9.0:1 questions or go 8:3.1

[AK_4g63t]

I bought a set of Wiseco 9.0:1 pistons along with a ton of other things when I first got my car with a blown motor. I'm now about to start the build again (1st time some things didn't go so smoothly) and I researched 9.0:1 compression and there are still some unanswered questions. In the future I want to run the FP3052 or FP3065 and I don't know if the higher compression pistons are going to do me more good than bad. This car will be a street driven car that will see the track only a few times a year (since it's 600 miles away). The bad thing is we only have 90 octane gas up here. I want to do a methanol set-up in the future. I guess my real questions are: (plan on 400whp)
-at what psi will I start to see knock with 9.0:1 compression?
-what octane will I need to run at 5psi, 10psi, 15psi, 20psi, 25psi?
-right when i get this car driving (everything stock except internals) will it be knocking with 90 octane at the stock turbo psi?
-should I sell the 9.0:1 and go with the 8.3:1 pistons instead?

All of everyones input would be MUCH appreciated!!! I just don't want to have to run my methanol kit 24/7 just to boost taking off from a stoplight because the kid in the stocker wrx next to me thinks he has something special...
-Donny

 

[Cs4g63]

You can run 9.0:1 pistons and a big turbo with 90 octane as long as you have an adequate fuel system and a good tune.

 

[95blackGsTurbo]

9.0 is the max you wanna go for pump gas. I would go with 8.3:1. It will allow you to run more timing and will probably net you more power than the higher compression would have.

 

[1g_tsi_awd]

Higher comp will lead to more knock unless you have a good tune. I would say go with 8.3:1, it would be better for a DD. Lower compression is easier to work with to a point.

 

[snox135]

You all ready own the 9.0:1 so keep them and save your money for more mods. They will give you more low end torque than the 8.3:1. Just keep the boost down until you can get the supporting mods for more boost. You can find a set of "yellow top" injectors which will help, I believe they are 500 or 510 cc and still run them on the stock ecu.

 

[Cs4g63]

The fact the EVO's come from the factory with 8.8:1 might help you figure out what you want to do.

 

[AK_4g63t]

Thanks for the input guys. I plan on buying a profec II bc, DSMlink, 850 injectors and a 255fp tonight. I want to know if I run the 90 octane & 15-25psi of boost if it's going to knock and if it does.. can i just adjust my timing for that or do i need higher octane? Also... how much harder to tune as well? This is going to be a daily driver and just a fun car to drive but still at the same time..... can own if I feel like it. I want real numbers from someone, help!
-Donny
*anyone want some Wiseco 9.0:1 std pistons for cheap cheap (maybe)?

 

[snox135]

With those mods coming I would still stick with the 9.0:1. Also if you are getting DSMLink just get 1000cc injectors.

Also don't forget the AFPR with the 255

 

[95blackGsTurbo]

You can always get meth/water injection to compensate for the high compression. It's like driving around on race gas all the time .

 

[wt71gas]

I would go with the lower compression. It is always easier to make more power by running up the boost a little bit. If you build a motor with too high of a compression ratio there is no way to go down if you get some bad gas or have to run some low octane pump gas. Lower compression will allow you to run shitty gas on the street and when you want to make more power you turn up the boost and put in the better gas. Hope that helps.

 

[AK_4g63t]

So what about:
-at what psi will I start to see knock with 9.0:1 compression?
-what octane will I need to run at 5psi, 10psi, 15psi, 20psi, 25psi?
-right when i get this car driving (everything stock except internals) will it be knocking with 90 octane at the stock turbo psi?
-if I run the 90 octane & 15-25psi of boost if it's going to knock and if it does.. can i just adjust my timing for that or do i need higher octane?
Thanks for all the help, -Donny

 

[Hop]

I'm not having any trouble with my 9.0:1 on my DD GT30r powered Galant. I'm hitting 80% IDC with RC550 injectors and 15 psi. No knock at all using 92 octane pump. I've since turned it up a bit to 18 psi but haven't datalogged IDC. I have some 770cc ready to go in but need a better fuel controller on the car first.

Isn't the air cool enough in Alaska year round to offset a couple octane points? I would think so.

 

[GVR4592]

So what about:
-at what psi will I start to see knock with 9.0:1 compression?

Impossible to know, there are too many variables.

what octane will I need to run at 5psi, 10psi, 15psi, 20psi, 25psi?

As high as possible.

-right when i get this car driving (everything stock except internals) will it be knocking with 90 octane at the stock turbo psi?

Most likely.

-if I run the 90 octane & 15-25psi of boost if it's going to knock and if it does.. can i just adjust my timing for that or do i need higher octane?

You could probably adjust the timing and boost but you'd end up with running some crazy low amount of boost. It wouldn't even be worth building the engine and running a large turbo if you're only going to use 90 octane fuel.

