Big power stock block - what you should know

[mituc]

First of all, when I'm referring to "big power" I'm not necessarily talking about high peak numbers, but more about amount of power produced in a given amount of time.

I've been through several states of tuning and various setups with this engine, now I'm rebuilding my engine for the second time and looking at the various types of damage I experienced over time I think I figured out a few things which showed up here and there in posts from various users but most probably never all together in one single post.

Therefore in this post I'll try to make everybody understand how power works with us when we want to have fun, and how it may work against us when it comes to engine longevity.

As we all know, the factory 2.3DISI-T can handle quite a bit of power.

For torque limits, the general consensus on this forum is that you should not go too much above like 350-375lb*ft or 475-500Nm to protect the rods which are another weak spot in these engines when it comes to handling big torque accompanied eventually by some detonation which will push even more the piston down having the effect of a lot more torque applied to the rod. Also, back in the day people were breaking rods because LSPI or heavy detonation mostly resulted from lack of upgrades available for the HPFP (let's exclude bad tuning, because that damages engines no matter what).

As for power, at some point there was some kind of a race for pushing these engines at or above 400bhp. Everybody's opinion was that as long as you don't throw too much torque to upset the rods everything else will be fine. And it is, under some circumstances, and it's not under other.

We know how much the rods can handle safe for a decently long period of time with a decent tune which keeps detonations at bay. But what about the pistons?

At these power levels (stock power up to, say, 400bhp) the pistons have one single big enemy: heat, or excess of it.
Heat is a bi-product of power. This is how combustion engines work.
In our case excess of heat can occur during a track day of an otherwise factory car with the factory tune, or on a drag strip of a 400bhp car repeatedly beaten on the 1/4 mile with very little driving in between and not enough sitting either. Or driving on the autobahn for 5 hours at 200+kmph/125+mph.

The factory piston ring tolerances and end gaps are pretty tight, as they are on any street car. Mazda states the ring gaps should be 0.14-0.24mm / 0.0063-0.01 inch. Heat expansion works on any material, it cannot escape it, and even if the materials different parts are made of expand together, they still expand differently.
When these rings cannot cool down the ends may meet. This phenomenon is called "ring butting". When that happens the rings will force against the cylinder wall generating more friction and will also generate tension on the ring lands.

All the hot gasses exit the cylinder where the exhaust valves are. The exhaust gasses contain vapours of fuel and partially burnt fuel which tend to wash or dilute the oil on the cylinder walls on that side. The heat will also shear the oil, as if washing it away with the remaining fuel wasn't enough.

The excess of heat also makes the piston crown more brittle and prone to cracking.

Cylinders #2 and #3 are the most prone to showing various types of failures because they're in the middle of the engine and not only the heat dissipates slower from there and the water jackets may not have the most fortunate routing, but any piece of solid material tends to expand more in the middle.

So let's see what we have: more tension in the butting piston rings which push against the ring lands, rub harder on the cylinder walls because of the same butting and lack of lubrication which is the effect if oil thinning and washing, heat which makes the piston head more brittle.

The possible effect of this deadly recipe:
- cracked ring lands:






- or if luck is present in a lesser amount... cracked cylinder walls:


So what we have here is not the effect of excess of torque, and not necessarily bad tuning, bad fuel, or careless maintenance. it's the effect of heat.

When rebuilding an engine one of the most important things is ring end gap. All performance pistons manufacturers will recommend at least 0.0045" x bore (bore = 3.445" stock), so a total of 0.0155" or 0.4mm which is double than the factory specs.

Another important aspect is heat control. So a larger radiator and having an active water+meth kit spraying that mix into the engine helps a lot. Remember, not only meth is important here, that will only provide additional fuelling and help controlling detonation allowing for more timing (just like in-tank meth or ethanol mixes do). The water evaporating in the exhaust stroke is what drives heat out of the cylinder.

