8.5:1 or 9:1 pistons

[Aproductions]

for MY build which would I be better off with, I've read some threads and they don't really go with my build.


Holset H1C turbo, rebuilt 7 bolt with what comp pistons?


like which it more power effective......most boost less compression, or less boost higher comp?

I use 93octane


also quick question......how many people have had problems with eagle rods...I always hear people spinning rod bearings with them

so would you prefer manley rods or eagle?

 

[Indian]

The people I know that have spun rod bearings with eagle was because they thought they could just slap them in their stock setup without properly measuring first. Eagles rods like mine sometimes come with wide spread journals.

 

[Aproductions]

oh ok thanks, what about comp? 8.5 or 9

 

[95eclipser]

8.5 has a deeper dish so you could run more boost, 9.1 you have a higher comp and could run less boost and make the same amount of power.

8.5 = 30psi 400hp
9.1 =23psi 400hp

this is just and example to give you an idea^^^^^

 

[Indian]

Well since you have 93 available,It wouldnt be such a problem running a higer compression. I personally have a lower compression since the only thing available around here is 91,and I didnt want to tune around timing being pulled all the time.

 

[Aproductions]

8.5 = 30psi 400hp
9.1 =23psi 400hp


yeah but where is it safe on each setup...like can I get an example of what conditions would be in the engine(knocking etc.)

is it better to run 8.5 with more boost or 9.0 with less?

 

[SBR Joe]

8.5 has a deeper dish so you could run more boost, 9.1 you have a higher comp and could run less boost and make the same amount of power.

8.5 = 30psi 400hp
9.1 =23psi 400hp

this is just and example to give you an idea^^^^^

You have the right idea, though your numbers are a bit misleading for the less informed, it wouldnt be that drastic

I recommend no less than 9:1 for any setup. Its not too high to where you need to worry about detonation, or running too much boost, etc. Like any setup, it all depends on the tune, it just depends more on the tune the higher you go in compressio. My 2g has 10:1 flat top slugs in it and im running over 25psi on 93 octane pump fuel, with no issues on a borg warner S256. Not sure of the power its making yet because i have yet to get my lazy bum to a dyno to dial it in perfect, but im shooting for 500+ on straight pump, just to give you an idea where high compression can go.

Yes, the higher you go, the more vulnerable you are to un wanted detonation, but as long as the tune is healthy and proper, you wont have any issues at all. But to your question, 9:1 FTW.

 

[BLINKY619]

they key is TUNE....

 

[95eclipser]

You have the right idea, though your numbers are a bit misleading for the less informed, it wouldnt be that drastic

In no way shape or form do i believe those numbers to be accurate, like i said it was just and example.

in every build the two key points i always pay attention too are

1. head gasket sealing
2. tuning

everything else will follow.

if your worried about knock in the engine get dsmlink, and set the check engine light to flash when link senses knock..

 

[Aproductions]

I have that with ecuflash.....so for 93octane....9:1 is better to go with, and I'll make the same power I would with 8.5:1 but with less boost.....with no more detonation?

 

[SBR Joe]

they key is tune....

pow!

 

[Aproductions]

I'm getting the head and block resurfaced though so wouldn't that up the comp too?

 

[SBR Joe]

I'm getting the head and block resurfaced though so wouldn't that up the comp too?

On a very minute scale. If youre only shaving a few thousanths off each surface, it wont make a difference that would ever matter. Especially assuming youre using a thicker MLS gasket with it anyways, it wont matter at all really.

 

[red_devil]

Yes Tune is all important.

For instance my future build I am considering going with 8.5:1 slugs due to my inexperience with ecmlink and it will give me some leeway for tuning it. I am also considering the fuel which is 93 only in my area so I want as much timing as I can get. Finally I have to consider that my turbo is more efficient at 25+psi so I have to factor that in as well.

 

[Aproductions]

anyone know when a holset h1c is effective?


and I think I wanna go with 8.5 with more boost but I could do 9 with less

 

[untouchablecc]

When you raise the boost pressure all your doing is increasing compression after a certain point. Which is the same concept as having higher compression pistons. The h1c is what im running on 7:8.1 which is stock 1g compression (super low). The holset h1c maxes out on how much it flows around 35 psi in a dsm bep bolt on housing. The real question is how far do i wanna push my setup. The engine will take more user error abuse from a lower compression and its less prone to knock. If your only concerned about hp and not reliability then your better off to go with the higher compression. Thats why the cars come factory tuned with lower compression so theres a less chance of someone blowing there new turbo car up by running 87 octane and turning the boost up.

 

[95eclipser]

just go with 9:1, arp head studs, felpro hg. and call it a day. i really don't think the grass is greener on the 8:5 side.

-what psi of boost are you looking to run?
-what kind of SMIM?
-injectors?

You cant go wrong with Manley rods had them on my first build they are great quality and perform great! Eagles are great also there just not as expensive.

 

[Aproductions]

evo3 intake manifold with 1000cc injectors and I have a 1bar spring in my tial mv-s external gate

so I'm looking at what is better for power and reliability....

like 8.5:1 with say 22psi or 9:1 with say 17psi....or whatever makes the same power. which is better for the engine...higher comp with less boost or less commp more boost or are they equal?

basically scale this for 350fwhp

sorry this is hard to explain

 

[jlr2196]

One point I haven't seen mentioned is the fact that higher compression gives the car a bit more "off-boost" throttle response which is desirable for some of us that run daily drivers. Speaking from experience, you can feel the off-boost response of higher comp setups. Which in turn seems to help decrease that laggy feeling when spooling up.

