Diff ratio and tyre help

Moderator: sandaltered

Re: Diff ratio and tyre help

Postby Bushchook » Wed Jun 17, 2015 9:42 am

My torque converter is a dominator with 5000rpm stall I have never tried lauching anything above 3000 to 3500 as I found it just dug a big hole as mention earlier.
Next time out I will try the 13 psi tyre pressure at max stall 5000 and see what happens, also I have the rear set pretty soft to squat and rebound slowly, there is a fair bit I can adjust with the four link but it's all trial and error.
Did u get to view any of my vids and photos of the ute
Bushchook
 
Posts: 14
Joined: Wed Sep 03, 2014 7:43 am

Re: Diff ratio and tyre help

Postby Straight Shooter » Wed Jun 17, 2015 10:06 am

I saw everything on your FB page. You have a lot to work with. It looks to leave right away. The chassis is very sorted as it is. It looks like it could handle a lot more of everything. Try just the rpm first. Then air it up all the way. Some fiberglass front end parts would help if you don't already have them. With that much tire I can't help but think wheelie bars are going to be in your near future. How far out does first gear get you and then about how far before the finish line is the 2-3 shift?
Best pass during 2015 races 3.092@104.4mph at Albany OR. All motor single 4 on race gas.
User avatar
Straight Shooter
 
Posts: 18
Joined: Wed Jul 16, 2014 2:20 pm
Location: North Bend Oregon

Re: Diff ratio and tyre help

Postby Bushchook » Wed Jun 17, 2015 10:30 am

At the moment 1st gear is very short maybe a half to a full car length 6000 to 6500 rpm I normally shift earlier as I thought using the torque of the engine would be better than reving the piss out of the engine, once I hit second that's when u really feel it pull away and normally get the win, the shift to 3rd gear normally doesn't happen or if it does maybe 20 to 50 m before the finish line, hence why I want to change my diff ratio, also the car originally was set up for the 1/4 Mile drag racing but decided to go dirt instead, for us to get tyres in Australia they have to come from the USA and by time u pay import tax they cost us around $2000 a set, thats why I went for the big digger 12 paddle as I Was told it was the best hook up tyre.
Do you recondmend a wheelie bar for traction purposes
Bushchook
 
Posts: 14
Joined: Wed Sep 03, 2014 7:43 am

Re: Diff ratio and tyre help

Postby Straight Shooter » Wed Jun 17, 2015 2:27 pm

The wheelie bar will be strictly to keep from dragging your bumper in the dirt. You are not there yet. Is the battery in the rear? lightweight body panels on the front will help too. We need to get the weight ratio moved back for now.

This is going to be a hard one to optimize. After playing with the ratios for awhile I agree the 5.20 is the next step. I would like you to use 1st for real and leave hard as possible starting with your curent tire pressure. Delay the shift until at least 7000 and preferably 7200. Then finish the run in second. Forget 3rd. We want to run the 640 engine long as we can before we shift it to the 520 horse mode. If it leaves okay try upping the tire pressure right to 13. What this does is give the max potential to the tire as far as it's ability to move dirt. The reason this may not work is if the tire moves the dirt out from under you too quick it will dig straight down and then have to climb out. No way to know until you try. Less air lets the cleats (paddles) fold back and dump some dirt so it digs slower. Watch the 60' times if they have them. One thing at a time. Up the launch at full and try the tire pressure. If that don't get it try 3500 rpm and go over it again. It's possible you might end up right back where your at now for launch setup. The only thing for sure is delay the shift as long as possible.

We are looking for 7000 to 7200 at the finish line in second. More air will act like a taller gear at the finish line so you can use that to tune that a little with as well. Be careful going down in pressure. The shutdown is kind of scary with real low rear tires. I would click 3rd and back down easy. If sand racing was easy everyone would be doing it.
Best pass during 2015 races 3.092@104.4mph at Albany OR. All motor single 4 on race gas.
User avatar
Straight Shooter
 
Posts: 18
Joined: Wed Jul 16, 2014 2:20 pm
Location: North Bend Oregon

Re: Diff ratio and tyre help

Postby Bushchook » Fri Jun 19, 2015 8:20 am

Well 5.29 diff ratio and 7300 rev pill on order i let u know the results thanks again for all help
Bushchook
 
Posts: 14
Joined: Wed Sep 03, 2014 7:43 am

Previous

Return to Tech Questions

Who is online

Users browsing this forum: No registered users and 2 guests

cron