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Making safe power: What it takes and why it breaks

30569 Views 86 Replies 15 Participants Last post by  SkyShadex

Many ask daily about mods to do next to make more power and some even just impulse buy mods to make power based on what others are doing or popularity vote etc. Few actually understand what it takes to make power and how to do so safely. Relying solely on trust from people or vendors is not enough and it's best to understand what it takes to make safe power and why things break when something is done wrong. I'll try to make this as simple as I can for the avg Joe to understand.

What it takes

High air density, high air flow, for high mass air flow

Things that aid in this are:
More boost (flow)
Colder air (density)
High flow air and exhaust mods (flow)
High barometric pressure/low elevation (density)
Low humidity (density)

Sufficient knock suppression
Things that aid in this are:
High octane fuel
Proper air fuel ratio
Water/meth injection
Colder and more efficient engine coolant
Colder heat range plugs

Good tuning
Good tune consists of:
A power curve that matches the use of the vehicle, mods on the vehicle, fuel used, that should be smooth and predictable for the conditions, without any harsh power changes during any part of the power curve, or reach power levels known unsafe for the weakest part of the build.

Why it breaks
Common failures in the VT are due to head bolts stretching, which cause headgasket failures, followed by internals failing. Also common is plugs or coils failing, causing internals failing. Then fuel lines are another issue in some VT that cause insufficient fueling, which can also lead to catastrophic failures of the internals. Some of this is due to poor oem tuning in the older cars, where the newer cars are not as bad, but also not that great. We can't forget these cars are made with priority towards emissions more than power.

Every failure is due to something wearing out that is not replaced when needed, improper part to start with, boost spikes, sudden timing changes(ignition or cam), insufficient knock suppression, insufficient fueling, among other variables.

250 whp is 250 whp right?

An engine can fail at 250 whp on one tune quicker than on another tune making 250 whp. I know many are like huh.....? Keep reading :)

WTQ and power curve
It's all in the wtq and shape of the power curve. The shape of the power curve is more crucial than the max tq it makes in most cases.

A VT can make 250 whp at 5k, 6k, or 7k rpm on the oem turbo no problem. This is because an engine makes tq and hp is calculated based on rpm. Tq is what is actually measured by the dyno. The one that will live longer will be the one that makes 250 whp at 7k rpm due to lower wtq and has a slow tq onset/climb. 250 whp at 5k rpm is 262.6 wtq, at 6k rpm is 217.8 wtq, and at 7k rpm is 187.6 wtq. The higher hp at lower rpm will require higher tq and quicker tq onset/climb thus will have a shorter service life. Every time you have a sudden tq onset/climb it stretches the head bolts and increases the pressure spike in the cylinder. The higher the spikes the more dangerous it is for the engine and the components.

This should be a good little beginner to get the gears turning in some heads without getting too technical.
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Air density vs power

Now to break down what changes air flow(cfm), mass air flow(lb/min), and thus air density in the cylinder, and how it effects power output. Going to do this starting with a screenshot of a pretty accurate power calculator, using data from a datalog during an actual bone stock 15 manual VT baseline dyno pull, that made 182 whp on 93E10 fuel. Then I will show how changing certain things in the calculator change the power output of the car.

This will not be exact due to how the ecu operates but will give a very good general idea on how certain things will effect actual power output.

Baseline VT 182 whp

Adding boost
Now let's add 1 psi boost to the baseline and keep everything else the same. This will increase the air flow through the engine from 257 cfm to 267 cfm, the mass air flow goes from 18.78 lb/min up to 19.52 lb/min, thus increasing power to 189 whp.

Colder air
Now let's see what the air temperature needs to be to make the same power as adding 1 psi boost to the baseline car. Looks like roughly 20°F colder air will have the same 19.52 lb/min mass air flow, from the same 257 cfm air flow as the baseline car, but make the same 189 whp as adding 1 psi boost to the baseline car. The air density increase from the colder air makes up for the added boost to get the same mass air flow for the same power.

Mile high elevation
Now let's see how placing the bone stock car a mile high in elevation(Denver CO) changes power output. Notice 16.87 lb/min mass air flow, but requires 280 cfm to make the same baseline boost at elevation, and still only makes 163 whp due to the lower air density from only a change in elevation from the baseline pull at sea level.

