Custom pistons

[Dave M S2]

Hi, I know this isn't exactly race car related, but the people posting in this section seem to be the most knowledgable on the wedge engine modifications.

I'm new to the forum & in the UK. I'm currently restoring an S2, working on the engine at the moment. Its got the 1565cc federal 821-30 engine in it. I've removed the head and noticed its fitted with the Renault flat top low compression pistons, so these are going to need replacing.

Searching on the net I've realised sourcing pattern ones isn't going to be an option. I noticed some people have had them manufactured by CPS in Italy, so I've contacted them & they'll do them for €180 a piston which is obviously expensive, but I don't have many other options at the moment.

They've requested a pattern to copy though, which I don't have. I wondered if anyone on the forum has had some manufactured themselves and has any advice, or drawings of the crown. if not an old worn, or damaged piston I could have/borrow to send them as pattern would be a real help. Any advice would be a great help?

Cheers

Dave

[Serge]

You don't have to use CPS, there are lots of people doing custom pistons. Omega (in the UK), JE pistons, Wossner, ...

The original pistons would have made a compression ratio of 10.25:1 if I'm not mistaken. You can have them design the piston from you to that compression ratio. It doesn't really matter what the crown looks like as long as it makes the compression you need. Most will ask for a mold of the combustion chamber. I suggest you contact a piston manufacturer and ask what they would need from you to make new pistons.

Kind regards,

Serge

[jbcollier]

Piston crown and squish band design have a huge impact on combustion efficiency.

[2483R]

Dave,

I used custom, made to my specifications, pistons in my TC.  They were made by JE Piston in California. I could not be more happier with them. The quality is excellent, cost was reasonable. It has been a few years since I rebuilt my TC, but unless something has changed in that time, I would recommend JE.

I remember talking to John at Lotus Racing West, who has built many TC race motors. He told me he tried all the custom piston companies, and JE was the best.

I sent them an old stock piston, as well as a list of piston specs I got from the workshop manual and Wilkins book. The JE salesman then called me, and he went over each spec in detail, making recommendations along the way for changes. I was impressed with his knowledge of piston design.

But as you are in the UK, shipping will be expensive. But if you can afford it, try JE.

[Valerio Leone]

I do not suggest to use CPS pistons unless you decide to change the rods as well.
The Stock pistons are bonded to the rods, no axle pins.
Bear this in mind when you ask for a piston set.

ciao
Valerio

 

[Dave M S2]

Thanks for the responses. I will try omega, see if they can do something for me, it would be easier to have them made here if I can. I'm reluctant to get them from the states unless I have to as I've been stung heavily on import charges/shipping in the past. I've seen Wiseco list them on their site though. I happen to be travelling through Italy in May so I could pick them up from CPS myself which would make that a reasonable option at the moment, plus the euro exchange rate helps.

I'd rather have replica's s of the originals & not alter the squish band, I used to work in the dynos at Lotus and can have seen it can make a huge difference to output, as mentioned.

Valerio, could you explain further about the rods having to be replaced. How are the pins secured in the pistons? Would I have to replace the rods whichever piston I used then, or is there something that CPS specifically do that means you must fit different rods?

I think it was one of your posts that put me on to CPS. Thats a very impressive spec. I was hoping to produce a 'fast road' tune engine, so it may be worth me increasing compression ratio as you did if having some custom made. Do you have to run on 98Ron fuel at 11.5:1?

Also, do you have any drawings that you used when you had them made?

Thanks

Dave

[Valerio Leone]

Ciao Dave,

The stock rods "hold" the piston wrist pin "bonded" within the rod
That's why you do not need circlip to retain the wrist pins into the pistons.
In my layout I asked CPS to make the wrist pin floats free within the piston and rods.
So that, I change the rods, using the ones from Mecaparts made for Alpine Renault. (saving 100 grams each rod)