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a32guy
10-10-2008, 07:56 PM
I went to the strip today and didn't have great results. First two passes were like on ice. Couldn't go WOT til 4th. Air'd the tires down to 25psi or so, then finally got some traction. Unfortunately I was getting extremely violent wheelhop and couldn't launch the car worth a damn all day long. A 2.150 sixty foot was one of my best with the new rubber. :(

On the bright side, I gained 4mph in trap speed with 4psi less boost since my retune. :)

http://www.smeraglinolo.com/hosted/turbom3/dragday02/slip.jpg

I wasn't gonna bother turning boost up or putting race gas in. Car scoots well with 16psi and 93 octane. However, all in all-- a depressing day. :(

F1SportsFan
10-10-2008, 08:06 PM
Sorry to hear that, at least you had a decent reaction time. :dunno

davidtm5
10-10-2008, 08:50 PM
what kinda tire are you running?

jfdmas
10-10-2008, 09:20 PM
bah, you shoulda went with the mickey's or slicks instead of the falcons.

el bob
10-11-2008, 08:21 AM
That's awesome! Wheel hop sure isn't fund, but you really got to test our your engine tuning! Consistent and reliable, I'd call that a win for sure.

Falcon tires, street radials? Sorry if I missed an earlier thread with this info.

StreuB1
10-11-2008, 08:49 AM
wheel hop means no weight transfer. do you have adjustable shocks??

a32guy
10-11-2008, 11:31 AM
No, just Koni yellows. Here's the thing-- I put in the stock springs in the rear, in place of my H&R race springs. I thought the height would correct my negative camber (which it did) and give a better contact patch. Think this screwed me?

m3jasper
10-11-2008, 11:48 AM
wheel hop means no weight transfer. do you have adjustable shocks??
Is the goal to have the rear shocks as soft as possible?

jfdmas
10-11-2008, 02:45 PM
Is the goal to have the rear shocks as soft as possible?

not realy but a softer spring. If i personaly had adjustable shocks i would adjust the front as soft as possible. Then i would disconnect the front sway bar. put soft springs in the rear. Id think a slightly stiffer shock setting for rear would be a good choice to help damper any kinda pottential hop and bottoming out of suspension on launch.

zemaestro
10-11-2008, 04:00 PM
Not to be a dick, but didn't you ask for advice on tires? You received good advice from myself and others, and chose to follow none of it. Funny thing, wise men don't need it and fools won't take it....BTW you need traction and sidewall to combat it....

a32guy
10-11-2008, 04:24 PM
Not to be a dick, but didn't you ask for advice on tires? You received good advice from myself and others, and chose to follow none of it. Funny thing, wise men don't need it and fools won't take it....BTW you need traction and sidewall to combat it....

Yes I realize this and appreciate the help. However I just couldn't justify putting $400 worth of tires on the car just for one drag event. I got a great deal locally on these Falkens, and they have a good amount of traction on the street compared to my last tires.

stanksbeamen
10-11-2008, 04:28 PM
Vids? Did you warm the tires up or just go with the tire pressured lower as stated above? Is that your 'best' time so far? Did you shift into fifth or able to keep it in 4th gear? Nice numbers, car must be great :)

StreuB1
10-16-2008, 01:56 PM
You want tough rear springs and valving thatll enable it to squat easily and release hard. aka soft compression and hard rebound. The springs support the weight of the car, the shocks determine how fast or slow the springs are allowed to do their job.

The idea is weight transfer. You want the car to squat and go and stay squatted. That means your weight transfer is staying rearward. If you transfer weight back to front back to front back to front (too soft rebound AND compression) your car will hop all over the place between shifts.

If you have too much compression resistance the shopck will inhibit your car from squatting fast enough and your car will stay erect (raked) the whole way down.

If your springs are too hard you also wont squat at all due to the sheer force required to compress them. If your springs are too soft youll squat too hard and too fast and the shocks will take a beating. Its a tough balance.

A good rule of thumb is to put a harder spring out back...like a decent road race spring and then adjust your yellows soft. This will allow the shock to compress quickly and the spring is just taking on the weight transfer.

In the beginning of a shake down session on a brand new drag car. There is a reason why they do 60' runs, then 330' runs then halftrack runs at half power, etc. This is to first dial in the rear suspension to get the weight tranfer down. This means changing the 4-link bars, spring rates and playing with the dampers.

