Upping the Boost on my VF SC'd 540. Testing the Failure Limits of the Stock M62?

[BMW540san]

Vow, what a great job. Very impressed and looking forward to find out where that limit is, but with good ending. VF could learn a thing or two from you.

[JimLev]

Thanks! I hope I end my addiction at this level and don't need to build a low comp motor. Lol. I see the guys on FI going that route every day though. I'm hoping this caps this car off on the power side of things.

Come on now, you know this isn't the end, it never is. You'll be adding the intercooler next.

[geargrinder]

DEFINITELY that is the case (never the end..)

The FMIC I don't think is going to be workable or at least sensible engineering. Not enough 'boost to spare'.. i.e. losing 3-4psi in pressure drop for a long FMIC setup (and on our cars there's not clean-short route to a tidy FMIC with light losses so indeed it'd be "lossey") is painful to a low PSI S/C setup, unlike the 20-30psi turbo guys who can just push the turbo harder.

I def think the low CR build would be great. Even if you just stacked HG's maybe although if you did an out-of-car build why you'd stop at that I dunno. Bigger valves. Then whack a bigger crank pulley on. Then blow up the V3Si blowers bearings so you have to go with a straight-cut-gear V7... And on it goes.

[Mach540]

What is the theory behind the low CR build? How does that work?

[philly98540]

Awesome doc Chris! I like the simplicity - not too elaborate, totally reversible if you needed to. It's way smarter than the VF design as it relies on idler-wrap for grip, not pure tension... I have zero doubt it will be way more forgiving of belt wear and tensioner spring fatigue than the factory design. And it's forgiving of 'homebrew' imprecision... if the locating holes are of by a wee bit it is inconsequential.

Might have to do this come warm weather... even just on factory pulley.

Couple questions...
1. Does the belt go on/off easier in this setup? Do you have more slack w/ tensioner released? That's always annoying as hell...
2. Is your alternate tensioner harder/easier/same to get wrench on vs the VF unit? If I had one other change to get out of this it would be a setup where it's not so hard to get the tensioner released.
Chris is throwing all-in to find out the ceiling here though which is awesome. (If he blows up his DD I'm def in to head down and help build a replacement motor on a stand... ;^) )

Thanks for the cudos JC! I struggled with many ideas and this one stuck in the end for all the reasons you stated.
1. Belt was new, so I located the idler so the belt was taunt with tensioner pulled down out of the way. After a couple of drives, belt is now a bit slack with tensioner pulled down. I set the pulley very close to the SC pulley to maximize wrap, so that has to be unbolted to get the belt off. Very easy though with two 13mm wrenches.
2. The access to the tensioner square hole is still close to the xtank so a grinded down belt tool works great. It's easy to move it toward the drivers side to relieve the tension.

I'll be taking you up on that rebuild promise!

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Come on now, you know this isn't the end, it never is. You'll be adding the intercooler next.

No plans for FMIC, but i think will free me up to do some cosmetic stuff. My car is still vintage stock pre facelift.

[mcgnms]

Long answer is its complicated but short answer is usually stuffing more air into the cylinder makes more power than compressing it more in this case. Dropping compression from 10:1 to say...9.5:1 can be made up for and exceeded by running a bunch more boost without (or lowering the risk) blowing a headgasket or needing different fuel for example.

Some of the theory revolves around peak cylinder pressure versus average cylinder pressure. Lowering compression and increasing boost can increases average pressure which is less dangerous compared to peak pressure and thereby saving a headgasket and preventing detonation.

Its situation and build dependent.

[philly98540]

JC, thanks for explaining the FMIC minuses for this SC type set up. Meth is the way!

[geargrinder]

Forced Induction 101... Normally aspirated motors need a lot more compression ratio than is needed or optimal for forced indictuion... With Normal Aspiration the intake is in vacuum so you like a lot of compression ratio to get the charge to the right density and drive good "VE" (volumetric efficiency i.e. how close to theoretically 100% efficient the engine is for given displacement). Lots of C/R A is generally great as long as you keep your octane up and avoid detonation from cheap gas, but as you can imagine, there is a ceiling on compression at which point you start to create detonation instead of power.

With forced induction the charge is being crammed into the cylinder as soon as the valves open and essentially dramatically raises the effective C/R, and therefore what was a great N/A C/R before can be too much compression and cylinder pressure under boost. This leads to detonation, which means chamber and exhaust gas temp (can burn valves and pistons) and timing issues (ECU constantly pulling timing to avoid the detonation), and with the levels of power that a big turbo can create, even blow headgaskets and/or lift cylinder heads, etvc. This is why with "stock" normally aspirated C/R a motor will generally be limited to relatively low boost levels. Especially in the modern age when even your grandma's Toyota has what mighta been thought of as "high performance C/R" back in the day. Knocking down that C/R means you can start stuffing more boosty goodness in there... the tradeoff is that the powerband will soften up down low where the motor is off boost (i.e. close to N/A and now you've made it a lower performance N/A motor...), but of course us stupid gearheads mostly end up preferring the huge kick in the asspants up high even if the low-end suffers a little bit.

