Valve spring pressure and boost
Valve spring pressure and boost
(OP)
Many highly respected engine builder/tuners will tell you that you need to increase spring pressure for high boost. There are even reports of fixing floating valves related to boost (However they determined that IDK) or performance issues by going to a stronger valve spring.
Now I don't believe this theory for one second. If the pressure differential is that great between the cylinder and the plenum then you are seriously liimiting the amount of air going into your engine to a point that I would find hard to believe. I mean if you had a 20 PSI pressure differential between the runner and the cylinder I would still expect a valve to close just fine unless the spring was already so precariously sized for the cam. On the other hand if you had a 20 PSI pressure differential between the two the amount of power that you are leaving on the table would be insane.
I'm confident enough in this that I'm not really even looking for confirmation although if I am missing something huge please tell me.
I am more here to talk about the stories of stiffer valve springs actually curing these issues allegedly related to the boost pushing the valve open.
What else could change with a stiffer spring? What would a logical explanation be that valve springs would actually fix the problem?
Or is it possible that they are running such an improper intake cam that they are actually preventing a massive amount of air to fill the cylinder?
In which case a properly sized cam would be the solution whereas stiffer springs are just going to help hide the problem.
Thoughts?
Now I don't believe this theory for one second. If the pressure differential is that great between the cylinder and the plenum then you are seriously liimiting the amount of air going into your engine to a point that I would find hard to believe. I mean if you had a 20 PSI pressure differential between the runner and the cylinder I would still expect a valve to close just fine unless the spring was already so precariously sized for the cam. On the other hand if you had a 20 PSI pressure differential between the two the amount of power that you are leaving on the table would be insane.
I'm confident enough in this that I'm not really even looking for confirmation although if I am missing something huge please tell me.
I am more here to talk about the stories of stiffer valve springs actually curing these issues allegedly related to the boost pushing the valve open.
What else could change with a stiffer spring? What would a logical explanation be that valve springs would actually fix the problem?
Or is it possible that they are running such an improper intake cam that they are actually preventing a massive amount of air to fill the cylinder?
In which case a properly sized cam would be the solution whereas stiffer springs are just going to help hide the problem.
Thoughts?





RE: Valve spring pressure and boost
With early Miller intake valve timing, the cylinder pressure will indeed drop below the intake manifold pressure by several psi, depending on the severity of the Miller timing. Of course, with OEM engines engineered for early Miller timing, it can be taken for granted that the valvetrain has been validated to behave itself under all foreseen conditions. Also, obviously, this delta P across the intake valve will occur regardless of the intake manifold pressure, so in this case it doesn't matter if engine is boosted or not.
On the other hand, a mechanically supercharged engine, assuming its exhaust system is worth a damn, will see significant delta P across the intake valve toward the end of the exhaust event. However, this is about the time that the intake valve should be opening anyway, so if it should happen to "blow" open, who would notice? At any rate, I have difficulty envisaging a delta P large enough to overcome the spring force.
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Valve spring pressure and boost
On intake valve closing one would hope that the pressure in the cylinder was very close to the pressure in the runner.
So the question remains though is there any possible truth to this myth and any way that stiffer valve springs could have any way of improving performance related to how much boost you are running?
People have reported the stiffer springs fixing whatever problem they were having.
Some of my theories.
Placebo effect. It has been pretty much proven that if you throw time and money at a car you will see, feel or find an improvement.
Something blamed on boost but maybe actually another issue. Maybe they raised their redline at the same time as boost and started floating valves which stiffer springs then fixed?
Any other possibilities?
RE: Valve spring pressure and boost
Dynamic lift closer to kinematic lift? Not sure why that's more important for a boosted engine though. Just one more thing, possibly, if you're already in the eeking out more power mode.
- Steve
RE: Valve spring pressure and boost
I have briefly thought about this before but never gave it a ton of my time but one of my customers goes to a technical institute and brought this up to me. His teachers are teaching that boost will cause valve float and that heavier springs are needed for more boost.
This bothered me because it means that either my theory is completely wrong or they are teaching bad theory.
So what are peoples thoughts on this being taught in a technical school?
Is this an old wives tale that rather educated engine builders can believe even though it can't be true?
Or am I still missing a very big piece that could make it bear truth?
My thought is that if it's possible for intake pressure to hold the valve open then the problem that really needs to be addressed is cams or cam timing to reduce or eliminate the delta P. Stiffer valve springs is not addressing the problem but just covering it up.
