Curt san, 👍👏👌, your effort, enthusiasm and perseverance is contagious. I am puzzled by that power drain device peeking from under your bumper, please elaborate. Someone already might have asked, but I am not done reading the thread yet.

Thanks, appreciate it! It's been a fun, frustrating, & rewarding...journey.

You've a good eye. :icon_tup: Yeah, I mention a time or two in my thread....it supports my other interest ...
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https://cimg1.ibsrv.net/gimg/www.rx8...e306d665cb.jpg

Just wondering if that bike cost more than a used 8???

About the same actually, Lol.

Fun fact: some summer months I put more miles on my S3 than my 8. :yesnod:

Update:
After moving my EBC control line pre throttle body, I began experiencing an odd boost anomaly. With a target boost of ~13.5 psi... the system would generate ~13.5 psi on aggressive accelerations, but on moderate accelerations...the system would only generate ~ 9 psi, i.e. my WG spring pressure. :scratchhe

I considered potential causes, e.g. vac line leak, degrading WG spring, failing WG solenoid, poor WG solenoid control, etc. Given the somewhat intermittent nature of the issue; I decided to start by looking at my WG control design. I was initially running a variation of the "2-port, Single Solenoid, Single Turbo Method 1" design (shown below)...except pulling boost source post IC... just prior to the throttle body. I initially chose this design b/c of its stated advantage for systems w/ potentially "high back pressure".

Today I transitioned to the " 2-port, Single Solenoid, Single Turbo Method 2" (shown below) ...while still pulling boost just prior to the throttle body ...to see what, if any, impact it would have on system boost control. I began testing w/ my EBC "SET" at 30% duty cycle, i.e. my existing LOW setting, which typically generated ~ 11 psi. Mistake. Did a 3rd gear WOT at the end of the hwy entrance ramp...and broke 'em loose...hit 18 psi. :SHOCKED: So..., throttled EBC "SET" solenoid duty cycle way back... to single digits and was still generating 16+ psi. It feels like winter power...mid summer.

This new WG control method generates ~ 15 psi at a solenoid duty cycle of ~6%, the previous method required ~ 43%. So, though still tuning...initial observations are that this control method

• ...seems to have eliminated the boost anomaly seen before
• ...delivers boost more readily / smoothly
• ...delivers more boost...on my system.

Next step... I'll reduce my WG spring from 9# to 7.5#... to both lower minimum achievable boost, and hopefully move duty cycle back into ~ 30% range for tuning to a target 13-14 psi :icon_tup:


WG Boost Control Methods:
Method 1:
https://cimg8.ibsrv.net/gimg/www.rx8...6f679653c4.png
Initial WG control method
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Method 2:
https://cimg6.ibsrv.net/gimg/www.rx8...e7db8824a7.png
New WG control method
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https://cimg9.ibsrv.net/gimg/www.rx8...fac8b77701.png
Boost profile...16.6 psi!

I considered a 4-port solenoid, but understand they yield increased boost range, but decreased tuning precision / "control".

The advantage of the 4-port solenoid is it's ability to generate boost up to 6x WG spring #, whereas the 3-port only generates boost ~ 2.5x WG spring #. That's a great feature for those wanting to run big #s &/or adjust boost "on the fly" over a large range, e.g. 8 to 30+ psi. Neither of those are my interest.

But the extended boost range of the 4-port relative to WG spring # comes at the cost of tuning precision / resolution..., which is of more value to me w/in the relatively small range of boost I'm running. So, in my case on a 7.5# spring, and 3-port solenoid my system s/b capable of running from 4 - 18 psi: 4 -7.5 psi w/ EBC off , and 7.5 - 18 psi ...w/ EBC on; where I only intend to run ~14 psi max.

I've run both a 3 and 4 port at various times. Have never noticed any control accuracy issues either way myself. I would put your intermittent fault down to a mechanical issue like a sticking WG,solenoid valve, or BOV rather than the way it's controlled.

That m/b true. If it's a mechanical issue...it'll manifest w/ this method as well. Time will tell.

