Do I actually need a tune (or a VEC1)?: 96 GTS heads/cam 511 whp (but then there's 675 nitrous)

[Tom and Vipers]

Thinking I should have changed the title to: Is there any reason to not remove a VEC1?

According to Roe website info for Calibrator in 2001: OE tune at high load is excessively rich (11.0:1) with little timing (18*), low and midload, lean and lots of timing (45*)

Cam: 224* @ .050, .550" @ valve, 114* LSA

 

[Old School]

According to Roe website info for Calibrator in 2001: OE tune at high load is excessively rich (11.0:1) with little timing (18*),

An interesting result of doing anything that results in more air flow (heads, cam, exhaust, etc) at wide open throttle is it will go leaner because the same fuel is being injected in spite of the additional air flow. It's running in open loop mode and just using a predefined fuel map. This will get you closer to the desired 12.5-13 AFR without any tuning. Won't help with the timing though.

If it were mine, I would tune it.

 

[Tom and Vipers]

RE: Open Loop WOT:

Please note my thought experiment here could be completely wrong:

Cam and heads will make engine breath, VE goes up: With the positive displacement engine now pumping more air, MAP will go down (more manifold vacuum) because of the restriction of the intake system. More vacuum => lower load => less fuel.

Engine also has 70mm throttle bodies which reduce the intake restriction, MAP will go up => ... => more fuel

I have no idea what the net change would be.

 

[Dan Cragin]

I should have a calibration for that cam if you PM me.

 

[vprtech]

RE: Open Loop WOT:

Please note my thought experiment here could be completely wrong:

Cam and heads will make engine breath, VE goes up: With the positive displacement engine now pumping more air, MAP will go down (more manifold vacuum) because of the restriction of the intake system. More vacuum => lower load => less fuel.

Engine also has 70mm throttle bodies which reduce the intake restriction, MAP will go up => ... => more fuel

I have no idea what the net change would be.

Sure, that is correct, but the same can be said with opening or closing the throttles as you are changing the manifold pressure.

When you improve or change the air flow efficiency of the engine, the engine flows a different amount of air at a given rpm/map , sometimes more - sometimes less, therefore you need to re-map the engine controller to accommodate the changed volumetric efficiency.

Regarding the rich running, keep in mind that when you drive the air fuel mixture rich, you not only lower EGT's, you shut down the catalytic converter, i.e. prevent the catalytic converter melting down, as all of the oxygen is used up and the catalyst can no longer consume the CO and HC's, this is why the factory calibrations run on the rich side.

Certainly it would not be a bad idea to tune the engine, I would not hesitate to remove the VEC1 however as it just adds a unnecessary point of failure electrically. Also, "tricking" the ecu by skewing the MAP sensor voltage in order to lean out the mixture is not the best way to do things.

 

[Tom and Vipers]

Sure, that is correct, but the same can be said with opening or closing the throttles as you are changing the manifold pressure.

When you improve or change the air flow efficiency of the engine, the engine flows a different amount of air at a given rpm/map , sometimes more - sometimes less, therefore you need to re-map the engine controller to accommodate the changed volumetric efficiency.

Regarding the rich running, keep in mind that when you drive the air fuel mixture rich, you not only lower EGT's, you shut down the catalytic converter, i.e. prevent the catalytic converter melting down, as all of the oxygen is used up and the catalyst can no longer consume the CO and HC's, this is why the factory calibrations run on the rich side.

Certainly it would not be a bad idea to tune the engine, I would not hesitate to remove the VEC1 however as it just adds a unnecessary point of failure electrically. Also, "tricking" the ecu by skewing the MAP sensor voltage in order to lean out the mixture is not the best way to do things.

Did you mean, "...that is why the factory calibrations run on the lean side." ? since rich shuts down cats?

Yes, yes, yes: "...it just adds an unnecessary point of failure electrically." 25 years old and while MAP signals soldered, there are still vampire clamps present.

Yep, MAP trick is not about mixture, it adversely affects timing: The two directions are 1) Burn Piston and 2) Pig Rich + No Power (when you MAP adjust, you Lean and Advance timing).

A question I have is if VEC1 removed, with heads/cam/headers, would WOT go richer (and possibly also retard timing)? If that is the case, would probably be safe for mild nitrous.

It has 70mm throttle bodies which would lower MAP indicating more load.... so from tables: Richer and Retard?

 

[Dan Cragin]

The VEC 1 was used before the production computer could be tuned and was a compromise. The electronics tended to not be automotive grade and failed over time.
With tuning software and lots development over years with those who are involved with Viper's. Tuning is more straightforward and calibrations are available for
most any combination. Chris, who posted here, has more experience doing this, than anyone. I've worked with him for 25 years.

In regards to NOS. I've done numerous over the years on Viper's. I can tell you the most reliable systems are the ones that are a "wet" system, have a failsafe, a
proper ignition retard and a heated system to keep bottle pressure consistent. The power level the system is putting out can effect all these factors and the complexity
of how it needs to be designed and staged.

 

[vprtech]

Did you mean, "...that is why the factory calibrations run on the lean side." ? since rich shuts down cats?

I mean that is why they run on the rich side, to protect the catalyst under high load , otherwise the catalyst will not live very long, especially survive the emission warranty .

Yes, yes, yes: "...it just adds an unnecessary point of failure electrically." 25 years old and while MAP signals soldered, there are still vampire clamps present.

100%

Yep, MAP trick is not about mixture, it adversely affects timing: The two directions are 1) Burn Piston and 2) Pig Rich + No Power (when you MAP adjust, you Lean and Advance timing).

Correct, it does cause the ignition timing to advance but it will also lean out the mixture, in addition it will skew the JTEC’s calculated altitude .

A question I have is if VEC1 removed, with heads/cam/headers, would WOT go richer (and possibly also retard timing)? If that is the case, would probably be safe for mild
nitrous.

It may be ok, but you should always check. Highly recommend getting a wideband datalogging setup. Here is one that you use a laptop to log and can measure rpm, map , tps by taping into the wiring. If taping into wires is not something you want to do you then you can get HP Tuners or I also make a data-logging setup.

It has 70mm throttle bodies which would lower MAP indicating more load.... so from tables: Richer and Retard?

Negligible difference.

 

[vprtech]

Link : https://www.zeitronix.com/Products/...2L4fzyPmbb8fgr-PK8OXnlmbbycdx7XerheHag6xB28M9