| I had previously run earlier this year a 12.79 @ 110MPH with the light stock NA wheels with 245's on the rear, 225's on the front. I also had pulled out the secondary battery in the rear for the computer and the spare tire was removed and the subwoofer and cabinet were also absent. This evening, with 24# 18" momo's, 235F and 265R, 2 car batteries, sub and cabinet I made this pass: RT .575
60' 2.081
330' 5.552
1/8 8.317
MPH 89.52
1/4 12.738
MPH 111.96 I couldn't get it to hook up real well at 10psi in 1st gear and my 60' time suffered. I can't dial in any less boost for the gear so I just had to deal with it. The track was rather slick and in 2nd gear at 15psi the tires were at their ragged edge of traction. I have pulled a 1.9s 60' before in that previous 12.79 pass, but that was without all the extra weight and stock wheels with tires that have better traction with a sizable sidewall in comparison to 35 series 18's. In all, I'm very happy with the results. I was consistently pulling 12's and putting 95% of the street legal domestics to shame with all the added weight as well. The car is making very good power. One interesting thing I am finding is that making the turbos produce more boost has less of an effect on power than changing the ignition timing, even when only by one degree. It is 'seat-of-pants' difference. It would make one think that more air+fuel = more power. I've found while that is true, that's too simple a model to really understand how to make good, power increasing adjustments. The thing being overlooked is how well the energy released from burning the fuel is converted from thermochemical energy to mechanical energy. In simple words, how much energy you put to the wheels from that air and fuel you are burning. The key is timing, and specifically, ignition timing. However, what is going on is more complex than just that. When the compressed air and fuel are ignited in the cylinder, the 'burn' process takes time to occur. While the fuel is burning, pressures and temperatures are quickly increasing. Pressure and temperature are directly related to each other as well... So as the pressure goes up, it also raises the temperature, and as the temperature goes up, it raises the pressure. It is a compounded effect where a phenomenon enhances itself with its own components. Since the pressure component of combustion is what pushes the piston down, you want to maximize the pressure in the cylinder so you can transfer that energy to the crankshaft. Remember when I said it has everything to do with timing? Well, the plug ALWAYS fires before the piston is at the top of the cylinder. This means the piston is still compressing the gases in the cylinder as the burn begins. You may be asking yourself, "Why would you start the fire which causes the pressure to increase while the crankshaft is still trying to compress the gases? Wouldn't that lower the power output?" The answer is yes, it does. However, what you must consider is that since the combustion process occurs over time, this means the pressure increases over a preiod of time. Although you are working against the crank by firing the plug before the piston has reached the top of the stroke, the pressures increases magnitudes more AFTER the piston has reached the top and is on its way down. This is where you are transferring (+) power to the crankshaft. So how does making the fire start earlier make more power? Well, that goes back to the whole pressure/temperature relationship. By firing the plug earlier, you are compressing expanding gases even MORE. This causes the air and fuel to more thoroughly burn and it increases the temperature/pressure as well. So when the piston is finally on its way back down, the pressure is even HIGHER (because of the increased temperature from compressing expanding gases) than it would have been with less spark advance and the same amount of fuel and air. It all comes down to maximizing the pressure generated by the burning of the fuel you put into the cylinder. Now there is a down side to all of this (isn't there with everything?).. The thing to keep in mind is the temperature element. Sure you are raising the pressure to make more power, but you are doing it at the expense of raising the temperature, which is something to keep your eye on as it can melt parts. EGT probes are key. Because of the increased temperatures, there is another problem aside from just melting parts. Detonation. It blasts things into pieces with very violent shockwaves. Remember how I said that the burn process occurs over a period of time? Well, admittedly it is a very short amount of time, (~10ms) but it is in tune with the speed of the engine so it is usable energy. Detonation is the burning of the fuel that occurs over a very short period of time in comparison to 'normal burning'. Instead of the pressures increasing steadily as the piston moves its motion, detonation is pretty much an all at once BANG! It occurs 100 times quicker, in the nanosecond time measure. This rapid increase in pressure shocks everything; piston, cylinder walls, cylinder head, head gasket, spark plug, and valves. It also generates very high temperatures. The combination of this shock and high temperature weakens the parts and makes them break. The primary reason detonation occurs is simply because there is too much heat and pressure generated