Boost threshold and cam questions.

[darkstarrocker]

On an all-stock rebuild, would a stage II Schneider turbo cam (part # 17043 here: www.xenons30.com/cams.html#Schneider) move my boost threshold from the stock 2500rpms, to about 3800rpms?

 

My father had the cam installed when my engine was rebuilt as a "surprise."

 

Can't get mad, as he had good intentions, but could this cam be causing my issue? I've already verified timing, and checked for exhaust, boost, and vacuum leaks.

 

Thanks!

[Zmanco]

What do you mean by boost threshold? If you're referring to the rpm when the turbo begins to build boost, then both RPM values sound too high. But if you're (improperly) referring to creating full boost, then the cam, along with the cam timing, is definitely a big part of it. You should verify the cam timing is correct, or even advance it some with an adjustable cam gear to generate more boost at a lower rpm if you prefer that.

 

Keep in mind that this cam should make good power to at least 6500 rpm, which is significantly higher than for the stock cam.

[darkstarrocker]

I am referring to full boost. Boost starts to build early, but seems to hang until I hit full boost until about 3800. Really snaps my head back when it does though.

 

Part of my problem is that I have no familiarity with my vehicle any more. Came back from Germany after a few years and it seems like everyone has diddled her. I'm still trying to put my finger on normal, largely relying on my memory from a few years back.

[Zmanco]

I used that cam with a T3/T04E turbo and live at 6k feet elevation and 3800 rpm was about right to hit 15 psi boost. Given you have the stock turbo and are (I assume) close to sea level, I'm surprised that you don't see full boost sooner. Again check your cam timing as a retarded cam will push the power band higher up the rev range.

 

Side note: make sure you run ZDDP in your oil and if possible, add the external oil bar. I did everything right with that cam (except the external oil bar) and it still failed (pitting and galling on lobes) in 10k miles. Schneider cam metallurgy is not very durable in our Z engines.

[darkstarrocker]

I've heard about the cam wear, I use a high ZDDP oil (M1 15W-50) and a bottle of STP Blue at every 5k change. 10k miles and no issues thus far.

 

What timing were you running? I'm at stock 20BTDC.

[roger280zx]

Off topic, but I would not go 5K between oil changes on an L28et even with Mobil 1. Use a good filter and change oil it often. Back to the topic... 3800 is aufully late for a stock T3 to start building boost. The threshold is the rpm where the intake becomes "charged" or pressurized. For example, my t3/t4 makes 2-3 psi in 4th gear at 2000 rpm, full boost (9.5 psi) by 2500. This is on a completely stock L28et with crimped 2" intercooler piping and a mkIII supra intercooler 2.5" crimped DP and 3" crimped exhaust, no cat and straight through muffler. It is however 30* or more before the boost hits, then tapering off as the boost comes on.

[darkstarrocker]

Blackstone says I can go further than 5k... And Nissan filters are the best, AFAIK. My oil comes out clear as new every time.

 

I start building boost around 2k as well, but full boost doesn't hit until 3800. I have no intercooler, it is a stock engine aside from the stage ii Schneider.

[roger280zx]

You should really open up the exhaust then. That is the absolute best mod for a turbo car IMO.

[Zmanco]

What timing were you running? I'm at stock 20BTDC.

 

I've found pulling timing around the torque peak is a good way to manage detonation as well as yielding a flatter torque curve, at least as measured by my butt meter. So there isn't one number to report. FYI, this is a very conservative tune with only minor det events at the track on warm summer days that MS manages via the det sensor. If I only drove on the street, I could probably add 4 or 5 deg.

 

[roger280zx]

Zmanco, do you think that has to do with his slow spooling? Do you think he's spooling slowly due to detonation? Seems to me 3800 is a little low for peak torque given his cam. If he does have stock exhaust I think that has more to do with the slow spooling than the above the curve timing. When my car had a 3" cat it spooled much slower than the 3" open, I can only imagine the stock 2" or 2 1/4" or whatever the factory cat is as the 3" is my only experience. If it were my ride and cam instalation and timing proved to be correct I would next focus on opening up the exhaust.

[Zmanco]

From the original post I assume he has a T3 running at 7 psi which is about 150 kPa at sea level. At that level of boost my tune is 24 - 27 deg and could probably add a few more. (My wastegate is set for 200 kPa so it's not easy for me to tune at 150). I'm sure that adding more timing advance (assuming it doesn't cause detonation) would help spool faster, but I doubt it would explain the change he's seeing of getting to full boost at 3800 vs. 2500 rpm.

 

I still think it's most likely cam timing...

[darkstarrocker]

So you think my cam timing is a notch or two off, not my ignition timing?

