Engine technology thread.

[Exage]

1JZ-GTE: (2.81in/12in) X 7000rpm X 2= 3,278 feet per minute @ redline
Rod to stroke is 125.25mm/71.5mm = 1.75:1
Compression ratio 8.5:1 from 1990-1995
CT12A: boost set at 8.5psi-9.8psi

Your correct about the higher rpm range affecting the components at high rpm. It can stretch connecting rods ultimately weakening them along with the following:

"Operation of an engine at critical torsional speeds and in excess of the rated speed will lead to engine shaft and bearing difficulties. Each multi-cylinder engine has one or several critical speeds which must be avoided in order to prevent possible breakage of the crankshaft, camshaft, and gear train."

"Over-speeding of an engine must be avoided. If the rated speed is exceeded for any extended period of time, the increase in inertia forces may cause excessive wear of the journal bearings and other engine parts, and in uneven wear of the journals."

I found something that may be of interest: "RB26DETT N1: Nismo balanced the crankshaft to a higher specification than stock, as the RB26DETT engine experiences vibrations between 7000 and 8000 rpm." My guess is they found a critical torsional speed (engine resonance) something a harmonic damper/balancer compensates for below those engine speeds. The 1JZ-GTE is somewhat similar to the RB26DETT...

[serialk11r]

Hey something I just thought of that I'd like to know:
What does tuning an engine for torque at higher rpm constitute?

[Dimman]

Originally Posted by serialk11r

Hey something I just thought of that I'd like to know:
What does tuning an engine for torque at higher rpm constitute?

What do you mean?

Peak torque can be associated with a certain intake air velocity. Intake velocity is affected by port size, stroke and rpm. Smaller ports generate more velocity, but generally flow less. So as designers open the ports for more flow, the velocity slows down. So more rpm is needed to flow a certain amount of air at a certain velocity. This relationship can be seen by looking at the evolution of the 3SGE from old Celicas to the BEAMS 3SGE. BEAMS makes more torque and power, but the rpm needed is much higher for both. There's other stuff like combustion efficiency, wave tuning and stuff, too.

I realize this is kind of rambly, ask for clarification after I get over my 'I might become a Scion owner' trauma...

[Dimman]

Exhaust/header/turbo manifold questions?

There've been a few in another thread.

Sometimes those questions are hard, so if anyone wants to throw in their 2 cents or explain the following, have at it:

• Equal length vs unequal length headers
• 4-2-1 vs 4-1 headers
• venturi merge collectors
• inertial scavenging
• pulse scavenging
• pipe diameter (primary and secondary)
• pipe length (primary and secondary)
• stepped pipe sizes
• how cam timing plays a role
• other stuff I've forgotten/don't know about...

[Exage]

May as well add turbochargers and intake manifolds to that topic!

Sequential and parallel turbocharging, twin scroll vs. single scroll and VGT turbochargers, waste-gating and blow off valves, A/R ratio, after-coolers, single and individual throttle bodies, EGR recirculation, positive crankcase ventilation (PCV).

All that good stuff.

[old greg]

Originally Posted by Dimman

Exhaust/header/turbo manifold questions?

There've been a few in another thread.

Sometimes those questions are hard, so if anyone wants to throw in their 2 cents or explain the following, have at it:

• Equal length vs unequal length headers
• 4-2-1 vs 4-1 headers
• venturi merge collectors
• inertial scavenging
• pulse scavenging
• pipe diameter (primary and secondary)
• pipe length (primary and secondary)
• stepped pipe sizes
• how cam timing plays a role
• other stuff I've forgotten/don't know about...

This is a series of questions with a single, long answer so I'll give a shot at doing the whole set at once. Bear in mind that I'm not an engine guy, just science-y and generally knowledgeable, so this isn't likely to be 100% complete or accurate.

Any old set of tubes will get the exhaust from your engine to the back of your car, but a properly designed exhaust system does it in a very specific way. The name of the game is scavenging; promoting the flow of gasses into and out of the cylinder, it's the foremost goal of any performance oriented exhaust system for a non-turbo car. There are two types of scavenging, inertial and wave.

