What makes more power? 10:1 w/ 23psi or 8.9:1 w/ 23psi. Timing is not a factor due to the use of 110 leaded fuel. I can run pretty much whatever timing I want to run. I know typically you reduce compression to be able to maximize spark and boost, but this isn't a factor for me. And boost is nothing more than added compression to the motor, so in theory, higher compression along w/ a decent amount of boost should produce more hp. Please someone shed some light on this. I'm being pulled in 2 directions right now and can't seem to find the right answer. I've been told about swept cc's, but a google search turned up nothing that I could find useful on it.



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4 Cams...32 Valves...5 Liters...This Could Get Fun!

10:1

I may get the why wrong, but as you lower compression the motor has to work harder to turn.

Quote:

10:1

Yeah, 10:1 will make more power providing you can control pre-ignition and you dont have to pull tons of timing. The gm drift solstice runs 13.5-1 and a few of the drag cars run 10:1. As well the original gm drag car ran over 10:1 comp.




"Go Before Show Yo."
CARCUSTOMS.NET, THE BEST SERVICE ON THE ORG!!!

With direct injection.... makes things like that possible

10:1 w/ 23psi with a TDO5-14B will be less then 8.9:1 w/ 23psi with a GT35R.......


But the turbo being the same, the higher compression should. But will be harder to tune.

That said, my Quad will be geting it soon...

Chris





'02 Z-24 Supercharged
13.7 @102.45 MPH Third Place, 2007 GMSC Bash SOLD AS OF 01MAR08

i'm going to be boosted with 10.1:1 on my DD. Mind you it will only be 7psi to start with untill i can get a proper tune, then Will be upping the boost to possibly 15 psi. maybe a little less. I'm trying for 94 octane on my hybrid LD9.

You think 10.1:1 compression and 7psi is okay to drive with an untouched SCreflash? May not be able to get a custom tune for a month after the engine's already in the car

Just because you are running 110 does not mean you can run whatever timing advance you want. Yes higher compression with the same amount of boost will make more power than lower compression and the same amount of boost, but tuning is soooo much more important than it already is.



FU Tuning

Its not just a theory its a well practiced thing. I know a couple 10.5 class racers that run High Compression, boost and a shot of some juice, mind you these are trackonly cars and I'm sure there a pain in the ass to use. The other thing is alot of professional dragsters use high comp. just for the sheer fact it makes power under boost but those guys spends months nailing a tune down for 6 to 9 seconds.

With that out of the way I say go for it. I'm contemplating building a 10.5:1 setup and the M62 supercharger. Positive displacement blowers love extra compression since your building on top of what the motor can do already. While urbos on the other hand area little bit finnicky. I tuned a 11:1 supercharged B16 last week and it took 2 days to get the tune even close to where I wanted it and then a 3rd day to get it just right.

Even with 110 race fuel you will have to turn down the timing some now if you aren't running alky injection yet on your set-up I'd throw it on that way you can maintain high timing with out alot of detenation.

The reason low compression is so popular with boost is it opens your safety threshold up pretty wide when tuning(I'm sure you already knew this as a fellow tuner). But you would have to ditch HPT and run full stand alone HP just doesn'y give enoughj of the full adjustments to maintain it.

Buy this book.

and this one,



Corky is a HOOT to talk to!

Chris




'02 Z-24 Supercharged
13.7 @102.45 MPH Third Place, 2007 GMSC Bash SOLD AS OF 01MAR08

I have maximum boost on my pc in a .pdf. As for the rest, I know I will have to pull a lil more timing but ultimately end up still advanced over stock. Thanks guys you made my decision a lil easier. See this is the kind of good info that's missing from a lot of posts.

My next mods include 11:1 pistons, a gt35r, and countless hours of tuning lol.



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4 Cams...32 Valves...5 Liters...This Could Get Fun!

Maximum boost = bible.

AND you will notice that in every chapter he implies the importance of cooling down the intake charge.



My Cav
I give up...
i'm buying a VW those people love trees, so they should love eachother too... "Andy"

Skunk wrote:I have maximum boost on my pc in a .pdf. As for the rest, I know I will have to pull a lil more timing but ultimately end up still advanced over stock. Thanks guys you made my decision a lil easier. See this is the kind of good info that's missing from a lot of posts.

My next mods include 11:1 pistons, a gt35r, and countless hours of tuning lol.

9.5-10.0....................... and be shure to clean up the head to get rid of "hot spots"


LOL, cooling the intake charge.... water injection!


Chris




'02 Z-24 Supercharged
13.7 @102.45 MPH Third Place, 2007 GMSC Bash SOLD AS OF 01MAR08

Its like I said I never run boost without water injection I love that stuff.

