Looking for 0.15...Gearing for ET?

[kmkalkhoff]

Best pass on the new build is 10.14 @ 137.7 with a 1.58 60'...I don't have my slip in front of me, but the 1/8 et was 6.5x @ 109.x.

My goal was to get a 9.9x pass this year, and as long as weather cooperates, I'll get one last shot at a track rental in a couple weeks.

Current wheel & tire setup is 20" forgestars with Michelin pss street tire up front and mt 305/35/20 et street ss on the rear. I have 17" forgestars drag wheels waiting and will mount a "skinny" on the front, but I need some input on selecting the rear tire.

This is a 4l80e car with 3.23 rear. First gear just seems to draaaag out and the car shifts into 3rd crossing traps at 5200 ish RPM. When you watch the car make a pass, it just sounds so lazy with these gears.

So, I want to run a MT ET Street R on the 17x10 wheel, and I'm contemplating running a 275/45/17 which is 26.1" tall. Looks aside, this should help my gearing over the 28.7" tire I'm currently running. I think it will look hideous without lowering the car since it's such a short tire, but will it hook enough to potentially get my 60' down to the low 1.5, high 1.4 range, which should be enough to shave 0.15 off the 1/4 et??

If not, I will just go with a 305/45/17, which is 28", and swap the 3.23 out for a 3.73 over the winter. Unfortunately I don't have time to get the gear swap done in time for rental.

26" tire @ trap is about 5,800 rpm
28" tire & 3.73 @ trap is about 6,100 rpm

Is the 26" tire a bad idea?

[acammer]

Originally Posted by kmkalkhoff

Best pass on the new build is 10.14 @ 137.7 with a 1.58 60'...I don't have my slip in front of me, but the 1/8 et was 6.5x @ 109.x.

My goal was to get a 9.9x pass this year, and as long as weather cooperates, I'll get one last shot at a track rental in a couple weeks.

Current wheel & tire setup is 20" forgestars with Michelin pss street tire up front and mt 305/35/20 et street ss on the rear. I have 17" forgestars drag wheels waiting and will mount a "skinny" on the front, but I need some input on selecting the rear tire.

This is a 4l80e car with 3.23 rear. First gear just seems to draaaag out and the car shifts into 3rd crossing traps at 5200 ish RPM. When you watch the car make a pass, it just sounds so lazy with these gears.

So, I want to run a MT ET Street R on the 17x10 wheel, and I'm contemplating running a 275/45/17 which is 26.1" tall. Looks aside, this should help my gearing over the 28.7" tire I'm currently running. I think it will look hideous without lowering the car since it's such a short tire, but will it hook enough to potentially get my 60' down to the low 1.5, high 1.4 range, which should be enough to shave 0.15 off the 1/4 et??

If not, I will just go with a 305/45/17, which is 28", and swap the 3.23 out for a 3.73 over the winter. Unfortunately I don't have time to get the gear swap done in time for rental.

26" tire @ trap is about 5,800 rpm
28" tire & 3.73 @ trap is about 6,100 rpm

Is the 26" tire a bad idea?

I think we're missing a few key pieces of information to really say what the "best" setup would be here. Specifically, the engine build, especially camshaft spec. With that kind of MPH I'm sure that's not stock. Also need to know about the converter.

Even without knowing that detail, I think you're definitely heading in the right direction getting the rpm up. I would think that if you're focus is purely ET then a 28" tire on a 3.73 rear is your best bet. Depending on the cam and how the engine makes power, and if you have a lock-up, you might do even better with a 3.91 locking the converter around 120mph to pull it back down into the meat of the power, and then run it out to like 6500.

The 26" tire isn't a bad idea either, assuming you don't sacrifice too much traction. Plenty of guys hook up a 275 slick just fine well into the single digit ETs - so I would think you're fine with the right power management.

[frankwjr]

watch the track temps....DA should be good and hopefully it will be a sunny day to put some heat down for traction...what track?,,,good luck..

BTW - make sure your F/R tire height is close..to much diff can cause ABS to freak..

[kmkalkhoff]

The car is a 2013 ZL1 so I'm limited to 3.23's and 3.73's with the ZL1 rear end.

Factory LSA bottom end
Ported TFS Heads
Ported Blower
102mm TB
BTR 3 PDS Blower Cam
E85
Jake's stage 3 4l80e
Precision multi disk 2800 stall

The car makes 770/770 to tire.

I currently have the converter locking about 85 mph, which is about half way through second gear.

[kmkalkhoff]

Track is MIR...front and rear will be matched accordingly.

DA and track prep are typically excellent.

[bct10985]

I have a similar setup to you and run almost the same time. Stock bottom end ls3, vortech ysi, 4l80e, 3600 stall. How are you controlling the trans? What rpm you shifting at? Your locking it in 2nd gear?
Mine was locking too early in 3rd and i left it unlocked and it went faster.

[kmkalkhoff]

I use HPtuners to control the trans.

1-2 @ 6300 rpm
2-3 @ 6300 rpm

Yes, I've got lockup commanded on the second gear shift, but it won't actually lock up until about 85 mph. If you watch the logs, it loses 2-3 mph when it locks up.

[kmkalkhoff]

I always just thought it was common practice to lock the converter as early as the trans can handle.

How much faster did it go unlocked? That's a simple adjustment in HP tuners.

[kmkalkhoff]

Originally Posted by bct10985

I have a similar setup to you and run almost the same time. Stock bottom end ls3, vortech ysi, 4l80e, 3600 stall. How are you controlling the trans? What rpm you shifting at? Your locking it in 2nd gear?
Mine was locking too early in 3rd and i left it unlocked and it went faster.

What does your car 60'?

[bct10985]

I have a u.s. shift quick 1 controlling my 4l80. It came a couple pre loaded tunes, 1st time i took it to the track it locked half way through 3rd gear. When i kept it unlocked through the whole run it picked up 3 mph. I shift around 6900 but thats with a centrifugal blower that keeps making boost

[bct10985]

1.6 every time. I need a higher stall converter, i too am stuck to 3.73 gears with the zl1 rear

[kmkalkhoff]

Originally Posted by bct10985

I have a u.s. shift quick 1 controlling my 4l80. It came a couple pre loaded tunes, 1st time i took it to the track it locked half way through 3rd gear. When i kept it unlocked through the whole run it picked up 3 mph. I shift around 6900 but thats with a centrifugal blower that keeps making boost

I can see it picking up MPH, but did it improve your ET? I would be curious to see what 2nd gear lockup would do for you.

I don't lose boost on the shift with the 1.9L Eaton.

1st gear peaks around 16.8 psi
2nd gear peaks around 17.5 psi
3rd gear peaks around 18.0 psi

I am going to increase my shifts to 6700-6800 RPM at the next race to see if that helps.

[Pro Stock John]

I'd be more a fan of 305/45/17s over 26s.

Skinnies along would drop a bunch of weight and rolling resistance up front, I'd get those now or borrow some.

[kmkalkhoff]

Originally Posted by Pro Stock John

I'd be more a fan of 305/45/17s over 26s.

Skinnies along would drop a bunch of weight and rolling resistance up front, I'd get those now or borrow some.

I'm with you 100% - the 26" tire would be a temporary fix. I think long term plan would look like this:

Light weight wheels
Skinny front tire
28" rear tire
3.73 gears
3600 Stall Converter