Inertial Scavenging uses the kinetic energy of the escaping exhaust gasses to create a partial vacuum in the cylinder just before the intake valve opens. When the exhaust valve first opens, the high pressure in the cylinder and the low pressure in the primary cause the exhaust molecules to accelerate out into the exhaust system. When the pressure in the cylinder equalize with and then fall below the pressure in the exhaust primary (after TDC) the exhaust gasses begin to decelerate. But their accumulated kinetic energy means that they continue down the exhaust pipe increasing the gas pressure ahead of them and reducing the pressure behind them. This way, when the intake valve opens the exhaust gasses help pull fresh air/fuel mixture into the cylinder. This is what "overlap" is all about, and also why overlap sucks at low rpm: there isn't enough velocity in the exhaust gasses for there to be any inertial scavenging, and you just pull exhaust back into the cylinder instead, ruining VE. A similar effect occurs between cylinders as well. When the exhaust gasses flow past a merge collector they leave a region of low pressure behind them. When this is timed right, that low pressure will help pull exhaust gasses from the next set of exhaust valves to open.

Wave scavenging uses the resonant frequency of the gases in the primary and secondary exhaust tube to help pull fresh air/fuel mixture into the cylinder. As soon as the exhaust valves open, a pressure wave (sound) begins traveling down the primary ahead of the exhaust gasses. Where ever this wave encounters a change in cross-sectional area, a portion of it's energy will be reflected back up the exhaust tube in a reversion wave. The thing to understand about pressure waves is that they create they create a region of high pressure ahead of them, and a region of low pressure behind them. The trick is to have the reversion wave bounce off the exhaust valve just as the intake valve opens, further lowering the pressure in the cylinder. For this to happen, the time between the opening of the exhaust and intake valves needs to match up with the length of the primary/secondary and the speed of the wave. This means that wave scavenging only occurs at certain rpms, and will work against you at other rpms when the pressure wave arrives at exactly the wrong time. When the pressure wave bounces back from a merge collector, it travels up multiple primaries. In this way cylinders can help scavenge each other if the timing is right.

With unequal length headers, half of the cylinders will have exhaust primaries and/or secondaries of a different length than the other half of the cylinders. The reuslt is that each set of cylinders will have different wave scavenging characteristics, reaching peak volumetric efficiency at a different rpm. This effect can be used to create a broader powerband at the expense of peak power. The problem being that whenever one set of cylinders is producing peak power, the other set is not. With equal length headers every cylinder will create peak power at the same time, maximizing peak power at the expense of powerband width. It should be noted that "equal length" is usually defined as ±1". An obvious side effect of unequal length headers is the sound. Pressure pulses from the cylinders will leave the engine evenly spaced, but half take longer to reach the merge collector. The result is that the exhaust pulses leaving the muffler are not even, producing a lumpy, irregular exhaust note. This is the source of the "Boxer Rumble", not the engine configuration.

That same lumpiness is also seen on I4 and V8 engines with crossplane crankshafts. Because of the firing order, the exhaust pulses do not leave the engine evenly spaced, and so naturally do not leave the muffler evenly either. This also means that the scavenging effects between cylinders will occur at different rpms, creating a wider powerband. 180 degree headers correct this in V8s by connecting two cylinders from one bank with two cylinders from the other with equal length primaries/secondaries such that the exhaust pulses reaching each merge collector are evenly spaced. This means that inter-cylinder scavenging will create peak VE in each cylinder at the same rpm, increasing peak power at the expense of powerband width. The most famous example of this is the old Ford GT40 and its "bundle of snakes". The most noticeable side effect of this is that it completely eliminates the characteristic "V8 rumble" and produces a sound just like a flat crank Ferrari V8 (except deeper due to the larger displacement). A similar but lesser effect is achieved by connecting the two cylinder banks after the merge collectors, with an X-pipe or H-pipe etc.

