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Sure thing Spencer. On a stock car, the ECU commands ~5* of timing at 850 rpm. At my warm idle of 1000 rpm, my ecu is commanding 10.5* of timing which gives the motor significantly more torque. I'm up to 12.3* at 1100 rpm, 16-17* at 1400, and 20*+ at 1600+ rpm, depending on how gently I take off. In addition, the car is setup to idle somewhat rich, which is important because our motors; with their large bores and (in my case) semi-batch fire fuel injection; have issues with intake pulse reversion which has the effect of causing one or more cylinders in a given 360* rotation of the crank to run lean unless the motor is intentionally tuned slightly rich. Besides that, peak torque is not made at stoichiometric ratios, but at ~12.2:1-12.5:1. AFR. (I actually shoot for a little leaner than this, about 13:1-13.2:1)
Why were our cars not tuned like this from the factory? Simple.
1: It raises idle emissions in a way that would be significant to an OEM
2: It would quickly overheat and destroy a catalytic converter.
3: The car might not pass low speed emissions testing tuned in this way.
Everything about the factory idle is a series of compromises...its far from the best idle the motor is capable of. My factory stock N/A car feels like it has less torque off the line than my 951. Tuning goes a looooooong way. The secret is to add timing and add fuel.
Oh yeah, by the way this is all being said while my 951 has an 8 lb billet flywheel... yeah...try taking off with the clutch on a stock tune 951 with a super light flywheel.
That somewhat depends. Advancing the timing wont hurt anything, but your cat probably wont like idling at 13:1. You could lean it out a bit and try idling at 14:1, but even that will technically effect the cat's lifespan because its going to want to be seeing stoichiometric. Its just that, with a batch fire engine, at an OVERALL AFR of 14:1, there will be some cylinders that will be leaner than this. In a 944 engine, this will be #4. #3 generally runs the richest, and the flow difference between #3 and #4 can be as much as 5%.
Yes I have the DME-tuner.
WB not hooked up currently though.
As far as vac lines goes, I am thinking of plugging the manifold ports and "re-arranging" the idle valve system to make it more accessible, don't really care what it looks like behind the airbox.
Let me know what end up doing with your lines, although you probably have less freedom because of CA emissions.
An idea I was bouncing off of Doug last night is to gut everything except the brake booster and FPR/damper. In order for a good idle, I was thinking of running an IAC from switched 12v separately from the aforementioned lines, mounted off to the side somewhere. It would not be part of the DME harness. It will ideally be a PWM stepper, but a binary "on or off" unit would be ok if that was the most feasible way to do it.
I am thinking that as long as my OEM auxiliary air valve is still in working order (which I am skeptical of) I will use that. If it ends up being even slightly sketchy, I am thinking about grabbing this and using a GM valve:
When I eventually get standalone, it will be easy to wire it in and have it controlled by the board. For now I would probably use the tach output wire and a DME common ground to send a voltage to an Arduino (I have one sitting around) and run a small harness from the Arduino out to the IAC. This will allow it to try and "maintain" a 950 rpm idle. When I'm on the throttle it will close, but when revs drop below a set threshold, it will open the valve until the threshold is met.
I've heard of people (racers usually) plumbing it such that they use an early 944 heater valve with the IAV hoses hooked to it, with a cable running into the cabin and they just use it like a manual choke on a carb.
I don't think the valve does a whole lot once the car is warmed up.
I've heard of people (racers usually) plumbing it such that they use an early 944 heater valve with the IAV hoses hooked to it, with a cable running into the cabin and they just use it like a manual choke on a carb.
I don't think the valve does a whole lot once the car is warmed up.
I knew a kid with an 83' that had it set up like that on a street car. Steel cable came through the firewall up to where the hood pull is. It worked, hella old school style. The same kid also had a second steel cable that passed through a hole he drilled in the floor pan, it controlled the butterfly valve in his exhaust cutout! N/A 944 at 6500 rpm + dumped headers = ouch. Whole lotta noise for not a lotta go lol.
BTW Spencer your sig quote about Luis is hilarious.
I've been out of town and just got back... first things first messed with the car and made some observations.
My vac system looks way more "thinned out" than I previously thought - the thermo valve (bunny ears) is already capped, and the only thing connected to my throttle body is a line which tees to the damper and FPR. Besides the aux air valve, I still have a few more mystery items under the manifold which I'll inspect in better light tomorrow. One looks like the picture Doug posted of an air control valve - almost dish-shaped, like the heater control valve.
