driveline problems...

[406shark]

Just got back from the track. It went pretty well... about what I was expecting/hoping for. Had the Caltrac's set the same as last season. Still running the 5 year old MT slicks.

Made 3 partial passes to test the 60 foot times and try and dial in the tire pressure.

First full pass came in at a 10.580 at 122.71 mph with a 1.451 60 foot time.
Second pass came in at a 10.562 at 125.33 mph with a 1.488 60 foot time.
Third full pass came in at a 10.563 at 125.43 mph with a 1.455 60 foot time.


The first full pass was run at 10 psi, 2 step at 4500 rpm, and I ran into the rev limiter lowering the mph. The second pass, 2 step at 4800 rpm, more tire spin off line, but didn't hit the limiter. It went into valve float at 7500 rpm. The third pass down to 9 psi, 2 step at 4800 rpm, less tire spin, but the rpm ran into valve float again at 7500 rpm. Way higher than the engine makes its power peak. The slicks are so hard that I had to keep lowering pressure down to 9 psi, and they still spun somewhat off the line and got squirrelly at the 1-2 shift.
Last season with less horsepower and less stall speed (3500 rpm), it hooked and pulled the front up pretty good. This season the front comes up, but not as much as last year because it it not hooking hard.

Any idea's as to why it's spinning so high on RPM's? It has 4.30 gears, currently running 28x10.50 slicks. I figured it would trap at about 7200 rpm with a higher mph. The engine makes peak HP at 6600-6700. I know if I can get the rpm down into the power band it will probably ET & MPH higher. How can I tell if I'm "blowing" through the converter? It has a new 8" converter from PTC with a 5300 rpm stall on the brake.

I think I'm going to have to go with a larger diameter slick to get the rpm's down. Probably move to a 29.5 - 30" slick.

Here are a couple of videos showing the last two runs. My friend was having problems with my camera. He got most of the runs, but shut it off just before the et showed on the boards. He did make a nice 3 1/2 minute video of the ground as he was walking around the pits. LOL


http://www.youtube.com/watch?v=use7C...eature=channel

http://www.youtube.com/watch?v=zHhqGXheKGM


Jeff

 

[grumpyvette]

first congrats on the rather impressive and fairly consistent runs , for the first few in several weeks plus, anytime your running mid 10s its impressive


First full pass came in at a 10.580 at 122.71 mph with a 1.451 60 foot time.
Second pass came in at a 10.562 at 125.33 mph with a 1.488 60 foot time.
Third full pass came in at a 10.563 at 125.43 mph with a 1.455 60 foot time.


the taller slicks will obviously increase the distance the car travels per revolution of the rear wheels and add some traction potential due to the greater distance between axle center-line and the slicks traction surface distance .
going from a 28" to a 29.5" slick should reduce the engine rpms about 400rpm.
If your slicks are 5 years old they may not be providing ideal traction and you may need to use traction compound, if your not doing so now.
(yes theres a big difference between some brands effectiveness)
you may also want to try moving the suspension mount points.
as to the converter speed Id have to have more info but if you don,t have a good effective trans cooler I can tell you from experience that as the trans fluid heats it tends to allow the engine to shift a bit higher, in some applications, now many guys feel its a decent trade as they do without the cooler and required plumbing weight and your not running that long on a drag race car, but its been my experience the large trans cooler mounted to the car need not be frontally located as it uses a electric fan and the extra durability is worth the weight sacrifice

http://www.calvertracing.com/caltracs.html

Id bet 40% of the members don,t know what those traction bars even look like or how they work, so for those members heres some basics

 

[406shark]

the taller slicks will obviously increase the distance the car travels per revolution of the rear wheels and add some traction potential due to the greater distance between axle center-line and the slicks traction surface distance .
going from a 28" to a 29.5" slick should reduce the engine rpms about 400rpm
as to the converter speed Id have to have more info but if you don,t have a good effective trans cooler I can tell you from experience that as the trans fluid heats it tends to allow the engine to shift a bit higher, in some applications, now many guys feel its a decent trade as they do without the cooler and required plumbing weight and your not running that long on a drag race car, but its been my experience the large trans cooler mounted to the car need not be frontally located as it uses a electric fan and the extra durability is worth the weight sacrifice

Yep, I have a double pass Derale transmission cooler with fan installed in the bed of the truck.

