Prep work for Nitrous and Turbo

[precisionboost]

It's important to do some prep work if your planning on running a turbo or nitrous.

Ideally you can do a few simple things to keep your engine from blowing up.

#1 decrease your compression.

The simplest way to decrease compression is to replace your cylinder head gasket with a thicker more robust gasket ( such as a Cometic MLS gasket )

You can't just pull the old one off and throw the new one back on..... you need to do some minor prep work to both the head and the engine block deck to make sure the metal gasket seals correctly.

Failure to do so could result in gasket failure within hours days or weeks. (we will get to this subject on prep work of MLS gaskets later )

#2 Retard Ignition Timing

It's very important to change the timing of the ignition on your vehicle when running a turbo or nitrous or you might end up with spark knock.

Normally your ECU triggers your spark plugs in advance of the piston ariving at TDC (Top dead center when the piston is closest to the cylinder head)

The reason for this is simple.... the air/fuel mixture takes a fraction of a second to get started and build up pressure.

Ideally you want the pressure of the burning air/fuel to hit the piston a couple of degrees after TDC.... which gives maximum power.

The stock ignition can not accomidate for situations where the air/fuel burns significantly quicker (as it does with nitrous and turbo )

The result is that stock ignition timing will allow for situations where the pressure front from the burning air/fuel will hit the piston before it gets past TDC

If it's only a degree or two... you will get a light "spark knock"

If it's 5 or 10 degrees.... well... the piston is being pushed up and the air/fuel is pushing down.... so either your piston fails or your connnecting rod breaks.

The way to combat this is to add an aftermarket ignition (most are not directly compatible with the Aveo system but there are adapters to make it work )

So when you are running an MSD aftermarket system with a "boost retard" feature it will retard the ignition signal slightly to accomidate for the faster burn time of the air fuel mixture.

When I say retard.... it just means that it delays the signal to the ignition coil so that the spark plug fires later... which makes sure that the pressurized flame front doesn't hit the piston until it has passed TDC.

#3 Use higher Octane.

The higher the Octane the longer it takes to burn.
The lower the Octane number the faster it burns.

So.... High Octane is slow to burn... but it results in a longer burn time

Low Octane burns fast and short.... just one quick blast of energy.

So..... if your having ignition problems such as spark knock you need to increase the Octane level in your fuel.

The flame front will take longer to hit the piston but it will burn significantly longer (which results in more power)

#4 Water injection

Water injection actually reduces power..... the water vapourizes and absorbs heat from the system.

This is bad for ultimate power but it also lets you run lower octane and more timing advance than a dry system.

The net result is that you can run more boost or more nitrous to more than compensate for the loss in power.

Basicly... the hotter the air/fuel.... the faster it ignites and burns.

So.... cooler is allways better.

One benifit of nitrous over turbo is that the nitrous will decrease intake temperatures significantly... which helps decrease the likelyhood of detonation.

[precisionboost]

Other preparations for turbo and nitrous can include work to both the pistons and connecting rods.

This is work that might require someone more experienced... but your average mechanic should have no problem at all in assisting you to remove the connecting rods and pistons while your changing out the cylinder head gasket.

(you don't need to remove the engine for these procedures.... but it makes it easier )

Connecting rods.....

Your stock connecting rods with have a parting line from when they were cast...... this is a major weak spot.


Debeaming (remove parting line) can be done at most performance automotive machine shops..... they will take a die grinder and carefully remove the parting line until they get an even surface.

Then the shop would ideally polish the rods to give a nice smooth finish.

Next comes shotpeening.... this is where they use steel balls to impact the surface of the rod.... which increases the strength of the rod (similar to forging )

Next is ARP rod bolts..... it's possible stock rods may need to be resized slightly to make everything work out... but this is easy enough for a performance automotive machine shop

Pistons........

Detonation typically occurs when a hot spot on a piston creates starts the air/fuel burning before the spark plug fires.

This causes pressure against the piston and when the flame front from the spark plug hits the flame front from the hot spot all hell will break loose..... typcially.... your piston is destroyed or at the very least weakened to the point where it will crack and fail at a later date.

