CIS mixture tweaking Q

[mrjones2]

Its my understanding that dropping the fuel pressure on a CIS-Basic actually increases the amount of fuel delivered. The fuel pressure is what "holds the door closed", so its opposite of what you would think.

I suspect that the fuel pressure is dropping during the pull (plugged filter, weak pump, cruddy warmup regulator) causing it to dump more fuel in. I have some really nice pressure transducers that I've been itching to use on the dyno, we just need to work out the plumbing

BTW, you Porsche guys drink a lot of

Kendall

[924Guy]

Its my understanding that dropping the fuel pressure on a CIS-Basic actually increases the amount of fuel delivered. The fuel pressure is what "holds the door closed", so its opposite of what you would think.

I suspect that the fuel pressure is dropping during the pull (plugged filter, weak pump, cruddy warmup regulator) causing it to dump more fuel in. I have some really nice pressure transducers that I've been itching to use on the dyno, we just need to work out the plumbing

BTW, you Porsche guys drink a lot of

Kendall
[/b]

They don't call us PUB Racing for nothing!! :026:

What you're describing is control pressure, as Greg points out; I'm talking about the system pressure. Yeah, we've got two fuel pressure regulators!

Warmup regulator is new, as is filter, and pump has no issues putting out that pressure (pushing 6 bar) - unless, as you're suggesting, it's old and weak. Too bad, we could've run the gauges on the dyno to confirm - yes, thanks, Greg, I do have them! - but didn't plan for mixture problems, only ignition...

We'll check again, but I'm 99% sure the control pressure is fine - it's only governed by the WUR (warm-up regulator aka control pressure regulator).

Since control pressure is from 1/4 to 3/4 of the system pressure, it has no problem bleeding the pressure down as needed - but it does make sense how the system pressure being too high could result in incorrect fuel flow, same as the control pressure being too low, since the fuel metering is completely determined by the pressure differential between the two. So you should effectively be able to bump your whole fuel curve up or down by re-shimming the system delivery pressure regulator (in the fuel dizzy).

Oh well, just goes to show you can never be too organized or prepared for a dyno session!

[jlinfert]

So you should effectively be able to bump your whole fuel curve up or down by re-shimming the system delivery pressure regulator (in the fuel dizzy).

[/b]

Messing with the main (system) pressure will do nothing good. Been there done that doesn't work!If anything shim it up to about 90 to 100 psi and then find a way to accurately regulate control pressure. The stock WUR will not do it right. What was your control pressure anyhow?We have a bolt on system that works flawlessly and would sell you one for $250.

[mrjones2]

Messing with the main (system) pressure will do nothing good. Been there done that doesn't work!If anything shim it up to about 90 to 100 psi and then find a way to accurately regulate control pressure. The stock WUR will not do it right. What was your control pressure anyhow?We have a bolt on system that works flawlessly and would sell you one for $250.
[/b]

Jeff- Can you send me info on that CPR setup? kendall at jonestechnicalgroup.com

Kendall

[924Guy]

Jeff- Can you send me info on that CPR setup? kendall at jonestechnicalgroup.com

Kendall
[/b]

Ditto! I'm at vaughan (at) vaughanscott.com - cheers!

You talking about your annual inspection, or did you get protested? If the former, that check has ZERO credibility (or supportability in a protest situation) as to the legality if items on the car; that's an annual safety check only.

If you want de facto and de jure proof of legality of a mod you've made, you need to follow the process specified in GCR 8.1.4 (p GCR 65 in the latest version). Otherwise, its legality is still up to argument.

Personally, as I noted above, I believe it can be done legally, and I'm sure the board here would be tickled pink to get into debating its legality. However, given your circumspect discussion of this "system" you've installed, I'm guessing you want to keep it proprietary; ergo you should make any potential customers aware that they are proceeding at their own risk.

Greg
[/b]

My impression is that it's nothing particularly special as far as implementation; all you're doing is bleeding pressure off one port and dumping it back to the return line to the tank. I suspect that, once you price out a decent regulator and gauge, then add the expense of compliant stainless braided hoses to plumb them in, with the right stupid metric fittings, any profit would be modest, and worth the effort to figure out all the bits.

I'm still gonna go home and, especially since the gauge is still plugged into my car, play around with the system pressure and watch the control pressure. I'd really like to see this in action, to improve my knowledge of how the system works. I think we've finally reached the point where we can stop struggling to just get the systems working properly, stock, and now look at modifications/tuning.