Dynamic Compression Ratios... and blown engines

[cld12pk2go]

I am under the impression that larger numbers in the table equate to moving the intake events closer to the exhaust events (the blue lobe shifts closer to the red lobe) resulting in a smaller LSA (or more overlap).

[djuosnteisn]

Seems to make most sense that way.

[06Speed6]

Originally Posted by cld12pk2go I am under the impression that larger numbers in the table equate to moving the intake events closer to the exhaust events (the blue lobe shifts closer to the red lobe) resulting in a smaller LSA (or more overlap).

I thought that was the way it worked at first, but the mechanism itself can only move one direction.


I also had a epiphany while driving home from work, anyone else notice that our cars stumble under load in the same rpm range that the VVT mechanism is changing its timing?

[Deadman]

was in my buddy's new subby and it stumbles as well under load. Was in it lastnite, and after reading what you said it just came to my head ha

[djuosnteisn]

Originally Posted by 06Speed6 I thought that was the way it worked at first, but the mechanism itself can only move one direction. I also had a epiphany while driving home from work, anyone else notice that our cars stumble under load in the same rpm range that the VVT mechanism is changing its timing?

The atr help file specifically mentions you can only advance timing, and not retard it, so just cause it only moves one direction doesn't really tell us whether the larger table values = less overlap or more, right? I'm 90% certain higher values = more overlap, but not 100%.

[06Speed6]

Originally Posted by djuosnteisn The atr help file specifically mentions you can only advance timing, and not retard it, so just cause it only moves one direction doesn't really tell us whether the larger table values = less overlap or more, right? I'm 90% certain higher values = more overlap, but not 100%.

This was already discussed.

I took apart the mechanism, it moves only one direction, it advances a max of 18*, and more advance = less overlap = higher dynamic compression.

There was some debate that since the mechanism only moves 18*, that the values in the code may be a percentage of 18*.

[djuosnteisn]

Great, then my confusion was simply with the direction of the term "advance" between the int and exh lobes. Just to solidify this for any other sad souls like myself

Higher atr vvt table values = more lobe separation = less overlap = higher low end torque = higher dynamic compression (i intentionally left out the term "advance")

... and is potentially a percentage of the available 18 degree range.

Sorry for throwing a dead horse in your thread, but i think it's best to be thorough. Thanks again for explaining so much about this shit!

[KoukiS14]

Isn't 18 degrees of camshaft rotation 36 degrees of crankshaft rotation? That would make the 30 degree values make sense.

[06Speed6]

36* still isnt 30* and thats a problem.

[cld12pk2go]

Originally Posted by KoukiS14 Isn't 18 degrees of camshaft rotation 36 degrees of crankshaft rotation? That would make the 30 degree values make sense.

That would make some sense to me. Perhaps we are limited in logic to 30° due to Valve to Piston interference issues? Or are we actually limited to 30°?

[djuosnteisn]

Realized i had a bunch of great scans that i've never even looked at. Sigh.

[Mfinlay04]

someone needs to data-log with the vvt table set to all zero's and compare it to their stock vvt table. We could go on for months discussing exactly how it works or doesn't work but until someone does this we will never "really" know. And it would be our luck that the ecu would have a way to compromise for the zeros on the vvt table. It'd be interesting too if someone has access to a dyno and can see what the dyno looks like with all zero's. If lowering or eliminating vvt lowers DCR then we could solve the blown motor issue. Props to 06speed6.

If this would explain blow motors with simple bolt on I/H/E then I will be the next speed owner for sure

[djuosnteisn]

This is prob the next best thing

It's not on a dyno, but it has all the pertinent information.

Basically, 30's on the VVT make the intake valves open up earlier (BTDC), increasing overlap, low end torque, and dynamic compression.

0's on the VVT make the intake open up later, up to roughly 2* ATDC, decreasing overlap, push power to redline and reducing dynamic compression.


I've always had the occasional PT KR pulling away from stop lights, and so i went ahead and expanded the region of zeros in the VVT here:


See that upside down triangle of low values around 2500-3000 rpm and 0.69 load and below? I pretty much expanded this triangle downward, decreasing the values at higher loads to essentially decrease the dynamic compression.

It seems to have worked like a charm, but i also having driven my car in a like 2 weeks or so.

[Deadman]

ya i get random ass kr cruising on the hwy around 2800-3000rpm. so as long as i drive like 75mph or under im good. Or 85mph + im good. 80mph is bad. LOL (occasional leaving the light kr as well)

sigh i love this car.


P.S i did just empty both my catch cans today so maybe that will change things?@! who knows only time will tell. When i see my DH throwing numbers @ me i just punch it and everything is good. pz

[djuosnteisn]

You have atr?

