Kaneman

iTrader: (5)

I was not sure which forum to post this to because there is either an internal motor issue or a PCM issue.

I have a 2000 Camaro 408, Comp 220/224 581 581 114, Crane duel springs, Yellow Terra rockers non adjustable, T76 .96 housing modified STS.

The issue I am having is no matter what gear so first gear maybe about 5-6 psi boost at around 5500 rpm the car just falls on its face. I can be at full boost 18 psi 4th gear but once it hits 5500 rpm it falls on its face. It is almost like there is governor on the car. I have checked all the areas where to ensure that the rev limiters are set to 6500 but this does not feel like I am hitting the rev limiter. We all know what it feels like to hit the limiter.

We thought back pressure when I had the .81 housing on so I switched to .96 no change. Thought it might be the fuel injectors so I changed from a 57 to a 79.

I have people telling me different things so I would like you alls opinions too. Some say the cam may be a tooth advanced so the valve timing is messed up so there is a fuel brining issue and others say it is the PCM.

Unless someone tells me different I am going to try the PCM tomorrow.

Thanks in advance for the help,

Kane

Sid447

From what you say it sounds like a tune issue,


You need someone who's good with dyno-tuning to sort it out for you IMO.

Kaneman

iTrader: (5)

Myself and a couple of other good tuners have gone through this car. I forgot to mention above I have a 3bar map. AFR is perfect when we had it at the Dyno 1320 felt it was the cam timing. It is really hard to explain the issue.

Thanks,

Kane

Nitroused383

iTrader: (10)

What heads are you running? You could have some valvetrain geometry issues that are not allowing you to rev any further. Possibly valve float, also what intake manifold are you running. A 220/224 cam in a 408 is probably not going to make any power past 5500rpm anyways. What intake centerline was the cam installed at?

Kaneman

iTrader: (5)

That is the issue the installer says the cam was installed straight up but others think it is advanced a tooth. The motor would make power past 5500rpm's with the same setup before I had an issue with some pistons. New setup makes good power but not beyond 5500 rpms.

We have cars with Z06 cams and boost making 700+ rwhp beyond 5500rpm's.

Kane

Nitroused383

iTrader: (10)

Do you have a dyno graph? Did you install a new set of valve springs, they could possibly be worn out. I would first check your cam timing and if that checks out ok have your valve springs measured. If you know this setup worked before than it can only be a few things.

DrkPhx

iTrader: (15)

Sounds like a mechanical issue, but it's hard to diagnose over the internet. Did you have the YT rockers on the previous setup? I would try the stock rockers just to eliminate that as a variable.

eamador11

Postup the dyno graph so we can see what the motor is doing at eveyr RPM. show the AFR graph as well

Kaneman

iTrader: (5)

Here are both my graphs. The higher HP graph is on a Dynojet with my .81 housing the lower HP is a Mustand Dyno loaded with my .96 housing.

I am going to attach an older graph same setup with my T67 .81 housing. I am noticing the power curve always dies around 5000 rpm's. So is Nitroused383 right the cam for the 408 is to small?

I have stock 6.0 heads with an LS6 intake Crane Dual Springs, LS7 lifters.

Kane

98Z28CobraKiller

iTrader: (17)

Take the charge pipe off and make some pulls(assuming you are on a SD tune ofcoures). See if it feels flat above 4700 as it appears in the graph. This will eliminate the turbo.

Kaneman

iTrader: (5)

Ok pulled the pipe off and ran the car N/A same issue. Check the scan out. Look how long it takes to get to 5500 and look at what happens after that.

Kane

1320

iTrader: (6)

Guys, I know Kane, Im glad he posted the graph. It makes peak power at 4700......and it falls off like its cliff.

Kane, I did have a problem on my car at one point, that is similar....It hit a wall, but didnt tapper, it lost all power. I had a rubber coupler on the throttle body that would get sucked closed. I put a piece of steel in it, to make sure it would stay open....and no more problem.

I would think that someone would have seen it though, while on the dyno. I know we couldnt, cause I was driving and you were logging. Maybe no one noticed?

Pretty unlikely but other then the cam I dont know

Nitroused383

iTrader: (10)

Valve springs, valve float, bent pushrods, something is going on. You need to check it out before some harm is done. If you have an adjustable timing set try retarding it 4 degrees or so. Atleast make sure its not off a tooth, I had an older xr 650 dirtbike that was off a tooth and it would not rev past a certain rpm at all. Kind of similar to this.

BuffJoeyD

iTrader: (2)

I would assume that 1320 has seen enough cars on the dyno so I would think he is right before anything else =)

I would be inclined to say that its a fuel issue - You didnt see any change after the injector but do you have something to watch the fuel pressure? But I wouldnt expect it to fall like that from fuel - Id think bad timing or wrong cam for combo.

After dealing with many of these PCMs I would change the PCM seeing as how it should be pretty easy to just try and run it up to 5500 and see if there has been a change-

what was changed in the "new setup" ?

1320

iTrader: (6)

Kane , I thought I was on something, but you have two threads going now....so I see.

Anyways, this engine makes no abnormal noises, no valve train noise, nothing like typical valve float, it just stops making power. I ve thought maybe ignition....but putting spark out is much more violent...then what this does.

Nitroused383.....thats interesting on your dirt bike, cause when I saw the dyno, (I was there) the only easy explaination I could think of would be cam timing, but I have never seen it before. Its not like I ever built one and made it a tooth off just to see what would happen? I m just guessing, if you advance the cam timing it brings the curve down.....a tooth might be way down. Quick, how many degrees is ne tooth on cam timing? Or do I have to go check.

If one tooth could be 1000-1300 rpm....that would put the peak right at 5700-6000 where it should be.

Zombie

iTrader: (2)

I accidentally installed my cam one tooth off on my 89 turbo probe. The cam timing was advanced by one tooth because of it and it had the same kind if issues Kane is experiencing. Spooled much faster then would not rev over 4500 rpms.

I'm on the cam timing wagon. Especially since it still happens N/A.

Kaneman

iTrader: (5)

Since this thread is rolling along and I will probably decide to put a differnet cam in the car. Since who knows this cam's specs may be way different then was originaly told to me becasue this cam is from APE and those of you may remember that fiasco.

What is a nice daily driving cam for a 408 with a T76 .96 housing?

Lingenfelter GT-7 208 / 230 .554" / .546" 1.7 ratio 121
Z06

Kane

ramair96ws6

iTrader: (8)

Hey Kane after seeing that it does the same thing NA its gotta be in the cam timing. Although I would still maybe try another PCM though since you have one confirm its not that. its only 2 bolts...

Once confirmed throw this cam in the trash put a z06 cam in it call it a day. Jeremy and Jon have both proved it works perfect for making big power.

you your current cam

Ps. Das Auto is in and the new exhaust is finished on the car. i just need a 5 dollar cable braket for the trans cable

Zombie

iTrader: (2)

If I did a 408 i'd probably go with something like a 224/224/114 .56x .56x cam or something close to that personally. I like smallish low lift cams for their street manners. I don't know how a z06 cam would do on a 408, seems smallish for the cubes.

Randy WS6

iTrader: (69)

I had a similar problem , I would shift at 7400 rpm, then after a while it wouldn't go over 6800rpm, would no clime any higher. I changed the valve springs to a new set and fixed it, Now i can rev to 7400 all day long.