Please read my post #74 again where I am talking about "cylinder pressure" and how the static compression of a motor affects "cylinder pressure". I am not talking about manifold pressure, that should be obvious by now if you were reading my posts. Obviously these pressures are much higher.

There is nothing in direct injection design that always requires a certain static compression ratio. In fact there are companies designing lower compression GDI systems today. Some of the first DI systems used lower compression. The manufacturers today are designing these engines for emissions and efficiency while still having power and they are counterproductive. They want to take advantage of that lean burn cycle to the max. Of course you lose power by lowering the static compression ratio of an engine, but in a turbo engine you can easily get that back and more by being able to safely run more boost with less stress on the motor as I explained in post #74.

Visteon Corporation: Low Pressure Direct Injection Fuel System

New technology turns petrol engines into low compression diesel!

you're on the right track KGB, I'm learning too. I haven't made a map I'm happy with yet, so I continue to use the OTS stg 2+ 93 v1.03 map from Cobb. I can't wait to see what Lex comes up w/ either. I'm convinced ATR is all we need to solve our tuning issues. Fuel and stronger rods are clearly another story but I see no reason why we shouldn't feel safe running a basic stg 2+ on the stock bottom end.

I give up, you arent understanding a thing im explaining to you. VW and Audi DI technology is not the same as BMWs DI technology, nor is it the same as Ford, Mazda or Chevy.

Im reading the middle of the book and you are still reading the table of contents.

I don't feel like you have explained anything well from your point of view. I don't even feel like we are reading the same book...LOL. You have made a few statements in this thread and most, if not all, of which I agree with. But, for some reason you have a problem with what I said about static compression and how it affects cylinder pressure when you raise or lower it (and what that means in a turbo application). What I have been talking about applies to any platform whether DI or not...it's physics. Cylinder pressure (not manifold pressure) can be calculated with mathmatical models that take different variables into consideration (static compression, intake temp, intake pressure, fuel mass, air mass, cylinder volume, starting temp etc.). Raising static compression causes an exponential increase in cylinder pressure and temperature. If you add more boost pressure to make more power instead of raising compression, this has a more linear relationship with cylinder pressures and temperature. This is why they lower static compression in turbo charged engines as compared to their NA counterparts; lower cylinder pressue, less detonation, lower temps, less stress.

Please enlighten me about what I don't understand without directly contridicting what I have said in post #74. We may be talking about completely different points, but I won't know until you elaborate a bit. Hit me, I'm sure I can understand it if you explain it better.

No hard feelings Haltech, I like to discuss and debate. I usually learn things from others perspectives when I do.

I have been reading carefully the whole thread but I'm not sure I understand.

First, what makes you say that the cylinder pressure grows exponentially in relation to the static compression ratio? Could you elaborate? I think that if you double the compression ratio, the product between pressure and temperature in the chamber will be double, whether before or after the burn, and that means the pressure alone is even less then double. So the relation is not even linear.

Second, are you aware that in a turbo engine the peak pressure is not so much higher than in a NA engine? The mean cylinder pressure is much higher, but not the peak, as the burn takes place longer after TDC.

Third, are you aware that this dreaded power is a function of a few variables like rpm, bore, stroke, number of cylinders and mean cylinder pressure during the power stroke? and if all the others are fixed, you cannot up the power in any other way than by upping the cylinder pressure?

Fourth, are you aware that fuel efficiency is a function of only a few variables, compression ratio being one of them? the higher the better?

And finally, are you aware that until you come on boost, the compression ratio ( figuratively speaking ) is what pushes you forward, in a slow or fast manner?

And then I ask you, what's wrong with a high compression ratio? It's nice of course to have a dyno queen, that makes gazillions of horses, but if you want to also drive the car you must have a decent compression ratio as well. The higher the better.

DI is what allows Mazda to get away with running such high static comp ratios + high boost. Without DI, this would be a race fuel only motor, as it sits. DI is like water injection, cooling the charge actually in the cylinder, keeping detonation in limits acceptable to street engine operation. If they used port injection, they'd probably have had to cut at least a point off static and maybe bump up the overlap on the cam timing to avoid det, which would make this motor a turd around town.

Are you aware that you say are you aware alot.

I'm going to input a little side note here:

What is so hard to grasp as to why people are breaking rods on their MS3? People throw on a shit load of bolts on and expect their car to a) do some 150+ HP/TQ without any severe ramifications- either in the short or long term (i.e GO BOOM) b) expect their car not to feel different or drive differently (i.e more vibes at idle, boost cuts, over-boosting, etc, etc.

