Quote:
Originally posted by ecoli@Nov 10 2003, 11:35 AM
You are goign to lose power if go from a good non-knocking pump gas tune to a C16 without changing anything. To get the most out of C16 you usually need to raise the effect compression or run a lot more timing plus lower your fuel output.
C16 is a denser fuel than pump gas so more of it gets injected in the same pulse width time. A pump gas tune that is running around an 11.5:1 A/F will usually turn into an 10.8-11.0:1 mixture when you switch to pure C16. So you need to remove some fuel one way or another, like going farther negative on an AFC. You aren't really leaning out the mixture, your just trying to get it back to the same air/fuel you started with on pump gas. However, you can usually goto a leaner mixture than you were able to run on pump gas and start picking up some additional horespower.
The easiest way for us to raise the effective compression ratio and make the C16 happy is to raise the boost. Along with the boost comes more horsepower. If you don't want to raise the boost for some reason, then your going to need to run a little more timing on the C16 to get the fuel to ignite at the right time to keep making the same old power. You can sometimes run a fair amount more timing and try to make some extra horsepower, if you aren't using up all the octane already in boost, lean A/F, poor intercooling, etc. Don't worry a lot about getting crazy high timing numbers though. The power gains are usually minimal once you reach a certain point.
Mara's power on her 1G compression usually stopped sees gains at all at 24 degrees. That is with the base timing advanced and the ECU running off of the final max flow timing map(the one that gives 22-23 max then goes down to 19 degrees around 7000). The advanced base would give a little power in the mid range and topend range past 7000 area where the ECU wasn't running as much timing. Peak HP wasn't really help at all, just in a few areas. On Andy Nash's car we went from a base of 0-1 degrees to an advanced base of around 8-10 degrees and saw a gain of about 5whp. Not a huge gain for a car running a retarded base timing going to advanced. It's usually better to just run more boost than try to push the timing to the limits.
If you want to run a lot of boost on pump gas and make decent power that way then run as little timing as you can get away with. With higher compression, you usually need even less timing. If you can get 20 degrees out of a 2G compression then I wouldn't spend too much time trying to go any farther. Stock without any AFC fooling going on the 2G ECU only wants to run 16 degrees of timing max on its highest airflow map versus the momentary 23 degree peak timing max on the highest airflow map in a 1G ECU.
On C16 you can usually push the limits of stupidity and still not knock. On Mara's car we did just about everything to the extreme edge of tuning and the C16 would take it. We ran high boost on a shitty intercooler, so a lot of the octane was used just to compensate for the high heatsoaked intake charge air temps. We shot for an airfuel close to 12.5:1 and we often upped the base timing from the stock of 5 to 8-10. We didn't always do the timing though because we knew that it did next to nothing and wasn't worth the effort and risk. Boost equals power, timing doesn't.
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my thoughts exactly.
C16 and higher leaded gases lets you go farther on the 'stupid meter' without blowing stuff up. By simply just switching gasoline, you do not and probably will not gain power. In turbocharged and supercharged setups, the only reason to go to a 'higher grade' gasoline is to allow you to turn up the boost and/or add timing to get back to the a/f ratio you were at, hince how 'c16' makes power.
As shane mentioned, leaded gasoline, especially c16 burns much slower than standard 92 octane. But in order to gain from such things you need to take fuel out to get back to where you were at, or add cylinder pressure to 'consume' the 'extra' fuel.
Another point is that leaded gasoline is usually more stable than unleaded. The gasoline is more constant as well as the fact that it is easier to control (burns slower), this allows you to run a different and slightly leaner a/f ratio without the worries of burning stuff up.
Hope this helps.
I also agree with lighteninggsx, IMO c16 is overkill in alot of applications used on the dyno. Most of the setups out there dynoing on 'race gas' really don't need 'race gas', they are just looking for that added 'kick' that there particular setup is missing. The only way I see it useful is when you have the cylinder pressure and temperatures so high that you need the more stable gasoline to 'cool' things down, or you have the timing so jacked up that you need it to avoid such things as detonation. The only other reason I think it should be used is when you simply run out of fuel on your setup with 92 octane and you need all the help you can get (too small of injectors and pump come to mind).
sorry for the rant.