As far as hp being higher on the shorter tire, that's correct, but the AVERAGE hp across the run will be affected when going to 5th gear, simply because the car will no longer be in it's peak range, and therefore have a lower avg hp while in 5th. That's the reason for the car not recovering to it's original speed prior to the 4-5 shift. With the speed actually decreasing in 5th before crossing the line, it would stand to reason, you could actually just hit the rev limit in 4th and be just as effective. Our goal is to keep the rpm's to a reasonable level until the bottom end is built this winter. When the rpm's can be raised, I might not mind taking the car to 8500, but not on a stock block with 500 crank hp. If it was my car, I would feel very comfortable with taking it to 9500+. Buschur builds great engines, but OKIX's car is still a daily driver, driven everyday on the street and 8000 is the max I feel it should go. As for shifting to 5th, well, I absolutely know that the car will decelerate. These are the reasons I purchased 17lb tires, same weight as the 24.5, but the advantage of having lower rpms across the traps, with very good 60ft times, and better ones to come.

 

Hey there vwjeff. long time no talk to. I've followed your results. Fantastic. The tuning gets in the blood. Looks like your getting it together, for real.

 

nice times, im hoping to run my car at IFO in dallas

 

You based too much of your decision on which tire to use based on the panda. I can think of ten things it has left out. This whole thing started by someones comment on your low trap speed. You were trapping the same on your heavy street tires of stock diameter. Going to a lightweight tire and wheel should have brought bigger gains in both ET and MPH. Your MPH suffered because you went to such a tall tire. You cant see this because you are relying on the panda and stuck on the misconception that shifting to 5th is gonna kill your ET, neither of which is correct.

 

Pardon me, my friend, but quite the reverse is true. You're making an assumption that the previous traps and et's were on heavy street tires and stock diameter. I don't think that CE28N 17's would be considered heavy. The tires were Nitto 245/45 555r drag radials. They might be heavy when compared to racing slicks, but the tire combination weighed 39 lbs. The new one is 29lbs. Please answer the following points.
1. Why do you discount the deceleration in the computer models.
2. Do you not understand that small turbos have different torque curves as compared to large turbos. Smaller turbos simply spool quicker and don't need the aid of shorter tires.
3. The IX has a shorter 4th gear, therefor will be maxed long before the VIII. With that in mind, and with the 'no longer accelerating when going to 5th' issue, the engine ceases to do what it was intended to do, 'ACCELERATE'.
4. Both tires weigh the same, so centrifugal advantage only has a slight advantage for the shorter tire. This advantage is somewhat countered by the momentum of the larger tire between shifts (less deceleration).
5. The comparisons of another car, with unknown fuels, and unknown controlled conditions does not validate, nor substantiate your position.
6. Other cars with exact same gearing as the OKIX car have issued the same concerns that I have, too many rpms before the traps. After reaching max rpm in 4th, they then become Sunday drivers for the next 200-300 feet.
7. As to your childish attacks on Panda, where in the world do you think that my car has anything to do with the choices on his car. Just because you saw PANDA at the top of the computer printouts, only means that I called up that MODEL in the files to create a beginning file to work with. Programmers, remember, that's what I do, do this all the time.

You're points are well worth listening to, but in the end, the results we make speak volumes. Your flat statement of 10.80 and 127 mph was in error. If you think that we can change the tires to 24.5 and go out and run 10.80 at 127, I have $1000 dollars that says you're wrong. Making overly zealous statements like that, didn't help to create an open mind as to your position.

 

Hey Tom and Tony was nice meeting you guys in person again congrats on your times and good luck on your goals!

 

Thanks Aniel. I wish we had more time to talk, but you know how it is at the races. Constant scanning of the logs to make the next changes. Maybe we can get together soon. Next time we go to Dallas, I'll give you a call and come over to the shop. I've heard a lot of good things about you and look forward to doing some further tuning on your dyno, since OKC can't seem to keep an AWD dyno.