Our cars are no different. This is where it really pays off running a coilover setup like GC...where you can goto the track with a few spring rates for not alot of money and fiddle a bit.

I am leaving out a pivotal part of the suspension scenario due to it being a little over head for this forum. People need to figure out the rear and remember to not use radials up front with slicks before we can talk about the other half...and the most important part of the weight transfer conversation.

Neil
10-16-2008, 05:09 PM
You want tough rear springs and valving thatll enable it to squat easily and release hard. aka soft compression and hard rebound. The springs support the weight of the car, the shocks determine how fast or slow the springs are allowed to do their job.

The idea is weight transfer. You want the car to squat and go and stay squatted. That means your weight transfer is staying rearward. If you transfer weight back to front back to front back to front (too soft rebound AND compression) your car will hop all over the place between shifts.

If you have too much compression resistance the shopck will inhibit your car from squatting fast enough and your car will stay erect (raked) the whole way down.

If your springs are too hard you also wont squat at all due to the sheer force required to compress them. If your springs are too soft youll squat too hard and too fast and the shocks will take a beating. Its a tough balance.

A good rule of thumb is to put a harder spring out back...like a decent road race spring and then adjust your yellows soft. This will allow the shock to compress quickly and the spring is just taking on the weight transfer.

In the beginning of a shake down session on a brand new drag car. There is a reason why they do 60' runs, then 330' runs then halftrack runs at half power, etc. This is to first dial in the rear suspension to get the weight tranfer down. This means changing the 4-link bars, spring rates and playing with the dampers.

Our cars are no different. This is where it really pays off running a coilover setup like GC...where you can goto the track with a few spring rates for not alot of money and fiddle a bit.

I am leaving out a pivotal part of the suspension scenario due to it being a little over head for this forum. People need to figure out the rear and remember to not use radials up front with slicks before we can talk about the other half...and the most important part of the weight transfer conversation.

Good information, but would you also adjust front shocks? If so, how?

Thanks.

Neil

MrBlonde
10-16-2008, 08:31 PM
You don't want the IRS to squat at all, that reduces contact path. You do want weight transfer.

jfdmas
10-16-2008, 09:11 PM
unless you add a ton of positive camber, but i see more neg then positives. the goal i guess for our cars would be to have the front lift as much as possible with just a touch of squat out rear. but then again i have yet to cut a decent 60ft so what do i know.:( however i just put the new tranny in and if everything seems good imheading up to the track.

MrBlonde
10-16-2008, 09:41 PM
Tuning IRS for drag racing is not easy. And all the advice the knuckle draggers have dating back from R&D gathered since the 1950s is not always applicable. This leads to misinformation. This means that lots of people struggle to get high powered, heavy IRS sedans out of the hole and yet have monster trap speeds.

Many knuckle draggers attribute this to lack of driver skill but that's only part of the story. Once you get a more level playing field like in Sport Compact pro RWD (and whatever they call it now it's moving back into NHRA group 2) then you find the inline 6 hightech turbo cars have the same short times given a live rear end and full chassis.

Yep IRS is a big handicap for us compared to muscle car racers. But that only makes it all the sweeter when you beat them to the stripe anyway.

StreuB1
10-17-2008, 07:11 AM
the goal i guess for our cars would be to have the front lift as much as possible with just a touch of squat out rear.


You have just described weight transfer

And you linked the aspect I was alluding to. You get a silver star for class today. :)

As far as squat being bad for our cars....yes thats due to their geometry...aka the arc they travel through isnt in a single plane. This causes negative camber where we want it the absolute least. There are ways around that though. At least for kenny and people that run anything before an E36 sedan/coupe.

bennyfizzle
10-17-2008, 07:50 AM
Wheel hop means no weight transfer?

I thought it was because of harmonics between the rear axles, the tires, the diff, the driveshaft, and anythine else in the driveline that spins.

MrBlonde
10-17-2008, 08:19 AM
Wheel hop means your suspension is oscillating and the rear tyre patch is not planted. That's shit.

morerevsm3
10-17-2008, 09:02 AM
You want tough rear springs and valving thatll enable it to squat easily and release hard. aka soft compression and hard rebound. The springs support the weight of the car, the shocks determine how fast or slow the springs are allowed to do their job.

The idea is weight transfer. You want the car to squat and go and stay squatted. That means your weight transfer is staying rearward. If you transfer weight back to front back to front back to front (too soft rebound AND compression) your car will hop all over the place between shifts.