RE: Valve spring pressure and boost
I just spent a while searching and most only include the combustion cycle. Others that include 720 deg of rotation don't have enough resolution to really see what kind of pressures you would expect during the exhaust stroke.
RE: Valve spring pressure and boost
Measure the diameter where the valve is seated, where it actually contacts the valve seat.
Calculate the area of that circle.
Calculate the pressure difference that would be required to open that valve.
Ask yourself if that is a plausible situation and whether there is any foreseeable condition inside the engine which could cause that.
Supercharging (not turbocharging) trying to open the intake valve late in the exhaust stroke, just before the valve starts opening anyhow, is one foreseeable situation.
On a turbo engine, excessive exhaust manifold pressure during the intake stroke is another one.
RE: Valve spring pressure and boost
I did just remember that I have a copy of Scientific Design of Exhaust and Intake systems and remembered that a good chunk of the book does focus on this very subject.
I snapped a few pictures of some of the graphs and thought I'd post them up here.
[img https://fbcdn-sphotos-b-a.akamaihd.net/hphotos-ak-...]
[img https://fbcdn-sphotos-d-a.akamaihd.net/hphotos-ak-...]
If we were to imagine a worst case scenario which would be a supercharged motor with an optimized exhaust we could guess that the intake and exhaust strokes would be similar to what they are here.
On a turbo the low pressure would be much closer to the pre turbine backpressure which is almost always higher than the boost pressure.
With a supercharger running extremely high boost on a motor with big valves and low seat pressure it does seem plausible that the valve could be pushed open by the boost pressure.
The 4AGE that I am used to dealing with has a 30.5mm intake valve or 1.2". Stock valve springs are about 35lb seat pressure so for boost to unseat the static valve it would require a delta of 30.9 PSI.
Granted these graphs are different motors and at much lower RPM than the 4AGE operates but all of those graphs show positive gauge pressure at the point the valve would be opening meaning your boost gauge pressure would need to be well over that 30.9 PSI to overcome the spring.
On the other hand if you had a big two valve V8 with a 2" valve and 35 lb seat pressure it would only take about 11 PSI delta to open the valve so in a supercharged motor with a high enough surface area to spring pressure ratio I can see this being plausible.
The same goes for the valve closing event. The stock 4AGE IVC is 44 deg ABDC.
The last graph shows the expected behavior of the pressure taking longer (IN reference to crank rotation) to hit atmospheric pressure. If the cam is sized anywhere close to proper the valve should be closing as the pressure in the plenum and pressure in the cylinder are the same. Unfortunately I believe these graphs are in reference to atmospheric pressure instead of port pressure but it starts to give us an idea.
Since these graphs are relative to gauge pressure I think it wold be pretty safe to say that cylinder pressure would never get lower than about 6 PSI below pre turbine backpressure.
If you have the perfect turbo with a 1:1 boost to PTBP ratio and are running 40 PSIG boost this means that cylinder pressure shouldn't go much below 34 PSIG leaving a 6 PSI delta between the port and the combustion chamber. This is at the point where the valve should be wide open. The delta would be much less at any other point.
RE: Valve spring pressure and boost
je suis charlie
RE: Valve spring pressure and boost
I was in the middle of typing the above doing just that when you replied.
On a turbo motor I supposed I could see the same issue on a motor with large valves and very light seat pressure.
I am less familiar with two valve motors but in a quick search I see seat pressure numbers over 100 lbs.
If you had a 35 lb spring on a 2" valve it would be quite possible for a small turbo to push an exhaust valve open.
Going back to the 4AGE that I know with a 25.5mm std valve and 35 lbs seat pressure you would need a 45 PSI delta to crack open the static valve or even stand a chance of stopping a closing valve.
The thing is that with a turbo motor the pressure in the chamber is going to be somewhere between intake pressure and pre turbine back pressure. It seems unlikely to me that you could ever achieve anything close to that 45 PSI delta even in the highest of boost applications.
RE: Valve spring pressure and boost
While this is true it is going to depend greatly on the pressure curve in relation to the valve travel.
It seems like we have narrowed down the likely points of float to be on the intake valve with supercharged motors and exhaust valve with turbo motors.
I am a little weak on fluid dynamics so my first question is whether the force being applied to the valve is directly proportional to the delta P when the valve is open and air is flowing past it.
As the air accelerates past the valve would it not create a low pressure zone around it?
