compression poll. (for my setup)

[Aproductions]

so I have been hearing 8.5:1 and 9:1 piston comp back and forth.

for MY build.......manley pistons and rods, evo3 intake manifold, fp race manifold, HOLSET H1C, fuel upgrades, tial mvs external wg, act2600 w/ act streetlite and a 3'' exhaust....etc.

this is my daily driver but I don't put many miles on....after this is over and I get more money I will try to get a new daily or street bike.

I have 93 octane here and I think there is 94 too....so I will run them.

I have ecuflash and evoscan on a reflashable ecu.

I know I can do 8.5:1 with more boost and 9.1 with less boost but where are they the same?


if I have 350fwhp with 8.5:1 pistons on 24psi with no knock
and 350fwhp with 9:1 pistons on 21psi with no knock......then what is the difference really besides psi?



anyways choose what you would pick for THIS setup....I never go to the track but sometimes people get annoying on the highway and try to do pulls,.

 

[fede]

9.1 for my built that its almost the same set up.

 

[DSMnoobsause]

the reason people do higher comp is for the off boost performance. you will pull harder off boost and it might help on lag just a bit.

 

[rstchris]

9 for DD and 8.5 for more raceability. (if thats even a real word)

 

[slickers111]

I voted 9:1

 

[Aproductions]

9 for DD and 8.5 for more raceability. (if thats even a real word)

its a real word in my dictionary.....anyways I don't race what what about highway pulls?

 

[Aproductions]

9 for DD and 8.5 for more raceability.

so what about pulls on the highway? is that under raceablity or DD?

 

[cookmeup272]

I vote 9:1 as that is what i will be running when i go all out over the winter. It will help spool your turbo faster and give you more power when you arent in boost. Your tune just has to be that much better or you run the risk of blowing up.

 

[Aproductions]

yeah but what is the margin like between the 2

 

[cookmeup272]

What do you mean

 

[Aproductions]

i mean what is the margin of error for tuning between 8.5:1 and 9:1

 

[cookmeup272]

I can't tell you personally, but I know when I get to that point....I will be starting with a VERY conservative tune and going from there

 

[TSimage]

I don't know where that "raceability" crap comes into play but 9:1 isn't extreme enough to worry about it. It is simply better than an 8.5:1 setup. Its still pump friendly yet has the higher cr response many seek.

The real jump is 8.5-9.5... Picking a 9 over an 8.5 is almost a no brainer, especially with everyone moving to E85, higher compression is that much sweeter.

 

[cookmeup272]

They don't really offer E85 over here, and even if they did I don't think I would utilize it. But still, 9:1 is like you said a no brainer

 

[Strm Trpr]

What are you tuning the ECU with?
Having the ability to finely tune Timing and A/F Ratio is even more critical if you choose the slightly higher compression ratio.

 

[Aproductions]

aem wideband and ecuflash with a reflashable 99 ecu

 

[fede]

you should be fine with 9.1

 

[98GSXtacy]

9:1 definitely. Off boost performance will be much better and spool will be a bit quicker. Also, if you are able to and choose to go to e-85 in the future, the 9:1 will be much better with it than the 8.5:1. And as long as you are careful while tuning and don't just set everything up the same as a 8.5:1 tune, you should be fine. It's not going to change how the car is tuned or anything, you will just be changing different things in different amounts at different times.

 

[romeen]

Theoretically, 9:1 should give you a more linear power curve which would be a good thing since you are FWD.

 

[Strm Trpr]

aem wideband and ecuflash with a reflashable 99 ecu

Will you be able to monitor knock with a flashed ECU?

 

[rx7ttlm]

assuming that you can monitor knock, air fuel ratio's etc on your setup like I can with my DSMLink V3 +Zietronics stage 11teen (yes that's what they call it). Assuming your able to run a high octane 100+ fuel the benifit of the extra compression is debatable, but from 8-9 jump you can see 2-4% difference on a properly built engine. *two percent was gains we made in NA roadracing engines, and the 4 is what some people close to me claim on turbo apps* hence why people run 13:1 na, and 10/11:1 turbo race engines. I haven't done back to back tests(for obvious reasons) but the trend seems to support more compression is more power on turbo's too. But you may find above 9.4-9.5 it becomes less forgiving on tuning.

In your case, if one is cheaper buy that one? . The LARGEST difference I have seen in street pistons is the material and the forging. if the skirt of the piston is to thin and you hammer on it its going to crack. if your running really high cyl psi (high hp or detonation)and high rpm you kill wrist pins. Or you have someone that thought they would improve detonation resistance by lowering the compression / oil rings down into the wrist pin galley. Then those are the things you will notice most. I would guess that a lot of the people that have these cars (from what I have seen) don't know enough about the basics or take the time to maintain their car to where they have missfires from dumb shit like clogged fuel filters and almost every time its one of my dumb ass friends that doesn't think spark plugs are consumables and is scared to spend 8 bucks My DD engine is 8.8:1, runs great on anything assuming I alter timing for the type of fuel i am running 91 vs 100 oct

 

[cookmeup272]

Also the thickness of your headgasket will slightly lower your CR which could give you just a little more help if you go the 9:1 route.

 

[Aproductions]

Will you be able to monitor knock with a flashed ECU?

yes, i have the stock boost gauge setup to show knock