Mahle gold pistons

A1ex · Post by **A1ex** » Thu Jun 14, 2012 1:37 pm

Does anyone know if these pistons fit the OEM rods, a5 or a7?

Also, if I was to get these install and no other work done, would the car need tuning before it could run safely or would I be looking at knock issues with the extra compression? I'm thinking of putting the 11.5:1 CR pistons to replace my 10:1 pistons

judderod · Post by **judderod** » Thu Jun 14, 2012 4:19 pm

If the small ends on the A5 or A7 are the same as the A2 which I think they are, then yes they fit but the rods should be honed out by an engine workshop to take a couple of thousandths off so the pins can just about slide in.

On a 4th you could potentially get going by just retarding your base timing on the distributor a few degrees. It's risky though and you'll need proper tuning to see any gains.

A1ex · Post by **A1ex** » Thu Jun 14, 2012 4:48 pm

The a7 rods are a little different tot he a5 rods, I believe the a7 rods have a slightly bigger small end already

It would need a full tune again then unless I'm feeling brave with the s300 (which im not) in which case it's off to the land of PAW to get the pistons put in and a fresh tune. May as well get the cams sorted while it's in too

judderod · Post by **judderod** » Thu Jun 14, 2012 5:03 pm

I thought it was the big ends and/or mains that were bigger... Actually now I think about it yeah the newer engines use sliding pins IIRC, so it should just be a straight swap.

If you're already tuned it shouldn't need much adjustment. You'll need cams to get the most out of high compression pistons

Post by **4thgenphil** » Thu Jun 14, 2012 8:13 pm

right, h22a has a pressed in wrist pin (gudgen pin?), the a7 has a floating pin and is bushed to suit already so the mahle should fit straight on. i THINK a5 has the same setup as the a7, but not 100%.

nellers2001 · Post by **nellers2001** » Thu Jun 14, 2012 8:32 pm

Is it not worth doing the rods and bearings while it's all apart for the piston change?

Post by **4thgenphil** » Thu Jun 14, 2012 9:21 pm

i think rods would be a little excessive on 11.5-1 comp! but bearings is a near must IMO

judderod · Post by **judderod** » Thu Jun 14, 2012 9:26 pm

Bearings definitely, rods no unless it's turbo. The stock rods are good for any NA setup on the stock crank (not stroked) up to about 8500 RPM, IMHO. Plus replacement rods ain't cheap!

I've never heard of a stock H22 rod that 'just broke' on NA. They go because of oil starvation/spun bearings, detonation, or 10,000+ RPM.

Post by **RattyMcClelland** » Thu Jun 14, 2012 9:39 pm

Hopefully my Mahle pistons are ok and i can sell them on. PAW will let me know im sure.

nellers2001 · Post by **nellers2001** » Thu Jun 14, 2012 9:41 pm

Fair enough. If you are definately staying NA then not to worry I suppose!