Variable exhaust valve (PKVEV)
01-28-2016, 01:54 PM
#16
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FYI, these valves let me address a pet peeve with 2.5" X-pipes - they don't fit the stock exhaust well. With all of my X-pipes I ended up Dremeling four slots in the ends and use a 2-1/4" muffler clamp to secure it.
Since I was cutting off the ends anyway, I used some adapters on the outlet side of the valves which slide INTO the stock cat-back. 2" ID (roughly 2-1/8" OD) fits perfectly into the stock cat-back but I had to flare the 2.25 ID section a bit more to fit the 2.5" ID valves.
If I were to do it again though I would have an exhaust shop make them for me. The 2" ID section needs to be at least 1/2" longer to seal properly, well past the end of the slots.
There must be some kind of damping built into those to absorb the individual pulses?
Since I was cutting off the ends anyway, I used some adapters on the outlet side of the valves which slide INTO the stock cat-back. 2" ID (roughly 2-1/8" OD) fits perfectly into the stock cat-back but I had to flare the 2.25 ID section a bit more to fit the 2.5" ID valves.
If I were to do it again though I would have an exhaust shop make them for me. The 2" ID section needs to be at least 1/2" longer to seal properly, well past the end of the slots.
There must be some kind of damping built into those to absorb the individual pulses?
01-29-2016, 06:27 PM
#17
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Ugh. I suppose it's fate. The delay-valve I received was not what was advertised AND it has no delay (broken). Other ones on ebay are $20.
The 996 'change over valve' is only $25 at my local parts place so I guess I'm going di-rectly to programming.
99660512301 = Pierburg 722280020
The 996 'change over valve' is only $25 at my local parts place so I guess I'm going di-rectly to programming.
99660512301 = Pierburg 722280020
01-30-2016, 06:27 PM
#18
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That's cool. Works pretty well right outa the box. I hooked it up just like it was, using manifold vacuum not stored vacuum, and the LH modulates the vacuum valve nicely. (Using manifold vacuum ensures the valves will open as manifold pressure decreases with load.)
Definately more grunt from idle-up. Feels like a stroker...without the expense (financial and mental) of a visit to GB.
The tank vent program (never bothered to see how it was coded before) keeps the solenoid open (full vacuum, X-valves closed) until the coolant is warm. After that, when the throttle is opened there is a delay of a few seconds then the solenoid progressively closes (X-valves vent & start to open). Around 2000 rpm the X-valves are fully open.
All I might have to do is reduce the frequency (divide by two is easy) so the valve opens a bit slower and maybe reduce the (acceleration?) delay a bit.
First, I'm going to slap on some big-mids and my RMB again, so I can hear the action better, and do some more testing.
Definately more grunt from idle-up. Feels like a stroker...without the expense (financial and mental) of a visit to GB.
The tank vent program (never bothered to see how it was coded before) keeps the solenoid open (full vacuum, X-valves closed) until the coolant is warm. After that, when the throttle is opened there is a delay of a few seconds then the solenoid progressively closes (X-valves vent & start to open). Around 2000 rpm the X-valves are fully open.
All I might have to do is reduce the frequency (divide by two is easy) so the valve opens a bit slower and maybe reduce the (acceleration?) delay a bit.
First, I'm going to slap on some big-mids and my RMB again, so I can hear the action better, and do some more testing.
02-01-2016, 09:56 PM
#19
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Yay! It works great. Even with just big mids and RMB, it is quiet at idle and takeoff (this is the worst with a big exhaust, IMO). Going up through the revs it gets progressively louder depending on how far I push the pedal. At a leisurely pace up through the gears it provides just a gentle rumble.
I did not have to code anything except to bypass the delay (and remove an addition to the fuel pulsewidth*), everything else was already programmed for the vent function. I doubled the timer for the opening-by-rpm slope and adjusted the existing (but zero'ed out) open times for deceleration, idle, and warmup. Full open in neutral doesn't happen until over 3000, but with more throttle it opens sooner.
It runs excellent right from cold start. 2nd gear starts, even somewhat uphill are no problem. (With the 2.20 diff this means I can roll out much faster without the first gear switch.) Why it is so much better from 600-2000 I cannot say for sure, yet. It could be better mixtures with pulse tuning or gas velocity or more ignition timing because of the EGR effect. When I have time again I can do some logging and perhaps figure it out.
Eventually, I'd like to make the opening times mapped by rpm and load. For example just before 2000 it could be a little quieter at low loads, at higher loads or WOT it could open faster.
*Fuel is progressively added to make up for the size of the air leak from the vapor recovery system, unread by the MAF.
I did not have to code anything except to bypass the delay (and remove an addition to the fuel pulsewidth*), everything else was already programmed for the vent function. I doubled the timer for the opening-by-rpm slope and adjusted the existing (but zero'ed out) open times for deceleration, idle, and warmup. Full open in neutral doesn't happen until over 3000, but with more throttle it opens sooner.