If you have too much compression resistance the shopck will inhibit your car from squatting fast enough and your car will stay erect (raked) the whole way down.

If your springs are too hard you also wont squat at all due to the sheer force required to compress them. If your springs are too soft youll squat too hard and too fast and the shocks will take a beating. Its a tough balance.

A good rule of thumb is to put a harder spring out back...like a decent road race spring and then adjust your yellows soft. This will allow the shock to compress quickly and the spring is just taking on the weight transfer.

In the beginning of a shake down session on a brand new drag car. There is a reason why they do 60' runs, then 330' runs then halftrack runs at half power, etc. This is to first dial in the rear suspension to get the weight tranfer down. This means changing the 4-link bars, spring rates and playing with the dampers.

Our cars are no different. This is where it really pays off running a coilover setup like GC...where you can goto the track with a few spring rates for not alot of money and fiddle a bit.

I am leaving out a pivotal part of the suspension scenario due to it being a little over head for this forum. People need to figure out the rear and remember to not use radials up front with slicks before we can talk about the other half...and the most important part of the weight transfer conversation.

I suggest you google "anti squat" because it appears you know squat about how to achieve traction, and not just IRS, ideally, you want the rear suspension arms trying to lift the weight of the car, through the rear tires. you want soft springs and soft rebound, hard compression on the front, hard springs, compression and rebound in the rear

got psi
10-17-2008, 10:53 AM
I suggest you google "anti squat" because it appears you know squat about how to achieve traction, and not just IRS, ideally, you want the rear suspension arms trying to lift the weight of the car, through the rear tires. you want soft springs and soft rebound, hard compression on the front, hard springs, compression and rebound in the rear Ther REAR suspension arms will NEVER transfer any lifting to the car on an IRS suspension. The torque is transmitted thru the rear center section,thru the axles and the tires. There is no housing to do the torque transfer. The suspension arms are just there for the ride and offer no support other than the spring load. The sooner everyone realizes this the better we will get our short times. Ok my opinion start at the front soft setting on the shocks. lower spring rate BUT longer spring so it will store energy in a longer travel so it will keep lifting the car at full travel. This is not like a road race spring where they want the bulk of the usefull spring rate confined to a small rise. This keeps te ride height almost the same when tracking. Not what you need forrag racing. Now go to the rear (IRS ONLY) you can't set it up like a live axle period. Good bushings on the sub frame (keeps it from torqueing up). good bushings on the rear center section ( as stated earlier this is the big problem area ) Why do you think we keep busting the center diff bolt? HMMMM? the bushings act like a spring they load up (all of them) then when the tire just slips just a little they unload, then the whole thing starts all over again...and again...and again. WHeel HOP at it's finest!!!!! We combat it like this stiffer springs in the rear so we can use the weight of the car to plant the tires, remember the arms will not use the torque of the car to plant the tires so you must use the car itself. Mid setting on the shock will help keep oscillations equal. If you really want to do something that will help build a torque bar that extends the front mounting of the rear center section further forward as to help lift the car on a launch. Sorry for the long essay but most here don't understand the IRS beast for dragracing. ///J.T.///

StreuB1
10-17-2008, 01:51 PM
I suggest you google "anti squat" because it appears you know squat about how to achieve traction, and not just IRS, ideally, you want the rear suspension arms trying to lift the weight of the car, through the rear tires. you want soft springs and soft rebound, hard compression on the front, hard springs, compression and rebound in the rear


Eh?!?!?

You mean to tell me a cars inertia and natural weight tranfer under the force of accelleration won't make the rear of the car squat lower? Are you also saying that when it supposedly does'nt squat lower....that this doesn't affect traction due to weight transfer?

The rear suspension arms cant lift the car. They can only push THROUGH the car. That is all they can do. If the diff/trailing arms were a single unit then yes. As JT said, the pinions natual desire to ride the ring gear is what causes the rear end to "wind up" and lift the car. Thats just not possible on an IRS. So you need to achieve squat and weight transfer entirely through spring rate and dampers.

Take a look at this video and tell me if this car is not squatting....

http://e-owned.com/albums/userpics/10057/MOV02311.MPG

StreuB1
10-17-2008, 02:03 PM
I will point out....Im not saying IRS cars CANT wheelstand. I will say they CAN under certain circumstances....like through brute force. For instance, when you throw big meats out back and pass 1500whp through them in a gutted car.