Most of the time carbon deposits are at fault..... they abosorb the heat from combustion and the carbon deposits get several hundred degrees hotter than the rest of the piston.

To combat heat absorbtion and carbon deposits you can get the crown (top) of the piston coated with various ceramic compounds.

The carbon won't stick to it and it helps keep the piston nice and cool. (relatively speaking)

[y2daniel1981]

oh lord does this need to be a sticky

[Nemasys]

agreed

[precisionboost]

The NUMBER ONE best tool for keeping your engine happy if your running nitrous or a turbo is a Pyrometer

Exhaust temperature readings are more important than air/fuel meters (which tend to be erratic and slow to compensate)

If you see your temperatures quickly rise past 1100 degrees and surpass 1400 degrees your in for a boat load of trouble.... expect to see holes in your pistons if you don't have a ceramic coating.

Some people will go crazy with Pyrometers.... they will install one in each exhaust manifold pipe as it exits the cylinder head.

Most people don't realize that there can be differences in the output of injectors..... the ECU sees the combined gasses from all cylinders.

So cylinder 4 could be running lean while 1,2,3 could be running slightly rich to compensate.

The ECU might be happy..... but cylinder 4 might be very close to it's maximum heat levels.

With one pyrometer you will see slightly elevated temperatures..... with four pyrometers you will see the temperature in cylinder 4 is too high.

Now don't get me wrong..... buying 4 pyrometers is probably a waist of money unless your building an extreemly powerfull motor.

Your better off to get your injectors tested to ensure they are balanced.

Some aftermarket fuel/ignition systems will allow you to tune each and every cylinder separately..... this not only maximizes power.... it makes it run smoother because each cylinder is putting out the same power levels.

Even the intake design makes a difference..... you may see situations where one or two cylinders get more air than the other two..... the factory tries to get them "close enough" that damage won't occur but when your pushing your engine to the limits it's important to get information on flow characteristics.

This can usually be done by a company with a flow bench ( many automotive performance machine shops will have a flow bench for checking their results from porting cylinder heads )

If you look at a company like Lexmaul ( UK aftermarket supporter for Opel/Vauxhall/Holden ) they will often spend a great deal of time designing their intakes so that they provide maximium flow to each cylinder.

[precisionboost]

Next topic.... intercoolers.....

There are lots of companies out there selling super cheap intercoolers that are better suited for diesel engines.

One important thing people loose sight of is the fact that you get a pressure drop accross an intercooler because it is a restriction.

So.... a very large intercooler may actually be worse for your setup than a correctly sized intercooler.

I have a formula for intercooler size but I will have to dig up some of my books.

I suggest that anyone who is serious about turbochargers or nitrous go to your local book store and pick up a copy of "maximum boost" by Corky Bell

This book will not only give you the information to design a good system.... it even goes into how to manufacture your own turbo manifolds and which types of materials to use.

Sport Compact Car also came out with a decent book.... It was called "Engine & Driveline Handbook"

Ok....lets see what Sport Compact Car has to say.... it's been a few years since I read it...

Considering I'm recommending their book.... they probably won't mind me quoting some of their section on intercoolers...

It's best to stick with a core that is only 3 inches thick or less. Eighty percent of the cooling occurs within the first 2 inches of an intercooler's core, so a thin core intercooler is usually more efficient than a thick cored one.

As a rule, unless you are trying to minimize lag by reducing intake tract volume, try to run the biggest intercooler you can stuff into the nose of your car - within reason. The guidelines of the Spearco catalog are a good place to start in picking your intercooler.

Remember that total airflow to the engine's radiator should be considered, because the intercoolder can block a lot of airflow to your radiator.

Well.... they talk about efficency.... but not much about intercooler design.... and I can't find my other book on intercooler design calculations.

Basicly it comes down to cubic volume of the intercooler.

If you have a thin intercooler with large frontal area it will be more efficent than a super thick monster sized intercooler.

Let me put it this way..... your turbo might be putting out 14psi prior to the intercooler and with a decent intercooler you might see 13.5psi on the other side.

On the other hand.... if your intercooler is way too big your air flows over more surface area.... which creates more friction... which increases the pressure drop accross the intercooler.

