I think, although I'm not sure, due to det at under 3.5k rpm, but can't hear it :confused: . I stop, turn ignition off, restart and all is well again.

 

All I have on my car is JDixon chip, Apexi filter, 1.2mm boost jets running at just over 12PSI and, found out on Saturday I have TRUST intercoolers :hyper: everything else (as far as I know) is stock, including Zorst.

 

How do I go about finding exactly what is causing it, preventing it and curing it

 

EDIT, also run on Optimax all the time uless I can't get there so I use BP Ultimate or that Esso Super stuff

 

CheerZ

Paople

Paul

ECU test for error code : http://www.ttzd.com/tech/diagnostictech.html

I think, although I'm not sure, due to det at under 3.5k rpm, but can't hear it :confused: . I stop, turn ignition off, restart and all is well again.

 

All I have on my car is JDixon chip, Apexi filter, 1.2mm boost jets running at just over 12PSI and, found out on Saturday I have TRUST intercoolers :hyper: everything else (as far as I know) is stock, including Zorst.

 

How do I go about finding exactly what is causing it, preventing it and curing it

 

CheerZ

Paople

Paul

sounds like your dett sensor is bad,do a search for the link to put a resister of the same value in its place,cant think where i seen this repair but it is out there bud

I would have thought that if the det sensor sensed det then the ecu would put the car into saftey :confused: so det sensor must be good.

I would have thought that if the det sensor sensed det then the ecu would put the car into saftey :confused: so det sensor must be good.

There are many causes for safety mode, the most common being det sensor and temp sensor.

I would have thought that if the det sensor sensed det then the ecu would put the car into saftey :confused: so det sensor must be good.

you,ve hit the button,"the sensor detted the dett before it detted" :D :headvswal

Dee doo doo doo, dee darr darr dett detted dettanated bang LOL

Dee doo doo doo, dee darr darr dett detted dettanated bang LOL

:duffer: oh fvck it lets have another drink, we,ll fix it later :duffer: :duffer:

:duffer: :duffer: :duffer: :duffer: :duffer: :duffer: :duffer: cehreZ hick ! :hurl:

if your det sensor circuit is at fault it will keep going into safety boost whether you're detting or not.

 

Vijay

The problem is simple, the det circuit is responding to a detonation signal and doing exactly what it is designed to do and go in to (tempory) safety boost, by that I mean after switching of the ignition and back on full boost is back until of course detonation occurs again and the cycle repeats itself.

 

If the detonation sensor had failed the result would be permanant safety boost, so you need to find out why detonation is occuring which could range from a batch of poor quality petrol, over advanced timing, over boosting or even errors in the eprom map (unlikely as John Dixon involved )

 

Less likely but worth checking, is the cable to the det sensor, if it is damaged in any way, movement of the engine may cause a fault.

 

Do an ecu check, if the sensor circuit has a problem it will be stored as a fault code (34) if detonation is occuring as mentioned above and the circuit is operating correctly there will not be a stored record of this in the memory and no fault codes will show (55)

 

Maybe worth checking the boost level with a good quality test gauge, also try filling up at a different garage, and of course check the timing.

 

 

Hope that helps

 

Jeff TT

This website is fantastic.

with a chip boost jets etc would a standard exaust not cause a problem !!! dont you need a bit of free flow with such boost and fuel !!

could this not cause awful back pressure in turn causing detination upon flooring it....

with a chip boost jets etc would a standard exaust not cause a problem !!! dont you need a bit of free flow with such boost and fuel !!

could this not cause awful back pressure in turn causing detination upon flooring it....

 

Yes, a restrictive exhaust will exacerbate detonation problems.

I think, although I'm not sure, due to det at under 3.5k rpm, but can't hear it :confused: . I stop, turn ignition off, restart and all is well again.

 

All I have on my car is JDixon chip, Apexi filter, 1.2mm boost jets running at just over 12PSI and, found out on Saturday I have TRUST intercoolers :hyper: everything else (as far as I know) is stock, including Zorst.

 

How do I go about finding exactly what is causing it, preventing it and curing it

 

EDIT, also run on Optimax all the time uless I can't get there so I use BP Ultimate or that Esso Super stuff

 

CheerZ

Paople

Paul

 

 

You know, I've got EXACTLY the same problem on my black Z.

