Piston & Rod upgrade or not?

[Dan944t]

Thanks very much Pete, I am going I have a read through it now If this answer is in your thread just ignor this question but as my car is producing something in the region between 320-370 (havnt dynoed as yet bit this is what a speacialist that drove it said it feels like?) I'm obviously going to change my clutch whilst I have the engine scattered all over my garage floor, and have been advised by a few people that if the 944turbo goes beyond 320 it needs a stronger clutch? woyld you say I need a racing clutch now and if so please could you tell me what you have installed or what are my options as I'm so confused of what to buy becuase of thise I have found have no springs in the clutch pad plate and some say that it will not be very nice for a road car which mine is, so I'm very confused of what I need and what are my options as not to ruin the comfort too much? I am desperate to buy the clutch soon as possible as the company that are fitting my wet linners are waiting on it in order to balance My flywheel , clutch, bolts crank, and pulleys.

tha for such a quick reply and I am looking forward to reading your build!

atb

Daniel

 

[PSH]

Hi Dan

I had just written a long detailed reply as to why I use the clutch that I have and then windows 10 decided to shut down for updates...lol I seem to have lost the keyboard lights too since so will keep this short and try to answer any further questions that may arise tomorrow as it's getting late now.

my car run with 368 bhp/382 torque on the standard (updated) Sachs clutch from 2007 till 2011 with no issues, this is when the engine was pulled for a rebuild.

Today with well over 400bhp I still use the Porsche recommended clutch for a standard car, the same clutch is also rated for the 930 and RS968 turbo, it is an upgrade from the original which had weak centre plate springs.

I would say though that if you intend heavy use on the track you'd probably want an after market paddle clutch. I personally don't like paddle clutches for road cars, I have driven my sons 500bhp cossie fitted with a paddle clutch and hated it.

Now how long the clutch lasts is an unknown, the car did over 50k miles when at 368 bhp with no issues, in fact it was still in good shape when the engine was pulled for the latest development stage although it made no sense to put the same clutch back on the car considering how big a job it is to change.

Since the rebuild, the car has covered just over 8k miles and it has been pushed hard at times, the clutch holds perfectly and I expect it to last for many years.

Now I can hear the gasps now from others who would disagree with my choice, I would say that I have more than proved over a number of years and thousands of miles what the clutches are actually capable of. I would add that the original clutch with the weak spring design lasted for well over 100k miles. The Sachs clutch for the 944T is a very good clutch..

Hope this helps, of course, you may drive like a complete nutter and get different results but I doubt it, i didn't always drive like an old man as I do today...well I still have the odd mad day....

regards

Pete

 

[Dan944t]

Hi Pete,

firstly I must say that I am really really enjoying your thread on your build and I'm also ready to hit the sack but just couldn't stop reading it. So far I am up to page 5 and I will be reading this back as I put mine all together just to go over a few helpful things such as those dowels on the girdle. That was very helpful as I'm not sure if I would have noticed one was missing and if so I will too buy another from Porsche and lathe it down to suit as I'd much rather x2 To lock the girdle. And I wasn't going to but I may too spray my block red as I've already sprayed the manifold and intercooler pipes with red vht paint from my last top end build.( I also like to be different )

secondly thanks for all quick responses so far I am very grateful.

Regarsing the clutch i too had no problems with slipping after my top end rebuild and a host of power mods with bundles more torque than before, and the disc is actually not in bad shape either but being of a past machanical background I wouldn't dream of refitting. So are you saying that the sachs clutch is what you are running in yours now the type with the springs in the centre apossed to the original rubber centered disc of old. The sachs is the clutch I was originally going to purchase as that's what I've always used in my 944s but I've yet to change one in my 944turbo.

These are around the £500 mark and If this is correct in what your saying then that is what I've been wanting to do all along then a well known speacialist threw a spanner in the works and got me stumped on weather or not I really need a race clutch that's going to eat x3 times the price of what I thought was fine before I pulled the engine out.

