... i was planning on using the dsm 450 injectors...do you think thats still necessary for 12-15 on HC?....i still havent gotten a rightup or anything on how to hook up the dsm injectors....with 12-15 psi on the 14b, will i still have to look for water injection...i dont have a problem doing it, i just want to know what to start with and build it up from there.... i guess it looks like im going with HC
doug

Originally posted by lickscissors
will i still have to look for water injection...i dont have a problem doing it, i just want to know what to start with and build it up from there.... i guess it looks like im going with HC doug

its a really simple system that a lot of people just assume 'oh you're going to waterlog!' lol thats a bunch of misinformed nonsense. theres only a few items, but check the DIY section here:

http://www.h20injection.com/forum/phpBB2/


_________
96 talon esi-t
san clemente, ca


as needles of ice
are the ill winds' talons
the coldest of shadows
they seep unto the bone

silent souls leave .308 holes

Originally posted by turbo8u

Originally posted by Skrilla besides proffesional turbo'd cars are using high compression

um, skrilla? wrx's are 8.0:1, thats low, not high. 911 turbos are 9.4:1 if i remember right. you must mean full race like f1 cars or something. all of this is relative to what size turbo you have, yes...high compression will make more power at a said boost pressure on the same turbo with lower compression, i think you lose what...5% per every point lost off the CR? cant remember off my head right now, i'm probly way off. the point of low comp is to dodge detonation at higher boost pressures. i'd love to see, say 30psi pumped into a motor with reasonably high comp 9.5-10+ without the hammers of hell knocking on its doorstep, especially in CA _________ 96 talon esi-t san clemente, ca as needles of ice are the ill winds' talons the coldest of shadows they seep unto the bone silent souls leave .308 holes

It's 4% gain or loss for every point you gain or lose, and yes I was NOT talking about production cars, I was refering to RACE which happen to run 10.5, 11.5 and 13:1 compression, of course their octane is 120+ sometimes

Originally posted by white_eclipse97
what works best..high compression low boost or high boost lower compression? what arethe pros and cons of these two setups and which would see better gains, just want to get a plan together before i start my project...thanks in advance!

High Compression and High Boost make the most power together. The high compression low boost, and vice versa stem from the days of points and carbs. With points and carbs, the edges of what we could get away with were not well defined, so you had to stay back farther from the edge. This ment running low compression with high boost, etc. We are running a drag bike with 14 to 1 compression with 28 psi of boost and it lives just fine, because we have tight control over timing and fuel. Keep in mind your running fuel injection and computer timing when picking your choices.

lots of detonation info here
http://www.armond30.com/adp/smartquestions.html
just scroll down