It runs excellent right from cold start. 2nd gear starts, even somewhat uphill are no problem. (With the 2.20 diff this means I can roll out much faster without the first gear switch.) Why it is so much better from 600-2000 I cannot say for sure, yet. It could be better mixtures with pulse tuning or gas velocity or more ignition timing because of the EGR effect. When I have time again I can do some logging and perhaps figure it out.
Eventually, I'd like to make the opening times mapped by rpm and load. For example just before 2000 it could be a little quieter at low loads, at higher loads or WOT it could open faster.
You have me thinking here. What if it is placement that causes changes. What if the variable valve was placed further downstream where the exhaust cools and becomes denser? The goal in every well flowing exhaust is to keep it 'hot' as exhaust is less dense based on temperature. Cooler particles, slower exhaust flow.
Last edited by PorKen; 02-02-2016 at 02:10 PM.
02-02-2016, 02:32 AM
#21
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I'm not sure it is something I can dyno (although I will surely try eventually) because of the low rpms and part throttle. I really doubt it could raise the torque peak at 3200-ish and won't do anything for HP at 6200-ish. I am curious to see if (highway) mileage might improve.
I did not see a difference in HP between the factory S4 muffler and a RMB. The big mids offset the weight of the RMB, so that's a wash too.
It's mostly a driveability thing. Same power, less (unpleasant) noise around town driving 'normally'.
I did not see a difference in HP between the factory S4 muffler and a RMB. The big mids offset the weight of the RMB, so that's a wash too.
It's mostly a driveability thing. Same power, less (unpleasant) noise around town driving 'normally'.
06-14-2018, 09:40 PM
#24
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The old hack of the stock LH code didn't control idle, decel, and low load/rpm cruise very well so I had gone back to running the stock muffler. 
Inspired by (this variable muffler thread) I wrote brand new code for the gas-tank-vent solenoid, adding more and more logic until it was perfect. Now, I'm back to running just big '87 mids and my custom RMB. Except for deceleration and heavy throttle, it is as quiet or oddly quieter than having the stock rear muffler. It does not run hotter and does not feel restricted, even at low rpm cruise, where the valves are nearly closed (at idle vacuum). It responds immediately to full throttle and pulls very strongly through the full rpm range.
I need to dyno it to see if I'm imagining more torque, but just the 'sound-on-demand' is very nice (and weight savings). I may try running going back to just the small '88- mids, next.
--
I'm running the valves at ca. the following openings - at full idle vacuum.
More load = less vacuum = valves open more.
95% closed - idle
99% closed - cruise <1400
95% closed - cruise <2100, low load (higher if ac clutch)
80% closed - cruise
60% closed - heavy throttle
40% closed - WOT <3700
fully opened - WOT
fully opened - decel
Without the extra restriction, idle to 2000 rpm at part throttle is pretty noisy and makes driving annoyingly slow around the neighborhood (or driving Ms. Daisy).
Decel needs to be full open to stop an annoying rattle and so that it doesn't close during gear shifts which causes a horrible bog. (With seperate control of decel vs. idle I was able to delete the limiter washers in the pictures above.)
I was surprised in testing that restricting WOT at lower rpms seems to make it pull harder. WOT is unrestricted at high rpm though because with the stock intake, exhaust manifolds, etc. vacuum levels start to rise at higher rpm!
Inspired by (this variable muffler thread) I wrote brand new code for the gas-tank-vent solenoid, adding more and more logic until it was perfect. Now, I'm back to running just big '87 mids and my custom RMB. Except for deceleration and heavy throttle, it is as quiet or oddly quieter than having the stock rear muffler. It does not run hotter and does not feel restricted, even at low rpm cruise, where the valves are nearly closed (at idle vacuum). It responds immediately to full throttle and pulls very strongly through the full rpm range.
I need to dyno it to see if I'm imagining more torque, but just the 'sound-on-demand' is very nice (and weight savings). I may try running going back to just the small '88- mids, next.
--
I'm running the valves at ca. the following openings - at full idle vacuum.
More load = less vacuum = valves open more.
95% closed - idle
99% closed - cruise <1400
95% closed - cruise <2100, low load (higher if ac clutch)
80% closed - cruise
60% closed - heavy throttle
40% closed - WOT <3700
fully opened - WOT
fully opened - decel
Without the extra restriction, idle to 2000 rpm at part throttle is pretty noisy and makes driving annoyingly slow around the neighborhood (or driving Ms. Daisy).
Decel needs to be full open to stop an annoying rattle and so that it doesn't close during gear shifts which causes a horrible bog. (With seperate control of decel vs. idle I was able to delete the limiter washers in the pictures above.)
I was surprised in testing that restricting WOT at lower rpms seems to make it pull harder. WOT is unrestricted at high rpm though because with the stock intake, exhaust manifolds, etc. vacuum levels start to rise at higher rpm!
Last edited by PorKen; 06-17-2018 at 10:37 PM.