If this is is the case I will be saving £1000 which I could spend on hoses and important silly bit's and pieces that I'd like to change whilst I'm in there.

and by the way serdi uk is where my short block and head are being done too I also felt like a kid in a sweet shop when I opened the door but wasn't sure about it when I saw the outside but that all changed as soon as I saw there's machinery and met them.

I must double check but i but I think I have the same pistons as you mension in your thread, I am buying them from John at serdi, but am thinking I may need conrods also as 2 of them have different corresponding numbers on the bottoms.

speak soon

Daniel

 

[slickv8]

Daniel / Pete, your killing me! So having made the decision to bolt mine back together I've now ordered a crank scraper and I'm desperately trying NOT to click the link to Petes build thread....Arrrrgh

As for needing big wheels - they're yet to be refurbed but yep, got that covered....

 

[924Srr27l]

Here's a thread worth looking at for the Turbo Lovers....but with a Twin cam head

http://forums.tipec.net/viewtopic.php?f=25&t=15322

R

 

[PSH]

Hi Dan

The rubber donut clutch that you mention was never on the turbo, only N/A engines. The turbo's originally had a centre plate with six small springs, it's these springs which had been known to fail long before the clutch was worn, happened to me on my first clutch. The updated clutch which I would hope is the only turbo clutch available today has 4 large springs which are rated to take much more torque, I'm not aware of any spring failures with this clutch As for the clutch in the car right now, yes it's the standard Sachs clutch, it's supposedly only rated for 350bhp but Porsche are well known for over-engineering their parts, as I said this clutch was great at 368 bhp for over 4 years of at times hard driving and when the engine was pulled the clutch still had plenty of life in it. I would say though that the flywheel face needs to be in good condition, any grooves will reduce it's effectiveness, a nice machined flat face with the Sachs clutch has given me no issues, I would though consider a paddle clutch if you intend to drive regularly on the track where conditions are much harsher.

Nick thank's for your kind words...hope the thread is of help which was the reason for it's creation, that and a log of what I did for my own record.

Regards

Pete

 

[Dan944t]

Thanks Pete that's made my mind up as I e no intention of tracking the car ever so it's purely for my pleasure on the road when Im lucky enough to actually get out with a wife a 2 year old and one in the way, and alsways a million things asked of me from the wife on the house like extensions and stuff Now know what clutch I need it will be good for my cash flow as I'd had it in my head that I needed the 4 paddle race type clutch so I've now got £1000 extra to use up on practical goodies Or maybe on buying genuine Porsche big and small ends instead of what I was going to buy which was glyco? What's your thoughts on glyco or shall I always stick with Porsches own.

i have asked John at sersi to reduce the flywheel but I thought of taking a little more off to lighten slightly but wasn't 100% of how much? Wasn't thinking too much at all just enough for a noticeable quicker rev/spo along with my pistons and hopefully race rods should hopefully feel something.

Nick don't read Petes thread as I'm already now spraying my block red when I get it back

I like your wheels by the way, I have the cup 1's which I really would like to get returned one day soon, and I e often thought of getting back the slight dish that they have diamond polished but who knows?

atb

Daniel

 

[blade7]

Adding rods wont [at this stage] give any tangible benefit without also looking at the pistons,

Your choice fella, but if I had an engine with cast rods out of the car and I could put a decent set of used Rarst forged rods in for say £100-200 I'd do it. The standard pistons are strong enough to take big power, or a momentary running glitch.

 

[PSH]

Hi dan

I had to look through my own thread to find what Porsche recommend for minimum thickness of the flywheel, I found that I had recorded that 25.2 mm is the minimum given, mine was taken down a little further, I can't remember the exact figure but it was 24. something? John should be able to advise as to what he feels is the best option, I wouldn't personally go too far, though, one for safety but also for the driving experience, the turbo will overcome whatever weight you may leave on pretty easily anyway. Btw say hi to him for me...

I would agree with Paul's advice re 'forged rods', you didn't elaborate as to what actually failed on your dyno run, I assume it's either the wrist pin on No.2 or the rod itself if it was a cast item. Porsche's Rarst forged rods are highly regarded as one of the best for the car even if using 80's technology, remember Porsche have a history of over engineering, their forged rods are a typical example. It has been recorded that the safety margin for cast rods is around 350bhp, some cars with these rods develop more power, others at that power have now been destroyed, if using cast rods I suspect that the tune needs to be spot on and remain so throughout if's life, there's no safety margin so to speak. Some here will remember better than I of Fen's car destroying itself due to a failed cast rod at around 350bhp and IIRC this was a new build.

