POLL: Alternate Crankshaft Pulley???
- Thread starter Banzai240
- Start date
Yes, but it's not as significant as George believes...
George, let's put this into a real-world perspective. While you now concur that there's no horsepower to be gained with a lighter crankshaft pulley, I think you're concerned with the ability of the engine to accelerate. Fine, that's a reaosnable argument. However, it's not as significant as might suspect, for a couple of reasons:
1. An engine under the load of an accelerating vehicle is not accelerating nearly as fast as you think, and
2. The mass moment of inertia of a large crank pulley is not as large as you might think.
Let's hit the first point: how fast is an engine accelerating under load? I'm not going to try any calculations here, but just close your eyes and imagine how fast your tach moves when you're in third gear at 60 miles per hour. It's not very fast. When considering how much a lightened crank pulley will affect that, just think about how fast the engine is accelerating; the faster your engine accelerated under load, the more lightened components will help you.
2. Mass moment of inertia. The mass moment of inertia is a measure of the distribution of the mass of an object relative to a given axis. It is calculated as the units of mass times the distance squared (Io=MxR^2)
In the case of a crankshaft pulley, that radius is relatively small. Pick any car with a large harmonic damper crankshaft pulley; what's the radius? Let's take a guess and say that most of them are around 4 inches in diameter. Radius equals 2 inches, r^2 equals 4. Multiply that times the mass and you get the value. For argument's sake, let's say it's 8 pounds; Io = 32 (and that assumes the mass is all concentrated at the outer edge of the pulley, which is innacurate).
So now, let's make the pulley lighter and larger. We'll knock off 5 pounds off the outside edge of the pulley and make it 4.5 inches in diameter. Resulting Io=15, a difference of 17.
Compare that to removing the same 5 pounds from the outside edge of a 10 inch, 25 pound flywheel: old Io= 625, new Io= 500, a difference of 125!!
So, my point is, "It's all about the distance, silly." Yes, it makes a difference, but not as much as you think it does (and not nearly as much as those chassis/tire dynos indicate.)
But let's start chatting about reality: how many cars still use these large harmonic balancers; and for those that do is it all about NVH or is it required for engine health? If it's just for NVH, racers will remove it in a heartbeat; if it's needed to keep the engine together then racers will leave them on.
"But Greg," you'll say, "isn't this unfair to the guys that can't remove them for fear of breaking the engine? Wouldn't that benefit a narrow subset of the community?" Sure, I'd say, but no more unfair or less beneficial to those that cannot change their accessory pulleys due to constrained space or lack of aftermarket support. It will always be the case where a mod will benefit one model or another, just as it will be unfair to one model or another when you don't allow one mod or another. Unless you're interested in a spec, single-marque class there will always be inequities; nothing you can do about it.
That's the technical basis for the change; you'll need to resolve your personal reasons for wanting or not wanting the change.
Greg
Uh, yes it is.
I have always concured with that point Greg. Visit my first post on the matter. What I got caught up in is wording. An inertial dyno will show a hp gain that in reality doesn't exist. It does so because it rotates the drum quicker.
Rather than play "let's pretend," let's use real world results, shall we? Low mass underdrive pulleys show a hp gain on an inertial dyno. No, this is not a hp gain. What it does show is the car will accelerate as if it gained hp. In the case of the SR20DE, it accelerates as if you added 7 hp to the engine. Not real hp, but faster acceleration.
We can dance around this issue all you like, but on an inertial dyno the gain is measureable and repeatable. The hp is not real, but the acceleration is. And again, it tells us the car will accelerate as if it has additional hp.
I'll place my bets on real instrumented testing rather than conjecture.
Yours for one Greg. The SR20DE uses an integral harmonic balancer. So, if the rule is made such that you must retain the harmonic balancer, the SR20DE will still have to retain the stock pulley.
Is this outrageous? Depends upon your point of view. It's certainly something that has been discussed. And if we let you change your main pulley (with integral harmonic balancer) they everyone sould be able to eliminate the harmonic balancer.
But, let's step back for a second.
Why do we even need to do this? I understand what it is supposed to accomplish, but I don't see a compelling need to allow this in IT. Again, how many people are blowing up engines because they cannot run an undersize main pulley?
I understand the technical points here. Probably better than most considering the arguments being made. Most are made from a purely personal point of view based upon their perceived impact on their car or some they are familiar with. You, in fact, assume that you will be able to run a underdrive pulley on your SR20DE, but that's not in fact the case if stock harmonic balancers are required to be retained.
If we do not look at this issue from all sides very carefully, there will be unintended consequenses and people will be bitching later. Then again, there will probably be bitching later anyway.
------------------
George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com
PS: BTW, an underdrive main pulley is smaller diameter, not larger.
[This message has been edited by Geo (edited May 12, 2004).]
lateapex911
Super Moderator
I'd like to add just one more thing, regarding unintended consequences.
When a car is classed, it is done in such a way as to take into account the perfomance gains expected utilizing the rules set in place at that point in time.
The competitor is expected to do due diligence when deciding to race a certain car, and take into account the advantages and disadvantages the rule set presents him and his particular car.