On a supercharged motor if there is a 30 PSI delta between the port and the cyl as the valve is coming to a stop and then returning back downward while the valve is open and air is flowing past it is there 30 lbs of additional force being applied to the valve spring?
On a turbocharged motor on the exhaust valve there is the pressure wave drawing the exhaust pulse out and the intake pulse in. If your cam is timed ideally the exhaust valve will close as that pulse is moving toward the turbo or at least before it has started to move backward.
If that pressure wave has enough time to come to a stop and revert and start applying any significant pressure on the exhaust valve filling the cylinder with exhaust wouldn't it be safe to say that the problem that needs to be addressed is cam timing and not valve spring pressure? This should be long after the valve has hit max velocity meaning that even when the RPM is slightly off and a small degree of reversion hits the valve at the end of it's closing cycle it would not only be facing the spring pressure but the valve inertia.
This would take us back to my original idea that on a turbocharged engine valve float would be a symptom of improper valve timing and not insufficient spring pressure right?
RE: Valve spring pressure and boost
je suis charlie
RE: Valve spring pressure and boost
As the motor spins faster it will have less time for a reversion pulse.
At low RPM there will be more time and it will be more likely for the pressure wave to leave the exhaust and for a returning pressure wave to have time to bounce back in through the open valve. As revs get higher it will be more likely that the gasses will still be flowing out the exhaust valve as it closes. Therefore the higher the RPM the less force holding the valve open. Or if the gasses are still flowing out then it would help force the valve closed.
With supercharging and on the intake valve it would take longer in terms of crank rotation to fill the cylinders so it would make sense that the intake valve would start closing with lower pressure in the cylinder creating a larger delta P. The question is how much? It seems like if you are maintaining a reasonable VE that there should still be a pretty decent amount of pressure in the cylinder.
I wish I could find some better cyl pressure graphs for a motor and RPM more similar to the motors I am used to dealing with.
Does anyone have any further thought on how the pressure would behave with air flowing past an open valve. Like I said I'm not great with fluid dynamics but it seems to me that when the valve is open and when the air is accelerating past the valve that the pressure being applied to the valve would be less than the pressure in the port. Is there any truth to this?
I think it's pretty safe to say that specifically in regards to a turbo motor it is extremely unlikely that pressures will have any significant effect on forces applied to the valvetrain. Does anyone disagree with this?
RE: Valve spring pressure and boost
RE: Valve spring pressure and boost
1. Valve float does not occur near the end of the valve-closing event. During this phase, the valve is approaching the camshaft and decelerating i.e. the valve is accelerating away from the camshaft - no spring force is required at all. Valve float occurs when the valve is accelerating towards the camshaft which occurs during most of the "middle" phase of the valve cycle. The cam profile is designed to take advantage of the available spring force as the spring length changes thus the peak acceleration towards the cam occurs at peak valve lift. (One advantage of pneumatic valve springs is the average acceleration can be much closer to the peak) So valve float is equally likely at any point where the acceleration (blue) curve is negative. 20 lbs of extra (gas pressure) force acting on the valve means 20 lbs extra spring force required to avoid valve float.
[img
2. Valve float occurs near the rpm limit (usually beyond) not the point of maximum VE where the camshaft is optimised. At the rpm limit it is very unlikely the valve has remained open long enough for pressures to equalise.
je suis charlie
RE: Valve spring pressure and boost
Then as BrianPetersen said and as I believe, the localized differential between either side of the valve face would be much lower and the overall forces acting on the valve faces should be lower than the differential as measured just a cm away.
RE: Valve spring pressure and boost
As an example a small block Chev intake valve is approximately 3 sq in area, so 1.7 psi differential gives 5 lb force. Relevant differential would be the delta of total (stagnation) pressures measured either side of the valve.
je suis charlie
RE: Valve spring pressure and boost
RE: Valve spring pressure and boost
It is also obvious that a marginal system might be "pushed over the edge", either by excessive rpm, or excessive delta P, or both in some combination. Based on the above discussion in this thread, a mechanically supercharged engine might experience a significant delta P on the intake valve at IVC, and thus be vulnerable to this failure mode. By the same token, the exhaust valve of a turbocharged engine with an adverse exhaust to intake delta P would also be vulnerable to this failure mode. Interestingly, the adverse intake to exhaust delta P is (generally) a positive function of rpm (at least as redline is approached).
From a symptomatic point of view, I doubt if you could tell the difference between intake and exhaust hydraulic adjuster pump-up.
