Went back to the dyno after cam swap and it LOST POWER

[AdsoYo]

I bought a bone stock 2007 Saab 9-7x 5.3i with 95,000 miles this September as a new wife-mobile. For those that aren't familiar it's a re-badged, re-styled Trailblazer. It has an all aluminum LH6 which is a 5.3L, cathedral port, gen 4 LS. I took it to my local dyno to get a baseline in stock form and it put down 205hp/230tq. Pretty anemic but I chalked it up to the 87 octane and crusty old air filter.

After the dyno, I spent the month of October installing these:

Cam Motion 214/226 .553/.553 116+3
GM single beehive valve springs
DOD delete (new non-DOD lifters and LS3 valley cover with PCV)
New oil pump
New water pump
New LS2 timing chain
NGK TR-55 plugs
MSD plug wires
New 3.42 ring and pinion front and rear
New O'Reilly Microgard air filter
Intake, exhaust, fuel injectors, everything else stock and untouched.

Went back to the same dyno today and put down 195hp/219tq. After massaging the PE and spark table we got a best of 201hp/223tq. While the numbers are smaller, they're essentially the same. There was no knock, it wasn't pulling timing, it wasn't running out of fuel, MAP was mid 80's where it should've been.

I'll post the stock and new dyno graphs. For some reason I can't post my HP Tuners file or log.

Anybody who knows these cars better than me, did I miss something in the tune? It's like it has a restrictor plate you see on race cars to even the playing field. Maybe a torque management setting? If there is a restriction the only thing I can think of are clogged cats. It's just so bizarre that the numbers are basically the same.

 

[Mooseman]

I'll post the stock and new dyno graphs. For some reason I can't post my HP Tuners file or log.

Should be able to upload them as a ZIP file.

Maybe it's the gears? I know it doesn't explain the drop in power but those are pretty tall. Mine had 3.73 and with just a canned tune, it was pretty decent using my butt dyno.

I don't know enough on how to tune. Maybe a remote tune could get you in the ballpark. I know Goat Rope Garage is pretty good. Maybe they can help out for a fee?

 

[AdsoYo]

I've watched Goat Rope Garage on youtube, his videos are super helpful.

I'm confident when it comes to tuning spark and fueling. It idles and drives perfectly. It just doesn't have the power. That's why I'm suspicious about a governor or torque management setting I missed. This is my first time tuning an E67 ECM and there are way more tables here compared to the 0411 PCM in my Trans Am.

As for the gears, I could believe they'd eat a few hp but I'm missing 50+ hp.

I'll see if I can create a ZIP and post it here.

 

[Mooseman]

What do you have for intake and exhaust? Maybe restrictions there, especially on the exhaust side. Check for exhaust back pressure. I know for intake, a lot of people have swapped out to the TBSS intake.

 

[AdsoYo]

What do you have for intake and exhaust? Maybe restrictions there, especially on the exhaust side. Check for exhaust back pressure. I know for intake, a lot of people have swapped out to the TBSS intake.

I have stock intake and exhaust. The 07+ 5.3's already use a TBSS intake so I don't think there would be a restriction. As for exhaust:

I did some testing today to rule out a restriction in the exhaust and torque management settings in the tune. I have an app on my phone that uses GPS to read 0-60mph time, 60'-330'-1/8th mile-1/4 mile times.

I went out to a flat, straight country road and ran the car as-is to the 1/8th. Then I loaded the same tune but with all torque management disabled and ran the same stretch of road. Then I went home and disconnected the y-pipe from the manifolds and loaded the same tune but with closed loop disabled and ran the same stretch of road.

All runs produced the same numbers. So neither the tune, nor the exhaust are holding the car back. I'm going to call Cam Motion tomorrow.

 

[Mooseman]

I'm no guru on cams or tunes at all but, how does this cam compare to the stock one? Is it a mild torque, stage 1, stage 2? I tried to look up that cam on their site and couldn't find it.

Good idea to call them. They might have some ideas on where to start with the tune.

 

[AdsoYo]

I told them how the car was going to be used and they spec'd this cam for me so it's not "off the shelf". It's essentially the same cam I have in my LS3 Trans Am and that one has their off the shelf "LS3 mild stage 2". I was a little concerned it would be too much for an otherwise stock 5.3 but trusted they knew what they were doing. It does run and drive fine, just makes no power.