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1. Belt was new, so I located the idler so the belt was taunt with tensioner pulled down out of the way. After a couple of drives, belt is now a bit slack with tensioner pulled down. I set the pulley very close to the SC pulley to maximize wrap, so that has to be unbolted to get the belt off. Very easy though with two 13mm wrenches.

That's ideal in my book - tight first time but then after break-in makes it just right.

I'd like to be able to pull belt w/o idler removal but nice thing about your design is if I want to give little bit more room I could always just slip my mount holes down a little bit. I think you are belt and suspenders here and have all the wrap and tension you'll ever need (too bad VF didn't go w/ this kind of design) so I might go that way.... Or not, taking the pulley off isn't too big hassle I guess... But again, nice thing about a simple design, easily tweaked and played with.

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Long answer is its complicated but short answer is usually stuffing more air into the cylinder makes more power than compressing it more in this case.

LOL simul post everybody answers the same question.

[philly98540]

That's ideal in my book - tight first time but then after break-in makes it just right.

I'd like to be able to pull belt w/o idler removal but nice thing about your design is if I want to give little bit more room I could always just slip my mount holes down a little bit. I think you are belt and suspenders here and have all the wrap and tension you'll ever need (too bad VF didn't go w/ this kind of design) so I might go that way.... Or not, taking the pulley off isn't too big hassle I guess... But again, nice thing about a simple design, easily tweaked and played with.

Going a bit lower or farther away from the SC pulley will work with the 3.25 SC pulley without issue.

If you do this with the 2.87 pulley, the belt may get too much slack and the tensioner will run out of travel. I'm not sure. If so, you could go down one belt size for sure and just drill the idler pulley hole where ever to suit. Really flexible design.

[angeleye540i]

Well boosting doesn't increase the C/R it just increases peak pressure, creating pre detonating / knocking, the actual ratio doesn't change and I know YOU know that, but I guess people can look at it that way... With water/meth and ~15psi+ he should be fine tho... The higher octane the higher pressure the fuel can take before detonation... that's why high performance/high compression motors like the ones used in BMWs need a higher octane fuel... so if you're making a Molotov cocktail 87 would be preferable than 93 because it is more easily detonated... For those of you who were wondering about octane... Water/meth increases and or can change the octane for each stroke which is pretty damn awesome.... A lot of people still think higher octane means "cleaner" fuel... Higher Octane = more stable under pressure / less likely to detonate like a diesel, which does so from pure compression... Just for those who are to afraid to ask I'm sure most of u already know all this... So boosting has the same effect as increasing compression ratio but doesn't change it... I know... derrrp,... But some people don't know... Knowledge is power

[Mach540]

Long answer is its complicated but short answer is usually stuffing more air into the cylinder makes more power than compressing it more in this case. Dropping compression from 10:1 to say...9.5:1 can be made up for and exceeded by running a bunch more boost without (or lowering the risk) blowing a headgasket or needing different fuel for example.

Some of the theory revolves around peak cylinder pressure versus average cylinder pressure. Lowering compression and increasing boost can increases average pressure which is less dangerous compared to peak pressure and thereby saving a headgasket and preventing detonation.

Its situation and build dependent.

Forced Induction 101... Normally aspirated motors need a lot more compression ratio than is needed or optimal for forced indictuion... With Normal Aspiration the intake is in vacuum so you like a lot of compression ratio to get the charge to the right density and drive good "VE" (volumetric efficiency i.e. how close to theoretically 100% efficient the engine is for given displacement). Lots of C/R A is generally great as long as you keep your octane up and avoid detonation from cheap gas, but as you can imagine, there is a ceiling on compression at which point you start to create detonation instead of power.

With forced induction the charge is being crammed into the cylinder as soon as the valves open and essentially dramatically raises the effective C/R, and therefore what was a great N/A C/R before can be too much compression and cylinder pressure under boost. This leads to detonation, which means chamber and exhaust gas temp (can burn valves and pistons) and timing issues (ECU constantly pulling timing to avoid the detonation), and with the levels of power that a big turbo can create, even blow headgaskets and/or lift cylinder heads, etvc. This is why with "stock" normally aspirated C/R a motor will generally be limited to relatively low boost levels. Especially in the modern age when even your grandma's Toyota has what mighta been thought of as "high performance C/R" back in the day. Knocking down that C/R means you can start stuffing more boosty goodness in there... the tradeoff is that the powerband will soften up down low where the motor is off boost (i.e. close to N/A and now you've made it a lower performance N/A motor...), but of course us stupid gearheads mostly end up preferring the huge kick in the asspants up high even if the low-end suffers a little bit.

