I've tried making pulls on a couple dynojets with my car over the past two years at various powers levels and each time I run into the same problems. In addition to spooling up slower and making a couple pounds less boost than on the street, the dyno doesn't seem to be able to keep enough load on the motor at the point where max boost is reached and levels off. I suppose it has something to do with the motor's rate of acceleration slowing slightly after the initial surge of boost, resulting in the dyno roller continuing to accelerate while engine slows it's rate of acceleration, further resulting in a breif loss of load on the motor. Here's the most recent example of what I'm talking about. Note: RPMS on chart are not correct..pull ended at about 6300 rpm. Car accelerates very strong while turbo is spooling.

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With lower boost levels the problem is reduced but not eliminated. I even tried reduced gate pressure and sensitivity (E-Boost II) to bring the boost up more gradually, didn't help. As soon as I reach the peak boost level, it starts dropping boost and falling on it's face and then recovers if the pull isn't terminated. It doesn't happen on the street the track or on a load bearing dyno (mustang)...just a dynojet. I see lots of people posting charts from a dynojet that don't seem to be having this problem, so I'm wondering why.

Combo is a Dart block 347, AFR205, Spyder, custom cam, PT76-GTS, Lentech AOD, FAST XFI in a 4000 plus pound T-Bird.

Curious if anyone else is having similar problems on a dynojet ?

David

 

Re: Problems with dynojet and turbo ?

They could be using Dynojets with PAU.

 

Re: Problems with dynojet and turbo ?

you might be spinning the tire

 

Re: Problems with dynojet and turbo ?

Will,

That was my first thought too, but we didn't get any sudden jump in rpms or find any other indications that the tires were spinning. We were data logging using FAST XFI during each pull. Weird that it only happens on dynojets.

David

 

Re: Problems with dynojet and turbo ?

Here is a video of the pull for the dyno sheet I posted. The oil smoke at coast down is also a new problem.

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David

 

Re: Problems with dynojet and turbo ?

was it just me or did it also sound like you cam in and out of the throttle? it sounded like the motor surged up and down as well

 

Re: Problems with dynojet and turbo ?

Your right, that's just how it sounded and how it felt, but my foot was on the floor the entire time. Only does that on a dynojet...weird.

David

PS: Backing the boost down to around 15 pounds resulted in what looks like a normal pull, but boost was actually falling off to around 11 pounds by 6000 rpms but it still made 584 rwhp 502 rwtq . Here's the video (right click save as) requires Quicktime to view.

http://www.fileupyours.com/files/83233/006.MOV

 

Re: Problems with dynojet and turbo ?

Almost sounds like it shifted, then immedaitely downshifted.
Thats an interesting glich on the graph too.

 

Re: Problems with dynojet and turbo ?

Converter locking and unlocking? Or coming on to the converter.

 

Re: Problems with dynojet and turbo ?

sounds like transmission slip to me or convertor. you get some flash from the trans slipping then grabbing at max torque capacity, but it doesn't reach further cuz it cant hold it any higher.

 

Re: Problems with dynojet and turbo ?

It's got a Lentech AOD with non lockup converter and full manual VB....doesn't feel like a transmission issue. Here's a dyno chart from a mustang dyno.

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David

 

Re: Problems with dynojet and turbo ?

My car has also had issues with spooling on a dynojet.

 

Re: Problems with dynojet and turbo ?

Youre making alot of power for those small tires....put 3 more people in your car or have 2 sit on your trunk. Make another pull with everything you got.

 

Re: Problems with dynojet and turbo ?

I suppose it's possible the tires could have slipped just enough to unload the motor and cause the boost to drop....that makes even more sense considering how the problem is reduced at lower power levels. I had M/T ET street radials (275-40-17) on the car during the dyno testing, and since they were getting shredded I switched back to street tires of the same size. Now driving the car is very exciting

David

 

Re: Problems with dynojet and turbo ?

We use a dynojet at the shop and we have had a lot of turbo cars on the dyno. We have a Solid-roller 331 with a PA Automatic with 4500 stall. We seem to have that same problem on occasion but it has to do with the stall converter slipping or spinning the tires. On the dyno chart where it shows power and torque you can change one of them to speed and it will have a line that should be straight. If the line is not straight than that shows some sort of slipping. I am at home and not sure but when I get to work I will check to see what you need to do to see if there was slippage during the run. Hope this helps a little.

 

Re: Problems with dynojet and turbo ?

Thanks, and yes it would be helpful to see that line on the chart your talking about.

David

 

Re: Problems with dynojet and turbo ?

Raced the car in Dayton last weekend. Ran a best of 10.76 @ 133 with a 4225# race weight. Could have done a lot better if they had done some prep to the track, best 60 ft was 1.854 spinning hard. Boost controller was set to the same settings as in the dyno video (made about 20psi on the track) and didn't do any of that goofy falling on it's face stuff that was happening on the dyno. Here's a pic.

http://www.sccoa.com/forums/attachment.php?attachmentid=26444&d=1178581491

David

 

Even tho not the same car, My 1987 Buick V6 Grand National did the same thing on the dyno last time there . It was also a Dyno jet. The boost would surge up and down and coulnt keep a constant. It would even pop and miss in the ignition. Unloaded the car worried and gave it hell on the street with none of the after mentioned simptoms. Took it to the track and went 9.54 at 143 with no changes.

My buddies stock motor GN did the same thing on the same dyno, especially the ignition problem. That car went 10 teens with no changes from the dyno.