The V8 Owners Forum -

Hopefully the new pistons will be fine they are certainly a lot better quality and having a full skirt at the bottom will help with stopping the piston going out of shape and causing that annoying rattle on over run that these engines suffer from a lot.
John Eales is building the short engine for me so should hopefully get it back in a few weeks.
Thanks again for the help and input.
Chris

A few things spring to mind...

If it still has the same deep cutouts, and uses same ring groove depth...then it will still have the same thin material area around those cutouts/ring groove.

Top ring placement vs top ring land area is still very high for a boosted application.

Also, those pins....are they really that thin, or are they tapered ?

And I dont really get why "old" engines do still use pistons with huge or full skirts. I dont think there is any need to when all modern stuff does not. It just adds weight really.....which if the crank is known to be weak, all that weight cant be a good thing ?

I presume these are just some pistons they have sitting on the shelf, rather than pistons for a boosted engine application ?

I'm sure they will be stronger than the OEM cast pistons, but I'd also be sure much much better could be done. What sort of money are they ?

TVR machine the skirts of the standard 4.2 pistons to just clear the swing of the 5.0L 90mm stroke crank. I'd wager that JE will need to trim locally the skirts of your new pistons slightly to clear the crank.
The reason the TVR pistons rattle is the position of the pin relative to the piston mass. The standard 4.2 pistons have another 12mm or so of skirt. The Modern pistons with smaller skirt will have the pin higher up the pistons body and this makes them more stable in the bore. Unless you change the con rods you are stuck with this piston arrangement and given that they are forged they will be set for a larger running clearance and will certainly rattle more when cold. But, this is all part of the fun.

It does look like an opportunity for someone to offer longer rods and shorter pistons.

Given how cheap the Chinese can get aftermarket rods down to....it should be possible to get affordable parts to market ?

Pistons always seem to hold good value though

Thanks Guys
I'm a novice at best when it comes to engine building and pistons cranks rods etc. But I do understand all that has been said. The problem is that unless I want to spend a silly amount of money having things purposely made for my engine I don't really have much of a choice. The pistons that I am getting from JE are his 4.2 cast pistons that are machined to fit in the 5.0. We spoke about the thickness where the valve cut outs are Tvr pistons had about 1mm of metal these will have about 3mm, to be fair the pictures of the two side by side are a bit deceiving.
The compression ratio of my car I measured at 10.5:1 with these new pistons the compression ratio should be down to 9.5:1 which should help with detonation.
Any improvement has got to be a step forward. I did not fit the Supercharger to the car it was done by the previous owner when the car had done 50k miles it lasted a further 10,000 miles on a best guess map with Dizzy distributor and detonating a lot and being driven hard by the previous owner. I have found at least 2 other pistons with cracks at the valve cut outs and believe they have been there for a while. With help from here and a lot of reading of other posts and information I managed to get rid of the detonation completely this included rolling road sessions fitting map-able ignition improving air flow to the intercooler lagging a lot of pipework to reduce under bonnet temps etc etc. I dont do that much mileage in the car and don't try drive the nuts of it all of the time.
I am fairly confident that with the new pistons crossbolting and dynamically balanced it should be good to go.

How much are those pistons ?

stevieturbo wrote:How much are those pistons ?

£650 for all 8 plus some extra for machining not sure how much extra yet.
Chris

Not even that cheap ?

Give Dave Powell at Performance Unlimited a shout to see how much a proper custom set would be.

You could send him the old crappy original ones for him to spec new ones.

Or do you have bore, compression height etc pin diameter details and search to see if there are other shelf pistons that could be used ?

Whilst probably still not ideal for boost, this rod/piston package for a 5.0 doesnt look too bad ?

http://www.v8tuner.co.uk/product.php?id=874

£850 for my forged ones