 

I have swapped from some japanese ecu to a JD and it made no difference, boost kept the same @ 0.8 bar, fuel: V-Power....

 

I have not had enough time to fully fault find the problem yet (it's been a busy year) but hopefully next year I'll sort it.

 

By the way Paul, did you fix your problem?

The text below is long but very descriptive and should go some way to answering the question about restrictive exhausts, however it is a generalisation and not specific to the 300zx personally having dealt with 300 or more chip /boost upgradeds over the last few years its not a problem that I have seen, I do believe there is more issues with badly set up engines and badly written eproms and there are more of those than is admitted to!

 

A proffesional set up engine will have had all the detonation issues dealt with, unless poor fuel used at a later date of course.This is one of the very reason buying an eprom from e-bay is a bad idea so is having an ecu done through the post as no engine set up or condition responsibility is taken by the person / company suppling the eprom, seen some sad results due to this.

 

Jeff TT

 

 

Exhaust Cycle and exhaust design

 

Let's start by looking at the effects of a less than optimum exhaust cycle.

 

A motor has fully exhausted itself (When it is really tired?) when the pressure in the chamber is equal to, or below atmospheric at the end of the exhaust cycle. Several things happen when the motor cannot fully exhaust itself. If the pressure is above atmospheric at the end of the cycle, the result is lowered volumetric efficiency, increased pumping losses, and reduced combustion efficiency as compared to an optimized exhaust cycle.

 

 

Swept Volume, Clearance Volume, and Compression Ratio.

 

 

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In December's port timing article, I stated that top dead center, or TDC refers to the point at which the chamber is at its smallest possible volume. The space in the chamber at TDC is referred to as the clearance volume, and this in part determines the compression ratio. The compression ratio is specified as (Volume at BDC/Volume at TDC) Using an '87 13B as an example, the chamber volume at BDC is 9.4 times greater than the volume at TDC, for a compression ratio of 9.4 to 1. The difference between the volume at TDC, and BDC is referred to as the swept volume, or displacement. This is the volume of gasses that will be displaced in one complete cycle assuming 100% volumetric efficiency. A little bit of high school algebra shows that the volume at BDC is 44.66 cubic inches, and the volume at TDC is 4.75 cubic inches, or 10.6% of the total volume.

 

 

Volumetric Efficiency

 

 

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The exhaust gasses that occupy the clearance volume will be carried around into the following intake stroke. As you can see, even at 100% volumetric efficiency the mixture will still only be 89.6% fresh intake charge. If the chamber pressure does not reach atmospheric by the end of the cycle, this 10.6 %, or 4.66 cubic inches of exhaust gasses will be pressurized, and will take up even more space once they are allowed to expand as the chamber volume increases during the intake stroke. This will reduce volumetric efficiency considerably, as the exhaust gasses will occupy space that could be used for fresh mixture. These exhaust gasses effectively "take away" from the swept volume, or displacement of the motor. The goal of the exhaust system then, should be to evacuate as much of the spent gasses as possible.

 

 

Inertial Scavenging

 

 

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Inertial scavenging is easiest to understand if you think of the gasses in the exhaust system as a big piece of elastic. While they are not directly connected, a change at one end of the system will have an effect on the gasses at the other end of the system. For instance, towards the end of the cycle, the flow through the exhaust port slows down, but the high velocity gasses from earlier in the cycle are still travelling through the system. (Note: A system made up of 100" long, 1/34" inside diameter header tubes, as you might see on a race car, will contain about six complete cycles worth of exhaust gasses per pipe.) These high velocity gasses will "pull" on the slower moving gasses near the exhaust port, helping to evacuate the chamber. This is inertial scavenging. Just imagine two cars rolling down the road, connected to each other by a bungee cord. If the car at the back slows, it will not immediately be jerked back to speed, but rather gently pulled back up to speed by the car in front. As some of you may have guessed, a series of resonances will then occur, with each car alternately pulling at the other. This is very much like what happens to the gasses in the exhaust system.