 

The following image is fairly representative of the accuracy of using a program to give approximate results of different wheel/tire combinations at various engine power outputs and transmission/final drive gearing. This is the file that I used several months ago, when trying to get a close idea of how the OKIX car would respond to 26.1" tires. Notice the rpms across the traps reflect 8019 and the tire height is 26.1. The accuracy of the 60ft is dead on (actuals were 1.59,1.53 and 1.57), the mph is down from the 126, but we're also not at the 10.829 yet. This is not being posted in regards to previous posts. It's being posted for those who don't know that something like this exists, or for those wondering how accurate something like this can be.

 

The above is a snap shot of my starting point in 'best guess' race conditions, without regard to weather, but using a 26.1" tire. This was done several months ago. Now, in light of truly wanting to make the car faster and quicker, I've spent time researching the conditions of the actual race day, including weather and tires used. I've also taken into account the fact the a 24.5" tire will put slightly more power to the ground, but usually that's due to the weight difference. Since both tires are exact same weight, I used a 10whp difference. This should be more than generous, due to the fact that both actually are of same weight. First, I used actual conditions and created an image. Then, I changed the tire input to 24.5" and raised the PEAK whp to 423 from 413. This tire change resulted in shifting to 5th about 310ft before the traps. Then, the 3rd image is my what if: What if we left it in 4th and let it runout in rpms? The result is actually the quickest, fastest of all. The figures used, are exact numbers for whp/wtq, peak power, shift points, etc that were used on race day. These are proven in logs and dynos. In summation, the 26.7" tire left in 4th has nearly and identical time as the one that is allowed to shift to 5th, but was using 24.5" tires. Main difference was a drop in mph using the 24.5" of nearly 3.5mph. This is what I expected by using a shorter tire on our car. What I didn't expect was the 3rd image. By leaving the car in 4th and running it out to over 8300 rpms, the et drops to 10.95 and the mph showed a .7mph increase in speed. All of the differences are due to no loss in momentum on the 4th to 5th shift. If a person was willing to trap 722 rpms higher, the et could be improved by .047 and the mph could go up by .7mph
Now the question is, would it be worth the risk of taking it to 8320 rpms to gain 47/1000ths vs safe at 7598? Again, these are EXACT conditions with allowances made for whp diff. I was surprised after keying in the weather conditions, how accurate the 'estimate' was to what actually happened at the race. The program is only off by .015 on the et, and about 1mph.

 

There is more than 10hp difference between those tires. The horsepower you put in that box should not be the peak dyno number. It should be the average HP over the curve you are using. That would make the results of that program quite different. The program has no way of knowing what the HP and torque is over the entire power curve. It enters that one number you enter for every equation and every rpm.

 

That dyno of wheels by SSC was done with tires of the same height. only the rim was changed from 15-17 inch. So the rim weight being moved out from the center 1 inch resulted in a loss of 8 whp on a 200 hp car. I pretty sure that translates to 16 hp on a 400 hp car. And in your case you are not only moving the mass of the tread out 1 inch. you are changing your rear end ratio from 4.69 to 4.30 at the same time. try entering 30hp. I bet you get really close to the 10.8 at 127 mark with a shift to fifth.

 

Congrats on those awesome times in what sounds like pretty poor conditions! 10's are a pass away... Do you know how much boost the car is holding at 8K? Not sure if that is effecting the MPH.. Cause I think that was a big factor on my MPH with the green, but I will have to test that at the track?? Congrats again

 

Thanks Freddy...Im not quite sure how much boost is holding at 8k. But Im heading to the track friday so I will see then

 

Gee, I'm sure glad you don't work for me. A 30whp gain, just by changing from a 26.7" tire to a 24.5", but both weighing the same?!!!???? OK, everyone go out and shorten your tires by 2 inches and gain 30whp and pick up .2 and 4mph. Your math and evaluations are lacking. I'm over with this conversation. Start your own thread, your now getting absurd.

 

We are equal. I know your estimated 10whp difference to be absurd. And your lack of entering correct HP figure in a program that requires an accurate HP figure to give an accurate result. And you work with programs everyday. wow.