Suggestions for chassis performance

[triniemi]

Hi,

Newbie asks advice for chassis adjustments. Two videos from same pass:

http://www.youtube.com/watch?v=v09NdnwtyZ4

http://www.youtube.com/watch?v=KTFlThL0scc

9.15 @ 146mph
1.306 60ft

The car:

It's a -84 tube chassis Toyota Corolla
509 BB chevy, about 750hp
PG, 1.76 first gear
4.11 Rear gears
2380 lbs, 59% front, 41% rear (I know, iron headed BB weights)
Shifting at 6000rpm, 6400rpm max rev limiter because I can't attach a chute. The rear of the chassis is made of under 1" tubing.
New Super Gas/Pro Stock GY tires, 32x14x15
Racing Super Pro ET, All NHRA rules.

Should I do something with the chassis? Loosen the inbound setting at rear shocks? Higher and shorter IC with the 4-link? Looser front end? 4.33 gears and more revs? Or what? Obviously, I want to get the car in to the eights. Please mama, I want to go fast! :lol: Also, lifting the front tires wouldn't hurt.

Any suggestions are welcome.

Thanks,

Mikko "dr" Niemi
Finnish Super Pro ET 1984

[mcracecars]

The nose of that car is on the heavy side. Any weight you can move back would help a lot.
Print out and read the "sticky" at the top of the chassis and suspension page. Lots of info there to get started.
Personally I would like to see a little more gear in that thing, depending on what rpm you want to cross the finish line at.
What do you mean that the rear is under 1" tubing and you cannot attach a chute?

[triniemi]

I mean that the chassis from the rollcage back should be upgraded to install the chute mount, it's too weak now as the chute will pull 1-1.5G.

I want to cross the finish line below 7000rpm and I think that moving from 4.11 -> 4.33 and 6400rpm -> 6800 rpm would help maybe 0.1 - 0.2 seconds and it still would stay under 150mph.

[triniemi]

With the weight I have few options:

a) add weight to the trunk. Not so interested.
b) buy aluminum heads, that would lose 80lbs and get the car maybe in the 57/43 range. Too bad I haven't 3000$ right now.

I could also try to remove the alternator from the front end but I think that would do more harm than good.

Is it possible to make a car this noseheavy to work better without moving weight? The wheelbase is only 100" so I think that helps a little with the weight transfer in the start.

How would looser front end and/or looser rear shocks inbound affect?

[buffjhsn1]

well i'm not a chassis builder, but it won't work being that nose heavy. you have about zero weight transfer.

think of it like a teeter-totter. the more weight you have on the back the better it hooks. that is why a dragster works so well, they have 70 some % on the rear.

just my .02

[triniemi]

I estimated that if I add 100lbs ballast to the trunk, I would get 55/45 weight distribution. Is this worth trying? Will my ET's be faster or slower?

[sp2816]

If the car is spinning, then the ballast in the trunk would help the ET. But in your case, when the car left the line, I saw at least 3 wrinkles in the slick and the car accelerated straight forward and didn't "fish tail" any. So, IMO the ballast might help pull the front wheels, but would not help on the et.
The spring rate on the front end could be too stiff. When I built my car it was recommended for me to install the 400lb/in front springs on my struts, because of the weight. It wouldn't pull the wheels, but the car would work OK. I then changed the springs to 350lb/in and 1" longer to help hold the front up, and then the car was able to pull the wheels a few inches and run a little quicker.
It is like mcracecars stated that your car needs more gear. If you are trying to get a car to run ET and not MPH in the quarter, you need to get it to accelerate as quickly as possible down low. I run a 4.56 gear in my car with the 16x33 slicks and my car has always been a little softer on the bottom end with the powerglide 1.76 and turns a little more MPH on the top. Moving the shift point up would probably help, also. I would think that you are losing some usable HP by shifting so low. Where does your engine make peak power? If not known, what size is your cam as that would give an idea?
Your 60ft ET is not that far off from what is predicted for your 9.15 quarter mile ET as it shows that it might be a 1.27. This is the link to some good calculators http://www.wallaceracing.com/Calculators.htm

At the speeds and times that you are wanting to achieve, I would add the bars to the rear that would allow installing the chute. I have had rear brake lines break before. You might be able to come off from the main hoop and add some larger bars that are tied to the inside of your existing framework to make a tether point.

Good luck on the 8's,
Bill M

[topsportsman1]

I want to cross the finish line below 7000rpm and I think that moving from 4.11 -> 4.33 and 6400rpm -> 6800 rpm would help maybe 0.1 - 0.2 seconds and it still would stay under 150mph.

That might work but go to a 4.29 gear,shift point will be 6800 and cross the finish line 6800,
8.90 @ 150 mph should be real close,thats what I ran for a set up years ago

[triniemi]

Thanks for great advices, I really appreciate them.

The cam is 272/278 @ 0.050, 0.708 lift and Crane states that it is a "oval track" profile whatever that means. Heads are ported Merlin iron rectports, big Dart single plane manifold and a 1050 Dominator. Headers are quite big, 2.375", so that might cost some torque. 12.4:1 compression (measured). I think 650 ft-lbs @ 5000 and 750hp @ 6500 is quite close. I use 50% Sunoco GT 104+ and 50% Shell V-power as fuel.

