Supercharger Tuning By way of Cam Choice and Cam Timing

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Camshaft tuning is an important a part of supercharger tuning. Camshafts orchestrate the valve opening and shutting occasions within the engine and resolve whether or not what comes out of our motor is gorgeous excessive energy music, or a multitude of dysphonics.

Using the correct supercharger optimized cam shaft can go a good distance in direction of supercharger tuning and provides appreciable energy positive aspects for the cash invested.

To know camshaft timing and camshaft choice now we have to know first:

Relativity: Altering when the valves open or shut (consumption or exhaust) modifications the the valve timing with respect to:

• The piston place contained in the cylinder. Relying on the place the pistons is within the stroke, and the place we’re within the combustion cycle, then opening the valves will exploit the stress distinction between the cylinder and the consumption and exhaust manifolds.For instance it could make sense that the best time to open the consumption valve is when there may be peak vacuum contained in the cylinder in order that when the valve opens, the utmost quantity of contemporary air will be ingested. Equally, it is smart to not open the exhaust valve till peak cylinder pressures have been achieved contained in the combustion chamber and the combustion is full and all the facility is extracted.
• The excessive and low stress pulses created by the design and runner lengths of the consumption and exhaust manifolds.It might make sense to open the consumption valve simply because the mirrored stress waves within the consumption manifold attain the consumption valve as a excessive stress portion of the wave, thus opening the valve at this excessive stress level provides a ‘ram air’ impact by means of volumetric effectivity resonance tuning growing air ingestion which will increase energy.Equally on the exhaust aspect, it is smart to open the exhaust valve, simply because the mirrored low stress (vacuum) portion of the exhaust wave (mirrored again from the collector) reaches the again of the exhaust valve. At this cut-off date there may be each peak stress contained in the cylinder, and vacuum within the exhaust which creates a better stress differencial and a quicker evacuating exhaust fuel.
• With respect to the ignition timing occasion, for instance a shorter period or superior exhaust cam, opens the exhaust valve sooner with respect to when the combination was initially ignited, which means though by advancing the exhaust cam we could have matched our header design and opened the valve with the bottom doable exhaust again stress for finest effectivity, on the identical time, now we have lowered the period of time that the combination is combusted and probably opened the valve earlier than reaching our peak cylinder pressures and thrown away some horsepower.
• The consumption valves with respect to the exhaust valves: and that is normally described when it comes to lobe separation angles (the offset in levels between the middle of the exhaust cam and between the middle of the consumption cam), or when it comes to what number of levels of overlap (the variety of levels that each consumption and exhaust valves are open on the identical time).

For the reason that combustion contained in the cylinder happens at a a lot greater stress than atmospheric stress, and since exhaust valves are normally smaller than consumption valves (for this identical excessive stress motive) then exhaust fuel velocity is far greater than consumption fuel velocity. So, in some engines it’s useful to open the consumption valve sooner than typical over the past a part of the exhaust stroke, that is referred to as overlap. Throughout overlap – on the very finish of the exhaust stroke – the quantity of stress left within the cylinder is low so it’s doable to breathe in new air underneath atmospheric stress, on the identical time, the excessive velocity of the exhaust gasses exiting assist attract much more contemporary air from the consumption aspect in an impact very like ‘syphoning’ the place the fluid (in our case air) flows as a steady stream drawing in new consumption air after the previous exhaust fuel leaves.

The opposite a part of phenomenon that pertains to timing consumption valves with respect to exhaust valves is the period of time the place each valves are completely closed, which is your energy stroke. That is the a part of the combustion cycle the place the combination will be compressed and combusted. If both (or each) consumption or exhaust valves are open you won’t be able to neither compress nor combust the combination, and absolutely the period of time (in levels of rotation) that your combination is combusted and allowed to achieve peak cylinder pressures is affected by camshaft choice and cam timing. One factor to notice is that the valve angle has quite a bit to do with exhaust scavenging, clearly you’re going to get most scavanging if the exhaust and consumption valves had ‘line of sight’ i.e. if the valves had been separated by an angle of 180*. In that case, the exhaust air can straight pull in new air. Conversely, you’ll have the least doable scavenging for those who had valves that had been at a slender angle (zero levels on the excessive) between one another, in order that the air would basically must make a U flip to return in by means of the consumption and get pulled out the exhaust.

