Nitrous and gear sets

[racer3]

I have a question about gear sets and nitrous. I now have 5.14:1, but I was informed that this could be to low. This truck is driven only at the track. Engine limit is 8000 rpm. I have a 31" x 14" tire. Would like some opinions on gear ratios. I have a set of 4.86's, truck should pick up mph. I am also thinking 4.11's, but how the nitrous effect rpms? Will I run out of gear at the big end or have a problem hooking? Any input would be helpful, thank-you, Al

[jjvette]

If your truck is truly set up correctly N/A you will run out of gear on N2O.
Let me explain. If you are at or near peak RPM when you go thru the traps you will run out of gear when spraying. I can't tell you what gear to run but my Vette runs 112mph @ 4600 RPM through the traps N/A. On the juice I go thru at 120mph @ 5000 rpm. That is with 3.07 gears. Yeah I know suck gears! My point is you will have to adjust your gear ratio for the juice.

John

[racer3]

If your truck is truly set up correctly N/A you will run out of gear on N2O.
Let me explain. If you are at or near peak RPM when you go thru the traps you will run out of gear when spraying. I can't tell you what gear to run but my Vette runs 112mph @ 4600 RPM through the traps N/A. On the juice I go thru at 120mph @ 5000 rpm. That is with 3.07 gears. Yeah I know suck gears! My point is you will have to adjust your gear ratio for the juice.

John

John, I go thru the traps at 134.73 mph @ 7500 rpm. This is with a 5.14 gear. How big a shot are you using? I see you gained 400 rpm with the N2O. How do you know how much rpm you are going to gain off a shot? 4.86's will give me another 7 mph on big end N/A. Truck has a 250 shot now. Looking for low 9's or high 8's.

[jjvette]

There is no real formula. It's test and tune! My brother picked up 14 mph with a 150 shot. Actually I was expecting around 12 mph or so with my 150 shot. I was running really rich. Diesel looking rich! Black smoke galore! I definately need to tune it.
I bet someone like the fella with the wheelie pullin wagon (hammered54) can help with gear estimating. He has alot of experience!

Cheers,
John

[racer3]

Thanks John!

[hammered54]

just read the post, sorry pm'ed first.
if you change to the 4.86 it look's like rpm will drop by about 300 rpm +/- so if you need to stay in the 7500 range ( 400rpm w/nos added) you should be right in the ballpark with this change.
although a lot depend's on how tight you converter is/is'nt, how is it 60ing? 2 or 3 speed tranz?
Matt

[racer3]

just read the post, sorry pm'ed first.
if you change to the 4.86 it look's like rpm will drop by about 300 rpm +/- so if you need to stay in the 7500 range ( 400rpm w/nos added) you should be right in the ballpark with this change.
although a lot depend's on how tight you converter is/is'nt, how is it 60ing? 2 or 3 speed tranz?
Matt

My converter is a ati 8" with a antiballooning plate. Truck's best 60' was 1.32, 9.75 @ 136 mph. I use a powerglide with 1.76 1st gear, 31" tire, this is in the 1/4 mile. How do you come up with the rpms w/nos added and gear change? Thanks for your reply. Al

[hammered54]

I used a rpm calculator and pluged in your rpm and both gear set's and there was only 300rpm +/- between the two.
so if you choose to replace the 5:14 with the 4:86 you should stay under the 8000 limit. 60's may drop n/a but mph should pick up, also with the spray 60's will pick back up quite a bit.
rpm's will climb at a much faster rate so your shift will come sooner and a good chance mph will pick up too.
check out Tim Mcamis.com he has some great formulas on the web page for just about any set up you may what to use. good luck Matt

[jjvette]

I used a rpm calculator and pluged in your rpm and both gear set's and there was only 300rpm +/- between the two.
so if you choose to replace the 5:14 with the 4:86 you should stay under the 8000 limit. 60's may drop n/a but mph should pick up, also with the spray 60's will pick back up quite a bit.
rpm's will climb at a much faster rate so your shift will come sooner and a good chance mph will pick up too.
check out Tim Mcamis.com he has some great formulas on the web page for just about any set up you may what to use. good luck Matt

Just as I thought! You da man!

[hammered54]

Just as I thought! You da man!

yeah, I was think'n bout just pull'n sumtn out'a my ass, but he's a bowtie guy! and we can't have that now can we!!!:shock:

[racer3]

I used a rpm calculator and pluged in your rpm and both gear set's and there was only 300rpm +/- between the two.
so if you choose to replace the 5:14 with the 4:86 you should stay under the 8000 limit. 60's may drop n/a but mph should pick up, also with the spray 60's will pick back up quite a bit.
rpm's will climb at a much faster rate so your shift will come sooner and a good chance mph will pick up too.
check out Tim Mcamis.com he has some great formulas on the web page for just about any set up you may what to use. good luck Matt

Hey, thanks Matt. This is very good info! Hope to be into the mid 8's! Chevy horsepower rules!:thumbup: