911 aircooled developments

[Neil Harvey]

Originally Posted by Fly911

Would it be possible to have the wrist pin even higher up in the piston? If you had a hole where I marked on the picture, and slid the wrist pin in, and then had a tight fitting plug that locked in place, with grooves for the piston rings, you would have a much better geometry. You would have to put the piston rings on after the rod was installed.

You would get less piston slap, a lighter piston, and a longer rod to stroke ratio. All making more HP... Or am I in the wilderness here?

Pin position is always limited by the forging. In this case the forging was determined by bore size.

Its not uncommon for the pin to interfere with the oil groove. I'm not a huge fan of doing this as you have to use a support rail which adds weight.

What you are suggesting is something not done to my knowledge.

Good luck on that one if you do.

[dkirk]

Good engineering practice is to center the wrist pin location with respect to the piston skirt length. Re-locating the wrist pin near the ring belt as suggested would result in piston cocking in the bore, driven by rod angularity and dynamic forces. This would create a noisy, short lived engine. The parts as shown look beautiful, well thought out, and designed correctly.

Congratulations Neil - I'm saving up for a set!

[Discseven]

Originally Posted by Neil Harvey

As pictured, Rod with bolts, Pistons and Pin, 914.50grams.

No clips or rings included in picture.

Thanks Neil

[Neil Harvey]

Originally Posted by Discseven

Thanks Neil

You are welcome.

I figured I should clarify the direction we have taken and the parts we are offering.

Two "things" every engine upgrade should be preempted with are, your performance goal and your engine budget. You may have to come off your performance objectives some to meet the budget. In other words, don't over buy parts that will not make any difference to the performance goal.

Performance Developments builds many high performance engines, used for off road purposes. These have a single objective, to produce a reliable performance level. Component design include features that produce higher levels of torque more efficiently, lowering frictional losses and the ability to rev quicker resulting in the engines torque band reached quicker in less time.

But when we looked at the street business, most of what is produced and sold is age old copies of parts designed in the 70's and 80's. Not a lot has changes. So we went about including features that will make a difference to a street engine in areas we consider extremely important.

The parts designed offer a modern higher level of technology to those customers wanting something engineered to recover some of the lost performance that has been considered normal and acceptable for years. The cost is higher as the quality and technology is higher, therefore, not for all.

We are not trying to compete against what is already available for these engines. If what is currently available meets your performance goal, our parts should not be considered.

[Neil Harvey]

Our on going parts development continues. Weight has been our focus here along with modernizing the components.

This is the new 2.9L rod that will be an addition to the existing 2.8L steel rod. This rod is a little more expensive as its designed with weight as its main criteria. Shown here is without bolts. The new bolts for these rods weight 24.5 grams ea.

This rod fits the stock crank journal but is longer in length and uses a smaller pin size. This lightens up the piston as well. Once we have the assy all together I will weigh as a comparison to the stock parts.

We are offering all of the stock Porsche and BMW rods sizes as an alternative to the commonly sold versions. Coming very soon are lightweight steel versions for the 74, 76 and 80 mmm cranks. The 76.40mm lightweight rods are designed for the 3.8L engines along with the GT3 variants.

We are currently involved in several high end air cooled projects and some of this technology is filtering back into main stream sales. The new head studs, exhaust and thru bolts, camshafts, valve springs etc are all coming out of these projects. The new head studs are in stock now and we expect to have the new "964 fit to everything engine cam" available soon. The design is completed and its undergoing Spintron testing now with its new Valve spring and retainer. This will add to our increasing cam inventory.

[dannobee]

Neil, have you entertained the idea of smaller rod journals, like the 1.85" journals currently used in nascar cup cars? They would likely help with the oil pump clearance problem on the long stroke cranks along with weighing less. And better and cheaper bearings are readily available.

[Neil Harvey]

Originally Posted by dannobee

Neil, have you entertained the idea of smaller rod journals, like the 1.85" journals currently used in nascar cup cars? They would likely help with the oil pump clearance problem on the long stroke cranks along with weighing less. And better and cheaper bearings are readily available.

Indeed we do, but the 2.8L and 2.9L rods were designed to run with a stock crank. The issue with the stock crank is the oiling holes. This limits the journal been cut undersize. The larger journals on the 3.2L and up cranks can be cut undersize. I think the max on them is 2.00". However, both of these rods have narrow beam widths than stock.

Custom engines we build use a lot smaller journal and a narrower beam thickness. But these use a non stock crank they have different pin oiling.

[jjeffries]

Neil, ignoramus question here: are these rods created by that process whereby they're cast (forged?) as a whole but the segment that is to become the big end cap is forcefully whacked/cracked/split off? Or is that only done with components mades from sintered metal? Thanks in advance for the lesson! John

[Neil Harvey]

Also to add to your question, the BE radius is designed to clear the biggest oil pumps using stock journal diameters.

To compare against the Titanium rods we use, they weight 403 grams with steel bolts but cost 3 x as much. So 461 grams for a longer steel rod with bolts, larger BE and longer CCL, we feel we have achieved our primary objective.