by the initial part of the air and fuel that begin to burn (at the plug gap) which causes the rest of the air and fuel to spontaneously ignite as well. So now you are burning all of the air and fuel at once rather than the burn progressing from the center of the chamber (at the plug) outwards towards the edges of the cylidner wall. By firing the plug too early, you risk raising the temperature and pressure so much that detonation occurs. This is the limit of timing advancement. One factor that increases the likelyhood of detonation occuring is the initial temperature of the air coming into the cylinder during the intake stroke. Large, efficient turbos and intercoolers lower the temperature of the air such that detonation is less likely to occur. This is why big turbos and intercooelrs can flow air at higher boost pressures without detonation, thereby allowing you to make more power without experiencing ground zero inside your engine. At this point you might be thinking, "mmmmmmmmmm. Big turbos, big power, yummy." The underlying reasoning to this is the fact that big turbos/intercoolers can simply flow more air and make more power. Big turbos and intercoolers are always good. :) However, just because you flow more air doesn't mean you make more power. Let me explain: Of course, at the track tonight I was shooting for some good ET's and MPH's. Duh. But I also had another reason for going. A test. Since I have been playing around with the Zemulator so much more lately and really working on finding the absolute limits of my engine (with the internal mods to OEM parts I made on my last rebuild), I wanted to test theory and find a good solid conclusion I could validate with proof. I made several passes at 15psi of boost, increasing ignition timing one degree at a time, bringing it to a maximum of 33 degrees of timing at peak boost until my EGT's broke 850C. 34 degrees proved to promote detonation and EGT's raised to 870C so I went with 33 degrees. I made the pass of 12.73@112 with 15psi of boost and 33 degrees of timing. Then I raised the boost to 19psi and began raising the timing until detonation occured. I could only squeeze 25 degrees of timing without detonation, but my EGT's were 870C! I had to back off on the timing to 23 degrees to get the EGT's down to 850C and guess what? The car was slower. Even on the best launch and a 2.1s 60', I could only squeeze a 13.028 @ 108MPH. The car simply made less power. The reasoning for this comes down to the stock turbos. At 19psi they are simply heating the air up too much to maintain a high spark advance. I had to kill the timing by 10 degrees just to run 4 more psi of boost! This resulted in less power and turbos screaming for a quick death. In an interesting co-inciding experiment, I have a buddy with a 5 speed 2+0 NA. He is stage3, has stock wheels and 225 tires, F+R. He also has the spare tire in and full interior. Tuesday this week we went out with his car and the Zem. We wanted to see just how much timing we could pull before we heard detonation. We carried the ignition timing to 38 degrees on pump gas and didn't take it any further. We heard no detonation and the car pulled like a mofo, well, for an NA ;-). I enleaned the mixture a few percent to bring it up to ~13.5:1 and made a few test runs, listening to the engine carefully. No detonation. We then loaded the stock program and made a few passes down the road and reloaded the new program we put together. I never knew there could be a seat of pants difference with the NA, but to say the least, I was VERY impressed. He was out at the track and is not a frequent drag racer. He only went out to see what it would do with the new program. His first run was a 15.008 followed by a 15.009. A little later on he came to me and we were both happy with the results, but I noticed his 60' times were 2.3's-2.4's.. I told him to drop his tire pressure to 12psi, do a small burnout, and launch it a little harder. His next pass was a 14.71 with only a 2.2s 60' time. The engine is obviously making good power. Why? Its all about timing. :) If you've made it this far, pat yourself on the back. I think this has got to be the most lengthy post I have ever made. But, if you are still reading this, you alrady had interest in some of this stuff, perhaps just curiosity, or maybe you really do want to learn this for tuning your own Z someday. I want to put in a disclaimer here as it comes to mind. Do not think you can just go out and jack up your CAS to add timing. You will increase timing if you do this, but you must realize that by turning the CAS, you are changing the ignition timing at every instance of engine operation. In the tuning I have done, only specific areas of the timing maps are changed - namely the high load section of the map. If you crank your CAS, you are also advancing the timing in the low load drivability area and it will lead to problems. You will, in fact, have very undesirable results. I hope you enjoyed the novel ;-) and would be even more satisfied to know that you feel you actually spent the timing reading it for something helpful..
[ ashleypowers.com ]
[ agpowers@bellsouth.net ] [ Zemulator Information Sheet ] When pigs dance, you better get it on video... "You never really learn to swear until you learn to drive."
-George Carlin
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