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Valve spring pressure and boost
On the same engine with and without boost, there is essentially no difference in pressure drops throughout the system. This is because volumetric flow through the system is unchanged. Mass flow increases with boost but this is due to density increase. The same applies to throttling where VE and volumetric flow rate is constant at any given rpm - what changes is density.
je suis charlie
RE: Valve spring pressure and boost
1- Supercharger of some kind is bolted to an engine, perhaps one that already has marginal spring pressure for the conditions seen at redline
2- Engine pulls harder, as it is supposed to do, especially near redline.
3- Driver repeatedly zings it past redline and into valve float due to engine's greater power. Before the days of rev limiters, this was not difficult to do.
4- Analysis ensues. "Ever since we put that blower on, the valves float. We need stiffer valve springs on a blown engine."
I could see this happening in the heydey of, for example, privateer NHRA competition, when most guys were learning the hard way.
RE: Valve spring pressure and boost
I think that was Hugh Macinnes' suggestion in his book "Turbochargers".
RE: Valve spring pressure and boost
This is exactly why I come to engtips to discuss theories like this and not boards like SpeedTalk.
There are a lot of very smart and extremely capable tuners and builders on boards like that but there is also a lot of bad science and old wives tales that exist because the answer may have solved a problem and so therefore must be correct.
I definitely suspect that may be the case here.
I also believe it would be much more likely in something like a supercharged dragster with 30 to 60 PSI boost pressure on the intake and atmospheric pressure on the exhaust.
This extreme scenario trickles down to a generalized understanding that any boosted motor needs more spring pressure.
RE: Valve spring pressure and boost
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Valve spring pressure and boost
Some of the heavier valve springs I sell are around 60 seat. 100 seems like a lot in the world I am familiar with.
RE: Valve spring pressure and boost
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Valve spring pressure and boost
I'll bet the mass on those valves is also quite a bit more than the four and five valve heads I am used to playing with.
RE: Valve spring pressure and boost
Recently, Katech did laser valve bounce measurements on various combinations of valves and springs of the LS7. While this was for a normally aspirated engine, I am sure that all aftermarket turbo valve train components and their permutations are also rigorously tested in this way so as to remove the possible experimental confound of valve bounce versus valve float due to pressure deltas.
http://www.superchevy.com/how-to/1406-how-to-maint...
RE: Valve spring pressure and boost
I think its a question of whether or not cylinder fill correlates 100% with the boost level in the plenum or charge pipe on the other side of the intake valve, port, and runner. Also, is the exhaust port and pipe evacuating it as well as it would N/A? How is flow friction in the ports being changed? How much more momentum and mass does the intake air have before it hits the (closing) intake valve?
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
RE: Valve spring pressure and boost
I did read somewhere that reducing backpressure can reduce valve spring float. So my question is, will adding a bigger downpipe with high flow cat or no cat at all help?
Also this generally happens only in 1st gear, it loses traction so fast the revs hit redline and thats when misfire happens. Would more traction also help? Changing springs is out of the question because its ridiculously expensive. Thanks guys
RE: Valve spring pressure and boost
What's the issue?
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Valve spring pressure and boost
During certain portions of the valve lift curve the valve open area enjoys sonic flow, implying a rather large pressure differential across the valve at that particular portion of the lift curve. Sonic flow is more prevalent closer to redline, after peak torque and peak power. *Any* pressure differential across either the intake or exhaust valve will add to (or subtract from) existing forces on the valve. Operating the engine in a 2 atmosphere environment (i.e. boosted), compared with operating the engine at 1 atmosphere, will result in approximately (for the sake of this thought experiment) twice the pressure differential across the valve at any point in the lift curve.
Opening the exhaust valve when there is more stuff in the cylinder due to boosting is obviously more difficult compared to NA and flexes everything not made from unobtainium which, if it doesn't break, 'unflexes' when the exhaust valve does eventually open and the pressure differential across the exhaust valve falls to controllable levels. This 'unflexing' brings us to valve train dynamics 101 and all sorts of instabilities. If you have pushrods think pole vault.
At the exhaust valve closing event the pressure in the exhaust port can be very high, particularly at RPM's higher than any exhaust header tuning range. If the exhaust valve cannot close as the cam closing ramp dictates due to the high exhaust port pressure and decreasing cylinder pressure due to the descending piston on the intake stroke (or re-opens simply due to the high exhaust port pressure) it will then crash into the valve seat and the exhaust valve will bounce off it's seat and probably seriously dilute the new cylinder charge with hot exhaust gas.