So get the car to the eights, I will try to:

1) Install the chute. I have to remove the body from the car to do this and relocate the fuel cell so it'll take time and people. And beer.
2) More gear and rpms. 4.29 or 4.33. 4.56 is too much if I want to stay below 7000. I believe I'll do this during the long and dark Finnish winter.
3) Try the ballast. It's cheap and easy to do and I can try it this summer. Should help also in the slippery airfield-tracks we have.
4) Aluminum heads to reduce nose weight if I can find the money. AFR 335 CNC's would be the dream.

[topsportsman1]

4.29 and 4.30 (30-7) are the same gear use the pro gear if at possible

4.33 (39-9) I don't think that gear will work very good for you,you may not even see a difference in RPM from the 4.11 (37-9) gear that you have in the car now,just my .02 cents here of coarse

[sp2816]

The size of the headers will have an effect, but I found that the length played more of an effect. There are some calculators out there for doing this for the exhaust pulses, but I think that you will want to make sure that your primary tubes are around 32" long. The longer that you can make them, the more it will help on the torque.
I tried shortening the headers once on a 7800rpm 427 with 2 1/4" headers. I lost about 1/10th when I shortened them from 30" to 24".

Bill M

[mcracecars]

It sounds to me like you want the car to leave hard, but you are handicapping it by trying to limit the top end mph so you dont need to run the chute.
It would seem more logical to me to do what is necessary to use all the power and tork the motor can make at the start, but limit the top end mph with some sort of throttle stop. Until you can get a chute on there of course. There is good reason to use a chute, not only to slow the car down, but it can straighten you out if you start to go sideways at the top end.
Why would you need to remove the body to redo the back of the car?

[triniemi]

Ed, you should see the car and you would agree with me. It's a very small car and the real chassis ends at the rear shocks. The "chassis" from rear shocks to rear bumper is very weak, only carrying the weight of fuel cell and battery. And the fuel cell fills the cap between the tires, so it has to be relocated too. There is no way I can attach the chute to the existing chassis, is has to be rebuild to handle the chute. And to rebuild the chassis, the body must be removed, believe me. No room to work anywhere.

[edvancedengines]

Ok, the car does not look bad at all. As has already been mentioned the 60' and the ET are pretty much right on the money as they should be.

I also agree that the front end to me looks too stiff. You could possibly use a touch more of what is now called antisquat but not much. You can likely get that just by loosening the shock a couple of clicks on the extension. That front end does look like too stiff of springs/too stif of shocks/ or no travel with it too much limited by limiters.

You will not like what I see as your main issue though. You are trying to run that thing at too low of rpm. You are severely limiting any horsepower making it wants to do. You are working the engine harder by restritcting the rpm to ranges it is in the highest destructive harmonics ranges, and likely holding it down just when it may want to start running. Turn that baby loose and let it eat dude.

Is that cam advanced much? I would want to retard it some It is not enough cam for your car or engine. It is usable though.

You can mount a good strong cross member at any place in the car where you find frame strength. Then brace it with triangulations. The chute should be tethered (Attached) no higher than the camshaft ht, and no lower than the crankshaft ht at the lowest. Too high will possibly unload front suspension and too low will definetly unload rear suspension. When you do put a chute on it, Keep your foot hard on the pedal when you pull the chute. Only let off the pedal when you feel the chute hit or if it doesn't hit. You will get used to how long it takes to hit after the first two or three pulls. When you get used to it, you will be pulling the chute just before the finish line.

Ed

[triniemi]

I measured the 4-link settings last weekend and fed them to my friends 4-link calculator. The IC lenght is 37.2" and 8.2" high. I got Jerry Bickel's book (Complete Guide to Chassis Performance) and it suggests for a low hp (under 900hp) and auto. trans car IC lenght 45"-50" and 1"-3". But it also says that weight distribution should be 51% Front, 49% Rear and that's something I can't achieve.

Any ideas where to move the IC or is it ok now?

BTW, thanks for the help with the chute attaching. I measured also the crankshaft height (12.5") and camshaft height (18") so between those numbers will the chuteanchor go someday.

[mcracecars]

those chassis books are great, but the info they give on settings is kind of generic, gets you in the ball park as they say, but you still need to play around with the settigs to see what the car likes the best.
plot out all the holes and possibilites for the 4 link, then you have some reference points.
try a lower and longer setting, ie drop the front of the lower bars down 1 hole and see it the car likes it. you may need to play with the shock settings to see if there is more improvement or non at all. Write everything down in a log book, you can never have too much information.
a test and tune day at the track is ideal for this kind of stuff as you do not want to do this on a regular race day.
you only need to do 60's or 330's for this, no sense wearing out the motor.

[triniemi]

Yes, I have measured all the holes in the frame and in the rearend.

If I'd drop the lower bars one hole lower in the frame, the data would change like this:

IC lenght 37.2" -> 43.6"
IC height 8.2" -> 6.1"
Antisquat 146% -> 92%
%Rise 83% -> 53%

How would that sound?

