Perrin Light Crank Pulley

[Chicane]

I dunno, it'd seem pretty stupid that Subaru engineers would design such an incredible engine without the ability to mate it up to a manual tranny. It's a sporty engine. Obviously they must have thought the SVX was going to be a success, and perhaps use the same engine in another car.

In fact, this is the ONLY car I can think of that has a completley unique engine, excluding exotics and whatnot.

Weird.

- Rob

[jsvxstyle]

Originally posted by Chicane
No offense, but I'm not really believing you here. The H6 is an INCREDIBLE engine, and aside from its leakiness, it's EXTREMELY durable. Mine has a 146k, and it doesn't burn a drop of oil. As with most of ours. I would think if there was a weakness in the internals of the H6 it would show up in a lot of the higher mileage SVXs, but it doesn't.

- Rob

well, you dont have to believe me, but i can say why would i lie about this.
yes you think its an incredible engine, but it has a few weak points. yes your engine has 146k, if let alone on stock eg33, you can get more years to come on the eg33 that 146k, but its putting extra load, cylinder pressure.
eg33 is not and incredible engine nor did subaru design it at there top pay. few step witheld this engine to only be alttile better. its just how you learn what goes wrong when you put it to the test, and inspect how did that treatment you gave it, punished it, and from there you know what has to be done to correct it.
aleast you can agree with me on that chicane

[oab_au]

Originally posted by mbtoloczko
Nothing snide or patronizing, but I do have many counterpoints to your points. :-)

I forgot to mention that the link I posted (http://www.dalemfg.com/dale_026.htm) shows harmonic twisting of a crankshaft for a Covair motor which is a 6 cylinder boxer. This shows that boxer motors, in general, are not immune to harmonic twisting. It also shows that 3rd and 6th order harmonics can be present and important to damp in at least one boxer motor. The plots on that page are very interesting. They show a harmonic at low rpm and at about 4600 rpm. Perhaps its just coincidence, but peak HP in the Covair motor is around 4400 rpm. I would speculate that if the crankshaft were made stiffer so as to have a higher natural torsional frequency, the harmonic peak at 4600 rpm could have been avoided. Maybe SVX crankshafts are stiff enough that their natural frequency is beyond any torsional vibrations that are induced in normal operating rpm ranges? Anyone have the answer? What about the WRX motors? I think there is evidence to suggest that there is a harmonic that can occur within the operating powerband of the motor. As best as I can tell from searching threads at NASIOC, at least a few people have seen odd problems when using a lightweight pulley where the motor begins cutting out at ~6500 rpm (normal cutout begins at 7000 rpm). Cobb Tuning has even stated that they've observed 2.0L motors cutting out at ~6500 rpm, and this was directly attributable to a lightweight pulley. (In response, they are developing a lightweight damped pulley. I don't know if they will be successful in developing a lightweight damped pulley that actually damps the torsional harmonics because the weight may be a neccessary part of the design to effectively damp the harmonics.) If the longer SVX crankshaft has the same basic diameter as the WRX crankshaft, it seems reasonable to expect that there could be a harmonic within the operating powerband of the SVX motor.

I'm not surprised that the aircraft people have not seen a problem as the harmonic vibrations, if present in our motors, occur at specific frequencies, and as long as they don't run their motors at those frequencies for extended periods of time, there would be no problem.

I did all this research on harmonic dampers because I would like to get a lightweight pulley if I could prove to myself that they are safe to use, but all the evidence I've seen tells me that there is a strong chance that harmonics are present. The degree to which the harmonics may be damaging the motor is inclusive though because no one has run a motor long enough. Running a car for 50k miles with a lightweight pulley with no apparent adverse affects is not good enough for me when Subaru motors are capable of lasting more than 200k miles. So, I think I'd rather take the cautious approach and not put one on until someone can prove to me definitively that they allow no damaging harmonics.

That's all I have to say. :-)

Good. post Mychalio, I have already had my say on this before, so I wont go over it again.
The chart shows the harmonics very well. I also checked out the NASIOC site, the reports on the timing disturbance, shows that even the short crank in the 4s will suffer from harmonic distortion, without the damper.

What is happening is the toothed wheel on the nose of the crank, instead of just passing the pickup in one pass, it is actually passing, moving back with the crank wind up and passing again, to producing repetative signals.

This shows the way the crankshaft will resonate without the harmonic damper. If you consider that the SVX crank is 50% longer than the 4s, harmonic distortion will be a real problem, with out the damper.

As I have said before designing anything in an engine is a compromise. Make the crankshaft strong enough so that the fundamental resonance is not in the useful speed range and the motor would be too long and heavy.

The SVX crank is as short as it can be, to keep the overall length short and to minimise the offset in the opposing cylinders so that the secondary out of balance won't be too large. Have a look at the cutaway pix in ARDUBS locker, fully machined, a lovely piece of work, but also very slim on the webs.