It is now plumbed with all 3/8" hard line.


Jeff

 

[406shark]

After talking to PTC today they recommended that I verify the rear gear ratio seeing as I didn't install the gears. They came with the truck, and the owner told me the gearing.

Today I went down to the shop and jacked up the rear and had one of the guys slowly turn the rear tire as I counted the drive shaft turns. Looks like it has steeper gears than I was led to believe. The drive shaft spun almost exactly 4.75 times for one revolution of the tires. Might explain why it was spinning up to 7500 rpm with the 28" tall slicks.

Looking through the Summit site it looks like it has 4.71 or 4.86 gears. Time for some 29.5" tall slicks...

I called MT and gave them the numbers off the slicks, they came back as made the 29th week of 1999! Could be why they wouldn't hook very well.
I placed an order with Summit's Race Shop today for a fresh set of MT slicks, a window net, and a new seat belt harness setup. My old ones expired 4/10. They tend to look at you a little closer when you get into the 10's.

My friend that was running the video camera said that during my 3 trial passes to the 60' marker I was pulling the front tires up out of the lights about 10" on the last two. He said the front tires didn't turn until it was a ways out of the box. I had the 2 step only set at 4000 rpm on the first pass, then went to 4300 rpm on the next two passes. When I raised it to 4500 rpm and higher is was spinning the slicks too much to hook.

It should be interesting to see how she leaves with some new slicks on it. Not to mention it should pull all the way down the track in the power band. I can't wait.


Jeff

 

[grumpyvette]

sounds like you've got things fairly well under control, if you've currently got 4.88:1 rear gears, that certainly explains the high rpm in the lights.
Id point out that your likely to spend more time in the power bands peak with both the new 29.5 slicks and swapping to something like 4.56:1 rear gears, but make a single change at a time

theres info and links in these threads

viewtopic.php?f=71&t=555

viewtopic.php?f=71&t=2817

viewtopic.php?f=71&t=237&p=282&hilit=+slicks#p282


If your going to use SLICKS the tire compound selected, the air pressure ,your driving style, the engines torque curve, if you use a traction compound , if you run only after several burn-outs to heat the tires, or just roll up and launch, all effect your results,
without knowing your engines power curve,car weight, transmission gearing,stall speed or clutch, the rpm range you currently launch at,the surface you run on, the rpms you go thru the lights at, the current traction issues if any, and how the cars suspensions set up, your 60 foot times and several other factors (a video of a current launch would help), your just guessing, if you have that info your still guessing but you can get MUCH MUCH closer to ideal results
a leaf spring car with traction bars, launches different than a 4 link or a ladder bar car etc.
knowing a good deal more about the application improves the chances of building a working suspension, you certainly don,t want the front wheels 6 feet in the air ,or the differential ripping the frame and suspension components loose or busted axles, you want rapid acceleration with max weight transfer, while still maintaining steering control and not busting drive-line or axle parts

you can make it fairly simple and just select a decent slick that fits your wheel well with decent clearance after carefully measuring wheel offset, and clearances and then ask for and take the advice of several racing tire supply vendors after explaining what your trying to accomplish and what your working with to get there, you then will make suspension. air pressure , launch rpm, and other driving style changes to maximize your results
its kind of like, you can approach the problem of the ideal slick a bit like selecting a girl friend/wife, you can either make a mental list of what you want and keep looking for an exact match (GOOD LUCK)to the intended use.
or you can get something thats darn close then make adjustments in how YOU react to it and compromises in what your doing to match what your working with (the more common course of action)