[Cloud9...68]

As many of you know through my numerous posts on the subject, I've decided to keep my car and convert it into a mostly-dedicated track car. My immediate goal is to significantly increase its "fun factor" at the track by completely upgrading the suspension (spherical/solid bushings everywhere, much stiffer springs and dramatically upgraded dampers, torsion bar delete, more track-oriented tires and wheels, etc.), taking as much weight as I can out of it, and rebuilding the engine, since I need to upgrade the connecting rods anyway.



But, while my immediate goal is track day fun and having a car that I won't "outgrow" as I make my way through the classes at the local driving academy (Driveway Austin), I'm also keeping one eye on the PCA club racing rulebook, with the thought that I might partake in competitive racing with the car one day, and this is causing me quite a bit of angst.



Here's my major dilemma: As long as I have the engine out and apart, it seems foolish to not take as much rotating mass out of it as I can through the use of lighter pistons, and I would like to lighten, cross-drill, and knife-edge the crank, since I'm only going to have it out once. But looking at the PCA rule book, lightening of the engine internals is strictly forbidden, not only in the stock class, but also, for all intents and purposes, in the spec classes. Plus, I'd like to use as light a flywheel as I can, but the stock class only allows the 18-lb flywheel (although the wording here is ambiguous - it reads, "Suggested substitutions are: ... 968 may use 944S2 or 968 Turbo S flywheel" It's strange to see a word like "suggested" in a rulebook...). So the 12-lb flywheel seems to be out as well. At least headers seem to be allowed. My point is that there isn't a whole lot that can be done to increase the power of these engines, so I want to do everything possible to improve the way the car pulls itself out of corners (that fun factor thing again).



Also, I'd like to do things like relocate the battery to the back, and while this isn't explicitly forbidden, the rules do state something to the effect of, "Just because something isn't explicitly forbidden, don't expect that you can do it," so I'm assuming this is a no-no as well. A lightweight hood (if I could find one) would also be great, but again, this would disqualify me from the stock class.



And then there's the matter of wheels. I'd like to go with 18 x 9's in front with 255/35 tires, and 18 x 10's in the back with 285/30's, but the rules for the stock class only allow up to 8.5" in front. This may sound like a trivial difference, but wheels are very expensive, and I like the idea of minimizing the difference in wheel/tire width between the front and back, since the car has a pretty much 50/50 weight distribution, and staggered wheels/tires on a car like this seems just plain silly.



So, do I say "the heck with the rules, let me have as much fun with the car as I can get away with," with the possibility of major regret down the road? If I'm upfront with the power-that-be (I'm a ridiculously honest person, plus I have no desire to prevail in a particular class by giving my car an undetectable advantage, however slight), and suggest added a little ballast weight to offset the internal lightening, do you think they'd let me run in the stock class? It seems foolish to start ones fledgling amateur racing career in one of the higher classes, right? Or should I forget all about this rotating mass lightening stuff altogether, and keep all other mods I'm planning within the rules for the stock class?



Sorry about the long post, but these are major decisions, and I'm literally losing sleep over them. Thanks.

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[Rap]

While some subscribe to the philosophy of it is better to beg forgiveness than ask for permission, you talk about a fun factor. Doesn't sound like much fun with the angst of trying to decide if you will get caught or not. Stick with the fun!

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[Cloud9...68]

It's not that I'm worried about getting caught - to the contrary, the last thing I want to do is break the rules, potentially giving my car an unfair advantage. I can't understand the mindset of people who would break their class rules to make their car faster than the rules allow. Doesn't that dilute the sense of accomplishment of winning? It's not like they're racing for money, after all.



My angst is over whether I should build my car to conform specifically to the rules for PCA stock class, or to make it as capable as I can as a track day car. Maybe I need to take a closer look at the NASA rule book; from my quick look, they seem to be a bit more flexible. I totally understand, by the way, why PCA wants to limit what people can do to their cars by way of mods to stay in the stock class - it's too keep costs down. Yanking your engine (if you pay someone to do it), and taking the crank to have it knife-edged is very expensive, after all.

