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[bison]

Murphs car has plenty more in the tank. His last outing really raised the bar. Anyone worried about the weight should go on a diet. You never know what's in the lane next to you.


BPE2013@hotmail.com

 

[murphster]

If anyone is interested in what I've done to save weight, I updated my post in the weight reduction thread to reflect some changes. See link below:

Weight Reduction List

 

[jdsgnx]

NICE!!!!!

 

[murphster]

Looked at the XFI log in more detail yesterday. On the faster second pass that I got out of it on, I let off at 6.9 seconds in the run lol. So I coasted for 2.5 seconds to a 9.48. I definitely think it was a 9.2 pass now as I should have been up a tenth and a half at the 1000ft mark. I tweaked my boost controller stage settings a little yesterday and next pass should be a steady 26psi for the whole run, about 1 psi higher than that last pass. Hoping to run this weekend and get that 9.2 or better.

Looking at the launch, I left with 11psi at 4300rpm on the 1.33 60ft. Was higher rpm than I thought but still didn't feel violent at all. Somewhere around 4100 or higher seems to start getting into the sweet spot to launch on my combo. If the track is hooking I may turn it up. Should be no issue for my suspension and drivetrain but I haven't made a lot of passes on the current suspension to see where the limit is.

 

[Street Lethal]

Still don't see how it is possible to drop 20-mph in 2.5 seconds without hitting the brake after the 1/8th mile, yet run a similar ET of 9.4x. Looking at the slip, it looks like you should be running in the 8's for crying out loud...

Looked at the XFI log in more detail yesterday. On the faster second pass that I got out of it on, I let off at 6.9 seconds in the run lol. So I coasted for 2.5 seconds to a 9.48. I definitely think it was a 9.2 pass now as I should have been up a tenth and a half at the 1000ft mark. I tweaked my boost controller stage settings a little yesterday and next pass should be a steady 26psi for the whole run, about 1 psi higher than that last pass. Hoping to run this weekend and get that 9.2 or better.

Looking at the launch, I left with 11psi at 4300rpm on the 1.33 60ft. Was higher rpm than I thought but still didn't feel violent at all. Somewhere around 4100 or higher seems to start getting into the sweet spot to launch on my combo. If the track is hooking I may turn it up. Should be no issue for my suspension and drivetrain but I haven't made a lot of passes on the current suspension to see where the limit is.


View attachment 239228

 

[pacecarta]

he didnt drop 20mph ...he lifted because he slipped, and he lifted before the 1000mark , he wasnt going 142 before the 100ft mark

and that timer put the run on track to be better than 9.31 so it should have been in the 9.2 highs

 

[Street Lethal]

I'm looking at the slip and plugging it into the conversion calculator. His trap speed in the 1/8th in the first run was 114-mph, and his 1000-ft time was 7.82. That was the run where he didn't lift. The second run when he did lift, he trapped 116-mph in the 1/8th, and ran 7.73 at the 1000-ft mark, but essentially lifted before that. I can't see how he lifted before the 1000-ft mark in the second run because he was on target for a 9.15 ET in the 1/4. He lifted, but somehow ran 9.48 at 122-mph. That 20-mph difference only equates to three tenths in 1/4 mile ET...?

 

[bison]

I'm looking at the slip and plugging it into the conversion calculator. His trap speed in the 1/8th in the first run was 114-mph, and his 1000-ft time was 7.82. That was the run where he didn't lift. The second run when he did lift, he trapped 116-mph in the 1/8th, and ran 7.73 at the 1000-ft mark, but essentially lifted before that. I can't see how he lifted before the 1000-ft mark in the second run because he was on target for a 9.15 ET in the 1/4. He lifted, but somehow ran 9.48 at 122-mph. That 20-mph difference only equates to three tenths in 1/4 mile ET...?

.3 or less the car has already been accelerated. I calculated 9.17 the day he was there if the pass was ran out the back with the same power as the eighth.


BPE2013@hotmail.com

 

[murphster]

If you do a little math, you can estimate how much time you should lose.... The only equation you need to know is distance/speed = time. For example, 100 miles/50 miles per hour = 2 hours. So lets say when I let off 6.9 seconds into the run I was going 125mph and had only gone 850 feet. This leaves 470 feet to go to get to the full 1320 feet in the 1/4 mile. I finished at 122mph. So keeping it simple, lets say my avg mph was halfway between 125mph and 122mph, or 123.5mph for the last 470 feet.

then distance/speed = time:
470 feet / 123.5mph = 2.59 seconds

FYI, you need to convert feet to miles by dividing by 5280 feet and convert hours to seconds by multiplying by 3600 seconds.

The math says it should have taken 2.59 seconds to finish the last 470 feet if I averaged 123.5mph after I let off. Add that to the 6.9 seconds when I left off and you get 6.9 +2.59 = 9.49 seconds for that pass, which is damn close to my actual 9.48 timeslip.

Now what if I had stayed in it the whole pass? I'll guesstimate that I should have finished at 145mph on that pass if I hadn't let off. So keeping it simple again, my avg mph for the last 470 feet would have been halfway between 125mph when I let off and 145mph, or 135mph. So how much quicker would that pass had been?

distance/speed = time:
470 feet / 135mph = 2.37 seconds

There you go, only about 2 tenths quicker giving me an ideal pass of 6.9 + 2.37 = 9.27 seconds.

