Changes I'm making on my quest for a 9 sec pass
10-12-2008, 07:59 PM
#1
Changes I'm making on my quest for a 9 sec pass I've been running low 10's since last season. My previous best pass on the T76 was a 10.13 @ 132.7 boosting 19 psi with a 1.48 60'. My best pass this year is 10.15 @ 136.6 on a 1.61 60' on 16psi. I think having to shift into 3rd gear is what is holding me back since I'm seeing 20% converter slip when I cross the line at 5800 rpms in 3rd... that's pretty bad. My converter slip at 7000 rpms in 2nd gear is 4% which is a huge difference. I still haven't cut a 1.5x 60' this year, but I'm hoping that will change. My current tire is 275/50/15 hoosier drag radial which is really short, it's only around 25.4" tall. It's noticably shorter than my 275/40/17 nitto drags I drive on the street.
I just spent a whole lot of money on changing my car to try and get myself the elusive 9 sec pass, I hope it works. Here is the break down of what I spent.
$320 Set of used weld pro stars 10x15 and 3.5x15 with tires, spacers and lugs. Rears cam with Hoosier QTP's with about 50% life left, the skinnies I found out are junk. They are wobbled and unusable, but the front tires are brand new 165/80/15 radials.
$117 tubes for the used QTP's since one of them had a screw hole.
$199 for some Jegs pro star knock offs to replace the weld skinnies.
$95 for 12 gallons of 111 octane so I can turn up the boost without worrying about detonation.
$225 Looked on craigslist and found some 28x12.50x15 ET street, brand spankin new with stickers and ******* still on em. Score!
So I just spent $1000 looking for 0.16 of ET... makes me sick. I can only imagine how much everything would have cost me new if I wasn't such a cheap bastard and always buying used stuff. Turns out I'm not going to need the tubes or the QTPs that came on the wheels now, I'll probably sell them as well as my Hoosier drag radials to try and recoup some $$.
So how much better do you think the 28" tall tires are vs 25.4" tires for 60's. I've been consistantly in the 1.6's this year on the radials, the track usually has questionable prep and I often have to make my passes after 20 FWD street tire cars do their ricetastic one wheel burnouts dragging watter everywhere. It's a regular ET street and not the stiff sidewall version, but beggars can't be choosers. I'll just rotate them every track day to extend the sidewall life.
I just spent a whole lot of money on changing my car to try and get myself the elusive 9 sec pass, I hope it works. Here is the break down of what I spent.
$320 Set of used weld pro stars 10x15 and 3.5x15 with tires, spacers and lugs. Rears cam with Hoosier QTP's with about 50% life left, the skinnies I found out are junk. They are wobbled and unusable, but the front tires are brand new 165/80/15 radials.
$117 tubes for the used QTP's since one of them had a screw hole.
$199 for some Jegs pro star knock offs to replace the weld skinnies.
$95 for 12 gallons of 111 octane so I can turn up the boost without worrying about detonation.
$225 Looked on craigslist and found some 28x12.50x15 ET street, brand spankin new with stickers and ******* still on em. Score!
So I just spent $1000 looking for 0.16 of ET... makes me sick. I can only imagine how much everything would have cost me new if I wasn't such a cheap bastard and always buying used stuff. Turns out I'm not going to need the tubes or the QTPs that came on the wheels now, I'll probably sell them as well as my Hoosier drag radials to try and recoup some $$.
So how much better do you think the 28" tall tires are vs 25.4" tires for 60's. I've been consistantly in the 1.6's this year on the radials, the track usually has questionable prep and I often have to make my passes after 20 FWD street tire cars do their ricetastic one wheel burnouts dragging watter everywhere. It's a regular ET street and not the stiff sidewall version, but beggars can't be choosers. I'll just rotate them every track day to extend the sidewall life.
10-12-2008, 08:10 PM
#2
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28's should make a big hook difference. Get all the boost you can at the hit and all the hook you can get.....adding power down track will help mph but not much ET. It's all in the hit.
10-12-2008, 08:17 PM
#4
Well, I believe if you are getting a fair amount of spin off of the line the 28in tire will help. But, if you are hooking well and just not leaving under much boost-the 28's will most likely hurt the launch. Yet, in either case; if it keeps you from shifting into 3rd during the run, that may be enough to overcome any et deficit from the launch (or simply add on to what was gained). All in all, the tire change should put you in the 9's.
10-12-2008, 09:11 PM
#5
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The larger tire should help you launch. Keep in mind the taller tire will also effectively reduce your gear ratio. Seen from past posts that you're running a very low ratio already (2.xx). Taller tire should help boost production by adding even more load to the engine, but I guess the jury is out whether it'll make the car run faster overall.