But atm...this new method is rocking...showing no signs of boost anomaly, and generating boost ....quite nicely. :yesnod:

And I like being able to reduce WG spring # as well. :icon_tup:

Well, I don't claim to be a SME on this...and haven't run a 4-port, ...am just reading the same forum info & literature as the rest. So, you are quite possibly right, i.e. that "experts" disagree. Or it c/b clever marketing phrasing...for example...in the marketing data you posted here:

• "Our 4-port boost control solenoid valve is designed to target a clearly defined boost curve and improve boost responses..."
  • ... compared to what? Inference m/b ...compared to a 3-port. That w/b incorrect. I presume this is actually compared to no EBC at all.
• "This differs from a traditional 3-port BCSV because it precisely directs pressure to the open and close ports of your wastegate diaphragm."
  • Technically true compared to a 3-port in the "Method 1" configuration. However, the "Method 2" config modulates pressure to the open and close diaphragm ports as well. ;-)
  • And even if so...this point states a fact of operation..., not a claim of improved "system performance". [Note: though there may be.]
• Seems the main claim to fame is the last point: "This allows much lower wastegate spring pressure for better low gear boost control and perfect high gear, high boost control."

But wait...there's more...;-) Notice the trailing note:

• "Note: If you are upgrading from a 3 port solenoid, the boost control tables will need re-tuning. 4port solenoids require small duty changes, so dial down the PID tables (single digit numbers) so it is not over-reactive."
  • Meaning... that it's granularity / precision... is more coarse, i.e. comparable tuning adjustments will result in greater system boost changes as compared to a to a 3-port.

End of day...I'm sure either device c/b used to achieve desired boost control..., but the 4-port is required for large boost #s relative to WG spring # &/or large on-the-fly boost adjust-ability.

No worries. Thx for the suggestion...the 4-ports are definitely worth investigating...

Having found a frayed WG vac hose while earlier changing up my boost control... I decided to revert back to Method 1 ...now knowing all hose connections were sound. Well, nada... test drive quickly determined that the inconsistent boost anomaly was still present. So, hoses weren't the issue.

So, at this point I know:
- The boost inconsistency exists w/ Method 1
- Though more tuning & testing is required here...the boost inconsistency does not appear to be present w/ Method 2. It's actually a "friggin' jet w/ this method".
- Integrity of all vac hose connections h/b confirmed.

So, next step is to reduce my WG spring # ...b/c atm even at 2% duty cycle boost levels are higher than desired for testing. Then add'l testing should reveal if something else is going on..., e.g. sticking WG, or BOV, etc.

Good to hear others agree regarding the 4-port solenoid...though there's nothing wrong w/ using one.

Lol, I quote the salient portion to what I'm replying ...to make clear to what I'm replying and to avoid the person deleting it, and rendering my response vague, confusing or meaningless. :). I view build threads similar to a journal...space isn't really an issue...w/ the digital thing you know. ;) So, IMV it's simpler...cleaner. :icon_tup:

I reduced my WG spring from 9 to 7.5#, which had the desired affect of reducing boost...though I probably could have dropped to a 6# spring. Initial testing seems to indicate that this control method is more affected by back -pressure than the Method 1 model.

- W/Method 1 boost increases slightly or holds constant with each successive gear.
- W/Method 2 boost decreases slightly with each successive gear.

I'll need more testing to confirm. If true, I'll then need to decide which control method better suites my need.

Edit: I'm thinking running a set-up which allows back pressure to mildly attenuate boost may not be an undesirable thing.

I do the same as Curtis for the same reasons . You might be surprised to know how often your comments are misinterpreted by others because you don't do the same.

It is very diffferent . Note here how I am just responding to this sentence and nothing else. Makes it easy for you or anyone to understand what I'm talking about


Now i'm responding to this little gem. I really have no idea what you are referring to or even who you are talking to , given that I wasn't even part of the original conversation. If you had quoted something, maybe I would understand. See how this works ? We are on a forum where multiple people are having conversations and others are reading them. You seem to think you can just throw out a whole lot of verbiage out of context and have everyone understand it ...

