VersaTune User Forum

Since I'm rebuilding my engine I thought I should throw in a set of CS cams and see how it will go with the gen2 GTX3071.
However, even if CS states their cams require no tuning I just wanted to be sure and rather ask.
Common sense says that the higher lifting cams should resemble with the behaviour of a less restrictive intake and exhaust (I will still be using the factory manifolds just because EGR).
However, is there anything that needs to be changed in the tune? Maybe use less VVT in the mid range? Anything else?

The way I always did VVT was I would do a basemap on spring pressure with 0 VVT commanded across the entire map, then once I had that I would run full VVT until the engine makes spring pressure and taper it from there. From there, you can dial the boost up to what you want to target, but I'd recommend dialing spool fueling in a bit first (richer helps spool, as does retarded timing).

That, with proper changes in timing, should give you decent spoolup and a nice flat torque curve.

The spool-up is on-point now with the current GTX3071 I have... I will probably have to dial it back a bit because the gen2 will spool faster.
So I will 0 out the VVT table and see how much the gen2 needs. In the current seup the mid range torque is already a bit on the high side (around 710Nm/540lbft) and I don't need more than that.
Thanks!

I'm curious what you find while messing with the cams and tune. I'm building my new engine as well and I'm torn between the kelford b and c cams.

I went for the Corksport cams because they're rather mild. I'm still shooting to make a 500whp car 100% compliant with emissions regulations. With bigger cams emissions will not meet the regulations at least at low RPM/idle. Same for larger valves.

If you shoot for more power then either 247-B and 247-C are more aggressive than the CS cams.

Enki wrote:The way I always did VVT was I would do a basemap on spring pressure with 0 VVT commanded across the entire map, then once I had that I would run full VVT until the engine makes spring pressure and taper it from there. From there, you can dial the boost up to what you want to target, but I'd recommend dialing spool fueling in a bit first (richer helps spool, as does retarded timing).

That, with proper changes in timing, should give you decent spoolup and a nice flat torque curve.

This is interesting. I know the retarded timing helps spool. However, I was under the impression running your tune leaner in the pool zone helped it spool faster.
Mind explaining the rationale behind this, or sharing a link maybe? I'm definitely not disputing this, just would like to learn more.

My memory on this could be faulty, but richer should help increase exhaust gas volume + retarded timing makes it hotter, further improving pressure between the piston and turbine. I might be mixing gasoline and diesel knowledge on this though, but cursory thinking says more fuel + same air (as leaner burn) = more exhaust, even if temperature of said exhaust is a bit lower. Pretty sure there are diminishing returns on density unless you're looking to shoot plasma through the hotside. Lol



As for camshaft selection, I'd be careful how far you go. There's issues with fueling logic (at least on genwons) that could result in burnt valves and/or windowed blocks.

There are 3 things which help spool:
1. richer mixture. the gasses will continue to expand and burn in the exhaust which will make them continue increasing volume there. That helps spooling the turbine;
2. retarded timing. Pretty much the same logic ig gasses continuing to burn past the moment the valves open, just that this time is achieved by igniting them later;
3. advancing VVT which increases the dynamic compression so the cylinder pressure.

With proper settings I could get 20PSI of boost on my GTX3071 gen1 at 2200rpm with proper loading (6th gear) within a second of full throttle. this is harder and harder if the gear is lower and but it is possible with proper loading (3rd or 4th gear uphill with no wheel spin).

mituc wrote:There are 3 things which helps spool:
1. richer mixture. the gasses will continue to expand and burn in the exhaust which will make them continue increasing volume there. Thank helpsspooling the turbine;
2. retarded timing. Pretty much the same logic ig gasses continuing to burn past the moment the valves open, just that this time is achieved by igniting them later;
3. advancing VVT which increases the dynamic compression so the cylinder pressure.

With proper settings I could get 20PSI of boost on my GTX3071 gen1 at 2200rpm with proper loading (6th gear) within a second of full throttle. this is harder and harder once the gear is lower but it is possible.

Thanks Mituc. The added VVT I was also aware of. Makes absolute sense.

How much richer is safe though is the next thing I'm wondering about?

Dolfius wrote:How much richer is safe though is the next thing I'm wondering about?

Depends on the turbo. Remember it's a balance between timing AND AFR, so usually a 11.8-12.5 in the spool-up areas are common.