Street Tires Suck

[SilentNight1647]

I went to the track today for the first time since I've been home and ran my 280ZX I was expecting a 12 out of it, man was I wrong. Massive wheel spin dashed all my hopes for getting a decent time, I ran a 15.9 on the first pass and a 15.2 on the next one, with 2.9 and 2.5 60ft times respectively. I staged up again and launched it really soft and only got a some mild spin in 2nd and a chirp into 3rd I got a 2.2 60 and 14.6 overall. Oh well looks like I need slicks. On the plus side the motor makes plenty of power when I stood on the throttle in 1st I spun for 40ft and continued to spin well into 2nd. I thought 10in wide Kuhmos would be plenty to get it to the ground but I guess I figured wrong, sometime this week I am taking it to the local dyno to see what kind of numbers I can lay down. I'll post the results when I get them, I wish I had some video for you all but I neglected to bring the camera, you would have laughed seeing a my car getting sideways at the lights (whatever happened to stickum?), one pass I was at about a 45 degree angle before the car started to move, the guy running the lights was not amused altough I thought it was pretty funny.

[naviathan]

Might want to get something better than Gas=A=Just struts also. You probably get massive rear squats with those.

[mario_82_ZXT]

Dang! Talk about not being able to lay down your power!

 

On my stock L28ET swapped 280z I ran a 14.4 with a blown head gasket...

Mario

[SilentNight1647]

Correct me if I'm wrong but doesn't the rear end squatting indicate good weight transfer thus helping the car hook-up? That's how we always set up our drag cars anyway. But your right it does squat down quite a bit on the launch. I still think I just need more tire I plan to run it again next weekend with a set of slicks so we'll see.

[patzky1]

Two words: bigger sidewalls!

[johnc]

Correct me if I'm wrong but doesn't the rear end squatting indicate good weight transfer thus helping the car hook-up?

 

The 280ZX semi-trailing arm rear suspension gains negative camber in bump (squat) so you lose some outside tread contact with the pavement.

[JMortensen]

The toe also changes quite a bit while the camber changes. Semi-trailing arm is not good drag suspension. You can make it work, but I bet you won't find any tube frame drag cars using semi-trailing arms if you go looking. I think the solution is going to be brutally stiff springs.

[Thumper]

I went to the track today for the first time since I've been home and ran my 280ZX I was expecting a 12 out of it, man was I wrong. Massive wheel spin dashed all my hopes for getting a decent time, I ran a 15.9 on the first pass and a 15.2 on the next one, with 2.9 and 2.5 60ft times respectively. I staged up again and launched it really soft and only got a some mild spin in 2nd and a chirp into 3rd I got a 2.2 60 and 14.6 overall. Oh well looks like I need slicks. On the plus side the motor makes plenty of power when I stood on the throttle in 1st I spun for 40ft and continued to spin well into 2nd. I thought 10in wide Kuhmos would be plenty to get it to the ground but I guess I figured wrong, sometime this week I am taking it to the local dyno to see what kind of numbers I can lay down. I'll post the results when I get them, I wish I had some video for you all but I neglected to bring the camera, you would have laughed seeing a my car getting sideways at the lights (whatever happened to stickum?), one pass I was at about a 45 degree angle before the car started to move, the guy running the lights was not amused altough I thought it was pretty funny.

 

What was your mph? It sounds like to me you are dumping the clutch. I found with the l28et you need to slip it so that you can get he boost up right away but not break the tires loose. One way to think about it is you are doing 30mph in second and punch it you will spin the tires all the way through second even modulating the pedal. But if you go from 15mph you won't spin in second because you slowly got the power on and the car accelerating. I dropped my 60's from 2.2-2.3 to 2.0-1.9 in my ghetto beast when I learned to slip the clutch. Good luck

[SilentNight1647]

The 280ZX semi-trailing arm rear suspension gains negative camber in bump (squat) so you lose some outside tread contact with the pavement.

 

Good to know all my other cars have been solid axle most of which had leaf springs so I'm new to this type of setup.

 

The toe also changes quite a bit while the camber changes. Semi-trailing arm is not good drag suspension. You can make it work, but I bet you won't find any tube frame drag cars using semi-trailing arms if you go looking. I think the solution is going to be brutally stiff springs.

 

Any idea where I can get some really stiff springs? Or am I better off converting it to a coil over style and use QA1s? The car has alot more in it I was trapping at about 95-98mph all day running high 14s low 15s so if I can get traction I think I can see 12s in it.

 

It sounds like to me you are dumping the clutch. I found with the l28et you need to slip it so that you can get he boost up right away but not break the tires loose. One way to think about it is you are doing 30mph in second and punch it you will spin the tires all the way through second even modulating the pedal. But if you go from 15mph you won't spin in second because you slowly got the power on and the car accelerating. I dropped my 60's from 2.2-2.3 to 2.0-1.9 in my ghetto beast when I learned to slip the clutch. Good luck

 

Your right I was dumping the clutch, my car doesn't spool very much boost anyway so I didn't really think about doing that I try to slip it next time I go racing thanks for the advice hopefully I can get it under control and run it where it should be at.

[80LS1T]

Assuming you drop your 60' down to say a 1.7 from a 2.2 with slicks your only going to shave off about .8 seconds of your ET. The general rule for 60' times is for every .1 you loose there you loose .15 seconds on your ET. Your MPH is really not high enough to run 12's if you ask me. Your probably going to have to be closer to 110mph to see 12's. I know "Cody 82 ZXT" was running a 12.9 @107.7mph. He is also running an L28ET.