 

[95eclipser]

One point I haven't seen mentioned is the fact that higher compression gives the car a bit more "off-boost" throttle response which is desirable for some of us that run daily drivers. Speaking from experience, you can feel the off-boost response of higher comp setups. Which in turn seems to help decrease that laggy feeling when spooling up.

+1 on this statement

 

[Aproductions]

so you are all thinking I should be good with 9:1?

even though I use 93 oct......what if my tune isn't right on?


the only reason I am thinking 8.5:1 is because because when I'm not right on with my tune I dont want detonation


how can we find out what is the route to go. like which will see less knocking for the power...

lets say I have 2 of the same cars...same mods...same everything but 1 with 8.5 and one with 9 comp.....
this is just a example...I don't know the real numbers.

8.5:1 with 22psi on a h1c makes 350fwhp

and with 9:1 with 19psi on a h1c makes 350fwhp......

if both weren't tuned which would I be seeing more knock on/higher cylinder temps?

 

[jlr2196]

so you are all thinking I should be good with 9:1?

even though I use 93 oct......what if my tune isn't right on?


the only reason I am thinking 8.5:1 is because because when I'm not right on with my tune I dont want detonation


how can we find out what is the route to go. like which will see less knocking for the power...

lets say I have 2 of the same cars...same mods...same everything but 1 with 8.5 and one with 9 comp.....
this is just a example...I don't know the real numbers.

8.5:1 with 22psi on a h1c makes 350fwhp

and with 9:1 with 19psi on a h1c makes 350fwhp......

if both weren't tuned which would I be seeing more knock on/higher cylinder temps?

This is the "great debate" that people have argued about for years but here is my opinion on it based off of my experience.

Less compression with more boost equals greater topend horsepower and it has been proven you will make more power with boost, but again, this is topend power that is great for vehicles geared towards 1/4 mile use only.

Higher compression with less boost gives you more "useable" power throughout the rpm range (solid low to midrange power), better throttle response with less turbo lag, so this is very desirable in vehicles designed for daily street use.

So ask yourself what you want to use your car for...daily driver or are you more of a track car? It's really up to you.
As far as which setup is going to knock more, that's pretty much a wash because knock based off of to much boost, timing or higher compression is equally destructive.

 

[SBR Joe]

One point I haven't seen mentioned is the fact that higher compression gives the car a bit more "off-boost" throttle response which is desirable for some of us that run daily drivers. Speaking from experience, you can feel the off-boost response of higher comp setups. Which in turn seems to help decrease that laggy feeling when spooling up.

I will also add a +1 on this point. Makes stop and go driving a bit more pleasurable having to not goose it as much from light to light to accelerate.

 

[SBR Joe]

This is the "great debate" that people have argued about for years but here is my opinion on it based off of my experience.

Less compression with more boost equals greater topend horsepower and it has been proven you will make more power with boost, but again, this is topend power that is great for vehicles geared towards 1/4 mile use only.

Higher compression with less boost gives you more "useable" power throughout the rpm range (solid low to midrange power), better throttle response with less turbo lag, so this is very desirable in vehicles designed for daily street use.

So ask yourself what you want to use your car for...daily driver or are you more of a track car? It's really up to you.
As far as which setup is going to knock more, that's pretty much a wash because knock based off of to much boost, timing or higher compression is equally destructive.

This is true to a certain point. Ive had cars tuned with similar setups with stock slugs (7.8:1) and then setups running 9:1, they were both able to run the same amount of boost, obviously with the higher compression making more overall power and a bit faster spool. In terms of street driving most people are OK with running 20-25 psi and thats it, so unless its some big hoonker snail like a 40r or something, generally you can make the same boost on either setup. In this case, debating 8.5:1 or 9:1, its not a drastic enough of a compression difference to really affect how much he could run without having to worry about knock and detonation. though the extra .5 compression bump would most definately affect performance on a positive note, i dont see it limiting him compared to what he could do if he went with the 8.5:1.

Its a debatable subject for sure, but when its all said and done, its really going to depend mostly on turbo selection, his target boost level goals, and the effeceincy of his entire setup...and most importantly, the quality of his tune.

 

[SBR Joe]

so you are all thinking I should be good with 9:1?

even though I use 93 oct......what if my tune isn't right on?


the only reason I am thinking 8.5:1 is because because when I'm not right on with my tune I dont want detonation


how can we find out what is the route to go. like which will see less knocking for the power...

lets say I have 2 of the same cars...same mods...same everything but 1 with 8.5 and one with 9 comp.....
this is just a example...I don't know the real numbers.

8.5:1 with 22psi on a h1c makes 350fwhp

and with 9:1 with 19psi on a h1c makes 350fwhp......

if both weren't tuned which would I be seeing more knock on/higher cylinder temps?

Just go 9:1 bud. You get the tune good, youll be able to run 22psi on the 9:1 and still be OK....and make more power than you would at the same boost levels as the 8.5:1. Like i had stated in my previous post, its not a drastic enough of a change to make it have a great affect, not like it would be if you were debating 8.5:1 compared to like 9.5:1 or 10:1 like im running.