Well, I've abandoned the Method 2 WG control model. It proved to have too little range of control. The car felt like a jet when using it, ... b/c peak boost levels were ~16 psi on a 9# spring. Problem was...these boost levels were at 4% or less solenoid duty cycle. So, there was zero downward adjust-ability...short of changing the spring.

Thinking it m/b a mechanical issue a couple of days ago I briefly reverted back to the M1 model to see if it exhibited a lack of control. Nada: control and boost levels were good. Hoses...check, connections...check, WG...check, and solenoid... check. Went back to M2, reduced the WG spring to 7.5#; and peak boost dropped to ~14 psi, but that was still w/ the solenoid duty cycle still very low, ~6% IIRC.

This h/b an interesting, but disappointing exercise... learning the limitations of M2 model...at least w/my solenoid. So, I'm reverting back to M1...on a 9# spring. Control and boost levels are good, 13 psi @ ~40% d/c... w/good adjustability up & down from there. Should the boost anomaly, which is why I initially changed control methods, return...and I expect it will... I'll have to resolve some other way.

Update: 4-port Solenoid on order.

As expected... boost issues using the M1 control and 9# spring are still present...in my high boost ...high rpm range only...which leads me to believe it's back-pressure related. So, while 3-port information indicates you s/b able to achieve psi ~2 - 2.5x WG spring #, ...my experience doesn't appear to validate that theory. Perhaps it's true for piston engines, but not a higher flow / back-pressure rotaries. So, 4-port is on order, which is cheaper than attacking back-pressure..., and more desirable than installing a larger spring; and I'm hoping it'll resolve my issue. :fingersx:

Some may recall when I had the boost spiking issue a while back on [full...partial...full throttle] maneuvers. In the past I'd seen spikes 3-4 psi above desired peak boost. The issue was ultimately resolved by moving my EBC control line from post to pre- throttle body. The boost anomaly, i.e. dropping to WG pressure, I'm trying to resolve now aside..., control is superb.....as long as I don't ask too much of her. Solid boost control is everything. ;)

The below is from a drive today ...from a chip, charge, ...and slaying of a Camaro and Challenger on the hwy. Edit: Think I'll dub her the "Singing Assassin". :lol: It's gratifying to hear their exhaust note change as they downshift, ...accelerate, try to pull away, ...can't ; and you pass. :yelrotflm Just a bit of fun.

Disclaimer: I do not encourage, support, or routinely practice disregard for posted speed limits on public roadways. :nono:
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Hopefully the 4-port solenoid will resolve the dropping out, otherwise boost control is very clean, predictable...no unintended spiking, or over-boosting above set point. :icon_tup:
https://cimg5.ibsrv.net/gimg/www.rx8...f23c83a64d.png

I understood the explanation just fine. Whether it's appropriate behavior on this forum is another thing. I think you've been listening to this too much myself:

Had high hopes for the M2 WG control model..., transitioned to it..., had issues controlling boost across an acceptable range, so reverted back to the M1 model.

The two issues that I was attempting to address were:

1. Under-boosting on "moderate accelerations...into WOT" maneuvers, e.g. 3rd gear @ 5700 rpm up a hwy entrance ramp ...behind other cars ...then going WOT once on the hwy. This is the only situation in which I'd see under-boosting.
2. Boost dropping to WG pressure in 4th/5th gear, upper rpms at 13.5-14 psi.

I recalled reading discussions...regarding the difference between air velocity and air volume moving thru the system. I began wondering if the APV opening timing m/b negatively impacting spool-up by increasing air volume..., at the expense of reducing air velocity precisely as the turbine is spooling-up...causing or contributing to the first issue described above. I believe mass air volume is key to support higher rpm HP, but air velocity more necessary for effective turbine spooling. To test...I increased the APV opening timing to 6200 rpm, and there's been no further under-boosting...in this scenario...on initial test drives. :rock: Again, initial results...hoping to see consistency over time.

