good compression for a 2.3 stoker

[tretiak]

ok im possibly going to be picking up a 90 tsi awd, it comes with a laser rs turbo parts car which i was thinking about making into a project car.for the laser i want to do a 2.3 stoker motor but i am unsure about what kind of compression i would like to do. i was thinking either 8:1 or 8.5:1. im just looking to see what everyone else is running to get an idea and see which would be better.

thanks in advance
zach

 

[andymoraitis]

The main consideration is what additional compression does to what's referred to as ECR (effective compression ratio). As an example, your 7.8:1 motor allows you to run higher timing and higher boost on pump gas while a 2G runs lower timing advance on higher compression. The more you raise your compression, the less boost and timing you can run, provided the octane is the same.

For every full point of compression, you can expect to pick up around 4% in terms of horsepower. Being boosted, this isn't much of a difference, but higher compression, although somewhat different to tune for timing, is much more fun on the street, especially on a stroker motor.

I currently run 8.8:1 and I can get away with 22psi on a turbo that makes a ton of heat (Big 16G). But, I have to run low timing advance (12 dgrees) to do it. The main concern for you is where the car will live. If it's destined for a lot of track duty, I'd recommend lower compression but if you're going to be on the street 99% of the time, higher compression can't be beat. If I had my choice, I'd have a 10:1 motor with a strong turbo running 20psi on low timing and methanol injection. That would certainly be a ton of fun.

Let me know if that helps,

Andy

P.S. Considering the minor difference between 8.1 and 8.5, I'd go with the 8.5 and tune it carefully. Something like DSM Link would be great in terms of customizing your timing curves to work with the compression increase. Besides, 8.5:1 is generally accepted to be the optimum turbo comrpession ratio although a bit more doesn't hurt.

 

[tretiak]

The main consideration is what additional compression does to what's referred to as ECR (effective compression ratio). As an example, your 7.8:1 motor allows you to run higher timing and higher boost on pump gas while a 2G runs lower timing advance on higher compression. The more you raise your compression, the less boost and timing you can run, provided the octane is the same.

For every full point of compression, you can expect to pick up around 4% in terms of horsepower. Being boosted, this isn't much of a difference, but higher compression, although somewhat different to tune for timing, is much more fun on the street, especially on a stroker motor.

I currently run 8.8:1 and I can get away with 22psi on a turbo that makes a ton of heat (Big 16G). But, I have to run low timing advance (12 dgrees) to do it. The main concern for you is where the car will live. If it's destined for a lot of track duty, I'd recommend lower compression but if you're going to be on the street 99% of the time, higher compression can't be beat. If I had my choice, I'd have a 10:1 motor with a strong turbo running 20psi on low timing and methanol injection. That would certainly be a ton of fun.

Let me know if that helps,

Andy

P.S. Considering the minor difference between 8.1 and 8.5, I'd go with the 8.5 and tune it carefully. Something like DSM Link would be great in terms of customizing your timing curves to work with the compression increase. Besides, 8.5:1 is generally accepted to be the optimum turbo comrpession ratio although a bit more doesn't hurt.

thank you andy that really helped me out considering that i do not have a clue what im doing when it comes to motors. but that will change soon since i am going to own a dsm. I know a reputable tuning shop about 5 minutes away from my house(psi motorsports).the owner frankie has been around dsm's for a while and he knows a thing or to about them since he built my friends motor for his 2nd gen gst. i was leaning towards the 8.5:1 and boring it .040 over.i plan on taking it mostly to maple grove and going to autox events. thanks again andy

 

[andymoraitis]

No problem. I was hoping that made sense. If you're going to autox, then the higher compression will be more fun and help to spool the turbo more quickly. Keep in mind that your turbo is also a prime consideration. A smaller turbo like an EVO III would give you the quick response for autox and still be strong on the drag strip. You could even run a 20G although it will spool later. For a dedicated drag car, you'd go much larger as evidenced by the amount of people running FP 3052's and 60-1's on their strokers.

It's a smart move to consult a professional since he'll be very helpful in recommending a combination to meet your goals.

Good luck!

Andy

 

[nightspeed87]

so in running 2g pistons on a basically stock 1g, (i have 190lph, afpr, ported 14b, 3in catless exhaust system, KnN, hacked mass, IC hardpipes, shaved head, ported polish manifold ports ) and since you say 1gs have more timing advance, does this timing advance automatically adjust after running it with the 2g pistons, or do you keep your 1g timing advance no matter what pistons you use as long as you keep down the knock..
And would you say, youd gain more power with more timing and less compression and more boost, or more power with more compression, and less timing applied with the same amount of boost.? ( I never plan on running over 20lbs anyways, and I didnt want to go as high as 9:1 because Im not goint to have the injectors or dsm link to supply initially, I dont even have safc or a logger yet...Plus I just want to get every hp per dollar I could with basically a stock set up... And will be on my ported 14b for a while, plans are not too much more than 300whp/300lbs of torque. Does this sound adequate for what im going for )

 

[andymoraitis]

Those are some very good and very valid questions.