If so, try reducing the VVT values in that range man, see if it works for you.

[Deadman]

ya i do have atr. I dont ever use it though... not gonna lie. Hrmm maybe you can help me later.. Ill pm you bit later dude.

[djuosnteisn]

Okay, cool.

[Mfinlay04]

i really wonder how the car would run with the vvt table set to all zero's... I know that when a few non-speed mazda3's turboed they used the cams out of the focus motor without the vvt, since it is difficult to tune when the camshaft keeps advancing. If we had a dyno to compare this to the normal value we could see how useful the vvt actually is. it might not be worth advancing at every speed x load...

[06Speed6]

Actually I like the VVT, it gives a tuner alot of options - if the tuner knows what to do with them.

[Fullmetal]

im going to be flamed for this but after reading the whole topic there are so many mixed responses and causing disbelief. when vvt advances in correlation to crank postion the intake lobe gets close to exhaust and there is a reason for this and thats why BT with stock block and stock tune have nearly 1/20th the problems verse stock turbo. Is due to the fact that it helps spool the stock turbo faster. engine timing is a direct impact on turbo performance. i think Mazda took one of there diesel turbos and engine managment and fit it to a direct injected gas engine. The 2 only differences in the Mzr verse diesel is- type of fuel used and ability of more then 4k redlines. IMHO the VVT timing is used to spool the turbo quicker to allow low rpm torque. hence why BT is going to benefit you on stock tune do to the increase volume of exhaust gases needed to spool the turbo. moving the spool range from 27k to anywhere from 32k to 35k. BUT this what is going to get me in trouble. MAZDA/FORD also designs there high performance engines to run at most optimal performance with stock configuration, so what we put on the car is what it needs. you add more this is at your own risk of failure. I know this for a fact. the svt focus 2.0 ZETEC was tune to its max point that with out any forced induction you will barely see any improvements in base line power nothing greater then roughly 30-40 hp.
With seeing the VVT datalogs and known failure rates i have a feeling its do increased boost compression ratios. With mods ppl put on there cars it allows boost to surpass its normal limits to allow for more power. and this increases DCR. Hence why modded ppl lean out to fast to cause detention problems. and pre detention is what is kill our cars.
Once the DCR passes the threshold of our engines we will run into timing issues. with what i have seen of spark events verse timing events and valve timing. Im seeing to much fuel and air in the given space needed for proper operation.

ok im out of wind ill continue my hypotheses later

sorry guys

[bast525]

I know this is an old thread but I stumbled across it looking for information on tuning VVT. Has anyone compared the stock mazda tune to Cobb's OTS map, looking at VVT? They are identical except at 5500 rpm and up. The stock map has all VVT values at 5500 rpm at 0, then goes back up to 4 for the 6000 and up cells. Cobb basically flipped this around, going with 4 degrees at 5500 rpm and 0 for all rpm after that. I've tried it both ways but felt no difference, and dont typically log maf g/s.... now I'm gonna have to try it both ways and log hat to see what happens.

I would expect the stock values to be slighty better, as I know you want more retard at high rpm/load. One other thing I noticed, and I figure these HAVE to relate though I'm not sure exactly how they affect each other. For ignition timing, Cobb only changed the values around 5500rpm and high load, retarding the timing significantly.

did they increase vvt at 5500 rpm to help reduce knock?

[06Speed6]

The bottom line with VVT is that we need to weld the actuator in a single position, slightly increase the duration of the intake cam, and double the lift.

It is near impossible to finely tune a car when the cam timing is shifting all over the place. The only reason Mazda did it this way was because they tried to have their cake and eat it too, they wanted the increased spool time of a low overlap cam with the high end flow of a high overlap cam, and they ended up failing at both like the Titanic.

We just need a low to mid range overlap cam and .500" lift on the intake and .350" lift on the exhaust. With the lower exhaust lift we can shorten its duration and increase the duration of the intake and still have a low overlap cam.

[mrQQ]

so are you saying stockers are goners? :p

[jordan4g63]

Originally Posted by 06Speed6 Anything less than 7.5:1 is bad for power and torque and anything above 8.5:1 will generally knock on pump gas.

I stopped reading this post after this statement. Are we talking about our particular engine, or any engine? Many engines (even boosted) run just fine with compression ratio's as high as 10.5:1 on pump gas. My DD is 12.5:1 compression, and on the right tune it has no problems with 93 octane at any load/rpm. Maybe I am misunderstanding where you are trying to go with this statement.

