Warpspeed

Yeah, I live not far away from Mondo, and as I am still looking for a Skyline have visited their car yard a few times. I always get the feeling that customers are not really welcome. Oh they want my money all right, but they cannot be bothered otherwise. They do not seem to be moving as many cars through their yard these days as they used to. I wonder why ?

There is only one problem with cutting springs, and that is how you cut them. If you just chop the end off with an angle grinder, the high temperature destroys the heat treatment in the end of the spring. However if you take it very gently, dipping the hot end into a bucket of water every few seconds, there will be no problem. I have done this myself many times with good results. A shorter spring will also have less active coils and will therefore be slightly stiffer as well. The stresses in the coil wire remain the same so the spring will not be overloaded. Take your time, and only cut off a small section at a time maybe 30mm. Refit it to the car and see how much it has been lowered. It takes ages to do, but costs nothing.

I have it on good authority that size does matter.

It is probably not that hard to get serious power from a RB25DET, the problem, as whatsisname says, will be keeping it alive for long enough to make it worthwhile. Any serious detonation is going to kill it real quick, slight timing change, leanout, hot day, a tank of dodgy fuel. RATTLE - BANG. So what is the point. If some hero can screw 400KW out of one and it lasts one week? Nitrous oxide is a good example of how to get huge power gains and blow up your motor on the dyno.

Torque is the twisting force that turns the wheels and accelerates the car. Sometimes called tractive effort. Power is tractive effort times speed. GTR king is pretty right in his statement. Torque = acceleration, power = speed.

Too true. A lot of guys on this forum brag about what power they are making at the wheels, but if you ask them what torque they have, you usually get a totally blank look.

Torque is a twisting force, just the same as you would apply with a spanner to do up a nut. Fifty foot pounds of torque is like a fifty pound weight on the end of a one foot spanner. Or five pounds of force on the end of a ten foot spanner. This is simply a force pushing, pulling or twisting on something. Power is the rate of work being done, or force times speed. If you do something twice as fast, it requires twice the power. So, power equals torque times speed. expressed Ft-lb x RPM. A long time ago a guy calld James Watt got himself a genuine hairy horse, and did some measurements to see how much weight his horse could lift or drag in a certain time. He decided that his horse could lift a 550 pound weight one foot each second, and this has now become the standard unit of horsepower. True ! We now have the formula , Horsepower = Ft-lb x RPM / 5252 Getting back to internal combustion engines, torque is twisting force only. The main factor deciding torque for a non supercharged engine, is the size of the engine, that is the bore, stroke, and number of cylinders. Power for a heat engine is the rate at which air and fuel can be burnt in a given time. So power has more to do with airflow through the engine than the size of the engine. I small high reving motorcycle engine can make a lot of power because it can spin so fast, but will not have a lot of torque because it is small. A huge truck engine will make a lot of torque because it is big. But because it cannot spin fast the power will be relatively low. A gearbox can reduce the speed of a shaft and increase the torque at the same time, but the power remains almost exactly the same. So a one hundred horsepower motorcycle engine fed through a reduction gearbox can produce the same torque and RPM as you would get straight from the one hundred horsepower truck engine. Does that help ?

Once again thanks Meggala for the information. I have been going through this and crunching some numbers to find out what the actual seat to seat valve timings are for the various engines. They are all over the place. Most have either no overlap at all, or only one to three degrees which is really zero. The R34 RB25DET neo engine has twenty three degrees of overlap, and the latest SR20 DET has twenty one degrees of overlap. Also lobe centres for both inlet and exhaust are also all over the place as well. I am sure Nissan have been trying very hard to stay within legal emmissions rather than seeking optimum power. I am sure a lot can be done with valve timing on a stock engine with fairly mild cams. Figures for a non VVT early RB25DE are not given. At a guess it may have a pair of 248 cams, and these might actually go rather well in a stock RB25DET, who knows ?