Put that same WHP and tire in a straight axle car and itll flip over then moment you launch.

Hope that explains....

http://www.youtube.com/watch?v=4hHUuVE0_Sc

bennyfizzle
10-17-2008, 02:07 PM
Oh, oh wow. :rofl

StreuB1
10-17-2008, 02:08 PM
To further cement Kennys words...

http://www.youtube.com/watch?v=hEnR_6GpLtk

bennyfizzle
10-17-2008, 02:13 PM
omg is he ok? :rofl

I'm a bit confused as to what that has to do with IRS tuning for drag racing..

got psi
10-17-2008, 02:37 PM
To explain that video (You need to explain why you posted that video) That is the result of using bias ply tires with radials. Granted they were at a track that used portable barriers that moved when impacted. This grabbed the car and tore it apart. The driver did not survive as I was informed.The intent was to show you the chance you are taking using tires not compatible with each other. There is a serious lack of information at the dealer level concerning tire usage . ///J.T.///

bennyfizzle
10-17-2008, 02:40 PM
oh I see. man that's terrible. Really horrific.

DADx2
10-17-2008, 04:03 PM
Video is no longer available.......anyone have a link?



Tried again and it worked.......WOW !!!!!

MrBlonde
10-17-2008, 08:13 PM
Yeah that's an Australian video (Ford Falcons) but I don't recognise the "track". It's not an ANDRA track, must be an unofficial track hence the dogshit barriers na dletting the radials/slicks car through scrutineering. Probably there was no scrutineering.

You can tell people not to mix radials and slicks all you like, they only seem to pay attention once they've had an incident.

morerevsm3
10-17-2008, 08:39 PM
Ther REAR suspension arms will NEVER transfer any lifting to the car on an IRS suspension. The torque is transmitted thru the rear center section,thru the axles and the tires. There is no housing to do the torque transfer. The suspension arms are just there for the ride and offer no support other than the spring load. The sooner everyone realizes this the better we will get our short times. Ok my opinion start at the front soft setting on the shocks. lower spring rate BUT longer spring so it will store energy in a longer travel so it will keep lifting the car at full travel. This is not like a road race spring where they want the bulk of the usefull spring rate confined to a small rise. This keeps te ride height almost the same when tracking. Not what you need forrag racing. Now go to the rear (IRS ONLY) you can't set it up like a live axle period. Good bushings on the sub frame (keeps it from torqueing up). good bushings on the rear center section ( as stated earlier this is the big problem area ) Why do you think we keep busting the center diff bolt? HMMMM? the bushings act like a spring they load up (all of them) then when the tire just slips just a little they unload, then the whole thing starts all over again...and again...and again. WHeel HOP at it's finest!!!!! We combat it like this stiffer springs in the rear so we can use the weight of the car to plant the tires, remember the arms will not use the torque of the car to plant the tires so you must use the car itself. Mid setting on the shock will help keep oscillations equal. If you really want to do something that will help build a torque bar that extends the front mounting of the rear center section further forward as to help lift the car on a launch. Sorry for the long essay but most here don't understand the IRS beast for dragracing. ///J.T.///
torque arms, 5th coil etc won't work with IRS, but you can get anti squat with geometry (and preferably a 5 link arangement) with IRS
the following is quoted from a speedway suspension vewpoint, but still applies


Anti-squat in independent systems is different than in live axles. In a live axle system, we can separate rear jacking forces under power into thrust anti-squat and torque anti-squat. In a typical Late Model, torque anti-squat is the lift we get from the torque arm, and thrust anti-squat is the lift we get from the geometry of the linkages at the ends of the axle, which most commonly attach to birdcages (brackets that can rotate on the axle). With independent suspension, we only have thrust anti-squat to work with, because axle torque reacts through the differential mounts and does not act through the suspension.
To get such properties with an independent system, you need geometry that makes the hub travel rearward approximately .15" to .20" per inch of suspension compression, and makes the upright rotate rearward approximately 0.6 to 1.0 deg per inch of suspension compression. In terms of side view geometry, this means a side view instant center something like 80" behind the rear wheel, and at or slightly above ground level.

the IRS commodore (pontiac GTO) cars that run any good here (at drags) add air bags to reduce squat...