Earlier than designed intake opening due to boost is probably very positive on engine output as a valve timing event, however if the early opening results in a valve lift greater than the gentle opening ramp describes and the lifter/cam follower slams into the cam profile then please refer to valve train dynamics 101.
Intake valve closing may be the most important valve event. Any intake runner tuning is magnified by boost, i.e. any pressure wave in a 2 bar system will be twice that of a 1 bar NA system. The spring seat pressure is required to stabilise the valve on the seat, at higher than optimum RPM, cylinder pressure will be lower than port pressure at inlet valve closing. If the spring seat pressure subtract the cylinder port pressure differential is not enough to stabilise the valve on the seat then by definition the valve will lift off the seat as the piston continues to rise (possibly a couple of times, eventually pushing charge back up the inlet port).
The highest dynamic pressure differential across the valve needs to be added to all other valve spring pressure requirements.
RE: Valve spring pressure and boost
je suis charlie
RE: Valve spring pressure and boost
RE: Valve spring pressure and boost
RE: Valve spring pressure and boost
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Valve spring pressure and boost
RE: Valve spring pressure and boost
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Valve spring pressure and boost
RE: Valve spring pressure and boost
RE: Valve spring pressure and boost
What is the point of opening the supercharger bypass? Airflow through the bypass will be away from the engine - recirculating through the blower and adding heat. In addition, the turbo compressor has to run at a higher PR and exhaust BP will increase as a result. Reduction in beneficial scavenge follows.
Even if you don't agree, do yourself a favour and be prepared to compare operation on the dyno with and without bypass open.
Lots of info on this forum in the "twincharging" threads.
je suis charlie
RE: Valve spring pressure and boost
As far as my setup goes and the logic on that, please correct me where I'm wrong because I am here to learn but here is my line of thinking/how I understand it. The purpose of opening the bypass is to reduce or eliminate the pressure differential across the supercharger, and therefore the work it has to perform and the associated drive losses. It would easily take over 100hp to spin that thing up top...not only can the 8-rib belt I currently have not handle that without slip even if I wanted to run full compound, but my supercharger causes more intake charge heating than the turbocharger does...especially at higher pressure ratios, and frankly, I don't need the extra boost up top anyway so why would I depend on my less efficient power adder there? My turbo will push 55psi if I want it to and my engine should only need around 35psi up top to max out the turbo as well as my fuel system. The recirculated air from the supercharger is not heated other than through contact with the warm supercharger rotors because it has not been pressurized by the supercharger, so bypassing it should not be an issue.
I do have refrigerated air/water intercooling after both the turbo and supercharger as well as direct port water/methanol injection so even if there is some heating during the bypass operation I can handle it, and I would certainly think it would be substantially less heating than taking that already compressed turbo air and compressing it again by a 2.4 pressure ratio with the supercharger. As far as scavenging goes, I have log manifolds going into a turbo and as stated before am nowhere near having any valve overlap...so I'm at a loss as to what kind of scavenging could I possibly hope to achieve anyway? Certainly none from having a higher intake pressure vs exhaust pressure since I am 44.5 degrees from having any valve overlap...and as far as exhaust scavenging goes, I just don't see that happening or having a significant effect either way with logs and a turbo, particularly with such relatively short valve duration.
As far as why I went twincharged and do use it down low in full compound is that it makes the car significantly more predictable and driveable. In turbo only mode it takes a lot higher throttle position to get the car accelerating at a decent rate and when the thing starts to spool it comes on so hard and fast that accidental wheelspin is inevitable. In twincharged mode I can accelerate at a much lower throttle position with a more linear and predictable power delivery...and if I want to go fast, the response is instant and satisfying. The transition when the bypass opens is actually fairly seamless, you can hear the tone of the engine change but that's about it. The loss in boost is mostly made up for by the corresponding loss of the cost of driving the supercharger and the turbo is spooling hard and replaces the lost boost before it's missed.
