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Car is a 427w, trick flow 205 11rs, twin S366 turbos, 3” downpipes to 2.5” dynomax ultra flows, have cutouts past the transmission crossmember in the 2.5” pipe pre muffler.

Had a few issues when motor was built and finally have it back in and running, my Pro-M ECU controlls boost and I have 2 Tial MV-R 44mm gates, with the smallest 4.350 spring in. When I went out to data log I was only seeing 1.5lbs of boost, I was able to get 2.5 on the Transbrake but only 1.5 on the road. I’ve eliminated the solenoids (3 port) from the equation and am still seeing the 2.5 on the brake, going out to test on the road again now.

I checked all of my cold side couplers tight (all have beads and t-bolts) except the one I have to remove the fender for. The intercooler is a 4” thick core, if I go test drive now and don’t get over 1.5lbs do I have a boost leak or do I just need to start with a different spring, the boost I’m seeing seems to be consistent, car runs phenomenal by the way, not sure if that is relevant or not, thanks in advance for any help...

 

So went out to log with the solenoids out of the equation, same thing only seeing around 1.5lbs of boost.

First gear WOT boost comes on at 5100 rpm, see max of .6 at 6400rpm, zero below 5k, shift to second and rpm drops to 5300 and see around 1.3lbs, these things should be fully spooled well before 5k.

Can only be one of two things I’m guessing, gate spring is too weak (no knowledge if even possible) or major boost leak.

I’m referencing the wastegate vacuum from just outside the compressor housing on the cold side piping, same for both turbos, my map sensor and boost gauge is referenced at the upper intake.

My next move is to probably swap springs in the wastegates and retest, I’ll also be making something to test for a boost leak, not much changed on my cold side from the prior motor and I didn’t have this issue, I do think I had 2 springs in though and don’t remember logging boost since I wasn’t running a map sensor at that time, I’ve since went from a 393 to a 427 and slightly better heads, dreading removing the gates but I think it’s gonna be necessary to figure out what’s going on.

 

You're on the right track. Add some spring to the gates, and make sure the valve seats are there. When you change springs try to identify the rated boost level of the springs, or at least bench test them. Testing of the cold side isn't a bad idea also.

 

I have an old boost controller that I’m not using anymore (eboost2) and a electronic gauge from speedhut reading boost from the upper intake manifold, gates are referenced just past the compressor in the cold side pipe, I may reroute the eboost2 vacuum line pre intercooler that way I have a reference of boost to see if it’s dropping thru the intercooler and plumbing on the way to the intake.

 

Pulled one wastegate, had a green spring in, mixed up the MV-S chart with the MV-R from a google search, no green spring listed alone on the MV-R chart. Now to decide where I want to start. 5.8 or 7.25...

 

Double check that the WG valve seats are in place.

 

Double check that the WG valve seats are in place.

 

I’m always up for smaller springs and using a controller to get you more boost. You could do that and use the old controller you have to start creeping up on some some pressure to give you more boost as you test.

 

Depending on style of controller, he may need more base spring. 6-7 psi is about as low as I go without air or co2.

 

I put in the 7.25 spring and went and did a test hit and saw 4.6, guess there is a lot of loss threw the IC, I’m going to see if the ECU can get me 10 psi through the controller, my injector duty cycle was only at 36%, I’m going to be testing out traction with it as is and maybe go up one more spring size if needed, ACT temps are around 106 with the water/meth right now

 

Spring ratings are pretty generic, and will vary some from combo to combo. It would be interesting to know how many psi it's making pre intercooler.

 

I have a bung I could use and source to hook up to see pre intercooler, I might test it out one day

 

I don't really have anything to add other than bench testing with a regulator helped me better understand what was happening with the wastegates.

Does it make sense to have both the wastegate reference and the controller reference on the same side of the intercooler or does it really matter? Might see a slightly higher boost pressure if you lower the reference pressure due to intercooler pressure drop but you have a 3 port valve so you can do about 9 psi now (2x).

Now I'm just rambling. Cool car. I also enjoyed reading through the DELETE thread

 

Couple things to note
1. Always use intake manifold pressure to push open wastegate. Using anything pre-intercooler is going to cause the boost pressure to wander around based on ambient conditions. For example when very hot outside the air density will be very low coming off the compressor, so when it goes through the intercooler and regains density the boost pressure will drop very far, perhaps even into a vacuum if you are only running 1 or 3psi. On the other hand, very cold days will have higher density compressor outlet result and the intercooler will be doing less to bring that temp back to ambient and therefore quite a bit less pressure drop throughput, resulting with higher boost pressure. This raises several issues including the tuning aspect which is going to be running along a different path through the tune (EFI breakpoint issue) depending on how hot the compressor side is getting.

