Anyone here use a chassis dyno to sort out thier cars?

I elected to not dyno my engine this time as it is basically a freshen up with a couple of small changes to the combo. However the weather has not been cooperating with getting it out and making some laps. The first race for me of the season is slowly creeping up and I would like to be ready to hit the ground running. made some other changes such as gearing and need a good idea where to start once we finally get out there. So the car has been sitting ready to rock. I would like to get it broken in and the fuel curve sorted out. Just wondering if this is a viable option or not? Any input?

I ran mine on a chassis dyno this year. It really helped getting the jetting and timing dialed in. I also found a major glitch that had been causing a high speed miss. Never would have found that running the car down the track.

You probably already know that the numbers might not be very realistic but that's not what you're looking for anyway.

I found out the hard way that the chassis dyno can be hard on the car. I didn't have a fan on my trans cooler and should have let the engine idle a lot longer after every pull to get the trans fluid cooled down. The fluid got hot enough to burn the paint off the converter, cook the fluid and damage the high gear clutch pack.

Maybe in a way that was good because now I have a new cooler, twice the size of the old one with a 10" fan mounted on top of it, plus a trans fluid temp gauge.

I used an old pair of slicks that were about gone and I'm glad I did. The rollers will do some damage.

All in all I think it was worth the time and money. I don't know what you'd have to pay but my dyno guy didn't even want to take any money. He just wanted to see the car on his dyno. My wife left $125 laying on his desk and I hope that was enough to pay for his effort.

I just had my junk on a chassis dyno last week and got everything tuned nice. The other option was to make a top gear blast on the street with the laptop, which was not an option! I paid $125.

Sorry to side track your thread Al but it looks like someone is holding out on us. What kind of numbers Theotherdodge.

lol... I was wondering when someone was gonna ask that!

The numbers themselves were not great. After the pull, both the dyno operator and tuner (person that did my turbo and FAST system) asked how big my converter was. When I told them it was around 4500 they both said, "that makes sense"...

411 rwhp.

They said a big converter like that will "hide" the true power numbers. He said don't worry about the numbers, just go run it. If someone asks what hp did it make, tell them "411 rwhp, do you want to run?".

I was told a tighter converter would show much bigger numbers on the dyno but could hurt et if I was not able to spool enough on the line. And, I may have too loose of a converter but suggested I try it anyway to see how it does. Also, I don't know the shape of this converter. It may be slipping alot in upper rpms. Im thinking about getting a 3500 Precision Converter.

Right now, the truck rips the tires and runs killer. I was thinking it made around 500+ rwhp..

so anyway...I will report what it runs when our tracks open next year.

Sorted out my last combo as far as baseline jetting and timing also found a gremlin in the fuel system on the chassis dyno. Well worth the time and money. Did also damage a slick on the rollers as well.

As already mentioned they can be a valueable tuning aid but can also be hard on parts. I am like you and prefer an engine dyno on a new piece but not on rebuild, unless it's free!

After 3 unsuccessful trips to the track I finally put the Dart on chassis dyno when I first put it together. It would drive around and idle fine but would die in the water box

During a pull on the chassis dyno to figure out the constant flow mechanical injection I could see enough flames to cook a hot dog inside the injection hat
So we pulled the heads off to find the material between #2 and #4 was not there! Fixed that and severe valve float and the rest is history!!
I don't like the engine braking with that #2k drum driving the tires, pretty hard on parts.

check the video

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The key to the tires on the chassis dyno is to run them with lots of air pressure. I've never hurt a tire like that...and my brother owned a chassis dyno and ran cars on it daily.

My slicks were at 11 PSI when we did the dyno pulls. That's as much as we could run in a 16 x 32 tire and still have most of the tread in contact with the roller.

I just wouldn't run a new set of of $700+ tires on one of those things.

when you use sticky tires, the readings will read much lower. even with drag radials.

i ran mine on a chassis dyno and the guy made me put 23lbs in the tires and it hit the top of the tubbs and slit both my new goodyear 14x32,s but all in all we did get it dialed in pretty good.

