More fuel for moderately modified F.I. engine?

[SunnySideUp]

A while back I was talking with a person who used to race Spiders "back in the day." After talking for a while about various mods and what I had done with the engine in my Spider he told me that what they used to add a micro-switch to the AFM to keep the "full fuel" signal going to the injectors for a longer period of time in the modified cars. Apparently the effect was supposed to be similar to the folks running twin IDFs and getting that kick-in-the-pants acceleration sensation.

Current mods to the engine in my Spider are 40/80 cams, high compression pistons, Computronix ignition system, and a heavily ported stock air box. It has a stock exhaust manifold but I'm not running a catalytic converter (test pipe instead) to the popular ANSA muffler.

So was this guy feeding me a line of BS or is there some truth to what he was telling me? If there's truth - how does a person go about modifying the AFM? I don't want to lay out the bucks for a programmable system (e.g. MegaSquirt) but am interested in getting a bit more out of my Spider if it's not too hard to do. I don't track the car but we do have some nice mountain roads with great twisties.

<edited to clarify thread title only>

[narfire]

Do you have the adjustable cam wheels with the engine degreed in properly?

I had a real notable difference between just cams ( Marks 274) and then after degreed in to spec.
At least a two inch exhaust system would help. I lightened my flywheel as well.

[FiatMac]

The turbo spiders used manifold pressure switches and resistors to vary the resistance in the coolant temperature circuit to provide enrichment under boost. The coolant temperature sensor has high resistance at low temperature and the resistance falls as the temperature increases. The ECU uses this resistance value to add injector pulse time (more fuel) when the engine is cold.

On an normally aspirated engine your load is a function of the manifold vacuum. You might be able to use a series of vacuum pressure switches and resistors to add resistance to the coolant temperature circuit as the vacuum falls under load. The advantage is that the vacuum falls instantly when you open the throttle, and the response of the ECU would be almost instantaneous. You would probably have to add some kind of system to cut out the O2 sensor because it will try to adjust the AFR back to stochiometric unless you are at wide open throttle. At wide open throttle the O2 sensor is cut out by the ECU anyway.

I am not sure how you would add micro-switches to the AFM.

[vandor]

Over 3500-4000 rpm at wide open throttle the AFM flap is fully open, so you are getting as much fuel as possible.
Maybe he meant that the switch would kick it into 'full rich' mode even before the AFM was fully open? That might do some good at part throttle, hard to say.

[carl]

Years ago when I had a fuel injected spider, I hooked up an air fuel meter and at full throttle the meter indicated a rich mixture. The throttle position sensor has an idle position which I assume was a fixed fuel amount, a full throttle position which gave a rich mixture and between those two fixed settings was the variable fueling which is probably controlled mostly by the oxygen sensor. From your description, it sounds like the guy was suggesting the full throttle rich mixture had a time limit to it but this is the first I have ever heard of such a thing, I didn't think the Bosch L-jetronic is that sophisticated and I can't think of a reason why a street car would need such a thing.....but then I'm carb guy so what do I know. Realistically, unless you are running at Bonneville, when would your street car but at full throttle for an extended time?

[SunnySideUp]

Thanks everyone for your insight on this. I will admit that I'm venturing into uncharted territory with this. I am hoping to meet up with the guy again at one the local car shows or FIAT events and pick his brain some more to find out exactly what he did. If it is bolt-on hardware I'm good. If it's fiddling with electronic settings I am very cautious or I just don't go there. As for the adjustable cam pulleys - I recently was able to source a set of used ones from a forum member and they are just waiting for installation and setting. One of my biggest challenges has been finding someone local who can "scope" the AFM and oxygen sensor settings and make any necessary adjustments along with tweaking the timing. I've found a former Ferrari mechanic who said it would be relatively easy once he has the time. (Apparently being retired and having a set of desired skills let's him pick and choose what he wants to work on - he has a waiting list). I had asked him what he thought about increasing the richness of the fuel mixture. He laughingly responded by asking me why I just didn't buy a Ferrari in the first place.

A related question I have: Given my current engine set-up, would installing larger injectors be a solution? Are larger injectors even available to fit the 2L (plug-and-play)?

[carl]

You really need to get an air/fuel meter. It will let you know if your fuel needs to be made richer. You may be chasing a performance issue that you don't really have.

carl

[So Cal Mark]

you really need to put the car on a dyno and see what the fuel mixture is throughout the rpm range at full throttle. Changing the fuel mixture any other way will likely cause a loss of power and possible engine damage

[SunnySideUp]

I'm taking the advice for the dyno and air/fuel meter assessment and will get that done once I get the adjustable cams installed and set. A couple of forum members have PM'ed me with some really good recommendations for mechanics who can do that kind of work in my area so I don't have to wait on the Ferrari guy.

[vandor]

If you go to a dyno, choose one that can print you a rpm vs AFR graph, otherwise you are wasting your money.
Some shops just have a separate AFR meter and rely on watching it during the run - like they are going to remember what the AFR was every 1000 rpm...

[ClarkTheShark]

You should not need to Retune the Bosch system theoretically.

It uses a mass air flow sensor, and should account for enhancements you make.

Anything you do to the head or the exhaust that may help the engine breath better should be automatically "sensed" (up to a point, They aren't going to be able to sense 500% or flow or anything, but within reason here)in the flappy paddle of the AFM and be accounted for. The same is not true for Alpha-N or speed-density systems.

That being said, the entire thing may need to calibrated for accuracy across the entire rev range. - And from the factory, Bosch used a narrowband o2 sensor for L-jet to keep everything calibrated.

Also, a trip to the dyno would be best, but wideband 02 kits are available for your own testing on the road. check out the innovate lc-2. Awesome stuff.