2. Part of what opens wastegate valve is exhaust gas pressure. The spring manufacturer automatically assumed some intake:exhaust pressure ratio (you can find out what it is by reading documentation, usually 2:1 iirc). Therefore is the exhaust gas pressure is higher than they anticipated, your resulting boost pressure will be lower than the spring is rated for. This can also double as a diagnostic feature, since high EGP results with more difficult raising boost as you turn the knob on a boost controller within it's control design, indicating that you peaked or maxed out turbine flow rate which is coupled to additional PSI of boost pressure without any net gain in power, a helpful dual diagnostic if you will.

3. How you measure the boost pressure matters. Map sensors have configurable outputs and voltage offsets. Gauges can be wrong and even ambient conditions can play a small role. Always use 2 or 3 sources for reading boost pressure, just like with compression testers, never trust just 1 source or gauge.

4. Boost leaks spell disaster, broken pistons, high EGP and high EGT, broken turbos, explosions and huge messes are possible. If the boost pressure is leaking out, the wastegate will attempt to compensate for the dropping boost pressure by shutting the gate, which increases turbine demand, which raises the EGP and EGT and that quickly leads to a melt down and broken engines.
Thus, Always ALWAYS pressure test your entire intake plumbing system before using any boost pressure. This is a absolute necessity and should not be overlooked. You will use an air compressor to fill the entire plumbing system, from compressor cover all the way through intake manifold, pressurize it to slightly beyond the boost pressure max you intent to run. The entire plumbing including intake should hold the pressure like a balloon... only slightly leaking down 1 or 2psi every couple of seconds due to an open intake valve during overlap or something like that, it will be very slight. With 2 turbos simply block one of the compressor covers off and fill the other cover with the air compressor.

 

Good luck with that. Any engine with 4 cylinders or more will always have an inlet valve open. This will add those cylinder's leakdown to the leakage. The pressure will probably cause the motor to rotate. 8 cylinder engines will almost always have a cylinder on overlap - this will create a massive leak.

The only way this will work is to mke sure all the intake valves are closed. This will be possible on some engines by removing a couple of rockers, backing off a couple of adjusters etc.

 

This is a common misconception. I don't blame you for thinking this way, but clearly, you've never done a pressure test, and still have a lot to learn. My friend please understand I am teaching here, not playing games or pretending. My words are not suggestions- they are derived from absolute law of performance application mastery, if you wish to become a true purveyor of performance you will learn these subtle, simple things I plainly detail.

Or face the consequences of learning at your own pace.

et al;
In our line of work (engine tuning) we have pressure tested thousand+ engines successfully, 1000+ of all different types, subaru, toyota, nissan, chevrolet, volkswagon, whatever. They all run using similar principles and they all pressure test identically suitably well to 20 30 40... 70psi of intake manifold pressure as needed. The pressure test is an absolute necessity before running boost through any engine, of any kind. It is one of the 3 major tests an engine must pass before I will tune that engine, every single time, every single engine.

Without the pressure test you are guaranteed a catastrophic engine failure at some point, I guarantee it, because even if there are no leaks today, there will be one day. And I've never found a freshly installed engine turbo-swap that didn't have at least one or two leaks right off the bat, out of thousands it is extremely rare to the point I cannot remember a single one that didn't leak at least a little bit at first on the first test. It's gotten to the point where I say "okay now lets find all the leaks" each time for a new engine, and we do find them.

A pressure leak will cause a rapidly rising IAT, EGT, and EGP which depending on the fuel quality, pressure ratio, compression ratio, may quickly or gradually decimate the engine in question. high quality fuel will tolerate high IAT but factory cast pistons will not tolerate high EGT or EGP. Only a fully forged engine using Alcohol fuels is technically able to resist the damaging effects of those high temp and pressure situations, but the resulting performance will be so pitiful and weak that you will be posting on the forum "looking for a missing 200hp" or something like that anyways. Not to mention the turbo will fly apart because its being over-spun trying to keep up with the leaking air in many cases. Bad, bad juju.

Here is a video of a pressure test so you can see for yourself the engine rate of leaking "overlap" is negligible.