4-2-1 vs 4-1 headers are usually described as, 4-1 is for peak power and 4-2-1 is for torque. This is the simplistic way of describing it. It comes down to scavenging. With a 4-1 header, the pressure wave is reflected from only one merge collector, so the wave that returns to the exhaust valve still has most of it's energy. It will only produce a wave scavenging effect at one rpm, but that effect is as strong as it can be. Further, scavenging between cylinders occurs evenly across all cylinders, producing more power at one (usually high) rpm by sacrificing powerband width. With 4-2-1 headers the pressure wave reverts twice, after the primary and after the secondary. The primary is the shorter of the two and creates wave scavenging at high rpm while the reversion from the secondary is tuned to scavenge at a low rpm. But the effectiveness of both is reduced as neither wave contains as much energy as the wave in a 4-1. Further, inter-cylinder scavenging peaks at different rpms for different cylinders. The result is a broader power band, with less potential for peak power. It should be noted however that a well designed 4-2-1 header will make more peak power than a poorly designed 4-1, and vice versa with low end torque.

A similar effect is achieved using stepped pipe sizes, at each change in exhaust tube diameter, a small reversion wave is created. The length of each tube section can be tuned to improve VE at certain rpms.

A venturi merge collector is shaped to prevent any increase in volume where exhaust primaries/secondaries meet in order to preserve exhaust gas velocity and by extension maximize inertial scavenging between cylinders.

A smaller Primary diameter will improve inertial scavenging at low rpms and increase back pressure. Back pressure will improve volumetric efficiency at low rpms by counteracting charge loss due to overlap, but will create pumping losses and reduce inertial scavenging at high rpm. Larger primaries will improve peak power at the cost of low rpm torque (lower exhaust velocity). If you want to get precise about it, there's an equation based on primary length and displacement per cylinder.

Primary Length is calculated using the number of degrees between valve openings and the rpm at which you wish to make more power. There's an equation.

Secondary diameter is mathematically related to primary diameter, there's an equation. All the same science-y stuff applies.

Secondary length is calculated using the same equation as primary length, however you calculate the overall length including the primaries. The actual length of the secondaries is the overall length minus the length of the primaries.

Primary and secondary lengths are the means by which wave tuning is accomplished. They determine how long it will take the pressure waves to return to the cylinder. How long they need to take is entirely dependent on your cam specs. The headers that work great with stock cams will not produce optimal results with a crazy 294 degree cam. Changes to the separation of valve events will change the rpms at which a set of headers is effective. This even includes adjustable cam gears.

There is a caveat though. All those fancy equations are approximations. The pressures waves traveling through the exhaust move at the speed of sound. The speed of sound depends on the density of the material it is traveling through, which in the case of a gas means its pressure and temperature. But neither the pressure nor the temperature of exhaust gasses are constant, or even necessarily similar from one vehicle to another. The equations will get you close, but they can't give you the perfect headers. In an ideal world, you'd produce several prototypes and dyno test them all back to back.

[Snaps]

Originally Posted by Exage

May as well add turbochargers and intake manifolds to that topic!

Sequential and parallel turbocharging, twin scroll vs. single scroll and VGT turbochargers, waste-gating and blow off valves, A/R ratio, after-coolers, single and individual throttle bodies, EGR recirculation, positive crankcase ventilation (PCV).

I'll help out a little here, take some of the heat off of the other guys I'm sure they don't want to be answering tech questions all of the time!

Sequential Turbo's: (as far as I know from the 2JZ-GTE). Two turbo's of the same size. All of the exhuast gases are routed through to the first turbo, in the beginning. Then as the engine reaches a certain rpm, or the first turbo reaches a certain pressure (both of which are judged/programmed by the tuner/manufacturer), the second turbo kicks in. How this is done is dependant on the setup - for example, on the Supra, vacuum switching valves (VSV's), which I believe are electrical solenoids attached to a valve of sorts (?), are opened at certain rpm's to let vacumm/boost into other parts of the turbo's intake system, this changes valves in the exhaust manifold and intake system, which then allow exhaust to flow through the second turbo, which sucks in air and sends it to the engine, at the same time as the first turbo (which has been continuously producing boost since low rpm's).

The benefits of this system, are that you get boost from very little load, and very few rpms, then when the second turbo kicks in, you usually get an extra boost of power (and torque). this can be tuned to be very smooth, and (for example) make a 3.0L Inline 6 feel like a large-displacement V8.

