[Tim Eaton]

Hello everyone, got my car to the dyno. Had some weird readings hoping to get some help on what to look for as the cause. As the rpm increased the graph had some instability. Thinking possibly valve train related but any advice on where to look is appreciated. Engine is a 496 bbc with hydraulic roller cam (244/244 dur @ .050, .649 lift int/exh) using Holley sniper xflow EFI. Spring pressure is 205 on the seat and 530 open. Using Isky HPx gold lifters.

Thanks
Tim

 

[B433]

Hello everyone, got my car to the dyno. Had some weird readings hoping to get some help on what to look for as the cause. As the rpm increased the graph had some instability. Thinking possibly valve train related but any advice on where to look is appreciated. Engine is a 496 bbc with hydraulic roller cam (244/244 dur @ .050, .649 lift int/exh) using Holley sniper xflow EFI. Spring pressure is 205 on the seat and 530 open. Using Isky HPx gold lifters.

Thanks
Tim
View attachment 799910

Could be springs, but also it could be spinning the tires at higher rpm on the dyno rollers . What kind of tires were on it street or drag ?

 

[Tim Eaton]

It had Mickey Thompson ET Street R tires.

 

[bracketchev1221]

Not sure on a chassis dyno but on an engine dyno springs normally just fall off fast when it loses control. They don’t fluctuate over a wide span.

 

[Tim Eaton]

Not sure on a chassis dyno but on an engine dyno springs normally just fall off fast when it loses control. They don’t fluctuate over a wide span.

Maybe flex in rocker studs?

 

[jjjaffo]

From my experience, what you're seeing is from the tires on the rollers at higher speeds. Most chassis dynos have what's called smoothing in their programs to make that less pronounced. Looking at your graph, I'd say smoothing was used.

 

[Tim Eaton]

From my experience, what you're seeing is from the tires on the rollers at higher speeds. Most chassis dynos have what's called smoothing in their programs to make that less pronounced. Looking at your graph, I'd say smoothing was used.

Thanks. I have some upgrades planned and trying to make sure everything looks right before I do them.

 

[Monk]

Perfectly normal, this is the same dyno run showing smoothing at 0 and at 5. If your dyno operator would have moved the "Power pop-up window" over, you would see the smoothing setting. He should be able to pull it up on his computer and tell you the setting it was on.

 

[Tim Eaton]

Perfectly normal, this is 2 dyno runs showing smoothing at 0 and at 5. If they dyno operator would have moved the "Power pop-up window" over, you could see the smoothing setting. He should be able to pull it up on his computer and tell you the setting it was on.
View attachment 800008
View attachment 800009

Thank you

 

[Monk]

Welcome-

 

[bracketchev1221]

Maybe flex in rocker studs?

Maybe flex in rocker studs?

Not with a 7/16 stud at that spring pressure. One thing that is odd though is that much seat pressure on a hydraulic roller. Are you sure the spring only tops out at 530 open?

 

[Tim Eaton]

Not with a 7/16 stud at that spring pressure. One thing that is odd though is that much seat pressure on a hydraulic roller. Are you sure the spring only tops out at 530 open?

Not with a 7/16 stud at that spring pressure. One thing that is odd though is that much seat pressure on a hydraulic roller. Are you sure the spring only tops out at 530 open?

It has a 500 lb/in spring x .649 lift + 205 seat is 529.5 lbs. The manufacturer gave me the 205lbs @ a 2” installed height. The springs are for a bigger hydraulic roller I plan to install with 255 dur @ .050

 

[bracketchev1221]

Well, I would just want to make sure the lifters are controlling at that pressure. It would take a pretty good lifter to handle that spring pressure.

 

[Tim Eaton]

I currently have the Isky HPX gold lifters

 

[68Chevele]

Possible valve float, BBC's have heavy valvetrain and hyd lifters don't help that.