To design a crank like this, the designer has to use the damper to to hold the harmonics in check, If not the crank will start to crack at the point that the two waves meet.

Harvey.

[cbx-man]

I've been watching this with interest and looked up this..


http://home.hiwaay.net/~langford/cor...gine_assy.html

This shows the corvair motor only having 4 bearing surfaces as compared to the 7 that the EG33 has. There must be some difference in harmonics because of that. Mostly due to the fact that there is less distance between the bearings for the crank to flex?!?!

[mbtoloczko]

Originally posted by cbx-man
I've been watching this with interest and looked up this..


http://home.hiwaay.net/~langford/cor...gine_assy.html

This shows the corvair motor only having 4 bearing surfaces as compared to the 7 that the EG33 has. There must be some difference in harmonics because of that. Mostly due to the fact that there is less distance between the bearings for the crank to flex?!?!

Sorry, but I don't think more main bearings will reduce the magnitude of the flexing. The flexing we are discussing is twisting of the crank and not bending. These twisting harmonics are quantified in terms of degrees of windup of one end of the crank relative to the other end.

[oab_au]

The crankshaft harmonics that we talk about has nothing to do with the primary or secondary balance of the engine.


The SVX engine has no primary out of balance, each piston and rod is balanced by the opposing piston and rod. There is a secondary out of balance that is generated by the opposing cylinders not being on the same center line, this is so the two big ends can lie side by side on two different crank pins. This secondary out of balance is felt in an opposed twin as a rocking couple, the more cylinders there are, the less the rocking couple is felt. Thus the 6 cylinder is smoother than the 4 cylinder.

The crankshaft harmonics are only related to the twisting of the crankshaft due to its length. The design of the motor has the drive taken off one end, other designs take the drive off the center of the crank to prevent the harmonic distortion.

To try to describe what this distortion is and how it comes about is difficult. If we just consider the crankshaft with no 1 cylinder only.

When the cylinder fires it accelerates the front of the crank, the flywheel and the drive train can not accelerate as quickly due to the inertia, so the shaft winds up till the flywheel accelerates up to speed. By this time the cylinder has stopped pushing and now requires driving by the flywheel, so the crank winds up the other way while the flywheel drives the no 1 cylinder around to the next power stroke.

So we have a wind up as the piston drives the flywheel and an unwind as the flywheel drives the piston. If this unwind arrives back at the piston, in time for the piston to wind it up again.

If we now double the speed of the engine and follow the wave action, the cylinder winds up the crank accelerates the flywheel, the flywheel unwinds the crank to drive the no1 cylinder, But before the unwind wave arrives back at the cylinder, the piston has fired again, to wind up the crank again.

So we have an unwind wave coming from the flywheel and a wind up wave coming from the piston. Where these two waves meet there is maximum rotational displacement of the crank. One side is twisted fully clockwise, the other side is twisted fully anti-clockwise. This is then call a critical resonate frequency. Every time the speed of the motor is doubled or halved, we develop another critical frequency.

So the designers have to ensure that the end design does not have the engine operating for long periods of time at any of these critical frequencies. If it works out that the cruse speed corresponds with a critical, then a harmonic damper is tuned to move the critical at least 10% away from the speed that the engine is to run at.

The damper uses a weighted rim, rubber mounted to the hub. The weight always moves in anti-phase to the harmonic and the rubber damps some of the energy.

As I have said the SVX crank is a great piece of design work but. The harmonic hamper is an integral part of it's design. Replacing
it with an aluminium light weight pulley, is to remove the safe guards that the designers have provided and you must accept the fact, that the crank may break at some future date.

Harvey.

[Trevor]

Harvey your in depth knowledge of the subject is obvious and appreciated but you have inadvertently left out describing an important factor.

Engine designers use the load available in respect of driven accessories as a means of damping torsional vibrations, particularly in the lower frequencies, as is exhibited in many engine designs, even those of vintage character. Electrical machines provide an excellent facility as do rotary pumps and fans. What is more any accessory driven by means of a flexible belt incorporates an additional damping medium.

The pulley in question drives a load and this load applied via the cushion incorporated in the pulley has greater effect than the inertia created by the weight of the pulley. However I agree with you that doing away with the pulley and integral damper on the basis of restricting inertia, in respect of a stock engine, is completely futile. The mass involved is quite insignificant.

The gullible will always present a lucrative market !!!!

Rergards, Trevor.

[oab_au]

Originally posted by Trevor
Harvey your in depth knowledge of the subject is obvious and appreciated but you have inadvertently left out describing an important factor.

Engine designers use the load available in respect of driven accessories as a means of damping torsional vibrations, particularly in the lower frequencies, as is exhibited in many engine designs, even those of vintage character. Electrical machines provide an excellent facility as do rotary pumps and fans. What is more any accessory driven by means of a flexible belt incorporates an additional damping medium.

