Can aftermarket cams cause boost loss?!

[Venumous]

Guys,

I have been chasing a problem for some time now that has me ready to pull my hair out. I have a boost problem that cannot be explained by any kind of boost leak or belt slip. I have changed and/or checked all of the vacuum lines that could possibly be the problem, pulled the blower off and reseated it with a new gasket (along with new lower intake gaskets), put on a brand new tensioner with Metco flex plate, sprayed the belt with VHT during the dyno shown below with no change. The car supposedly has Stage 3 Comp Cams (it definitely has cams, that's for sure) with diamond pistons (0.20) and comp valve springs. As you can see, not only does the car drop boost, it never even reaches a reasonable boost at all for the pulley combo and actually made less net boost on a 3.00" upper than a 3.25" upper while on the dyno (2 different belts and tight enough that it's almost impossible to get them on with the tensioner tab broken off). It also has a 4lb lower. The blower itself seems fine. It makes zero noise and spins freely and easily. The car also gets extremely hot. I've had an 03 Cobra before with a Whipple and it did not get anywhere near this hot under the hood.

Image below shows my car in solid and an 03 Cobra with a 2.3 Whipple without cams (dotted) on the same dyno reaching 17.3 psi and holding (light blue curve). Is it possible that the overlap is such that the boost is able to bleed off through the exhaust valve?

 

[GodStang]

Yes cams can drop your boost. Less restriction so less boost.

I have also seen many many crap modular cam installs were the intake and exhaust were open near the same and it just recycled heat.

 

[Venumous]

When I say boost loss I mean the tapering you see in the dyno vs the stock cam cars' profile. The car has a 4lb lower and a 3" on that run shown with the solid light blue line. That is more than enough to get to 17psi plus in what I see for others with the same cam. The peak boost and boost taper are obviously related.

 

[s351]

Did u degree the cams?

 

[Venumous]

I bought the car as is outside of all of the remedial work that I've done attempting to fix this problem. I wouldn't know to believe it if I was told they were degreed. My guess is no based on other things I've found on this car, including a disaster for a rear differential. The car runs well. You would not know it didn't make the power it should if it wasn't on the Dyno or at the track and trapping low (haven't taken it yet bc I know it isn't making what it should nor performing as it should with the boost curve it has). That is why I asked if it is possible. I've posted about this problem 3 different ways and always get things like "belt slip, vacuum hose, etc" which are not the case here. I'm at a point where I'm ready to pull the motor and see what the hell is going on. I just want to confirm that cams installed improperly can result in exactly this situation.

 

[ViperRed91GT]

Is the boost bypass adjusted correctly?

 

[NastyNate420]

Valve float ??

 

[svtshadow]

Probably poor cam installation that never got degreed. Why dont you do a compression test and a lick down test. That may steer you in the right direction to solve your problem

 

[2003cobra22]

lick down test.

Give me the number to the shop you use:lol:

 

[Venumous]

The boost bypass seems to work correctly to me. I put a vacuum tester on it and it held 10in/mg just fine fully open. After I try to repeat the compression test that I failed on Sunday (bought a cheap kit at HF, warmed car up, pulled all plugs, pulled relay, had wife hold throttle to floor and crank 5-8 times... if this is wrong someone let me know... but the gauge would not hold a peak value after any crank, it just bled back to zero in every cylinder. I also tried to jimmy it to my air compressor and confirmed it will not hold a peak value). Anyway, after I try this again, I plan on pulling the blower back off as I'm at a point where it has to be the blower or the motor. At that time I will take the bypass apart and inspect it as well.

 

[Venumous]

If I do in fact swap the stock cams back in, I have the stock springs. What else will I need if the pistons/etc are fine?

 

[cj428mach]

I can't think of any reason why you would need to swap springs. You could just run the aftermarket ones although its over kill. In theory you can install the cams without pulling the front cover but I think since you're trying to eliminate all possible problems you would want to pull the cover and make sure it goes back together right.

 

[DSG2003Mach1]

you should be able to look at short term fuel trims for each bank and compare, that might help give an idea if they were degreed or not. Although that will just tell if you if they are degreed the same bank to bank, it wont help with how theyre degreed which may or may not explain the issues

 

[brian97cobra]

short answer

YES!