Parallel turbo's: The simplest of the twin-turbo types, I think. Once again, two turbo's of the same size (though in theory, they don't have to be). Both turbo's are usually powered by half of the engine's exhaust gases (for example, the R35 GTR uses Parallel Twin Turbo's - is a V6, and each bank of cylinders routes to a seperate turbo), this means both of the turbo's spool up at roughly the same time, and you get a huge increase in power and torque when they do. A lot harder to drive to the limit, as the power delivery is not very linear.

The benefits to this system is that parallel turbo's are generally lighter, and simpler, and cheaper than both Compound and Sequential Turbo systems.

Compound Turbo's: One big turbo, one small turbo. The exhaust gases first pass through the small turbo's exhaust housing, then pass through the larger turbo's exhaust housing. The intake routing passes through the smaller turbo first, then passes through the larger turbo. At low rpm and low load, the small turbo can spool up and produce boost, this produces good power and torque low in the rpm range, however, there is not enough exhaust gases to spool the large turbo. At higher rpm's, the engine spools both the large turbo, and the smaller turbo simultaneously. The pressurised air from the smaller then passes through the larger turbo and gets pressurised even more, creating more power.

The benefits of this, is that you still get power and response at low rpms, but you also get huge power at higher rpms. However, this setup is generally heavier and more complicated than both sequential and parallel turbo's, and is rarely done, as the other two methods are simpler. I would expect one of these systems to be harder to tune than the others, too.

Wastegates: Controls the amount of exhaust gases passing through the turbo. When an engine spools a turbo, if it had no wastegate, the turbo would continue to spool faster and faster, as long as the engine could flow enough, and as long as the exhaust housing of the turbo wasn't restrictive. The problem then becomes that either the turbo spins itself to peices, or goes out of it's efficiency range (more boost = more heat, more heat = less power). This is where a wastegate is employed. As exhaust gases flow through the exhaust housing of the turbo, the turbo spools and creates pressure on the intake side. A boost reference line is then taken from the turbo or intake plenum (varies, always taken from intake side though) and routed to the wastegate. When the boost created by the turbo reaches a certain pressure, as governed by the strength of the spring in the wastegate, the wastegate opens and allow exhaust gases to bypass the turbo's exhaust housing, when this happens, the turbo begins to slow down, creates less boost, and the wastegate closes once again. this happens over and over again, causing the turbo to not overboost and destroy itself, or your engine.

Blow-off Valve: Used to relieve pressure on the intake side of the turbo system. When a turbo spools, creates pressure and flows air into the engine, if the throttle plate closes (accelerator is released) too quickly, pressure can build up in front of the throttle plate (as the turbo is still creating pressure for a short time after the throttle plate is closed), this pressure can force it's way back into the turbo and damage the turbine, or in more rare cases, damage the throttle plate. The point of a BOV is to release this pressure before it can do any damage. The BOV works very similarly to a wastegate - a reference line is taken from the intake plenum and routed to the BOV, when this line is in vacuum (when the throttle plate is suddenly closed, and more no air is allowed into the plenum, but the engine keeps sucking) the BOV is opened, allowing pressure to escape to either the atmosphere (venting BOV) or is recirculated back (recirculating BOV) into the un-pressurised part of the intake (before the turbo).

I would expand on other topics, but I need to get to bed!

[Exage]

Awesome I'll continue the definitions.

I should add that a recirculating BOV is sometimes referred to as a BPV (Bypass Valve) or CBV (Compressor Bypass Valve). They all vent after the MAF (mass airflow sensor) and before the compressor inlet.

A/R ratio: There are technically 2 ratios. 1 for the inlet housing and 1 for the exhaust housing. Typically it is referred to only on the exhaust (turbine) side.

A/R ratio description. It is the area of the inlet over the distance from the middle of the turbocharger wheel (turbocharger centreline) to the middle of the the of the area of the inlet. Note that A/R is only compared with similar turbocharger output (usually the same turbo with a different housing).

