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View Full Version : Off-throttle Fuel Cut-off Prior to Corner Entry



Hemissary
07-22-2011, 02:16 PM
Some time ago I broadcast asking about whether it would be possible to simulate on our platforms a more traditional carb/cable linkage system where "off-throttle" truly meant off throttle.

The problem was that for various reasons (fuel emmissions for starters) the PCM takes it's time first cutting sufficient fuel then all fuel after the throttle butterfly has actually been requested to close (taking your foot off the accelerator pedal).

This meant that on a road course the higher the corner entry speed the less effective engine braking assist was. If you have huge aftermarket brakes like I do, it's less important. However the effects of engine braking become painfully evident if you get into someone else's ride and do some laps.

Johan from Diablosport agreed to help see if we could do something. Well, the end-result is what I wanted; to use engine braking like any other cable-driven road-course vehicle is capable of.

Now, from well over 240KmH I can go deeper and bring the land yacht into turn 1 off our very long straight-away effectively using engine braking, while putting less stress on the binders.

I won't comment what variables are altered, but talk to Johan about the the Road Course Deceleration Feature. This gentleman knows his craft well...thank you Johan.

MadCharger
07-22-2011, 02:20 PM
How does it act at low driving speeds - or is this a road course only tune?

Hemissary
07-22-2011, 02:38 PM
Normal drivability is not altered at all. At low driving speeds Decel Mode is even less noticeable; by this I mean the lower the entry rpm prior to Decel Mode the less effect....just like on a carburator-equiped vehicle with a mechanical throttle.

I doubt you will notice anything out of the ordinary during normal driving except that when you let off, it actually decelerates now. Just occured to me that quicker idle-entry and the resulting fuel cut-off might even save a smidgen of fuel. Those with widebands, you can actually observe the behavior.

Cruisin1966
07-22-2011, 02:40 PM
Okay, you've convinced me. Once the bumper on the Magnum is replaced I'll ask Johan about this tune mod for the off-white beastie

Adanac Charger
07-22-2011, 02:49 PM
Subscribed

joelvan
07-22-2011, 07:19 PM
Im interested in trying it.

lafrad
08-04-2011, 10:05 PM
yeap, easy to do. Just ask your Tuner to tweak your tune for it.


It IS a bit weird to have it kick in too aggressively in rain/snow... ABS can't speed your engine up.

MikahB
08-05-2011, 08:22 AM
Are you guys having problems with rear brakes overheating?

Reason I ask is that you really don't want your engine to be doing the braking for you - that's what your rear brakes are for. Engine braking only acts through the rear brakes (unless your car is AWD). So, if your engine is what's pulling the rear wheel speed down, then your rear brakes are not doing their job.

If you have proper front/rear bias WITH engine braking, it means you are lacking rear brake force without it and, thus, giving up speed and braking capability.

Adanac Charger
08-05-2011, 08:34 AM
Are you guys having problems with rear brakes overheating?

Reason I ask is that you really don't want your engine to be doing the braking for you - that's what your rear brakes are for. Engine braking only acts through the rear brakes (unless your car is AWD). So, if your engine is what's pulling the rear wheel speed down, then your rear brakes are not doing their job.

If you have proper front/rear bias WITH engine braking, it means you are lacking rear brake force without it and, thus, giving up speed and braking capability.

Just looking to shorten braking distance. If the brakes don't have to fight against the motor, they become more effective and you can go deeper into a corner before needing to get on the brakes.

Hemi31
08-05-2011, 08:35 AM
How does it act at low driving speeds - or is this a road course only tune?
your car won't engine brake? That sucks....mine does....must be the tuner;)

bigjim
08-05-2011, 11:06 PM
your car won't engine brake? That sucks....mine does....must be the tuner;)


Smart a$$

Mine is happy again, Johan rocks!

Hemissary
08-05-2011, 11:42 PM
So...how about some track feedback?

Those that actually track these platforms (any platform), let alone understand the significant benefits of engine decelleration into all but the slowest of corners...let alone late-braking shinanigans...engine braking plays an important role...it can also save money.

technically less pad wear...

Hemissary
11-19-2013, 06:29 PM
Update; also talk to Mike Doban at OST Dyno. He tweaked my set up to the point I'm down to 25KPa (can't remember area of the tune :^), engine braking performance is awesome...

Meech
11-19-2013, 07:03 PM
Very nice write up.

The Track Mistress is a driver running on the same set of pads as my first HPDE back in January 2012, last oil change, September 2013, I still have 2/3's pad thickness all around. My brake bias is set such that the car is very balanced, 52/48, or somewhere in that neighborhood. When I hit the brakes hard at the track, or on the street, it decelerates the drive train smoothly and efficiently, never had a problem diving into the right hander at the end of NJMP Thunderbolt or Lightning for that matter from 130mph to 90mph.

Rubber never broke loose, not even in the rain event, the car was very stable. I love the way the car handles the deceleration, torque management and all. Not sure what the specifics are and what my kPa values are, but does what I want it to do. My tune is done by Josh @ HHP. He spent a good amount of time tweaking the car to do what I want it to at the track.

Meech

Hemissary
11-19-2013, 07:18 PM
Agreed; the BAER monoblocks and 16" F / 16" R rotors on the Magnum are effortless as well. Maybe Johan has already tweaked your :^)