Timing is not affected unless it's controlled by an outside source like DSM Link or an AEM. Provided that you're on the highest airflow map (above 2.1g/rev) you'll see maximum timing. It all depends on the ECU. You could run 10:1, retain the 1G ECU, hit that high airflow map and it'll try to run timing as if it was still a 7.8:1 motor. In short, the ECU doesn't know that you've raised or lowered compression and simply looks at your airflow numbers.

With respect to what makes more power, it comes back to boost and timing over compression. Let's be hypothetical and say that on a 9:1 motor, you could run 18 psi on pump gas and 16 degrees of timing before pulling timing from knock. On an 8:1 motor, you may be able to get away with 22 psi at 18 degrees of timing without knocking. A lot of this depends on your charge air temps and how cool you can keep that intake charge. But, in looking at both of these scenarios, the full compression point increase will only make an average of 4% more power than the lower compression setup, however the 8:1 motor can run more boost and more timing which will make more power than less timing and less boost on higher compression. In the presence of high octane fuel, the higher compression motor will make more power since the octane increase will slow the flame front and allow for higher timing and higher boost.

Another thing to consider is what kind of turbo you'll be running. If you're staying with a 14B, it's not a turbo that can run efficiently in the 25-26 psi range. In that light, I would go with higher compression and try to make as much power on the motor as possible while still keeping the turb efficient. You'll have to do a little work with the timing or perhaps use more octane to fight off the knock (depending on whether it's a 1G or a 2G), but it will spool the turbo a bit faster and be much more fun to drive. At 9:1 you could even run something that generates less heat in the air charge and is more pump gas friendly and have a great time with it (i.e. a turbo with a 3" compressor cover like a 20G, FP Green, 50 trim, etc).

Here's my best take on the situation since I have a stroker on an undersized turbo.

Stock 2.0 at 8.5:1 with stock cams: I ran 24 psi daily on 93 octane with 18 degrees of advance
Stroker at 8.8:1 with Comp 200's: I can run 22 psi on 93 octane at 12 degrees of advance ( I could try and run more, but the 16G won't flow enough air to keep up with the stroker)

Keep in mind that the 16G is a hair dryer when you push it past it's efficiency range and creates a hot air charge which doesn't help in fighting off knock. My overall impression though is that while the 2.0 likely made more power on pump gas, the stroker is SO much more fun to drive and has greater potential for what I want (a fantastic street car). As I move up my upgrade path, I'll either run a Green, 20G or 50 trim and since the charge air will see less fricition and temperature as a result of running a more efficient and larger compressor cover, I'll be able to run more timing at the same boost level (22 psi) on a turbo that flows much more air and thereby make considerably more power than I am now.

There's a lot of info in there, so feel free to ask if there's something you don't quite understand.

 

[nightspeed87]

Wow yea thats a lot of info to absorb...

Well first its good to know the ecu doesnt pull timing automatically just because you increased compression, so therefore everytime I increase boost to whatever hp output I end up with, with the 8:5:1 Compression pistons I will gain approx 4% power increase over what I would have gained on 7:8:1 correct?( I think thats what you ment, )
Therefore the 2g pistons in a 1g will give more power for it than it did the 2g since the 1gs come with more timing advance intially right?
If So, say on the same boost and engine mods but with the different compression, say a 1g engine packing 288 hp at the 4% increase would equal 300 hp on 8:5:1 pistons approx....( As long as timing wasnt pulled back for whatever reason ) Therefore roughly put, thats a calcuated value of the power difference from the 4% increase in compression.

Maybe Im wrong about all that but thats my view of what your saying as far as compression supposing there on the same timing advance. ^

AndyMoraitis: Stock 2.0 at 8.5:1 with stock cams: I ran 24 psi daily on 93 octane with 18 degrees of advance
Stroker at 8.8:1 with Comp 200's: I can run 22 psi on 93 octane at 12 degrees of advance ( I could try and run more, but the 16G won't flow enough air to keep up with the stroker)

Do you remember the hp of each set up? Im sure the stroker was pulling more power sooner and was more torque'ky and thats why you say its more a street pleasure.
( by the way my tuner building up my 6bolt has a gst with a 2.3/ a 16g and a crap load of other mods and feels the same way as you about his turbo selection )

But anyways, when you increase your timing is this done with dsmlink or have you ever done it manually with cam gears or anything?

And then for what your saying turbo wise for my setup, I will mostly go with the super 16g eventually, ( Thought about 18g but dont know too much about it, and 20g may be past the hp level I will be happy with )

But basically you recommend a bigger turbo so the efficiency range will be better for those boost levels, so that Im not blowing heat and raising knock on my higher comp ratio correct. ( I dont plan on ever running over like 24lbs, no matter the turbo, so whats the most youd push a ported14b with my set up on 8:5:1? And then what turbo would you recommend for my engine in the future for say a 20 to 21 lbs of boost daily set up with that ratio without it knocking. ( Of course ill have more supporting mods before then thats why I havent raised boost yet. )

Sorry for all the questions but youve helped me understand a little more on this timing and compression thing.