Whether it's a DI engine or any other engine (STI, EVO, etc) you can't expect your stock engine to be the same or NOT BLOW if you throw a shit load of bolts-on parts or even just a few and not expect this thing to blow. You're loading the car with so much more load when you increase the HP/TQ that the engine simply wasn't design to handle beyond factory specs and it just so happens to be the ROD that goes 99% of the time on this car.

Somebody said that this is a weak engine- well, what engine isn't weak when you try to operate it beyond it's factory specs and then being surprised that the engine blew? Sure in fact, other engines have more tolerance then others to operate beyond factory specs (whether it's 60HP or 100+HP)

This engine if done right has great potential. If you're going to start modding your car- even something as a cheap CPE CAI you're already begining to operate the car beyond factory specs. Going into heavy mods (meth, headers, FMIC) etc... well, that's history.

Like others have stated in the past a lot of people that blow their engine don't exactly state what exactly happened (what blew or what was the cause of the engine blowing). Majority of time, people slap quite a few blots on and don't even get the car tune, don't take care of it and wonder why their car goes BOOM) that is not to say that the car won't blow with a tune because if you push it will- duh.

Sorry, just started to rant. Nevertheless, the load on the internals simply increases when you increase the HP/TQ and the internals just can't handle this.

Build your internals and you'll rest more easily. That's why it's more safe and logical if you know you're going want to push this car to high HP/TQ ratings to actually have the engine build first and then go with the bolt ons. Other wise, slapping on a shit load of bolts on parts and have the engine go boom- shouldn't be a big surprise but it's seems it still is to some people.

I agree with you, but traditionally, not all Japanese, high hp turbo cars were built to operate WITHIN spec or below the 20% uprating, like our MS3's. Take for example, the 300ZX, TT Supra, and even the RX7's. Those cars were OVERBUILT/OVER-DESIGNED, meaning their stock components can handle MUCH more output than they were designed for. It was not uncommon to see 600whp 300ZX or RX7's and 900whp Supra's...and a lot of the current generation of enthusiasts are from that era or have been inspired by those beasts from the East.

As someone else has pointed out, this is no longer the case with current gen of cars. Starting with the ITR and then the S2K, Honda pushed the envelope of what is deemed a factory motor, by releasing high-strung, factory-tuned engines. Even tho you can get a little more power out of them, it became increasingly hard to rely on the old tricks of just upping fuel/air/boost with forged internals to make more HP.

With DI, not only are we pushing the envelope of current design but also faced with realities of manufacturing that to cut costs, you can't over-build and over-design anymore. Give it a couple more generations, and not only will DI make more hp, with better efficiency, but another form of combustion should come along...homogenous charge compression ignition, anyone?

I agree. The thing is that was in the past; years ago. Manufacturing has changed (obviously) a whole lot since then. Yes, don't get me wrong there are many cars that you can push the engines to beyond its operating specs (whether it's a Mustang, EVO, STI, etc)

It just seems it's hard for some people to grasp this especially those who mod the hell out of their (for example MS3) without an engine build and are surprised why their engine blew or BETTER YET, some are even more surprised why JON DOES's car who is fully bolt on (doing let's say 330WHP & 350TQ) didn't blow but their car blew with just (let's say) a FMIC, CAI, HEADERS and a tune (whether it's AP or STANDBACK). This is where the problem begins for those who don't understand. Not all MS3's coming out of factory will be the same- period. One could blow to a shot load of bolts on while the other will not- it all depends.

Regarding this engine it shouldn't be a surprised and it should also be a lesson to the people who are actually starting to mod their MS3's as to how much tolerance this engine has to operate beyond factory specs.

Just for the sake of argument I'll use me as an example. I don't like to post as to what mods I have and shit but currently my peak power is roughly 340HP at 4RMP and peak TQ is 350 or so... I have to look at the chart again but that was from my 1st tune and I'm going back to get a second one within a few weeks. Since, then, I did a lot more mods.

I personally understand if my engine blows why it blew. I was going to only spent about 3 grand on bolt ons with a tune and operate the engine not far beyond factory specs since I'm going to be rebuilding the engine ( a whole new block, etc) this winter or early next spring. I told myself, if the engine decides to blow in the mean time, well, that's my lost.