Good luck to ya'
Good luck to ya'
10-12-2008, 09:34 PM
#7
Well, I believe if you are getting a fair amount of spin off of the line the 28in tire will help. But, if you are hooking well and just not leaving under much boost-the 28's will most likely hurt the launch. Yet, in either case; if it keeps you from shifting into 3rd during the run, that may be enough to overcome any et deficit from the launch (or simply add on to what was gained). All in all, the tire change should put you in the 9's.
Great idea... if I had overdrive! I currently turn 3000 rpms at 80 MPH on my nittos, if I went to a 3.70 gear i'd be turning 4000 rpms to go 80, that's not very street friendly.
I've never heard of anyone using a th400 like a 2 speed trans before. I'm sure it's been done before, but I haven't found anyones results. I'm hoping for harder launches and higher MPH from this. I'll post up the results even if the idea fails on friday night when I get back from the track. If it works, this could be a good way for the cheap bastards out there to go 9's and still have good street manners with a cheap th400 vs a 4L80e setup.
Assuming the overall diameter of the tire will be 28.5" with growth I should be able to go 142 mph in 2nd gear at 7200 rpms allowing for 6% converter slip.
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10-13-2008, 12:43 AM
#11
I just checked my data logs, here are the numbers I've calculated for the 25.4" tire
in 2nd gear at the 1/8 mile on 25.4" tires I have 8% slip (108 @ 6400 rpms)
in 3rd gear at the 1/4 mile on 25.4" tires I have 19% slip (136 @ 5900 rpms)
So with the new tires I should be around 12 % slip at the 1/8 and 4% at the 1/4 and have the ability to 60' better and be at full boost 1 sec sooner if I can launch at 9-10psi. Data log shows 2.0 sec to reach 16psi on a 5psi launch. If I launch at 9psi I get to 16psi in 0.9 sec thus raising my average horsepower at the most critical portion for ET on a pass, in theory of course. I'm also only making 1 gear change vs 2 gear changes so that saves me some time too. I think it has to work better staying in second vs spending 2 seconds in 3rd at 19-20% slip.
Yeah, I know I'm weird with my thinking, but it got me to several low 10 sec passes with a combination that looks like it was designed by Fail Inc. on paper. The math looks good to me. I'm a nerd and this is my project, I have few pre concieved notions so my thinking tends to be out of the box sometimes.
Besides, if the idea fails, I just go back to my old tires
Last edited by Zombie; 10-13-2008 at 12:49 AM.
10-13-2008, 07:54 AM
#13
9 Second Club
Remember, run as much of the pump gas out on the street as you can before you go to the track. Then load it up with the 111. That will give you some options to go with 1-3psi or a couple degrees of timing depending on what the weather and the air are when you get to the track. Don't get greedy and do both on the same pass though. 
The tires will probably get you a consisent 1.45-1.55 60'. You won't want any more than 8-10lbs at the line because it will just blow the tires away if your suspension is marginal.
You'll get it and it will be worth it.
Rick
The tires will probably get you a consisent 1.45-1.55 60'. You won't want any more than 8-10lbs at the line because it will just blow the tires away if your suspension is marginal.
You'll get it and it will be worth it.
Rick
10-13-2008, 10:29 AM
#16
Yes, my fabricator does't have time. The smallest pipe is 2.25" so I know it's holding me back some with my 450 ft/sec velocity. I wish I could do some of it myself, but I have no space and almost lost a battle with a cut off tool yesterday. Watching me use power tools is like watching a monkey hump a football.
Last edited by Zombie; 10-13-2008 at 10:35 AM.
10-13-2008, 11:01 AM
#17
The plan is to start at 7 psi and work up from there. I'm not going to change anything but the tires until I see how they affect my times. I'd like to see if going to 18psi on this higher octane increases my mph at all. If I can go 1.45-1.55 60's all the time I'll always be in the high 9 low 10 sec range. BTW, my only susp mod is LCA's, rest is stock stuff, torque arm is stock but adjustable.
Yes, my fabricator does't have time. The smallest pipe is 2.25" so I know it's holding me back some with my 450 ft/sec velocity. I wish I could do some of it myself, but I have no space and almost lost a battle with a cut off tool yesterday. Watching me use power tools is like watching a monkey hump a football.
Yes, my fabricator does't have time. The smallest pipe is 2.25" so I know it's holding me back some with my 450 ft/sec velocity. I wish I could do some of it myself, but I have no space and almost lost a battle with a cut off tool yesterday. Watching me use power tools is like watching a monkey hump a football.
Good luck keep us posted
10-13-2008, 11:57 AM
#19
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I wouldn't focus so much on trying to run the quarter with 2 gears, I would run the 28's and come out on more power. On my 16 psi 10.05 pass, I cut a 1.51 and it left very soft on maybe 6 psi.
