Diff ratio and tyre help

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Diff ratio and tyre help

Postby Bushchook » Sun May 03, 2015 8:14 am

Hi all I am currently running a ford ute (640hp) with a C4 coan transmission 5000rpm high stall, ford 9inch with 4.56 gears - running big digger tyres 33/15/15 set at 6psi (average time on 200m track is 8.2 seconds at about 93mph) I am currently crossing the finish line in top gear at approx 5000-5500rpm. I am looking at going to a 5.2 diff ratio - any suggestions tips or advice would be greatly appreciated . I have also researched tyres and I'm lead to believe that big diggers lose top speed when compared to super scoops. Anyone have any further info about that? I've posted the link to a test n tune run from yesterday
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https://www.facebook.com/goldfieldssand ... 633270001/
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Re: Diff ratio and tyre help

Postby Straight Shooter » Fri Jun 12, 2015 6:17 pm

We don't get the Ute here in the US. I wish we did. That is a super cool looking rig.

Super Scoops are really hard to pull over 75 mph compared to a Hooker cup. I would drop to a Kevlar reinforced hooker with 18 cups staggered for this rig on the same size casing you have now. This should get you out of the hole just as good and free up a bunch of power down range and you have an awful bunch of downrange.

Listening to it sounds like it's laying on the converter the whole way. You are going to need a bunch more gear. To get your gear ratio on sand figure 25-30% slip combined from the converter and the ground. Going so far your slip figure might be a little less but I doubt you are ever getting under 23% with 640 hp. To go 93 mph you need to turn 5.57 gears at least 6579 to get a minimum of 116 mph at the tires to equal what you have now. Forget where your torque is. Sand racing is all about horsepower and rpm is power. Our goal is to gear it as deep as we can, then twist the piss out of it without blowing it up on the top end.

The ideal converter stall on sand is 1000 to 1500 below your peak power rpm. For 100 yard drags I like the 1000 or a little less below peak power. You are going 200m or 218 yards for me. We have run way out the back door before and it doesn't really take much more rpm to cover the last 100 yards. To start I would get the lower gear. From a 4.56 to 5.20 is only going to raise the finish line rpm about 14% from 5500 to about 6250 assuming it was off the stall and hooked up at 5500. I wouldn't expect a big change in ET even going to the 5.57's. Depending on the budget and assuming your peak power rpm is closer to 7000 I would do at least 5.80's to who knows. I have 7.00 to 1 gears and still need more gear and we only run 87-91 mph at 8000 rpm. I weigh 1700 pounds and figure it would be real close if I went 200m gear wise. I hope the Ute has a 9" rear in it.

Then get the converter right. At least a 8" converter but a 7" might be more efficient if you need over a 7000 stall. My 660 horse engine peaked at 8300 rpm and we found it went quickest and fastest at 7300 stall. Once you are up on the cam you can get more bite and less drag by airing your current tire up to 13 pounds. The car will handle a lot better and a lot less tendency to bounce in the shut down. Even before the gear change try shifting at 200 rpm past your power peak. If it labors that last bit before the shift you need deeper gears or less tire. Lower to shift to right on the power peak. With a 3 speed first gear is going to run out real quick. An air or electric shifter will be a big help at least on the 1-2 shift. The goal is to cross the stripe just over your power peak or at least right on it.

I think it would be a blast to run 200m.
Best pass during 2015 races 3.092@104.4mph at Albany OR. All motor single 4 on race gas.
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Re: Diff ratio and tyre help

Postby Bushchook » Mon Jun 15, 2015 10:36 pm

Hey
Straight Shooter thanks a lot for your helpful tips all make sense, I am going to get a set 5,40 to 5.60 gear and see how I go
Do have a few more questions I found when I use my tran brake with stalling it over 2000rpm just makes the ute dig a big hole and slow the launch down having the ute to climb out of the hole.
I have found adjusting my my stall rpm to 1500rpm(tran brake ) with a lower tyre pressure (6-7psi) seem to give me a better launch, I have a adjustable rev limiter on my trans brake so I can still sit on the tree with my foot flat to boards with the desired rpm until i hit my lauch button.
Also run a four link rear with a 9inch with anti diff roll, on lauch I get the ute to squat nicely and slowly comes up seems to be tuned ok.
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Re: Diff ratio and tyre help

Postby Bushchook » Mon Jun 15, 2015 10:41 pm

https://www.facebook.com/video.php?v=10152932711342881

Try view this link here Straight shooter it was a run again a R1 a couple of weeks ago for fun
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Re: Diff ratio and tyre help

Postby Straight Shooter » Mon Jun 15, 2015 11:21 pm

Try 13 pounds and leave at full stall speed. That is where your max bite should be. The higher pressure helps keep the cups from rolling back and dumping the grip. One secret I found is running tubes helps stiffen the tire and makes it grip even better. Hit the tires as hard as you can should help it transfer weight and get max bite. I can't view this new video but just guessing I would say let the front suspension have some rise in it will help. When it starts wheeling you can start tying it down to help control it.

My car now 60's as low as 1.17. That's leaving at 6000 with a 8800 rpm stall speed in a 1700 pound car. When I ran my 660 horse engine I left at full stall of 7300 with peak power at 8300. That setup 60' in the high 1.26-1.31 range. In a Jeep that setup ran 4.23" The Jeep it is in now runs 4.0.

