[POS1SS]

Hello everyone, new to the forum here. I’ve done some research but can’t seem to find the answer. I have 2016 1SS with gpi stage 4 cam, rest of mods in signature. On cold start my car will surge from 500 to 1000 rpm for the first 10 seconds but then levels out to the set idle rpm at 900. After the first initial cold start it drives perfect, no surge or anything , and any starts after the first cold start it doesn’t surge. Every now and then it will die but most of the time it levels out. Is this something that could be tuned out , or should I just leave it along since everything else seems to be perfect. Anybody else had this problem with a big cam?

[jaybee924]

Sending you a PM

[KingLT1]

That is one of the trade offs with a big cam.

[Hyper SS]

Originally Posted by POS1SS

Hello everyone, new to the forum here. I’ve done some research but can’t seem to find the answer. I have 2016 1SS with gpi stage 4 cam, rest of mods in signature. On cold start my car will surge from 500 to 1000 rpm for the first 10 seconds but then levels out to the set idle rpm at 900. After the first initial cold start it drives perfect, no surge or anything , and any starts after the first cold start it doesn’t surge. Every now and then it will die but most of the time it levels out. Is this something that could be tuned out , or should I just leave it along since everything else seems to be perfect. Anybody else had this problem with a big cam?

Did you fly cut? Mill heads?

[POS1SS]

Originally Posted by Hyper SS

Did you fly cut? Mill heads?

The cam I have is gpi stage 4 no flycut, but the heads have been milled. Have Chevrolet performance gen v head gaskets I think 0.54 thickness with gpi cam phase limiter (4 degrees. I’d have to call the shop that did the work I don’t remember them saying anything about flycutting the pistons but with as big as the cam is and the heads being milled, do you think they would have to be right? But I would have noticeable problems if the piston/ valve clearance was to tight? I’ve been driving this setup for about 3,000 miles.

[GTO_Gregory]

Sometimes the Piston to Valve clearance is safe if the vendor sinks the valves in the head a little bit. A compression check might tell you if there's P/V touching and things are bending. The engine can run with bent valves. It's when parts break that it gets noisy.

My LS2-402 ran with eleven bent valves, but it only made noise after a piece of broken valve guide was bigger than the piston to head quench area. The speed shop advanced the camshaft without properly checking piston to valve clearance with hydraulic lifters. It lost like thirty horsepower on the chassis dyno.

[Nabush]

GPI stage 4 with milled head and no fly cutting must be really close....

Does your engine start right away cold ? When I first tuned my cam I had to bump my cranking airmass a lot and of course adjust my rpm setpoint from cold to hot engine.

If your rpm setpoint cold engine is at 800-900 rpm it is going to surge a lot. I start at 1300 rpm and go down to 850 rpm after 60s in a linear way.

After that it could be your virtual torque table off around idle for certain airmass (more airmass engine cold). Need to make sure that if your tuner left dymanic airflow enabled he tuned the VE correctly. If MAF only it should not be an issue.

100% positive it is in your tune.

[POS1SS]

Originally Posted by Nabush

GPI stage 4 with milled head and no fly cutting must be really close....

Does your engine start right away cold ? When I first tuned my cam I had to bump my cranking airmass a lot and of course adjust my rpm setpoint from cold to hot engine.

If your rpm setpoint cold engine is at 800-900 rpm it is going to surge a lot. I start at 1300 rpm and go down to 850 rpm after 60s in a linear way.

After that it could be your virtual torque table off around idle for certain airmass (more airmass engine cold). Need to make sure that if your tuner left dymanic airflow enabled he tuned the VE correctly. If MAF only it should not be an issue.

100% positive it is in your tune.

I contacted the shop and the heads were only milled 0.010” for cleanup, and they used a 0.54 thick gasket. Also you know what the thickness of the stock gasket is? And yea it starts right up just has a big surge until it levels out at 900.

[KingLT1]

Originally Posted by Nabush

GPI stage 4 with milled head and no fly cutting must be really close....

Does your engine start right away cold ? When I first tuned my cam I had to bump my cranking airmass a lot and of course adjust my rpm setpoint from cold to hot engine.

If your rpm setpoint cold engine is at 800-900 rpm it is going to surge a lot. I start at 1300 rpm and go down to 850 rpm after 60s in a linear way.

After that it could be your virtual torque table off around idle for certain airmass (more airmass engine cold). Need to make sure that if your tuner left dymanic airflow enabled he tuned the VE correctly. If MAF only it should not be an issue.

100% positive it is in your tune.

I agree it's likely tuning related and not mechanical, However the GPI stage 4 has A LOT more Overlap then a TSP VVT3. There becomes a point when you introduce enough overlap into the system, you will get some odd behavior that you didn't have when stock.

For reference:

GPI SS4 +21 degrees of overlap.

TSP VVT3 +5

Stock LT1 cam -29.5

I certainly wouldn't expect a cam with 21 degrees of overlap to behave like stock. That is race car stuff...for a street car I would keep overlap under 12 degrees on a DI motor and under 8 degrees on a PI motor. DI can tolerate more overlap since it doesn't suffer the same reversion issues being that fuel is sprayed directly into the combustion chambers. jmo