The problem is that heat management can work fine in certain situations. But with a relatively big engine with a turbo strapped to it during a prolonged track event during an 85+F/30+C day after a few laps heat will simply build up and do what it usually does, sooner or later depending on how open or how technical the track is.

So use your stock block wisely.
- Do not track it for too many laps and decrease the number of consecutive laps depending on how much you stay WOT and how much power you make.
- Should you go WOT in 5th and 6th? Man, you don't want that stock mk1 R35 GT-R or V8 bmw m3 to get away and laugh in your face, do you? But assuming you proved your point from the 1st or 2nd run which did not happen each for more than like 10-12 seconds and a few good dozen of seconds apart then back off, let things cool down so that you can get him again when he comes back with a louder exhaust and a more expensive tune.
- do not set the rev limit above the factory setting even if you have a turbo that can push well above that. The rapid movement of the pistons and the tight ring end gaps will start working against your happiness.
- at least once tuned - ideally unconditionally - you need to develop an OCD for spark plugs, oil change interval, oil type, driving habits (avoid short trips on a cold engine, short meaning less than like 5 miles with long pauses in between, no high PT or WOT before 15-20 minutes of normal driving);
- pay attention to your tune settings and monitoring. Avoid lean conditions no matter their origin (HPFP malfunction, too lean target AFRs, too lean MAF cal and so on);

With a good tune, good oil and wise hooning you may eventually crack ringlands with 0 damage tot he cylinder walls, crank journals, cams, and soon. At that point you can rebuild and make more use of that setup which brought you to 350-400bhp, but you still have to remember that the packaging in these cars is relatively tight and cooling is still a concern under some circumstances, even if not that much as for the stock block.

[BuddySpeed3]

Fantastic information! Are those pictures of pistons 2 and 3 of your engine? How much power/torque where you putting down? Do you reckon it happened at the track from prolonged heat buildup?

This also brings up an interesting thought in regards to extremely advanced ignition timing.

For example a 320 whp K04 with 22* at redline, or a 320 whp BNR S4 with 9* at redline.

I would imagine that the pistons and cylinder walls with the K04 setup are absorbing much more heat from the expanding fuel mixture because they are exposed to it for longer. We all know that when we advance ignition timing, EGT's decrease (indicating that the engine internals are absorbing more heat). With less ignition advance, EGT's increase (indicating less absorbed heat by the engine internals). I know that it's a balancing act between boost and timing to reach a certain power goal, but in my mind, more boost with less timing seems to be safer, especially when it comes to heat management, and these ring land issues.

The question is, since the power output is the same on both setups, are the engine internals absorbing the same amount of heat? I personally don't think so when it comes to engines. If you think about it, with the BNR S4 setup, the pistons and cylinder walls are exposed to MORE heat, but for a SHORTER period of time. With the K04 setup, we are exposing the pistons and cylinder walls to LESS heat, for a LONGER period of time. The problem is that it takes longer for heat to transfer from the pistons and cylinder walls into the coolant jackets, then it does for heat to ventilate out through the exhaust valves, so heat starts to build up. Although the BNR S4 setup generates more heat from higher boost and more fuel, it gets ventilated out through the exhaust faster than the amount of time it takes for heat absorbed by the pistons in the K04 car to dissipate. It's all about minimizing the heat exposure time.

I have not done any form of testing on this, but it seems to make sense.

[mituc]

Originally Posted by BuddySpeed3 Fantastic information! Are those pictures of pistons 2 and 3 of your engine? How much power/torque where you putting down? Do you reckon it happened at the track from prolonged heat buildup?

Yes, those are my pistons and I have a feeling it happened at the track (two 30 minutes track sessions) because the engine started buzzing under engine braking. I was putting down about 320hp at the time (so 320Whp) on pump gas and about 21.5psi.
I didn't loose any power at the moment, did not have any oil consumption until a few months later when I started throwing more boost at it (25-25.5psi) and revving higher (7000rpm rev limit) and hooning on the street, no prolonged track days or anything like this,
All these on pump gas, about 9.5-10 degrees of timing at 6000rpm, about 11 to 13 at 6500-6700 depending on the weather.