 

[AK_4g63t]

Thanks a lot GVR4592 and everyone else. I wouldn't be just using 90 octane only. I would use the methanol injection when it came time to really turn up the boost. I want to build a high boost car that can still be a daily driver. I don't have ANY tuning experience and it doesn't seem like it would be that hard. I'm a GM mechanic and I deal with timing, a/f, and sensors all day but I have never been able to change the values so that would be the tricky part for me to get use to. I'm going to go ahead and order 8.3:1 Wiseco pistons that way I can take my soon FP3065 to it's full potential! Again, thanks everyone.
-Donny

 

[nightspeed87]

9.0 is the max you wanna go for pump gas. I would go with 8.3:1. It will allow you to run more timing and will probably net you more power than the higher compression would have.

Precisely...

Me personally ( especially if you want to run 20 + psi on 1g timing maps on that octane value )

Id even throw a thicker head gasket on there as well, to knock compression down a little further from the 8:3.1 to bring it a little closer to the 1gs stock compression range..
( Assuming your head isnt shaved that is...)

Wait never mind I just realized you were a 2g, so yea with your stock timing maps you could run the 8:3.1 with no problem scratch the headgasket idea ( which is still good if your trying to run big boost)
or you could just run wiseco 8:8.1 compression pistons which is still close to your stock comp ratio..
You could get away with 9:1 also but more precise tuning would be nessecary.. Me personally im not a big fan of high compression on turbo cars unless its a strict well tuned race car only running race gas...
You dont gain much power from compression maybe 4 % max, youll get the biggest gains from boost and timing so id rather just have compresion low as possible to keep it fools proof and run high timing and boost..... Good luck.

 

[Hop]

I don't see what your concern is with the 9.0:1. It's all in the tune really. I put 8.5:1 in the Talon and now that I know how it's reacting should have gone 9.0:1 in that car as well. Have you thought about keeping the 9.0:1's and using your money to buy a better fuel controlling ECU?

 

[AK_4g63t]

I have thought about that but I'm able to return the pistons to the company and they will send me the lower compression ones with a 10% restocking charge ($45) which isn't bad. I've just been reading up on everyone saying that the really fast dsm's have compression in the 7's and I do plan on running high boost on this car. Maybe one day I'll buy a 1G and do the 9.0:1 and make it a track car once I get the experience and tuning part down. I just got my block and head back from the machine shop so hopefully I'll be on the road soon!
-Donny

 

[rhamlinii]

I've seen 10.0 to 1 motor make 400whp on pump gas, it's truely up to the tuner. However, I decided to go with 8.5 to 1 with the hope of running boost w/ Nitrous.

 

[Hop]

What do you consider really fast? ~55 psi Shep fast or 30-ish psi 10 second DSM kind of fast?

 

[nightspeed87]

Shep runs 55 psi? Whoa...

 

[AK_4g63t]

55psi is a huge amount of boost... a little too much for me. I don't know what the FP30's can run but I would love to try and use it to it's full potential. I actually think I want to build a fun street car, still reliable but able to push 450-500whp. I think I, never had experience with a turbo or tuning a car, will stay away from the 9.0:1+ for now but maybe one day...
-Donny
55psi.... Jesus

 

[GVR4592]

If you plan on using meth injection for high boost, there's no reason to go with the lower compression pistons. 9:1 is perfect for a daily driver, in my opinion, you just can't use 90 octane fuel. You won't be able to use 90 octane fuel with the 8.3:1 pistons either, so it's really just a waste to exchange them.

 

[AK_4g63t]

Well everyone says,"keep the 9:1, you can just tune it out" but I've never tuned. I work with the numbers but I've never 1, worked on a turbo charged vehicle and 2, never been able to change the timing and fuel pressure and all those other variables. So I'd rather keep the high compression where theres little room for error for another time when im more experienced with tuning and go with the lower compression since I'm a "noob". Also, this wasn't even my main concern. The main thing was... I don't want to have to run the meth. kit all day everyday. I want to run some boost all the time cause it's fun and with that in mind... am i going to have to run meth. from 5psi and up? Cause if I would.. how much is methanol? If I'm able to just run 15psi on 9:1 without worrying about knock due to my mad tuning skills, is this cause DSMlink is able to change ignition timing through some sort of function that alows several different timing settings throughout the rpm ranges? This, again, is my first dsm and I have not even had it running yet and I don't want to jump neck deep into some high maintenance, hard to tune, for the experienced dsm'r vehicle when I'm at the point where I can just switch out my pistons and make my life easier. I just spent a good amount of money buying all these engine parts to make a bullet proof 7 bolt (ha) and it would really suck to knock all day everyday unless I run meth. all day everyday as well.... thus making me go bankrupt buying high octane gas and meth. all the time when I can easily avoid it right now. If it's not that much harder to tune (since I will have all the supporting mods) and I will be good on 90 octane until 10psi+ then let me know and 9:1 i'll stay... guy's with 9:1, talk to me!
-Donny

 

[tkelly27]

I vote for sticking with 8.3. I think you've got the right idea, a little breathing room never hurt anyone when they are learning to tune, especially wtih an upgraded turbo on street gas.

It's not that huge of a step power wise either
http://www.fao.org/docrep/T0512E/T0512e0w.gif

 

[1g_tsi_awd]

In Europe they mainly run high CRs with high boost... You are gonna need a good tune. Anything can be done with deep pockets.