High flow bolt ons
Now let's see how bolt on parts with better flow increases volumetric efficiency(VE), thus increasing air flow, mass air flow, and air density in the cylinder to increase power. Notice the VE changing from 80% baseline to 90% with better flowing parts increased air flow to 289 cfm, and mass air flow is up to 21.13 lb/min, which bumps power to 204 whp.



I can't show how humidity changes power in this calculator however it will slightly change power output. Lower humidity(dry air) has a higher air density and will make more power than higher humidity(wet air). Dry air also has the ability to have greater air temperature drop when using water/meth injection kits, which means colder air, higher air density, higher mass air flow, and thus higher power output.
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Making some edits to old posts and new posts so read back over everything to hopefully better understand things. Trying to make this simple for most to understand but enough details at the same time without being too technical. I'll let the information so far sink in a bit for everyone before adding further information or posts.
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Sufficient knock suppression

The ecu will adjust ignition timing +/- and thus power output +/- by itself based on the amount of knock the engine has at any given time. Higher ignition timing equals more power, lower ignition timing equals less power.

High octane fuel

Higher octane fuel resists knock thus allows the engine to run higher ignition timing without knock than lower octane fuel will allow. This is one reason why 93 octane fuel will make more power than 87 octane fuel.

Proper air fuel ratio

The VT ecu operates on lambda instead of air fuel ratio. 1 lambda is 14.7 air fuel ratio on pure gas with 0 ethanol added. Most pump gas now has 10% ethanol which lowers the air fuel ratio at 1 lambda to 14.1. For simplicity let's stick to the pure gas scale.

The range of the air fuel ratio to not cause knock or suppress knock will be in a small range. This air fuel ratio range will usually be from the 10's to 12's. Below somewhere in the 10's will actually cause something called rich knock. Being too rich(below 10's) in general will kill power and knock kills it further. Being too lean(12's and higher) in general will kill power and at some point will cause knock that will kill power further.


Lets say a tuned VT makes 250 whp with 11.5 air fuel ratio and does not pull any timing. Car is leaned out to 12, makes 255 whp, and does not pull timing. Lean it out to 12.5, makes 250 whp, but pulls timing. Now it's not safe as the ecu is now pulling timing from insufficient air fuel ratio. The safe afr would be the point just below where the ecu will pull timing due to knock in a given scenario/conditions.

Now the same VT is richened up to 11 air fuel ratio, makes 245 whp, and does not pull any timing. Richen up to 10.5 air fuel ratio, makes 240 whp, but now pulls timing. Not only is more fuel to make less power inefficient, but richening to the point to cause knock is dangerous just like being too lean.

The oem tune has the air fuel ratio in an efficient area to make power safely in a very small area. Most areas and conditions it will have fueling too lean and at other times too rich. Some aftermarket tunes widen this area of making safe efficient power and some do not do as well.

Water/meth injection

This adds air density and mass air flow at a given air flow from intake air cooling, which can be referred to earlier, and knock suppression through in cylinder cooling from the water, or the same plus added octane from methanol. Methanol cools better than water and has more benefits of the added octane which is why higher methanol content will make more power. Water on the other hand will cool things better inside and after the cylinder. Meaning it will also help lower the temperature of the turbo and exhaust gasses so things live longer.

Colder/more efficient engine coolant

The colder and more efficient the coolant the more timing and power the car will make due to less knock. Stock engine coolant tends to run in the 180°F area. Better thermostat and coolant will lower those by roughly 20°F. Doing this along with a more efficient coolant will allow in the area of 1°-1.5° more timing and usually nets 3-5 whp more.

Colder heat range plugs

The VT first came out with a heat range 6 plug which is a hot plug. In the 14 MY they went to a colder heat range 7 plug to help resolve misfires/knock. In the 16 MY they went to a colder heat range 8 plug to further resolve issues with misfires/knock.

The colder the plug the more efficient the plug is at staying cool. The cooler the plug the less chance of the plug being a hot spot in the cylinder to cause misfires/knock and thus power loss. The con is if you run the plug too cold it can get build up and also cause a loss of performance over time. So best to match the plug to what will work best for the car.
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Good tuning

Knowing the limits

It's very important that the tune in the ecu does not go beyond the limits of the weakest link in the build. Examples: do not tune a car to 24 psi if you know the turbo will surge or head bolts will stretch, or will have knock on the given fuel, etc.

