Technical > Spud Miller's Cave

Taller gears for nitro?

(1/3) > >>

msundstrom:
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

Spud Miller:

 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

Blind Mule:
Spud you ran a 2.91 rear gear :o

Spud Miller:

 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

Blind Mule:
 :o ;D

Navigation

[0] Message Index

[#] Next page