here is a good article on rear suspension geometry
http://www.raceglides.com.au/TechInfo.htm

morerevsm3
10-17-2008, 08:44 PM
video was at Townsville, driver is on performance forums, luckily had fairly minor injuries considering the wreck

got psi
10-18-2008, 01:02 AM
here is a good article on rear suspension geometry
http://www.raceglides.com.au/TechInfo.htm
Not one thing in this link has anything to do with IRS suspension. ///J.T.///

morerevsm3
10-18-2008, 02:03 AM
Not one thing in this link has anything to do with IRS suspension. ///J.T.///

it all has to do with IRS, it is talking about where the force from the wheels trying to move forward is going, by altering the geometry, you can get anti squat, that part it is irrelevant if it is IRS or not, the article is refering to linear force, not rotational

got psi
10-18-2008, 10:37 AM
it all has to do with IRS, it is talking about where the force from the wheels trying to move forward is going, by altering the geometry, you can get anti squat, that part it is irrelevant if it is IRS or not, the article is refering to linear force, not rotational
Funny every one of those dia. are suspensions hooked to a standard axle rear end NOT IRS there is a rotational element involved in all those examples and NONE of it will transfer to IRS. ///J.T.///

BlownShovel
10-26-2008, 09:58 AM
Tuning IRS for drag racing is not easy. And all the advice the knuckle draggers have dating back from R&D gathered since the 1950s is not always applicable. This leads to misinformation. This means that lots of people struggle to get high powered, heavy IRS sedans out of the hole and yet have monster trap speeds.

Many knuckle draggers attribute this to lack of driver skill but that's only part of the story. Once you get a more level playing field like in Sport Compact pro RWD (and whatever they call it now it's moving back into NHRA group 2) then you find the inline 6 hightech turbo cars have the same short times given a live rear end and full chassis.

Yep IRS is a big handicap for us compared to muscle car racers. But that only makes it all the sweeter when you beat them to the stripe anyway.


Some of the advice given by the musclecar crowd is improper as live rears act/react different than ours do. Heck, some of those chassis can run 10's w/o issues in near stock trim. They don't understand our setup/pain.
As far as the bias ply problems... I have seen many wrecks that were caused by under-inflation of soft sidewalled bias tires. The weight of the car walking on the sidewalls at speed is a scary thing. I run radials all around on my vehicles. Stiffer sidewall and more stability IMO

BTW... I HATE wheelhop too

MrBlonde
10-26-2008, 07:57 PM
Agreed about low pressures in small slicks on heavy sedans. The slicks we can fit under out cars are TINY by comparison to the big boys. 26"x8.5" or 26"x10" is minute compared to the rubber they run. And our street cars are very very heavy in comparison to their cars. 3500 lbs compared to 2100 lbs.

Add it all up and it means that the knuckle draggers who urge you to run 6 or 8 psi in your slicks are not giving you very good advice. Start at 18 psi and work your way down CAREFULLY.

BlownShovel
10-26-2008, 09:44 PM
Agreed about low pressures in small slicks on heavy sedans. The slicks we can fit under out cars are TINY by comparison to the big boys. 26"x8.5" or 26"x10" is minute compared to the rubber they run. And our street cars are very very heavy in comparison to their cars. 3500 lbs compared to 2100 lbs.

Add it all up and it means that the knuckle draggers who urge you to run 6 or 8 psi in your slicks are not giving you very good advice. Start at 18 psi and work your way down CAREFULLY.

withu 100% My chevelle weighs 3800lbs... why do folks tell me to run 8-9psi? I'd be grinding rim. Depending on the tire my lowest setting was 13psi with some hoosiers way back in the day. Most tires(bias) like 15-16 on my car and I run more in MT Drag radials. Steady and stable...almost safe. a 12.5 tire and live axle is way easier to work with than our BMW offerings... but not necessarily as fun

got psi
10-26-2008, 10:22 PM
Generally you need a higher pressure when the tire is smaller. Big tires like 16x33s use 6 to 8 psi but that would never work on a small tire like we use. People figure they are like their big brothers....NOT. ///J.T.///

jfdmas
10-27-2008, 05:02 PM
Yep, my rear bias ply's are at 15.5psi and i think thats pushing it for my 26X9.5X16's. I started at 20psi and worked my way down to a 1.5 60ft. Its tuff with the skinny slicks we fit under our bimmers along with our limited selection.

morerevsm3
11-12-2008, 06:12 AM
Not one thing in this link has anything to do with IRS suspension. ///J.T.///

right at the bottom of this, it deals directly with IRS
http://home.earthlink.net/~whshope/