Fuel is priority

First thing I confirm is that fueling is good. This means that the rail pressure and lambda/afr are meeting tune commands and not causing insufficient fueling be it too rich or too lean. Your tuner will be able to tell you all of this if remotely good at what they're doing. Fueling is priority because it is required to make power and is required for in cylinder cooling which Di engines are very good at.

Ignition timing

The timing curve upon wide open throttle should increase with rpm. A drop in timing at any time will mean a drop in power and could mean danger is occurring or just around the corner. If the ecu is tuned to pull timing for safety is ok but if timing is pulled due to knock/misfires then that is more of a sign of danger.

Boost and throttle control

A good tune will have predictable and repeatable smooth boost and throttle control. Upon wide open throttle it should remain wide open until you want it to close. Some tunes I've seen will have surges in power due to poor boost and throttle control which makes for unsafe conditions and unsmooth power delivery. Also seen tunes only have partial throttle opening with the pedal to the floor. This is not good and means the tune is not good for the mods. Similar to the oem tune in a car with good bolt ons will be at 30%-40% throttle due to hitting limiters in the tune.

Power curve vs service life

A power curve that the tq climbs slowly and lower will have a longer engine service life than a power curve that climbs quickly or higher. Often many push engines as hard as they can but get long service life as well. This can be done but can be difficult to do. Important to be realistic in power goals and do everything right in regards to what I state in this thread on every level.

Piggyback or chips

All of these just fool the ecu and modify signals to make the car have more power. Some are cheaper than ecu tune some cost more. None of which will be as safe/reliable as a good ecu tune, will make as much power as a good ecu tune, and none are undetected by a dealer that wants to find something if things go wrong. The only plus for this way of adding power is sometimes convenient and sometimes cost less. The people who do these either have no clue they're dangerous or do not care. If the ones that cared knew how the ecu operated and all of the reasons why/how based on the maps in the oem tune then most would never consider the option.

Dyno curve woes

If you ever see anything less than smooth in a dyno curve do not be scared to throw a flag and ask questions. A good tuner will know the answer and be honest and tell you. A bad tuner or someone that just cares about taking your $ will not know the answer or will not be honest and feed you a lie or a partial truth. A mediocre or bad tune or piggyback can usually be spotted easily in a datalog, dyno pull, or both when you know what to look for.
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When the stars align.....

When all things are in place the results will speak for themselves. Check out this dyno of an elantra sport manual transmission with above avg bolt ons, big turbo, methanol injection 1k cc/min nozzle, 93E10 pump gas, and 28 psi tune.

This car holds the record for the most power from a stock G4FJ (hyundai/kia 1.6T-GDi). Curve looks good and power look good no doubt. However, once you realize that the parts could be better, tuning could be better, and methanol injection could be better, you come to the realization that these numbers could have also been much higher. How much you say? Based on my calcs, 440+ whp at the same 28 psi and 7k rpm redline. Most of this would be from tuning and methanol injection setup changes. This car blew the intake manifold apart attempting this before and was 10°F over ambient during this pull shown so obvious the methanol injection kit was not setup properly. I say this because I have yet to damage anything from running or setting up methanol injection kits on any car in the last 20 years and can get 50°F-60°F below ambient on any platform thus far. :)
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Hp/psi can vary greatly based on all the factors mentioned already.

An increase in IAT is not beneficial for power but rather a decrease is. At what point is it no longer beneficial I have no clue as that would be a very situational condition to even answer that. I've tested down to around 0°F and still seeing benefits on cars.

On a stock VT seeing 110°F IAT the power would be lower from the air density and the ecu pulling power and timing for that IAT. With methanol injection you could easily see ~60°F IAT drop which would add 11.8% air density, 11.8% mass air flow, which translates to minimal 11.8% more power. On top of that the ecu will add a lot of timing from the colder IAT itself and more timing for the added octane and in cylinder cooling that both suppress knock. Timing also = more power. On water or water/meth mixes the gains in power will be slightly lower due to less IAT drop, less in cylinder cooling, less octane added, and knock suppression.