Another interesting thing I noticed is a splice coming off the brake booster. It's a small line which then splits into two. One goes through the firewall (???) and one continues into a black bell-shaped thing where the cruise control mechanism would normally be, near the battery tray. I tried google image searching for it, but I couldn't find a single 944 engine bay with this in it, so I'm thinking maybe it's custom/aftermarket. It feels like a hollow chamber - maybe a resonator of some sort to dampen vac pulses?
The bell thing is a vacuum reservoir so your power brakes work with the car off a few times.
On 83 cars they were mounted by the CC. After that they moved it to behind the battery under the cowl...all 944s have it though.
Under the manifold the heater valve is in the back, the idle valve between #2/3, and there is the hose from the AOS which plugs into the J-boot that Ts with a smaller hose going to the evap system.
At the other vac port on the intake manifold should be connected the power brake assist hose, which Ts to the Jboot just after the AFM/MAF and has another T for the AC auxiliary valve.
Sure thing Spencer. On a stock car, the ECU commands ~5* of timing at 850 rpm. At my warm idle of 1000 rpm, my ecu is commanding 10.5* of timing which gives the motor significantly more torque. I'm up to 12.3* at 1100 rpm, 16-17* at 1400, and 20*+ at 1600+ rpm, depending on how gently I take off. In addition, the car is setup to idle somewhat rich, which is important because our motors; with their large bores and (in my case) semi-batch fire fuel injection; have issues with intake pulse reversion which has the effect of causing one or more cylinders in a given 360* rotation of the crank to run lean unless the motor is intentionally tuned slightly rich. Besides that, peak torque is not made at stoichiometric ratios, but at ~12.2:1-12.5:1. AFR. (I actually shoot for a little leaner than this, about 13:1-13.2:1)
Why were our cars not tuned like this from the factory? Simple.
1: It raises idle emissions in a way that would be significant to an OEM
2: It would quickly overheat and destroy a catalytic converter.
3: The car might not pass low speed emissions testing tuned in this way.
Everything about the factory idle is a series of compromises...its far from the best idle the motor is capable of. My factory stock N/A car feels like it has less torque off the line than my 951. Tuning goes a looooooong way. The secret is to add timing and add fuel.
Oh yeah, by the way this is all being said while my 951 has an 8 lb billet flywheel... yeah...try taking off with the clutch on a stock tune 951 with a super light flywheel.
coming back to this...how would changing idle fuel/timing affect stoplight driveability if you are off idle when taking off from a stop? unless you just let the clutch pedal out on its own to go?? wouldnt the normal way be to adjust low-load low rpm timing/fueling to take off nicer? depending on load/rpm the "takeoff" range on an NA-tune car is 23-28*...??
Sorry for copying & pasting what I just responded to someone else's thread but I've wanted to communicate this to you for a month or so Sausagehacker:
I have had a really rough *cold* idle problem. Tried new ecm & chip, New injectors, fuel reg & spark plugs/wires & idle valve has not helped. Cleaned grounds, No vaccuum leaks, adjusting the throttle and replacing tps hasn't helped. Interesting to note when I take needle nose vise grips & close off my icv to j-boot, then it smooths out.
Sorry for copying & pasting what I just responded to someone else's thread but I've wanted to communicate this to you for a month or so Sausagehacker:
I have had a really rough *cold* idle problem. Tried new ecm & chip, New injectors, fuel reg & spark plugs/wires & idle valve has not helped. Cleaned grounds, No vaccuum leaks, adjusting the throttle and replacing tps hasn't helped. Interesting to note when I take needle nose vise grips & close off my icv to j-boot, then it smooths out.
Interesting. You have a 88 right? The late cars have a different ICV system but they accomplish the same goal. My car also idles a little oddly, it seems like it's missing every 5-10 seconds. Runs great and never misses under load, but you can sometimes hear it miss...only at idle. New FPR, plugs, ignition switch, resoldered DME, running great gas, recently rebuilt injectors and throttle body... oh well. In my case it's probably a TPS idle switch issue, it's just so minor that I don't really care.
There was a thread somewhere about resealing the ICV, have you looked into that? In my case I got it working, but the valve closes too soon. So it'll idle at 1050 for about 1 min, then clocks out, so I idle at 800 for 3 mins, before the engine is warm enough to come up to 1000. I think there's a nut on it somewhere you can adjust.
guys..all this is very interesting..I find that "Hacker" has the right idea...Simplify and go. so, on another thought, what kind of AFR meter are you guys running? Want one on my early car so I can tune it better...Thanks, Tiger 03447
01-08-2015, 10:11 AM