SCHOOL ME HERE.ON A ENGINE DYNO ITS ALL THE MOTOR. WHAT IF CONVERTER OR TRANS IS HAVING ISSUES,OR TRANS IS SLIPPING ENOUGH THAT YOU CANT TELL ON A DYNO. HOW ACCURATE IS THE CHASIS DYNO AT THIS POINT? THESE WILL AFFECT THE MOTOR HP AND TORQUE.

Al, you know me and how inexperienced I am with racing.. but when we installed the nitrous in the 73 for PAO, we used the chassis dyno to set the timing and a/f ratio..

So for you and your car, I would recommend buying some time.. and if would help to cut the cost, I could bring the 70 up and tune it at the same time..

I have a chassis dyno in my Conyers shop and it's a great tool for set up, and finding problems. Everything from drive train, to A/F. I really don't care how accurate the power reading is. I use it more as a comparison of where we start, to where we finish. Jetting, nitrous, timing curves, and so on are a snap on the dyno. For sure a good data logger at the track can’t be beat, but at least traction is no issue on the dyno. I can grab the motor under full load and make sure everything holds together, and that the mix isn't going to be destructive. Better sitting still and finding a weak point than at 100 mph.

Merry Christmas everyone!!! The only thing I might add is the effect of hoodscoop air pressure at speed will effect jetting. I have an old set of 14X32's with plenty of rubber left you can have Al if you want to pay shipping.

Thanks for the input guys. I dont care what the numbers are power wise. I know what the engine makes, it was dynoed last time and should be close to those numbers. I am more concerned with getting it broken in and making sure all is well and the tuneup is close. Also how hard it can be on the car itself, tires converter etc. I have a big cooler and fan so no worries there. I just wantto find the best tune up I can. If it dont happen I am sure we will be fine, after all it is basically the same engine and we have the old data.

Now gotta runa dn start and finish my Christmas shopping. Good thing I am a big ticket guy, usually makes it go quick. One gift a piece ya know

A dyno jet chassis dyno is a inertia dyno and thus measures power by rate of exceleration and engine RPM,(That is why you do the pull in high gear 1:1) then computes torque if you so ask it. Remember that the horsepower is what the dynojet is made to read first so as long as the operator sets the parameters correctly and the spark is clean and not erratic its results are usually correct .

I take EVERY car that leaves my shop to a friends dynojet before it goes racing. I would rather spend a hour or two on the dyno then a day at the track looking for a issue. The other bonuses of the chassis dyno is you are logging way more than the average car has, you can watch gauges, you are using the cars ignition and fuel system, you can video blower belts and....., you can make instant changes without worrying about the track and or the weather. I could go on but you guys see what i mean.

Tire pressure is critical, you need a minimum of 20lbs or the tire is not round!! and we tie he car down tight unlike a car sitting free going down the track. I use 25lbs. Do not use new slicks or the webbing on the rollers will tear them up. High power cars with drag radials or slicks need to be screwed to the wheels because when the dyno gets loaded they will slip on the wheel's and may come off the rim.


Its like other tools, when used correctly its great. Unfortunately it may not always be the *number* you are hoping for.

Quick example. Car is on the dyno and looking at the plugs versus the AFR we are lean at the top of the pull. We put more jet in it make another pull car is the same, we scratch are heads go back and look at all of our data fuel pressure, AFR, boost. Nothing there ok we measure our jets and throw in a even bigger set of mains, smaller air bleeds to, now we are way fatter up until 1000 rpm to our rpm limit. Hmmm fuel pressure is good, were fatter GUESS what, the single needle and seat holley bowls would not let enough fuel by them and the bowls were emptying out. this took 2 hours at the dyno. Nothing got hurt and the problem was found. New bowls a week later one pull all is good. So how would you have ever figured a problem like that out driving up and down the track making attempts every hour or so without a data logger on this guys 1200 RWHP street car??

These guys didn't have much luck on the chassis dyno...

http://www.streetfire.net/video/fail-900hp-dyno_2181566.htm