The water/meth kits I setup will see the following gains on avg:
Water 4-8%
50/50 6-10%
Methanol 8-12%

Better than avg when real hot and/or real dry air and worse than avg when real cold and/or real humid air.
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For example I had a customer VT make 250 whp at 18.3 psi boost with 53.6°F IAT and 15.5° timing. Same setup with 26.6°F IAT did 15.5 psi with 16.5° timing and made little more power. So power went from 7.6 whp/psi to 8.3+ whp/psi with 27°F colder IAT as the only change. So much more efficient power being made.

If the car were to be tuned for the colder IAT to make the same boost or was a setup that was held to a set boost pressure then the power output would be ~273 whp at 18.3 psi at 26.6°F IAT vs 250 whp at 18.3 psi at 53.6°F IAT.

This is ~9.2% power gain from a 27°F drop in IAT in below avg temperatures. In above avg temperatures the gains by % would be higher due to how most tunes operate.
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More Boost: The right and wrong way

More boost is the easy way to increase air flow. There is a right way and wrong way to do this. Many get greedy and want to take the cheap way out with different boost hacks, boost controllers, chips, and piggyback tuners. Others do it the smart way with a good ecu tune which usually costs more $ but not in all cases.

The wrong way

Boost hacks and boost controllers that manipulate things mechanically are a bad idea. The more out of the loop the ecu is on how things operate the more danger in the tune doing this. Now this will add some power in the VT however the ecu an tell electronically that something is off and will shut things down. It will use the wastegate, BOV, and throttle mostly to shut the power down before you gain much power at all.

Chips and piggyback tuners fool the car electronically to raise boost. Some are better than others at doing this but in general not a good idea. In general not good because it's modifying things off of a mediocre or unsafe oem tune. Raising boost in this case will often show poor boost control, throttle control, inadequate fueling, misfires, misfires/knock, and timing fluctuations.

The right way

Good ecu tuning is the right way to do this. It raises the boost and all the appropriate associated maps involved in the car running safely with the proper fueling, timing, and more. All safety maps can be addressed that the oem tune may not address well in general or for elevated power levels. Many things in the ecu that a proper tune can address that could make or break how safe the car will run that no other method can possibly do. No other method can possibly achieve the same results either.

There are limits though

Regardless how you decide to increase boost there will be limits. Boost can be limited by a mechanical limitation, a physical part, a chip/piggyback abilities, the tune itself, fueling, atmospheric conditions, knock suppression.
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Speaking in terms of power output only:

Safest will be lowest peak tq with the slowest tq rise/onset. Most unsafe will have the highest tq peak and quickest tq rise/onset. Quickest will have the highest avg tq in the rpm area being used.

If you want to post specific dyno plots to compare then do so. I can answer the pro con and which car would be quicker in what scenario etc. No tuner name needs to be mentioned here to keep things unbiased.
Very interesting. You did not explain this in detail but your comments lead me to believe you understand the implications of dyno results. I have spoken to some very successful mechanics and an engineer, they simply do not get it. A dyno run shows real time torque for an engine but not HP. HP is work over time, a ten second dyno run showing 300 hp is only extrapolating the engines hp potential by using torque figures. The dyno can say if this engine was run at this torque for an extended time it is capable of producing a given HP, not that it produced that hp in ten seconds. If you really want to piss someone off calculate how much hp a car actually produced in a 12 second run.
Can't go into too much detail or most people will be lost on this forum. :)

Yes, dyno measures tq, hp is calculated from the tq and rpm.
TQ × RPM ÷ 5252 = HP

HP make sales, TQ wins races :)

I love doing a calculation to show the revolutions the crank actually turns during a 1/4 mile pass.
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Cold air

Colder air is more dense and makes more power per psi boost. Here is an example of a 250 whp VT at a set psi boost being fed different intake air temperatures. Notice power goes from 250 whp to 261 whp due to a 12°C colder intake air as the only change.


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Higher flow parts

Having parts that help the engine flow air more efficiently, be it on the intake side, charge air side, or exhaust side, will improve the volumetric efficiency of the engine which improves power at any given boost level. Here is an example of a 250 whp VT with the only change going to increasing the volumetric efficiency by 10% which in turn increases power by 10% now up to 275 whp.


