Launching turbo bugs...

Matt Keene · Post by **Matt Keene** » Mon May 21, 2001 12:38 pm

A little question of how to launch a turbo car properly...
I'm having problems launching my turbo powered 54 and wonder if anyone can shed some light on the subject. I've been playing with my two stage rev limiter in order to try and find the ideal rpm at which to launch and can't seem to better a pathetic 2.1 sec 60 ft time. The car runs great (13.1 @ 105 mph) but suffers serious wheelspin off the line, but it should really run in the twelves. I run a close ratio solid mounted gearbox which is tied into the roll cage, so engine hop is not really an issue. Although I run radials on the strip, they are really re-cut slicks in soft compound so they should grip.
So far I have tried 4000 rpm launches, 4500 and 5000. It wheelspins at all these launches and then hooks up at about 40 ft and accelarates like mad on boost. Would it be worthwhile launching at say 6000 rpm to really get the turbo spinning, or maybe dropping the rpm and suffering lag? I maybe need to take a closer look at weight transfer as well... Do drilled stock shocks on the front end work well with turbo cars? Muffler Mike- any thoughts on this?
Should I just give my car death on the line and treat her like I hate her or is there a more scientific approach?
Thanks guys.

Muffler Mike · Post by **Muffler Mike** » Mon May 21, 2001 2:45 pm

This is always a hard one to answer without actually being there and seeing whats going on. But from what I can make out from your message, you are on the right track with the weight transfer. Still in the mid 12?s and street tires, you need all the transfer you can get. Ideally, you want just a touch of wheel spin even up to 5 maybe even 10 ft out if that?s what it takes to keep the motor in a resonable rpm range.
I am not a big fan of drilled out shocks, but for some, it works. At this point, you can try them and little money is invested that way. But you will want to make sure you have full front end travel as well. you should have a link pin front end still, check and see when you jack up your car, that the arms fall and rest on the stops in between the two arms. Even try and pull the rubber off the stop and see if it falls even farther. That?s where I would start first.
Get some video tape of your car from the side so you can see whats happening. If in the video, your front end is not fully extending, they this is what you need to work on. The thing I do not like about drilled out shocks is once you pass that first 5 feet and all the up momentum of the front end is gone, it falls like a rock and lets all your weight that you developed on the rear fall back on the front and lets those tires spin.
From a launch rpm, you may want to think about a boost retard control box. This way you can run a lot more advance timing until you come on boost and then it retards. This way you can launch on a lower rpm and the extra advance will assist some in reducing that lag.
You may find a fine line between pulling hard and falling on its face. And when in competition, always lean on a little spin then a bog.

------------------
Muffler Mike
www.MufflerMike.com

Chuck Schneider · Post by **Chuck Schneider** » Mon May 21, 2001 5:20 pm

Is the car lowered in the back? Is there any camber of the rear wheels? The wheel has to be perfectly strait up and down on the launch to get max traction, If the tail end is squating and the wheels start to tip in at the top then the traction will suffer.I am also gonna have to say lose the street tires. Get a set of slicks. I run 12.70 with a 1.65 60ft. That 2.1 is way slow, that is front wheel drive 60 fts. With that much power you need to get it to the ground with slicks.
My suspension is stock height with a set of stock oil shocks with a lowered front end and it has never had a traction problem unless I run street tires it won't hook up until the top of second.

------------------
12.70 @ 104

GDRBO · Post by **GDRBO** » Mon May 21, 2001 9:00 pm

Before I tryed drilling the shocks I try to find a pair of seriously used stockers, something with a little dampening left. I would also try a little less RPM off the line 'cause if its hookin' its gittin'. I have a friend who runs a Sand drag fuel funny car who continues to run quicker and faster by dialing in more clutch and dialing down the HP - hookin' and gittin'!

