Supercharger Tuning Through Cam Selection and Cam Timing

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Camshaft tuning is a vital part of supercharger tuning. Camshafts manage the valve opening and closing events in the engine and decide whether what comes out of our motor is lovely high power music, or a mess of dysphonics.

The use of the correct supercharger enhanced web cam shaft can go a long way towards supercharger tuning and offer significant power gains for the cash invested.

To understand camshaft timing and camshaft choice we have to understand first:

Relativity: Changing when the valves open or close (intake or exhaust) changes the valve timing with respect to:

The piston position inside the cylinder. Depending on where the pistons remains in the stroke, and where we are in the combustion cycle, magnuson supercharger jeep jk review ,then opening the valves will make use of the pressure difference between the cylinder and the intake and exhaust manifolds.For example it would make good sense that the ideal time to open the consumption valve is when there is peak vacuum inside the cylinder so that when the valve opens, the maximum quantity of fresh air can be ingested. Similarly, it makes good sense not to open the exhaust valve till peak cylinder pressures have actually been accomplished inside the combustion chamber and the combustion is complete and all the power is drawn out.
The high and low pressure pulses created by the style and runner lengths of the consumption and exhaust manifolds.It would make sense to open the intake valve just as the reflected pressure waves in the intake manifold reach the consumption valve as a high pressure part of the wave, therefore opening the valve at this high pressure point gives a ‘ram air’ impact through volumetric effectiveness resonance tuning increasing air consumption which increases power.Similarly on the exhaust side, it makes good sense to open the exhaust valve, just as the shown low pressure (vacuum) portion of the exhaust wave (reflected back from the collector) reaches the back of the exhaust valve. At this point in time there is both peak pressure inside the cylinder, and vacuum in the exhaust which develops a higher pressure differencial and a quicker evacuating exhaust gas.
With respect to the ignition timing event, for instance a shorter period or innovative exhaust camera, opens the exhaust valve faster with regard to when the mix was initially sparked, this means that although by advancing the exhaust webcam we may have matched our header style and opened the valve with the most affordable possible exhaust back pressure for finest efficiency, at the exact same time, we have reduced the quantity of time that the mixture is combusted and possibly opened the valve prior to reaching our peak cylinder pressures and thrown away some horse power.
The intake valves with regard to the exhaust valves: and this is typically described in regards to lobe separation angles (the offset in degrees in between the center of the exhaust camera and in between the center of the consumption webcam), or in regards to how many degrees of overlap (the number of degrees that both intake and exhaust valves are open at the same time).
Considering that the combustion inside the cylinder takes place at a much greater pressure than air pressure, and because exhaust valves are usually smaller sized than consumption valves (for this same high pressure factor) then exhaust gas speed is much higher than consumption gas speed. So, in some engines it is advantageous to open the consumption valve earlier than typical throughout the last part of the exhaust stroke, this is called overlap. During overlap – at the very end of the exhaust stroke – the quantity of pressure left in the cylinder is low so it is possible to inhale brand-new air under air pressure, at the very same time, the high velocity of the exhaust gasses exiting help attract a lot more fresh air from the intake side in an effect just like ‘syphoning’ where the fluid (in our case air) flows as a constant stream drawing in new consumption air after the old exhaust gas leaves.

The other part of phenomenon that connects to timing intake valves with respect to exhaust valves is the period of time where both valves are absolutely closed, which is your power stroke. This is the part of the combustion cycle where the mixture can be compressed and combusted. If either (or both) intake or exhaust valves are open you will not have the ability to neither compress nor combust the mixture, and the outright duration of time (in degrees of rotation) that your mix is combusted and allowed to reach peak cylinder pressures is impacted by camshaft choice and web cam timing. Something to note is that the valve angle has a lot to do with exhaust scavenging, clearly you will get maximum scavanging if the exhaust and consumption valves had ‘line of vision’ i.e. if the valves were separated by an angle of 180 *. If so, the exhaust air can straight pull in brand-new air. On the other hand, you would have the least possible scavenging if you had valves that were at a narrow angle (no degrees at the extreme) in between each other, so that the air would basically have to make a U turn to come in through the consumption and get taken out the exhaust.

So various motors react in a different way to overlap depending upon the exhaust back pressure and the valve angle.

