running HKS 272's. Reason being is, before the intake cams were available for the IX we ran just the HKS 272 exhaust cam. So now we just matched it on the intake side.

 

Not too sure how you're doing your calculations but, 24.5" tires mean higher rpms in same gear (4th) when you reach the traps. My calculations show that when shifting at 8000 in a IX with stock 4th gear, you'll be in 5th gear 200 feet BEFORE the traps. That means winding the motor harder and going into a lower average horsepower range, just to make a quicker 60. The figures speak for themselves. 1.53 is no slouch, 11.0 is one of the best on a 20G-Lt you'll see posted. How did you calculate your mph/et and still keep the motor in it's peak hp range without going to 5th. Remember, we're on a IX, not an VIII. I'm happy with what we're doing and where we're at with current mods. We're not on a bigger turbo like a 35 with higher rev range for the horsepower curve. It's a 20G-lt. I'm also curious how someone who hasn't even seen the hp/torque curves could make that statement. Don't confuse bench racing with actual tests. Sometimes they're night and day.

 

This post demonstrates exactly my point. A IX has a shorter 4th (yes, we could change it and go to an VIII 4th gear, then buy new tires to get a higher mph, but probably the same ET) than the VIII, which simply by law of mathematics puts the rpms higher. Only 2 Evo IX's are listed in the 10.70 - 10.99 list. One is RACeRs and the other is VWJEFF. One is using the IX 4th gear, 10.869 @ 123mph, the other uses the VIII 4th gear in a IX tranny. He posted I think a 10.7 @ 127. The difference in mph is simply the gear. Both cars are excellent running cars, well driven. BOTH have 35R turbos, with higher rpm/hp range, but the one with the IX gear made the following post. Notice, HE said that he ran out of gear and had to coast the final 300 ft before the traps. The IX vs VIII 4th gear is a BIG difference for the MPH. Yet they both are 10.7-10.8. We ran 11.02 @ 123 compared to the larger tubo'd 10.869 @ 123. It appears as though our 123 on a smaller turbo aint too shabby. We also know that we'll be in the 10's very shortly. Like my earlier post, we're only 15 hundredths away from the 35R's times and speed. Putting things in perspective becomes important when comparing mph/et's.
https://www.evolutionm.net/forums/sh...00#post4280300

Also, vwjeff's personal observation as to rpm's vs speed using stock gearing. Simply put, the IX runs out of gear long before the traps (provided you stay in 4th, 5th just kills spool and loses mechanical advantage).
The solution is taller tire if your leaving the stock gearing, or change gears/final drive to keep the rpm's down across the finish. OKIX's 1.53 doesn't reflect he lost anything by going to the taller tire, but gained a little mph while still lowering his rpms. Good swap.
https://www.evolutionm.net/forums/sh...=297153&page=2

 

9sec9
I am not bench racing. I am 100% certain your car would improve with 24.5 tires. The 26.7 tires was just plain a poor choice. Curt Brown tried both on his evo and went faster on the 24.5 tires. Here is my text on the subject with some simple math and explainable examples.
https://www.evolutionm.net/forums/sh...d.php?t=254995

There is a also a recent post of a guy who just bought a bushwacker tranny with the 8 forth gear and went slower at the track with no other changes. I can pull that up for you as well.

 

