Get my car to launch better...

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juvat

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I'm looking for your guys' thoughts on what to start on first to get my car to launch better. It's a street car, but I want to be able to take it to the strip and start bracket/index racing on the weekends. Here's my current set up and quarter mile performance.

72 Demon
4 speed
3.91 sure grip rear 8 3/4" with ESPO leaf springs
275/50/R15 Mickey Thomspon ET streets on 8.5" wide rims
pinion snubber
cheap shocks all around

LA 360 10.5:1 compression
Eddy heads
Comp XE268 solid cam
Air gap intake
Holley 750 double pumper
Small tube headers

Prior to getting the ET streets I ran a 13.93/106mph on street tires. With the ET streets I ran a 13.19/105.8mph. My best 60' time is 2.16 and I get some tire squeal as I leave the line, so I end up easing the clutch out as I feed in power making a gradual launch. I've also had wheel hop if I try to just power through the tire slip. I think with my MPH I could be in the high 12's.

Should I be doing a burnout with these tires (if so how much)? I try but I never get a lot of smoke that the other guys have when they burnout. I think this is because I don't have a line lock to hold the front brakes while burning out. Maybe I should be dumping the clutch in the burnout and then holding the brake with my left foot?

I've put together a list of things that should help transfer weight/plant tires better. Which of these would help the most/be most cost effective? I don't want to tub it, move springs inboard or lighten the car.

1. Line lock to help me heat up tires more, or use a better burnout technique
2. Put battery in trunk
3. Subrame connectors
4. Caltracs
5. Drag shocks
6. Use a better launch technique

I'm open to all suggestions, but I still want to be able to drive it on the street regularly. Thanks!
 
Quit wasting your time with street tires. Get some slicks so you can actually find out how it performs without any tire slipping.

I used to put my rims with slicks in the back seat, my jackstands and jack in the trunk, and tools on the passenger side floor. You can drive to the track and swap to the slicks in the pits. Otherwise you will never get a true read on how the car will perform. JMHO. Plus this way you can tease the guys that trailer in slower cars.

You mentioned pinion snubber; is it an adjustable snubber? Once you put some slicks on it, experiment with it until you find out what it likes to leave at. Don't be afraid to beat on it some also. My big block 71 Duster didn't like to leave without less than 5300rpm. Everyone else there thought I was crazy launching that hard, but she'd stumble everytime if I tried with less. Of course everyone else was running much lighter cars with automatics also.
 
Brad - I'm running Mickey Thompson ET Street Drag Radials. Am I missing out on that much by not having a full slick? I heard great things about those drag radials, but if full slicks are that much better I'm game for trying a set out. I currently have the adjustable snubber set about 1.5" below the pan, and I'm leaving at 3500rpm. I had traction problems trying to leave at higher rpms or by just dumping the clutch.
 
Rear suspension needs work before new tires, to be cheap, buy an adjustable pinion snubber, and set it 1/2" from floor. 1/8" oversize plate welded to floor would be nice; I used to bend the floorpan with one.
 
Definitely need a line lock to get them tires nice and hot with a 4 speed.

What tire pressure are you running?

Alot of guys with 4 speeds do their burnouts in 2'nd gear in the water box.
 
On the MT drag radials I went down to 15psi, but my best time was when I was at 18psi. It was a cold night (45 degrees), so tire temperature was probably more of a factor than tire pressure.
 
juvat said:
Brad - I'm running Mickey Thompson ET Street Drag Radials. Am I missing out on that much by not having a full slick? I heard great things about those drag radials, but if full slicks are that much better I'm game for trying a set out. I currently have the adjustable snubber set about 1.5" below the pan, and I'm leaving at 3500rpm. I had traction problems trying to leave at higher rpms or by just dumping the clutch.
Click to expand...

You are missing a lot of performance if you are spinning at all. It is difficult enough to be consistent with a 4-speed, if you are spinning at all you are shooting yourself in the foot. I would also set that adjustable snubber at least one more hole up. I used to run mine no more than 1/2" from the floor while at the track and then adjust it back down to max travel for the drive home.

cudaspaz is also right. You need to get a line lock and do your burnouts in second gear. Stay in the throttle on your burnout and then release the line lock once the engine starts to bog from the slicks starting to grab.

Another trick is to lock your right leg to the floor immediately after you launch. If you don't already have one, get a rev limiter so you don't blow the engine in case you miss a gear. Don't let your gas pedal come off the floor at all after your launch. Just quickly step on the clutch pedal with just the toe of your shoe and then let the pedal slam back up as soon as you've got it in the next gear, but don't move that gas pedal from the floor.
 
you might want to get shocks that extent longer in the rear....

if you shocks are bottoming (topping out) out....it will cause the rear end to wheel hop...
 
70aarcuda also makes a good point. Your rear shocks need to be at least 28" long when fully extended to allow for full travel of the rear suspension when the car attempts to plant the rearend and the rear of the body raises up in the air.
 
Launching your ET Streets with no burnout at all wont help all that much over good street tires. That's probably the biggest of the problems and the easiest to deal with.