 

[AdsoYo]

Just got off the phone with Cam Motion, they recommended degreeing the cam, measuring pushrods, and ensuring the intake manifold isn't leaking. Great.

 

[AdsoYo]

I was pretty busy the last 2 days and ruled out some more things. I did a compression test, measured pushrods, and logged injector duty cycle.

The compression test went great! All 8 were between 170-175 psi. The spark plugs shocked me at first because they were all orange and only have 500 miles on them! After looking up what could possibly cause that, a lot of answers said octane booster will do it. The first tank of gas after my cam swap I added a can of octane booster since I still had a half tank of 87 so that explanation works for me.






Then I measured 4 pushrods (no time nor desire to do all 16). 2 DOD cylinders, 2 non-DOD cylinders. I have a Comp Cams adjustable pushrod and extended it against a fully torqued rocker arm until there was no more up/down movement. All were +/- 7.38" with 0.050" of preload factored in. I'm confident all valves are opening and closing completely.

Finally I drove around and logged misfires and injector duty cycle. There were a few misfires infrequently when idling and injector duty cycle hit a maximum of 75% at the top of 2nd gear.

So for now the mystery of the missing 50hp is still a mystery. I guess next step is removing the timing cover and inspecting the timing gears + chain, and degreeing the cam?

 

[AdsoYo]

Just spoke with Cam Motion again. I told them about all the troubleshooting I've done so far and what my planned next steps were. He looked at my original order form where I said I'd like to supercharge it someday and had an answer for the poor performance right away: he said this cam is intended for use with a supercharger.

I guess I have a lot to learn about camshafts and how they affect different engines. I figured a cam with these specs would still produce SOME improvement over stock. I asked him if he could explain using technical language why it's not making power and didn't get much of an answer. I can't think of a good reason either but I'm no engineer.

His recommendation was to install a cam intended for N/A use and said either of their stage 2 offerings would work well for my case: either a 206/210-115+5 or their Titan stage 2 at 212/220-112+4. Eventually I would absolutely love to slap a TVS1900 on this with its current cam. Wouldn't happen until after winter though.

 

[azswiss]

I suspect that what you are seeing is loss of air charge in the cylinder just before the valve closes since the new cam is designed to stay open longer and open wider to accommodate the boosted (higher pressure) air flow rather than non-boosted airflow.

Per Google AI (caveat emptor!) the intake valve on a stock 2007 5.3L V8 closes around 40 to 43 degrees *After* Bottom Dead Center (ABDC).

Compared to the cam you installed (214/226 .553/.553 116+3), the stock cam has both less duration (196/201) and less lift (.481/.481).

The new cam opens the valves further and stays open longer in order to take advantage of the boost. Without the higher pressures from the boost the result is that air is getting pushed back out at some point during the extended period the intake valve is open (vs. stock).

The net effect would be the same as if you had a restrictor plate: less air charge in the cylinders. How do the fuel trims look? Assuming a stock tune, I would expect to see ever so slightly lower trims.

 

[AdsoYo]

I suspect that what you are seeing is loss of air charge in the cylinder just before the valve closes since the new cam is designed to stay open longer and open wider to accommodate the boosted (higher pressure) air flow rather than non-boosted airflow.

Per Google AI (caveat emptor!) the intake valve on a stock 2007 5.3L V8 closes around 40 to 43 degrees *After* Bottom Dead Center (ABDC).

Compared to the cam you installed (214/226 .553/.553 116+3), the stock cam has both less duration (196/201) and less lift (.481/.481).

The new cam opens the valves further and stays open longer in order to take advantage of the boost. Without the higher pressures from the boost the result is that air is getting pushed back out at some point during the extended period the intake valve is open (vs. stock).

The net effect would be the same as if you had a restrictor plate: less air charge in the cylinders. How do the fuel trims look? Assuming a stock tune, I would expect to see ever so slightly lower trims.

Great comment, thanks! The trims were actually WAY lower. The log isn't on this current computer otherwise I'd take a screenshot but they were -10+/- in most of the cells.

Losing cylinder pressure is one of my theories but that still begs the question: why does this same cam work so well in my 6.2L LS3? If they're both LS engines then shouldn't they behave the same as far as valve events? Obviously displacement and cathedral vs rectangle ports are different but from a technical standpoint, why would this cam give me +50hp in one and -10hp in the other? Not trying to be confrontational or argue or anything like that, I genuinely don't understand.

