Car Climbing Out Of The Dyno - Advice?

[CEF11E]

Hi All,

I have recently finished tuning my R32 and had some issues.

I did a light tune on the RE customs dyno and the car made 280rwkw plenty of torque and was fairly well behaved, T

The dyno operator did back off on the first few full power runs as it was coming on that hard it felt like it was going to climb out but it was fine.

A day later I fixed a boost control issue and ran a few more PSI with the AFR's tidied up and took it back to the dyno. this time it was a different story. the car was strapped to the dyno from the rear cradle exactly the same as the first time and the chocks were under the front wheels exactly the same as before.

the car was fine at low boost. as soon as the boost was set to 19psi the car would alpost launch out of the dyno. it would shudder hard and sit of the front rollers and then bounce back and sit on the rear rollers. the chocks then had to be pulled out from the front wheels to get the car back where it should be between the rollers.

While this was happening the graph was all wavy the same as if you had wheelspin but much worse. during these runs it was making 310rwkw but possibly considerably more. I called it quits. even though the car was strapped down I thought it was a safety issue.

I have tuned cars on dynos for years and never seen this before.

the only thing that I had different was semi slicks on the back and they were HOT by the time we finished as were the rollers.

can anyone shed some light on what might have been happening? I mean 300odd kw is a lot but nothing compared to some cars.

[PM-R33]

What kind of semi slicks? Full slicks are ment to be an issue, but i wouldnt have thought semi slicks would be.

[GTS-t VSPEC]

Never use semi-slicks on dyno's you'll wreck them. Cheap shitter tyres with plenty of tyre pressure if your better option.

Sounds like the car needs to be strapped down a bit more. Most dyno's can handle way more powerful cars that that without any issues, so I think the operators need some more practice.

[CEF11E]

yep, I think i buggered $600 worth of tyres.. they are fedral 595rs-r's in 255/45/17.

we tried strapping it harder. perhaps not hard enough by the sounds of it.

[juggernaut1]

I'd say its the semi slicks causing the prob and probably not tied down on the dyno sufficiently.

You probably did have wheelspin but semi slicks have stiffer sidewalls than pure road tyres and therefore less forgiving and causing the shuddering you speak of when the wheel spin occurred as the semi slick could be skipping accross the roller in wheel spin conditions. The shuddering could also be a function of worn shocks or mismatched springs/shocks when wheelspin occurs particulalry when coupled with the stiffer sidewall semi's.

Until semi's are hot I've always found they offer less traction than a decent pure road tyre.

Edited September 30, 2009 by juggernaut1

[Guilt-Toy]

what was the ramp rate you are using on the dyno? how have you got the car strapped down?

try and add another strap through the car as well?

my RB30DET can have issues and will climb out of the dyno if not strapped down correctly. once i fixed it and worked out the best way to strap it down there was no issues. the max i was getting was 380rwkw without any issues at all.

what brand dyno are you using? where exactly are the straps ? do you have the front of the strap on the front of the dyno ? or do you have it going around the lower control arm and then hooked onto the rear bar?

[Lithium]

Hopefully more and more people start going to Dynapacks for this kind of reason, I just won't run my car on rolling roads - don't trust them.

[R31Nismoid]

Nothing wrong with rollers if you know what you are doing

As stated already - most likely tyres, never use semi's. Just get some cheap rubber on stockies or something.

If you get the ramp rate right and so on you don't even need to strap

Mine with over 300rwkw never gets strapped

[CEF11E]

strapped with 2 straps from the lower control arms going to anchor points on the floor behind the dyno, with the straps on a 30 degree angle with enough tension in the straps to make a twang noise if you struck them.

unsure of the ramp rate but we added more ramp with no or little difference.

I will chalk it down to wrong tyres and leave it at that. the tune is right so the only reason to stick it back on the rollers would be for a power figure.

cheers all!

[Guilt-Toy]

good luck with it

strapped with 2 straps from the lower control arms going to anchor points on the floor behind the dyno, with the straps on a 30 degree angle with enough tension in the straps to make a twang noise if you struck them.

unsure of the ramp rate but we added more ramp with no or little difference.

I will chalk it down to wrong tyres and leave it at that. the tune is right so the only reason to stick it back on the rollers would be for a power figure.

cheers all!

[Lithium]

Nothing wrong with rollers if...

... list bunch of things required to work around the inadequacies of rolling road dynos? Changing ramp rates, using different tyres etc all alter variables etc. I have decided that my runs on rolling road dynos have been about as useful as taking a drunk mate home from the pub and asking him how fast it feels in terms of looking for comparing power figures - the main use a rolling road dyno is you can go WOT in a controlled environment for tuning etc. Unless your car tries to jump off the dyno.

Vid of mine running fairly low boost on a roller dyno, needing two people in the boot and still moving enough to whack one of the people in the boot on the head when the car "unloads" after the run which is more of a testament to how dodgey using rollers is than to any grunt my car was (or really wasn't) making. Even without obvious wheelspin, the torque curve never mimicks that of on a hub dyno - it seemed to alway be clipped after it reached a certain point in the rev range where the equivalent setup on a hub dyno would follow a more standard torque curve shape.

Edited September 30, 2009 by Lithium

[R31Nismoid]

Im not even gonna waste time looking @ the vid, because i know you aren't running a 600rwkw machine, so simply comes down to poor strapping/operating by the dyno staff.

This is not an argument about dyno's.

[mad082]

have to agree with nismoid, except i did watch the video and it doesn't really look like the car is even strapped down.

and i've seen more powerful cars move less than that on the dyno when strapped down properly

[Lithium]

This is not an argument about dyno's.

OK yeah I started pushing it bit more off topic - the initial point was the best solution would be a hub dyno but if you don't have one available there clearly must be ways of making them hold most of the power.

[Guilt-Toy]

OK yeah I started pushing it bit more off topic - the initial point was the best solution would be a hub dyno but if you don't have one available there clearly must be ways of making them hold most of the power.

You are a expert dyno operator who knows what he is talking about.

[R.I.P.S NZ]

I always use street tyres where possible and there is a real trick to tying down a higher power car on rollers.

We've had around 750wkw on rollers safe and sound.

Due to the trans and rear track of the 240z we were never able to run it on hubs but it would have been interesting to see what it said although it wasn't a big deal as the black dyno tells pretty acurate whp numbers anyway.

Rob

[CEF11E]

hehe... had to think about what a black dyno was for a second there

I will take it to the strip when I get a chance...

Would low 11s be possible in a 32 rb30det with 300 odd rwkw with propper suspension set for drags and a pair of semis god and warmed up? I have a fairly consistant launch and usually pull a sub 2 60 foot time.

[R31Nismoid]

300rwkw is 10's.

[DCIEVE]

Show me a full weight, manual skyline running 10's with 300rwkw.

Didn't think so.

[R31Nismoid]

VL's can do high 10's, have for many years, they are similar weight to a 32

(im assuming semi's he means drag semi's, if not, well, that changes things)