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here is the Mclaren MP4/4 setup. they did have boost control in the cockpit, but they were running more than 6.5psi they were only allowed 150liters of fuel, so they weren't running full boost all of the time
Just thought I should update this thread with some results of my experiment with the 3psi springs. During this past spring/summer/fall, I've done a bunch of road tuning to setup closed loop boost control with my Link G4+. To spare you all a long back-read, here's the back ground on my single turbo FD setup and what I'm trying to accomplish:
Setup a "daily driver" boost profile that controls boost at a consistent 10psi maximum boost, and a "full power" profile does the same but up to 15psi max boost or 400RWHP, whichever comes first. I don't need or want more than 400RWHP on my FD.
Turbo is a BW S300SX-E series, ~87mm compressor, & ~76mm turbine wheels, 1.0 A/R turbine housing,
Welded stainless Turblown engineering manifold with the WG placement & orientation optimized for WG function.
Dual 40mm external TurboSmart Gen IV Comp 40 (40mm) WG's that recirculate back into the 3" downpipe near where the DP bends to enter the mid-pipe section. The dumps both enter the DP at a 90* angle, so I'm getting too much back pressure in the dump piping,which tends to keep the WG closed beyond spring tension (when running on springs alone). Crappy design, but I'm stuck with it unless I pony up the cash for an expensive fabrication job.
To try to work around the less than ideal WG dump piping problem, I tried a few lower tension WG springs to see if I can get the boost control response where I wanted it. Recall that with the 7psi springs, I was seeing in excess of 10~11psi boost with boost control disabled (i.e., 0% boost solenoid duty cycle/springs alone). I tried and extensively road tested/tuned the 3psi springs, and the bottom line is those springs alone will keep max boost under 7~8psi. Enabling and tuning closed loop boost control with those springs met my "daily driver" mode goal with a 10.2psi boost target, but the boost solenoid duty cycles required to get there and hold boost consistently was up to 70~80 % when the closed loop PID corrections were factored in. Which basically means is for my high power mode (target 15psi boost), I'll run out of duty cycle before I get there.
Here's one of my old logs showing the "daily driver" boost control profile in action. In this particular log, I was still about 1.3psi short of my 10.2psi boost target (24.9psi MAP), and the DC % was at 44%, once PID corrections were accounted for. Subsequent pulls/tuning iterations closed the gap and consistently got me to the 10.2psi boost target, with excellent spool up response and consistent boost in various conditions across the 3 seasons (spring/summer/fall), but as I mentioned, I'm already up to 70~80% DC to get there.
Since the car is running so well now with the low boost/daily driver profile, and the weather is still nice enough to drive it, I'm holding off on messing with it further until winter hibernation to deal with the high boost profile. Couple of questions to further sort this out:
1 - If I retain the WG solenoid plumbing as-is (see diagram below), and swap in the 5psi springs, do you guys think I'll have enough control flexibility to net the low & high power modes after re-tuning CL boost control? Recall that 7psi springs alone would boost beyond 11psi, 3psi springs alone could hold it down to 7~8psi max, and 5psi springs are unknown at the moment. Figure that as long as the 5psi springs alone keep max boost CLOSE to 10psi, I should be able to get good CL control of the low level mode with smaller DC %, maybe 40~50% max, and I'd have enough head room to do a high power/15psi target at something around 70~80% DC?
2 - Does the brain trust think I can get the desired level of control for low & high power boost target modes by altering my 3 port boost solenoid plumbing as shown below without running out of duty cycle? Or perhaps switch to a 4 port solenoid?
it does sound like 5psi springs would work, if the 3psi does 7-8psi, and 7psi do 12. 5psi would be right in the middle.
it is probably not going to be that linear,
but you could compromise, probably. maybe in DD mode it doesn't open the throttle 100 all the time?
keep 3psi spring with 4-port solenoid control setup
I have no experience with 4-port but my reading about it I've learned it works for lower base spring while enabling higher boost but it is very sensitive to duty cycle changes and has to be tuned with more care/precision, hard to control in closed loop but ok in open loop.