Pete

edit: oh...sorry just realised that I'm answering questions from two people, sorry Dan your car didn't fail due to a Rod, that's Nick's...note to self...'pay more attention fool'....

 

[slickv8]

sorry i never answered that one did I - it was actually a rod bolt that stripped off and shot out through the sump. The head and crank etc all miraculously survived unscathed but the block was toast.

 

[PSH]

sorry i never answered that one did I - it was actually a rod bolt that stripped off and shot out through the sump. The head and crank etc all miraculously survived unscathed but the block was toast.

ahh... the reasons for this are numerous and only close investigation will tell you what really happened...as we are talking 944 was it by chance No. 2 and if so did you check the wrist pin, if this seized (the most likely thing for this engine) then this can break the bolt and thus destroy the engine . Engine braking from high speed can also do this, I'm guilty of using the engine a little to brake but never from high speed and the throttle is always 'blipped' prior to downshifting. Not really good practice, brake pads are far cheaper than engine rebuilds but it sure does sound good.

it's the boy racer in me..

 

[blade7]

sorry i never answered that one did I - it was actually a rod bolt that stripped off and shot out through the sump. The head and crank etc all miraculously survived unscathed but the block was toast.

Have you had the crank checked to make sure it didn't bend a little ?

 

[Dan944t]

Hi Pete

thanks for the measurements of the flywheel, I shall measure mine and see how what it is at present.

So did you have your standard one lightened by john, Pete or have you got a LR item or ferenza?

Do you think I should get John to take any weight off the crank or just get it balanced and look into a crank scrapper? Or all Of the above but not excesive with the crank weights? Just don't want to regret doing any performance mods whilst my engine and bits and bobs are with serdi.???

sorry for all the questions but I'm loving the answers as it's setting me up for everything I need for this rebuild That I've been struggling to find out what's best

Atb

Daniel

 

[924Srr27l]

PSH the wrist pin, if this seized then this can break the bolt and thus destroy the engine . Engine braking from high speed can also do this,

Engine braking, what's this lifting off and costing?

From High speed as in High RPM or MPH ?

And why or how is this likely to make a Gudgeon Pin seize in the piston ?

R

 

[PSH]

Hi Pete

thanks for the measurements of the flywheel, I shall measure mine and see how what it is at present.

So did you have your standard one lightened by john, Pete or have you got a LR item or ferenza?

Do you think I should get John to take any weight off the crank or just get it balanced and look into a crank scrapper? Or all Of the above but not excesive with the crank weights? Just don't want to regret doing any performance mods whilst my engine and bits and bobs are with serdi.???

sorry for all the questions but I'm loving the answers as it's setting me up for everything I need for this rebuild That I've been struggling to find out what's best

Atb

Daniel

Hi Dan

To answer in order

I lightened my original flywheel, I did a lot of research for my latest build and I had learnt a lot from the previous builds, I've now owned this car for over 17 years and the mods started in the first year. I'm not a fan of a lightened flywheels , you are losing stored energy which is very important for our cars with their long gear ratios and weight.

No...IMHO, leave the crank alone, you can balance if you wish, i decided not too and didn't remove any weight. Never bore the crank9some do) to lighten either as you gain nothing, there is no point taking away weight from the centre of the crank, god knows who thought that one up. The crank scraper is a great device and lightens the crank far more than removing metal from it. I can't remember the technical terms, partly due to my memory being badly affected these days due to meds, but hey that's another boring story. The crank scraper reduces greatly the oil that sticks to the crank and thus reduces extra weight and drag. The higher the rpm the more oil that gets suspended around the crank, some engines at high revs drain the entire contents of their oil pan which sticks to the crank, I am talking drag cars here but it gives you an idea of just how much oil is suspended around the crank, there is a name for it which again I can not remember.