Marty · Post by **Marty** » Mon May 21, 2001 10:29 pm

Hey man, I have been there and done all that.
First, the only time you should leave on the two-step is if you have really good tires (slicks or super sticky recaps)and the track is good. The higher the rpm on the two-step, the harder you are hitting the tires. I only launch on the two-step when I have something to prove (and the track will take it) or there is money on the line. I have launched at Pomona when the track was not real good (street legal drags) at 5000 rpm on the two-step and I was holding at 6 lbs of boost, the car did a 180 off the line. the track would not take it and I was using 10" ET Street tires. Next pass I left at 5000 rpm and no two-step. No problem at all (big wheelie still) and the turbo really started to hump about thrid gear. That was a 10.70 pass with a 1.42 60 foot.

Michael Ghia · Post by **Michael Ghia** » Tue May 22, 2001 12:54 pm

Matt, I'd make the back end nice and soft, use stock oil shocks. If the back end has sagged a bit, re-adust it up a bit. That should help the wait transfer.
Godd luck.
Mike Ghia

------------------
Modification is a form of Art.

Bobtail · Post by **Bobtail** » Tue May 22, 2001 1:08 pm

Matt what is the next meeting you are going to?

Matt Keene · Post by **Matt Keene** » Tue May 22, 2001 11:28 pm

Thanks for the replies guys. I run an IRS rear end at stock height and fairly stiff shocks. The front end is lowered and there is a definate rake to the car's stance. Video footage showed that the car was not weight transferring properly, so I am going to try raising the front end slightly and change the front shocks for some drilled or worn out shocks. I run a Jacobs boost retard system: Mufler how much total advance would you recommend off boost? I run 30 degrees at the moment and figure this could easily be raised.
I have found that if I launch at a lower rpm the engine bogs slightly before coming on boost and 60ft times suffer. I go with Mike in that slight wheelspin keeps the turbo spinning.
I think weight transfer could be the key here guys. Any more thoughts?

Matt Keene · Post by **Matt Keene** » Wed May 23, 2001 10:33 am

Maybe North Weald rwyb on June the 17th. Bug jam for sure.

moggy · Post by **moggy** » Wed May 23, 2001 2:59 pm

If you're going to N Weald on the 17th I'll see you there. Let me know if your definitely going nearer the time.

Bobtail · Post by **Bobtail** » Wed May 23, 2001 3:13 pm

Matt, If you don't already know him seek out Russ Fellows and tell him I sent you

He should be at Bug Jam.

Matt Keene · Post by **Matt Keene** » Thu May 24, 2001 11:15 pm

spoke to Russ at the Big Bang about intercoolers and co2 etc. He's one innovative guy!

Bobtail · Post by **Bobtail** » Fri May 25, 2001 2:10 am

No Matt he's just gullible, he does everything we tell him to do

Matt Keene · Post by **Matt Keene** » Sun May 27, 2001 9:21 am

just fitted a pair of drilled front shocks to my Oval and have been practising some more launches in an unused car park. The front definitely lifts much more quickly and seems to rise higher than with standard shocks. I wasn't getting much traction as the road surface wasn't the best.
I was quite surprised to find that the car didn't handle too badly on the road: I expected to bounce all over the place but was pleasantly surprised, although a series of ripples on the tarmac did make for interesting driving once or twice! I am gonna try softer rear shocks on the back and less weight up front (aluminium beam, fuel tank) shortly- I'll keep you all posted...

flying tomato · Post by **flying tomato** » Sun May 27, 2001 5:55 pm

Here's an idea that Ron Lummus suggested to me..
For my 1900lb swing axle street car that has run 12.04 109 with slicks the set up he suggested...

Slicks with 30mm torsion bars with no down stops and adjustable rear spring plates.

Put the spring plates on with no preload. Set the rear just slightly decambered. Now launch the car, the slicks will be rideing on the inside edges, too much spin then adjust the spring plates a little more positive till you find the balance where the tire spin is acceptable and allows the trans to live.

The 30mm torsion bar will not be preloaded so the rear of the car should not want to rise as quickly on deacelaeration. Also straps to limit rear up travel would gently stop the up travel compared to welded in stops.

A set of purpose built rear shocks would be in order as well.
Sounds like it might be worth a try to me.

As for front drilled shocks or 90/10 shocks. If the car wheelies at all you will want the 90/10 for sure, it really calmed my car down in first and second. At 100mph (on a smooth drag strip) they felt the same to me.