Well, spending 3 grand on bolt ons didn't want me to spent additional few grand on a whole new rebuild engine and the mod bug kicked in and I got carried away with the bolts on. My car at the moment is sitting waiting on few replacement parts and it will be drivable within a week or so. Everything has been done to the car expect a new rebuild engine which will be done late in the winter or next spring. Now, I know, that if my engine blows I know why it blew. If it blows while getting it tuned on a dyno, a week after or a few months later, simply put I'll just look at what blew and call it a day. I'm not going to waste my time speculating at the exact reason why it blew or what I could have done to prevent it because those answers are obvious:

a) If I didn't want it to blow- I shouldn't have heavily modded or have my internals build sooner.

b) why did it blow- uh, bolt ons, operating the car beyond it's capabilities of handing so much more load then it was designed to handle or operate within.

If my engine does last till I build it I guess I could consider myself lucky. When it's build, I'll have a brand new engine fully build and all my bolt ons as well as a spare stock engine.

So, nevertheless, like I was going to say it's all about MONEY MONEY MONEY for the manufacturer. Like somebody else stated earlier, they don't care about the 5% of car enthusiasts on the planet- all they care about if making a car that will sell and make them profit. They make an engine and the whole car to specs for mass public. Each engine, has a given % of tolerance as to how much it will handle beyond those factory operating specs.

If an EVO's stock engine has a tolerance to handle 200HP on stock internals good. From experience and people posting their results on the forums of blown engines we know how much tolerance we have over stock specs before you ask for this engine to blow.

Wouldn't it be nice if stock internals could handle 200 HP.... once could only dream.

I am aware of that sir, but only when circumstances call for it :-)

We are breaking rods because Adolph Hinkle hits them with the ban hammer on Mazda6Club.

I am talking about a static compression increase versus an increase in boost pressure. Increasing the static compression ratio will yield a much higher pressure and temperature during the compression stroke (pre ignition). This is because you have a chance to remove the heat generated during compression in the turbo with an intercooler before it enters the cylinder. If you increase the static compression of a motor, then more heat is generated in the cylinder during the compression stroke. More heat, more pressure, thus it is much more efficient and safer to make the same power using more boost pressure. This is why turbo engines that run higher boost typically have lower compression ratios. Can you build a high compression motor to take higher boost? Sure, to an extent, but it isn't as practical and economical.

Exactly. This is why we need a good balance between thermal efficiency and volumetric efficiency if you want to handle higher boost reliably and still have a streetable daily driver. You don't want to lower your static compression too much as that will lower your thermal efficiency and thus drivability when boost (volumetric efficiency) isn't available. If Mazda had lowered our CR 0.5 from 9.5:1 to 9.0:1 or so and not been quite as aggressive, it could have made the difference in our longevity without sacrificing much low end power at all (and they also could have used stronger rods:sad:). Find the delta equation for changing CR and do the math, we would probably lose ~2% of our low end power by lowering our compression ratio by 0.5. This would have lowered cylinder pressure/temps and also fuel economy by a bit. I don't know about you, but I bought this car for its volumetric efficiency, not its thermal efficiency. I would have gone for a Prius or a Civic if that was my desire.

DI hypes that injecting the fuel directly into the combustion chamber has a cooling effect and thus allows for a higher compression ratio. This is very true when we go WOT. I'm sure its working nicely then. But under part throttle, low boost and especially during the transition from closed loop to WOT, I don't feel like our DI platform is doing us much justice in this area...its just saving fuel and pushing us into lean conditions during the transition that sacrifice the longevity of our motor. I think those using meth have the right idea.

good read

Post of the year!

Ahh, this is why I love this forum!

how many 3s 6s and cx7 units have been built and sold compared to how many we can count that have blown engines? turbos are rough on engines built or otherwise. its hard to work out bugs with limited money and resources most of us arent positioned to be able to afford failure like a big company. trying to blame our insecuritys of blown motors on mazda is a waste of time. we should be working on options and pool our knowledge together to make our cars great instead of giving mitsu subaru and honda fan boys shit to link and make themselves feel better about there played out shit, this is still a young platform to pioneer and there are plenty of pioneers here i read youre posts all the time.

If we didn't have threads we wouldn't be able to share knowledge and experiences...

Who cares about mitsu/subaru/honda?

Mitsu EVO is a great track car and a shit daily driver.
STI is a pretty good combination of the two but the interior is still mediocre and its 15k more.
Honda? Got torque? They dont...Honda makes excellent cars but so does Mazda.