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[flash]

you could solve all of this by getting out of PCA and running in a different organization that is not so stuck in the mud with rules that don't make sense a lot of the time - i think you are going to continually bump into a wall on this until you get into an organization that is just horsepower to weight determined, and not model specific

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[Cloud9...68]

Yes, I agree. Since my original post, I spent some time looking at the NASA rules, and they seem to more logical, and, as you say, hp/weight based, with a points system that adjusts your car's classification appropriately based on the types of mods that have been done to it.



Again, with how little I drive my car on the street, my goal is to significantly increase its fun factor on the track. The driving academy I plan to re-enroll in when my car is done allows cars of all types on the track simultaneously, so I'd like to be able to keep up with most of them (within reason). If and when I actually race this car, I'll worry about what class it may fall into then.



Speaking of fun mods, if you still have that 12-lb Fidanza flywheel available, I'd be interested in taking it off your hands....

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[flash]

yeah- i think you'll be a lot less frustrated with NASA - i think you would continually feel like you were limited by this or that in PCA - the people running there are generally motivated by other things, designed to make sure the "old guard" continues to win their class - they couch it in "keeping an even playing field" but then don't make room in other classes for cars that are modified outside that tight set of rules - it's very easy to have a car you cannot race because it is stuck between classes - it's as if they only want certain cars racing, and not others - that attitude is exactly why many people leave and move on to organizations that are more about the racing and less about specific setup rules



re flywheel: sorry - sold both of them a couple of months ago

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[RS Barn]

OK,

Rules are the rules but sometimes what seems like the best option isn't always so. For example the 12lb flywheel isn't the best option for this engine. The 964 also had the same problem. They both like a certain amount of mass to help the torque off the corners. This engine makes peak torque at 4200-4600rpm even with wild cams. power falls off at 6500 no matter what you do, so the 18lb flywheel is tuned to that.

Another problem with these motors is the crank mass. Sounds like removing weight would be best-but, these cranks flex before removing material. A much lighter billet crank may work.

We use the Enkei 18 x 8.5 wheels front and 18 x 10 rear and the combination works great. I tune out under steer with spacers on fron when needed. usually only when track is cold or greasy.

Pete

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[Cloud9...68]

Pete,



Thanks for the input. A couple of quick follow-up questions:



So, would you say 18 x 8.5 wheel up front are a better bet, irrespective of any class rules, than 18 x 9's? Assuming I stay normally aspirated and go with your headers and chip (and I'm keeping an eye on developments you're working to to eek more power out of these engines for track applications), and run with a car weight of about 2800 lb for starters?



And as far as the crank, are you saying removing weight from the counterweights (and the areas around the rod journals to balance) will increase the crank flex? Seems counter-intuitive, but I'm certainly not the expert. Thanks.

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[flash]

i have no idea what the mixture is like on the chips, or how safe the timing advance is - also, these chips did not make as much midrange as the rs barn chip, so i want to start off by saying that i am in no way taking any pot shots at anybody, but i've heard about the power fall off at 6500, and it didn't seem right to me, but i had to go back and look to be sure - here are some charts clearly showing continuing gains up to 7k or better - the red line on the dave greimann chart is a weltmeister chip - the red line on the other is a racer x, and the blue line on that one is stock, which also shows power continuing right up to the fuel cutout at 6700



all of these runs were with a stock airbox, filter, and no changes made to the engine other than the chip



again, this is not in insinuate that they are better or anything of the sort, or that they are even safe (though we have no indication so far that they aren't) but rather to merely show that power can be developed above 6500 - all reference to power output has been removed to avoid distracting and pointless discussions about what did better than what - we've done that one to death



it is entirely possible that once other mods are made, that the curve shifts, so take this for what it's worth, and not a commentary on anything else



   





   

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[Cloud9...68]

Thanks, Flash.