 

 

Pumping Losses

 

 

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Well, here we are at pumping losses again! Luckily this is quite easy to explain and understand. It all comes down to exhaust flow. Not just the airflow capability of the exhaust port, but of the entire system from the port to the end of the exhaust pipe. Quite simply, if the exhaust flow is insufficient, the blowdown period will only account for a small amount of the total exhaust gasses, and the remainder will have to be squeezed out by the rotor itself. Physically forcing the gasses from the chamber through a restrictive exhaust system requires a substantial amount of horsepower. So much in fact that many diesel truck engines have a mechanism which blocks the flow of exhaust gasses to slow the vehicle down, thus saving wear on the brakes. Just think about slowing an 18 wheeler with nothing but exhaust pressure, and you get an idea how much this can affect your engine.

 

 

Combustion Efficiency

 

 

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We have already discussed how insufficient exhaust flow reduces volumetric efficiency, but the presence of exhaust gasses in the intake charge (Exhaust gas dilution) causes other problems as well. The rotary engine is known for its poor combustion characteristics. Due to the shape of the chamber, and the location of the spark lugs, a large percentage of the intake charge does not burn in the chamber. The end result is a fair amount of unburned gasses, or hydrocarbons being passed into the exhaust system. This reduces power output, because a portion of the mixture that we tried so hard to put into the engine did not burn. This also reduces fuel economy, and increases emissions. Another effect that is not often realized is excessive exhaust gas temperatures. These hydrocarbons will then burn in the exhaust system raising the exhaust gas temperatures.

 

The addition of exhaust gasses to the intake charge will reduce the already poor combustion quality. The end result is that the mixture is harder to ignite, and when it finally does light up it will burn at a slower rate further reducing power output. In a turbocharged engine excessive exhaust gas dilution will cause its own unique set of problems.

 

Detonation

 

 

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We tend to think of combustion inside of the engine as a series of explosions, but in fact the combustion occurs at a very slow rate, at least compared to an explosion. In the absence of detonation, the mixture in the vicinity of the spark plugs is ignited first, and the "flame front" travels from that point, through the rest of the mixture in a fairly controlled manner. Detonation occurs after the combustion has initiated, and the pressure, and temperature in the chamber rises to the point that the remaining mixture literally explodes. Anyone who has ever experienced detonation understands that it certainly is an explosion! Detonation is caused by a combination of heat, and pressure, and so it stands to reason that excessive exhaust gas dilution, (remember these are hot gasses) will increase the likelyhood of detonation. As most of you know, detonation will destroy a turbocharged engine in a big hurry.

 

 

A "Perfect" Exhaust Cycle

 

 

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Now that we have all of the pieces, it is time to put the puzzle together. I personally have a hard time understanding anything unless I can see it in front of me. For that reason I will refer once again to the illustration of the engine during its different phases.

 

As the exhaust port opens, (#13 in the illustration) the high pressure in the combustion chamber will force the gasses through the port and down the exhaust system at a high rate of speed. This, as you remember, is the blowdown period, and a large portion of the gasses will exit the chamber at this time. At the same time that the flow is initiated, a high pressure wave will travel towards the end of the exhaust system at the speed of sound. (Note that this high pressure wave will help to propel the slower moving exhaust gasses with it.)

 

Further into the cycle (#15) as the pressure differential between the chamber and the exhaust system has decreased, (ie., the chamber has "blown down") the velocity through the exhaust port will also decrease, and the remaining flow will be the result of the decreasing chamber volume. At this point, approximately half of the exhaust gasses will have exited the chamber.

 

At 135 degrees after bottom dead center, (between #15, and #16) the chamber will be at its maximum rate of decrease of volume. In other words, it is at this point in the cycle that the rotor will be travelling at maximum velocity. If the exhaust flow is insufficient, it will require a great deal of force to expel the gasses from the chamber. This is where the pumping losses during the exhaust stroke will be the greatest. Keep in mind that these losses cannot be eliminated, but they can certainly be lessened by providing sufficient exhaust flow.

 

Moving on to #17, and #18, the chamber volume is decreasing at a very slow rate, and the motor is doing very little to mechanically expel the gasses from the chamber. It is at this point in the cycle that pressure wave tuning comes into play. The high pressure wave that originated when the exhaust port first opened will have travelled to the collector, and been reflected back as a low pressure wave. (Remember last months section on pressure wave tuning?) If timed correctly, the wave will arrive at this point, just before the intake port opens. This low pressure wave, in conjunction with the "pull" created by the high speed gasses still in the exhaust system will lower the pressure in the chamber to sub atmospheric. When the intake port opens, this vacuum will help to initiate the flow of fresh mixture into the chamber, which will increase volumetric efficiency.

