Performance Developments

[QUOTE=Chris White;14358740]Some good stuff here, just to make sure all get the point - balance shafts have nothing to do with crank balance or crank lightening. They are there to (somewhat) attenuate vibrations caused by an inherent in line 4 dynamic balance issue. For some the issue becomes a little more obvious when you look at the location of the pistons when the crank is half way between TDC and BDC - most would think that the pistons woudl be at the mid point in travel between top and bottom - they are not. They are all below the mid point due to the angle of the con rods. This means that the piston traveling from TDC to 90 degrees is traveling faster than the piston going from BDC to the same point, creating an imbalance. this imbalance cannot be solve with any mods to the crank, rods, pistons or any thing attached to the rotating or reciprocating mass.
The amount of force created by the balance shafts is relater to the mass of the pistons and about 1/3 the mass of the connecting rods - so if you lighten the pistons (which they desperately need!) you might think bout modding your balance shafts.


Its good to know there are others out there understanding what is happening and trying to educate the rest as well.

These may be old engines but that doesn't mean that sound engineering should not be applied.

Add to what Chris mentioned, a 4 cyl in line engine multiplies the imbalance by a factor of 2 times, as two pistons travel the same route at the same time.
This makes the issue twice as bad as many may think.

As for building and engine for $1500.00, I find no issue with that at all. My first 2 questions to potential customers are in this order, what is your budget limit and what are your performance expectations.

You answered the first one and the performance should be understood as being close to the limit of your budget. Nothing wrong with that. I often wish I could build an engine with this sort of thinking. You get caught up in the demands of performance and as a business we have to do whatever is necessary to reach the performance goals reliability and within the given budget. If we don't the backlash on a business is the opposite to that shown to the DIY guy.

This is why an ex Formula One colleague of mine is flying in from London and meeting me in NY. We are limiting ourselves to $1500.00 in total expenditure, to buy a car including gas, food, lodging and drive it across the states to LA. This will make us live the life of the DIY, the shade tree mechanic and drop us back down a few pegs and understand the other side of this game we call work.

951and944S

Explain. Are you saying that they are grooved around 270 degrees/75% of the two shell's inside diameter...?

If so, that information is false. Each bearing shell makes up 180 degrees/1/2 and only the uppers are grooved. The entire support for the bearings, upper and lower is grooved for feed but not the lower bearing. Exception is the front bearing but it's grooved approximately 225 degrees, not 270.

The feed holes in the crank itself are more than 180 if that;s what you meant but that makes the condition worse because for any rotation past 180 degrees there is a window where the rods are cut off completely from feed. Minute due to engine speed but still present by design.

If the cam sprocket's intent was to act a a flywheel, to "smooth out cam rotation " as you put it, then they forgot to put one on the intake cam on the 16V engines.
We were talking about torsional flex differences between the front and rear lobes in my context, not balance and the other comments were about cam timing only as related to torsional changes in the crankshaft which drives the cam. I would have guessed this to be absorbed by the pliability of the belt in between the crank and driven cam but that's just my opinion.

T

951and944S

It's not a matter of purposely choosing a budget build, it's all that's allowed.

You have to keep piston weight as per stock for instance in SP1 and 2 (which we currently race). The stock cast pistons are fine for the 165 crank hp and 7000 rpm limit of the stock DME so why would I spend $1k+ for forged pistons when their lightness and strength benefits are not needed, not to mention that we are not allowed customization of reconfiguring pin location, etc,etc.

Same with the rods...., they must be the factory weight so either stock rods or the sinter forged 944T rods are used in an Sp1 or 2 class engine, spending $1200 for rods the same weight of stock doesn't make sense when the 944T rods are plenty strong enough for a 165 hp NA engine.

944 Spec cars in PCA and NASA sanctioned racing are all about budget grassroots and evenness of competition level, that's why they will not allow dry sumping.

We have to play by their set of rules.

My $1500 race engine example above just beat the national points leader at Road Atlanta in the 1.5 hour enduro on sheer speed and lap times, not some traffic incident or pit stop malfunction. And he had the +200cc 2.7 liter carrying the mandated +100 lbs car/driver weight which is still probably and advantage over our 2.5 with a straight as long as RA.

Now, 944s in PCA and NASA GT classes are open to any list of performance mods that you can think of throwing at it given that the weight of the car places it in correct sub class.

The engine you have for Patrick would fit in here.

I would move there also to a GT class because I love tinkering with aero but there are no competitors that show up in these classes in our region.

It's more exciting to go up against 10 cars in class....which is why we are moving to SP3. This class is populated with 3.0 liter 944S2, 968 and 944T now because they were formerly classed E with the SC 911s but all left and moved to SP3 because they barely stood a chance at full weight because Porsche Club always favors the 911.....

T

Dave W.

The groove in the main bearings may not be exactly 270 degrees, but it's not 180 either. In this pic you can see the groove extending down from the edge of the bearing.

951and944S

Yes, that's the tapering on/off transition.

The front 1 piece bearing has it too.

You got me, 190 degrees then.

Far from 3/4.

T

Chris White

sounds like fun - you need to make a stop at Watkins Glen on the trip. They have track tours at noon every day. three laps for $25 and they don't go slow!
I am an hour away - ill buy lunch at teh Seneca Lodge - Emerson Fittipaldi's Laurel wreath from his F1 championship still hangs on the bar wall!

Performance Developments

Know that place well. Stayed in one of those cabins out the back all the years we went there.