How much TIMING will a NA car handle?

[Sean Roe]

VEC2 Tuning issue

Hi Guys,
I came up with an idea after sleeping over the issue of the V notch and have an idea regarding the VEC2 / software. The common thread is the timing advance.
Give me a couple days to look into it and see if I can work out a test. It "could" be a error in the software / firmware algorithm, but it's just a theory at this point.
One thing we've learned about these cars over the years is, they can all be a little different. If I can put together a test, I'll have to send the parts to someone like Jack who has seen the issue on a repeatable basis.

Regards,
Sean

 

[Jack B]

Re: VEC2 Tuning issue

Sean:

I am going to dyno on Tuesday, if you get me some info prior to that, I will be the test mule.

 

[FE 065]

Re: VEC2 Tuning issue

Vipers need a lot of timing because their bore is large, the spark plug is way off to one side, and they use an old style combustion chambers. As rpms rise there's less time to complete the burn and they need more advance to be able to burn the mixture completely to make max hp. As you add more advance the piston had to fight that earlier explosion and the push of the crank/connecting rod.

Catch22


The old Hemis would keep making more hp as you dialed up the advance past 40deg BTDC (sometimes to suddenly grenade when advanced too far!)
because their combustion chamber was so large.


If we could add another spark plug on the other side of the chamber the engines would need less advance.

It might pay to compare notes more deeply about the cars that are suffering the V notch dip. Are they using aftermarket injectors that might not be atomizing the fuel as well as OEM? What camshaft are they using? Maybe there's a common thread.


Do some of the spark plugs in that engine inadvertantly have their plug gap facing the combustion chamber wall instead of the combustion chamber center, making the trip the flame front has to travel even more difficult?

 

[Jack B]

Re: VEC2 Tuning issue

FE065:

The common thread is they are a viper. My mix covered the gambit from stock, to modified, to a Gen1. My own car did it with stock injectors and with 50 lb injectors. My car did it with the plugs indexed and not indexed. MOJO's car did it with one range colder plug and then with two ranges colder. Then there was a completely stock Gen1. PaulS's car was a new arrow rebuild.

All these cars exhibited the same notch, somewhere between 4500 and 4800 rpms. As soon as all additional advance is removed the notch disappears. The condition seems to be aggravated by the number of runs. It does not seem to be detonation, it is more like a misfire. The mixture is forced lean by the event, this lean mark on the curve is also common to a misfire.

 

[FE 065]

Re: VEC2 Tuning issue

OK... I think I mentioned this on the other thread but how about running a car with those symptoms at 4500-4800 for 20 seconds, killing the engine at that rpm, and pulling the plugs? It'd tell you whether it was the same cylinder each time, and confirm mixture strength in each cylinder at that rpm to boot. Seems like the thing to do. Well, I'm wondering how the mixture reading at the O2 sensor shows being forced lean by the event when the mixture's regulated by the computer? Wouldn't a misfire of any sort leave unburnt fuel to register rich on an O2? I'd go with a plug chop repeatedly on the same car and see if the condition varies from cylinder to cylinder indicating a general Viper problem (now and then) or something in 1 particular cylinder on the cars the problem turns up on.

 

[Jack B]

Re: VEC2 Tuning issue

FE 065

A misfire registers lean and the computer is in open loop and not making any compensation. This event is probably max torque/load related and probably will won't show up when not under acceleration. It would be interesting for someone to run for that 10-15 seconds at 4800 and see if the misfire occurs.

Trying to catch this event would be difficult. It doesn't do it each time and you probably couldn't catch it before it recovers, therefore, you would lose the plug condition.

I looked at one of my car and a Gen1. The depth of the notch will vary, however, on both cars the length of 1/2 the notch (misfire time) is .4 sec. In this case they were both about 20 hp notches. They can be much greater. My notch was at 4800 and the Gen1 was at 5500. In this case the 20 hp is not alot, however, it is happening in my car as the hp is climbing. It is hard to tell what the overall affect on peak hp is.