Note at the beginning It is merely the intake manifold being tested. But at the end of the video it showing the turbo being filled with air, which is being compressed all the way to the intake manifold- revealing a leak somewhere near the intake manifold.

I will post another video of another pressure test with better quality and more details soon (1-2 weeks max I suppose). Until then know I would not mislead or waste anybody's time if these tests were not absolutely necessary, and as you can clearly tell by the responses ("huh? what? Impossible!") Nobody in hobby land is performing them. Well its time to change all that, time to bring the professional top level of performance to the general hobbyist.

 

My humble apologies master. I did realise I was in the presence of such greatness. Your video has allayed all my doubts and answered all my questions.

 

I know you jest, but I am serious and willing to indulge because I am waiting for a cancer cell culture to grow in an incubator atm so I have the time and patience. I know it is impossible to tell over the internet who you are talking to. And if I list all of my qualifications here it would look like bragging- and at the end of the day it doesn't matter how many years of experience or what kind of education a person has, or how many cars built or tuned, the paper and years and cars is all meaningless, as everybody learns at a different pace and has different funding to support their ventures. E.g. a person building a single 400hp vehicle with low/no income may posses far more knowledge than somebody who owns several multi million dollar sports cars with high list of modifications that run 6 seconds, because being poor and having to use junk parts teaches the necessary lessons while having unlimited funds means other people are probably doing all the work.

Also this is not a copy and paste from anywhere. I wrote this while waiting TONIGHT and simply broke it up into chunks at the end because the post will only allow 1000 words. That is why it is multiple posts.

preface
The human race has conquered, and is replacing, combustion engines in the near future. That is to say: we have mastered them. The efficiency and production of combustion engines has reached a plateau of severe diminishing returns. 'We' continue to make them "better" but it is within 0.1% or 0.01% at a time, a slight margin of improved efficiency as every possible advantage is eeked out for just 1 or 0.1mpg at a time as power output continues to climb beyond inane values thanks to computer aided design and modern microprocessor control theory continually improves everything from parts production en mass, stress resistance including vibration/resonance energy flow (vibration is energy that may be harnessed to do work or it can rip the engine apart) in order to develop the most powerful and successful of antique combustion engines ever seen.

So what I am really saying is, "yes we have mastered combustion engines" We is the human race, not me, not I, no credit here, not a narcissistic A-hole just because I can read a textbook and perform basic maths that every engineer can do better than I can... I like so many engineers am not really a car person. I see myself as more of a spacecraft/architect/researcher, where every tiny detail can mean life or death, every atomic interaction must be predictable at every possible situation and even for those impossible situations but I digress.

What I am trying to say is, because the OEM have mastery of combustion engines... then by virtue of unraveling their design process, so has every performance enthusiast willing to read and understand the concepts and mathematics which lead those OEM engineers to the pinnacle of modern design and high efficiency.

We find so many people on forums are interested in cars but lack engineering concepts and mathematical ability- mathematical methods (wave equation, laplace, darcy & newtons laws, etc...), fluid mech/dynamics, dynamical systems and control theory... higher maths and electrical concepts which we may use to unravel the original (OEM) engineering designs of the extremely simplistic combustion engine and make them our own. Make no mistake, as I'm going to repeat this for a third time: combustion engines are essentially antiquated, simple, historical, obsolete shortly. Eukaryotic life evolved some 1.5? million years ago so 100 or 1000 years is not a long time in comparison, thus my wordage "shortly" with respect to development of complex organizational abilities of cell colonies... arguably the original engineers are inside us (the biology of life is as mechanical as it is electrical, for example the ATPase is 63 times as powerful as a diesel engine of the same size according to the molecular and cellular biology book). But I digress? The point being, for somebody to say "I fully understand how a combustion engine works" is a very realistic proposal now, considering how simple they are and what knowledge is available to us.

My goal here:
1. Help people understand the genius of OEM engineers clearly, and to unravel the copy/paste AND advertisements of aftermarket parts and their misleading statistical gestures (using stats to obscure the whole truth by providing only part of the truth through the use of clever statistics (I recommend reading "The art of computer systems performance analysis" ))

