My 1988 LFX F40 build. (Page 36/68)
Daryl M JUN 04, 06:43 PM
In 6th at 60mph the engine will only be at just over 1600rpm. That may call for the vacuum booster auxiliary pump.
Joseph Upson JUN 04, 07:52 PM

quote
Originally posted by Daryl M:

In 6th at 60mph the engine will only be at just over 1600rpm. That may call for the vacuum booster auxiliary pump.



I believe it's pretty important, especially if the OE PCM is used, currently there is a recall regarding the vacuum assist pumps used on a number of GM trucks and SUVs as a result of stopping difficulties and accidents resulting from vacuum assist pump deterioration and failure. It's a different style of pump, but none the less an assist pump. VVT coupled with direct injection apparently allows for cam manipulation that results in higher performance/emissions goals to be achieved, although with additional supporting equipment, such as the electric pump. I do not believe it is used on any of the port injected 3.6L.

I've been logging my cam angles in tables setup in HPTuners and every degree of camshaft variability available appears to be used. The cams are closest to the overlap point at low rpm, part throttle input.
mender JUN 04, 09:36 PM

quote
Originally posted by Daryl M:

In 6th at 60mph the engine will only be at just over 1600rpm. That may call for the vacuum booster auxiliary pump.



I missed that you were using a 6 speed. You're correct, the pump is a good idea.
pmbrunelle JUN 04, 09:49 PM
I understand that when you're cruising at 1600 RPM at 60 mph, there might be little engine vacuum.

However, assuming that you lift the throttle before braking, won't you get back your vacuum due to the closed throttle?
Daryl M JUN 05, 12:41 AM
I don't know what happens with vacuum on the lfx when decelerating. I think I am going to use the electric pump in addition to engine vacuum . With proper placement of check valves, it shouldn't hurt. I can monitor vacuum under normal driving conditions to see if the auxiliary pump can be removed later.
Daryl M JUN 05, 12:46 AM
Not to change the subject, but I have been looking at options for front springs. What are thoughts on methods for lowering the front by 1-1.5 inches? Are springs available? Can stock springs be trimmed ? Thoughts?
Joseph Upson JUN 05, 06:35 AM

quote
Originally posted by pmbrunelle:

I understand that when you're cruising at 1600 RPM at 60 mph, there might be little engine vacuum.

However, assuming that you lift the throttle before braking, won't you get back your vacuum due to the closed throttle?



That's the beauty and pain of these modern systems. The PCM makes decisions on how to apply pedal input. For starters, you may only be allowed to cruise at 1600 rpm at very low speed/gear where engine generated vacuum may not be an issue. At higher loads approaching lugging the motor in an auto, the PCM may not allow it to that extent. I've encountered this when shifting the auto manually, where an upper and lower limit is set to what I can shift to relative to rpm. Also remember there is no EGR valve, so the cams are being used to this effect quite frequently which is likely where the low vacuum conditions are most prominent. It is correct however, that at times when the PCM is in efficiency mode, it may allow a good bit of throttle input before kicking down a gear, but that falls into adaptive territory. For those not aware of this, the PCM has adaptability and can change performance characteristics based on driving habits, although I'm not sure if the feature is active in all platforms. If you drive the car aggressively, shift characteristics will change to compliment it. Much of the drivetrain performance can be changed in the tune, but the transmission parameters appear to be more complex than the engine management as far as what to change and how. The modern PCM calibrations make OBD I look like the simplest of arithmetic. It's anything but straightforward.



quote
Originally posted by Daryl M:

Not to change the subject, but I have been looking at options for front springs. What are thoughts on methods for lowering the front by 1-1.5 inches? Are springs available? Can stock springs be trimmed ? Thoughts?



Be very careful here in order to have a good outcome. I first tried Eibach lowering springs that were said to be 1" drop. I had 225/40R18s on the front. The car seemed to have more like a 2" drop. The bump stops had to be cut for this. The stock style shocks could not prevent the car from bottoming out which eventually ate away at my wheel well dust shields. I eventually removed them and cut about 3/4 of a coil from the stock springs and was much happier. If you can get stronger shocks you shouldn't have much of a problem, but OE grade equipment probably will not cut it. Also keep the tire size in mind using what I listed as a trouble spot for me. I had 18x8" front wheels and did not want to go to narrow on the tire so that did not help my situation with the Eibachs which were made around OE wheels and tires.

[This message has been edited by Joseph Upson (edited 06-05-2020).]

Daryl M JUN 05, 07:00 PM
Joseph, did removing 3/4 of a coil give you the drop you wanted? I am also planning on 18s.
Joseph Upson JUN 05, 07:42 PM

quote
Originally posted by Daryl M:

Joseph, did removing 3/4 of a coil give you the drop you wanted? I am also planning on 18s.



Yes it did, my shocks started working again and the tire stopped touching the fender area. I installed homemade coil overs on the rear.
Daryl M JUN 05, 09:43 PM
Joseph, after cutting the springs, did you heat and bend the end to flatten it?

[This message has been edited by Daryl M (edited 06-05-2020).]