LS3/480 and Cam Surge

Dan Carter

Supporter
Sorry gents this is an old topic but could not get search to dig up the old thread for me but I need an assist from the forum. I am building a street car and wanting to have typical city street driving comfort from this engine like any stock manual car. I have read numerous times that the 480 is hard to tune but tunable (need to define that I guess). Well, not being a “camologist”, and fully grasping the impact of all the cam specs, engine selection was a calculated risk, and I’m beginning to realize not a good one so far.

After hours with two independent tuners (both with solid reputations, not the shade tree guy, hence lots of money), I have a car that fails to meet my standard for drivability. I did like many and added the Dakota Digital to supply speed reference to the ECU (0 speed on dyno obviously). In trying to hold say 30 or 35 MPH on dyno with steady state throttle, the cam surge begins to kick in and the car bucks very uncomfortably.

So, if anyone knows what technique your tuner used and can share, I’m looking for an out before I go last resort and pull the 480 cam out and install the stock 430 HP GM cam.

Any advice or recommendations is greatly appreciated.
 
Is your fuel regulator vacuum port uncovered (as it should be)? It should not be capped or hooked up to a vacuum source. Can you confirm what your fuel pressure is? Do you have a mechanical gauge inline somewhere?

Post a picture of the top of the engine near the air intake tube and throttle body. No open vacuum ports on the front or back of the intake?

Your problem could be due to the fact a mechanical vehicle speed is not being seen although the symptoms usually show up when you let off the gas and decelerate.
 
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Dan Carter

Supporter
Ken

Confirmed regulator is NOT capped. Set/runs 60 PSI. Will get smoke generator and check for vacuum leaks. Will post picture in the AM. Thanks
 
Hi,

can't talk directly to the LS3/480, but I had the same issue on a multi-point injected 383 SBC with aftermarket engine management on it in a project car for the street which had manual transmission, and where manners were really important. I had a hydraulic roller cam of similar specs to the stick you're using.

In the end my problems were solved after I realised that the engine needed to be rich, even at light and steady load, until about 1600 rpm. It also needed more light and moderate load timing than i had previously been trying. I ended up with idle and off-idle AFRs of 13.3, and high idle and light cruise AFRs of 13.6. The engine would not work well at light and steady loads at stoich AFRs of 14.6.

I deduced that intake reversion was diluting the intake charge and reducing the efficiency of the engine in that range, and that I needed to accept that and give the engine more fuel and more spark lead. This smoothed it right out and it become very well mannered.

Once I changed my base fuel and ignition maps and made sure the target AFR table reflected the richer values required in this range I was good.

Hope this helps.

Cheers, Andrew
 
In my experience, Andrew has this right. A big cam will cause reversion issues at what used to be considered low RPMs. Now days, everyone expects to be able to run around town keeping a V8 between 1000 and 2000 rpm. With carbs, we never had that expectation. The last wild cam (for the street) carb'd small block I had would buck and kick below about 1800 rpms.

With the control we have with EFI, it is possible to tune around these issues, but they tend to need tuning solutions that may seem off-base.

I would go with something along the line of Andrew's suggestions and see if it gets you headed the right way.

The other option is ITBs (since they cure the reversion issue). But unless your selected tuner has good experience with your selected ITBs, getting those tuned can be an even bigger issue.
 
Does putting the Dakota digital into diagnostic mode and having it it out a steady 60mph signal cure the issue? I found my car surged pretty badly once warmed up but if I put the DD GPS into diagnostic mode, idle went ruler flat. I still need to understand why it’s doing this but if your issue is similar you have O2 and other sensors available real time that could indicate what’s different.
 

Dan Carter

Supporter
Cam

There are two VSS wires in the GM harness. DD says to connect to their speed 2 and set for 128k pulses. Did you use the VSS hi wire to speed two? Did you then ground the VSS low wire or leave it disconnected?

Andrew: I have requested copies of my AFR tables so I can see how it’s set. I hope my tuner shares, good input, thanks
 
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PeteB

GT40s Supporter
Dan,


Although I get a little bit of bucking with my LS376/480, it's not unmanageable. Here's how I have my DD unit set up:


From the VSS plug on the GM wiring harness, I connected the purple/white wire to the GPS unit and the other wire to ground.

I am using Speed output #2, "AC speedometer". GPS unit set to 128000 pulses.


I still haven't got the throttle error issue solved though... :(
 
Dan - same as Pete just described, low wire to chassis ground.

Pete - what’s your throttle error issue?
 