It seems to me that on a road car the two most important features are having closed loop, and also a proper airflow meter. MAP sensors assume that the airflow through the engine is a certain amount at a certain manifold vacuum or pressure. If something changes anywhere in the engine or exhaust system, the whole thing needs to be retuned. An airflow meter actually measures the airflow, and adds the correct amount of fuel. If something changes the airflow, then the fuel mixture remains correct. If like me you are constantly messing about with your car an airflow meter is far more forgiving. Closed loop control at light throttle is also very good for the same reason. In my opinion having a MAP sensor and no closed loop on an everyday road car is silly, and is going to cost heaps in poor fuel economy and performance.

Thats what I like most about driving a sleeper. No one ever bothers to take me on. But sometimes I see some smartass showing off, so after having a real good look around, slide up beside them at the next set of lights. I can maybe gain half a car length before they realise, and the look on some guys faces is absolutely priceless.

Hi Gradenko, thank you very much for the cam information, I have been looking for this for a very long time. Valve overlap can be both a good thing and a bad thing, but is mostly bad. If you increase the cam duration you will get to a point where both valves are open together around TDC, as both valves are both at the ends of the lift curves they may not actually be very far off the seat, but both WILL be open together. What happens at TDC overlap depends entirely on the relative pressures in the exhaust manifold and inlet manifold. Understanding this is the key. If the exhaust manifold pressure is lower than inlet manifold pressure, then the exhaust will suck fresh mixture across the combustion chamber, clearing out all the hot exhaust remnants. This can happen at full throttle in a highly tuned normally aspirated engine with open exhaust, in a supercharged engine, or a turbo RACING ENGINE where boost pressure is higher than turbine inlet pressure. If exhaust pressure is greater than inlet manifold pressure, exhaust will flow backwards into the inlet runner, then be sucked into the cylinder during the induction stroke. This is very bad. It will always occur at less than full throttle on any engine, so for a road car, excessive valve overlap is not a good idea. If the engine is only ever driven flat out, as in drag, or circuit racing it is less of a problem though, and the longer valve duration will give more top end power. The original manufacturers these days are concernrd with emmissions as well as making a smooth running engine. The standard valve timing is almost guaranteed to have minimal or no valve overlap. If all you care about is power at full throttle, and do not care about part throttle operation, you can run a bit more overlap. How much depends on the relative exhaust back pressure and boost pressure. This is very important to understand. A stock turbo is going to have a fairly small exhaust turbine and housing, this will give a low boost threshold and less lag. It will also probably have a fairly restrictive exhaust system. Flat out at full throttle, the exhaust manifold pressure may be TWICE boost pressure, or even more ! If you wind up the boost higher it gets a lot worse. Putting a large overlap cam into such an engine will definitely lose you power. On the other hand a monster turbo with large turbine may only produce usable boost high in the rev range, but the exhaust back pressure will be quite low, perhaps the same as boost pressure, or only slightly above. Long duration cams with a lot of overlap are going to really help airflow and peak power. How much cam duration and overlap you can run depends on the relative exhaust and boost pressures. You either need to experiment yourself, or seek expert advice. So there is no single answer, it all depends on how radical you want to go.

Ah yes, Mondo Motors again. Lots of customers...... lots of stories. They are becoming quite famous.

Now there IS an interestin question. How far can you get on a pushbike on a slab of beer ? If you fall off it does not count.

Let us know how it all goes Michael. Cheers, Tony.

rob77 is quite right. Be very careful after making any changes, that the boost does not suddenly and unexpectedly rise above a safe level. So gently does it, while watching the boost gauge after any adjustment. A restrictor is just a small hole. You could solder up the inside of an existing brass fitting and then drill a small hole. Or push a round piece of metal/plastic with a small hole up a rubber hose. I would start out with a fairly large hole maybe 3mm, you may then find that you cannot get enough boost even with the needle fully open. Go a bit smaller, and see what happens. If you do it this way, the needle when fully closed gives stock boost, fully open will give some safe maximum, with lots of adjustment inbetween.

The wastegate actuator only requires pressure to operate, it is a dead end. Unless there is a leak somewhere. Putting a restrictor in the line will not reduce the pressure IF THERE IS NO FLOW. Think about it. Now if you add a needle valve that deliberately causes a controlled leak after the restrictor, there is going to be flow through both the restrictor and the needle valve. If you use the previous example, with 14 psi boost, and a 7psi rated actuator. If the restrictor AND needle valve have EXACTLY the same flow areas then the same air is going to flow through both. There will be a 7psi drop across the restrictor, and a 7psi drop across the needle bleed valve (if they are set to have identical flow areas). By adjusting the needle valve you can vary the relative pressure drops across each restriction.