So you might pump out 14psi and only see 12.5 on the other side.... which means you turbo has to work harder to give the same amount of boost at the intake.

Working harder means temperatures will rise.... so in the end the larger intercooler might actually give you higher temperatures on the other side.

Now don't get me wrong..... you want a large intercooler.... but you have to be carefull not to go too large or you will end up making things worse than if you had gone too small.

[exodus]

Any insight on intake/exhaust length/shape/etc. I've heard, and have been lead to believe, that one of the keys to keeping a performance tuned engine is keeping everything harmonized. That's to say tuning intake length/shape and exhaust length/shape so that the engine vibrations are kept minimal. Is there an optimal length/shape per engine, and would the outcome to getting everything "just right" be worth it for your average weekend warrior?

Perhaps intake and exhaust would be the last steps in this after having all the rotating parts properly balanced.

[precisionboost]

If I find the calculations for the correct volume of intercooler for the 1.6L I will post it.

[precisionboost]

exodus said:

Any insight on intake/exhaust length/shape/etc. I've heard, and have been lead to believe, that one of the keys to keeping a performance tuned engine is keeping everything harmonized. That's to say tuning intake length/shape and exhaust length/shape so that the engine vibrations are kept minimal. Is there an optimal length/shape per engine, and would the outcome to getting everything "just right" be worth it for your average weekend warrior?

Perhaps intake and exhaust would be the last steps in this after having all the rotating parts properly balanced.

Darn good question...... there are very specific calculations for "tuned port" intake and exhaust runners but they are so complex that you need a supercomputer to model all the information.

So.... most companies do it the old fashioned way.... they make a bunch of different designs ( 10 or 20 ) and test them all to see what it does to the power graph.

Some companies will sell the one with the highest horsepower gain......which isn't allways the best design.

The ideal design takes into account the gains throughout the power band.... not just peak power.

Let me put it to you this way..... If I had two cars that were exactly identical..... one is turbocharged and makes 200whp.... the other is naturally aspirated and makes 200whp.

The difference is that the Turbo makes the power from 2500 RPM forward to 6000RPM while the all motor naturally aspirated engine makes it's peak power at 7000 RPM.

The net result.... the turbo car will completely destroy the all motor car in a race.

So.... I wish I could give you a formula for ideal lenght but it's just too complex to explain in detail.

[precisionboost]

I will mention this..... the intake and exhaust runners (tubes) are no different than the tuned ports in a subwoofer box.

Just as a sub box has a port tube that is tuned for a particular resonant frequency.... so do intake and exhaust runners.

As a rule.... smaller intake runners will make more power in the higher RPM levels while longer runners will make more power in lower RPM.

Variable Geometry uses two intake paths to maximize power in two different areas.

So one intake path might be designed with a resonant frequency of 18 hertz ( 18 X 2 X 60 =2160 RPM) while the other intake path might be designed for a resonant frequecy of 37.5hz (4500RPM)

At resonance with the correct design you can get a negative restriction..... which is hard to explain..... but the air flows with less resistance than if it was "free air" with no intake tubing.

F1 racing teams spend thousands of hours making ultra efficent intakes.... they can have really really wierd designs.... they could go from a 2" tube to a cone extending out to 4" then back down to 3" with a trumpet (rounded edge)

This strange intake might allow maximum power at exactly 11,000 RPM...... which might be their statisitcal average RPM level for a particular race.

It might not work worth a darn at 3000 RPM but given they spend most of their time at 11,000 RPM their car will be faster than another identical car without the strange intake design.

[exodus]

Aye, I wasn't expecting the formula, let alone the specific design for the 1.6l. Just affirmation that this really is something to take into consideration while building a motor.

I recall being in my friends old nova years ago and becoming nauseus from how much it vibrated. It occured to me that this vibration is lost energy and there has to be a way to keep this energy from being transferred into the chassis/body and kept in the drivetrain. I'm curious as to what the power gains could've been by tapping into that lost energy.

[precisionboost]

This is starting to move a little off the original topic.... oh well...

