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not sure what was done regarding the TB plenum
splitter and pre TB air splitter?
I dont see a pre-TB splitter anywhere.
a bit surprised that more have not jumped on this one? maybe I am missing something?
It's a giant PITA.
a short time ago I was helping a friend work on his 1997 jaguar xk8. the pedal response on that 4 liter was almost annoying! touch the pedal
and the car shot off the line like a rocket. I would like to move the needle more in that direction, and from what has been written, it seems as
if this might accomplish just that.
May have been a direct ratio throttle as well, the 928 is on a (initially) constantly reducing radii cam so that from a stop the throttle plate moves very little.
It's a GT car, not meant to be a wound up emotional basket case of a car to drive. I switch to my wife's MS3, and people are rockin in their seats when I drive it..its just made to BE different for specific reasons...and it will feel different. A lot of torque on a fast throttle is anything but smooth from a stop. It's also why we start from a stop in 2nd gear.
I cant find a good photo, but if you look at how the throttle assy works, you'd see it.
...good or not?? might be interesting to investigate further...but is it really worth it...like speedtoys mentionned this car won't appear in any Ken Block vidéos...
I can’t say that the throttle felt much different after I carried out the modifications as per OP’s feedback. My modifications also included the lower manifold air splitter.
in my mapping programme I’ve discovered the reason the ignition map has a ramp coming off a closed throttle. That is to make the acceleration more progressive and less hair trigger like. I’ve ended up reducing my ignition values under 2k rpm and pulling back values up to 37% load higher up to improve drivability.
Im not sure how my results translate to stock but I’d guess that adding some ignition advance at low load off closed throttle would perk things up more than changing the manifold.
Sharktuning is the same for any/all modifications.
Fine tuning the fuel map to optimum AFR levels at WOT, and to a lesser degree managing spark timing for optimal HP output...but fuel is most of the effort done with a ST.
Yes, with the sharktuner. I’m remapping for ITBs, a steep but achievable learning curve. The Sharkplotter program is invaluable for setting the fuel values.
And for what it’s worth running richer than stoich seems to improve the part throttle responsiveness as well.
^^^^are you also using an adjustable FPR, or no need with ST? and you are getting better pedal response?
No need, assuming the injectors are large enough.
Remember that the stock intake has a cam arrangement between the throttle plate and the cable, so that initial pedal travel has a small effect on throttle opening, increasing rapidly as the pedal is pushed down. This is the major component of throttle response, and is done for driveability. Perfect when the sheriff is behind you, but can be frustrating at other times. Just push the pedal farther.
Some throttle arrangements-- such as Nick's ITB's-- have a much more direct-acting throttle. For example, if pushing the throttle down 20% opens the throttle 20%, then at low-ish RPM that's a lot of air. We had an Audi (A6 allroad 4.3L v8) with that characteristic-- odd, since it was a fly-by-wire throttle-- and it was a real nuisance to drive smoothly. And Greg's prototype plenum intake had a direct-acting 4" throttle plate. We had that on our GT (in 5.0L trim) for testing and it was a real handful around town. If you weren't first at the traffic light you had to remember to wait for room ahead-- there was no such thing as a "leisurely" takeoff.
Nick's technique of backing off timing in that situation is a good one, but I think that is only needed for alternative (direct-acting) throttle arrangements.
One thing that would be interesting to try is re-sculpting the cam arrangement on the stock throttle for more opening with less pedal travel.
There may also be some lag with the MAF when opening the throttle a bit at part-throttle, but that may also be the requirement to run the part-throttle mixture at 14.7:1 to keep the cats happy (if so equipped).
So many variables, so little data
Remember that the stock intake has a cam arrangement between the throttle plate and the cable, so that initial pedal travel has a small effect on throttle opening, increasing rapidly as the pedal is pushed down. This is the major component of throttle response, and is done for driveability. Perfect when the sheriff is behind you, but can be frustrating at other times. Just push the pedal farther.
Some throttle arrangements-- such as Nick's ITB's-- have a much more direct-acting throttle. For example, if pushing the throttle down 20% opens the throttle 20%, then at low-ish RPM that's a lot of air. We had an Audi (A6 allroad 4.3L v8) with that characteristic-- odd, since it was a fly-by-wire throttle-- and it was a real nuisance to drive smoothly. And Greg's prototype plenum intake had a direct-acting 4" throttle plate. We had that on our GT (in 5.0L trim) for testing and it was a real handful around town. If you weren't first at the traffic light you had to remember to wait for room ahead-- there was no such thing as a "leisurely" takeoff.
Nick's technique of backing off timing in that situation is a good one, but I think that is only needed for alternative (direct-acting) throttle arrangements.
One thing that would be interesting to try is re-sculpting the cam arrangement on the stock throttle for more opening with less pedal travel.
There may also be some lag with the MAF when opening the throttle a bit at part-throttle, but that may also be the requirement to run the part-throttle mixture at 14.7:1 to keep the cats happy (if so equipped).
So many variables, so little data
11-25-2018, 07:54 PM