The block is not mine, it's from a 100% stock 3MPS/Mazdaspeed3 with less than 100k kms/60k miles on it probably doing a lot of high speed german autobahn miles with the oil changes performed by the book (15k kms or 9k miles or so, which is way too much especially when using the Mazda factory Dexelia Ultra 5w30 oil).

Originally Posted by BuddySpeed3 This also brings up an interesting thought in regards to extremely advanced ignition timing. For example a 320 whp K04 with 22* at redline, or a 320 whp BNR S4 with 9* at redline. I would imagine that the pistons and cylinder walls with the K04 setup are absorbing much more heat from the expanding fuel mixture because they are exposed to it for longer. We all know that when we advance ignition timing, EGT's decrease (indicating that the engine internals are absorbing more heat). With less ignition advance, EGT's increase (indicating less absorbed heat by the engine internals). I know that it's a balancing act between boost and timing to reach a certain power goal, but in my mind, more boost with less timing seems to be safer, especially when it comes to heat management, and these ring land issues. The question is, since the power output is the same on both setups, are the engine internals absorbing the same amount of heat? I personally don't think so when it comes to engines. If you think about it, with the BNR S4 setup, the pistons and cylinder walls are exposed to MORE heat, but for a SHORTER period of time. With the K04 setup, we are exposing the pistons and cylinder walls to LESS heat, for a LONGER period of time. The problem is that it takes longer for heat to transfer from the pistons and cylinder walls into the coolant jackets, then it does for heat to ventilate out through the exhaust valves, so heat starts to build up. Although the BNR S4 setup generates more heat from higher boost and more fuel, it gets ventilated out through the exhaust faster than the amount of time it takes for heat absorbed by the pistons in the K04 car to dissipate. It's all about minimizing the heat exposure time. I have not done any form of testing on this, but it seems to make sense.

That is an interesting topic.

In the first case you produce 320hp around redline with less fuel and air but with more timing. That means that the ignited/exploded mixture starts pushing the piston down sooner, which also means it will do it for longer.
In the second case you do it with more boost/air and more fuel, probably richer mixture as well because in the first case I reckon you must be using an ethanol mix or in-tank methanol or something like this. Which means the explosion will be of a larger magnitude than in the first case but will push the piston down for a shorter amount of time, possibly some of the mixture will burn during the exhaust stroke.

I'm not even by far an engine expert but I think in both cases the total amount of heat seen by the pistons and cylinder walls is the same during the power stroke (same power =~ about the same lost amounf of heat, think "absorbed heat") but in the last case (typical for pump gas setups) you will have a lot higher EGTs torching the valves and turbo in the exhaust stroke.
Also in the 22 K04 setup you may experience faster oil shearing because the oil on the cylinder walls is exposed to heat way above the flash point for longer, while in the BNR case you will have more oil washed away from the cylinder walls especially on the exhaust side and that side of the wall eventually contaminated with fuel.

For ignition and knock control you probably have an alcohol mix with the K04 setup running 22 degrees at redline, while with the BNR and pump gas you'll have lower and more consistent BATs.

So there are advantages and disadvantages in both cases once you exceed a certain amount of time of hard/track driving.

[Mazd1222]

Great info. I do have a question though I freektuned my car bnr s3 pump gas and e33 tune.
I tuned the car on autolite xp one step colder plugs. Ngk's were not available at the time.
I bought the car second hand original owner had a top mount. I switched over to a treadstone tr8. When I go into high boost the car sputters with the NGk and the Denso but runs fine on the Autolites any Idea what that could be?

[mituc]

Originally Posted by Mazd1222 When I go into high boost the car sputters with the NGk and the Denso but runs fine on the Autolites any Idea what that could be?

Send your tuner a log with the sputtering but not before checking the spark plugs gap and learning how to post on-topic.