Dyno Question

[DSPTurtle]

For those of you that have had your 930 on a dyno... how did they strap it down? Supposedly IRS cars are tough to strap down. Are there any good connection points to tie the straps to? I have an appointment on Tuesday and his only comment was that it might take a little while to find a good tie-down point. So I figured I would ask the experts and offer your advice to him when he gets started. Once he figures it out it will be awesome since he is so close to the house. I am getting my baseline stock run done before I do any of the power mods. Any guesses on output? I am thinking 220 at the rear wheels. 1985 930S (Euro).

[Porschephd]

We strap and the chain them through the rear trailing arms at the base of the mount. The fronts we actually use the two hook in the bumper. Works perfect.

[spuggy]

Originally Posted by DSPTurtle

For those of you that have had your 930 on a dyno... how did they strap it down? Supposedly IRS cars are tough to strap down. Are there any good connection points to tie the straps to? I have an appointment on Tuesday and his only comment was that it might take a little while to find a good tie-down point. So I figured I would ask the experts and offer your advice to him when he gets started. Once he figures it out it will be awesome since he is so close to the house.

I think my guy uses the chassis behind the wheels somehow. He doesn't grovel under there for long.

When I went back recently with more power, he opened both doors, added a strap through the body behind the seats after the preliminary pull...

I am getting my baseline stock run done before I do any of the power mods. Any guesses on output? I am thinking 220 at the rear wheels. 1985 930S (Euro).

My 1978 RoW with 8:1 C/R and SC cams (but otherwise completely stock) made 268 RWHP @ 5680 RPM last year. That's 310 FWHP, with 291 ft/lbs @ 5200 RPM.

The usual bolt-on mods (GHL, EVO intake, BL WUR, Kokelyn, K27/HF) has it making more RWHP now than it made at the crank last year.

As I understand it, 'S' 930's were all special wishes, so there's no set power figure that applies, but most should be up at least a little on a stock 930, maybe 20-30 HP or so. One German customer apparently ordered one with 400 BHP, which wasn't actually legal for road use in Germany at the time...

[fredmeister]

My 79 930 with stock engine and 3LDZ turbo. Only mod was still US exhaust but with thermal reactors replaced with cast collectors.
Made 248hp at the wheels. 278ftlbs. of torque. If you convert to crank hp and torque it was within 1-2% of factory claims!
We used tie downs wrapped around the mounts where the shocks bolt to the control arm. My dyno guy was nervous about this but I insisted it was ok. No problems.

[Jeff Alton]

Just had my NA 3.4 on the dyno the other day. I have hooks on my rear shock bolts and front suspension. We used those and the car never moved around at all. Still nervous sticking my head in the engine bay at 6k to check timing.....

Cheers

[A930Rocket]

I use the front hooks like the Doc says and the shock mounts like Jeff. You can also use the rear hooks if the angle is't too much. I've seen cars with just a strap through the doors. Anyone who suggests this should be shot.

[TimT]

I've cars with just a strap through the doors. Anyone who suggests this should be shot.

thats a pretty stong sentiment! care to explain?

[RarlyL8]

Trailing arms and front hooks. Works as good as the care taken to place them.

[A930Rocket]

You have to be kidding? You don't think a car strapped down by just one going through the doors is a problem? What keeps the car straight on the dyno? What keeps it from going from side to side? WIth all the options, that seems like the worst one.

Originally Posted by TimT

thats a pretty stong sentiment! care to explain?

[DSPTurtle]

Thanks for all the responses guys!!! Seems like the trailing arms and the front tow hook are the way to go. Our local Porsche guru is intrigued enough that he is planning to come down and watch the pulls. I am sure he will give some decent advice and make sure the tie downs are on solid spots too. As a 930S is shoudl have had 330hp at the crank. But the car has 100k miles on it so I am guessing it will be a little down from that now. I just wanted to do this as a baseline before I add the turbo, intercooler and 1.0 Bar spring to see exactly how much it adds. I had the AFR set on Friday so at least that is now in good shape. It was at 15.5 and is now at 12.5-13.0. Funny part was that right after setting the AFR the idle went to the correct 900 rpms (was 600-700) but yesterday it went back to 600-700 at idle. Oh well, at least on Tuesday I will do the dyno run with the AFR being checked throughout the pulls.
Any other goodies that are worth getting plotted? He said something about also being able to plot the boost levels on the graph but any extras will start to add up quick. Look forward to hearing your thoughts. Will post the graph after the pulls.

[mppickett]

Power, torque and boost should be plenty (especially for a baseline). I noticed that after you start seeing over 300 hp at the wheels you may need some sticky spray on the tires to keep them from spinning on the rollers. Your dyno guy should have it on hand.

