LT4 Hotcam Question/Problem :)
 

I just completed the Head, Cam and Intake swap. The car actually fired up and runs however I think I have a problem. At idle I have ~15 whatevers :confused: of vacuum and the gauge slightly deviates up and down. When I give it gas initially the gauge moves down to about 10 as I suspect it should and then will rise to 20 with constant application. Is this normal? I have used a can of carb spray to check for leaks around the intake manifold and all the fittings and there was no increase in idle. Here are my known issues (possible) the egr valve is on the manifold but the exhaust tube is not connected (yet), the throttle body is 54mm, the intake plenum has been opened to 58mm, I adjusted the rockers and I may not have done it correctly (the car runs and idles with no tapping). Anyhelp would be appreciated...... Thanks Guyz.

without proper programming it doesn't suprize me atall that you get just 15inches with the HOT cam, I believe with proper programming that number will come up a little, probably 17-18".

the hot cam is a more aggressive cam than stock, so you may be getting what you get bacause of the higher lift and longer duration. i'm not sure what the specs for that cam are, but my cc306 cam was at around 15" on a 383.....with programming. i had issues coming to a stop and not dieing. it was crazy...but power was decent, and lopey sound, kind of.

the shake in the needle probably relates to the longer duration and lift too. what's the lobe seperation on that cam??? after about 20% more than stock and you'll be shakey.

Thanks. Here are the specs on the cam:

Intake Duration at 050 inch Lift: 218
Exhaust Duration at 050 inch Lift: 228
Duration at 050 inch Lift: 218 int./228 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.525 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.525 in.
Valve Lift with Factory Rocker Arm Ratio: 0.525 int./0.525 exh. lift
Lobe Separation (degrees): 112

Sounds right. The deviation could be the guage itself or perhaps you have a bit of blowby. Do a leakdown or compression test if you want to know more. My more conservative 211/219 cam did 19" at idle.
Also... you should take the EGR off and use a block off plate or hook that EGR/exhaust pipe up. You are emitting unmetered air into the intake which causes the PCM to compensate and can be a performance hinderance.

Thanks for the help guyz. I readjusted the rockers again using the crank till one is down and do the one thats up technique (if it is a technique) and started it. The vacuum went to 17 +-1 and seemed better. Here is the issue with the EGR, I live in the Peoples Republic of California thus I must keep as much as possible visually correct. Yes the headers are going to be interesting to explain, but the part I left uncovered is the part that goes into the exhaust manifold. Is'nt that shut off by default unless the EGR opens???? If so I'm going to program the EGR out of the computer anyway, it's just going to be there so when the smog tech looks he says yup it's there. I think I'll know better when it goes for a tune.

Anyone have a .bin or .lt1 file for a LT4 hot cam so I can drive it the 45 miles to the dyno tuner??? Thanks again...

Yes, when you open the throttle initially, vacuum is reduced. When you are cruising at higher than idle RPM you will see better vacuum, because the cam overlap has less effect at highr RPM.

If I read this correctly, you have the port on the headers for the EGR tube wide open. If that's the case, put a plate on it immediately. Its allowing air into the exhaust, and screwing up your A/F ratio, since is causes the O2 sensors to indicate "lean", and the PCM pours in fuel tha isn't needed on that bank of the engine. An air leak that close to the exhaust port may allow enough backwash to burn a valve.

And, when you are driving, and the EGR opens, your flowing air into the intake manifold, further causing a lean condition, and forcing the PCM to compensate. You need to cover both the hole in the header/exhaust manifold, and the hole in the intake manifold.

One way to do that is to simply cut a diamond of the correct dimensions from a soda can, and sandwich it between the riser tube and the back of the manifold. Looks "complete", but no flow.

Of course, there is absolutely no performance loss from keeping EGR, so you may be just overcomplicating the whole process by trying to delete it.

Thanks for the responce, I will plug the hole. Ya lean, well I haven't actually finished the exhaust yet, so no O2 sensors yet, but one ugly blaring red light on my dash (Check engine)(GUESS THE CODE :D ) The EGR will be gone that is why I did the LT4 Hot Cam. I will be driving it to an exhaust shop (- O2 Sensors) once my bmw hydrobooster comes from Kragens so they can connect the shorties to the rest of the exhaust. The stock exhaust manifolds are out of my car, I had isses with fitment since I needed to use a passenger manifold on the drivers side to clear the steering column which caused seiously hot under hood temps.

The EGR was the major problem on my car, it just would not open at the right time (smog time). I verified that it WOULD open but it was way later than it should be. A dyno tune place told me it was because my car weighled less than the donor vehicle (My car weighs 2980lbs) thus there was less engine load (MAP and tps have to be certain level for the EGR to work) and no egr function for my smogs. I had to retard the total timing to ~17-20 to make it smog otherwise the NoX emisions were 1400+. This cam will smog in California with no weird issues accoring to the dyno tune place.