So totally different motors reply in another way to overlap relying on the exhaust again stress and the valve angle.

Period:

Cam period is the variety of levels of the whole 360* rotation that the consumption or exhaust valve is open. The longer the period, the extra air you may get into the motor, the extra overlap you’ve got (which helps extra with greater rpm energy efficiency), the shorter your energy stroke is (which reduces your combustion period and your peak cylinder pressures decreasing low rpm gasoline efficiencly and clear idle….and so forth

Elevated period (with it is elevated overlap and scavenging) additionally provides the chance for exhaust gasses to get to the consumption, or consumption gasses to leak to the exhaust, and so are extra delicate to correct timing occasions in any other case we are able to get some detrimental results from being ‘overcammed’

Elevate:

Elevate is how far or how deep the valve opens into the cylinder. The extra carry you’ve got, the much less the valve is a restriction to incoming air as a result of it’s farther away from the direct path of getting into or exiting air. Including carry typically provides energy to all rpms, relying on how properly the camshaft (and valve prepare) can speed up the valve to a better carry quantity in a brief period. It is like a ramp, the shorter the period and better the carry, the steeper the ramp. So what occurs right here is that in case your valve prepare is not gentle sufficient and properly managed (By way of correct valve springs or hydraulic lifting and damping) to function that quickly then carry gives you improved efficiency at decrease rpms (the place there may be a number of time to maneuver the valve to peak carry) however lowered efficiency at greater rpms, the place there are extra rounds per minute and so much less time per spherical, and thus much less time to go up the steep ramp and push the valve out to full extension.

Elevate is sweet, however normally individuals do not attempt to radically enhance carry on their aftermarket cams due to a couple of issues:

1. Ensure that at this new carry, that there’s nonetheless sufficient clearance between the valve (at full extension) and the cylinder (at prime lifeless heart) to forestall any catastrophic mechanical failure.
2. Improve to lighter valve prepare, with stiffer springs or twin valve springs to have extra management over the valve with this steeper cam profile.
3. It does add energy however it does not shift the facility curve up or down as radically as altering cam period does, and so in most aftermarket purposes we actually need a cam to offer us peak energy at a sure rpm vary and so we care rather more about one of the best period (and a few added carry).

I do know this can be a considerably complicated matter, however I would like to verify we’re talking the identical language earlier than we go into how this pertains to superchargers. Earlier than you resolve which camshaft to make use of (or learn how to modify the timing in your inventory cams) you must take a look at one essential factor:

Your exhaust system and exhaust again stress:

You probably have a inventory log kind exhaust manifold, with a detailed coupled cat, with a twin cat exhaust system, small exhaust tubing, and a few restrictive mufflers in your automobile then it’s doable at peak energy to have as much as 10psi of again stress.

If so, my first advice can be to improve to a excessive move, low stress exhaust system due to the potential energy positive aspects; nevertheless, I do know that a few of our readers have vehicles that they’re organising for his or her mother and father or for twin use the place their accomplice or the legal guidelines of their location …and so forth are actually strict in the case of any added exhaust noise or any aftermarket exhaust. On this case, the place exhaust upgrades will not be an choice, then you will need to choose your camshafts, and tune your cam timing to the place you’ve got ABSOLUTELY the minimal doable quantity of overlap. You probably have important overlap, then the extra you rise above about 4500 rpms the extra your supercharger will endure and the extra energy you’ll waste. If the supercharger is geared to 7psi of increase for instance, then throughout overlap, the cylinder sees 7psi of increase on the consumption aspect, and 10psi of again stress on the exhaust aspect, the web result’s that air will move from the excessive stress zone (the exhaust) to the decrease stress zone (the consumption) and so your cylinder will begin to fill with exhaust gases. Because the rotation continues, the exhaust valve will shut and overlap will finish, and the consumption valve will keep open for the rest of the consumption stroke (for the remainder of the period of your consumption cam), and the remainder of the cylinder will fill with contemporary air.