The speed3 gives you power, great responses from behind the wheel and a superb interior, especially given the quality of the new 2010's. All it takes is a little research to know that stock and mildly bolted cars are pretty reliable especially when properly tuned.

The car isn't as strong as an EVO/STI but its not the same car and was never intended to be.

Sorry but I can't do the math. The formulas needed I can find out easily, but all the values of the parameters that go into those - a bit more difficult.

It's all a matter of where you find the good compromise. You say lower the CR to 9. I ask - why not 7? If 9 is better that 9.5, why wouldn't 7 be better than 9?

So I choose to trust Mazda on the good compromise - 9.5 - until someone with real knowledge comes up and proves that there is a better one in reference to some criteria that I can relate too.

For me, 1/4 mile and dyno numbers are not relevant.

However I do agree that power needs to be up top - I wouldn't mind moving to a bigger turbo that spools later in the RPM. But I do not want to have a slug all the way to 3500 RPM - and a higher CR gives me some reassurance that it will not happen.

It's just my point of view about my own good compromise. I am not saying a lot of people wouldn't benefit from lowering CR, depending on their own criteria.

So it would technically be safer to run a reworked K04 since it spools a little later, thus making peak torque higher in the rpm range?

Yes, I agree, it is all about compromise and ones own criteria. My criteria sounds like it is much like yours. I am not looking for a dyno queen, just some decent breathing/tuning mods that modestly increase power, but keeping it driveable and safe. With platforms I have worked with in the past, this was easily doable without worrying about throwing a rod. Quarter mile times and dyno numbers are of interest to me because this shows us what mods work and what our limitations could be.

The equation for calculating thermal efficiency when CR changes is simple and it is widely known what happens when you increase or decrease your static CR when other parameters are fixed. Going from 8:1 to 9:1, the equation tells us that a theorietical increase of 3.5% can be obtained. In reality, these number can potentially change, but not drastically. We also know, due to how the variables of the equation relate to each other, that a change from 8:1 to 9:1 will increase thermal efficiency more than a change from 10:1 to 11:1. I am simply postulating a 0.5 decrease because that would be a sensible place to start to make our engines safer. Lowering it to 7:1 would be an idiotic choice by anyone that understands how this stuff works. You would have definitely have a slug. In a turbo engine, it safer to make more power by reasonably increasing the volumetric efficiency than pushing the thermal efficiency to the brink of safety. If you want room to increase your VE safely, and your engine is already running on the brink of safety, you need to lower CR unless you are increasing the strength of your internals or doing something else to lower cylinder temps.

When an engine designer decides upon a static CR, there are many variables to be taken into consideration. When you mass produce an engine that will operate in variable environments (hot/cold, high/low elevations etc.), it becomes very difficult to determine the sweet spot between performance, efficiency, and safety. For example, if we were all running in 70 degree temps every day with some humidity to suppress detonation, choosing a higher CR would be safer. Or, if we were all running in very hot and dry conditions, choosing a slightly lower CR would be wise. Engineers can run all the models they want to determine this sweet spot, and I'm sure they do. But, only hindsight we tell whether or not they got it right to be safe for the strength of the chosen internals (as well as what happens when a couple breather mods are installed that modestly increase output). Most modern engines are designed to run on the brink of detonation to get better fuel economy and better emissions. More stress is being placed on the engine on average even when detonation is being avoided by increasingly intelligent preemptive/adaptive ECU technology.

All this being said, Mazda has built a nice engine in stock form. If they would have decreased the CR a bit, we would be in a safer position to mod and make more power on the stock block. I don't blame Mazda for these decisions, the platform is what it is. But, most of us are interested in making some power gains and it is good to discuss our limitations. If they would have put stronger rods in place, we wouldn't be here discussing this at all.

Sorry for the book folks, but in written form it is very hard to get your point across without being flamed, espically on more complex subjects.

um...this theory makes sense...except for the fact that most of the blown motors were at partial throttle or even cruising.

If this was true...then ALL of us would blow at full throttle at 3,000...since others blow at partial throttle

Did anyone happen to catch this info from Cobb posted over on 247

Take it for what it's worth

That would comfort all my worries if cars were throwing rods at WOT only.

Car doesn't have to be at WOT to generate large amounts of pressure/torque on the itnernal components.

What? He was responding to what the people from Cobb are saying, which contradicts what Lex is saying.