Also, any engine that I have ever messed with seems to be the most vunerable at peak torque (when cylinder pressure is the highest) OR at high rpm. Generally, High rpm detonation will kill an engine much quicker than low rpm. In fact, the owners manual of my dodge ram 1500 hemi clearly states that some spark knock at low rpm is NORMAL and is harmless. Spark knock at peak tourqe and at high rpm is generally deadly.

[jordan4g63]

Originally Posted by 06Speed6 The bottom line with VVT is that we need to weld the actuator in a single position, slightly increase the duration of the intake cam, and double the lift. It is near impossible to finely tune a car when the cam timing is shifting all over the place. The only reason Mazda did it this way was because they tried to have their cake and eat it too, they wanted the increased spool time of a low overlap cam with the high end flow of a high overlap cam, and they ended up failing at both like the Titanic. We just need a low to mid range overlap cam and .500" lift on the intake and .350" lift on the exhaust. With the lower exhaust lift we can shorten its duration and increase the duration of the intake and still have a low overlap cam.

Did you word that correctly?

[06Speed6]

A dynamic, real world, end of the day, the engine is actually running compresion ratio of more than 8.4:1 will generally be knock happy on pump gas. A static compression ratio of 15:1+ is possible on pump gas engines provided that there is enough cam overlap, low VE, and ring gap that enough air isnt actually available to acheve 15:1. Also with engines with ported heads, the static compression ratio is almost always lower than what is advertised on the piston so sometimes you need to run a higher than normal static compression ratio in order to maintain the pre port job static compression ratio.

On our DI engine with VVT, we need a low overlap cam or we will have fuel blowing out the exhaust and reversing flow in the intake. The problem is that we also need lift and duration so that we can get enough air into the cyl. The solution, since there is a limit to the duration we can use, is to add lift to the cam. The problem with that is the ramp velocities would require a valve spring that is so stiff that we physically cannot use it. One trick is to weld the VVT solid and use the extra ~15* of timing to add more lift without increasing the tension of the valve spring.

If you had actually read my thread, you wouldnt be asking stupid questions. This isnt a 4g63, you have much to learn son. Noobs flamin my thread Someone get me a noob swatter...

[jordan4g63]

Originally Posted by 06Speed6 A dynamic, real world, end of the day, the engine is actually running compresion ratio of more than 8.4:1 will generally be knock happy on pump gas. A static compression ratio of 15:1+ is possible on pump gas engines provided that there is enough cam overlap, low VE, and ring gap that enough air isnt actually available to acheve 15:1. Also with engines with ported heads, the static compression ratio is almost always lower than what is advertised on the piston so sometimes you need to run a higher than normal static compression ratio in order to maintain the pre port job static compression ratio. On our DI engine with VVT, we need a low overlap cam or we will have fuel blowing out the exhaust and reversing flow in the intake. The problem is that we also need lift and duration so that we can get enough air into the cyl. The solution, since there is a limit to the duration we can use, is to add lift to the cam. The problem with that is the ramp velocities would require a valve spring that is so stiff that we physically cannot use it. One trick is to weld the VVT solid and use the extra ~15* of timing to add more lift without increasing the tension of the valve spring. If you had actually read my thread, you wouldnt be asking stupid questions. This isnt a 4g63, you have much to learn son. Noobs flamin my thread Someone get me a noob swatter...

Cry noob, but a lot of what you have posted is very generalized.

Example: "All ported heads change static compression ratios"

What? Only if there is chamber work done...static Is a physical measurement. Nothing before the valve matters.

[06Speed6]

Originally Posted by 06Speed6 Also with engines with ported heads, the static compression ratio is almost always lower than what is advertised on the piston so sometimes you need to run a higher than normal static compression ratio in order to maintain the pre port job static compression ratio.

Originally Posted by jordan4g63 Cry noob, but a lot of what you have posted is very generalized. Example: "All ported heads change static compression ratios" What? Only if there is chamber work done...static Is a physical measurement. Nothing before the valve matters.

Note that I said "almost always"... reading fail.

Also with a ported head, the valves are nearly always done and if the seats are not replaced with a stock height replacement, the compression ratio is lowered because the valve sits lower in the head.

This is a very generalized thread, no real information here.

[jordan4g63]

Originally Posted by 06Speed6 Note that I said "almost always"... reading fail. Also with a ported head, the valves are nearly always done and if the seats are not replaced with a stock height replacement, the compression ratio is lowered because the valve sits lower in the head. This is a very generalized thread, no real information here.

I guess when I think of headwork being done, usually there is some machining done to ensure a flat surface probbly offsetting valve work/ chamber work.