 

[V10 MOJO]

damnn!! and here i was thinking that my viper needed more HP, well, i better call heffner and tell him forget that stroker as now, fortunately, i have seen the light and dont NEED that extra alleged power

 

[Tom F&L GoR]

This would be taxing the capabilities or budget of bench racers, but maybe someone can cobble together one of these:

individual exhaust temperatures to look for a cylinder that is behaving differently than others

some ignition systems use the ionization effort to monitor cylinder performance - is this applicable or an add-on that would again point to a particular cylinder?

ideal case would be individual cylinder pressure measurements, real-time, and simultaneously.

I'm just throwing ideas, maybe someone clicks an idea on how to narrow it down to a cylinder (or not) and that helps solve this.

Something really esoteric - I've seen high speed videos of intake valves and fuel injector sprays; it's eye-popping to see what really happens. The injector sprays on the back of a closed valve, partly puddles around the perimeter, when the valve opens, the blow back and immediate vacuum shoot the fuel upstream and then immediately downstream into the cylinder. It makes me wonder if the Viper issue is a torsional in cam timing. I apologize for not studying all the posts, but has this happened with an aftermarket cam?

 

[FE 065]

damnn!! and here i was thinking that my viper needed more HP, well, i better call heffner and tell him forget that stroker as now, fortunately, i have seen the light and dont NEED that extra alleged power

Overall it's probably better to look for the extra hp somewhere else rather than explore the fringes of timing limits.

 

[KenH]

Just bumping this thread to see if anyone has new info.

Has someone tried cooler plugs yet?

 

[txlen]

This would be taxing the capabilities or budget of bench racers, but maybe someone can cobble together one of these:

individual exhaust temperatures to look for a cylinder that is behaving differently than others

some ignition systems use the ionization effort to monitor cylinder performance - is this applicable or an add-on that would again point to a particular cylinder?

ideal case would be individual cylinder pressure measurements, real-time, and simultaneously.

I'm just throwing ideas, maybe someone clicks an idea on how to narrow it down to a cylinder (or not) and that helps solve this.

Something really esoteric - I've seen high speed videos of intake valves and fuel injector sprays; it's eye-popping to see what really happens. The injector sprays on the back of a closed valve, partly puddles around the perimeter, when the valve opens, the blow back and immediate vacuum shoot the fuel upstream and then immediately downstream into the cylinder. It makes me wonder if the Viper issue is a torsional in cam timing. I apologize for not studying all the posts, but has this happened with an aftermarket cam?

yes...this has happened to me with an aftermarket cam too...so i don't think it's cam related...i think it's more heat related..than anything else....Len

 

[txlen]

Just bumping this thread to see if anyone has new info.

Has someone tried cooler plugs yet?

as far as colder plugs i tried them too...i went 2 steps colder..it still missed..so i took 3 degrees timing out in the 4000-4500 area and 2 degrees out in the 4500-5000 area...the car is flawless now...Len

 

[Tom F&L GoR]

Can the OBD-II misfire sensing system be used to track which cylinder is contributing?

One the the older NASCAR power tricks was to time each cylinder individually, rather than as a group. They are all different due to length of runner from carb, angle of manifold runninger into cylinder, left or right bank on an oval... Lots of these aren't issues with a fuel injected engine, but for odd reasons, one cylinder can want more timing than the neighbor.

 

[jp]

Well guys I've been experiencing the same problem since lats year. So far this summer have I tried three different VEC2 boxes, no difference. I have tried with and without advance, with and without fuel curves etc etc. The problem is even there when I run the box without programming, just the stock signals throug the box. We have had this problem for 5 races now, still don't know what the problem is, but the last weekend did I notice a sudden 20psi dropp in fuel pressure above 4500rpm...looks like something suddenly is cutting the power to the fuel pump...I'll let you know.
As it is right now is my only solution to run the car with the stock box.

 

[KenH]

I just got done doing a little more experimenting. I put all timing back to stock and only adjusted fuel to richen it in the lower RPMs and lean it out in the upper RPMs to bring my A/F up to about 12.5 during some 4th gear pulls on the road. A/F measured with WBO in header. Temp was hot at around 95F, 92 octane gas in the tank. I got some pinging and a couple of stumbles. Disappointing since I thought I could at least dial in the a/f to be better than stock even if I couldn't benefit from any timing advance yet. The stumbles did not necessarily occur at a particular RPM range, but at times seemed more related to modulation of the throttle as when running up through the gears.

