Piston & Rod upgrade or not?

[PSH]

Hi Dan...

I didn't look much into aftermarket rods, knowing that I already had good cast rods in the early 86 car, being are well known for their extra strength. Others may be able to help more with this although I do believe that most if not all come from the USA. Going back to the clutch be sure to get the right one, I can't remember the details but I do recall that I found two versions, it may just have been the earlier 6 small inner springs versus the 4 large springs but that's all that i can remember now, I think the 6 spring one also has 4 larger springs around it so it's confusing... you should be able to tell by the price, one being a lot dearer than the other, or course you want the dear one... I do recall that the same clutch was also listed for the 930 (early 911 Turbo) and I believe the 968 RS turbo too, it may be a little bigger in radius although still fits the 944 flywheel. I only wish that my memory was better...lol

Pete

 

[Dan944t]

Thanks allot Pete, I think the one they sell on Ebay is the one you describe or at least I hope so it's around £500 but I will have to look into it ? I know it shows 4 large springs in the photo but doesn't say wether it's the uprated version at all in the discription.

would you advise I go for Porsche shells aposed to glyco which is what I was going for but only becuase that's what LR sell also.

I sure can't wait to drive my car again mate it's been nearly two years since the bore cracked and put her off the road!

Daniel

 

[PSH]

yes to original Porsche shells, i did look at glyco myself but had read of some problems so decided to play safe, iirc John sourced some of my shells for me. If you need undersized shells, that is if the crank needs to be ground, these are a lot more expensive and i think only available from Germany. they are not always available so look into this sooner rather than later.

Although I have a number of LR items on my car I'm not a great fan these days and have had problems with some items which IMHO was down to bad engineering practices, they have had a number of publicised engines fail in recent years too so beware, my son is a definite anti LR person so I have that to deal with as well... I had a quick look at sachs and from what I can tell the 930 clutch does indeed fit the 944T, it's the same part number so you can use that as a guide, btw Sachs do a number of higher performance clutch plates if you're worried at all, they do both solid plates and paddles for extra torque, can't really say what the driving experience is, though, my son's paddle clutch wasn't a Sachs item.

Pete

 

[Dan944t]

Thanks for the great advice Pete, you really have helped me allot in only a few days and I'm truly grateful, this has been something I've left and left as the decisions seemed to be endless and all I had until now was American forums to go on as all my serches Came up with people from reinlist ect, so I was always a bit unsure as we all know they more times then not go to town with pretty much everything, so didn't think some of there answers would be right for what I needed.

I shalll keep reading your building thread as it will be very helpful when I start putting mine together and has inspired me to get my arse in gear as up to know it wasn't the effort that was daunting for me, as I'm hands on and not scared of anything but more was unsure of the right parts I needed for my needs.

im sure there's a few other things I'd like to pick you brain on but for now I think I'll give you a break.

many thanks for all your time!

atb

Daniel

 

[924Srr27l]

PSH well, we clearly have different ideas of what's best, that's fine, everyone has their own opinion..

Yes but a lightweight crank spins up quicker and makes a car faster accelerating is a fact not an Opinion.

If you fitted a stock fly and a lightweight one on the same car and did (3) 1/4 mile tests each time the fastest would be the car with the lighter flywheel.

PSH 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

Why is it not wise? and what's more important in having a quicker car unless this is not the objective?

'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, Now your description of the engine braking hard when lifting off is exactly what i was trying to describe

I have no idea here what you mean, bucking? & Braking hard? The engine does not Brake HARD, it just decelerates at a quicker rate than it did on the other 7 Transaxles (Inc 968) I've owned which all had stock heavy flywheels.

As for your last comment, I doubt if you've saved over 300kg off a 924s

Most weights quoted are Curb weights with no fluids, this can add nearly 100kg + Options even more electric seats, aircon, power steering etc...

My car had none of these and started life on a local weighbridge at 1260kg, when the car was corner weighted each corner was just over 250kg, the total 1010kg (Very little fuel and no driver) so the total loss was 250kg not 300kg??