The pulley in question drives a load and this load applied via the cushion incorporated in the pulley has greater effect than the inertia created by the weight of the pulley. However I agree with you that doing away with the pulley and integral damper on the basis of restricting inertia, in respect of a stock engine, is completely futile. The mass involved is quite insignificant.

The gullible will always present a lucrative market !!!!

Rergards, Trevor.

Yes Trev, that is a point. Most used to have the damper weight separate to the accessory pulley. Subaru has it as the driving pulley also, so these must be considered as part of the damper mass.

I agree with it being a pointless mod, when you consider the inertia removed, is very small when you add the flywheel, transmission, drive shafts, differentials, half shafts hubs, disks, wheels and tyres. Then there is the 3500 car mass that has to be accelerated. A few pounds on a 5 " diameter is about 2 tenths of " Sweet Fxxx All"

Harvey.

[Trevor]

Hi Harvey,

I think we had BOTH best stay out of MOD Mania. By expressing fact we may wind up in very hot water !!!

If the need arises let us stick together in the ANZAC spirit and then we can NEVER be got at. Dare I say it but I will, " some of the stuff posted here is bloody stupid. " I may now need your back up and covering fire !!! Take aim with your pistol. ( another thing we should OT on ).

Trevor,

P.S. I wonder if anyone has tried removing their wheel nuts. ( I think I should say lug nuts as they still must have split rims and not wheels up top ! ) Lots of mass there for sure. Why not remove the rims and run on the spokes for a truly invigerating ride !!

[elninoalex]

<<<However I agree with you that doing away with the pulley and integral damper on the basis of restricting inertia, in respect of a stock engine, is completely futile. The mass involved is quite insignificant.

The gullible will always present a lucrative market !!!!

Rergards, Trevor>>>


Yes, but with a 5 spd and a light flywheel, this made a noticeable difference on my car. This is not an opinion or theory, this is spoken from experience. The notion that I may have compromised the longevity of my motor by adding this pulley is valid. But very few go fast goodies don't carry that baggage. Has anyone lost a motor by putting one on? I don't believe the hype about anything. I want to see for myself. That's why I have tried seven different custom exhaust systems. I have built my own cold air intake, as many have. I run a very aggressive shot of dry nitrous, even though everyone said the injectors couldn't hack it. My reward is that I can go faster than pretty much any other SVX. I am originally from DC so I learned at an early age not to believe everything I hear. So excuse me if I don't consider myself gullible.

[Trevor]

Please advise how you confirmed and measured " the noticeable difference ".
Scientific proof is required not advice as to what you perceive as has occured after becoming happy as a result adding a talking piece. No personal offence is in any way intended here.

You have been able to address me in person. I would like you to afford me the same courtesy.

Trevor

[elninoalex]

The noticeable difference is real. I did not measure a before and after with just that mod. I lumped it together with the intake, exhaust and 5 spd mods(w/G-tech pro). For that, I apologize. I just don't have enough time to do everything I would like to. The total difference came out to be a second and a quarter quicker to 60 mph. To be honest, I didn't expect to feel much of anything when I put it on. But I was nicely surprised. It just revs more freely now. Otherwise it would be for sale somewhere. I have tried a couple of things that I had high hopes for that I didn't like. The true dual exhaust for example. After two weeks of designing, fitting and welding, that lasted one day on my car. Fortunately I was able to rework it into something I like. But anyway, I could put the stock pulley back on and compare the times. But the times aren't nearly as consistent as with the AT due to the launch factor and we are probably only talking about .2 seconds at the most. Maybe if I did like five of each, it might play out. I haven't even done five hard launches yet with the 5 spd. Nor have I filled the tank yet. No $$$ right now. Do you think that might be 'scientific' enough? That's about the best I can do.

Stephen
PS. I have a tremendous amount of respect for you and Harvey and read all your posts like a student in class.

[Trevor]

Stephen thank you very much for your excellent reply,

I think you have disclosed the problem so often present in these issues. You did not test each modification you have made individually. You can not be sure which contributed and which did not. One in fact may have proved detrimental. I do not think we should expand on the issue.

It is a basic rule that when tuning or making any alteration in an effort to improve something two or more operations should not be done at once prior to testing. The same criteria stands good in respect of fault finding.

Special regards, Trevor. *<)

[elninoalex]

For clarification, I did each mod separately and gave it the 'seat of the pants' testing individually of the other mods. Although I didn't run the times separately. I actually don't like pushing the car too much. But I have modded enough cars to get a feel for the before and after difference. And this one was more than I expected. It had about the same effect as putting a light flywheel on my RX-7. Probably wouldn't make as much of a difference on the AT though.

Stephen

For the record:
intake mod- no discernable difference
exhaust mods- noticeable difference
light crank pulley- noticeable difference
5 spd- KICKS ASS!
Nitrous- HAHAHAHAHA!

[Trevor]

Accepting that argument is futile, all I will say is that you have illustrated quite remarkable powers of perception. As long as you are happy stay with it.