What occurs right here is that we get a cylinder that stuffed for 30* of overlap with exhaust air, after which stuffed for an additional 210* (of the unique 240* of period for a typical avenue cam) with contemporary air. The result’s a cylinder that’s solely 85% full of contemporary air or an engine that’s actually 15% smaller in displacement! Alternatively, if our supercharger is geared for 18psi for instance, then throughout overlap we may have 18psi on the consumption aspect and our exhaust again stress of 10psi on the exhaust aspect, the web results of this overlap is that our supercharger is successfully solely producing 8psi value of differential stress between the consumption and the cylinder and so we’re solely going to get an influence increase of 8psi throughout overlap. So, throughout these 30* of overlap the supercharger is just successfully producing 8psi of increase, and after that when the exhaust valve closes, the supercharger will be capable of return to working at full increase for the opposite 210*. The web result’s one thing like 16psi of increase so 2psi (or about 12%) of our energy was wasted.

Supercharger tuning by means of cam choice and cam timing

Consumption cam:

Due to the detrimental results of overlap on a supercharger automobile’s efficiency, and particularly within the case of excessive exhaust again stress as is the case with most manufacturing unit supercharged vehicles, we discover that the optimum cam period for the consumption cam is usually 30-40* of period lower than a usually aspirated camshaft for a similar peak energy RPM. The choice to cut back the consumption cam period relatively than break up the period discount between the consumption and exhaust cams, is that the consumption cam will move air underneath pressurized circumstances (because of the addition of the supercharger and the rise in consumption manifold stress) and so at a lowered consumption cam period the engine will nonetheless be capable of get it is full share of consumption air. On the identical time, the excessive rpm effectivity enchancment from the discount of overlap can even increase energy manufacturing with a extra conservative cam. Lastly, if we want to get extra move from the consumption cam, there may be nonetheless the choice of utilizing a better carry camshaft (with a steeper profile because of the decreased period) with supporting valve prepare modifications to verify valve float does not happen at greater rpms.

Consumption cam timing:

The cam timing for the consumption cam would ideally be retarded which might transfer the consumption cam opening occasion farther away from the exhaust valve closing occasion in order to cut back or eradicate overlap, and as a aspect impact the facility stroke period will enhance by retarding the consumption cam which might additionally compensate for the misplaced energy from the period discount.

Exhaust cam:

The exhaust cam period and carry for a supercharged model of the motor must be much like a nitrous camshaft, within the sense that the exhaust cams on nitrous particular builds have:

1- Very wholesome cam period & very wholesome cam carry to permit a severely elevated quantity of exhaust gases to have the ability to effectively exit the motor when the nitrous is activated and the horsepower (and thus the exhaust gasses) have each doubled in amount.

2- As little or no overlap if doable, as any overlap would imply that nitrous can be sprayed from the consumption aspect and out the exhaust, which is wasteful of our restricted provide of nitrous. Equally the extra overlap now we have, the more durable the supercharger should work due to what we defined earlier about both exhaust reversion into the consumption, or the supercharger pressurizing the exhaust.

Exhaust cam timing:

Advancing the exhaust cam each opens and closes the exhaust valves sooner. Opening the exhaust valve sooner barely reduces the facility stroke, however on the identical time it reduces overlap and makes higher use of our supercharger. Usually an a sophisticated exhaust cam mixed with retarded consumption cam will present one of the best outcomes on a supercharged automobile, particularly with a restrictive exhaust.

If we had a excessive move exhaust system put in, then it will not be useful to advance the exhaust cam, a excessive move exaust system that’s optimized for our engine’s energy necessities can clear the combustion chamber of all it is gasses very effectively. Having a excessive period exhaust cam, a low again stress exhaust system and a no overlap what so ever camshaft implies that we’re giving the exhaust fuel loads of time to exit they cylinder, the consumption valve nonetheless hasn’t opened (as a result of the now we have resolve to retard it, or use a conservative cam with much less period) and so the supercharger shouldn’t be pushing any new contemporary air in but, now the cylinder is void and so among the exhaust fuel can revert again into the cylinder, then the exhaust valve will shut, after which the consumption valve will open solely to seek out the cylinder already partially full of exhaust gases.