The 4-port solenoid delivery h/b delayed d/t Covid-19. So, still hoping it will resolve issue 2 when received. :fingersx:

Why? I'm simply attempting to use sound principles & an understanding of how the engine works to optimize it, or solve problems as they are discovered. The question is which spools the turbine better...increased air velocity or volume flow? Moving the APV timing later to 6200 rpm sustains high air velocity a bit longer before increasing volume flow for higher rpm HP. So far, so good. :fingersx: that there are no recurrences of under-boosting.

Certainly w/h been beneficial if I'd experimented w/ lower AND higher APV open timing when I initially looked at this while investigating it's affect on HP back ~ post # 720.

I don't recall you recommending it..., but no matter. A good idea is ...a good idea no matter the source. It's all about the Renesis. bro. :icon_tup:

Lol, ok, you're referring to my pending switch to a 4-port solenoid. My post was primarily about delaying the opening of the APV. So, of course...that's what I thought you were referring to. A quick "quote" ;) ... or reference to "4-port"...w/h put me on the same page. :)

So, about your 4-port post ...you deleted. So, it didn't happen, right? :rofl: J'king. But......c'mon, man... w/ your penchant for various, sundry, sarcastic, off topic posts..., you here say you didn't want to "clutter my thread" ??? Lol, well......I appreciate that...really.

Specifically, regarding the 4-port... you'll recall I wasn't against it,... just wasn't convinced I needed it. I was not convinced at that time that my 3-port solenoid was insufficient to reliably achieve my desired boost range w/ the WG spring # I want to run.
Since then, ... testing has led me to believe that I m/b currently at the limits of the 3-port solenoid boost range ...again for the WG spring I want to run, ...causing boost to drop d/t back pressure at high gear, high rpm. This is my "theory", which yet m/b right or wrong. Now.....IMV it makes sense...for $50... to try a 4-port solenoid, which will address, or eliminate, two potential causes: bad solenoid, &/or excessive back-pressure. If this doesn't resolve the issue...I'm probably looking at a WG.

My approach all along since installing my kit h/b to cost effectively enhance... or "solve problems"..., i.e. avoid extravagance..., redesigning..., or changing things that ain't broke.
But bro, .....if I'd recalled you mentioned it... smh...I wouldn't have done it. .................... :lol2: Really, ...yes, IIRC you were the first to introduce the 4-port to the discussion . Thanks. Appreciate you. :icon_tup:

Speaking of.... special delivery from our USPS pony express...
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https://cimg8.ibsrv.net/gimg/www.rx8...2950da8221.jpg

Having difficulty w/ getting proper function from the 4-port solenoid. Tested & confirmed that the solenoid switches properly w/ an independent 12v source. But when hooked up to my Greddy Profect B2...no love. I continue to only get spring boost pressure well into the [SET, GAIN, SET GAIN] ranges where I s/b seeing boost elevation above spring.

For testing I ran the following:
SET: 2 ...thru... 40 %
GAIN: 24%
SET GAIN: 60

Thoughts? What am I missing? :scratchhe

With engine off, and ignition on , put enough pressure down the signal line to trigger the controller. Solenoid should start cycling.
Fault find from there.

Thanks. Will do...

Troubleshooting so far:

• solenoid switches on independent 12v source
• solenoid switches on independent 12v source, and properly diverts air flow
• solenoid switches / modulates on Greddy Profec command...per Brett's recommended method.

I've no reason to suspect the control line integrity at the WG...as 3-port solenoid was working fine.

Will confirm today that air is properly diverted from bottom to top port ...when modulated under Greddy command. If that checks out......what next....EBC settings?

Test:

My guess is , whatever the problem was before is still there and has been exacerbated.
I'd be pulling the WG to inspect it and checking BOV.

Brett, Thx. I've pulled & checked the WG recently ...when swapping springs ...when I was running the M2 control method; and didn't find any sticking, binding, torn diaphragm, etc.