[Neil Harvey]

variants

Originally Posted by jjeffries

Neil, ignoramus question here: are these rods created by that process whereby they're cast (forged?) as a whole but the segment that is to become the big end cap is forcefully whacked/cracked/split off? Or is that only done with components mades from sintered metal? Thanks in advance for the lesson! John

No, these are made from a forging with typical parting lines with dowels. Material and after processes will remain confidential at this time as we have a huge amount of time and many prototype sets involved in these first finished parts.

These are special lightweight variants but we offer all of the stock Porsche sizes as alternatives to those commonly sold in the aftermarket. We wanted to also offer a more "custom" line of steel rods for those engine customers who want something special over the standard parts sold in the aftermarket.

[Trackrash]

Dumb question. If I use light weight rods and pistons do I need to modify the crank for optimum performance? In other words, with light weight rods are the counterweights on the crank too heavy and should they be knife edged to compensate?

[dannobee]

opposed engines aren't balanced with bob weights like V engines are, so as long as the pistons and rods all weigh the same, you won't have any problems. If you cut down the counterweights or knife edge the crank, it will need to be rebalanced.

[Trackrash]

Originally Posted by dannobee

opposed engines aren't balanced with bob weights like V engines are, so as long as the pistons and rods all weigh the same, you won't have any problems. If you cut down the counterweights or knife edge the crank, it will need to be rebalanced.

Yes, but I am wondering if the stock counter weighs are now more than needed with lighter rods/pistons. Then again, Porsche added more counter weights when they went to the longer 76mm stroke motors, including the GT3s.

[Neil Harvey]

Originally Posted by Trackrash

Yes, but I am wondering if the stock counter weighs are now more than needed with lighter rods/pistons. Then again, Porsche added more counter weights when they went to the longer 76mm stroke motors, including the GT3s.

Good point and you are correct in your thinking. These engines and their layout with narrow cylinder spacings do not lend themselves to a great crankshaft design.

The 993 cranks that have a 0.750' wide rod journal in difference to the earlier cranks that have 0.866' wide journals, were done to add width and mass to the mid sections, to help stiffen the cranks due to the added stroke.

All cranks including Porsche cranks twist back and forth from torque pulses. The longer the stroke, the heavier the masses reciprocating and rotating, the higher the combustion pressures all add to the stresses and movement placed on that bent piece of steel spinning at 7000 RPM.

The more you can lighten up the masses helps. Going in this direction as opposed to going heavier, certainly helps. But, as you suggest, calculating the counterweight required is important. The % of counterweight on all Porsche cranks allows you to lighten up the masses without having to remove weight, unless you are turning the engine at very high speeds. In just about every air cooled version I can think of, the engines ability to pump air for those speeds is zero. Counter productive.

What I can tell you is this, if you do remove counter weight material, (knife edging) you are not doing the engine any favors. This is the wrong way to go. You need what weight is there to help counter the flexing. If you had larger counterweights with a higher % number, then yes, but this is not the case with Porsche flat six opposed crankshafts. This is why we choose to go in the other direction and lighten up the rod and Piston assembly. Effectively, we are increasing the counter weight %, helping to lower the crank movement.

[Neil Harvey]

We have the 1st lightweight 2.9L kit ready for assembly. This kit uses the new lightweight, longer rod we designed for both the 2.8L ,2.9L and up to the 3.4L applications. These all use the 74.40mm crankshaft.

The combined weight of the 2.9L lightweight kit is 920 grams with rings, clips, pin, rod and piston. The other kits may be slightly different due to piston size. I have the 2.8L piston weight somewhere and can weigh the 102.70mm piston along with the 104.00mm pistons we have in stock. Weights to follow.

A standard Porsche IRP rod can be substituted if required, along with standard spec piston. We are offering these kits as an alternative to all of the existing rod and piston kits that have been sold for many years.

PD is offering IRP rods as an alternative to the aftermarket rods, commonly used. All stock Porsche applications are available as well as the lightweight "custom" kit versions. These are more expensive and are designed for those applications requiring a more engineered solution.

We also designed lightweight rods for the 76.40mm and 80.40mm strokes that will be sold for the 3.6L, 3.8L and 4.0L engine kits. Pistons are available as well. To go along with all of these kits we have new Camshafts, Valve springs, Head studs, Ex studs with more parts in development.

At present, until we can catch up, the Rods and Pistons are available with a min 4 week delivery time. Our intention is to carry these in inventory, but we have a lot of development underway and our resources are stretched to the max.




Pictured is the "standard" rod and the new lightweight rod, to give a comparison.

[racing97]

Are you sure the Rod pictured as your 2.9 package is not the BMW rod you manufacture, the reason being the sipes on the side of the big end which is common but not always used for pairing rods on one common journal such as a V8

regards

[Neil Harvey]

I can guarantee the two rods shown are for a Porsche air cooled engine.

The lightweight rod (2.9) has taken almost 1 year to get to this stage. My bank balance tells me this every day!!!

It very difficult to lose weight, retain strength and stiffness.

This rod weighs 412 grams without bolts. It will lose another 20 grams as we have trimmed some more weight where it’s not needed.

[racing97]

Just curious as to why the sipes in one and not the other

[KTL]

I was thinking the same as racing97. Usually the sipes on the thrust surfaces are used as squirters for the pistons? We don’t need those since the case has the squirters, right?

[Neil Harvey]

We are removing all added weight that serves no purpose. I’ll take from wherever as long as it doesn’t affect strength.