Chip, having read the thread through, the above intrigued me.
I always thought (probably in ignorance) that forged pistons were preferable to cast. Could you help me get my head round your statement?

Top thread by the way

 

just bought a set of group a cossie pistons,7.2 cr,with valve cut outs,the only reason i never bought mahls was that i would have to get them machined down to that cr and valve cut outs machined in to them,making the final cost about the same as a set from cosworth


cheeRS stu

 

Rod....as you may be aware i am not a one person kinda person...i ask everyone and THEN decide myself..TRUE DIY

I am NOT a Madette sorry Rodney I am IMA Racing

 

Phil
MAD can & has
IMA Racing aint & wont
Remember that Phil when you get a bit cocky.
Rod

 

Rodney...i aint planning on beating anyone If it does 170mph i will be happy BUT if it has the power then there is no reason why it wont go 185mph plus

Learn one thing Rod...i am not competative in the slightest...if i was i'd be taking your title

 

I don't think this thread is forged vs. cast, it's rather Mahle vs. Cosworth. All technical data about cosworth engines I always read said (Mahle forged pistons).

 

phil your keep lowering the bar!

stick to your target

 

he wont and cant...

in fact he'll never prove this engine.

All IMO based on phil's endless posts about EVERY engine he has built!

Alex

 

I know that
But Chip did make an interesting observation (as an aside), and I'd like to know why. I'm always hungry for knowlege. Sorry if it is a bit off topic

Chip?

 

Ryan...i aint lowering the engine spec...just trying to fit in more as the haters dont like anyone into there cars as much as me

 

Maybe not but youve just knocked 10mph of the top speed you were going for

 

Deano its called "dont brag" or the freaks come out with the bows to shoot you down...infact i am aiming for the RST record now only

 

yeah thats what i meant, i mean 170 mph

tiff nearly did that with 360+bhp, im using tiff as a example as his was time and the onyl one i could think of.

 

Ryan.......Tiffs is a mighty NMS car......and there is no way i can compete with the GOD of tuning....its not possible... Infact has Karl ever been a carpenter?

 

ok well im sure there are loads of 400bhp 3dr& saph that have acheived 165+mph down brunters.

 

In theory with just 480bhp i should acheive 185plus...as according to popular belief the 3 cossies aint that far from each other ref aerodynamics

Remember Bruce ran 194 odd mph with approx 580bhp including gas..BUT he ran the full RS500 downforce pack...i will not be .....and hopefully running around 650bhp+ genuine....i say 150mph before it explodes

 

bttt on the subject of mahle V cosworth

 

.....and forged v cast

 

I don't think there are any YB cast pistons...

 

What about the AE ones you can get, and see cheap occasionally?

 

Bernie, in essence there are only a couple of issues of any real significance both caused by the same issue.

The issue is the grain size of the alloy material. In forged pistons the grain boundaries are much closer than in a cast alloy.

This gives rise to the first issue, expansion with heat - close grain boundaries result in a higher expansion rate with heat in comparison to a cast material. This requires bore clearances to be optimised for the piston expansion.

The second issue is thus strength. Any material with closer grain boundaries will be a stronger material. however this is where people often get confused.

In reality if a piston is going to fail through poor mapping (i.e. running lean, heavy det etc) then it will fail no matter whether forged or cast. However where a forged piston is of great help is when we have to consider loadings and fatigue nearer to the pistons physical strength. This is primarily in relation to the piston ring lands where a lot of force is exerted on a piston, and in more severe loadings the gudgeon pin bosses inside the piston. In both these examples a forged piston will survive considerably more stress before cracking occurs and hence is why its always the norm in most competition and high stress engines.

 

Dunno - I always thought there are only Mahles and various uprated ones...

 

May I also add that we can consider high pressure die cast pistons to have closer grain boundaries and hence has properties similar to a forged piston.

 

This had always been my thinking Karl.
However, Chip said on a previous page that in some circumstances, cast was preferable to forged.
This aroused my curiosity....

Nice to meet you the other day, by the way

 

Chip?

 

After 5 years.... What is your advice now for 380bhp road YB, std mahle or forged(for example CP pistons)?

 

WTF!!!!!

Why bring up an old thread?? Why not just ask the question in a new thread?!?!?!?!?!

 

Why not in this one? jog alot of peoples minds reading the old post's.....

 

Because if I start new one, you can say "use search.." )))

 

How are Pistons noisy - what sort of noise do they make?

 

Sorry for the late reply didnt notice your question first time around!

The advantage of cast pistons is (as per Karl's reply) that they expand less, so you can run a tighter piston to bore clearance safely than you can on a forged piston, which is better for high milage use.

Basically for out and out strength, forged are the way to go, for a moderately strong piston that will last a lot longer in general use, cast is king.


Regards


Chip

 

chip ya twat................i've been waiting for this................all my life.......