If the BOV were stuck closed....I'd see overboosting, which I'm not seeing. If... stuck open, I'd experience underboosting, which I am. But not laggy boost build-up and underboost. Just inability to generate boost above WG spring #. And I was not seeing laggy spool response, or underboosting of this type... when running the 3-port solenoid.

I'm going to try more dialing in the EBC settings...b/c this isn't making sense.

agreed!
When crap like this happens you really have to go deep into how everything works and figure out how to test that every item that can influence it is doing what it should.

Well,...full disclosure...in my exasperation I swapped the 3-port back in, ... went for a spin expecting that 13+ psi jet feeling. Nada,...no love...8 psi :eek:. 🤣.....🤨.....😢. Something's changed. She's put away... in time out...at least until the long weekend.

As you suggest...plan to throw her on stands, and check all the control lines and hardware.

Exhaust manifold leak? I've had similar symptoms when the wastegate v-band wasn't seated correctly - no exhaust leak noise at idle, just real laggy and lower boost than expected.

Jimmy, Thanks. I hope it's not an exhaust mani leak. A poor WG v-band seal wouldn't be too bad. I'll check tomorrow.

Pulled the WG, and found the culprit: evidently the spring was in slightly angled...causing the plunger to rub/ catch against the v-band inner ring seal. Everything else checked out.

She's boosting about normally again. :ylsuper: 4-port solenoid is going back in.

Couple pics:
- 1st pic: you can see the trace of the spring grinding into the inner WG base wall (riding up diagonally) .
- 2nd pic: ...where the plunger was "catching" on the inner side of the v-band ring.

:worship:

https://cimg0.ibsrv.net/gimg/www.rx8...4ab17a0a7f.jpg
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https://cimg3.ibsrv.net/gimg/www.rx8...caa809e2ee.jpg

Update: Hybrid WG Control

I was still seeing boost drop to spring pressure occasionally...in certain situations. Additionally, I've gained confidence that my system can run a bit more boost ...safely and before needing to further upgrade injectors. Since I couldn't get the 4-port solenoid to work properly... :dunno:, and rather than purchase a boost by gear EBC ... @ $300+, I decided to try a hybrid WG control method to both resolve the boost dropping, and raise boost to ~14 psi.

Four pressures act on the WG: two on the bottom, ...two on the top.
Top: (spring) + (EBC modulated)
Bottom: (boost line pressure) + (back-pressure)

Theoretically, by attenuating the "boost line pressure", the WG c/b held closed to a higher system pressure ...w/out installing a larger spring.

Pre change estimated system pressures:
Top: (9# spring) + (13 psi, EBC modulated) = 22#
Bottom: (13 psi boost) + (~9 psi back-pressure) = 22#

So, I installed a MBC ($45) in the WG bottom port boost line, and attenuated the boost ~30%.

Post change estimated system pressures:
Top: (9# spring) + (13 psi, EBC modulated) = 22#
Bottom: (9 psi, MBC Adjustable) + (~9 psi back-pressure) = 18#

Therefore, giving "EBC Control" 4 additional psi "headroom" to modulate for higher system boost ...before the WG opens.

Initial tests are positive: no dropping out, ...14.x psi w/ ease, and no identified drawbacks as yet. Still tuning to bring it down to lower 14's psi, but fairly close to "done".

I plan to swap in a 6# spring w/ this method ...which should have no issue still reaching low 14's psi peak.

https://cimg1.ibsrv.net/gimg/www.rx8...6ece8efc02.png
MBC installed inline w/ the WG bottom port
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https://cimg0.ibsrv.net/gimg/www.rx8...98cc0d7fb9.png
14.x psi boost profile

interesting conclusion and results; thank you for sharing them with us.

Looking forward to your next progress.
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Where'd you get the 9psi backpressure figure from? I'd expect this figure to be >20psi at redline. The small amount of experimenting and reading I've done suggests it would usually be 1.5 to 3 times boost pressure at redline.

Good question. It really was deduced from the working of things. Back pressure is dynamic relative to boost, and I make the assumption that it c/b represented as ...[back pressure = boost x coefficient], so that b-pressure increases as a factor of boost.