I have been sand racing since 1983. Started with a 3200 pound Willys Jeep with a 327. Worked my way up to our current 1700 pound car running 3.209@103.3 in 100 yards. That was the first outing and we had some dead valve springs and one broken.

Here is my current ride. This run had to be aborted as it got to out of shape to continue. Even aborted it still ran a 3.26 at 74mph. We should be in the 3.0's soon.
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Best pass during 2015 races 3.092@104.4mph at Albany OR. All motor single 4 on race gas.
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Re: Diff ratio and tyre help

Postby Bushchook » Tue Jun 16, 2015 5:18 am

Ah that's a killer looking rig there, yeah me myself only got into the sandrags about two years ago. It is mainly bikes that Run over here in oz but the car and buggys are now starting to get a class of there own which is good,
My home track where I live and race is called Goldfields Sand Drags if you tube it, I will try and post some vids for you soon of a few runs to see what your thoughts are
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Re: Diff ratio and tyre help

Postby sandaltered » Tue Jun 16, 2015 8:17 am

Straight Shooter wrote:My car now 60's as low as 1.17. That's leaving at 6000 with a 8800 rpm stall speed in a 1700 pound car. When I ran my 660 horse engine I left at full stall of 7300 with peak power at 8300. That setup 60' in the high 1.26-1.31 range. In a Jeep that setup ran 4.23" The Jeep it is in now runs 4.0.

I have been sand racing since 1983. Started with a 3200 pound Willys Jeep with a 327. Worked my way up to our current 1700 pound car running 3.209@103.3 in 100 yards. That was the first outing and we had some dead valve springs and one broken.



If you don't mind me asking what is your engine combo that you're running now? Sounds like you're just getting started with it.
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Re: Diff ratio and tyre help

Postby Straight Shooter » Tue Jun 16, 2015 9:02 am

Only 10 passes so far. This is our first year with it. It's an SB2.2 sbc. Single Book Dominator, cast GM intake. It's a short stroke big bore 399" in a Bowtie CGI block. 3 Stage external wet sump. Q-16 fuel. Peak power is at 9800. We haven't had it over 9600 yet. 7" Coan converter. 1.76 glide with 7.00 in the 9". Once we get a handle on the handling we will turn it up. The top end is shifting it at 10,300. I need a lower rear gear or a smaller tire. We are crossing at only 9000 now. I kind of think we may get away with 20.00's now. I would like to see it at peak power or just over to get the max out of it. I want to get a Racepak on it before we start turning it up. Right now we are using a Go Pro to record the gauges but we can't see everything I need to keep an eye on. This car is all mild steel. It weighed 1360 with the 23 degree engine. SB2's are at least 20 pounds more. We probably really only weigh 1650 or so. Since class racing is gone I haven't been on the scales in a couple years. Now I just need the son to stop growing and it wouldn't hurt to drop a few pounds. Eventually I want to get it in the top eliminator class. A chrome moly chassis will dump at least 100 pounds. I have a huge radiator in it we could switch to a smaller one if we go to towing it back. It will be big fun running a NA single 4 small block in the TE class. As long as I don't go broke buying valve springs.
Best pass during 2015 races 3.092@104.4mph at Albany OR. All motor single 4 on race gas.
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Re: Diff ratio and tyre help

Postby Bushchook » Tue Jun 16, 2015 8:40 pm

Yep that would be right in saying just getting started, the is combo is as follows ford Cleveland 351 block coverted to a four bolt main half grout filled bored and stroke out to 393cubes scat crank and rods Dimond Pistons with total sealing rings lifter bore restrictor kit to keep more oil down stairs, custom grind cam, CHI Alloy 3v heads full roller cam and rockers, 950cfm 5140series Holley menthol carbie.
After engine was built was put on engine dyno and spec were @5500rpm produced 525flbts and around 520hp then as it climbed to 7000rpm torque starting decreasing and hp increased to 639hp.
We shut it down at 7000 as this is a safe number and a Cleveland block originally was only built for around 400hp even though it's had all the mods.
I have got another block and bottom end which is a arrow block which I plan on going supercharged once I get my setup perfect, 1000 hp plus for next comb.
Can u tell me how to upload vids and pics to this site
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Re: Diff ratio and tyre help

Postby Straight Shooter » Tue Jun 16, 2015 9:50 pm

Based on that little bit of info a 6000 stall would be minimum. Ignore the torque numbers. A Dominator will be worth 20 horsepower across the board at 5500 rpm and up. Race gas will pick up the horsepower a bit more.

To post pictures they must be hosted first to a hosting site. I use Image Shack .com. It cost me $5 a year or something like that. Once hosted you use the image url and put it in between [img]XXXXXXXXXXXX[/img] code and it will show up. remove the x's and replace with the image url. For youtube videos just copy and past the url from the top of the youtube page and just list it in the text and it will embed the video link right on the forum.


https://www.youtube.com/watch?v=FWjOCXpEpg8
Best pass during 2015 races 3.092@104.4mph at Albany OR. All motor single 4 on race gas.
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