Now that it is hot outside, I will try to put all settings back to factory stock, but with the VEC2 in-line and see if I still have the same issues by only having the box process the signals as per JPs comments. Frankly I'm about to give up on this project and pull the whole setup if someone doesn't come up with a fix soon.

--- Ken

 

[Sean Roe]

Hi Ken,
Will you send me the cbc file you were running on? E-mail to [email protected]
I only have a couple questions:
1. Are you using stock spark plugs?
2. Have you checked to see what your long term fuel trim adaptives are? I'd like to see them at a slight negative number.
3. Does the car drive the same (ping, stumble) without the VEC2 on it, when tested back to back?
Does anyone have a dyno graph of the "V" to post, fax, or e-mail? I've been running our car on the test track and it keeps pulling smooth (I'm almost sorry to say).
Here's what the car is:
Stock original short block with 78cc heads, 70mm TB's, factory airbox, S&B filters, Bosch FR8DC spark plugs, MSD Super Conductor wires, MSD fuel injector connectors, ground booster (wire) at front and rear of the car into the factory PCM / sensor ground system, Supercharger running 8 PSI, 1.7 rockers, B&B 1&3/4" headers, B&B cat-back, 93 octane pump gas, 180 thermostat (never goes over 195) and aluminum flywheel. VEC2 programming adjusted with an 11.8:1 A/F ratio running 3+ degrees midrange advance, with timing retard ahead of and behind it and a long term fuel trim of 0 to -3%.
If any of you guys see something I'm running that you're not, please let me know.
If it would do something wrong, I can log it with the O-scope.
Regards,
Sean

PS to JP,
Email me and let me know what has been going on with you as I wasn't aware you had a VEC2 on your car now. I'd like to hear what it's doing and if it's the same as what some of these guys are desribing. Your's sounds more like an injector connector problem (except for the fuel pressure issue) if you haven't changed them.

 

[KenH]

Hi Sean,
I'll send you the cbc file when I get home tonight. Basically I have set the fuel load to 4 and the RPM curve to -70% at about 4000RPM and higher to bring my A/F from mid 11.2 up to 12.5 (approximately) with some fuel added at the lower RPMs.

1) Spark plugs are stock champions, stock gap, replaced this spring and now have about 2500 miles on them. Magnecor 10mm wires about 2 years old.

2) I do not have a way to monitor the adaptives. My ODBII reader isn't sophisticated enough to do that. I am running the stock injectors, so figured it wasn't important.

3) I have not tried taking the VEC2 completely out of the circuit yet. I will try running the stock program on the way home tonight. If I still seem to be having the problem, I will next disconnect it and see what happens.

Per your last comment, I notice that you have a supercharger and I don't. I'm pretty sure that's the root of the problem. I'd be more than happy to install an evaluation supercharger on my car with everything else left the same to see if that resolves the issue

 

[Sean Roe]

Per your last comment, I notice that you have a supercharger and I don't. I'm pretty sure that's the root of the problem. I'd be more than happy to install an evaluation supercharger on my car with everything else left the same to see if that resolves the issue

If we don't come to some sort of conclusion, I just may take you up on that.

 

[KenH]

email with .cbc sent.

I put the stock settings back into the VEC 2 and the car ran fine under the same conditions as noted above. No ping and no stumble. With the stock settings back in I was actually running right about 11.0 AFR vs 12.5 with the settings in the .cbc and as noted above.

 

[JimT 99RT]

Here is what I saw:

My 99 was dyno'ed with the S/C, 7 LB pulley, Roe High Flow cats, 70MM throttle bodies, 50lb injectors, stock headers and Borla cat back exhaust with Sean's 9 card and the dip occurred about one out of every 3rd pull and was about 60hpr at 4300 RPM. With the same setup but using the 6 card the dip was only about 30hpr when it happened.

I re-dyno’ed the car with T&D rockers, a full 3" exhaust with Valaya Headers, No Cats and a switch to a 1996 PCM, and the dip was at 4500 rpm but was only about 20hpr with the 6 card.

-Jim