my mate took his yb to mountune a few years ago,the engine had brand new

cosworth pistons in it,but mountune took them out and fitted mahle's.

reason dave gave was that the cossie pistons were a high expansion piston

and therefore had to be set up with alot more piston to bore clearance,

whereas the mahle's could be set up a lot tighter,about one and a half thou'.

I,ve got mountune mahle's in mine,dyno'd@ 500bhp at harveys,no probs.

puddy

 

BTTT for a good topic

 

I'm looking forward to further input on this! Come on folks lets here your best ideas!!

 

would you not want a high power unit built "loosely" anyway?

 

What about your input?



After this topic I don't know which ones I would like to buy :-(

 

Oh come on Karl.......tell tell...........please put us out of our misery NOW

 

Well Doug, before I say anything I'd like to here from the source, why they think Mahles are better?

 

doubt cossie are the same but i have forged pistons (all be it accralites) in my car which are similar to the cosworth ones...As i understand it the only reason anyone would think forged/race pistons are worse than mahle is because they have a cental gudeon pin.. and 'rattle' when cold due to it taking time for the material to expand... this is going to cause more bore wear etc..
which means the engine is gonna need a re-build more often.
BUT who the fuck thinks a BIG power cossie or RST engine is gonna last forever anyway... even with 12000 of HARD use i expect the engine would be tired

 

But Phil (IMA) may not be on-line for days........rumour has it he's
building the worlds first "Internet YB Engine"

 

Oh the suspense............come on do tell

 

We may actaully have a good topic here for a change. I have no idea what piston is better out of the 2 so i am happy to wait for the debate to begin.

 

I know Karl uses Cosworth pistons in his engines

Bruce Read did 191mph using Mahles on the other hand. Strength is a bit of a strange one, if it is detting enough to damage Mahles then the Cosworth pistons will probably last a fraction of a second longer anyway at high engine speeds...

From what I have seen of the Cosworth items they are a huge amount lighter which has to be a benefit of some sort.

What are the piston skirts like on the Cosworth items? This is a big contribution to the cold start rattle effect from what I have read...

 

Surprised to read above about mahle pistons only wanting 1.5 piston to bore clearance, im not a YB man historically, but on vauxhall turbo motors i would build them with 3 times that clearance, it doesnt sound like much room for expansion at all to me for a forged piston.

Normally the differences between race and road pistons are as much due to the ringland placing as anything else, its not a case of one being better than the other just more suitable for different applications, bit like forged versus cast, on a lot of applications cast are far better.

 

Anyone got a decent set of pictures of both pistons, as cant really guess on the reasons one are better than another without seeing them!

 

oops, double post *edit*

 

if you are worried about det then why just get the pistons ceramic coated along with the combustion chamber base of the valves ect.
but you are more than likely to blow the head gasket then.
f1 cars use that and without a doubt all the high powered cossies(500+) do as well.
some car manufacturers like seat already fit pistons like these to their models which can run at higher compression ratios for fuel economy.Hence seeing huge power cossies running cr's of over 9:1 so you get less lag and the car becomes more resposive.

 

chip, re bore clearance. don't forget that yb's have oil spray cooling on the pistons

 

ive got cossie pistons (pa1079 i think) 0.25mm and i was gob smacked at the clearance when dry building. had to measure them over and over to make sure everything was correct. you could rock the pistons in the bores (cant remember the clearance but might have been about 5 thou summit). i rang cosworth to check that the final honed size on the box was not a misprint. remeasured the boores again - all was ok they just got loads of clearance.

when you start the car from cold there clatter till warm but then they are fine.

come on Karl - whats the answer then

 

chip-3door,
forged pistons have greater co expansion than that of a cast piston so that is why you need greater clearences + vaxhall worked to tolerances of +-1.0mm
and ford+-0.005mm LOL

 

Mine were bought on Karls advice, and i'm very happy with them. They are rattly when cold, but when warm are fine. Not really convinced that there is really much more wear going on, especially as it's driven very gently until oil is at least 160F. I'm more worried about the stainless steel valve's chewing up the guides...

 

Vauxhall pistons are forged too mate, and there is no way on earth that vauxhall pistons are +/- 1mm, so i assume that you are joking there?

The ones in mine in fact vary in size by 0.0000" (didnt have anything accurate enough to measure any more accurately than the nearest tenth of a thou and they were all spot on to the nearest tenth)

Mind you mine are a one off set made by Aria.