I am not trying to bust your balls, but when every post I read seems like someone is saying bt (like a 400hp capable turbo is big) all through a thread, I question what the knowledge level truly is around here. You seem on point and make some good observations in this thread.

For me, to get out of low rpm high load issues, a bigger turbo+turbine housing is needed:phillyb: I do have a billet pt 62/65 in my shop, but it seems like rods are a big issue with these engines. I surely don't need boost under 4k rpm.

[06Speed6]

You cannot really machine the head gasket surface on this head, if it is warped enough to need machining then the cam bore is going to be warped as well. Since we dont have cam bearings, it is extremely difficult to line bore the cam bore back to spec. Basically if the head needs to be machined, its junk. Thank you Mazda.

If you are talking about a couple thousanths for a good seal, that will not measureably affect the chamber size.

Completely off topic, but the rods are plenty strong. There is a drag car that runs a stock MZR-DISI short block to north of 1000hp with no modifications.

There are no low rpm, high load issues either. I run 20psi at 2700rpm on the stock snail and I probably have more miles on my car than anyone on this forum.

[phantom3]

Personally, I would kill for a VVT delete kit with adjustable cam gears. I wonder of we could simple buy a second exhaust cam gear and swap it out... That might just be wishful thinking though.

I have 67,800km on the clock and my VVT Actuator just crapped out me. I'm pretty sure once I open her up I'm going to find that the chain and tensioner need to be done as well... YEA!

[06Speed6]

The exhaust cam sprocket will not go on the intake cam.

I have about 165km on the clock and my VVT is fine =P What have you been doing to it that it broke...

[sidekick]

So I know this is old, but is anyone still interested in some no VVT logs?

I zero'd out my VVT table for a while and honestly, I kind of liked how the car felt like that. The turbo didn't spool up slower, but it wasn't so violent on spool up, like it is with VVT.

Unfortunately, you lose quite a bit of low end torque without VVT. I added about 10° of VVT back in the low end and picked up 20+ft/lbs in virtual dyno. If you're okay with that, then I don't see any reason not to zero it out. It makes the power feel more linear. I'll post up the logs and VDs when I get home if anyone is interested.


Edit: @06Speed6; holy fucking mod list lol

[06Speed6]

Thanks man, extra low end torque from +vvt is certain, and it is or should be definitely noticeable. Whether it helps turbo spool is where it gets murky.

[sidekick]

Originally Posted by 06Speed6 Thanks man, extra low end torque from +vvt is certain, and it is or should be definitely noticeable. Whether it helps turbo spool is where it gets murky.

I don't think it helps with spool much, at least not in my limited experience with zero'ing out the VVT table. The boost curves in VD looked almost identical, but the the VVT definitely made it "hit harder". Like an on/off switch vs the power coming on more evenly.

Edit: I might just make a new revision of my current map with no VVT. Then I can make a direct comparison on the same map. I think I made some small revisions between my no VVT map and +VVT map. It's kind of cool how you can bump the VVT up 5-10° and watch the torque curve change in VD.

Edit #2 : I just made a map for OTS VVT, No VVT, and my current VVT settings. Hopefully I'll be able to get some logs tonight.

[sidekick]

I did each run within 10 minutes of each other, so conditions were pretty much identical between each pull. Here are the results:
All three:


No VVT:


Custom VVT:


OTS VVT:


My settings and no VVT had almost identical results, but there was a pretty big increase in torque with the OTS VVT tables. I've attached the logs as well.

[btstarcher]

I like the increase in torque, but I'm also not a fan of my motor blowing while cruising. I'm thinking about dialing it back a bit under low load conditions but not sure what values yet and at what loads.

[cld12pk2go]

Originally Posted by btstarcher I like the increase in torque, but I'm also not a fan of my motor blowing while cruising. I'm thinking about dialing it back a bit under low load conditions but not sure what values yet and at what loads.

~350wtq should be pretty safe with a decent tune...Are you talking about dialing it back below that?


I have been well over 350wtq for ~3.5 years at this point.

[btstarcher]

Sure, at WOT everything is fine. When I was tuning myself with e50 I saw a peak of 383 lb-ft. It's the partial throttle cruising I'm concerned about.

[Lex]

I believe OEM VVT is too advanced if you're modifying the car or even stock in the gen1 car. You can tone it down a bit and still get great results.

The K04 can achieve 20psi of boost at around 2000 RPM. Spool will not be an issue but torque down low will be with less VVT.

Any way you cut it, the OEM turbo spools so quickly it is almost counter productive. I am making more peak torque on a larger turbo than OEM yet have much better traction. Ramp up in boost/torque and the ability to modulate this is important and difficult with the K04 but easier with a larger turbocharger.