2. See #1

And that is it. The OEM engineers have already figured everything out; you just need to realize this, adapt it to suite your needs, and the engine correctly chosen can live a long healthy life at some reasonable output. My words and teaching are simply the factory OEM methodology regurgitated into a performance venue. In other words I am not giving you any new information, or any unique methods, I am merely repeating what the OEM has been saying since computer aided design took over production quality.
-Groundwork
Understanding the forces applied to beams, surface area, bearing lubrication &c (fluid dynamics & static forces) will help you understand how much power an engine is capable of, and the integral of torque applied over some useful range of connecting rod angles is related to piston&rod stress. Understanding material science, stress and 3D Stress tensors(Adv mechanics of materials) will help relate combustion forces to parts breakage potential. Combustion chemistry and 3D atomic representation of individual fuel and air components is understanding steric hindrance, the chain reaction, carbon chain relationship to fuel octane (branching of carbon chains is responsible for gasoline octane rating) this is an organic chemistry course knowledge, not included to most engineering backgrounds unfortunately. Mathematics will clearly define expectations for all aspects of performance before you buy a single part. And finally that Health and efficiency supersedes power in almost every application- remember that next time you see a turbo without an paper air filter (or sometimes NO air filter!)

 

We will Learn to avoid aftermarket hype by learning WHY the OEM engineers design the way they do. There is ALWAYS a great example for anything you can imagine- want a daily driver turbo engine to go 300,000 miles? Toyota and Nissan have done this since 1992 using technology that Chevrolet didn't introduce fully until 2002 (hint: don't buy Chevrolet engines made before 02 rofl).
Toy/Nis both produced 200hp/liter capable engines which supplied mountains of statistical evidence amounting to their successful use and set the bar for small displacement around 30 years ago, which hasn't been replaced by any large margin... that is, there is some maximum expectation from using certain size parts that even with perfect design implementation, cannot be overcome. In other words in 1992 we have 3L engines capable of approx 800rwhp or 1000rwhp (Toyota Supra is easy) and today we still have roughly the same power potential/displacement using OEM pistons/parts, some 30 years later it hasn't gone up much or at all. This is because physical forces applied to those engines(mechanics of materials) and the parts which are designed to handle those forces are all essentially the same size category and made of the similar materials for 30 years, owing in part due to the availability and production constraints of cost effective materials for production vehicles. Since the factory has knowledge of ALL the forces of combustion and rotational torque possibilities, even for poor situations, they tend to design every part within a similar range of capability... meaning that, if the engine is experiencing forces which can damage 1 part, it is likely that those forces might damage many of the other parts simultaneously. Sure the weakest link will fail, but ALL of the core components may become a "weak link" at roughly the same time, depending on the nature of force being applied (i.e. torque applied to shafts from large/sticky tires in precarious situations will generally snap transmission shafts first whereas properly applied forces of combustion could easily damage a piston OR connecting rod depending on the engine type). This is because in order to achieve maximum economy and efficiency, ALL excess weight must be removed, therefore parts are ONLY made as strong (heavy) as they need to be. Of course, In some situations they may use alternative materials to increase strength while decreasing weight, and some parts are inherently much stronger than others where possible, because the increase in strength:weight is tolerable for those components. For example Toyota engine 2jz-gte block can support much more power than the OEM internals can. The block will never break before the rods/pistons will for that engine because the block is superior in durability BY DESIGN- And this is the next key to examining and utilizing OEM engineering concepts, being able to identify WHICH parts/blocks will handle far more power than the other internals would have you believe is possible. The best way to do this is through statistical analysis: look for 100 or 1000+ examples of real world engine configurations making XXXX power using those parts, for how many seasons/miles/hours of run time successfully and see some of them torn down after catastrophic failure and categorize the possible/potential ailments ("In poorer hands" of misused engines, still handle XXXX power for YY mileage). For example, This is how I found out the L33 5.3L engine from 2006 is capable of handling approx 1600bhp (~1200rwhp) stock bottom end for 200,000 miles of durability in a daily driver application. The same way I already know 2jz-gte from 1995 will tolerate at least 700rwhp for 20 years and 250,000 miles (supraforums stats). And that Nissan sr20det 1995-98 will 500bhp for 20 years, 200k as well (Australian stats)
When used properly, statistics is a potent ally, and it can correlate OEM engineering design strategy to real world results which allow for higher chance of success than any other avenue. For example if you buy a brand new 2021 vehicle right now, what are the stats on when it will break down, and what for? Nobody knows yet. It will be 15 or 20 years before we know with 99.99% accuracy exactly what parts are prone to breakage. The worse the design, the sooner you find out. Example: All those 'recent' (2012?) corvettes with bad heads, some specific year range all need new heads and even then some still fail. People finding titanium shavings in their oil.
That is statistics working for US, the performance purveyor. We would like to buy engines that have proven themselves, with a significant track record, and deeply investigate the OEM design strategies which lead them to those success rates. In other words, a random Chevrolet truck from 2005 with 150,000 miles that has been properly maintained has a 99.99% chance of going another 150,000 miles if still properly maintained, and coming apart with fairly mint bearings and very little wear and tear. I've seen them go 1000rwhp for 300+ dyno and racing passes, coming apart with mint bearings after suffering a wastegate malfunction which snapped a connecting rod, leaving the rod still attached to the crankshaft with factory bolts intact. Statistically, one of those engines is 1000% or even 10,000% more likely to survive 200,000 mileage or 300,000miles than any crate or new engine from any manufacturer in the world, because not only has the design process been 'ironed out' they have been put to work for over 20 years in millions of trucks and generated a relatively large population of statistical evidence for us to review and create confidence intervals of success, which is how I get to 99% so easily. Less than 1 in 100 of those trucks has any significant bottom end issue, the real number is something like 1:1000 or 1:5000 and even so is likely attributed to maintenance concerns or modifications. Which I will get to in a minute.