 

Looking back to December's port timing article, you can see that the intake port does not open until approximately 30 degrees after top dead center. That means that for the first 30 degrees after TDC, (The distance between #18, and #1 in the illustration) the chamber volume is increasing, but because only the exhaust port is open, the chamber will be filling with exhaust gasses by pulling them back out of the exhaust system. This is called exhaust gas reversion. If the exhaust gas velocity is low, (Such as at low rpm) the vacuum created by the increasing chamber volume can easily reverse the flow and pull the gasses back into the chamber. If, on the other hand, the exhaust gas velocity is high, it will take a great deal more energy to reverse their flow, and the result will be less exhaust gas dilution. This is why large exhaust ports, and large diameter exhaust tubing reduce low speed power.

 

 

Low RPM Operation

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The above paragraphs describe a "perfect" exhaust stroke, and unfortunately this can only happen over a very narrow rpm range. Let's look at what happens when we halve the rpm. We will assume that the above example is at 8000 rpm. Now let's look at the same cycle at 4000 rpm. Since the exhaust cycle lasts twice as long at 4000 rpm, the chamber will have reached sub atmospheric pressure approximately half way through the cycle, assuming of course that we have sufficient exhaust flow. This sub atmospheric condition will send a low pressure wave travelling towards the end of the exhaust system at the speed of sound. (Remember that a pressure wave is intiated anytime pressure deviates from atmospheric.) This wave will reach the collector, and reflect back as a high pressure wave. Since we have halved the rpm, it is likely that this wave will arrive near the end of the exhaust stroke, (#18) and so the chamber pressure will be above atmospheric when the intake port opens. This will result in excessive exhaust gas dilution as compared to the 8000 rpm example. In addition to this, the exhaust gas velocity will be low, and during the period from TDC, to intake valve opening, the exhaust gas flow will reverse momentarily. This will also add to the amount of exhaust gas dilution.

 

If we wanted the exhaust stroke to be optimized for this lower rpm, several changes would be necessary.

 

1. Later exhaust port opening. Since we have more time to exhaust the chamber, the total exhaust duration can be lessend. The result of this will be that we can hold pressure in the chamber for a greater period of time. This will increase the amount of time that torque will be applied to the eccentric shaft.

 

2. Smaller cross sectional areas. Decreasing the cross sectional area of the port, and the exhaust tubing will increase the velocity of the exhaust gasses. This will result in less reverse flow, or exhaust gas reversion after top dead center, and will make the inertial scavenging towards the end of the cycle more effective.

 

3. Longer tuned lengths. Since the exhaust cycle occurs over a greater period of time at low rpm, the pressure wave must be further delayed if it is going to arrive at the appropriate time. In the case of optimizing the system for 4000, rather than 8000 rpm, the header lengths would need to be approximately twice as long. This is easiest to understand if you think of the headers as a delay source. What we are trying to do is delay the wave from the time it initiates to the end of the exhaust cycle. The further that the wave travels, later it will arrive at the exhaust port.

 

As you can see, we can only optimize the exhaust cycle over a fairly narrow rpm range. If at first this seems discouraging, it is important to consider that an optimized cycle over a narrow range is much better than a less than optimum cycle throughout the operating range. A "perfect" intake stroke can also only occur over a fairly narrow rpm range, and so it is important to consider the trade-offs when contemplating performace upgrades. If for instance you wish to "street port" your engine, you must understand that the increase in top end power will be accompanied by a decrease in low speed power.

 

The intent of these articles is not to make specific reccomendations, but to give you the knowledge to make informed decisions, and sort through the hype. For all of you racers, using the lessons learned from the exhaust system articles will allow you to make sense of exhaust tuning. If you apply these theories, and do some trial and error testing, you will likely unleash some hidden power. Now that you have the facts, you will understand why one system affects the engine differently than another, and this will make it much easier to arrive at the "correct" setup.