Every dyno I have seen from twincharged cars it seems they have done the comparison turbo only, supercharger only, and full compound and from what I have seen turbo only always makes the most peak power. I assume this is mostly due to the inherent problems with trying to drive a supercharger on a street car with that kind of power requirement. Now that may change if you needed the extra boost pressure to get enough flow through your engine (say you had a really small displacement relative to your power goals), but trying to get 1000hp out of 3.8L isn't exactly the stuff of legend. That's not to say I don't intend to find out for myself and what works on my setup, but my opinion is that if your most efficient power adder can make the goal power on its own then that's the one you should use. Can I make more peak power with both in full compound? Provided that I keep the charge cool and keep the belt on the supercharger and don't demolish any engine parts then I would say the answer is obvious, yes I will make more power with more pressure available at the intake valves. But frankly, if I wanted more peak power I would run a bigger turbo...
The purpose of the supercharger for me is simply to provide me with an instantaneous 2.4 PR of boost to enable me to spool a very large turbo very quickly, as well as having a driveable powerband when I am below the boost threshold of that turbo...and it does both of those things extremely well. The purpose of my question in this thread was really that I am intending to ramp up the duration and pressure of the compound boost portion of my car and I was curious how that might affect my valve spring requirements.
RE: Valve spring pressure and boost
I would agree with gruntguru that valvetrain inertias are the primary consideration. So if your existing valve spring setup is performing OK, leave it alone. A failed valve spring can result in a very expensive repair bill.
RE: Valve spring pressure and boost
RE: Valve spring pressure and boost
Drive torque is mostly a function of delta P (supercharger) so shouldn't increse much further as rpm increases. Of course belt slip is also a function of speed (centrifugal tension unloading the pulley-wrap area) but this is less pronounced on multi-rib vee belts. Your drive must be pretty marginal at low revs if it slips at higher revs.
If your bypass reduces supercharger drive power by say 100 hp, the increased exhaust back pressure will cost some power in pumping losses alone. The big loss however, is combustion quality due to reduced scavenge (or increased passive EGR).
A positive delta P (engine) is highly beneficial (especially in boosted engines). "Scavenge" should be considered as a variable that exists on all engines and ranges from negative values (passive EGR) through to positive. Any change in delta P will change the "scavenge" value.
Note: Not advocating increased boost here - all the above assume same boost - with and without bypass.
je suis charlie
RE: Valve spring pressure and boost
I am not sure I quite agree with your drive torque, the equation I have seen is (.00467hp * cfm airflow * psi boost)/compressor efficiency %. That makes airflow through the supercharger and pressure ratio equal influences on the drive requirements, and since for all practical purposes at a given boost compressor flow on a roots supercharger is linear with RPM, the increase in drive requirement is also very linear with RPM. To answer your question, yes my setup is pretty marginal since the supercharger I am using has a 10-rib drive from the factory and I am making due on an 8-rib as well as significantly higher pressure across it (smaller displacement engine). I have been strongly considering adding auxiliary iders or tensioners near the snout to improve belt wrap.
With that said, I was also planning on setting up a more progressive means to control the crossover from supercharger to turbo, so if I can come up with a valve that has a much more variable lift to recirculate the supercharger boost I could possibly experiment with different combinations of supercharger and turbo boost up top to see what has the best results. I would like to do this with a large external wastegate, but am having trouble finding one that can be configured to operate on direct pressure inputs that high (they all seem to require boost controllers above about 25psi).
Part of my difficulty with this build is that I want the car to remain a daily driver, as well as continue to be as inconspicuous as possible. Suffice it to say, it's a sleeper, so that's been my big hesitation to get a cam, or do any number of other mods that would make life easier but give away the car's secrets. I love the fact I can start the car up on a freezing morning and it sounds and idles 100% stock smooth.
RE: Valve spring pressure and boost
Looks more like a formula for power than torque.
je suis charlie
RE: Valve spring pressure and boost
Or am I mistaken and is it simply the added inertial loads from accelerating the supercharger that is causing the slip at higher rpms, not necessarily the higher HP draw? If that were the case it may not be present at a fixed load even at the higher RPM? I'm not trying to be argumentative, I am just trying to understand.
RE: Valve spring pressure and boost
je suis charlie
RE: Valve spring pressure and boost
RE: Valve spring pressure and boost
RE: Valve spring pressure and boost
If boost is proportional to blower torque (true if efficiency is constant), blower torque will remain constant as speed increases. Slippage is a function of torque (not power) so the tendency to slip will remain constant (neglecting centrifugal tension loss).
je suis charlie
RE: Valve spring pressure and boost
RE: Valve spring pressure and boost
RE: Valve spring pressure and boost
RE: Valve spring pressure and boost
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Valve spring pressure and boost
RE: Valve spring pressure and boost
RE: Valve spring pressure and boost