Meth has been something I've thought about. We'll see if she needs it.



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4 Cams...32 Valves...5 Liters...This Could Get Fun!

Water*

Chris


'02 Z-24 Supercharged
13.7 @102.45 MPH Third Place, 2007 GMSC Bash SOLD AS OF 01MAR08

Its really worth it. I have seen huge gains on friends cars and its a healthy mix of them srt-4s, evos, a boosted teggy and civic,

Skunk wrote:I have maximum boost on my pc in a .pdf. As for the rest, I know I will have to pull a lil more timing but ultimately end up still advanced over stock. Thanks guys you made my decision a lil easier. See this is the kind of good info that's missing from a lot of posts.

My next mods include 11:1 pistons, a gt35r, and countless hours of tuning lol.

Well then, looks like I need to talk to you about some pistons again eh? LOL... I can go as high as 16:1 on the Ecotec if you want

-Karo

Yes sir Karo. You are gonna be the man I come to when the time comes.



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4 Cams...32 Valves...5 Liters...This Could Get Fun!

Your statement that having 110 octane negates any worry with high compression and boost is incorrect.

Every fuel has its limit... surprisingly, SCR is just a small factor in the grand scheme of things.

Clearly doing simple math the higher compression ratio is going to yield more power, since the static compression ratio + boost will be higher. But there are a lot of factors to consider for even that. Turbo size, cams, etc all affect it.

Lets consider this - the biggest deterrent to timing is heat in the combustion chamber. We all know that a T25 at 15 psi is more of a blast furnace than a turbocharger... well the same is considered in this case except we're clearly using a larger turbo.

Corky suggests that you go with a higher compression ratio and less boost to create the same power level... depending more on the Engine rather than the turbocharger is good practice, especially on a street-driven vehicle. This will provide you with a more satisfying powerband and will still remain decently easy to tune.

If you want to ramp up the compression ratio yet keep the boost level the same, you will need to consider going with a larger turbocharger that is in its peak efficiency range at your desired psi. Personally I would not go this route as you would be going in the opposite direction that is suggested.

Now I know your argument will be "meh I can pull timing so it'll be fine"... but there is a certain point at which timing being pulled no longer yeilds a gain. This is why many people go with lower compression.... Lets have an example:

Car A - 8.0:1 static compression ratio, 20 psi of boost.

Car B - 10.2:1 static compression ratio, 20 psi of boost.


Car A ends up with a 18.88:1 compression ratio at that level of boost.

Car B ends up with a 24.08:1 compression ratio at that level of boost.

(Those #'s assume an altitude of 0 feet over sea level... above sea level the # goes down and below sea level it goes up)

That's a staggering difference when you consider how much compression that is. Each point of compression compounds the temperature in the combustion chamber. As you can see, octane and timing can only go so far, you will hit a certain point where raising the boost level will yeild little to no gain. This isn't even taking into account the size of turbo, effectiveness of the intercooler, ability of the motor to expel heat, any external oil coolers, etc.

As you can see you're fighting something of a monster... this is not a simple task.... there's lots to take into account... especially if you want to run very high boost with high compression.

Personally, if I was you and you wanted to redo the motor and recalculate everything in order to make a move to higher compression....

I would go with about 10.5:1 and find a turbocharger that is in it's PEAK efficiency at 15-17 psi... this is where it's running at it's best and at its coolest. You will yeild a compression ratio of 22.64:1... which is close to what my motor is making at 29 psi.

The difference is if you get a properly matched turbo and keep the compression at that level, your combustion temperature will be a a VERY managable level, especially with 110 octane. At this point you can begin to advance the timing to something useable rather than in the low single digits, if not the negatives.

In my opinion it is better to run a boosted motor with more timing than a boosted motor with more boost. At that level with 110 octane you could probably run just below the stock timing (within 5-7 degrees but I'm making an educated guess so don't hold that to anything firm) and make PEAK efficient power through the turbo while still maintaining torque and driveability with just the engine... your turbo will spool faster due to utilizing the engine more than the turbo, not to mention your spool will come on at a decent range rather than just up top. Also keep in mind with your higher octane fuel you can further advance the timing over stock with the higher compression to yield even more off-boost power. You'll never have an issue waiting for boost to come on. lol.

Further to that, I would invest in every heat coating possible for the pistons and combustion chamber, as well as the exhaust ports and turbo manifold. Anything to help the engine run a cool as it can while you're putting it in that environment of extensive heat.

That's my recommendation to you.

Regardless, break out a pencil and pad of paper, and some books. You have a lot of math to do. (And please do it after your pre-designated 2 cups of coffee!)

-Chris-



-Sweetness-
-Turbocharged-
Slowly but surely may some day win this race...