what your example fails to point out is the fact that as rpms are kept higher (4th gear instead of going to 5th) the engine doesn't fall out of boost nearly as far, and the engine has a higher mechanical advantage, since it's ratio is now at better than 1:1.
Also, shorter tires are by nature and mathematics used to get quicker accelleration. Since the car moves from 0-??, this would mean that the 24.5 should move the car better than the 26.1 on a 0-60 ft run, yet the 1.53 is above average for most cars posted, and since we spun the tires fairly hard, but still got the 1.53, it's reasonable to assume that a 1.4? is very attainable. If a 1.4? is attainable, how much better do you think that a 24.5" tire is going to move the car and with that said, what would 9000+ rpms do to the horsepower curve on a stock IX 4th gear. What I'm hearing you say is that OKIX's 60's could be in the 1.3? and the rpms are ok at either leaving it in 4th at 9000+ on a stock internal engine, or go ahead and shift to 5th, drop out of boost and forget about the additional time that is required in completing the shift to 5th. If the gearing was better (1:1 in 5th and the first 4 were linearl, I would agree with making the shift, but not when 5th is .7?) Your original example put the car 127 and 10.80, how can that be without acceleration, since 5th definitely won't be accelerating and 0-60 is indicative of acceleration, but how we're already at 1.53. We'll continue with the success, and let those with better ideas beat us, if they can with same mods. Show me another example of a 20G-LT running faster, quicker times. Also, we've only made about 17 total passes at this point and compare our 20G-LT to 3065's and 35R's. I'd say we were on track for the same times as those, and better in most cases. Explain the posts I used as examples, by those who have also been there, but ran out of rpms. Again, big difference in VIII and IX gears.

added: By the way, most if not all of the quickest 60's (his 1.53 would be 10th on the fastest list) are large turbine (35R and larger turbos) which don't spool as quickly as the smaller stock type turbo. Because of that, they need all of the bottom end they can get to get out of the hole. Their higher rpms, 9000+, allow them to use the shorter tires, which they also happen to need for the bottom end performance losses of no boost at low rpms. Small turbos don't need the quicker acceleration, they have it naturally. Different horsepower curves require different approaches.

 

You guys have got to bring this car out some Saturday night. Come hang out!

 

Hey 2theMAX, I would but I guess I don't have enough years of experience to compete with the younger crowd. OKIX has been saving his money, so he's not out and about as much. After I apply all of the knowledge by so many people, I'll be able to build a fast car. THEN we'll be on the streets again. JK, but I'm sure he'll be out cruising again soon. Been to the track lately?

 

there is a huge hp difference between 26.7 tires and 24.5 tires. You will gain 2-3 car lengths advantage on the 24.5 tires. you will loose 1/3 car by having to use 5th. what you gain in acceleration in every gear is far more than what you loose by having to use 5th. dont know how else to say it.

it is easier to launch shorter gear ratios. imagine trying to launch in second. as long as tire compound and width is the same you will have a better shot at 1.4 60ft with 24.5 tire than you would 26.7. launching at low rpm is much easier than launching at higher rpms. higher rpms are more likely to blow the tires away. making tires or gears taller requires higher rpm stutter. more chance of wheel spin.

you are missing my points. I am not missing yours.

tell you what . go buy the 24.5 tires. if they dont make the car faster let me know what they cost and I will buy them from you.

Curt Brown is a record setter. pretty much far and beyond anyones records on here. His record setting talon ran 23 inch slicks when everyone else was running 24.5 and bigger. he cut record setting 60 ft with those small tires. he went 145mph on a 3065. Curt also went 10.59 on the stock turbo. 128 if I remember correctly. He never got a good pass in on the 20gLT but his 1/8mph went from 100 on the 16g to 105 on the 20g.

 

Your points have also been well taken. Problem is your theory only exists in a vaccuum. When you stated in your reference post that only rpm's decrease and the car does not decrease in speed, that's wrong. I have taken the time to run each tire through a program specifically written for drag racing. I used my son's car as an example, e.g., weight, gears, peak hp rpm, torque, tire height, width, rim size, shift points, and .25 seconds per shift, excluding the 4-5 shift which would be slightly slower than a 3-4 shift. Here are the results. Summation shows a slower et with 24.5, slower mph with 24.5. These facts are not tweaked in any way. Only the tire height. Each car is different and using another person's car, engine combination will not always apply across the board to everyone. I'll let the program pics speak for them selves and how they reference your earlier statements as to how OKIX would be running 10.80 at 127mph with the shorter tire.
Notice the decelleration during the 4-5 shift, it also occurs in other shifts, but aerodynamics and gear diff's make the 4-5 shift more dramatic as to the loss of speed.
In the example, the car actually LOSES 1mph before it begins to re-accellerate. Also, notice in the bottom 2 images the computers calculation of et and mph. The taller tire outperforms the 24.5 in both et and mph. I assume that Curt Brown's car did not have the same power curves as ours. It doesn't really matter in the end, since I can build ours, you can build yours, and if we meet in the same class, we can compete head to head, and neither one of us will have to do mental gymnastics just to be correct.

