924Board.org

[fblade]

Found the link to lildudes solution https://www.924board.org/viewtopic.php?t=44931&start=0&postdays=0&postorder=asc&highlight=

Can't find the other one but will keep looking

[924RACR]

Thanks for the tip; I'll have a look at the ignition side of mapping then, probably is some room to play there. Down low in the revs/high vacuum etc, I've mostly been focused on idle speed control... hadn't really thought about the tip-in behaviour...

Yeah, I drove my 931 many years with the stock DITC and CIS, and it always had that characteristic, had to be extremely careful feeding the throttle in off a slow crawl to not get any jerk...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Beartooth]

I'd also have to agree that the difference between sequential and batch or continuous injection probably isn't going to improve on/off throttle transients. Sequential injection helps with atomization, mostly at idle and light throttle where it can take advantage of the intake pulse to compensate for limited airflow. Without the "assist" of being able to time it, batch and continuous setups have to add more fuel to maintain smooth running at idle and off-idle. At mid and full throttle, you have a bigger slug of air being pulled past the valve, which helps pull any puddled fuel in, and also add to the swirl and turbulence during compression. That's why most of the advantage of sequential is at idle and off-idle, as I understand it.

That said, even older setups can be pretty smooth: my Mercedes is pretty close to more modern cars off-idle. It is a newer setup (CIS-E) and very much engineered around smoothness, but it's pretty unsophisticated compared to a new car, and shows it can be done. It's a single butterfly, but the throttle linkage is progressive with a lot of pedal movement for the first bit of throttle opening. Anyway, to echo kondzi and Cedric, the ignition and drivetrain have a lot to do with it. I suspect fiddling with the fueling setup would give you some improvement too; there's definitely ground to make up, it just depends on how much you want to tweak on it. I doubt it would ever compare to a new car, but that's part of what I love about the old stuff: I do my best to get the most from the limited systems, then drive around the rough spots. I always get the sense in a new car that it's trying to out-think me; with the old stuff, there's no question who the real ECU is!
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1980 931 diamond in the rough

[Shurick]

Cam sensor can be placed on a timing belt cover with a reference mark on a cam gear: make a threaded hole and put a stud inside. It may be a goof idea to replace bushings that hold belt cover with some solid shims to make more stable gap between sensor and reference mark.
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WBR, Shurick
'79 931 -- intercooled K26-3060-6.10 turbo @ 1.2 bar, EFI+EDIS, 951S brakes, stripped interior, 951 look.
'86 924S -- R.I.P.
https://www.instagram.com/ru_pacecar/

[safe]

Cam sensor reading a tab on the wheel works good, I would mount the sensor rigidly.
Sequential or batch fire, that's more emission than something else, doesn't affect the overall performance.

I run my 924 sequential and my 911 3.2 as batch. Both have separate coils and no distributor.
One thing to maybe consider, the ECU in my 924 is a bit limited on inputs. In hindsight skipping the cam sensor for a wheel speed sensor would have been more usefull. Maybe I'll upgrade the ECU instead.
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/Magnus, Stockholm Sweden
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Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe

[kondzi]

More than enough inputs in my ECU fortunately

Found my adjustable cam gear. It will be easier than I thought.

I will use one longer bolt and a nut from the back side. VR sensor plus a bracket to the head or so et voila



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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)

[Shurick]

safe one more consideration is injector flow and dead times. For example it's hard to get good idle with Siemens-Deka 630 cc injectors on 2 liter engine in batch mode. More modern Bosch Motorsport 630cc injectors are much faster though. =)
_________________
WBR, Shurick
'79 931 -- intercooled K26-3060-6.10 turbo @ 1.2 bar, EFI+EDIS, 951S brakes, stripped interior, 951 look.
'86 924S -- R.I.P.
https://www.instagram.com/ru_pacecar/

[safe]

[kondzi]

980cc
I was taught injectors should be at 80% of their DC when engine is maxed out. High impedance ones. This means around 500HP at crank?
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)

[safe]

[madislandguy]

[kondzi]

Nah, that way I’d need to bore a hole in the cam cover. I prefer adding stuff than destroying. Timing gear and a nut will work like a charm.
I built an engine for a friend’s Ford Capri (2.3L I4 bottom and Escort RS2000 Head and there was stock VR sensor in the cam cover, so this works fine in general).
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)

[Shurick]