Fair point about the under oil piston cooling, but still surprised to hear that people are running as little as 1.5 thou on a big power YB, that really doesnt seem enough room for expansion to me, oil cooling or not.

 

Chip as said before you are very knowledgable...just not on Cosworths...which is fair enuff as you are a Vauxhall person!

Please remember people Karl is very young with minmal actual experience mainly just theorys...the people i deal with are experienced which to me means a hell of a lot more...MY OPINION.

 

Phil listen to Julian and you will go along way If Julian theory's are so wrong why does he build for the best

 

hece the LOL bit
if your pistons vary by only 0.0000"that is only room temperature size! and i assume that you have taken into consideration the thermal co expansion figures at certain temp to come to the conclusion to run such big bore to piston clearances on the vaxhall motors.

 

By vary by 0.000 i didnt mean the expanision of one piston i meant that we measured all 4 pistons and they were (as far as to the nearest tength of a thou) all exactly the same size whilst they were at the same temperature as each other.

Phil, you're right im far more of a vauxhall man, but the LET and YB engines are amazingly similar (as you would expect as they were both designed by cossie), so it seems strange the numbers are so different.

 

How old am I Phil?

Rick, yes mate you're quite right stainless steel valves do cause valve guide wear issues. The real solution is to chrome plate the stems but sadly all the aftermarket stainless valves dont come with them. :-(

 

10?

 

sure my cossie pistons we put in with 4 thou clearance,
well thats what the box said

 

LOL, Do you think Simon Norris is too young that he knows fuck all as well?

 

That sounds FAR more like it.

Thats what i would use on a moderately powered LET engine, and about 6 thou on something like the one for my mini.


Certainly makes FAR more sense than the 1.5 thou that bosch_man etc are agreeing with and telling me that vauxhall engines are totoally different, they are both forged pistons and bore iron blocks so i cant believe the cossie ones should be that tight, hell i run more than that on A series mini engines with forged pistsons and thats on a poxy little 73.5mm bore!!!!

 

Simon has PROVED he knows his shit

Dont get me wrong you are very knowledgable just blinkered....imo...and base all your views on theory and not practise.....i just dont work like that!

 

Phil, I've built dozens of engines, mapped several hundred , produce dozens of ported heads each year, design my own engine compnents etc etc and been working on and tuning cars for over 10 years. In addition I do contract and consultancy work for many big OE firms. When it comes to practice I can assure you there's not much I have'nt done, and do actually do a lot more hands on than the majority of tuners. For example I've produced a number of one off chassis's for various race cars, as well as a couple of twin engined cars.


Your comments do insult me Phil, but I know from talking to you that you're an idiot so it comes of no suprise that you can be so ignorant.

 

Oh dear lol. If only u knew how many engines Karl has dynoed, fettled with, brought to the point of det, back again, on the dyno, on the road.... As Mr Duckworth himself said, development is a symptom ofbad design...

Karl - Can old valves be chrome plated? Ie, if i freshen my head up, can i get them done then?

Rick.

 

Karl - he's not actually an idiot - very bright in fact - he just knows how to play people and likes to see how far he can push people.

 

Rick,

I've actually been experimenting with a new type of guide (new material and machined finish), that we can replace yours with to freshen your head up. They're not cheap I'm affraid and will come in around £100 for the 8 guides, but they have proved to be very good. You can of course as you have suggested have your valves chrome plated. Give me a shout when you're ready.

 

Karl....so you call 10 years full experience?..Were you never an apprentice?...Or were you reading Haynes Manuals in the womb?


As for after speaking to me you thought i was an idiot...you are right Sir as after speaking to you i thought you knew stuff....funny how we can fool people aint it

Still i am going for the first idiot to 600bhp+ award...

 

TEN YEARS is a bloody long time IF you are pushing the limits all the time, you can learn loads in that time.

Its very much a law of diminishing returns with how many years you put in, you learn far less each year than you did the last one generally.

 

Phil you really do talk some complete shit sometimes.. do yourself a favour and think about what you say occasionally before making yourself look a complete tw@t..

 

Karl sounds good Be a while yet hopefully, as she runs like q well oiled machine should

 

Its my opinion.....after dealing with him and looking at his replies for over 2 years.


The thing is i know i come across as a twat but then i aint running a tuning business.