Once a rod has fatigued or has developed a crack, it does not take maximum pressure to have it fail. Gear changes create momentum and force changes in the rotating assembly even at low RPM that can take the fatigued part over the edge. Remember that decelleration (vacuum) "pulls" on the rod while cylinder pressures apply compressive forces to it.

Are you aware that evo 9s with simple bolt ons like exhaust...intake...bigger FMIC core...can reliably get into the 400 whp range from a good tune off the stock turbo?

If you ask me...compared to other similar cars (4 cyl turbo) our car is one of the weakest in terms of popping motors.

Your missing the point.

It is not comforting to know that we can "break" our motors when we are not even pushing them as hard as they should be able to go (partial throttle)

Im still not convinced that this is the problem. If we really are "straining the internals to much" then we would be popping left and right at WOT...not ONLY (for the most part) at partial throttle.

Not so sure about the simple bolt-ons getting 400whp. It requires a little more than that. And even if they are at 400whp, they usually don't make more peak torque than we do.

you consider meth and a fmic heavy mods? last time i check they didnt add much hp on their own, a fmic is an efficiency mod and meth will only clean and help your engine run cooler and rid knock.
So please with your vast knowledge explain to me why our forged block cant operate beyond factory specs, when people start blowing wot il start believing our motors are weak, but until then and we continue to blow at p-t and low load i dont believe it.

Get rid of our knock, make sure you have a fp, and tune the car right and these motors would stop blowing, our turbo is way to small for a 2.3. Our peak torque is way to low and thats also a main problem, theres a reason mazda changed the ecu settings on the newer ms3's.

Look at dynos between the 07's and the 08.5's or 09's and youll see we dont have a huge tq spike like we used to at 3k, now its more gradual and higher in the rpm band the way it should be. Look at the recent liquid motorsports dyno stock and tuned and look where the tq is, its where its suppsoed to be and the tune is a lot safer even stock then the older ms3's were.

what about cams that move the powerband to the right?

what is also interesting is this... subaru's can make 400ft lbs on stock internals by 3000 rpm and those do just fine

I understand that by is that partial throttle seems to be the time when most of the motors have popped? because most daily driving is part-throttle low rpm?

Thats part of it and when you look at how the boost comes on as we've discussed in the past, the boost comes on pretty hard right around 3k rpm so part throttle in 5th or 6th gear at 3k rpm could put a lot of strain on the internal components especially since that force can't be disapated by spinning the rotating assembly because the driver is in a higher gear.

I know that people are concerned with the part throttle blow-ups. These are certainly explainable - and I think the short article below from hot rod magazine clearly explains how fatigue and material impurity can lead to brittle fractures. This is why some guys last longer stock and some don't. When a brittle fracture starts to happen, you won't feel anything until that fracture has grown enough to cause the rod to snap. The fracture will most likely let go under vacuum or when engine RPM changes (gear changes) since the rod is being "pulled apart" at that point if you will.

Cylinder pressure, high RPM, etc all play a part in exploiting a material flaw if it exists in the first place and bring it out of the wood work faster.

If you look at MS3 rods, you clearly see that the surface finish is not smooth (machined) like it is in aftermarket forged rods.

thanks for the information. I'm subscribing to this thread. Shit scares me.

It's good advice for any motor not to go WOT in high gears at low rpm. This puts MAXIMUM strain on the rotating assembly. Get at least 3K on before stepping on it fully and I bet you'll be fine. I know the short gearing and the 6K chokeoff sometimes conspire to place you in higher gears sooner but, nothing wrong with a downshift to make sure you don't overload it.

NOW, if you're just cruising about at crack throttle, the load is so slight, there's nothing to be concerned about.

not by 3000rpm, with stock turbos they usually make peak torque around 3600-3800 never 3000 and ive never seen below 3500

Here's a thought i had while ago...

You say that vacuum and coasting and hard on the rods cause it stretches them (and i agree fully), and that rapid rpm changes exaggerate this stress, and this exposes the potential small fractures which causes us all to blow at part throttle, light load, or gear changes right?

Well wouldn't a BSD further exaggerate this, cause the rpm change while shifting is much much faster. rpms fall alot faster with the balance shaft removed cause of less inertia and they also rev alot faster with clutch in, so wouldn't there be more bsd cars popping if this was the cause?




I'm sorry to bring the bsd into this conversation, cause i'm sure by now everyone hates the fucking topic.

Wouldn't the same hold true, if not more so, with a lightened flywheel?