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Discussion Starter #1
Can i do it? should i? boost in 5th
I have 410 gears and i will run out of gear in the 1/4 mile. i was over 6k rpm in 4th gear and was wondering if it is safe to boost in 5th.
what options do i have so i wont have to shift to fifth?
current size is 315/35/17 on a 17 by 10 1/2 rim
with 350 hp 350tq i ran down the track at 116mph trap
just got my car re tuned and its making 415 hp 407 tq. obviously i don't want to push over 6k rpm on the stock motor.
sorry for the gathering of thoughts just wanna know what my options are:tomato
 

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Swap to 3.73's or try a larger tire, just switching to 5th will lower your ET, and boosting in overdrive is too hard on the car, even more with stock internals
 

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To be honest, having to hit 5th gear is going to hurt your ET more then anything. With 4.10's and hitting boost in 5th isnt that big of deal. Just dont do it a lot. Ive done it a few times.

BTW, I have a vortech and shift at 6300rpm, my tuner told me to shift to 6500rpm. You should be able to wind out 4th alittle more.

I would look into 28" tires for a higher top speed in 4th for the track, or 3.73s for a permanent higher top speed in 4th.
 

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Discussion Starter #5
thanks for the quick response!! lowering gears is an option but kinda pricy. i need some new tires asap anyways. i don't know if they make a taller tire(looking for dr) for a 17 by 10.5 rim. that would be an easy fix. searching now...
 

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i could only find a taller tire in the form of a slick. i don't have a built rear end so i really don't wanna buy slicks. might have to just switch gearing.
 

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In a manual transmission fifth is just another gear. First gear is 3.38, second is 2.00, third is 1.32 and fourth is 1.00. Fifth at .67 (or .62) is just one more step higher. At any point in time you could make the case that WOT is harder on the motor in the next higher gear. The thing about the next higher gear is that you stay in it a lot longer than the gears below it. I have read that one of the reasons that Ford changed the oil quantity recommendation from five to six quarts is the possibility of pumping the oil pan dry during prolonged high rpm runs. And that is definitely hard on the motor. But that should be a problem on a short run.

Think of it this way. 4.10 x .62 = 2.55. So it would be the same as accelerating in fourth with 2.55 gears. Its not ideal and it will take a long time to build rpms.

I have read that you cannot do the same thing with an automatic transmission. Apparently they get stuck between third and overdrive.
 

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Just buy some 28" tire like everyone has said, i run them and I havent run outta rpms yet with my mph. And Et streets are arent a slick. You can get them in a drag radial that will be tall enough
 

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In a manual transmission fifth is just another gear. First gear is 3.38, second is 2.00, third is 1.32 and fourth is 1.00. Fifth at .67 (or .62) is just one more step higher. At any point in time you could make the case that WOT is harder on the motor in the next higher gear. The thing about the next higher gear is that you stay in it a lot longer than the gears below it. I have read that one of the reasons that Ford changed the oil quantity recommendation from five to six quarts is the possibility of pumping the oil pan dry during prolonged high rpm runs. And that is definitely hard on the motor. But that should be a problem on a short run.

Think of it this way. 4.10 x .62 = 2.55. So it would be the same as accelerating in fourth with 2.55 gears. Its not ideal and it will take a long time to build rpms.

I have read that you cannot do the same thing with an automatic transmission. Apparently they get stuck between third and overdrive.
5th gear has an extra gear setup kind of like reverse. I would not get on it cause it is not very strong of a set up. Get some 15 inch wheels and run 28 inch 2 ply tires. They are easier on your rear than dr.
 

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i could only find a taller tire in the form of a slick. i don't have a built rear end so i really don't wanna buy slicks. might have to just switch gearing.
Bias ply slicks are going to be easier on a stock rear end than drag radials will, plus you'll get better traction. It's a win-win to me. Get some dedicated drag rims and run a 28" d.o.t. slick like a Quick Time Pro from Hoosier

EDIT: I just noticed I posted basically the same thing as Stal. Great minds think alike.
 

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Ive discussed it a few times that the added stress of boosting in 5th is the cause of input shaft failures. Its def gonna add alot more stress and not help you with a good time.
 

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From what I've read the input shaft failures come earlier, like second or third. I won't disagree that fifth is probably a weaker gear. I have never known anyone to drag race in fifth. But a drag radial that doesn't stick so much is better than a slick that does. ET Streets have been know to break input shafts. 555r's? Not so much. If you want to launch at 5500 rpms, you had best beef up the drive train.
 

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From what I've read the input shaft failures come earlier, like second or third. I won't disagree that fifth is probably a weaker gear. I have never known anyone to drag race in fifth. But a drag radial that doesn't stick so much is better than a slick that does. ET Streets have been know to break input shafts.
Im not sure if you have ever raced with slicks but you can feel how much energy they absorb on the launch. Yes you can still break axles and input shafts with them but those people are the ones coming out of the hole dumping the clutch off the red line
 

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i could only find a taller tire in the form of a slick. i don't have a built rear end so i really don't wanna buy slicks. might have to just switch gearing.
This is why I went with 18x10s, much larger option for tire sizes

From what I've read the input shaft failures come earlier, like second or third. I won't disagree that fifth is probably a weaker gear. I have never known anyone to drag race in fifth. But a drag radial that doesn't stick so much is better than a slick that does. ET Streets have been know to break input shafts. 555r's? Not so much. If you want to launch at 5500 rpms, you had best beef up the drive train.
Its not the gear thats weak, its the stress the low 5th gear puts on the input shaft to the transmission. And if your slamming gears and hit 5th alot its gonna hurt. Input shaft failures arent common and seem to be sparadic, all different power levels. Trying to put big power down in 5th isnt good. It would be like goin to 3rd or 4th and flooring it while at 2k rpm, you wouldnt do it.
 
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