So, assuming my engine stays normally aspirated, capping peak power very optimistically (assuming that someday things like ITBs become available) at about 300 hp at the flywheel, and that it spends a fair amount of its time above 6000 rpm, what's the consensus about lightening the crank? Lindsey racing does varying degrees of this, up to a full knife-edge treatment. It isn't cheap by any means, but my thought is that I'm probably only going to have the crank out of the car once, so as long as it's safe, reducing the rotating mass through lightening the crank seems like something I would regret not doing. But I'm caught between differing opinions from two renowned experts in the 968 world - Pete at RS Barn is cautioning against it, while Mike Lindsey says he has a solid history of doing it to race cars using these engines (although he is by no means trying to talk me into doing it). I need to make a decision soon...

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[flash]

pete has always said the crank flexes, and i tend to think that's a misnomer, though the result is the same - while i doubt the crank itself actually flexes, and more likely it's that to which it is bolted, it could easily be dancing around in there due to a change in harmonics, and result in the same effect as if it were flexing - i haven't done any research into this particular crankshaft or engine internals, but a lot of factors play into that



the power pulse and its balancing would be key here - whatever you do to the crank, you need to do accordingly to the flywheel, rods, and pistons - when you remove mass from one, you need to remove mass from the other - also, the balance shafts come into play, as they are designed to counteract a specific rotating mass - change that mass, and you need to change the balance shaft design to match - they all work together (or against each other if they aren't right)



so, it's very easy to imagine an engine literally trying to tear itself apart due to taking weight off at the wrong place



the bottom line is that somebody is going to have to do the math, and then build up a test engine for measuring harmonics - unfortunately nobody i know but porsche ever did that - that means it's trial and error by the small shops that now play with these



also, be sure you are talking about a 968 engine when talking to lindsey, as it is entirely different than the 944 when it comes to harmonics and mass adjustment - the idea is the same, but the result is different

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[biotechee]

My only comment (serious grain of salt here since I have absolutely ZERO experience with racing and internal engine modifications...) would revolve around longevity.



If one desires to build a motor which has increased horsepower via lightening of internal components, increasing rev limits, etc., one should be prepared to "rebuild" said motor on a rather frequent basis.



If you are the type of person who doesn't want to tear down a high perf motor regularly to keep it running "high perf," be it for money reasons, time reasons, whatever, then I think you should focus on making the engine robust. Make the engine bullet-proof and drive it for a long time to come without having to worry about it falling apart due to harmonics, grenading, and so on. Keep the balance of the engine and get the 18 lb flywheel- that automatically reduces your driveline loss, netting an increase in RWHP.



There's a lot of weight to be removed in the rest of the car- depending on how crazy you want to get. The more weight you remove, the less work your robust engine has to do to move the car.



Making sure you have a bullet-proof engine also allows you to look into things like ITBs and FI in the future. I'd be overly nervous of boosting a high perf, lightened, NA motor.



Just my $0.02.

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[flash]

agreed



that being said, even reducing flywheel mass can have a deleterious effect on harmonics - how much is determined by the differential between one rotating mass and its counterweight - the weight of the flywheel evens out the gap between pulses - reducing that allows for those pulses to have more of an effect on other components, though it allows for faster acceleration of that same mass



there is no free lunch - that's for sure

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[Cloud9...68]

Thanks for the inputs. I've also contacted a few other knowledgeable folks in the FEWCP (Front Engine Water Cooled Porsche) racing community, and there are apparently some very good reasons to keep the crank at stock weight, particulalry on the 3.0 liter motor. Flash's post does a good job of highlighting them. The good news is that this simplifies my build, and saves me some money. Between my cylinder bores being in very good shape (a total of only 0.0007" taper top to bottom) and this, I may yet have this beast on the track before 2011 runs its course...

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[RS Barn]

I have run hundreds of dyno runs with all sorts of mods and never had power maintain until 7K. Even using the same chips mentioned. It has nothing to do with chips or A/F or timing or raised rev limit.

I have spent thousands of hours testing and tuning these engines. I've also tried many combinations of intake and exhaust trying to raise peak power above 6500rpm. Not for street use but for racing where raised rpm and power has a defined benefit.