I've heard mostly bad things about 4-port boost solenoids, they tend to be too touchy with lots of overshoot and undershoot.
I've heard mostly good things about adding a second 3-port solenoid and configuring it to vent pressure from the bottom port of the wastegate. Basically controlling the two paths that would be present in a 4-port setup, but only venting the bottom port of the wastegate when the boost target is very high. It's hard to find a diagram or drawing showing an example, but I think this is the configuration I've heard good things about: https://forums.linkecu.com/topic/175...boost-control/
it does sound like 5psi springs would work, if the 3psi does 7-8psi, and 7psi do 12. 5psi would be right in the middle.
it is probably not going to be that linear,
That's what I'm thinking, the 5psi springs should split the difference. Obviously I'll need lower DC's to hit the lower boost target, and I should have enough DC head room now to hit the higher target. If it wants to creep beyond the low target or high target, I've already built in an over boost protection that relies on the DBW throttle that works well
Originally Posted by j9fd3s
but you could compromise, probably. maybe in DD mode it doesn't open the throttle 100 all the time?
^That's an interesting approach that I haven't even considered yet. I've been using the DBW throttle as a reactive over boost protection scheme, but you're suggesting it can be used proactively - if you prevent WOT from happening in the first place, you should be able to limit boost from the intake side.
Originally Posted by neit_jnf
5psi spring current control setup or
keep 3psi spring with 4-port solenoid control setup
I have no experience with 4-port but my reading about it I've learned it works for lower base spring while enabling higher boost but it is very sensitive to duty cycle changes and has to be tuned with more care/precision, hard to control in closed loop but ok in open loop.
^That's what I understand for the 4-port solenoids, they tend to be very touchy with CL control, tiny changes in DC result in wide swings in boost up/down. With my existing 3-port solenoid, I've found that the Link does a fine job of closed loop boost control - boost comes up fast & linear in all gears, and the boost control vs. target over time and ambient conditions is tight. Given that, I'd rather not revert to open loop control. Plus it was fairly easy to road tune the CL controls following a slick method I picked up from Evans.
Originally Posted by scotty305
I've heard mostly bad things about 4-port boost solenoids, they tend to be too touchy with lots of overshoot and undershoot.
I've heard mostly good things about adding a second 3-port solenoid and configuring it to vent pressure from the bottom port of the wastegate. Basically controlling the two paths that would be present in a 4-port setup, but only venting the bottom port of the wastegate when the boost target is very high. It's hard to find a diagram or drawing showing an example, but I think this is the configuration I've heard good things about: https://forums.linkecu.com/topic/175...boost-control/
Same here, I've seen an Evans video where he describes the dual 3-port solenoid approach, will need to revisit that. The only downside to that is it would consume my last available 3D PWM controllable AUX output to support the 2nd boost solenoid. Was trying to reserve that AUX for a future integrated water/meth injection system.
So I have a game plan now:
1. During winter hibernation, swap in the 5psi springs. During the spring thaw, get out & road tune the closed loop boost control for my low & high targets. Might have to defer the high boost target tuning for the dyno, or track time, as it's too easy to run out of road or get arrested doing that on the public roads near me.
2. If it still looks like I'm going to run out of DC % to do my high target with 5psi springs & existing 3-port solenoid in CL control, then consider doing the dual 3-port CL control approach.
So I have a game plan now:
1. During winter hibernation, swap in the 5psi springs. During the spring thaw, get out & road tune the closed loop boost control for my low & high targets. Might have to defer the high boost target tuning for the dyno, or track time, as it's too easy to run out of road or get arrested doing that on the public roads near me.
2. If it still looks like I'm going to run out of DC % to do my high target with 5psi springs & existing 3-port solenoid in CL control, then consider doing the dual 3-port CL control approach.
12-19-22, 09:15 AM
they were only allowed 150liters of fuel, so they weren't running full boost all of the time