LOL simul post everybody answers the same question.

So what your saying is: "It allows higher boost levels"........... Gotcha.......

[mcgnms]

Correct. It sorta lets you increase average cylinder pressure without (or minimizing) increase in peak cylinder pressure. This comes at a cost of fuel efficiency however. Something tells me nobody here cares about that though.

[joekitch]

This comes at a cost of fuel efficiency however.

oh no! i'm down to 12 mpg!

[philly98540]

^^Lol. I'm getting only about 275-300 miles a tank around town due to lead footing. I can get 400 per tank on a long steady drive. Still pretty decent all considered.

[geargrinder]

Well boosting doesn't increase the C/R it just increases peak pressure, creating pre detonating / knocking, the actual ratio doesn't change

Well. It's the real deal. The Science And Engineering type term is "effective compression ratio" (notice my use of "effective" above) which means "how it really behaves not how the geometry measures". No its not the geometric or static compression ratio, but neither is what you get ever in a N/A engine in actual operation due to imperfection in actual real world gases and pressure/density changes. Never in actual operation is ECR going to be exactly geometric, it'll usually be less, excepting some rare freak of nature... by cramming more mass during the intake (& partially the compression) stroke however w a blower, we get more air mass jammed in than the full size of the cylinder at BDC, and the effect is as if we indeed much large piston for the same combustion chamber size.

Going a bit lower or farther away from the SC pulley will work with the 3.25 SC pulley without issue.

If you do this with the 2.87 pulley, the belt may get too much slack and the tensioner will run out of travel. I'm not sure. If so, you could go down one belt size for sure and just drill the idler pulley hole where ever to suit. Really flexible design.

Hmmm.. Anybody else thinking "machined slot"? Would solve my hypothetical question anyway, loosen the bolt so you don't have to remove completely, drop the pulley down to the bottom of the slot, pop belt off, Bob's your Uncle and Fanny's your Aunt.

To be super duper duper cool you'd radius the slot to the center of the blower pulley but that level of precision not necessary, probbers.

[mcgnms]

GG, everything you said is on point. However effective CR IMO only confuses people. May as well say effective displacement. Both blur the lines between what compression and mass displacement are. One is about adding mass while another is not. One changes behavior of the combustion stroke entirely different than the other.

I would seperate things such as boost and displacement from compression (and dynamic compression for that matter). Not saying the other way is wrong but it makes it more intuitive in my opinion. Just my $0.02.

[angeleye540i]

I understand u GG u don't have to explain to me... But others might not, and even tho it may be the correct term I think mc is right about it confusing people....

But why over complicate this... More air = more O2, more O2 = more hydrocarbons (liquid fuel)needed/given to react (to burn) = bigger boom = stronger power stroke... Too high of pressure + to low of octane = bad = knocking = sad face = predet = sad panda - damage - loss of performance or function all together...

But that explains why turbos are so efficient because they run off the essential "run away" reaction from the initial boosted charge, not engine revs (like super chargers) which do not directly reflect amount of reaction products in cylinders, whereas turbines drivin by these reaction products does directly affect the next charge / next turbine feed... And yes GG u are obviously right about everything just trying to simplify it for anyone...

I think someone selling there Turbo M3 today said a year they didn't know how a turbo worked so I assume it's not common knowledge.,.

[geargrinder]

Uh. No.

Apparently DO have to assplain it to you cuz you didnt get it, argued with it, and said its not real, and completely missed the "effective" bit until after its explained and now "gee you already knew it all". Uh no dont believe you. You dont need to play games, you didnt really know about ECR before, now you do, its OK.

A scientist or engineer will tell you the static CR is what is not real - real life applications dont follow ideal gas behavior so ECR is far more real and static / geometric is what is really hypothetical. Intuitive for a garage monkey to understand? Sure. But do you want to be accurate and a little complcated but have all the information and understanding possible, or, wrong but easy to understand? If the latter - i can help you - engines run on magic invisible fairies trapped in tbe cylinders that live on gasoline and air. There ya go. Simple! Easy!

It is TOTALLY useful in a case like Chris's. At 12PSI he is ~ 18:1 effective CR. Thats helpful to know as a reference and bring into consideration for mods. At 14psi he's near 20:1. It is real and it is legit and on forced induction is far more useful to know than static which is just the starting point for a calc that can and should be done. Shows how near the edge that build might be too. Provides a benchmark to other builds.

