PorKen

Forget what I 'imagined' in the previous comparison posts.

With near identical air temp (a little higher) and pressure (blue line is manifold vacuum), compared to -8°, there is no loss at ~2800, and a gain, starting at ~4500. Properly tuned to suit, it is also faster (higher rpm vs. time - thank goodness, after all the hassle).


The bumps in airflow at the rpm peak are where the rev limiter kicks in. This is interesting to see, as it shows how much airflow is possible when fuel (& exhaust?) is removed.


I drove around a bit in celebration, actually using 1st and 2nd - which I'm not used to because I do all the WOT runs in 3rd/4th. OMG! 1st is all tirespin, 2nd spun the tires when it hit 5000 or so, and it just keeps accelerating madly until the rev limiter hits.

PorKen

Having finished the tune for a 92 octane chipset for both manual and automatic, I decided to try 87 octane with the -12° cam retard.

Instead of a 'huge' amount of ignition advance using 92, I figured it would be better to just run the faster burning lower octane 87 with the lower dynamic/corrected compression ratio. Still many degrees advanced over the 92 octane chip for 0° cam, 87 performs well so far on the auto.

More notes
- Idle vacuum is ~18", down from ~20" at 0° cam.
- Highway cruise is exceptionally quiet and smooth (X-pipe)
- I tightened the Bowden cable 2 turns for a higher shift point.


I haven't been able to go a full tank with 'regular' driving, so I'm still not sure about mileage, yet. (Nearly all WOT runs. On my auto, I realized that I had neglected checking the brake pads; they were so worn, the front calipers were stuck, brakes on all the time... )


The idle has a 'tick', but if I can run 87 octane, get better mileage, and higher performance, I'm sticking wit' it. (Almost $4 a tank cheaper, 87 vs. 92!)

GlenL

How about 16V engines especially Euro S cams?

I thought you were working on an adjustable 16V sprocket but I don't see it on your website.

Maybe I should go back into the offset key setup and make both sides late by 3 degrees and see what happens.

dprantl

So it seems that with the cams at -12 degrees, you get more top-end power with minimal effect on low-end torque, better cruising gas mileage and little to no effect on emissions. I am curious why the cars would not be set this way from the factory if there were no downsides to doing this?

Dan
'91 928GT S/C 475hp/460lb.ft

PorKen

Glen - not sure how far the big 16V cams can be adjusted ± safely, or if they would show the same effect.

From what I read on the internets, a cam that makes more HP with >4° retard needs more duration. IE. S3 cams aren't big enough for the engine.

Note the tools I made for the 16V->32V gear conversion could only show ± 0°, 4°, 8°, 12° (crank°) because of where the marks are on the rear cover.




Dan - there may be some increase in HC, as there are frequent 'misses' at idle/low rpms with this much retard, but NOx should be lower.

This setup is not ideal, and may only work well if the engine is at peak tune. It is very sensitive to AFR at low rpm. -8° had much better idle quality. -10° may be a better tradeoff overall, and is easy to adjust to. I am running non-resistor plugs with a 1.0mm gap, which probably helps keep the -12° reasonable. Not sure how it would run with stock gaps.

'Customers' would probably rather have a nice idle and generous torque off the line. Newer cars with variable valve timing have much more radical advance and retard for the best of both.

PorKen

Cold start/run is better with 87 octane, less ignition advance, at -12° cam retard.


I'm going to take another leap and say that instead of increasing the ignition advance, a similar benefit could be had, up to a point, w/o custom EZ programming, by lowering the fuel octane rating, while increasing cam retard.

EG. normally require 92 octane at 0° cam, then:
08-10° retard use 89 octane
10-12° retard use 87 octane


Note: Your Retard/Octane May Vary!

PorKen

The only thing I have to get over now is, sheepishly telling the attendant (can't fill your own gas in OR) to fill it with Regular, instead of being Mr. Cool w/Supreme.





Too much trouble to try to explain cam timing, tuning, etc...

antlee928

So I have read most of this interesting thread and do not profess to understand all the ins and outs of the cam timing. Can someone suggest the most appropriate cam timing configuration for a ROW (Australian) S4 MY89 Auto that runs always on 98 octane fuel. It has Roger's X-pipe and hi flow cats and standard exhaust system cat back - small resonantors and standard rear muffler. The rest of the car is standard. My interest is more faster throttle response and quicker acceleration through the geear and particular in the mid-range. Given our draconian and myoptic speed limit laws in this country (speed kills ya know........any speed) top end is not so important other than for bragging rights. I do not track or race the car and much of its mileage is highway/freeway (80%).

So should I stay with factory standard cam timing or is there something a better?

cheers

Bill Ball

Unless you can tune ignition timing, I would just keep the stock cam timing. Every S4 I have seen with retarded cam timing ran lousy and had terrible throttle response and responded very well to being put back to stock cam timing.

antlee928

Hi Bill. so if I were to use Sharktuner to refine the existing factory tune and also ignition timing. Would this be the trick?

Cheers

Bill Ball

That's what Ken did although I don't know the specifics of his ignition timing changes. I wouldn't know what this will do with your configuration.

dprantl

My understanding of the process is:

- Retard cam timing
- Advance ignition timing
- Increase fuel in fuel map

A way to modify ignition and fuel maps, as well as a wbO2 to monitor AFR is mandatory for this to work IMO.

Dan
'91 928GT S/C 475hp/460lb.ft

Bill Ball

What Dan said.

I have x-pipe , no cats, stock maps. I have not tried doing the cam retard with all the extra fiddling. The car seems fine on stock maps. Fueling is good according to WBO2 I have. Don't have a Sharktuner and don't have the money for all the dyno time to determine if some other settings might produce some more power.

PorKen

What Dan said... if you continue using Super (92 AKI/98 RON).


87/89/92 octane all have the same energy potential, just different burn rates. Retarding keeps the intake valve open longer, letting the engine breath better, but lowers the effective compression ratio, so a lower octane/faster burn rate must be used to keep the ignition advance constant for best power.

Conceptually, it has been difficult for me to accept 'Regular' but I'm getting used to it.


My '86.5 auto has much more useable power running on 87 octane at -12° cam retard. After further logging, the LH and EZ chips are now very little changed from my normal 92 octane chipset. The main change is using the gears more, requiring just a little tightening of the Bowden cable, and hitting the kickdown switch more often.

I imagined that the (small) loss of low end torque would be a bad thing on the auto, but the auto changes gears so quickly that it has proven to be nicer to drive than my manual trans car.


S4-up stock WOT fueling is over rich, the LH manages it's own idle speed, and the EZK knock sensor loop should manage what I've had to do by hand. If I had a S4/GT, I would reset the ECUs and try ~8° retard, with 89 octane (95 RON).

It would be nice to have a SharkTuner to see the knock count, if you want to use 87 with even higher retard.

PorKen

More on downshifting... the tighter Bowden cable will knock it down a gear sooner, but nothing special happens most of the time from that. You think you've hit the floor because it's kicked down once, but push a bit more, and it's like a supercharger kicked in.

2nd gear goes to 80+ mph (130 kph), there is big jump in torque over 5000 rpm (see -8° dyno), HP keeps climbing higher and higher with rpm, so merging is a lot more fun. With less compression, it revs easier too, so it doesn't sound like the engine is going to 'bust a nut' when it kicks down to 2nd at 60+ mph.

BTW, I'm switching to 15W50 M1 on the auto... I have been running 10W40 up until now, because I so rarely rev'ed it very high.


Come to think of it, (early) S4s might be able to run less retard for 89 octane, as they have less static compression, IIRC. (S3 and GT are true 10:1.)