[TimT]

You have to be kidding? You don't think a car strapped down by just one going through the doors is a problem?

nope not at all

We have had a dyno in our shop since '98 Our first dyno was a single drum inertial dyno, agree that with a dyno of this type you have to be particular in the method you use to secure the vehicle.

We went out west years ago to attend a the Unichip class to become certified installers... and we learned the dyno protocol they expect...

There is no single method to secure every car. Each type of vehicle, and each type of dyno require a bit of investigation.

We found that our old inertial dyno was only good for measuring power, and not a "tuning" aide.. so we decided to sell it and purchased a loading dyno. The old dyno was a single drum, the new a dual drum. On the dual drum the car centers itself... no more precarious tensioning of straps etc..

What keeps the car straight on the dyno?

on any dyno the drive wheels square up the car.. I don't care how hard you cinch down the straps.... the car will wiggle and jiggle till it finds center... cinch the car down and drive slowly .. the car will find center... then re tension the straps

We typically dyno 4-6 cars a week... sometime a bunch at a time... i.e. if we get a club that want to do a dyno throwdown.

some recent rides on our dyno have been:

a 3 rotor mazda = almost 1000 hp
our 935 clone 700+ hp
mercedes 190 with ITBs Haltech etc.. 185 hp


We do alot of dyno work..

we also tried using the traction gunk... it doesn't work well and makes a mess of the rest of the shop... aerosolized all that gunk and it settles on everything else in the shop

[A930Rocket]

I don't have a dyno and didn't go to dyno school, but I can't help but think that the dyno mfgs say it's OK to just run a strap through the car doors and call it safe...

If anyone suggests it to me, I'll pass (and I've dynoed mine many times on various dynoes).

[Porschefile]

The few times I've had my Carrera on the dyno, the rear trailing arms were used, which is perfectly safe. Depending on the angle of the straps, you might want the straps to cross the car and attach on the opposite side (cross like an X basically) to keep the straps from touching the tires. As for the fronts, they used the tow hooks which worked just fine on my car.

I'd check and see if they have a wideband O2 sensor as it's always nice to check your A/F curve and make sure there isn't something out of whack.

I've never seen any dyno shop run a strap through the doors. Maybe it's perfectly safe but, better not to find out. Using the tow hooks and trailing arms works perfectly fine and is what most dyno shops do for most cars of this nature with a trailing arm rear setup.

[David]

Mine was strapped to the swing arms in the little holes and in the tow hooks up front.

The only problem was when we were trying to get the boost controller to work and it wouldn't open the waste gate. The tires would start spinning at about 3500 rpm as the torque was rising like a 700 cu in V8 . We stopped the runs as soon as this happened, I hate imagine what would have happened at 6000 rpm with the waste gate closed .

[Porschefile]

If everything is properly strapped down tightly, it takes ridiculous amounts of torque (like 1000lb/ft+ territory) to really come close to spinning tires on the dyno. Better check those straps! j/k

[David]

I guess I shouldn't have said spinning, but the car did move an inch or two as the torque curve took off at an unusual rate.

[briankeithsmith]

I wouldn't strap mine through the doors. no way boss....

Don't really have any physics to back it up, just a personal preference thing...

I'll watch someone else do their car that way though - might make for some good YouTube video

[TimT]

Perhaps the braintrust can show me the error of my ways.

The following pic shows a 996 we had on the dyno for tuning..I think we installed a unichip on this one.. cant remember for sure.

Note the layout of our dyno. We do have eyebolts embedded in the concrete which are out of the picture.

What led us to start putting a strap through the doors is we noticed on high powered cars the wheels would start to climb the roller. The strap not only secures the car quite well, but it also allows us to preload the suspension a bit, keeping the tires in contact with the rolls better, mitigating wheel slip.

We typically notice wheel slip up around 700 hp depending on whether the car is on slicks or DOT tires.

Its pretty amazing actually when you get wheel speeds up over 150 mph or so.. watching the tire deform..

I mentioned in an earlier post each vehicle and each type of dyno require different methods of securing the car...Then again we do this every day, have a bunch of cars on the dyno every week. So tell me how should I secure a car to the dyno?

[FLATTOP]

Attached is a picture of my BABY RSR on a Hub Dyno. It bolts directly onto your car's hubs at the sideshaft. The hub is shown on the right hand side of the picture. No jerking backward and forward on the rollers. The control of the rpm, I believe, also improved.

For what is is worth the "Baby RSR" with its 3.6lt engine with compressor generated 373kw and 609nm on the hub.