If you do a little reading you'll discover how important it is to keep the crank and flywheel reasonably heavy, try reading this link, http://www.w8ji.com/rotating_mass_acceleration.htm it's long and it's technical but it should tell you what you need to know, you can then make your own decision as what to do, i have laid out what I did and I'm very impressed with how my engine responds to my right foot.

Regards

Pete

 

[924Srr27l]

Hi Pete

thanks for the measurements of the flywheel, I shall measure mine and see how what it is at present.

So did you have your standard one lightened by john, Pete or have you got a LR item or ferenza?

Do you think I should get John to take any weight off the crank or just get it balanced and look into a crank scrapper? Or all Of the above but not excesive with the crank weights? Just don't want to regret doing any performance mods whilst my engine and bits and bobs are with serdi.???

sorry for all the questions but I'm loving the answers as it's setting me up for everything I need for this rebuild That I've been struggling to find out what's best

Atb

Daniel

Dan,

The standard crank from memory is around 28kg? and the Steel flywheel 7kg

I had nearly 3kg taken off a 951 Crank (Knife edged) and also installed a 2.7kg Aluminium Flywheel,

All part of an American (Sourced & Tuned) 2707cc Engine 3.0 Block honed, 2.5 Rebuild and gas flowed cylinder head, Californian Camshaft,

and with lighter Forged Wossner Pistons , Rods, and lighter Balance shafts.

The end result is a total loss around 8kg all these spinning parts!

This in combination was a dramatic decrease in vehicle weight (250kg) and unsprung weight (Wheels & Brakes 10kg)

Has made a Massive difference to the way the engine RPM increases (whips up) and decreases slows quicker with less inertia

that the very heavy stock crank usually provides for excellent Motorway cruising

I think if you machine off a Kilo from the Flywheel you'll not notice any difference whatsoever ! also to remove weight from

the crank is not a cheap job (done by experts), the Knife edging alone cost nearly £800 ! But it was done by Lindsey Racing who have decades of experience

and success with Racing and modified Road Engines.

Pretty pictures available here: http://924srr27l.co.uk/engine/

I've picked up on two things you've mentioned;

"I've been struggling to find out what's best" & "I've no intention of tracking the car ever, it's purely for my pleasure on the road"

I think the question has almost been answered?

Leave the crank & flywheel and get it up an running, save your money or put it on the cosmetics..?

It sounds like your going for a wide boy slammed and Rimmed machine and not something you'll be visiting Brands Hatch

or Santa pod with ?

Roger

 

[PSH]

Hi roger

Engine braking is just that, letting the engine brake the car alone, rather than use the brakes, doing this from high speed or high rpm puts much more stress into the engine especially the crank and rods, this can cause a rod bolt to shear.

This has nothing to do with the wrist pin though, I was giving two examples of what can make a rod throw. A stretched rod bolt that gives way and a seized wrist pin, these are but two reasons. If a wrist pin alone seizes (nothing to do with engine braking)the next part most likely to give is a rod bolt due to said seized pin.

I probably haven't explained that very well, hopefully, you can understand part of my ramble.

regards

Pete

 

[924Srr27l]

Hi roger

Engine braking is just that, letting the engine brake the car alone, rather than use the brakes, doing this from high speed or high rpm puts much more stress into the engine especially the crank and rods, this can cause a rod bolt to shear.

regards

Pete

Oh you mean by changing down a gear too early and increasing the RPM ?

Whilst we on the subject of lighter cranks, Flywheels etc... That link you quoted on "Rotating mass" is quite confusing, contradictive and from someone with other interests in Antennas and receivers ?

Here is the real rule of how this works.... If we are spinning up a very large diameter mass, or a very heavy mass, and we do it rapidly, we sacrifice a lot of available power.

So in the case of accelerating a car with a Heavy Crank, it uses a lot Engine power to move it and get it rotating,

And if this Heavy object is lighter it can be turned quicker, which means in this case the car can and will accelerate quicker.

How quickly and often a rotating mass speeds up or slows down. Every time it is forced to speed up or slow down, it takes or releases energy

So in the case of a car with gears changing up the gearbox quickly a lighter crank will achieve a faster time from point A to B.

