Forged pistons [Archive] - SaabCentral Forums

: Forged pistons


Janne Selinummi
14th March 2002, 06:33 PM
A guy at a Finnish performance bulletin board claimed that the forged Mahle pistons
(as used in all Saab Turbo models) are not reliable when running more than 1 bar boost.
He said that at that kind of boost level, the pistons wouldn't last very long.

Is that completely bull$hit? I mean, not all you people driving around those heavily modded c900s have some custom racing pistons, or...????

Can I use my T8 APC pistons to run 1.4 bar of boost?

Fan-TC
15th March 2002, 04:29 AM
Well i have never experienced any inherrant weaknesses with the Saab Spec pistons (unless you allow detonation).

One excellent Mod i once saw was a 2.0L 9000 turbo motor that had been stripped and rebuilt with stock low K's rods and crank and used very early model low compression pistons (bout 7:1 with 16v head i think). This was then put back into the 9000 (cause of its strong gearbox) and was fitted with a turbo from an early 930 Turbo porsche and 9000 IC (2bar Boost).
I never rode in the car but with the aftermarket engine management it ran beautifully, although slightly laggy.
It ran a high 12 quarter mile on slicks (owner disapointed) before it was destroyed by a big tree.

However these were Second Hand Saab Spec pistons suporting 2bar (400hp+) without breakage.

Eric van Spelde
15th March 2002, 02:01 PM
Yes, this is complete bullsh*t. Apart from unlikely and unfortunate coincidences that mostly involve a complete drainage of engine oil, the only likely way you'll break a stock Mahle piston on a Saab is allowing your engine to knock.

Alanb
17th March 2002, 10:33 AM
Didn't Raul destroy his pistons (or was it bent rods?) by running at 30psi?

In my experience these pistons can take a hell of a lot so long as knock is kept at bay.
Alanb

Eric van Spelde
17th March 2002, 11:01 AM
Well, IIRC the reason he got to 30 psi in the first place was him removing the APC system...

Smackrazor
17th March 2002, 11:05 AM
And secondly his car was completely unmodded besides that :smile:

Matthew
30th June 2004, 10:23 AM
What is the weight difference between a cast and forged pistons? Assume they're for the same application.

Alex
30th June 2004, 11:57 AM
Not sure what the weight differences are but on the Mk1 Impreza the WRX used cast and had a 7000rpm limit the WRX STi used forged and had an 8000rpm max.

nutcase
30th June 2004, 12:21 PM
All I know is an equivalent forged item will be heavier than the cast version.

Alex
30th June 2004, 01:32 PM
But due to the superior material properties available when forging something, less material thickness needs to be used so the item can be made lighter.

4saabstoomany
30th June 2004, 01:56 PM
those after market forged pistons are a pain anyway. Don' you have have to let your car warm up a while to let the pistons expand so they don't jar around in teh cylinder? or something.

nutcase
30th June 2004, 01:59 PM
I'm not doing very well today! Just nosed through my A series books and you're right. I got it the wrong way round again!

4saabstoomany
2nd July 2004, 10:44 AM
we'll let it slide today nutcase;)

so whats the verdict? are they worth the hassle?

ejenner
2nd July 2004, 04:54 PM
I was looking at a site yesterday http://www.thedodgegarage.com/the_reliant.html where a guy had decided to wrench some extra performance out of some really ugly (IMO) American car. He was using the thing for drag racing and it explains how he managed to melt a piston.

http://www.thedodgegarage.com/reliant/reliant_23.jpg

He explains that this happened because he fitted a new intercooler which allowed lots of air into the system and effectively reduced the octane in the fuel. These pistons were stock cast pistons and not forged. He was running 21-30 psi with extra injectors which was getting him 12.6 @ 108mph over the 1/4 mile. He replaced with forged pistons and managed to get his time down to 10.5 @ 130 mph. This required lots of mods tho... It was an interesting read.

rally900
5th July 2004, 04:37 PM
A guy at a Finnish performance bulletin board claimed that the forged Mahle pistons
(as used in all Saab Turbo models) are not reliable when running more than 1 bar boost.
He said that at that kind of boost level, the pistons wouldn't last very long.

Is that completely bull$hit? I mean, not all you people driving around those heavily modded c900s have some custom racing pistons, or...????

Can I use my T8 APC pistons to run 1.4 bar of boost?


I don't want to burst your bubbles here guys but...

...all stock saab pistons, turbo or otherwise, are CAST not forged. However i have never had any problems running up to 18-20 psi and even ran one engine at 22-25psi for 100,000 miles before the bottom end started getting soft (rings, and the bottom end had 250k at that point).