Hi Prank, I would go with the Koni adjustables myself. But it really depends on the relative spring rates. I am not a great fan of super stiff springs on road cars. The fantastic dry weather handling, switches to horrible slither around instant death in the wet. Slightly lower and stiffer springs are fine. Stock cars are damped for comfort, dial in a bit more damping, and get some stiffer antiroll bars as well. Do it with the antiroll bars, not with the springs.

MIC33R, my apologies the article that I suggested indeed does not use a restrictor. So I will attempt to put it into words myself. The wastegate actuator that is fitted to the turbo has a diaphragm and spring that opens the wastegate at a particular boost level set by the original design of the actuator. What you need to do is arrange for the pressure fed to the actuator to be less than the actual turbo boost pressure by some fixed proportion. For example if stock boost is 7psi, and you want 15psi boost, then the actuator must still see only 7psi when the boost is actually at 15psi. The way to do this is to fit an air restrictor into the control hose to the actuator, and an adjustable air bleed needle valve to atmosphere teed into the control line after the restrictor. The flow path is, boost pressure, restrictor, tee fitting, actuator. The other branch of the tee goes to the adjustable air bleed out to the atmosphere. If you close off the air bleed fully so it is completely closed, boost goes through the restrictor into the actuator and you will have the stock boost level. You can then unscrew the needle valve a bit, and the boost pressure will rise above stock by some amount. Hope this helps.

Hey turtle. INASNT has just offered to take all our oil and bury it in his back yard. I think that is really clever, soon he is going to have more oil in his back yard than the whole of the middle east. He will then be able to live in a palace, have a harem, and lots of really fast cars and stuff.

Think the new format looks fantastic. Makes the "other" Skyline forum look like the blue death."

Hi Michael. It is difficult to explain, so check out this article from Autospeed: http://www.autospeed.com/A_0028/page1.html Cheers, Tony.

The only thing lower than a journo is ....... hell I can't really think of anything lower than a journo, can you.

Where and how is the bleed valve fitted ? I assume you have teed it into the wastegate actuator line. You will also need to fix a restrictor of some sort into the line before the bleed valve for this to work properly.

Hi Meggala. The cams I measured came from the same source as a RB26 short block I purchased, which is fitted with the R33 oil pump, so I assumed the cams were from the same engine. Measuring cams, particularly mechanical cams is a bit tricky. The clearance ramps are very gentle, there is only small lift for a lot of rotation. These ramps blend into the main lift curve, so it is impossible to tell exactly where the ramp ends and main lift begins. There is no standard. Wade Cams in Melbourne have something like 4500 grinds available. I have listings of some of these. The quoted ramps vary from .006"to .017" on different grinds. The valve timing point is at the end of the ramp. If you do not know where the ramp is supposed to end you cannot tell what the official duration is. Suppose you measure 260 degrees at .008" lift and 245 degrees at .018 lift. What cam is this ? ? ? As the ramps are extremely long and gentle this would not be unreasonable. On these GTR cams I have, I measured very close to 240 degrees duration for the inlet cam, and 250 degrees for the exhaust cam assuming a .012" measuring point. This seemed reasonable at the time. It is quite possible though that the official Nissan duration figures are a few degrees different because they measure at a differnt lift point. So 246, or 253, or something could actually be correct. In contrast hydraulic cams have absolutely no lift, then it suddenly takes off at one particular point. Standard measuring points for these are .005"or .007" lift, in practice the durations are very easy to measure and are quite repeatable. I would dearly love to know whatever cam information you have, simply because junkyard cams are a very low cost way to experiment. If you know a certain version RB20 had this cam or RB25 that cam, it would be very handy indeed to know. My computer simulation program Dyno 2000 allows testing of any camshaft you can possibly imagine with in n/a, turbo, or supercharged engines. It works like majic and gives a very good indication of what is best.

Ah so !