Hi , when i rev after 2 seconds the RPM comes up , what causes this ? the RPM is lag , what do u think guys ?

 

There shouldn't be a very noticeable lag when you just sit there and rev. There is a little bit of a lag b/w actual engine rpm and indicated rpms. For example when racing and logging data I've seen 6700 rpms actual and around 6400 rpms on the tach.

 

sometimes the RPM comes to Zero when i'm racing , sometimes keeping at 6000RPM about 5 seconds , can u help me guys ? do u think this problem with any sensors ?

 

anyone ? can help ?

 

Does it sound like the rpm is lagging or are you just going by the tach? Put it on hp tuners etc.... and you will know for sure.

 

yes the RPM is lagging , after 2-4 seconds by revving it comes up , when i installed fast manifold the problem comes , with LS6 manifold there are no problems with RPM lagging

 

Have you gotten it tuned in any way since swapping to the FAST? It shouldn't be "required" going from an LS6 to a FAST but it will help and may be necessary depending on your setup. I think what you are saying is there is several seconds of hesitation after giving it gas and sometimes the RPMs will drop to zero (and the engine will die). Did you check to see if you have a vacuum leak after installing the new intake? Did you use the FAST valley cover button head bolts so that it fits correctly?

 

yes i tuned the car when i installed the Fast , how can i check if there is a vacuum leaks ? what is the FAST valley cover button head bolts ? can u show me a picture for those

 

^^The FAST valley cover button head bolts are exactly what it sounds like (valley cover bolts). They're what bolts down the valley cover that sits directly below the FAST intake manifold. The stock valley cover bolts are a little too tall and the FAST sits lower that stock so when you bolt down the FAST then the heads of the stock bolts push up into the bottom of the FAST and can cause the intake to crack. If you have cracks down there it could leak to a vacuum leak as well.

 

They are button head allen screws so they sit lower than the stock hex bolts. I have a new set of the bolts from FAST that I can get pics of later if you need them. And if you need the bolts (you need them if you still have the stock ones on there because your FAST intake can crack) let me know and I'll be willing to try to ship them to you for the cost of shipping plus a few dollars.

 

And to check for leaks you need to spray something like carb cleaner, brake cleaner, or starting fluid around the intake while engine is running and see if there is a change in engine RPM or pitch. I could not get a reaction even when spraying directly into the intake from carb or brake cleaner but starting fluid worked well . Some people use a small propane torch (just turn the gas on, no flame of course!) and go around the bottom of the intake to see if the engine speed changes. If you can't get a reaction spray a little into your intake to make sure it's working.