I also considered that WG operation as described above was entirely controlled by four pressures:
Top: (spring + EBC boost)
Bott: (control line boost) + b-pressure).

In my system the WG was being forced open, i.e. boost dropping to spring pressure, reliably at ~ 13.5 psi. I presumed two things were true at this point:
1. The EBC was passing on all available boost through the solenoid to the top of the WG, 13.5 psi, in this case.
2. This point represented equilibrium, i.e. the point at which the pressures acting on the bottom just exceed those acting on the top.

Then, setting top forces equal to bottom yields: (9# + 13.5 psi) = 13.5 psi + back pressure). Solving this identifies back pressure of ~ 9 psi, i.e. boost x a coefficient of 0.67: 13.5 x 0.67. Now in reality the solenoid c/b passing along something less than current boost, 13.5 psi, in which case you w/b right that back pressure is higher e.g. (9# + 13.5 psi) = 10 psi + back pressure). Then back pressure w/b 12.5 psi. The actual back pressure is less important ...than the fact that the sum of control line boost and back pressure equal forces acting on the top of the WG at this point.

Realizing this...and the fact that the EBC can't "create" boost, but only modulate the boost which exists; then I realized that by attenuating the "control line boost" I could create an imbalance in my favor ...so that the EBC could, using the boost available to it, maintain greater force on the top of the WG than was present on the bottom.

Ex. If the control line boost is attenuated by 10% then the equation becomes:
Top: (9# + 13.5 psi) = 22.5
Bott.: (12.15 psi + 9 psi) = 21.15

...and in this scenario the EBC will have an added psi "range" to modulate existing boost to keep the WG clamped shut.

In this case boost c/b raised to 15.75 psi before WG bottom pressures will equal those on the top...and force the WG open:
control line = 15.75 x 0.9 = 14.18 psi
back pressure = 15.75 x .67 = 10.55 psi

Top: (9# + 15.75 psi) = 24.75
Bott.: (14.18 psi + 10.55 psi) = 24.73

So, by attenuating the control line boost 10%, system boost c/b theoretically raised from 13.5 to 15.75 psi.

*Note:
1. The #s are estimates...I was more concerned w/ the theory that this hybrid WG control could enable the system to achieve higher system pressure w/out installing a larger spring.
2. I only pursued this b/c I couldn't get my 4 port solenoid to work...which is the preferred method to which I will likely revert at some point. But thought I'd share...b/c it works.

On another note I believe my Pineapple oil pan gasket is leaking. :pat:. Was hoping to be done w/ pulling and reinstalling this oil pan, but...looks like it's coming off again and getting re-installed w/ old faithful: gray Permatex.

At 14psi boost pressure with your setup, backpressure will definitely be over 20psi at peak rpm... You really should be measuring this now that you are experimenting with elevated boost.

The diameter of the wastegate valve that sees backpressure is maybe 42mm ish . Whereas the diameter of the diaphragm inside the WG housing will be more like 60mm . Just a guess there, but my point is, that needs to be in your calcs.

perhaps it should be clarified as either total pressure or differential pressure. Because I’ not entirely sure which you mean.

Fair points ...on both accounts.
- You have mentioned before...and rightly so...I s/b measuring back pressure. I will get this done ...at some point.
- And yes, you're also right ...the diameters of the surface areas the pressures are acting on w/in the WG will definitely have an impact, and s/b included in the equation. That would explain why my estimated back pressure is off ...as Jimmy also pointed out.

Thanks, Jimmy & Brett, I'll get those diameters, revise the equation, and see what results.

T, Not sure what you mean by differential pressure. But fair enough...I am addressing boost from a number of differing sources. I try to identify each pressure by it's source:

Top: (spring + EBC pressure)
Bott: (control line pressure) + b-pressure).

EBC pressure: EBC modulated pressure
Control line pressure: This is the WG boost/ pressure control line tapped directly off the charge section. Therefore, the "actual" system boost at the point in time.
Back pressure: Back pressure as seen at / by the WG
MBC pressure: This is the "Control line pressure" after attenuation by the MBC.