The effects of A/R ratio determine the characteristic of turbocharger:

Smaller A/R (smaller inlet area) will cause the turbocharger to have greater back-pressure at high rpm reducing hp. However the turbocharger will respond faster at lower rpm and have a quicker boost rise. This can reduce lag at low engine rpm the expense of hp at the top end. It's generally recommended more for a daily driver build.

Larger A/R (larger inlet area) will cause the opposite effect. At high rpm, flow is increased however it may have a slower boost rise or lag at lower rpm. It's much better for a race application or when maximum bhp power is desired.

Garret has a good page on this: http://www.turbobygarrett.com/turbob...o_tech102.html

The results are staggering similar to exhaust pipe sizing!

After-cooler, intercooler, charge air cooler

Typically when a gas is compressed it is heated. In this case air is heated when compressed by a turbocharger or supercharger. The principle behind the after-cooler is to cool the compressed air after the compressor causing the air to become more dense increasing the amount of oxygen in the air intake charge and decreases the risk of detonation or pre-ignition due to high intake air temperatures entering the engine and being compressed further.

There are 2 basic types: Air to Air, Air to Liquid

Air to Air is simple, charged air is cooled by ambient air passing over a heat exchanger. A popular and simple modification was to redirect the windshield washer system nozzle outlets and have them spray onto the air to air heat exchanger to rapidly cool the heat exchanger and thus charge air.

Air to Liquid works on the same principles as a radiator. However we are using the coolant system to cool the encased charge air rather than air to cool the coolant.

[old greg]

Just a quicky...

EGR (Exhaust Gas Recirculation) is used by automakers to reduce NOx emissions. Exhaust gasses are leaked into the intake manifold, typically at concentrations of 5-10% by mass for roughly a 50% reduction in NOx. However, this reduces flame front temperature and speed, potentially reducing combustion efficiency (power) at high rpm.

This is mostly done on gasoline engines, as it causes increased particulate emissions in diesels.

[Dimman]

Originally Posted by old greg

Just a quicky...

EGR (Exhaust Gas Recirculation) is used by automakers to reduce NOx emissions. Exhaust gasses are leaked into the intake manifold, typically at concentrations of 5-10% by mass for roughly a 50% reduction in NOx. However, this reduces flame front temperature and speed, potentially reducing combustion efficiency (power) at high rpm.

This is mostly done on gasoline engines, as it causes increased particulate emissions in diesels.

Also used to cook early generation 1JZGTE turbos...

[serialk11r]

Hey I feel like this question is incredibly stupid, but what exactly is the problem with a wide bore? Poor combustion efficiency? Greater heat loss through the head? Can't they just use 2 spark plugs or something?

[Dimman]

Engine predictions:

FB20 standard bore and stroke:
84mm bore X 90mm stroke: 200 bhp @ 7000 rpm, redline 7500 rpm (also redline of the Mk1 concept's interior, so...)
But not too mod-friendly.

FB25/20 de-stroked fantasy:
94mm bore X 72mm stroke: 205 bhp @ 7500 rpm, redline 8500 rpm
Very mod-friendly.

Edit:

Originally Posted by serialk11r

Hey I feel like this question is incredibly stupid, but what exactly is the problem with a wide bore? Poor combustion efficiency? Greater heat loss through the head? Can't they just use 2 spark plugs or something?

It has to do with the shape of the combustion chamber when compressed. The tighter together it is the better/faster it can burn, and the more charge motion is maintained.

Edit 2: Tighter is not really the right word... Wide and thin is bad. The analogy I've heard is that a hockey puck shape is better than a pancake shape, with the same volume. (hockey puck may need to be googled for the non-canadians...)

So combustion efficiency.

[Snaps]

^Actually, that probably relates to a calculus related rates of change problem... distance covered of fuel burning with respect to time, and then maybe volume of combustion chamber with respect to the shape, or bore for a specific volume... Hmm , I wonder if any of the car manufacturers use anything like this to optimise combustion...

[Dimman]

Originally Posted by Snaps

^Actually, that probably relates to a calculus related rates of change problem... distance covered of fuel burning with respect to time, and then maybe volume of combustion chamber with respect to the shape, or bore for a specific volume... Hmm , I wonder if any of the car manufacturers use anything like this to optimise combustion...

Ow.