MAHLE Rover V8 pistons

[gramos]

I am building an Austin Healey 100 engine and have been running Rover 3.5 pistons for many years with no problems .
The new engine will have Mahle pistons of the same size but whereas the original Rover pistons had a slight dish the new ones have valve pockets on one side of the crown ,
so I want to find out whether there will be any advantage in fitting them with the cutouts on one side ?
How are these pistons fitted in the 3.5 V8 engine ?
there must be some effect on the swirl / flash , on which way round they are fitted ?
Hope some V8 heads can help me out there ?

cheers,
Gramos

[mwstewart]

Is the compression height and bowl capacity the same? If so, the cut outs aren't a problem - I've mixed pistons from manufacturer X in blocks from manufacturer Y for high output turbocharged engines (which are usually far more prone to detonation than N/A) and I haven't experienced any detectable problems.

[gramos]

I have dealt with the comp ht difference and calculated 8.75 CR , thank s,
my question is about any benefit in fitting the pistons with the cutouts on the inlet side or plug side ?
as they will fit either way .
which way round are they fitted in the Rover engine ?

[xtruss]

Looking at some Google images the 3.5 rover engines shows the cut out to be on the inlet side, probably to accommodate valve lift.

[mwstewart]

gramos said:

I have dealt with the comp ht difference and calculated 8.75 CR , thank s,
my question is about any benefit in fitting the pistons with the cutouts on the inlet side or plug side ?
as they will fit either way .
which way round are they fitted in the Rover engine ?

I'm with you. If your cam doesn't have sufficient lift to require the cut outs then it doesn't really matter, but usually the cut outs are for the larger inlet valves.

Hopefully an SD1 expert can chime in.

[Boosted LS1]

Rovers don't have valve cut outs as stock but they are machined sometimes when using high lift cams.

Cut outs are on the intake side as that's where the valve comes to greet the piston.

[gramos]

thats right , the valves will not be close to the pistons so the cutouts are not needed .
I am wanting tto know if there could be any benefits to fit the cutouts on plug side of combustion chamber or
the tip of the " kidney bowl" ,
I am posting some pics to help explain , many thanks , guys

[gramos]

[99hjhm]

You want the flat area on the piston where the quench pad is on the head. Are you 100% sure there is no directional markings on the pistons?

[Boosted LS1]

There are 2 quench areas on the piston. There may be directional arrows but it's usual to have the cut outs on the inlet side of the head. I have no idea if gains could be made fitting the piston in the alternative position. Also, there may be an offset pin to consider. I to wonder about direction arrows.

[gramos]

Head is Weslake design inlet/ exhaust same side , siamesed ports , 2 inlet 3 exhaust a la A series

[mwstewart]

One of the cut outs is larger, isn't it? It looks like it on my screen - the right hand side. If so match that to the inlet.

[Boosted LS1]

^ We're way past that. We need a fluid dynamics specialist to sort this baby :-)

[Mignon]

Pistons normally have an arrow pointing to the front of the engine because the gudgeon pin bore is slightly offset to one side of the piston.

[gramos]

thanks , everyone ,
these pistons are from Mahle , for the 3.500 Rover engine and they are being fitted to an Austin Healey 100 . c. 1953
as they give a 62.5 thou overbore . This is the maximum stretch as the block is 65 years old !
the question is , are there any benefits of fitting one or the other way round ? as there is a choice ,
the valves do not reach down the bore so the cutouts are really academic , there will be no danger of valve / piston contact .

[Mignon]

If the squish area on the piston crown completely covers the squish area in the chamber then it doesn't matter which way round you fit them OTHER than any gudgeon pin offset. Here is an article from David Vizard which covers this.

https://www.chevydiy.com/chevy-big-block-performan...

The pin should be offset towards the thrust side of the block. If you look at the front end of a block in which the crank is rotating clockwise (the normal situation) then the thrust side is on the left.