 

Good launches takes lots and lots of practice. I know in my 280ZX I have to slip the cluch to get it too hook decent.

 

 

Guy

[SilentNight1647]

The trap speed would be much higher if I wasn't spinning for the first forty feet, I wish I had a video so you could see how bad it was. And isn't a 110 awfully high for a 12? IIRC I trap about 115-120 in the Nova, it runs an 11.3-11.7 with a 1.6-1.8 60ft depending on how cool it is outside. I'm definetly going to slip the clutch from now on though I think it will make a big difference as well as slicks.

[vrocious]

The car has alot more in it I was trapping at about 95-98mph all day running high 14s low 15s so if I can get traction I think I can see 12s in it.

 

was going to say the same thing about that. that gate speed is about right for that time. in my v8 i can get around 14.7-14.3 in full street trim and was getting around 95-105mph at the gate, dependant on how i set up my air intake

 

good luck with your pursuit anyway. what type of street tyres are you using? i know you said kumhos but what traction and tread wear do you have? i know federal make a good semi slick

[SilentNight1647]

Their Ecsta Supras I don't know the treadwear right off hand I'll look later but I can tell you they are rock hard, I thought about DOT slicks for a while but I would just assume get a real set since I have such huge traction problems.

[sweetleaf]

Put some smaller diameter wheels on with good rubber and drop the pressures.

If you have a set of stock 14"'s use them. You definately may want to stiffen up the rear too.

[SilentNight1647]

Thats the plan, I am looking at a pair of Diamond Racing wheels right now and some Hoosier's I'm not ready to change the suspension just yet I really don't think I'm losing that much outside tread and I think at this point weight transfer is more important to getting the car to hook. Maybe I'm just old fashioned but I was always taught that if the car won't hook get more tire and make it transfer more weight over the rear wheels.

[Afshin]

I think that people make much more out of the semi-trailing arm theoretical limitations. Porsche was running semi-trailing suspension until the 90’s and 280zx,s won enough races as well to show that the real life difference is not always as significant than suggested by theory. According to theory current 911 should also have grossly sub-par handling with a rear mount engine, But then they dominate.

Here are Bernard’s numbers with a 280zxt with stock pathetically soft and worn suspension:

60ft: 1.6909

330ft: 4.9192

1/8 mi: 7.5660@93.21

1/4 mi: 11.7589@117.55mph

This was with slicks, time was I believe in low 12’s on street tires.

 

Point being, while the suspension design is not “optimal”, it’s certainly not the limiting factor at this point in the game.

You fist need to control the wheelspin. Also with a trap speed of 98 mph you probably don’t have the power to break into the 13’s no matter the tire. I would expect low 14’s with good tires and good launch.

Here are some of the numbers from other members:

http://forums.hybridz.org/showthread.php?t=115056

 

BTW, what amount of boost and EFI are you running?

You seem to have enough goodies on the car to make much more power than you currently have.

[SilentNight1647]

I only spool about 5lbs of boost which isn't alot but the motor has alot of compression (10:1 on a whistle) and I'm afraid to turn it up past that I know I'm a sissy but this is the first turbo motor I've ever put together. The EFI consists of a Q45 throttle body, '78 manifold that has been extrude honed, and stock injectors from a 280ZXT. I've got a Digital 6 on it right now, I've also got a box from Jet that I got when i bought the car but haven't hooked up it's supposed to adjust the fuel injection via two dials I couldn't find it on their website though so I don't know how to hook it into the factory harness. One thing I've never bothered to ask anyone is how much RPM I should be turning before I shift, right now I only turn about 6000 should I turn more or shift alot earlier? It's really weird though the car feels alot faster than it performed it even seems to pull harder on the highway than it did the day I raced it. I'll figure this damn car out one or another even if I have to rebuild the motor in the process.

[vrocious]

Their Ecsta Supras I don't know the treadwear right off hand I'll look later but I can tell you they are rock hard,

 

there are several model of those as i've tried a few. the best one probably in that rack is the 712 as it has a treadwear of 230 which is bloody low. awesome grip but low endurance on a high hp car. even on my other car it was 210rwhp but being a v8 had heaps of torque and a stage 2 shift kit melted them within a year(and i do not do static burnouts) i've since gone 2 other compounds as the 712 is no longer available in australia. I now run the Ecsta SPT KU31 on my fronts as it has a treadwear of around 270-320 so for non driving wheels it offers great wet and dry grip as i do several motorkhana events per year as well as drags. On the rear i run the Ecsta AST KU25 it's a much harder compound but still maintains a AA traction rating but a treadwear af around 420 which will last me a lot longer, all of mine are 235/45zr17. i know a lot of the guys in my club who also do track racing go the type r's from federal. lot more expensive but once you get in the operating temps stick like ♥♥♥♥ to a blanket and these are all ls1/ls2 v8's sunning between 300-650rwhp

 

edit: i remember you also said you have got home, meaning you have been away. how old are the tyres? if tyres sit there for a while you will well know they go rock hard and lose performance

[SilentNight1647]

The tires are about a year old I did have the car with me the whole time though, the treadwear appears to be a 300 on all the wheels which makes me wonder what I was thinking when I put those on. Where can I get some of these Federal skins? I can't seem to find any in the states.

[sweetleaf]

Well your Q45 TB is overkill, were you even able to port match it to the intake? The compression definately seems high, even for 5 psi but I would say your biggest limiting factor is the stock injectors. What are the specs on you cam? That combined with the other build parameters, should determine when to shift.