My 968 was over 1400kg on the same weighbridge, so compared to this and some standard 952's with all the trimmings it will be 300+kg less

which is why the power to weight figure is better than any stock transaxle 924 / 944 & 968

(except the rare 968 Turbo)

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

Of course I can compare it's the same chassis / car, and of course any Turbo and N/A car behaves differently but many a time the pick of the crop is regarded as the 3.0 S2 944 because the turbo is so much more difficult to drive.

I'm keen to drive a stock S2 or 952 just to see how heavy and sluggish both of them are...

I did 80+ laps today at Oulton Park, amongst many powerful Porsches with hundreds of Horsepower...GT3 RS's , GT4's etc, the 924 performed well and ran faultlessly and only I needed 3rd and 4th gear around the whole lap. Many cars had twice or more the power but the difference speeds on the straights were not reflective of this huge advantage or was it embarrassed at all quite the reverse. It was a shame there was no other transaxles there apart from a 928 to see how they went but an old stock 952 would not embarrass a 968 on the road without trying too hard not to mention my 924S either.



R

 

[PSH]

You're not hearing what I'm saying, or perhaps I'm not explaining it very well which is very possible. I'm not saying that a lightened crank isn't quicker off the mark, it is, well as long as all other parts attached to it are, but it loses stored energy and for a road car this is not good. I except that yours is a lightweight chassis but we are not talking sprint cars here. We are talking daily drivers that remain weight wise as Porsche intended. The last thing you want/need for such a car is lightened engine internals, not unless you like stalling or thrashing the thing between each and every gear change to smooth out the ride and more importantly doing rebuilds on a regular basis. You need that rotating mass for such a car, you most certainly don't want the stress that's put through the system each time you lift off the throttle, you are then braking a heavy vehicle with weakened internals, not a good idea. As i said although evidently not very well, we are talking two completely different animals here, you are talking a purpose built lightweight, that's fine I hear what you are saying, I am talking a modified car retaining it's original weight, add turbo and long gears and it should be obvious what I'm trying to get across?

At the end of the day, it's all about driveability, hope this clears things up a little, if not I give up....

Pete

 

[924Srr27l]

PSH I'm not saying that a lightened crank isn't quicker off the mark, it is

Excellent, that's my point confirmed.

or perhaps I'm not explaining it very well which is very possible

maybe,

but it loses stored energy and for a road car this is not good

If the car decelerating when you lift off is this the only drawback for you (less fuel economy),

then yes it's not for you but you're missing out on faster acceleration !

...not unless you like stalling or thrashing the thing between each and every gear change to smooth out the ride and more importantly doing rebuilds on a regular basis.

As I've attempted to inform you, my car has no issues with the several words and descriptions you keep declaring?

- Stalling

- Bucking

- Thrashing between each gear?? etc..

- Smooth out the ride what's this?

I have a feeling you've been absorbing too much (corrupt) internet forum gossip, which many other people pick up and digest as gospel!.... talking of which I'm not a fan of people slagging companies on forums etc... despite what you've experienced. I know many fiends that have used lindsey Racing's expertise and customer service, I also have had nothing but 100% from them over 3+ years and my current build has (so far) been 100% and also produced a very high set of power figures.

At the end of the day, it's all about driveability, hope this clears things up a little, if not I give up....

I'd strongly suggest you (or anyone) if you have the chance to visit North wales to see what a joy and how easy this car drives sat alongside me, there's no question whatsoever that if ever a car was to be described as really driveable it is this 2.7 Normally aspirated lightweight car. Sprint or long distance, shopping or a trackday it does it all very well.

It will pull from 20mph in 3rd gear very nicely, from 80mph in 5th also strong...there's nothing but an instant surge

(No lag) from anywhere from 1000 to 6000rpm. It certainly does not need revving the nuts off it at all to move along at a brisk pace. It isn't however a whoosh and shove in the back feel (like a turbo car) which many people like to have. Others like myself prefer no assistance but instant throttle response when it's ordered and not with any delay or when it arrives a big surge this is what I call "NOT good driveability" which as I've mentioned before the 944 3.0S2 is often talked about as being the best all round road car compared to the peaky turbo.

R

 

[slickv8]

quick update - I've decided to lighten [skim] my existing flywheel as a 'best of both worlds' solution. Theres no real science behind it, more taking the middle ground between the stock and full-on lightened aluminium opinions. Its now 5.3kg - down from stock 6.8kg so we've taken a bag and half of sugar out of it. I'm hoping that'll leave me with some on-road manners while giving the engine a chance to spin up a little more freely too.

