What gear do you guys usually trap a 1/4 in?

[Bbuchanan11]

Finally got my truck to the track for the first full run on it (broke the crank last year) I always put it in manual and select 5th to keep it out of 6th.. I almost swear it was on the rev limiter going through the traps granted this truck is faster then my last one but I always raced it keeping it in 5th and it had 28 inch tall sticks on it and I never had a problem but only trapping 115... my current truck judging by looking at a lot of the high ten second time slips on here my 1/8 mph was 98.99 which is like one off from a lot of the ten second passes but only trapped a 11.04 at 121.. tires on this truck are 315/45/16 drag radials. I figure shifting to 6th that late in the run would slow it down.... what do you guys think? Thanks Brendon

 

[coker6365]

Hold onto 5th if possible. No sense in defueling for a 6th gear shift. Figure out what RPM you need to hold 5th for your desired trap speed based on tire size and ratios, make sure it is reasonable for your valve train.

Sent from my SM-G965U1 using Tapatalk

 

[DAVe3283]

It really is case-by-case. If your HP starts to fall off too far as you push RPM, it might be worth the defuel and shift to get back in the powerband. You need to look at the average HP output over the last part of the run. That means how badly does your engine choke out as you rev, and how much defuel do you have to deal with? Each of my built transmissions has had a different amount of defuel at WOT.

At WOT, my current trans will only defuel the 1-2 shift, and every other shift holds 120mm³, so I let it shift 4-5 at 95 MPH then cross the line a second later at 104 MPH. It can do 104 MPH in 4th, but I am falling off the HP curve and it is actually slower. But this math all changes if there is a large defuel for the shift.

If you let it shift to 6th and it barely gets into 6th before you cross the line, probably not worth it, just stay in 5th and rev it out. If you are holding 5th for what seems like forever, and it feels like power is dropping off, you might want to let it hit 6th. You can look at logs and see how much defuel you have, look at a dyno pull and see how badly your HP curve falls off as you rev, and do the math. Or, you can just do 2 runs and see if hitting 6th makes you faster or slower :thumb:

 

[Bdsankey]

I have a 5 speed truck. In the 1/4 it took 5th but I don't know at what point. I ran a 7.498 @ 100.90mph in the 1/8th mile and ran a 11.391 @ 126.85mph in the 1/4 mile.




I know it needed 5th but my setup doesn't pull hard off the line due to the big single, big stall converter, and 35" old BFG mud terrains.

 

[2004LB7]

Sounds like regearing the rear end may help you a lot

 

[Ne-max]

Sounds like regearing the rear end may help you a lot

I hope his truck is 2wd

 

[Bbuchanan11]

I did only get to make one run and I forgot to data log it...and for how small my turbos are I’m sure it was out of power I just didn’t expect it to run out of rpm or gear whichever .. might try to get to the track again tomorrow night and see what 6th gear does

 

[Bbuchanan11]

No it’s 4wd that’s why re gearing probably won’t happen

 

[Mike L.]

I would keep it out of 6th. In 6th you're putting a bigger load on the engine with the rear planet spinning.

 

[Bdsankey]

A 315/45R16 drag radial is only 27.16" tall, that may also be part of your problem.


What is your limiter set at? Do you have a dyno graph to see where power carries to or how far past peak it nosedives?

 

[Ne-max]

When you hit 6th it will feel like you lost all power. Your tire height is a issue but you should still see higher trap speeds.

 

[Bbuchanan11]

I have never had it on a dyno and I’m not sure where mark set the limiter... I’m honestly starting to second guess myself to it being in 4th gear instead of 5th. After I did my burnout I was creeping to the staging light and a guy on the track backed me up to wait for the guy beside me... so I had to pull it back in to M and then select the gear again... I feel like I should get more then 121 out of 5th gear.... guess I might have to hit a back road tonight and find out.

 

[Bbuchanan11]

Well just took it for a ride it was definitely in 5th gear

 

[Bbuchanan11]

And I also measured my tires on the truck and they are only about 26 and a half inches tall... looks like I’m gonna need some new tires.

 

[PureHybrid]

It really is case-by-case. If your HP starts to fall off too far as you push RPM, it might be worth the defuel and shift to get back in the powerband. You need to look at the average HP output over the last part of the run. That means how badly does your engine choke out as you rev, and how much defuel do you have to deal with? Each of my built transmissions has had a different amount of defuel at WOT.

At WOT, my current trans will only defuel the 1-2 shift, and every other shift holds 120mm³, so I let it shift 4-5 at 95 MPH then cross the line a second later at 104 MPH. It can do 104 MPH in 4th, but I am falling off the HP curve and it is actually slower. But this math all changes if there is a large defuel for the shift.

If you let it shift to 6th and it barely gets into 6th before you cross the line, probably not worth it, just stay in 5th and rev it out. If you are holding 5th for what seems like forever, and it feels like power is dropping off, you might want to let it hit 6th. You can look at logs and see how much defuel you have, look at a dyno pull and see how badly your HP curve falls off as you rev, and do the math. Or, you can just do 2 runs and see if hitting 6th makes you faster or slower :thumb:

35" tire? Mines at the top of 4th at the 1/8mi ~85mph

 

[DAVe3283]

35" tire? Mines at the top of 4th at the 1/8mi ~85mph

Yeah, ~35". BFG KO2 in 315/70R17.

 

[TROJAN366]

A while back I was looking to run drag radials on pyos and had an issue finding anything tall enough for a 16” wheel. I ended up grabbing a set of 18s and 305/45 Mickey Thompson ET street R’s. They measure 29x12.5. I was happy with them and went 10.6 but the 60ft times weren’t as consistent as my full slicks. Probably due to my lack of track time though.

 

[2004LB7]

And I also measured my tires on the truck and they are only about 26 and a half inches tall... looks like I’m gonna need some new tires.

with that size tire it looks like you would be pushing about 3900 rpms to go 115 mph

 

[Bbuchanan11]

I went 121 and I know I was over 4000 because the tach was straight up as I just glanced down it was almost in the red and I’m pretty sure on the rev limiter Trojan what size are your full slicks? Reason I ask my truck has qa1 coil overs in the front torsion bars are cut out so I can’t even fit a beer can under the front cross memeber the whole way to the trans pan so I’m very limited to how big of a tire I can go. I wish now I woulda kept my Hoosier 28x11.50 but my trailer ended up breaking so I drove over an hour away with the drag radials so that’s kinda why I would like to stay with radials

 

[TROJAN366]

I have had two sets of 30x14 m&h cheaters. If you are that low the Mickey Thompson’s might be a good option. Lots of offset ofprions for 18s and they aren’t too wide compared to other options. Might let you turn a bit. The 30x14s rub on my setup and I’m not that low.