PeteB

GT40s Supporter
Cam - I keep getting a check engine light, then the throttle stops responding and I get code 2138, throttle sensor position error. I've replaced both the throttle pedal and the throttle body and still have the problem. I plan to take it to a tuner in the spring to see if they can program the ECU to ignore the code. I don't know what else to do short of replacing the entire wiring harness.
 

Howard Jones

Supporter
I think before and after vacuum data especially at a common idle figure would be very helpful. Does anybody have a "430" number and idle rpm. We will need a hot cam number also. If the hot cam data could include cam data that would be perfect.

My research into after market FI system points to vacuum (or lack of) associated with "hot" cams as being a major issue. I think that in the end building large CI engines at moderately high compression, with very efficient head flow and mild cam tuning is the answer. We seam to be trying to use modern fuel control equipment on old school wild cam timing and it isn't working.

A 450ci 11 to 1, with high flow heads and a mild cam still should make 1.1 - 1.15 hp per inch. That will be in the neighborhood of 500 hp.

One last thought. How about using a vacuum canister on one of these problem engines as a test to see if it helps............
 
The GM "hot cam" camshaft was designed in the early nineties for I believe the LT1 engines. It is far from ideal for the flow characteristics of the LS3 cylinder heads unfortunately. There are far better choices for drive ability and performance. The Katech LS3 "torquer" is a good choice.

For a $25 fee there is a fella by the name of Pat G that will custom spec you a cam for your particular application. He takes into account the car weight, gear ratio, intended use, cylinder heads used....etc etc. He has high dollar computer modeling software and has done hundreds and hundreds of dyno tunes. He has a huge following and his work is highly praised on the LS1tech forum. He spec'd the cam for my SLC. If you do decide to change the cam out then I would highly recommend him.
 

Dan Carter

Supporter
Ken, your being very politically correct about this cam......its poor at best. Lingenfelter has some good options as well. There is so much to know about the impact a cam has, I assumed (and we know what that means) GM had its Sierra together. I will try yet another tuner and if that fails me, this cam has got to go. Its a lot of work, but I simply don't want to have to manage the cam when I drive. I want smooth and easy to drive. The car will get enough attention just being what it is. How can I contact Pat G?
 
Ken, your being very politically correct about this cam......its poor at best. Lingenfelter has some good options as well. There is so much to know about the impact a cam has, I assumed (and we know what that means) GM had its Sierra together. I will try yet another tuner and if that fails me, this cam has got to go. Its a lot of work, but I simply don't want to have to manage the cam when I drive. I want smooth and easy to drive. The car will get enough attention just being what it is. How can I contact Pat G?
The Guerra Group
 
Dan,
My old LS376/525 crate motor had none of the issues you're talking about and GM markets that as a hotter cam than your 480. I'd describe the drive, as you put it, as smooth and easy to drive.

It's my understanding the LS crate motors 2+ years ago were a little rougher than they are today - when did you purchase your motor?

Best,
John
 

Dan Carter

Supporter
Lucky me....2015. What are the LSA and overlap specs on the 525? The 480 LSA is 112.0 with overlap of 2.0. A stock 430 cam LSA is 117.0 and -12.0 overlap. That's hard to overcome I think.


Ken. What they offer is impressive. I sent in an inquiry to see if they think they can help before I spend more money without desired results. Thanks
 
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Howard Jones

Supporter
Holley EFI 550-406 Terminator EFI 4bbl Throttle Body Fuel Injection System - Hard Core Gray

These do require vacuum input and from what I have learned so far radical cams that produce very low a vac sig will cause the learning softwear issues. I don't what to spend the $3000 it will take to do this and then spend the next 6 months learning how to make it work.

I know it's a bit different than a LS crate motor setup but if I had some hard data on cams and CR I think it would help me with this question.

Maybe a new thread in the engine page would be better.
 
Cam - I keep getting a check engine light, then the throttle stops responding and I get code 2138, throttle sensor position error. I've replaced both the throttle pedal and the throttle body and still have the problem. I plan to take it to a tuner in the spring to see if they can program the ECU to ignore the code. I don't know what else to do short of replacing the entire wiring harness.
You can't ignore the code without bricking the ecu - that's a critical failure code for safety.

If you've made sure to match the throttle body to your ECU style (i.e., gold or silver throttle body) I would replace the wiring harness. I can't begin to count how many defective GMPP wiring harness I received. One of them had a problem with the DBW - it would intermittently stop and start working.
 
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