Learn engineering. Use the right words. Dont hide behind oversimplifying to wrong "because its easier that way".

Have to connect you with the guy who doesnt believe in corner scales and corner weighting uhh becuase "uh like cuz physics" yet thinks "equal and opposite reaction" doesnt explain exactly why scales DO work.

Now chris is gonna hafta give me a timeout for being honest (see mcgjmaxssshs yer not the only one i abuse! I'm an equal opportunity troll!)...

[dk500]

Uh. No.

Apparently DO have to assplain it to you cuz you didnt get it, argued with it, and said its not real, and completely missed the "effective" bit until after its explained and now "gee you already knew it all". Uh no dont believe you. You dont need to play games, you didnt really know about ECR before, now you do, its OK.

A scientist or engineer will tell you the static CR is what is not real - real life applications dont follow ideal gas behavior so ECR is far more real and static / geometric is what is really hypothetical. Intuitive for a garage monkey to understand? Sure. But do you want to be accurate and a little complcated but have all the information and understanding possible, or, wrong but easy to understand? If the latter - i can help you - engines run on magic invisible fairies trapped in tbe cylinders that live on gasoline and air. There ya go. Simple! Easy!

It is TOTALLY useful in a case like Chris's. At 12PSI he is ~ 18:1 effective CR. Thats helpful to know as a reference and bring into consideration for mods. At 14psi he's near 20:1. It is real and it is legit and on forced induction is far more useful to know than static which is just the starting point for a calc that can and should be done. Shows how near the edge that build might be too. Provides a benchmark to other builds.

Learn engineering. Use the right words. Dont hide behind oversimplifying to wrong "because its easier that way".

Have to connect you with the guy who doesnt believe in corner scales and corner weighting uhh becuase "uh like cuz physics" yet thinks "equal and opposite reaction" doesnt explain exactly why scales DO work.

Now chris is gonna hafta give me a timeout for being honest (see mcgjmaxssshs yer not the only one i abuse! I'm an equal opportunity troll!)...

Lmao I don't see what is so complicated here. My chem teacher even used this as an example to explain how ideal gasses are almost useless.

[philly98540]

Screw the C/R saga guys. Its a good lively discussion nontheless. Effective is what is important on any engine. So many variables at play you can go crazy trying to figure it out. What we know from real world is, too much boost starts to cause issues. Lowering CR alleviates these. I'll be playing in the zone that should be fine for this style of engine, if I get a solid tune and keep Temps in check.

I like the slotted hole idea for the pulley GG. I may do just that.

[nikatkimber]

Lol. It's kinda like "frictionless pulleys" and "massless ropes" and what not that you use at a basic physics level.

[angeleye540i]

"Equal opportunity troll" LOL I think we could get along if we could only sit and talk... in person... Sorry Philly, wasn't trying to thread Jack, just trying to simplify some engine concepts for folks who don't understand as mc pointed out... ANYWAY... This is your daily driver ? So when's all the work Getting done AND how's it driving pre tune?

[angeleye540i]

Lol. It's kinda like "frictionless pulleys" and "massless ropes" and what not that you use at a basic physics level.

right

[mcgnms]

Weeeeez. Pretty sure this was just a misunderstanding between you guys. I just advocate to not compare CR and ECR because they're just totally and completely different things. Its not that one is more important or less important. Seems Angeleye540i was just trying to say that.

ECR involves just changing mass while things like CR and rod:stroke actually effects how the combustion chamber's size changes with respect to time.

ECR just tries to account for VE and some forms of the equations also use dynamic compression (where the valve closes). Also with ECR in most cases its more accurate to square root the number when you divide boost and atmospheric before multiplying by the static ratio.

For example GG got the number 18 by taking the absolute pressure post compressor divided by atmospheric and then multiplying that quotient by 10 (static CR). That gets 18 if you run 12 PSI.

Normally the better formula is square rooting that quotient first. That gets a 13.5 ECR.

The other big reason I think they should be separate is that it can almost be taken as trying to make it sound like boost and compression are sides of a coin and they just aren't. ECR that is mostly from VE behaves completely different than ECR that is mostly static CR. 13:1 static CR is a different world from 8:1 static CR and a bunch of boost that yeilds a 13:1 ECR. Its important to note that, all I'm saying.

[philly98540]

A little lively discussion is good stuff. We are all here to share and learn and these type of convo's bring out the good stuff. Just keep it civil.

This is my daily. Every day for 15 years. Lol.

Trying to schedule at retune now, but ttfs must be at defcon 5 or something. Had a phone call with them, but nothing moving yet.

Car drives great. I swapped to the 3.25" pulley till tune time.