Now the bits this article quotes in relation to stored energy I totally understand, like one of those HUGE Container ships, that (Take ages to get going up to cruising speed) they also take ages to slow down coming into port! Such is the huge amount of Energy and (momentum) it literally drifts along for miles...

The opposite of this is what I now experience with not a little, but a BIG decrease in spinning weight (7 - 8kg)

which simply is a big deceleration when I lift off! Lots of Engine braking, no inertia because the weight has been reduced, it now has in my case much LESS Energy stored as this linked article describes.

But the acceleration is heading more towards a Motorcycle, as is the way it changes gear all much faster than the stock set up, this alone makes for a quick car. I'm very fussy and like my luxuries and there really is no downside to this for a performance car I had or can see so far after 2000 miles...

However the HUGE quarter of a ton vehicle weight loss has benefitted the engine's spinning parts being lighter has also the less unsprung weight, all of it together feels so easy to pull away from the lights with no difficulties and nothing but ease to pull away effortlessly and accelerate with great gusto and response from a Normally aspirated engine.

I can understand a 400+ bhp 944 turbo 400+ kg more heavy car on heavy 18" Wide ass rims etc...could have an issue

with lightened engine spinning components needed to get it off the line...

R

 

[Dan944t]

Thanks to Peter and roger ,

i just wrote a huge huge message to you both then just as I was about to send my phone died and on tuning back on found that it has wiped out everything that I wrote so I will keep it short.

Ive taken all advice on board and have decided to leave crank weight but as I'm refacing my flywheel I am still going to get serdi to take it down to around the 24 mark, as if I don't, I know I will regret it.

I will indeed concentrate now on my parts i arts I need to order and get my new clutch ordered so I can get serdi to balance everything together.

one thing I do need help with is would any of you know what's a good aftermarket con rod, how much am I looking at and is there any available in this country that are reasonable? I did call arrow about them but the prices were eye watering. I do want to buy some as my numbers are all miss matched and I would like the piece of mind that they are new items after all this work.

Alb

Daniel

 

[PSH]

well, we clearly have different ideas of what's best, that's fine, everyone has their own opinion..some of what you say backs up why it's not wise to reduce the weight of crank and flywheel, there are other things more important.Now your description of the engine braking hard when lifting off is exactly what i was trying to describe to you when talking of 'bucking'. Not so bad on a box with close ratios but the 944 especially the turbo isn't that close and thus gear changes unless very, very quick will not be smooth and probably slow you down, certainly not speed you up and will not be very nice for a road car.

The link I gave was just the first that came up tonight when searching for crank and rotating mass to try and explain things rather than have to spend hours 1: trying to figure it all out again and 2: writing it all down , plus some of the calculations are over my head these days, i leave my son to such things now, there are plenty more links out there.

As for your last comment, I doubt if you've saved over 300kg off a 924s which btw in standard trim is only 85 kg less than an 86 951. Yes, I have 400+, no i don't have heavy 18" wheels, as I stated elsewhere, bigger heavier wheels slow you down and far more than the difference between a lightened or non-lightened crank due to it's rotating mass being very close to centre, unlike big wheels with a large radius of mass which are big no,no's for acceleration.

For example the race cars in the Porsche Michelin cup back in the 90's struggled to loose much more than 300kg, this was after literally everything was stripped from the car, including all sound deadening which actually weighs an awful lot, nothing left, no carpet, no seats, trim, panels and I believe glass too...the best they could do was hitting the 1000kg (later models) mark and that wasn't easy I'm told.

MarkK of this forum could answer better, Andrew Sweetenham again of this forum but not very active these days could most certainly give accurate figures as he was racing a 951 during this period and I followed him to some races over a number of seasons, those were fun days....

I have no doubt that you have done a great job on your car, but you can't compare an N/A car even when lightened to a turbocharged car of similar size, they are different animals and believe me a standard turbo will probably embarrass you without trying too hard on the open road, I accept that tight twisty roads are a different matter, as i say they are very different animals, even us old heavy ones....

Pete