However I have heard many instances of piston melt from running high boost with improperly tuned engines. But yeah, forged pistons are worth it. and you don't have to go aftermarket- there are a number of stock cars that came with forged pistons from the factory. the escort cosworth for one. and yes, the pistons fit, with just a touch of machine work.

james
team saabworks

ejenner
5th July 2004, 04:42 PM
Everyone on here believes the pistons from the Turbo cars are forged. How do you know they aren't?

I only think they are because so many people mention it so often..

Matthew
5th July 2004, 05:01 PM
The stock pistons are most definitely cast. Every authorititive source on the subject has stated clearly that to be the case.

For the 0.8bar boost that a stock T16 uses, forged pistons simply aren't required.

nutcase
5th July 2004, 05:32 PM
I thought the rumour was the 99T pistons were forged? Of which I have no idea about. The manual lists teh dish depth and diaemter, but just has a - for weight (the others are listed).

rally900
6th July 2004, 10:55 AM
Everyone on here believes the pistons from the Turbo cars are forged. How do you know they aren't?

I only think they are because so many people mention it so often..

When ordering replacement Mahle pistons all 99/900 applications are spec'd with cast pistons. As was pointed out, the stock boost levels do not warrant using a forged piece. The factory specs also list cast pistons as the only option for pistons.

james
team saabworks

aeroman
6th July 2004, 11:41 AM
I broke an engine because of detonation, the car was a 900 turbo 16 with just a 3.3fpr and a mbc (so the apc was disconected) the pressure of the turbo was about 1.25bar, I broke this engine at 220 km/h, I used to drive this car as a crazy guy. When I think about it I think that the pistons of the 900 are very strong!!

now my car is running with still the MBC and a very high boost pressure (1.5bar) but with lots of others mods to prevent detonation:

air/water intercooler
aquamist water injection and 1mm injectors
27lb/h injectors
3.3fpr
2.3 head cylinder

Now no problems and I am still runing it so hard!!

4saabstoomany
7th July 2004, 02:32 PM
someday i'll havemomney to finish my car and be able to drive it like a mad man!
untill then.. college :(

Saab-Daniel
7th July 2004, 03:10 PM
Hehe, same here, but isn't that why they have loans 8)
Just kidding, want to go crazy when I get a job after education...
Daniel.

900 spg
8th July 2004, 07:05 PM
Hello to everyone,
just to add to the confusion. Does this mean that in principle all pistons, rings and crankshaft (and other parts) are all the same for all 900 engines ( 8v, 8v turbos, n/a, 16 v n/a, 16 valve turbo) ?

I am asking as I have a nice clean 900 n/a engine sitting around. I got the car as a spare parts car as the body is quite bad.

Best regards

Dusan

El_Raul_Turbo_Freak
8th July 2004, 10:39 PM
All saab pistons are CAST aluminum MAHLE mad pistons with heat espantion stoppers inside the piston. These pistons are awsome but they are heavy. They will hold good until you detonate. Detonation will crack the piston as it did on my car.

forged pistons are garbage, they will make noise when cold.

rally900
8th July 2004, 11:49 PM
Hello to everyone,
just to add to the confusion. Does this mean that in principle all pistons, rings and crankshaft (and other parts) are all the same for all 900 engines ( 8v, 8v turbos, n/a, 16 v n/a, 16 valve turbo) ?

I am asking as I have a nice clean 900 n/a engine sitting around. I got the car as a spare parts car as the body is quite bad.


not quite: they have different compression ratios due to different shape of the top of the piston.


and raul, improperly fitted or poor quality aftermarket forged pistons will make noise when it's cold. Good forged pistons won't. it all has to do with forged metal heat expanding more than cast metal. cast pistons contain as much as 25% silicone to reduce heat expansion, however newer forging techniques (using nickel to allow more silicone in forged metals) have pretty much eliminated this problem. if the metalurgist forged them right they won't heat expand significantly more than cast.

james
team saabworks

900 spg
9th July 2004, 05:03 AM
Hey James,

Thanks. But the connectiong rods and crankshafts and crankshaft bearings are the same, right?

I know that the tops of the pistons are different as there are suggestions to use pre APC pistons when modding your engine and to use a 2.1 L head as well.

Best regards

Dusan

Matthew
9th July 2004, 05:03 AM
Does this mean that in principle all pistons, rings and crankshaft (and other parts) are all the same for all 900 engines ( 8v, 8v turbos, n/a, 16 v n/a, 16 valve turbo)?
I have been led to believe that the pistons are different between turbo and non-turbo cars (EPC confirms this). Also according to the EPC, the valves, springs and washers, crankshaft and piston rings are all the same.