Might just be my misunderstanding because I’d prefer to use the term differential pressure rather than back pressure. What are you defining as B-P at the wastegate then; pre-turbo manifold pressure - post turbo exhaust pressure?

I was actually trying to figure out what Brettus meant with the 20psi reply because of the terminology. There is total manifold pressure and the differential pressure between it and boost pressure and then also the differential pressure between it and the exhaust pressure. I had his name in the reply, but reworded it and left that out. Sorry for the misunderstanding.

Right on...excellent point. :icon_tup: I'm referring to the force directly acting on the WG valve, which I believe to be pre-turbo exhaust manifold pressure. So, I was incorrect in labeling it back-pressure.

I'm not sure how the differential pressures you describe come into play.

My understanding is that the term 'differential pressure' implies you are looking at the difference between two pressures.
The term 'Turbine Back pressure' is used quite commonly to describe the exhaust manifold pressure or EMAP.
If you were referring to pressure post turbine you would call it 'exhaust backpressure'.

Edit: In this post when I state "backpressure", I'm talking EMAP, not turbine back pressure.

"Boost" is cold side pressure, "Backpressure" is hot side pressure in PSI above atmospheric. The backpressure is the pressure of the hot exhaust gas in the exhaust manifold trying to press the wastegate open, acting against the force of the WG spring.
Brettus and I started measuring back pressure on our respective setups around the same time to guide us towards more efficient turbo setups. You can reduce exhaust backpressure by improving exhaust flow after the turbo and/or wastegate, by changing the turbo wheels and housings, and reducing pressure drop the coldside across piping and inter cooler (sometimes at the expense of spool). Any modification that reduces backpressure while keeping the boost level at the same value will result in the engine flowing more air (I.e. more power). The trick is to lower back pressure ratio without losing spool. You can see on Brettus' new exhaust manifold that there are small pressure signal lines tapped into the front and rear sections of his manifold. These lines are each connected to boost sensors/gauges and used to measure the exhaust pressure as seen by front and rear sections of the manifold (I.e. front and rear scrolls of the turbo). If you can capture these front and rear exhaust back pressures (hot side) along with boost pressure (cold side) and rpm and mass airflow, you can measure conclusively whether each change to the turbo setup is an improvement on efficiency of the turbo setup. Of course, on most rx-8 turbo setups the front and rear runners of the exhaust manifold are joined, so one pressure line is sufficient. When Brettus made the decision to reduce turbine housing AR on his setup, this may seem counter-intuitive, but it was guided by the front and rear exhaust back pressure readings he had logged, and it resulted in a more efficient setup. Correct me if I'm wrong here Brett!

Edit: Here's a link to my back pressure experimentation. I installed the sensor, recorded some results, upgraded the turbo, then recorded more results to compare old and new turbo. This was all on a Greddy manifold (t25 turbine flange).
https://www.rx8club.com/series-i-maj...3/#post4730979

I actually don't have the front half tapped to measure EMAP just the rear. But yeah ............agree with the rest of what you are saying.


wat ?

Not trying to make an argument, but the terms used on BW’s Matchbot are; intercooler pressure drop, exhaust back pressure, manifold pressure, engine differential pressure. There are potentially more than that. Note that they all have a reference though.

Because the only point is there are multiple back-pressures depending on where you’re referring to and how you’re looking at it. Without a reference on which one it was, I wasn’t sure. Because with a 14 psi boost and 20 psi manifold pressure it could be said that there’s 6 psi back-pressure, which is the engine differential term used in matchbot. Which that 6 psi differential figure is also going to include exhaust back-pressure. Somebody else might interpret that as 34 psi manifold pressure thinking 20 psi back-pressure was the differential. Like a lot of other things people seem to disagree with me on, not really sure why you wouldn’t just called it what it is; manifold pressure.

With that size turbine at that output though, I was thinking it’d be less than 6 psi, but that might depend on the exhaust.