Lots of people are using the ET Streets and getting 60' times on par with slicks. You will have to experiment a bit with the tire pressure. Somewhere between 15 and 18 usually works best for me. The consensus is that you need to get the tires hot but not a super hot burnout like a slick. A line lock makes it easy to do but its not necessary. I also have a 4 speed and ET Streets. Here is what you do; get the tires wet in the water, roll out and pop the clutch in 2nd. Go easy on the gas because the tires will spin like you are on ice. While the tires are spinning, I just touch the brake to keep the car from rolling, just as if it were an automatic. You will feel the tires grab and you will just adjust brake and gas until the tires are heated. After that you are good to go, just don't forget to go back to 1st.
 
Thanks everyone for your inputs. Here's my plan:

Set the correct pinion snubber height, reinforce floor pan
Measure rear shocks and make sure I have at least 28" extended
Put battery in trunk
Install subframe connectors
Install rev limiter - I'm thinking about the mallory hyfire ignition
Practice 2nd gear burnouts using 684mulas' technique
If I can't get his technique to work - install a line lock
If still no luck after all that maybe worth looking at slicks

Anything else anybody think I'm missing? Would drag shocks be a waste of money for my power level?
 
Here`s a few cheap things you can do to help :


Use long shocks in the rear like the guys have mentioned
Install clamps on the front segment of the leaf springs
Use front shocks with no less than 40k miles on them
Use small diameter torsion bars from a slant 6 car
Move the battery to the trunk
Do a burnout but skip the water, it can get trapped in the tread
Install a line-lock
Definitely experiment with different launching techniques
 
Where do you find longer shocks? I'm assuming you could just go to autozone and ask for a shock for a truck, but what model truck or car has the length needed?
 
mopar performance should have them. if you start your burn out in 3rd then shift to 4th immediately, you will have more wheel speed with less engine rpm. this will be easier on your motor. you don't need a line loc to do a burn out like this because you get wheel really fast.
 
Okay guys, just finished some measurements. I started with the pinion snubber, put it 1/2" from floor pan.

Next was pinion angle. Pinion is down 1 degree. Engine on front crankshaft pulley is up 3.5 to 4 degrees, meaning tailshaft is down that much. I think that means I have a 4.5-5 degree down pinion according to my research on here. Cracked - I saw you helped someone else with this and said they should have a 5 degree down pinion for a street car. I'm thinking my pinion angle isn't the problem, but does it differ if I measure it at the tailshaft? I think it shouldn't matter, but I don't know how much sag and machining slop there is inside the engine/tranny assembly. Is this a good angle, or do I need to shim it and if so, how much?

I also measured my shocks. With car sitting empty shocks are 19" in length (bolt center to bolt center). I then put frame of car on jackstands and measured that the shocks were 22". Then I tried to remove bottom of shock and couldn't because it was fully extended and binding the supension from full travel. I jacked up the rear end to remove the bottom bolt of both shocks and then saw how far it would travel without binding. It measured 23" from bolt to bolt. Therefore I need a shock that gets at least 23" at full travel, unless it can spring even further than it hangs while static. Unless someone has a suggestion I'm going to ask for a dodge truck shock tomorrow at autozone and measure it and then go from there (looking for at least 24" at full travel).

I have also researched front clamps. Can I just put one on the front of each side where the second longest leaf gets close to the front hanger?

Thanks for the help, this if the first time I've really started looking at the dynamics of a rear suspension.
 
I`ve read somewhere that some of the older Ford trucks had a long shock that could be used for the rear on our cars but I know that Mancini carries MP and Comp Eng. rear shocks and they`re not expensive. The Comp shocks are adjustable. The overall length should be about 28". The clamps can be bought through MP or you could go to Home Depot and buy some flat bar and some bolts to make your own. If you clamp one just in front of the axle housing and then one at your second longest spring towards the front it should stiffen the front segment sufficiently.
 
Thanks for the tip on the clamps. I'll go to homedepot - faster, cheaper and it will be made in the USA; maybe not the steel, but the fabricator (me) is American. Is there any advantage to unclamping the rear section of the springs?

For anyone else wondering about the shocks, if you go to Autozone and ask for a shock for a 1969 Dodge D100, you can get Gabriel part number 82054, and those are 24.5" extended. On Monroe's mounting reference sheet it says the Darts and D100s have the same mounting hole size and style. On the website it says they are only $16.99 each. I'll probably try those and get some front drag shocks.
 
The pinion angle looks acceptable. The harder you are hitting the spring, th more it need to be rolled down. Looks like a 4.5-5 down situation.

People cheap out on shocks and torque converters. Do yourself a favor and buy a decent adjustable shock. You don't need to go full kill, double adjustable. The Rancho 9 ways are good, QA-1's something that will dampen worth a darn. If the car leaves the line and porpoises, you don't have a good or at the least a mal-adjusted shock on the car.

I'd do your burnout in 3rd gear. You need about 80-90 mph tire speed to get them heated up well.
 
I just thought I'd update this - I put longer shocks in, and clamped the front section of the rear springs. The wheel hop is completely gone, but I'm still spinning off the line. Everything worked better when I lowered tire pressure to 16psi. I was at a track at higher density altitude (3000'), so my total ET was higher - 13.426, but my 60' times dropped from a previous best of 2.16 to 2.02. I tried doing burnouts in second, but when I try to hit the brakes to hold position my rpm slows, the tires grip and I almost stall the car. I'm planning on putting battery in trunk and installing a line lock to compensate for my lack of athleticism doing the burnout. My plan is to put the line lock right after the front output on the master cylinder before it hits the proportioning valve. Anybody see any problems with that plumbing plan?
 
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