jaredb900rr

I went to a Test & Tune at Rocky Mountain Raceway (at about 4,000ft elevation) today in West Valley, UT and ran a new best of 12.48sec @ 112mph. I was hoping for lower 12's, maybe an 11, but my launch needs some help (only a 1.928 60ft time). I rolled up to the staging area and as soon as the first staging bulb lit, I began to build up boost. Got up to about 10psi (manifold pressure for my twins) then crept forward til the second bulb lit and started to build up more boost. It seemed like the rear tires were starting to break loose at maybe 13psi or so, and that's where I launched. Do I just need to press harder on the brake pedal? What kind of psi are you guys launching at? Probably could've aired my 35" tires down as well, they were at 50psi.

Here's the YouTube link to the video,
http://www.youtube.com/watch?v=CczwQUZAcHw

Here's a link to the time slip,
http://i27.photobucket.com/albums/c1...k/timeslip.jpg

This is only about my 5th time down the track, so any advice would be appreciated!

Jared

JohnX

If your in 4wd, then you should be able to break one set of tires loose....even if it feels that way. Hold the brake harder and try to get some more boost out of her. I've run a 2.0 60ft in my truck, so I know yours can do more. I would shoot for 20psi on launch....more than that and your gonna break something. 20 might be too high When I ran a 2.0, I launched at under 10 psi, but I was floored and building boost when I let off the brake. Try to avoid building the boost and holding until the lights go green. I would say your on the right track with 10psi, creep the second bulb, hard on the brake and get on the throttle.

Hintz

Yea Id try to launch at 15-20 PSI, and air the tires down to 30psi. With what you have you are runnning SLOW, no offense, but you should be in the 11's easy. The only thing thats probably hindering you is the wheels/tires size, but something doesnt seem right.

mulisha

well if he has a tight t/c, he wont be able to build 20psi at the line.i cant. i can only build 12-15 tops, before i cant hold her there anymore.agreed you should be running close to me for sure.what a beautifull track and scenery.

samsneeze

something isnt right I ran a 11.7 with a silver bullet and *** 4's and evil twins on 33's with no cam or springs in yet. cant wait to see what the cam,springs and the 71mm do with and without spray

desertchecker

I also agree u should be knocking on high 11s easy , the 35s are not helping out !

try 4x4 15 lb + boost launch keep it under 20 or U WILL break something ....... try & run 30lbs in rear tires 32 lbs in front

jaredb900rr

I appreciate the advice! I still have my stock powdercoated rims that have 33" AT tires on them, so maybe I'll pull those off my Chevy work truck and put them on for next time. I'll air them down and practice some launches before I get to the track next time, too. And I won't forget to use the lockup switch, either!

Jared

soulezoo

Hey Jared,

Be careful with the boosted launches... especially with the 35's... the extra leverage those tires put on stuff is hard on parts. Also bear in mind, I snapped an output shaft just building boost at the line... I was just under 15psi when it let go (the light wasn't even green yet). Not all "15 psi" is equal. I used to launch at 20 psi with the old 3b set up no problem. I had to back down to 10psi on this setup. All I am saying is be careful! You don't know when it is too much until it is too late!

cquestad

Soul,

You need a stronger tranny! ;-)

Jarred,

You will just have to practice a bunch...to find the sweet spot. 15 psi is all I can do...before it is 4 tire nuclear meltdown.

05CTDN8

I am turning 1.66 60' and launching at 15-20 LBS. Lose the 35's and the 20" anchors....my 30's dropped my time 4/10ths. as well, I didnt see a flexplate in your sig....if you dont have one, GET ONE!!!

05CTDN8

once again...I destroyed my flex plate at our diesel event using the lock up switch. If you are running huge tires and tons of HP it is but a matter of time before you find the weak point. Your 60' concerns me....I know I am no expert, but you should be at or near 1.6x-1.7x 60'. Once you launch are you hammering it? As soon as I break the line I am at WFO until I hit the end of the track. Dont feather around the "slippage"...use more brakes. Drop your tire pressures down to 25-30 lbs and when you engage the lock-up switch make sure you are in second or better. I locked mine in between 1st and second. Took out my flex plate, tc, front seal, and scarred the input shaft.

this was on 536HP and 1036TQ. So have fun, but I agree with the above statement, not all boost is the same! Find the sweet spot that your truck likes...I bet it's right around 13-15lbs....then hammer down!

jaredb900rr

I think 13psi WAS actually too much (with the tires at full pressure), cuz it really felt like the rears were spinning. When I'm out "goofing around", I usually let off of my boosted launches at about 7-10psi. Those launches have felt much stronger than the one I did at the track. I just figured I'd try to lay into it a little more since I was at the track.

Terry, I think it was you that first explained that people usually see a decrease in boost pressure once you get head work done. Is this only at max boost pressure or would I notice this while building boost at the line as well?

Yah, looks like I just need to air the tires down and practice launching and see what hooks best.

I know, I'll prob end up putting my other rims on, I was just hoping to get closer to 11's on the 35" tires. I've got a fully built DTT tranny, so I'm covered in the transmission department.

jaredb900rr

Yep, I'm WFO and letting off the brakes as soon as the third green light comes on. I've used the lockup switch in 2WD (just after shifting into 2nd) while I'm out goofing around, but usually it just lights up the tires for a little while and then takes off. I just need to go out and practice with the tires aired down to find the sweet spot.

Thanks for the advice and the warnings on the flexplate and lockup switch.

AK RAM

I didn't see ladder bars in your sig. You can knock .2 off your 20psi launch with a good set.

paulb

On my 05 if I am bracket racing I will leave at 15psi. This will net about a 1.65 60' and an 11.20 e.t., and is very consistient. For heads up, I launch at 18psi, and will end up with a 1.58-1.59 60', and run ~11.08. This is on toyo proxies, and the truck weights 7150 with me in it. This was with the Flux 4.7 injectors.

The thing that bothers me about your run is the mph. With the power you should be making, you should be closer to 120. What boost are you seeing going down the track? When does it shift to OD (before the 1/8 mile?)? What is your rail pressure?

Paul