So if you want to see why it only costs a couple tenths letting off before the 1000ft mark and coasting the rest of the run there is the answer. I would have only covered the last 470 feet a couple tenths quicker while accelerating to 145mph vs coasting. Its all about the 1/8th baby!

 

[bison]

Thanks for the math lesson Murph. Haha


BPE2013@hotmail.com

 

[Street Lethal]

If you do a little math, you can estimate how much time you should lose.... The only equation you need to know is distance/speed = time.

Your leaving out weight in your calculation, and what I am arguing is easing off the throttle after the 1/8th in comparison with hitting the brake, with the latter being a bit more factual when dropping 20-mph in less than 3 seconds when you already have the momentum of the weight moving with you, and not from a dead stop, which would be more in lieu with such a calculation method you chose to utilize for your estimate...

 

[Street Lethal]

Its all about the 1/8th baby!

Get that truck ready already, and we'll run your 1/8th mile... baby lol.

 

[murphster]

Your leaving out weight in your calculation, and what I am arguing is easing off the throttle after the 1/8th in comparison with hitting the brake, with the latter being a bit more factual when dropping 20-mph in less than 3 seconds when you already have the momentum of the weight moving with you, and not from a dead stop, which would be more in lieu with such a calculation method you chose to utilize for your estimate...

I can't explain it any more clearly than I already did........

 

[Street Lethal]

I can't explain it any more clearly than I already did........

It's not in an explanation Murph, I'll video the speedo in the C4 going up to 130-mph at wot on the highway, let off, and see how long it takes to get from 130-mph to 120-mph, let alone 140-mph to 120-mph, and I am positive it will exceed over three seconds without braking, and the C4 with me in it is five hundred pounds heavier...

 

[Street Lethal]

Here, my buddy Justin's car, his 1/8th mile was essentially the same during both runs; 123-125....

First run he lets off after the 1000- foot mark (just like you), second run he doesn't (just like you). His ET in the 1/4 mile has a difference of two tenths (essentially just like you), his trap speed virtually stays the same in both instances (unlike you, your 20-mph less). You had to of braked...

 

[Street Lethal]

Thanks for the math lesson Murph. Haha


BPE2013@hotmail.com

Bison, I am not arguing his 1/8th mile, I am arguing if he braked after that 1/8th mile or not. Such a drastic decrease in mph by just coasting after the 1000 foot mark, at the same time running only two tenths slower than his target. You don't feel he braked, and just coasted...?

 

[bison]

Bison, I am not arguing his 1/8th mile, I am arguing if he braked after that 1/8th mile or not. Such a drastic decrease in mph by just coasting after the 1000 foot mark, at the same time running only two tenths slower than his target. You don't feel he braked, and just coasted...?

Never really cared. There's no log to look at g force and know exactly what he did. The run was wasted after his foot came off the accelerator. Took eighth mile et and multiplied times 1.56. Gets high 9 teens.


BPE2013@hotmail.com

 

[Street Lethal]

Never really cared. There's no log to look at g force and know exactly what he did. The run was wasted after his foot came off the accelerator. Took eighth mile et and multiplied times 1.56. Gets high 9 teens.


BPE2013@hotmail.com

I'm going back and forth with Murph texting on the phone. My argument was based on thinking he exceeded 135-mph in that run, and then braked down to 122-mph. He is telling me he peeked at 125-mph by the 1000 foot mark and then let off, which is something the timeslip doesn't indicate, it obviously just shows 1/8th speed as the last mph factor, and a quicker 1000 foot time than his other slip, thinking he was still in it way after that mark. Only the log would show when he let off, but your right, at this point, who cares.

 

[pacecarta]

the log does and he told you so in post #24
i watched it and we finally had the time to go over the log , besides when he lifted i also discovered his two step couldnt have been active leaving only the boost controller launch setting to limit the launch rpm , found a wire came loose that triggers the two step

grasp this
the 1000 ft marker was tripped at 7.73 and he posted that the log showed he was off the throttle at 6.90
its as clear as it can be
6.90 is when his foot came off and tps went to 0 and remember that couldnt have happened until after he felt the tires slip .

 

[Street Lethal]

No, he told me not too long ago in a text. The very fact that I questioned a 20-mph drop from 140 to 120 should tell you I had no idea he let go at 125, which is why I was saying what I did. I initially thought he somehow reached 140, eased off, dropped to 122, yet still ran a 9.4, which is why I emphasized braking, as well as credited him for 8 second potential. Also, those calculations don't use drag, weight & aerodynamics as variables, as engine braking alone from an auto would make a difference from say depressing the clutch within 320 feet...

Edit to your edit: I seen that post, it didn't mention 125-mph, it only said he let off at 6.9 seconds into the run, yet he ran a quicker 1000 foot than the other run by a tenth of a second at 7.730. I have no idea where he let off to tell you the truth, but it seems it was after the 1000 foot mark, but just knowing now that he peaked at 125 and pulled answers my original questions...