Period:

Cam period is the number of degrees of the whole 360 * rotation that the consumption or exhaust valve is open. The longer the period, the more air you can enter the motor, the more overlap you have (which assists more with higher rpm power efficiency), the shorter your power stroke is (which reduces your combustion duration and your peak cylinder pressures lowering low rpm fuel efficiencly and clean idle … and so on

. Increased period (with it’s increased overlap and scavenging) likewise provides the opportunity for exhaust gasses to get to the intake, or consumption gasses to leakage to the exhaust, therefore are more sensitive to appropriate timing events otherwise we can get some negative effects from being ‘overcammed’.

Lift:.

Raise is how far or how deep the valve opens into the cylinder. The more lift you have, the less the valve is a limitation to inbound air due to the fact that it is farther away from the direct course of going into or exiting air. Including lift in general includes power to all rpms, depending upon how well the camshaft (and valve train) can accelerate the valve to a greater lift number in a brief period. It resembles a ramp, the shorter the duration and higher the lift, the steeper the ramp. So what occurs here is that if your valve train isn’t light adequate and well managed (Through proper valve springs or hydraulic lifting and damping) to operate that rapidly then raise will offer you improved efficiency at lower rpms (where there is a lot of time to move the valve to peak lift) but reduced efficiency at greater rpms, where there are more rounds per minute therefore less time per round, and hence less time to increase the high ramp and push the valve out to complete extension.

Lift is excellent, however typically people don’t try to significantly increase lift on their aftermarket cameras since of a couple of considerations:.

Ensure that at this brand-new lift, that there is still adequate clearance in between the valve (at full extension) and the cylinder (at top dead center) to avoid any catastrophic mechanical failure.
Upgrade to lighter valve train, with stiffer springs or dual valve springs to have more control over the valve with this steeper webcam profile.
It does add power but it does not shift the power curve up or down as significantly as altering webcam duration does, therefore in most aftermarket applications we really want a camera to provide us peak power at a certain rpm variety and so we care far more about the very best period (and some added lift).
I know this is a somewhat complicated subject, however I require to make sure we’re speaking the same language prior to we go into how this associates with superchargers. Prior to you decide which camshaft to utilize (or how to adjust the timing on your stock web cams) you have to take a look at one really important thing:.

Your exhaust system and exhaust back pressure:.

If you have a stock log type exhaust manifold, with a close paired cat, with a double cat exhaust system, small exhaust tubing, and a number of restrictive mufflers on your car then it is possible at peak power to have up to 10psi of back pressure.

If this is the case, my first recommendation would be to update to a high flow, low pressure exhaust system due to the fact that of the possible power gains; nevertheless, I do know that a few of our readers have cars that they are setting up for their parents or for double usage where their partner or the laws in their place … etc are truly strict when it concerns any added exhaust sound or any aftermarket exhaust. In this case, where exhaust upgrades are not a choice, then you need to choose your camshafts, and tune your camera timing to where you have ABSOLUTELY the minimum possible quantity of overlap. If you have significant overlap, then the more you rise above about 4500 rpms the more your supercharger will suffer and the more power you will waste. If the supercharger is geared to 7psi of boost for example, then during overlap, the cylinder sees 7psi of increase on the consumption side, and 10psi of back pressure on the exhaust side, the net result is that air will stream from the high pressure zone (the exhaust) to the lower pressure zone (the consumption) therefore your cylinder will start to fill with exhaust gases. As the rotation continues, the exhaust valve will close and overlap will end, and the consumption valve will remain open for the rest of the intake stroke (for the remainder of the duration of your consumption web cam), and the rest of the cylinder will fill with fresh air.

What takes place here is that we get a cylinder that filled for 30 * of overlap with exhaust air, and then filled for another 210 * (of the initial 240 * of period for a typical street cam) with fresh air. The result is a cylinder that is only 85% filled with fresh air or an engine that is actually 15% smaller in displacement! On the other hand, if our supercharger is geared for 18psi for example, then during overlap we will have 18psi on the consumption side and our exhaust back pressure of 10psi on the exhaust side, the net result of this overlap is that our supercharger is successfully just producing 8psi worth of differential pressure in between the intake and the cylinder and so we are only going to get a power increase of 8psi throughout overlap. So, during those 30 * of overlap the supercharger is just efficiently producing 8psi of increase, and after that once the exhaust valve closes, the supercharger will be able to return to operating at full increase for the other 210 *. The net outcome is something like 16psi of increase so 2psi (or about 12%) of our power was squandered.

