VENOM 650R w/High RPM Flutter????????

[utahviper]

I just got a 99' Venom 650R w/500 miles on it. It doesn't quite make the power I thought it would. I think partially it has to do with a 5900-6200 rpm flutter, it is almost like a rev limiter but it is not. I don't think I could hit the 6200rpm rev limiter even if I wanted to because it looses so much power.
The car has been sitting for 2 years and so I had the spark plugs changed, fuel injectors flushed, changed the fuel filter, adjusted the valves, and changed the oil. None of these affected the flutter. I have also installed a VEC1 and cranked it all the way up and it still didn't make a difference. I was trying to rule out a fuel problem.

I am looking for some suggestions on what to try. Tomorrow I will be getting it dynoed and sending the results to Hennessey but I don't hold much hope in getting anything out of that. Also, the technician will be listening, with a "sonic ear", for a floating valve but other than that I am fresh out of ideas.

I know I don't have a bent valve but my technician said I could have a collapsed lifter or maybe a burnt valve.

I am going to go to the viper days event if any guru would like to look at it. I am hoping to have it fixed by then but who knows.

Thanks In Advance
Todd

 

[Marc Lublin]

If the car really feels like it won't make it to 6200rpm you might also want to check your cats. I don't know if Vipers have had problems with breakage and subsequently getting stuffed, but I have seen it in a bunch of other cars. Let us know how it turns out.

 

[Martin D]

Hey Todd,

Still not fixed.... Sorry to hear that. Another suggestion - Try new plug wires.

Please Email me the Dyno results.

Regards,

 

[Russ M]

Just curious, you mentioned that it sat for 2 years and you changed all those parts. Did you also change the fuel in the gas tank? After sitting for 2 years that gas has alot of water in it, and the octane rating is horible. If you have, then ignore this point.

Second when you go to the dyno, if the above is not the issue then have them use an air/fuel analyzer and you will instantly know what is going on.

PS Also consider this Viper Tach's are very inacurate, mine hits the rev limiter showing 5700rpm. And it is supposed to be 6200, or so. Perhaps you are just riding the rev limiter that is why it feels so weak.

 

[Mike Adams]

It is pretty hard to diagnos anything with what you have said. When you did plugs was a compression test done ? Is the 650R kit recent or has it sat 2 years since the upgrade ?

Ignition wires are always a possibility. You will usually feel wires when under load up hills or when speeding up. Without a ride it is always hard to say what is wrong. I even had a bad coil pack.

Start with a compression check, check fuel pressure and get you tech to hook up a computer and check how accurate your tach is.

 

[JimDavis MT 97GTS 650R]

Hi Todd, My 650R does the same thing. The engine will pull like crazy up to about 5800 RPM, but then the rev limiter seems to take hold. Really,I don't gain much by trying to exceed this point anyway. I have always suspected the early cutoff was part of the MoPar Performance Engine Controller program strategy. Hennessey used this unit in his 650R package. If you have a doubt which controller you are running, just check the part number on the PCM. When in doubt, contact John Hennessey. Your best bet is by email. Hope this helps. (JD)

 

[utahviper]

I think I have found the problem. I changed the computer out with another computer and the problem has seemed to go away.

I will have some dyno results later on today and we will see what kind of power it is making.

Thanks for all the suggestions.

Also, it seems curious that you don't have to change or modify the computer with these mod's. With other performance cars you have to change the computer or at least have it reflashed with some different programming. Hennessey told me it was a stock computer in my car but he said that on his current models he uses the mopar performance computer. I have read some posts on this subject on this forum and it seems to have some mixed reviews.

Thanks Todd

 

[Martin D]

I pulled 564.8 with the Mopar PCM.

I have thought about swapping back to the stock unit, but I am ok with just 565......

Regards,

 

[JonB]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by JimDavis MT 97GTS 650R:
..... I have always suspected the early cutoff was part of the MoPar Performance Engine Controller program strategy. Hennessey used this unit in his 650R package. <HR></BLOCKQUOTE>

JD et al......

Actually, one of the best-kept little secrets of the (now defunct) MoPar ECU/PCM is that it RAISED the rev limiter max by +250 rpm !


And the speedo recal or lask thereof with a gear swap {normally} should NOT recal the tach.......just the speeedo.

My advice after clean gas: Swap WIRES...then the computer!

 

[JimDavis MT 97GTS 650R]

Thanks for the info Jon. Tune-Tune-Tune.....

 

[treynor]

Ditto here. With the MOPAR ECU, my '01 would stop revving at 6000 RPM; without it, 6200 RPM.

 

[Mike Adams]

Steve how much did the mopar computer gain you as far as times at the track in NJ. This the computer everyone says does not work ?

I have had independent testers find 9 hp and 32 ft/lbs of torque gained !! (Have dyno charts the customer sent me to prove it )