You might ask "why do they change if they are so successful?" In other words "if engines from 92 can go 200,000 miles with XXXpower, why do new engines fail at random or unreliable in some newer years?"
The answer is, the OEM is forced to abandon certain previous designs in order to maintain new efficiency and mileage / emissions standards. New engines must be lighter, cleaner, and may use cheaper parts as time goes on, not just to save money but also reduce production time and man hour involvement. The whole design process is constantly being reorganized to provide for new goals and fewer errors- but during these changes there are always mistakes being made, always new materials will be hit or miss once production ensues for 10,000,000+ copies and the resulting 200,000 mileage benchmark is applied over the course of 20 years for those vehicles. The original engineers often don't find out until long after the design is replaced whether it was good, or bad, and even if it was good it was probably too heavy or could be improved in some small way anyways. And the original engineers might not even be around anymore to have anything to say about it. New engineers don't always have the same background and knowledge as the previous ones...

 

Lets talk common modifications that cost reliability. This is getting long but might as well dish it out. Typical mods which cost engine health:
-Air filter "upgrades"
-Removal of PCV
-Opening an engine for any reason without being 'clean roomed'

First, your air filter sucks. High performance manufacturers are quick to point out that their filter will provide 8hp or 20hp or whatever. They love that the OEM manufacturers never put a great air filter on anything it seems. What they fail to tell you, or maybe they don't even know this themselves: The factory air filter paper is designed to create a pressure drop of approx 1.5"Hg to 3" Hg post filter, once it gets a bit dirty from daily driving (it takes 500 miles sometimes). This is approx 1psi of vacuum after the air filter, at wide open throttle. At atmospheric pressure of 14.5psi, a 0.5 to 1psi pressure drop is going to subtract maybe 4% or 7% of engine power- there is your 8hp or 20hp you lost from the factory filter.

BY DESIGN being the key words here. That tiny sacrifice of 4% to 7% engine power is what drives the WOT pcv action. It effectively pulls a vacuum on the crankcase during WOT which is what literally keeps the engine healthy, alive and oil-leak free for 200,000 or 300,000 miles. PCV IS OIL CONTROL STRATEGY. For every 1 truck owner, there is another one that removed the OEM air filter, and installed a high flow aftermarket version... and after approx 10k or 30k miles notices that his engine is either leaking oil or blowing oil from the valve cover into the intake manifold. He will go on the forum and complain "my (fairly) new truck engine has a faulty PCV system and it is filling the intake manifold with engine oil. The factory sucks at making engines. " And then they will buy an aftermarket catch can to collect the oil from that point, and tell everybody that they too will require a catch can because the factory engine blows oil from it's baffle apparently.

Never realizing that it was the aftermarket filter that lead to that point. If you've ever broken a piston into pieces you will notice that suddenly oil goes blowing out of every orifice, especially during boost. This is the exact effect you will replicate by using a 100% free flowing air filter, it is basically like having NO air filter at all (if the filter flows perfectly then it is "invisible" and no pressure drop is provided for PCV suction). The other aspect to this is the critical pressure test which I keep insisting upon: Even if you are using a factory air filter, if there is some air leaking between the engine and filter, then you have basically bypassed the air filter exactly as if it were not there. Therefore, naturally aspirated engines ALSO require pressure tests if for no other reason than to ensure their air filters are properly driving PCV action at wide open throttle.