Supercharger tuning through web cam choice and camera timing.

Intake webcam:.

Due to the fact that of the unfavorable impacts of overlap on a supercharger vehicle’s performance, and specifically in the case of high exhaust back pressure as is the case with a lot of factory supercharged cars, we discover that the optimal cam duration for the intake camera is normally 30-40 * of period less than a generally aspirated camshaft for the very same peak power RPM. The decision to lower the consumption web cam duration rather than divide the duration decrease between the intake and exhaust cameras, is that the consumption web cam will stream air under pressurized conditions (due to the addition of the supercharger and the increase in consumption manifold pressure) therefore at a decreased intake cam duration the engine will still be able to get it’s full share of consumption air. At the exact same time, the high rpm performance improvement from the reduction of overlap will likewise increase power production with a more conservative camera. Lastly, if we would like to get more flow from the intake webcam, there is still the option of using a greater lift camshaft (with a steeper profile due to the decreased period) with supporting valve train modifications to make sure valve float doesn’t occur at higher rpms.

Intake cam timing:.

The web cam timing for the consumption webcam would ideally be retarded which would move the consumption camera opening occasion farther away from the exhaust valve closing event so as to reduce or get rid of overlap, and as an adverse effects the power stroke period will increase by retarding the intake web cam which can likewise compensate for the lost power from the period decrease.

Exhaust web cam:.

The exhaust camera duration and lift for a supercharged variation of the motor need to be similar to a nitrous camshaft, in the sense that the exhaust webcams on nitrous specific builds have:.

1- Really healthy webcam period & very healthy webcam lift to permit a significantly elevated quantity of exhaust gases to be able to effectively exit the motor when the nitrous is triggered and the horsepower (and therefore the exhaust gasses) have both doubled in amount.

2- As little or no overlap if possible, as any overlap would suggest that nitrous would be sprayed from the intake side and out the exhaust, which is inefficient of our minimal supply of nitrous. Likewise the more overlap we have, the more difficult the supercharger will have to work due to the fact that of what we explained earlier about either exhaust reversion into the consumption, or the supercharger pressurizing the exhaust.

Exhaust camera timing:.

Advancing the exhaust cam both opens and closes the exhaust valves sooner. Opening the exhaust valve sooner slightly lowers the power stroke, but at the same time it lowers overlap and makes much better usage of our supercharger. Generally an innovative exhaust webcam combined with retarded intake webcam will offer the best results on a supercharged vehicle, specifically with a limiting exhaust.

If we had a high flow exhaust system set up, then it may not be advantageous to advance the exhaust webcam, a high circulation exaust system that is optimized for our engine’s power requirements can clear the combustion chamber of all it’s gasses very effectively. Having a high duration exhaust cam, a low back pressure exhaust system and a no overlap what so ever camshaft means that we are giving the exhaust gas lots of time to exit they cylinder, the consumption valve still hasn’t opened (since the we have decide to retard it, or use a conservative camera with less period) and so the supercharger is not pressing any brand-new fresh air in yet, now the cylinder is void therefore some of the exhaust gas can revert back into the cylinder, then the exhaust valve will close, and then the consumption valve will open just to discover the cylinder currently partly filled with exhaust gases.

This isn’t an issue with a restrictive exhaust because a restrictive exhaust will take a while to clear the cylinder at a lower velocity, however with a higher circulation exhaust system we should beware not to call out ALL of the overlap in the cam timing, or to over-cam the exhaust camera (using excessive period).

So exhaust camera timing can be advanced or retarded, depending on the exhaust modifications and the consumption web cam choice and hence need to be dyno-tuned.

It is very important to note that with all of these modifications in cam selection, overlap, power stroke duration, and cam timing, that the power stroke duration is effected and if it is efficiently reduced then we may require to retune the car’s timing bear down the dyno (for increased advance) to gain back losses in period of the power stroke (once again this versus popular thinking of never ever to advance timing on forced induction automobiles, if we have actually a reduced power stroke, or an application with substantial overlap then it might be needed to do so).

So we see here that completion outcome here a lop-sided camshaft with a conservative duration, high lift webcam on the intake side, and a regular period, high lift cam on the exhaust with minimal lobe separation angle and minimal (but not necessarily no) overlap.