[Zmanco]

So you think my cam timing is a notch or two off, not my ignition timing?

In your original post you said you had verified timing so I'm assuming that isn't the issue. The new cam has longer duration so you can probably run a little more advance, but it's hard to imagine that would explain it. With an all stock turbo motor except for the cam, you should be able to hit 7 psi long before 3800 rpm.

 

If you want to do it right, there's an excellent post by BRAAP about how to degree a cam. But if you want to do a simple test (and I'm assuming you don't have an adjustable cam gear), you could try moving the cam to the 2nd or 3rd hole. IIRC, each of those advances the cam 4 deg to correct for timing chain stretch (not sure that "4" is the right number going from memory). It's a simple experiment, just make sure to put a spacer down into the timing cover so the tensioner doesn't pop out.

[Zmanco]

Zmanco, do you think that has to do with his slow spooling? Do you think he's spooling slowly due to detonation? Seems to me 3800 is a little low for peak torque given his cam. If he does have stock exhaust I think that has more to do with the slow spooling than the above the curve timing. When my car had a 3" cat it spooled much slower than the 3" open, I can only imagine the stock 2" or 2 1/4" or whatever the factory cat is as the 3" is my only experience. If it were my ride and cam instalation and timing proved to be correct I would next focus on opening up the exhaust.

I'm going on the assumption that the only change besides rebuilding the motor is the cam, hence can't see that the exhaust would be the issue. Now if he was putting a bigger turbo on and increasing the boost pressure, then that's another story...

 

BTW, I didn't mean to suggest that cam has a torque peak at 3800 rpm. In my engine, using the Megasquirt VE table as an indicator, the torque peak with that cam was between 4500 and 4800 rpm.

 

I can't comment on how much of a difference a freer flowing exhaust would make. I never ran with the stock turbo or exhaust - I started with a T3/T4 and 3" pipe all the way. I also use a larger wastegate housing from ATP Turbo. But if you think about how a turbo harvests the energy from the exhaust, it makes sense that you'd want as little back pressure as possible.

[darkstarrocker]

Let me try to edit this to how it should have been from the start:

 

On an all-stock rebuild, would a stage II Schneider turbo cam (part # 17043 here: www.xenons30.com/cams.html#Schneider) move the point where I hit max boost from the stock 2500rpms, to about 3800rpms? I see boost start to build from around 2000rpms, which is normal, if I remember correctly. All I have to go off of is the last time I drove the car, which was before it was rebuilt, about 4 years ago.

 

My father had the cam installed when my engine was rebuilt as a "surprise."

 

Can't get mad, as he had good intentions, but could this cam be causing my issue? I've already verified ignition timing @ 20BTDC, and checked for exhaust, boost, and vacuum leaks. Every thing is stock, aside from the exhaust. I have a 2.5" from the downpipe back and no catalytic converter.

 

So... Should I purchase an adjustable cam gear so I can get the most out of this cam? Or should I advance the cam timing a notch?

 

And as a side note, M1 15w-50 is more resistant to shearing and has a higher ppm of ZDDP than almost any other off the shelf oil. Add 1oz of Lucas TB Zinc Plus per 5qt of oil and you'll be right around 14-1500ppm of ZDDP, which is ideal for the spring tension in our flat tappet engines. STP Blue works if it's all you can find on the shelf, but it'll only get you up to around SM levels. If I get cam wear it'll be because of an internal lubrication issue, not as a direct result of the oil I'm using.

[NewZed]

Just a neophyte, but wouldn't the Schneider guys have some notes on the grind - http://schneidercams.com/270-60F-14_LET6.aspx

 

Still in business and they have a phone number. Just a thought.

[Zmanco]

So... Should I purchase an adjustable cam gear so I can get the most out of this cam? Or should I advance the cam timing a notch?

 

It's up to you how you want to approach this. I tend to have more time than funds for these types of issues so using the existing cam gear to at least verify that advancing the cam improves this would be my next step. But if you're paying for labor, then it might be worth having an adjustable cam gear installed so you can do it yourself from then on. Again, there's a proper way to do this as I mentioned before - I believe BRAAP did a great writeup for setting cam timing showing it step by step.

[darkstarrocker]

I spoke with Schneider cams. The cam is best used when advanced to the 3rd mark or about 4degrees. Told me I'm not the first to have this "problem."

 

Gonna get at it ASAP.

[Leon]

FWIW, each hole is 4 degrees advanced. Hole three would be 8deg from hole one, not 4deg.

[darkstarrocker]

Thanks for that. :thumbup:

 

My plan was to move it one, drive it, then move it to the next if need be. I guess the one hole will do it, since he told me about 4deg.

Edited August 21, 2012 by darkstarrocker