Received a new Sachs clutch kit today so all being balanced tmrw before refitting the engine early next week.

 

[blade7]

Going back to crank scrapers I checked the 2.7 sump I've got and it's got a turbo oil return port, a crank scraper on the plastic baffle and also a scraper cast in to the bottom of the sump.

 

[924Srr27l]

quick update - I've decided to lighten [skim] my existing flywheel as a 'best of both worlds' solution. Theres no real science behind it, more taking the middle ground between the stock and full-on lightened aluminium opinions. Its now 5.3kg - down from stock 6.8kg so we've taken a bag and half of sugar out of it. I'm hoping that'll leave me with some on-road manners while giving the engine a chance to spin up a little more freely too.

Received a new Sachs clutch kit today so all being balanced tmrw before refitting the engine early next week.

I'll predict you'll notice no difference at all, the crank is so heavy (24.5kg) with your original flywheel @ 6.8kg this totals 31.3kg

Your 1.5kg reduction to 29.8kg equates to a 4.8% loss.

I took off 30% (9.5kg) off the Crank / Flywheel / Pistons & Rods & Balance Shafts, which has made a Big difference

to the speed the RPM Increases, also helped with 250kg less Vehicle mass to move.

(Block / crank / Alternator / Inlet & Exhaust Manifold / Radiator & Fan / Flywheel / Pistons & rods / timing Pulley /

balance Shafts / Airbox / Alternator & bracket / Washer bottle / Header tank / Water & Antifreeze)

All of the above were lightened or replaced, the total reduction was 42kg.

R

 

[u63af]

Surely the position of where the mass is removed from will have an influence upon the effect? If say 2kg from the outer of the flywheel is removed then this will have a greater effect than say 2kg from the crankshaft as the mass has been removed from an area further away from the rotational point? maybe I am wrong.

 

[PSH]

Surely the position of where the mass is removed from will have an influence upon the effect? If say 2kg from the outer of the flywheel is removed then this will have a greater effect than say 2kg from the crankshaft as the mass has been removed from an area further away from the rotational point? maybe I am wrong.

you are not wrong sir...

Pete

 

[924Srr27l]

Surely the position of where the mass is removed from will have an influence upon the effect? If say 2kg from the outer of the flywheel is removed then this will have a greater effect than say 2kg from the crankshaft as the mass has been removed from an area further away from the rotational point? maybe I am wrong.

Yeah Makes sense to me, which is why the Knife Edged Crank work removed metal from the top of the Counter Weights,

R

 

[924Srr27l]

You can't really reduce the diameter of a Flywheel though to get the weight more to the centre point, as it has to have the Pegs for

the DME triggers..

The theory would also work though with lighter pistons bobbing up and down at 100 times per second at 6000rpm

Heavier ones will take more effort to push up and down..

Only (1) Weight Balance shafts fitted.

R

 

[u63af]

understand the knife edging but the other benefit of that is less resistance by cutting through the oil in the sump more efficiently which is better but not specifically due to weight. all I was meaning was that if say you drilled holes in the crank to lose say 2kg of mass then you would not notice as big an effect as say losing 2kg from the outer of the of the flywheel. to be fair when I rebuild my turbo engine, I will get crank lightened and knife edged together with a fidanza alloy flywheel, but then the whole dilema of putting the 3.0 crank in to either make a 2.8 or overbore and make a 3.0. I think if I was going down the line of pistons and rods non it makes sense to just chuck the 3.0 crank in and make a 2.8. Thts my issue with doing a re build and at this stage the car works perfectly so am trying to stop my horrible problem with spending £££££ on these old cars... Ha

 

[924Srr27l]

understand the knife edging but the other benefit of that is less resistance by cutting through the oil in the sump more efficiently which is better but not specifically due to weight. all I was meaning was that if say you drilled holes in the crank to lose say 2kg of mass then you would not notice as big an effect as say losing 2kg from the outer of the of the flywheel. to be fair when I rebuild my turbo engine, I will get crank lightened and knife edged together with a fidanza alloy flywheel, but then the whole dilema of putting the 3.0 crank in to either make a 2.8 or overbore and make a 3.0. I think if I was going down the line of pistons and rods non it makes sense to just chuck the 3.0 crank in and make a 2.8. Thts my issue with doing a re build and at this stage the car works perfectly so am trying to stop my horrible problem with spending £££££ on these old cars... Ha

Yes there are a few configurations with the different cranks, blocks and heads but pretty much always one common denominator ! The Costs!

