Bottom end refresh winter project

[GT2EvoGuy]

I have a professionally built 3.4L 930 engine that has a pretty much stock bottom end and Ive been thinking about redoing the bottom end myself this winter - both as a challenge and also to save myself a few grand in labor.

Eventually Id like to redo the top end with new cams and better headwork but thats a whole lot more funds than Id like to spend right now. The engine has about 7k miles on it since it was completely rebuilt a few years ago so what Im looking to do is basically substitute stronger components vs. stock not do a complete rebuild. I want a bottom end that will hold together up to 8000rpm and that means lighter stronger components and better bearings/oiling.

The motor currently has:

3.6 964 crank
stock 3.3 rods with ARP bolts
stock 3.3 P&Cs
964 oil pump
ported and twin plugged 930 heads with GT2 cams, GT2 head studs
Motec EFI
GT4094r turbo
Mode headers and intercooler
3.6 plastic intake manifold

Im looking to open the motor up down to the case and install:

1) Motorsport bearings for high RPM use (do I need to do any other oiling mods to the bottom end?)
2) Carillo rods
3) CP pistons and have my OEM cylinders bored out to 98mm and re-Nickasiled. Id like an effective compression ratio of 8.0 (my planned boost range is 1.0 to 1.4 bar).

I figure the parts will run me about $5k. How many hours would this take me (I have experience working on a few BMW engines but no Porsche engines)? What other things will I need (gaskets, other replacement items and supplies)? Is this simply a plug and play type deal or is it a lot more involved?

[911st]

So somthing like 500-600 hp in a 2200 lb car is not enough?

Not an expert on this but not counting an R&R or out sourced machine shop labor a qualified Porsche mechanic expects a book rate of about 40 hrs for a full rebuild.

I suspect over about 7200rpm getting oil through the crank is an issue and would require cross drilling the crank so there is a supply in the center to augment the two at each end of the crank.

With the 964 crank there might be some harmonics issues but not sure.

You might check with Smart Racing about there coated bearings. I think it might be NASA tech $tuff.

Might want to look into if you should increase the oil relief valve pressure also.

As you know the 3.3 rods are a significant weak point. It is not the HP but you do not want to take them to 7k to many times.

Might be worth looking into Nickies for cylinders if you are going to go larger and just selling off your P&C set. They seem to be thought to dissipate heat better which will then become your biggest concern. Deleting your case oil cooler a-la C2 might give you more air for cooling.

As you know you will need bigger cams and ports to flow up there.

Now you need a turbo that will reach that far which means less low or mid range response.

Another way to go would be to sell off your long block and build a 3.8 turbo motor on a 3.6 case.

Please double check this info as I am just a nut that loves this stuff.

[911st]

Oh, and you might check what % duty cycle you are operating at. You may be close to there max already.

[Speedy Squirrel]

I couldn't disagree with 911st more. Absolutely DO NOT cross drill your crank if you want to set a rev limit higher than 7K.

When you turn the crank faster, it is harder for the oil to counteract the centrifugal force on its own weight and get to the rod bearings. In order to correct this problem you need to have plenty of volume capacity (you have a good start with 964 pump), and plenty of pressure (you need to raise the relief pressure). Cross drilling hurts both (bleeds off volume and lowers pressure). No less an authority than Scat Crankshafts, who have been making VW cranks for years, will not warranty their parts if they have been cross drilled. Neither will Porsche. Here is the Scat Crankshafts statement on the subject: http://www.scatcrankshafts.com/scattechpdfs/Cross_Drilling.pdf

The "NASA" bearing mentioned are referred to as "sputter" or "vapor deposition" bearings in the industry. Here is a link to the Federal Mogul/Glyco site that describes these bearings:
http://federal-mogul.com/en/AftermarketSolutions/EMEA/EngineSolutions/Products/EngineBearing/GlycoBearings/SputterBearings/

I can hook you up to a set, but I need your crank data. PM me if you are interested.

For a true 8K rev limit, I can only recommend Titanium connecting rods. The Carrillo rods are lighter (173 recip vs 195 recip for stock), and have 9.5mm bolts vs 9mm for stock, but I would like to see more margin than that for a true 8K motor. Remember, the rob bolt load goes up with the square of engine speed. Ti rods cost twice what Carrillo rods do. That is why there are very few real 8K motors out there. It takes alot of intake, head, and exhaust work to make use of 7.2K, let alone 8K. For most it makes more sense to build a 7.2K motor and keep making the mortgage payments.

[GT2EvoGuy]

911st - yes the sickness is strong with me hahahaha- I want 700whp++++ as my next goal (currently making 585whp at 1.2bar).

My shop built a 935 replica that has a 3.4 motor which revs to a true 8000 rpm and makes 750whp at 1.3 bar and I know that this was done without anything super exotic. It just takes attention to detail and tons and tons of time spent on the heads, custom cams, intake.

That motors bottom end consists of a stock 3.3 crank, their own sourced bearings, Carrillo rods and CP pistons so Im basically just going to copy what they did with the only difference being my 964 crank. Their motor has run that kind of power and revs for a few race seasons now so I know those components will meet my objective.