The software I'm using is Performance Trends Inc. 4Link Calculator v2.0

[triniemi]

Good news from Finland, Alastaro dragstrip! 8.987 @ 147 mph with 6400 max rpms, shifting at 6000! I lowered the launch rpms from 4400 -> 3600, raised the tire pressure from 6.7psi -> 7.0psi and made a big burnout throuht the starting line. Also the throttle wasn't all the way open before but now we got it right.

Here's the 8 second pass video: http://www.youtube.com/watch?v=GF-Rf_4eVXc

We broke the transmission on the next run but I did got a spare trans and we even manage to win the eliminator with it! Next race is 5. July and I think we're going to try the four link setup a mentioned before. It seems that the body rises at the starting line. I want it squat or be neutral.

Also I weighted the car with a full fuel cell and it isn't so bad that I thought. 56.6% front, 43.4% rear, 2410lbs.

Corner weights:

LF: 749 RF: 615
LR: 502 RR: 543

Comments?

Thanks,

Mikko

[sp2816]

Congratulations on getting your 8 second time slip. I know that it had to feel good to do that and to also come back and win your eliminator.

Bill M

[buffjhsn1]

welcome to the club! great feeling isn't it? :lol: :lol:

[BillyShope]

I would be VERY cautious about moving weight back. Looks to me like you're close to ideal. The goal is to leave so little weight on the fronts that the effect on rear loading is negligible while, at the same time, avoiding a wheelstand.

Page 28 of the following can help you in adjusting a 4link. See Page 9 if you're interested in canceling driveshaft torque effects:

http://home.earthlink.net/~whshope

[edvancedengines]

Mr. Billly my friend,
Welcome aboard. Good to see you here.

Ed

[topsportsman1]

Billy

Thanks for joining in here at RJ,its nice to see you here.And welcome to RJ


Tom

[triniemi]

Hi again!

I can't still believe it, but another victory and now we are the points leader! There is only two races to go this season and anything can happen with the championship so wish me luck.

We didn't change the four link before the race, but we did it afterwards with the scales and set the preload just the same. The next race will be on a slippery airfield (treated with rubber and VHT) and we hope that the change with the links will help us to get more traction. It's only 1/8 mile track so that will be also interesting.

Cheers,

Mikko

[Racefab57]

GOOD LUCK! sounds cool to me!!! david.

[triniemi]

We managed to do the hattrick, three wins in a row! I think that everybody else was scared from my 0.037, 0.006 & 0.007 reaction times in the first rounds and they all redlighted againts me, so it was almost easy to win (it was a 16-car ladder). There is still the final race to go but nobody can't catch me anymore if I can pass the tech and get the points from the first qualifying lap.

The traction at the airfield was MUCH better than I expected and I think that the car liked the change we did with the 4-link. It went straight down the track so the preload was just right. We might change it even more lower & longer and see if we can make it squat really hard. The IC would move like this:

lenght: 43.6" -> 48.4"
height: 6.1" -> 4.4"

Thanks for the all help I got from this board, it has been all good!

-Mikko

[triniemi]

Hi,

Two videos more from the first ever finnish Super Pro ET champion!

Best time for the car 8.964 at 150mph http://www.youtube.com/watch?v=73zyD6FTJ30

And some incar video with another 8 second ride http://www.youtube.com/watch?v=SIVu32g3wkU&mode=related&search=

I tryed 6600 and 6800 shift rpms and the car liked it just like some of you said. The 330ft time dropped from 3.71 to 3.67. The trap rpm with 4.11 gears was 6600. And now I have to get the chute to the car as the fastest pass was 151mph.

The final race rained away but I couldn't be more happier with the racing season 2007.

Thanks,

Mikko

[edvancedengines]

We might change it even more lower & longer and see if we can make it squat really hard.

Why do you want to change a decent car to make it to squat?

You planning on taking a dump soon? That is the only reason to squat is if there is not a toilet to sit on, you have to squat. :D

Man' I hate that expression. Squat. Anti-squat.

There is never any circumstance I can think of that would warrant trying to make a drag racing car to squat when launching. Forget the crap you read on Baseline Suspension and in magazines. about the Pro Stock cars squatting. They do not squat. It looks like they squat to the observer with no data or clue what is happening.
Things happen quicker than the eye can see.

If you are going to move your 4-link bars why are you making two different radical chnages at the same time?

Are you trying to remove tire hook? By doing what you say you should remove a bunch of rear suspension action.
Or to use the SQUAT WORDS. You should end up with much less Anti-Squat and more Squat. Why?

Ed

[triniemi]

I don't know. It has always seem cool to me to see a car squat hard on the line and leave really hard. I think my car is now near to the 100% anti-squat line and would like to try go lower IC.

[gdmii]

Are you sure it's really squatting or are the tires geting smashed from the hit? Right now, mine is at 75% anti-squat and still hits the tires so hard on the launch that it balls them up even with 8 psi in them so I'm making a change on the 4 link to about 52% to take away some hit. If it starts squatting too much you can stiffen the bump on the rear shocks to tame it somewhat if you have double adjustables on there.

George