This is not an issue with a restrictive exhaust as a result of a restrictive exhaust will take a while to clear the cylinder at a decrease velocity, nevertheless with a better move exhaust system we should be cautious to not dial out ALL of the overlap within the cam timing, or to over-cam the exhaust cam (utilizing an excessive amount of period).

So exhaust cam timing will be superior or retarded, relying on the exhaust modifications and the consumption cam choice and thus should be dyno-tuned.

It is vital to notice that with all of those modifications in cam choice , overlap, energy stroke period, and cam timing, that the facility stroke period is effected and whether it is successfully shortened then we could must retune the automobile’s timing advance on the dyno (for elevated advance) to regain losses in period of the facility stroke (once more this towards common pondering of by no means to advance timing on pressured induction vehicles, if now we have a shortened energy stroke, or an software with important overlap then it might be obligatory to take action).

So we see right here that the tip end result right here a lop-sided camshaft with a conservative period, excessive carry cam on the consumption aspect, and a traditional period, excessive carry cam on the exhaust with minimal lobe separation angle and minimal (however not essentially no) overlap.

The exception to the rule:

Typically individuals take a automobile that begins off with a 9000 rpm redline, has an 11.5:1 compression ratio, and a 280* period camshaft, and an aggressive naturally aspirated-esque timing curve and resolve to supercharge it for extra energy. One suck instance is kleemann’s kompressor for the SLK55 AMG (which already makes 400 hp in usually aspirated type from an 11:1 compression ratio motor). In this kind of software, for those who use a extra conservative cam, and dial out all of the overlap, and enhance the facility stroke, together with an already excessive 11:1 compression ratio and a wholesome quantity of increase stress (7psi or above) you’ll find yourself with a motor that produces extraordinarily excessive peak cylinder pressures and people intense pressures and warmth could simply begin off a sequence response of pre-ignition and detonation and you’ll find that regardless of how a lot you retard the timing that the setup will find yourself each powerless and nonetheless not that protected.

On this case, I’d take into account RPM and compression my major energy adder, and my supercharger as my secondary energy adder (that’s until I made a decision to alter that and went forward and lowered the compression ratio of the motor). On this case it’s OK to sacrifice some supercharger excessive rpm effectivity for stopping high-load & low-rpm detonation. Moreover, to beat the overlap inherent in this sort of excessive rpm usually aspirated power-plant it could be very advisable to make use of a centrifugal supercharger that’s able to producing extra increase and move with elevated rpm relatively than a roots kind charger that can simply run out of increase and move capability (CFM) when going through an aggressive camshaft ‘leaking’ increase away.

Right here is a superb instance of how cam tuning can have an effect on supercharged energy:

The automobile is a 1.8 liter Honda motor geared up with:

• Supercharger optimized massive primaries and brief runners Kamakazi header
• A greddy 2.5? SP2 catback exhaust system.
• An LHT ported “S” supercharger inlet tube
• An LHT ported consumption manifold ( Non intercooled)
• A Carbon fibre consumption
• A Jackson racing eaton M62 supercharger geared for 7.5-8 psi.

The black line is the baseline run with all of those modifications earlier than tuning with peak energy coming in at: 223 wheel hp @ 7600 rpms.

The blue line is the facility achieved after a full tine (camshaft timing redone for lowered overlap, ignition timing re-optimized, and air gasoline ratio optimized for peak energy), with peak energy coming in at 248 hp @ 8400 rpms.

You possibly can see on by the dyno outcomes that by decreasing overlap and correctly tuning the automobile the facility peak not solely elevated by 25 horsepower, however extra importantly shifted up by 1000 RPM’s as a consequence of elevated supercharger excessive rpm effectivity from lowered overlap.

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Source by Haitham Al Humsi