As for the top end, after talking with Xtreme in Florida Im looking to eventually spring for his own bare castings. The fresh castings apparently allow for much more radical portwork (especially on the exhaust side) than anything that can be accomplished by reworking factory heads. They are BIG $$$$$$$$$$$$ but apparently flow outstandingly well. Id like to match those with some very aggressive custom matched cams and possibly go to individual throttle bodies.

All the other items currently on the motor should be up to the task - its got a full width Mode intercooler and Mode racing headers. Those will support that kind of power. The GT4094r turbo I have will flow that as well at 1.3-1.4 bar.

So it sounds like I will need to get a stiffer pressure relief valve spring or maybe shim my stock relief valve spring slightly? Makes sense. As for titanium rods I agree light weight is better but then u are also looking at replacing those more often (dont they a much shorter service life than Carrillos?). I think the piston weight savings is much more critical than the rods because that is the mass furthest away from the crank. Does anyone know what a CP or other forged 98mm 930 pistons weigh vs. the stock 930 piston? The bearings are interesting. I will have to find out if that is what they used in their engine.

Are their any other bottom end tricks employed for high RPMs on this engine? I know on my BMW race engine (a 2.0L M10 that revs to 10,000!) we modifed the main bearing oil galleys for a bit more oil flow. Will the longer stroke of my 964 crank vs. the 930 crank prevent me from revving to 8k?

[Speedy Squirrel]

Are you thinking of aluminum rods, maybe? They are used in drag racing and get changed after 10 passes or so.

Proper assembly is very critical. Lot's ignorance on rod side clearance and crank endplay ot their. Just common practice for those that know what they are doing though.

Ti has similar material properties to steel, except for stiffness. It is less stiff than steel, so the rods have a bit larger cross-section. Looking at them you would think they would way a ton, until you pick one up. the service life of a Ti rod is about the same as steel, which is to say infinite. You don't design rods to work outside their elastic region, since that would mean the bores would distort, so fatigue is not an issue.

It is your 964 crank that I am concerned about. Never seen one used at high revs and boost, hence my suggestion for the extra insurance. hate to see anything happen to those expensive heads...!

[911st]

As I said I am not an expert and I do respect thoughts different from mine as I have been wrong more than once.

Of course check with Mode and other pro tuners before making any major changes.

My understanding is the longer the stroke the more difficulty. A 2.0/ 2.2 can be made to work to 8 k w/o working the oil supply circuit. A 2.7/3.0 can do about 7500...

For most cross drilling is just another bragging point. However, cross drilling or adding a center supply is a proven part of extending the RPM on a Porsche motor. Most oiling related failures happen in the center two rod journals as it is difficult to get the oil that far down the crank under the forces involved.

As I noted the oil relief circuit should be investigated as that determines the peak oil pressure. I have not heard of anyone else discuss this before but I lost a very expensive cross drilled crank because the builder overlooked this and I was not even up to stock pressure.

You can imagine the sick felling I had in my stomach when the next day before a planned visit to the track I took my new 2.4S racing motor out and quickly started hearing the deep down knock that comes with pounding out my #4 rod bearing, notching a cylinder and pounding a head. For the second time!

I suspect A VW with a supply at each end is in par with a 6 cylinder Porsche crank with a supply added to the center.

I wonder what the GT 3 motors do?

[GT2EvoGuy]

I will ask my shop about the TI rods. Maybe with the longer stroke of the 964 crank that could be necessary....Also along those lines would a different rod length help? Ive read that stroker motors benefit from long rods. How does that affect the torque curve?

As for the crank cross drilling I will find out if its best to stay with what I have or do cross drilling for oiling purposes. Would having the crank lightened and rebalanced help the motor rev higher?

At the end of the day it may just be too cost prohibitive to get the motor to rev to a true 8000. Im sure 7500 is very doable with the right components without breaking the bank.

[beepbeep]

double the revs = quadruple the forces on rods and rod bolts.
930 rod bolts = same as Carreras (stretch easily if revved beyond 6000 RPM's frequently)

I believe that steel H-beam rods, lighter pistons and better rod bolts will get you far without need to delve into exotic (and very pricey) Titanium hardware. Of course, high revs are not usable if engine cannot breathe, so you might want to change camshaft to something that will keep breathing above 6000 RPM. Which brings you to another high-rev issue: valve springs and rockers.

[911st]

Longer rods help with the forces that are imparted when the rod is at an extreme angle. With a longer stroke you of course end up with shorter rods. The go to longer rods you need to stretch the motor. I saw this done once to the extent where the cooling shroud had to be chopped and stretched.

Do not forget the valve train.

There are different ways to get to 700hp RPM's is one. More boost is another. A bigger motor is yet another.

The challenge with going with RPM's is the centrifugal forces encountered and making a motor that is still drivable in the low to higher range. Being efficient up high so one can make the HP the cam timing has to be such that you will probably lose drivability. You also they would benefit from redoing your gears to match.

More boost is a possibility as some are making that kind of HP. The challenges now being managing the heat and detonation.

The third option of making a bigger motor (3.9?) is low to midrange drivabity is retained and it makes most existing gear sets even more usable.

You already have the plumbing in place for a 3.6 based long block. It would not be that hard to sell off you long block and start with a 3.6 block. Check on the Nickie's cylinders as I think they can build you a set that could take you there. It would probably be less expensive and have less challenges in the way from achieving your goals.

I find a broad band motor with the right gears to be more usable on the track, in the real world and faster overall.

Just a thought.