Port velocity is the most important factor for peformance engines.... which is based upon the shape of the port.

So if you have a intake runners designed to make maximum power at 4000RPM and you change the size of the ports it will throw off the resonant frequency and change the location of the max power band.

(sort of like taking out a 10" sub and throwing in a 15" sub..... the port size won't match )

Most guys go as large as possible with ports..... this is not allways the best route.... it really depends on what kind of engine you are building.

Increasing the area of the port will slow down the flow of air (decrease port velocity ) which can lead to really poor idle and low RPM operation..... but it will make more power at redline.

You ideally want to increase the port size just enough to allow for more air to enter into the cylinder head without screwing up the port velocity at lower RPM.

It's like the turbo vs N/A engine.... large ports might give you more power at the top end..... but your total power throughout the power band will decrease and make your car slower.

One fellow who is a very well known port shaper will take a sample head and remove material until he is within a fraction of an inch of the cooland and oil channels in the head.

Then he fills in the ports with clay and plays with it on the flow bench until he finds the best flow for the engine the customer is creating.

In one case he has did a Honda K20 head and ended up adding a little bit of material !!!!

If you ever look at the ports..... they are huge.... you can stick your finger in and touch the back side of the valve.

It's the ultimate design for high RPM power but in this case he was trying to shift the power curve towards the lower RPM slightly.

[precisionboost]

Here is a copy of a spreadsheet I made for calculating the reduction in compression for various Opel based engines.

www.daewootech.com/forum/album_pic.php?pic_id=1611

The 1.6L is at the bottom.

[precisionboost]

Here is some info from Cometic... www.cometic.com/catalogs/AutoCat04.pdf#search='cometic%20MLS'

They offer MLS gaskets in the following sizes...

0.027" (0.686mm)
0.030" (0.762mm)
0.040" (1.016mm)
0.045" (1.143mm)
0.051" (1.295mm)
0.060" (1.524mm)
0.065" (1.651mm)
0.071" (1.803mm)
0.074" (1.880mm)
0.120" (3.048mm)

Now keep in mind my little spreadsheet was just a rough estimate.... it's probably within a few percent off of the actual value but the only true way to get a perfect set of data is to physically measure the different volumes.... the compression ratio might say it's 9.5:1 but it could actually be 9.53764:1 who knows.

Anyways.... for the 1.6L a good thickness would be roughly 0.75mm

Now.... this is just the "spacer" thickness.

To buy a single gasket we must add the 0.75mm to the stock head gasket thickness.

I had that info at one time.... but I can't seem to find it... I think it's around 1.25mm to 1.3mm

So... you would need a 2.00mm to 2.05mm this MLS gasket to get 8.9:1 compression.

Given it jumps from 1.880mm to 3.048mm I would think that the 1.880mm gasket would work just fine.

It should give a compression ratio in around 8.9:1 to 9:1

Some might think this is a little "high" for a turbo but there are lots of turbo engines out there running 8.8:1 to 9:1 compression.

As well...... you really shouldn't go past 10psi to 15psi when using a gasket.... if you want more boost.... get forged low compression pistons.

Keep in mind that the higher the compression ratio the more power a turbo engine will make and the more likely it is to have detonation.

It's a trade off..... more power vs posibility of detonation

Personally if you want to run around 8-10psi.... this spacer is the easiest solution.

The thicker the spacer...... the lower the compression..... but at the same time..... a thicker spacer will increase the gap between the piston and the cylinder head.... which can also lead to detonation.

So you want to be somewhere in the middle..... lower boost levels with only a slight difference in the thickness of the gasket..... compression ratio between 8.5:1 and 9:1 is perfect in my mind.

In the older engines it was common to run 8.8:1 in a naturally aspirated engine..... the management systems were poor and they typically used throttle body injection.... so the posibility of detonation was high.

So older turbo engines usually ran around 8:1 as a general rule....... now it's more common to see turbo ratios around 8.8:1 or even higher. (with the exception of the SRT-4)

[y2daniel1981]

I'm about to install my nitrous kit with the ZEX air injector. What plugs should i look into getting (i know 2 steps colder, but what's the "number or rating" should i be looking for