You would think agressive camshafts would raise peak hp limit. This doesn't happen with our motors. Changing header and exhaust doesn't affect either. All fall off after 6500rpm

The intake manifold is the limitation and glory of our motors. The intake adds close to 10 HP and Ft/Lbs of torque from 4k to 6500. Any mod to this can and does reduce power. The only way to increase power above 6500rpm is a completely different intake. I've spent a bunch on them too.

While testing my 300hp NA motor with special intake, I was able to make power well above 7200rpm and would continue to 8K if desired. The downside was loss of torque in the usable 4500-5500 range.

I was able to gain 15HP @7300rpm and lose 25ft/lbs of torque @5K. Not a good trade off

So now I have 292 RWHP at 6700rpm and 268FT/LBs TQ at 4800. All peak gains are only 200rpm above peak levels I've seen with many combinations of Air, Chips, Headers, Exhaust

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[flash]

well, i'm not sure what the problem is, but it's hard to argue with charts - there were quite a few people watching too, and we were very careful to calibrate everything for the testing



in real life experience, my car pulled with the racer x chip all the way past 7k too - the "natural" shift point was about 7400 - dave's car was about the same with the weltmeister - with other chips the shift point was lower, as was the case with the rs barn chip, but there was better midrange, so it was a good tradeoff - i haven't looked into what exactly the difference was and why things were what they were, but they were there nonetheless - it wasn't a pleasant thing to have to rev it that high to get to the peak power though, and i was happier in the end when i didn't have to



that being said, i also have quite a few charts from other people showing fall off after 6500, so it's not abnormal - perhaps it's the kind of dyno



the intake is definitely a limiting factor though, as is the case with any tuned intake like ours - any real power at high rpms will come at the expense of a lot of things, and not likely to be particularly efficient even if you do get it happening - ITBs or a log ram would surely make more upper end power much more easily



nobody is arguing the wisdom of making the power lower - obviously that is more desirable

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[Cloud9...68]

After having been guilty of doing it to others a number of times myself, I now have the pleasure of saying, "Hey, you guys have hijacked my thread!" <img src="/forum/images/smilies/968/biggrin.gif" class="smilie" alt="" />



It's OK, as your discussion about how and where these engines can produce power is actually somewhat relevant. In any event, I'm glad I've settled on not lightening my crank. Over the next month or two, I will be buying an 18 lb flywheel, new clutch kit, RS Barn headers (II'll check to see if anyone, like someone who had them before going to the SC, has any they could sell), RSB cat back, the latest RSB chip, a windage tray, solid steering rack bushings, whatever firewall brace is available, racing seats, chassis brace/rollbar (Flash's, if it's available), wheel and tires, along with assorted seals and o-rings, and probably a bunch of other stuff that escapes me.

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[flash]

lol - sorry about that - i was worried about it when i posted the charts, but i wanted to show that it can be done - i was afraid that it would turn into such a discussion though, and i am hoping we can avoid it continuing to be a distraction from the point of the thread - we can always start a new thread about such things



sorry, i sold my header, but i think mrmister has one he'll sell - i know mark does, and he will probably be pulling it off his car, as it won't run well with it on there now that he has the supercharger, but it will probably be a while as he is too busy to even deal with the car



i'm working on the new firewall brace this week - i got sidetracked with the 2 events



i will be taking orders for chassis braces in the next week or so - i am just waiting for the welder to be done with the supercharger parts before i burden him with more stuff



back on topic, on the subject of tires and wheels, i would look into what limits you have there in the rules too - also, consider that the wider you go, the more load put upon the suspension components - ours were designed for 90's tires - even stickier street tires nowadays add a lot of load to components - race tires add even more - the wider you go, the more load - i would look carefully at the hubs and spindles, as well as the ball joint pins, to be sure they can handle whatever you are adding

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[tamathumper]

Chassis brace orders? Do tell...!

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[flash]

i'll start a new thread in the next week or so - i've already sidetracked this one enough

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