-Removal of PCV
PCV is an oil control strategy. Most with a 2000hp racing engine running a dry sump, specifically sets their crankcase pressure to some exact number such as 11" Hg or 13" Hg or whatever. This is what keeps oil inside the engine while it makes all that power, and protect the oil seals from blowing out, controls blow-by and maintains oil quality.
This is exactly the same effect you wish to replicate using OEM pcv except with much less vacuum signal, you only need 1" to 3" Hg of crankcase pressure to achieve great results using OEM style PCV on wet sump engines even up to 1000-1200rwhp in my experience is quite satisfactory.

Removing or disrupting PCV (modifying the air filter or deleting the pcv valve and intake manifold suction etc...) is going to guarantee you oil control related problems. Not immediately- it is alot like start smoking. The day you start smoking there doesn't seem to be any affects... but keep doing it for long time eventually the symptoms begin to pile up. Similarly you can't suddenly connect the pcv system on an engine which has been run without one for sooo long a period of time, and expect it to correct all issues related to oil control overnight. Just like you can't stop smoking after 5 or 20 years and expect to get better suddenly.

Last, Opening the engine without being clean and a return to air filtration.
Major offenders here is, airbourne debris & filthy 'mechanic' hands. i.e. not using gloves and not being careful with microscopic debris when working on the engine. The factory OEM design (for 89+ Japanese engines and 02+ Chevrolet engines, specifically) precludes a necessity of absolutely flawlessly clean engine oil with no outside debris. Even a tiny particle can lodge/embed and disrupt oil flow to components.
Partially combusted hydrocarbon conglomerates "blow by" are fine because they mimic short damaged chains of engine oil and are hydrophobically compatible, these generally leave with engine oil during a change and do not stop in oil filters or clog passages, these are what seem to 'water down' the oil over time. Blow-by gas also contains CO2 which is inert, and H2O which in a properly warmed up engine (200*F+ engine oil) will avoid the engine oil and leave via PCV system harmlessly.
Anything else, and I mean anything- is a disaster for the engine. And you might not realize this yet so here it is: The air filter is the life of the engine. The air filtration is the only thing standing between your engine and its demise, disaster, failure. The air filter is 99% of what allows an engine to achieve 300,000 or 1,000,000 mileage. No other part or component matters nearly as much. And the reason is simple: outside air is absolutely full of microscopic debris. Normal air contains some ridiculous amount, perhaps 200,000 parts per million of debris outside everywhere anywhere in the world. Most of it is biological in origin: carbon containing forms of life, which include atoms and molecules of life, specifically almost everything from the first 2 or 3 rows of the periodic table including sulfur, potassium, sodium, molybdenum, iron, chlorine, etc... for example fungus and pollen are found everywhere in the world in outside air and contain all of these and many many more components. Inside the engine there is applied HEAT and PRESSURE which from chemistry you may recognize as reaction-inducing (chemical reactions happen more easily under heat and pressure) and because we are talking potentially 800*F to 2000*F and 1000PSI it can form many many random conglomerates containing these atoms and many compounds which easily embed to nearby metal materials, ruining the engine. For example the piston ring is a seal which must glide easily along a clean film of engine oil, and each of these particulate from outside air represents a sort of "shard" that will lodge into the ring/oil film and break the oil film, causing cylinder wall damage and unwanted wear. The products of high heat and pressure are not flimy & soft but rather more diamond-like, hard carbon containing deposits which include myriad atomic elements of life including metals and silicone "products of rock debris" for example. And in the blow-by gas some of this debris escapes into engine oil, where it is washed throughout the engine, often making it un-rebuildable. Sure it will look re-usable but you will never see 200 or 300k mileage from it once its been exposed to outside air for any length of time- either on a shelf or from poor air filtration. There is no coming back from that sort of debris inclusion, no cleaning method can repair that sort of damage because the bonds that form within the engine orifices are covalent, atomic, due to the wild wide nature of assorted random molecular interactions per second (one second of running an engine without an air filter leads to millions or billions of microscopic debris inclusion to an engine air pathway, a small percentage of which is "blown by" into the crankcase and circulates in hot engine oil). I am not saying that 1 second without an air filter will ruin an engine permanently, I am saying that after some length of time of poor filtration, depending where the engine is (some places are more "dusty/dirty" than others) it will become this way. It depends also on the flow rate of the engine, an engine at idle isn't going to ingest as much as an engine as WOT for example, it is knowledge for precautionary & exemplary use.