I was set for a 2.5 Litre Engine, but the block the Yankies had lined up for me under closer inspection turned out to be more worn than they had thought.

I'd already sent them a 2.5 N/A Cylinder head for Stage II porting, so I was left with having to use my old engine which was not my plan.

The old 150bhp 924S engine worked great, but I wanted to fit another complete modified unit, so I asked a silly question: Can you fit a 2.5 head on a 3.0 Block?

As they had told me they had good 3.0 blocks in stock.

The 3.0 Block is 4kg lighter than the 2.5 and the Windage ports are better designed and give more power.

I didn't want to go down the route of Boring and Sleeving a block.

Yes was the answer, they modify the water passage on the 2.5 cylinder head and the once the Piston sizes were measured and ordered

they said the actual capacity was 2707cc with a 10: 9: 1 CR

So that sounded good with me and hence I went with this solution. So my crank is a genuine 951 Crank

fitted to a 1990 3.0S2 Block, then 968 Rods and new Wossner pistons.

The lightweight internals seem to suit the shorter 2.5 stroke, and I wonder if a longer stroke and another 283cc with a 3.0 Crank

would of made it more lazy had I of gone for a 3.0 8v?

It was an unusual cocktail ! but I was being guided by many professional and experienced Racing Engineers and builders so I went with it, and I'm very

pleased it not only produced higher powers figures than seen before but it also runs like a dream.

I'd say it was money well spent having the crank & Fly balanced as also the rods and pistons blueprinted etc...

I'm running Porsche Rubber OE Mounts and there is no vibrations whatsoever at any RPM, even with the "half" hearted balance shafts.

Generally you get what you pay for which can be scary but if your going to do some serious tuning right, don't skimp or half do it I've learnt is the best way.

R

 

[blade7]

understand the knife edging

Don't do it...

 

[924Srr27l]

Surely the position of where the mass is removed from will have an influence upon the effect? If say 2kg from the outer of the flywheel is removed then this will have a greater effect than say 2kg from the crankshaft as the mass has been removed from an area further away from the rotational point? maybe I am wrong.

I'm thinking the shape of any mass doesn't matter when moving it, but it does have an effect when slowing it down?

So a solid 1" tube in a lathe weighing 10kg v a 4" diameter (Hollow) tube also weighing 10kg they will both require exactly the same Torque to move

them from static.

However the larger diameter tube will have more inertia? and take longer to slow down.

Or are you thinking the bigger diameter tube will be harder to speed up because it has more mass further away from the centre?

R

 

[924Srr27l]

understand the knife edging

Don't do it...

If you have a lot of Hills in you area ? a heavy fly will assist you get up them.

But if you want to accelerate Faster you want more power to be available quicker than a heavier stock fly.

The heavy wheel located between the engine and the gearbox builds up rotational force with speed and momentum.

Effectively storing the energy and helping the car resist changes in engine speed - good for cruising at a steady speed but bad when you need a fast engine response.

Drawbacks – it takes more effort to get the wheel rotating and stops the engines revs increasing or slowing down quickly.

A lighter wheel takes strain off the engine and allows the engine to rev more freely, as a bonus as there is less weight the engine is able to release more power.

You’ll notice a race-tuned engine increases and decreases revs a lot more quickly than a standard engine.

The big downside to a lighter flywheel is that engine momentum or inertial spin is reduced – most noticeably on a hill.

The weight and size of the flywheel depend upon the nature of variation of torque required. In the case of a heavy flywheel, it is hard to change the rotational speed of the engine. As it takes a moment to accelerate the heavy flywheel, the rotational speed of the engine does not rapidly increase even when the accelerator pedal is depressed.

The responsiveness of the engine declines with an increase in weight of the flywheel.

R

 

[blade7]

I was referring to the crankshaft.