Author Topic: Taller gears for nitro?  (Read 13177 times)

Offline msundstrom

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Taller gears for nitro?
« on: February 06, 2013, 07:41:22 PM »
Hi Spud,
This is not directly about fuel but related. My question is about gear ratio. I will be setting up with methanol and then switching to nitro. Should not take too many passes for this. I ran 4.10's last year but have 3.89's . It seems like your progression has been taller as you added more juice. Will 25% be that sensitive to more load?
(FED/BBC 466 Stack Hilborn  33x12 tires)
Thanks
Mark Sundstrom

Offline Spud Miller

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Re: Taller gears for nitro?
« Reply #1 on: February 06, 2013, 09:05:26 PM »

 Hi Mark!

 Below 30% or so, gear ratio won't be a huge factor. The old rule is: the more torque you have, the less gear you need however. So, as you sneak up the power you really will need less gear.

 If you run nitro the "dry" way or AFR method, load isn't a biggie. You'll burn it all and tune pretty much like methanol, keeping the AFR correct and tuning by plug color. You'll make more torque and I found that 3.73's were just about right with a tire that big doing that up to 75% or so.

 If you run nitro over 80% you need to go to the wet, sloppy mixture (start by doubling the volume from the AFR method - I call it the "OMG Method" ;)  then it becomes totally dependent on motor load.

 Example: I started turning my converter into mush (over-powered it) and began driving through it at half track. The instant it would do that, the load went away to the point that all 8 cylinders went out! Raw fuel out of all 8 zoomie tubes and it was like throwing out the anchor. Just like hitting the kill switch. New (bigger) converter, no more issue.

 To increase the motor load and kill tire shake, I kept losing gear. Finally at 2.91, magic! Amazingly, best 60' ever (1.69 low gear too!) and it's burning 10 GPM at 62 degrees of total timing.

 So...to summarize: With the lighter load, you could shed some gear ratio but it won't affect tuning too much. With the heavy, high volume mixture, it's totally dependent on load (and spark timing).

 Spud

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Offline Blind Mule

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Re: Taller gears for nitro?
« Reply #2 on: February 08, 2013, 06:44:41 PM »
Spud you ran a 2.91 rear gear :o

Offline Spud Miller

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Re: Taller gears for nitro?
« Reply #3 on: February 08, 2013, 08:51:55 PM »

 Yup, still do. 2.91's are fantastic for a dragster with a converter on big loads of nitro. I didn't discover it on my own. I had to be at the end of my rope and then convinced by a guy who'd been there before...Pat O'Neil. He was right!

 If you run the typical drag gear ratios with that much torque and torque multiplication, it will either blow the tires off or shake so hard that parts break off the car (or driver) on every single pass.

 Oh yea, and you combine it with a 1.69 low gear :)

 Spud

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Offline Blind Mule

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Re: Taller gears for nitro?
« Reply #4 on: February 08, 2013, 10:22:55 PM »
 :o ;D

Offline AF150

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Re: Taller gears for nitro?
« Reply #5 on: February 09, 2013, 11:30:00 AM »
I agree...we ran a 407" FED w/ a glide, injected on 30-35% for NE1. A 3.70 gear was just about
right with light load of nitro. Would run 7.50 @ 180+ all day long. Very successful combination.
MB
MB

Offline Blind Mule

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Re: Taller gears for nitro?
« Reply #6 on: February 09, 2013, 04:10:06 PM »
That gear must really load the motor!

Offline Spud Miller

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Re: Taller gears for nitro?
« Reply #7 on: February 09, 2013, 08:22:41 PM »

 Yup, I was afraid it would be a slug off the line but was ready to live with it to get down the track.

 Best 60' is a 1.04 so far and that's keeping 17 degrees out of it at the hit. So the gears were good all around.

 Spud

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Offline masracingtd1167

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Re: Taller gears for nitro?
« Reply #8 on: February 10, 2013, 02:23:51 PM »
Hi Spud I was reading your post about the gear ratio and that you use a 1.69 low gear . I run an injected small block that we spray with nitrous . Our cars are similar in weight and horse power I have gone 6.94 at 192 with mine . I use a 12x33 tire . I have been thinking about going to the 1.69 low gear from a 1.80 to help controll my wheel speed . Right now I bring the nitrous in at .2 but I would like to bring it in earlier without it blowing the tires off or shaking . Did the low gear help ? Thanks Bill Masiello 

Offline Spud Miller

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Re: Taller gears for nitro?
« Reply #9 on: February 10, 2013, 07:15:22 PM »

 I never ran the 2.91's with the 1.76 or a 1.80 low...I changed to those rear gears and the new planetary at the same time. Originally, I was after 1.60's but BTE quit making them. No regrets - the 1.69's work great.

 I think it would probably accomplish what you're after...less gear sure cured the shaking. I think not blowing the tires off now is probably more due to taking timing out at the hit.

 Spud


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Offline gregm784

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Re: Taller gears for nitro?
« Reply #10 on: April 08, 2013, 08:21:39 PM »
Just so hard to comprehend the torque numbers that little motor has to be making to pull a 2.91 gear!  must sound AWESOME
Greg
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Offline Spud Miller

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Re: Taller gears for nitro?
« Reply #11 on: April 09, 2013, 09:29:00 PM »
Quote
Just so hard to comprehend the torque numbers that little motor has to be making to pull a 2.91 gear!  must sound AWESOME

 I too am amazed. Also at how much liquid is going into the engine...imagine the 392" naturally aspirated engine running at 8000 RPM and TWO guys each pouring in their own full 5 gallon bucket of nitro at the same time...straight into the engine in 60 seconds.

 Choke! :o  Cough!  ???  Gasp!  :P

 I'll be trying for two SIX gallon buckets in June.

Spud

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Offline gregm784

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Re: Taller gears for nitro?
« Reply #12 on: April 09, 2013, 09:54:02 PM »
110 pump blanked off?  that is a TON of fuel!  I gotta get up there this summer.  Let me know when you're going to run. It's like a 8-10 hour bike ride. I'll need a couch though. or a work bench. or a shop floor. to sleep on.
Greg
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