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Elevation/barometric pressure

The barometric pressure which can change with elevation and weather conditions will also change power output. Here is an example of a 250 whp VT at sea level vs the same car at the same boost in Denver CO only making 230 whp.


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Actually it takes torque and hp to win races. Plenty of very high torque engines out there that can not win races. Most HD and large air cooled v twins, tractor engines, off road heavy equipment engines all make massive torque. Large torque figures are great and provide impressive initial acceleration response but a high torque engine that can not rev and turn that torque into work over time, hp, falls on its face. A modern 600cc sport bike has little torque when compared to a 1600 cc v twin yet will absolutely bury the twin at the drag strip. The 600 may have less torque but at 14k rpm it can apply its somewhat lesser torque 3 times more in any given time interval than the higher torque but slower turning v twin. Torque=right now, hp=work over time. Look at it this way, you put a two foot breaker bar on a wheel stud thus exerting great torque. You can easily move the car this way due to the torque applied. But how long even at this high level of torque would it take you to move the car 50 miles? Now introduce hp, how many times can I exert that torque in say one hour? The answer for a human is very few, far less than 1 hp. Yet a high hp engine can move that load 50 miles in less than an hour.
All about the power curve and having the torque where you need it to win races. HP is calculated and not measured like torque as you know. Peak hp or peak tq is only good for bragging rights and making sales. This is what the saying means. :)
And the best way to make that air cold.... NITROUS OXIDE BOOSTERS

Name the movie and win... nothing.
I guess I need to make an informational post on N2O next is what you're telling me.....

Doing my best to inform and not lose people as is.....
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Sure. I'll read it. I've seen some reports of good gains with nitrous on gf4j's. I think the gains were higher than the shot. I assume that would be due to the cooler charge. AND, I think that was a dry shot.

And the movie was Black Sheep with Chris Farley and David Spade..
The power gains can be higher or lower than the jet suggests but many factors go into that. Bottle pressure, jet location, IAT, and state of tune are the biggest determining factors.

I've seen a car make 299 whp with an 80 shot after being tuned to 220-225 whp area. Want to say mods were intake, catless dp, tune, and the N2O kit. The transmission did not want any more than that due to slip and I cringed watching the dyno pulls. State of tune was not great.

A dry shot is never a good idea on these cars nor is a sudden or large quantity. The shock to the parts and/or sudden fueling changes will break things quicker than anything else. This is why I make custom fuel line for the VT peeps to run a wet kit if they want to run N2O.
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Good thread @trdtoy and thanks for the knowledge spill. 🙏🏽👍
Subscribed and will read through it shortly. 😷
I'll add more later when I have more time and gather my thoughts on what to add next.
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I have a question. Recently saw a build on YT of a VT1 with a N2O cooled intercooler, reporting a 50whp difference (impressive!). You've talked about the benefits of IAT's on this application. I'm wondering if that is an efficient use of the N2O or would it be better spent as a wet shot?
Intercooler sprayers of any type cool the intercooler core down which lowers the IAT by the efficiency of the core itself. If using N2O for example it would gain more power injecting that into the engine as you do not lose the inefficiency of the intercooler(with proper nozzle placement) and will thus cool the air charge more. Also the N2O will make more power with a more efficient cleaner burn of the fuel. So simple answer is wet shot will make more.
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guess he is going to have to make that post on N2O lol.

I'm all for WMI. I just don't know which is more temperature efficient, Methanol or N2O (or CO2). Would a 50shot to cool the intercooler better at adding that power through cooling, or at 50 wet shot? How does that compare to running Methanol? Both? Diminishing returns with charge temperature? The possibilities! (totally not me plotting ways to blow my DCT for fewest $$$'s)
N2O is the most efficient cooling when injecting into the engine than methanol injection. Also N2O is way more costly to use than methanol injection. Can run both no issues as long as setup and tuned correctly.

Not many VT out there can take advantage of N2O to the point of making it worth the investment. The one I'm building I'm toying with the idea of having N2O wet shot on it with a big single G35-900 or G35-1050 turbo to get to 1k hp. Not quite sure the path yet I already have the N2O kit designed and mostly made.
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