I drove the truck down to Louisiana back in March and had it tuned for sealevel at Lethal Racing. It made 520 whp and the same torque on their Dynojet dyno with 8 psi of boost. I was impressed with the tune. The torque comes on really hard at low RPMs which I like because I have a pretty mild converter, 2600 rpm stall speed. Anyway, I drove it over to Houston to watch TX2K13. I ran it at the track on TnT day with Mickey Thompson DRs on the back. When it dead hooked it made a strange fluttering noise from the engine bay and a slight hesitation in power delivery until the fluttering stopped and then it would give full power. This was killing my 60', best I could do was a 1.94 sec. My initial thought was it must be the supercharger bypass valve. I haven't called anybody about it yet, to be honest, I was so caught up in the automotive euphoria of TX2K13 that I basically blew it off. I have had a bit of down time lately so I figured I'd post it up and see if I'd get any hits. Has anybody ever experienced this issue?

 

Nice setup! Don't know how heavy your truck is but it seems to me that it should mph more with that kind of power. I guess either problem would make your mph low. Sorry, wish I could be more helpful.

 

not sure on the sound u described, any videos of it doing this? maybe some belt slip, still on a 6-rib set up?Is there any torque management left in your tune? maybe your trans is starting to hate life with that power/weight of your truck. just a couple suggestions.

 

It is pretty heavy. It's a NNBS crewcab with an iron block. Probably bumping 6000 lbs with fuel and me in it. It only has a 2 inch drop so it still sits a bit high, about the same aerodynamics of a firetruck. As far as the power, I think 520 rwhp is a bit optimistic, it made those numbers on a Dynojet, would probably be more like 480ish on a Mustang Dyno I'm guessing.

 

I'm sure there is no torque management, we tuned that out completely when I had the built transmission installed. I thought about the possibility of the trans being the issue. It just doesn't seem like that would be the case because it's not like it gained RPMs when it was "fluttering". I could hear it in the supercharger noise. When I would brake stall it to about 2K it would start whining like they do, and then when I'd let off the brake and stand on it, the noise in the blower changed from a whine into a flutter for a split second, then back to a whine and full power after 3000 rpm. I've heard belt slip in my truck before, before I installed the mechanical belt tensioner, it didn't sound like belt slip. I should have taken a video but I didn't I am at work overseas at the moment so I will have to wait a month before I can make a video of it, and it may not do it in Colorado it loses about 100 hp at my altitude.

 

What throttle body do you have? Do you have any software to monitor (EFI, HPT) to see if its trying to suck your throttle body blade closed?

 

AAHHH, now that does make sense. I haven't thought about that. It is the stock 87mm throttle body. I use the Android App "torque" for monitoring on the fly. I may try it when I get home. I remember seeing the PID "throttle position %" is available but I'm not sure if that would be commanded or actual. If that doesn't work, I'll talk to my tuner and see if he can help me out. I appreciate the help. Thanks alot.

 

I've never experienced that, maybe it's the bypass valve?

 

I'm glad you responded. You're the only other guy I've seen on here really doing anything with the Vortech brand Lysholm blower. I notice your stall speed is 200 rpm higher and you are pushing alot less weight. I've only noticed this when the engine is under heavy load (deadhook & crewcab truck) and under 3000 rpm. I feel like that combo is the issue. I was thinking that maybe the combination of the camshaft and the previously stated situation is not good with the vacuum setting that the bypass valve is working with. I think I need to contact Vortech.....