 

[azswiss]

Nothing confrontational or argumentative here, just good discussion. In the case of the 5.3L, the lower trims confirm the reduction in air charge.

Compared to the stock cam for the 6.2L LS3, the new cam has higher durations (214/226 vs. 204/211) and lifts (.553/.553 vs. .551/.525). Lobe separation angle is 116+3 vs. 117 stock (note: stock LSA on the 5.3L is 116)

Although the new cam has higher durations and lifts as compared to both the stock 5.3L & 6.2L cams, the magnitude of the differences is noticeably smaller in the case of the 6.2L.

That would appear to leave lobe separation angle & cam timing advance as potential suspects.

Seems like the 6.2L got pushed into a sweet spot whereas the 5.3L got pushed out of it.

How did the trims compare on the stock vs. new in the 6.2L?

 

[AdsoYo]

Had to go back into my old logs but it looks like they were around -2 after I got all the hardware bugs worked out and BEFORE I started tuning MAF and VE. My base file was a stock LS3 Corvette. I actually never ran the LS3 with its stock cam. I swapped cams on an engine stand and then dropped in the car.

 

[Zaab]

I told them how the car was going to be used and they spec'd this cam for me so it's not "off the shelf". It's essentially the same cam I have in my LS3 Trans Am and that one has their off the shelf "LS3 mild stage 2". I was a little concerned it would be too much for an otherwise stock 5.3 but trusted they knew what they were doing. It does run and drive fine, just makes no power.

I think OnAllCylinder says if you use LS3 cam, it will have huge loss on low end? 9-7x need truck cam. And a cam for supercharger may not work well in NA.

 

[AdsoYo]

I think OnAllCylinder says if you use LS3 cam, it will have huge loss on low end? 9-7x need truck cam. And a cam for supercharger may not work well in NA.

Yeah at this point I'm heavily leaning toward this all being normal for this cam N/A. The car runs and drives perfectly and gets 19 mpg. I emailed Cam Motion one more time and included my logs and dyno graphs and asked if this is how they would expect this cam to perform N/A. If they say yes I'll move forward with the supercharger. If not, I guess I'll troubleshoot more. Getting a straight answer out of these guys has been like pulling teeth so I'm not getting my hopes up.

 

[AdsoYo]

I went ahead and did a WOT run to give people something to look at, and I'll take any excuse to go WOT. Since I can't post HP Tuners files, I screen capped the run and uploaded it to YouTube. I set the software to run it at half speed to make it easier to follow.

A few things:

• Torque management only engages during transmission shifting which is normal. You can see "spark torque management" flash "Trans" during shifts.
• There are a few times we see a fraction of a degree of knock retard, no big deal for the main issue in this thread.
• The MAF g/s peaks between 250-260 which is about right for 300-325 crank hp. Subtract 25% for AWD drivetrain loss and you get 244 whp. About where I thought this cam should be.
• If you plug the engine torque value of 275 ft/lbs @ 5850 rpm into the formula: HP = (TQ x RPM) / 5252 you get ~ 306 crank hp.
• I didn't set up the chart correctly for MAF g/s so we get no line graph, apologies.
• I also recorded TPS volts instead of %, apologies again.

Here's a shot of the MAF g/s line graph after realizing my mistake:



Looks like maybe we just didn't spin it fast enough on the dyno. The cam still lost power everywhere under the curve so a supercharger is definitely still happening but it makes me feel much better seeing these numbers.

 

[littleblazer]

You happen to have a cam card for the cam in both your cars? I think that will tell the full story.

 

[AdsoYo]

Yes I have a picture of the Saab's cam card but the Trans Am's is buried in a box.



I finally got a direct answer from the employee at Cam Motion who designed and sold me the cam. He said: "With this camshaft having a later intake closing event than a stock camshaft to accommodate the blower, in NA trim you will need to turn more rpm to before seeing peak power. Once the blower is installed the rpm will change a good bit."
I then asked the follow-up question after attaching my logs and graphs: "Is this what you expect to see from this cam N/A?"
He replied: "Yes, with this camshaft being more tailored towards the blower application this is about what you would expect in NA form at that rpm."

So it boiled down to a lack of understanding on my part. Zaab and azswiss were right. We've been daily driving it this whole time and it's been great. The supercharger should be here in about a month.