In other words, tough luck if you need something the rules don't allow after you make your decision.
We get into trouble when we change the rules post classification, and some cars benefit more than others. The ECU rule is a most henious and classic example.
------------------
Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]
When a car is classed, it is done in such a way as to take into account the perfomance gains expected utilizing the rules set in place at that point in time.
The competitor is expected to do due diligence when deciding to race a certain car, and take into account the advantages and disadvantages the rule set presents him and his particular car.
In other words, tough luck if you need something the rules don't allow after you make your decision.
We get into trouble when we change the rules post classification, and some cars benefit more than others. The ECU rule is a most henious and classic example.
------------------
Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]
I agree completely Jake. The ECU rule is the first thing that comes to my mind as I ponder this issue. I see little upside for the category and lots of downside.
------------------
George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com
fiat124girl
New member
Dave Ebersole
New member
No.
Dave Ebersole
O=00=O
Dave Ebersole
O=00=O
"No!"
Wait, If I get the Honda classed and it would benefit me "YES", if it doesn't benefit me, then "NO"
Almost everyone is in agreement that it would benefit some cars and not others, right? Why would we want more rules that would benefit one model and not another when we know that going in ?
[This message has been edited by Quickshoe (edited May 13, 2004).]
Wait, If I get the Honda classed and it would benefit me "YES", if it doesn't benefit me, then "NO"
Almost everyone is in agreement that it would benefit some cars and not others, right? Why would we want more rules that would benefit one model and not another when we know that going in ?
[This message has been edited by Quickshoe (edited May 13, 2004).]
lateapex911
Super Moderator
Darin, that may be true, but the timeline is important here. Changing rules post classification is what throws off the competitive balance.
Now it may help the parity, aiding the slow cars more than the fast cars in a certain class, or it may hurt the parity, but it can, and will have an effect.
It's tough for me to predict whether the benefits will outweigh the potential issues.
------------------
Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]
Now it may help the parity, aiding the slow cars more than the fast cars in a certain class, or it may hurt the parity, but it can, and will have an effect.
It's tough for me to predict whether the benefits will outweigh the potential issues.
------------------
Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]
Originally posted by Banzai240:
Competitive Balance??? I'm pretty sure I didn't just hear you 'say' that...
Um, correct me if I'm wrong, but much of the effort of the ITAC in the last year has been to improve the competitive balance in IT.
------------------
George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com
Banzai240
New member
You are very correct... HOWEVER... VERY little of that work has actually made it into the rule book (it's mostly pending a BoD vote in August...), so until it does... I'll continue to make light of the thought of there being any "competitive balance" in IT, because it's currently something that simply doesn't exist... Well, unless you consider tipped-scales "balanced"...
Some may... I guess it depends on which car you happen to own...
------------------
Darin E. Jordan
SCCA #273080, OR/NW Regions
Renton, WA
ITS '97 240SX
[This message has been edited by Banzai240 (edited May 14, 2004).]
Bill Miller
New member
Jake,
What would the car being 'significant' have to do w/ anything? You may not have one today, but you might have one tomorrow.
[HIJACK]
GRJ,
Sounds like you're saying it's ok to cheat if you feel that it's a safety issue. The VW hub issue is a pretty well known problem. I ran one of them, and had hub failures, so I know first-hand. That's also why I changed them on a regular basis, and used the German-made hubs. I've known several people that have had hub failures in A1 VWs. However, I don't know anyone that had the problem if they changed them in a timely fashion, or installed them correctly. Sure, you can get defective parts, but that can happen if you use the legal ones, or the illegal ones. I don't even need to go into how much experience Lesley has w/ VWs.
[/HIJACK]
------------------
MARRS #25 ITB Rabbit GTI (sold) | MARRS #25 HProd Rabbit
SCCA 279608
lateapex911
Super Moderator
Bill. Well made points regarding the VW hub. Congrats on the concept and delivery.
Regarding the pulley issue, I guess what I was thinking was, every rule change will have its pros and cons. I was thinking about the cost vs. benefit ratio.
In this case, the benefit could be reduced cost and simplicity. The cost could be the unintended consequences, such as somecars getting a boost in performance.
I would be against the change as I don't feel the benefit is that great, unless the only cars that could possibly benefit were so obscure, and clearly longshots in their class, that the benefits would out weigh the costs.
------------------
Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]
Regarding the pulley issue, I guess what I was thinking was, every rule change will have its pros and cons. I was thinking about the cost vs. benefit ratio.
In this case, the benefit could be reduced cost and simplicity. The cost could be the unintended consequences, such as somecars getting a boost in performance.
I would be against the change as I don't feel the benefit is that great, unless the only cars that could possibly benefit were so obscure, and clearly longshots in their class, that the benefits would out weigh the costs.
------------------
Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]
Bill Miller
New member
Thanks Jake.
------------------
MARRS #25 ITB Rabbit GTI (sold) | MARRS #25 HProd Rabbit
SCCA 279608
------------------
MARRS #25 ITB Rabbit GTI (sold) | MARRS #25 HProd Rabbit
SCCA 279608