Im going to start rebuilding my bottomend because im fed up with piston slap. What pistons are good. Im going for 450 but im not sure if i would go for more down the line. And wheres best place to get them.

 

Mahle
Mat lewis motor sport 01543 379524

 

What him up there said

 

Are they ok for that power? Whats there limit roughly

 

500 bhp is their limit due to the higher rpms required
the quietest of all the pistons and they came free with any yb 88 onwards

 

My cars 89 but the guy rebuilt it with ford motorsport forged pistons but i hate the piston slap its loud when cold. And when its warm you can still hear it pain in the tits

 

Make sure you replace the little end bushes in the rods too. They can cause a rattle when worn.
I went with cosworth pistons and im more than happy with them. But lots of people go with mahle too!

 

I have wiesco pistons .... only built up in short motor for now , wont be happy if they are crud

 

thats what im going to be building thats what im worried about building 1 and its got piston slap

 

well I was going to get the mahles but there were problems with the guy doing the cut outs , so i got told the wisco are just as good so i got them instead so as said wont be chuffed if that info is wrong , however a lot of jap stuff seems to run the wisco with no problems so heres hoping , will see how it runs not so long from now

 

Same pistons here and they're quiet

 

What problems did the guy have as i am going for cutouts as well. Who were you going to use

 

I went with cosworth pistons as they came with the cut outs ,
I was going with mahles to start with but I didn't want the hassle off getting someone to machine them,
I've been more than happy with them tbh

 

Where did you get them are they quiet tho?

 

Yes mines are quiet ,
I got mine from that PEC company, but I'm just off there website and it looks like they don't do them anymore , I can only see cosworth pistons for Subaru s !!
Maybe if you gave them a bell they could sort you out

 

I will have a look about is there any noise even when stone cold

 

Forged pistons like the cosworth ones require bigger clearances as they expand more, consequently they are more likely to slap when cold and are more prone to wear out (more clearance means more hot gas getting past in the first place, esp during cold starts)

So the Mahle (which are sort of a semi-forged) that Tony mentions (ie OEM spec) are the best ones if you want it to stay quiet for high miles, as they expand less and hence can safely run tighter clearances.

 

Mine takes 10mins to quieten down but you can still hear it a bit. Is there a problem gettin cutouts on mahle pistons.

 

There is plenty of meat on the standard pistons to allow you to increase the size of the cutouts without excessively weakening the piston.

 

There are no valve cut outs on std pistons Chip

 

Thanks for the correction, I should have put there is enough meat to "add valve cutouts" not to increase them.

Although most of the secondhand pistons have small cutouts in them by now anyway of course

 

What pistons would you recommend for power above 500 bhp??

 

Custom CP pistons

 

I was thinking about these, do these suffer with piston slap like other brands as they are forged??

 

Yes, it will effect ALL fully forged pistons.

 

Ive got Wiseco and no complaints!

 

They wont last 100K miles and still be quiet like the mahles can mate.

Hence OEM spec is Mahle despite them being far from the cheapest option.

 

I`d be surprised if they did. Always a compromise. If I was building the engine I`d have gone shorter piston, longer rod but I didn`t so errr I don`t!

To be honest my car will be lucky to do 1500 to 3000 miles tops per year.

 

I had wossner in my old RS Turbo and they seemed pretty good.

Is there a reason people go with the CP's for cosworth? Maybe less piston slap or longer wearing?

 

i'm sure when they changed from 2wd to 4x4 they changed the pistons to have a offset gudgeon pin to hep with the piston slap

 

What problems were they. And who was going to do the cut outs

 

Why do the standards have a 500 bhp limit, is the due to the material of the piston or the design, eg pin position etc

 

sorry took so long to get back to you , I bought all my parts from matt lewis and was going to get the mahles and he was getting the cut outs done for me but who ever it was doing the job damaged one (think it fell and cracked or something along those lines, so I did not want to wait any longer and said the wisco ones are just as good so I went for them and got them quicker , as for them lasting 100k I would be well happy with that it would need rebuild by then anyway lol
to look at them ie the finsh of them it looks great and comes with an info sheet telling you what the bore should be and I gave that the machine shop and they seemed to like them and said there good

 

what spec are the wiesco?

 

cant remember but I will check it tomorrow for you and let you know

 

I've known a few that used wiesco and they didn't give good feedback at all.

 

Surely it's more down to using the correct bore sizing and installation than the metallurgy of the pistons? It's not as if there is only a few cars in and out of the cosworth world using them.
After all if you've built the engine yourself, you're hardly likely to blame yourself for failure and on the other hand if your engine is professionally built and either fails or is noisy, what is going to be blamed? Workmanship or material failure?

 

you can get cut out put in std pistons by scs (specialist car services)

http://www.specialistcarservices.com/


think they were about £80 + postage took about a week to do

 

right I have found the info sheet so here goes
comp height; 1.608
bore size ; 3.6023
suggested clearance; 0.0030
skirt of piston measured at lowest point ; 1.300"

don't know if that will help or not mind you , few other sizes but its just for clips and rings