 

You keep saying my points are in a vacuum. What part of the eclipse example that went .5 second quicker did you not understand? This was a real world example of a car with same 4g63 engine /20g turbo/3300lb car/ 5speed tranny.

There was an article in SSC years ago. They dyno tested a honda with 15inch wheels and then again with 17inch wheels. There was a 8hp loss with the 17inch wheels. This was a 200hp car.

If you used a G-Tech and made a run with 26.5 tires and then bolted on 24.5 tires on and made another run. The G-Tech would show about 40hp difference between the two runs.

I give up here. I will let you figure out why your panda machine is not giving you the real world results.

EDIT: okay. I will be nice. You are entering the same HP numbers in your panda machine. The rotational mass of a 26.7 tall tire is much greater than the mass of a 24.5 tire. car will not dyno the same numbers on both sets of tires.

 

First of all, we're not talking about MY car. We're talking about my son's. Secondly, I'm a Database Administrator and Programmer and have been for 30 years. I think my history and results will speak for themselves.

None of your Curt Brown examples can be used as argument, since none of those examples make true direct comparisons of one tire to the other under exact same conditions. The examples I gave you in the pics directly relate one tire to the other and what an outside program, NOT YOURS, NOT MINE, says will happen with the given parameters. I disagree with your assesments, but that's ok. That's what makes for good argument. By the way, I mentioned the vaccuum, since aerodynamics have not affect in a vaccuum. Without aerodynamics playing a role, the car would not decellerate as much. Only the mechanical drag of friction. As for the car not getting real world results, tell that to all of the other 20G-LT owners. 11.0 isn't exactly the norm.

 

I've purchased 2 sets of Wilwood Lightweight brakes from AMS. I custom ordered and waited 7 months for a set of 15x7 CE28N's. We're using 26x9.50 15 lightweight Hoosiers, as opposed to standard weights. Not sure if those tires were the same ones used in your examples, but difference in weights in same size tires is about 4-5 lbs each. Rotational mass and weight savings is nothing new to me. I think we'll be in the 10.80's with the slow, tall 26.7's and maybe even get into the 1.4's in the 60's. Want to make a wager on it?
By the way, the 24.5 tire weighs EXACTLY the same as our 26.7's. They both weigh 17lbs *advertised weight.

 

I am trying to help you. I dont want to argue with you. I am giving you real world results from myself and others who traveled down these roads before. Your car will be faster with the 24.5 tire. The engine program is only as good as the numbers you enter into it. In this case the numbers entered are not correct. HP is greater on the smaller tires.

 

So you're still saying that we'll run 10.80 at 127 by just changing to 24.5? How do you explain the decelleration time with the 4-5th shift. Notice that the car decellerates so much, that it finally traps at slightly less than the speed prior to the shift. Again, both tires weigh the same, with only SLIGHT advantage going to the 24.5 due to rotational mass, but this is offset some by the ability of the taller tire to maintain it's momentum between shifts. Those are minor differences in the scheme of things. Your beginning statement was that the car would run 10.80 at 127. No way that's going to happen with current gearing, which was taken into account before choosing the tires. If I listened to everyone's advice on how our car should be built, I don't think we'd be running 11.0, nor having a 1.5 in three consecutive runs. Argument just brings out the basis for taking a stance, it's all well taken.

 

Very nice man