pics of my DIY low compression pistons

[IbiVR 0]

Well with the VR in bits for a good service and fitting the ARP main studs, rod bolts and head studs, Didnt really want it to go back together again with the spacer to drop compression, and didnt feel like spending £££ on forged pistons, we thought we'd see what could be done with the std pistons.

Stock VR rods with arp bolts can hang on to 600bhp easy, can the pistons... maybe. Worth a go.

So a trip to a local machine shop and a bit of asking nicley to borrow their mill, 3 hours later this was the result.

Std VR piston as it came out on left, after milling in the middle, and all polished up on the right:

Made the dish bigger but not deeper, we cut a piston in half and theres not really enough meat in there to start going deeper, also played with the valve pockets.

Got enough out of them to drop cr to a nice round 8:1.

Another pic:

and finally all of them in the block with the ARP studs:

Initial impressions are good, car runs great. Was running 20-25 psi on std pistons, have to see how much more these ones will take.

Tom.

[jon@vagworx 0]

Lol, nice one mate, worth a go i spose :-d

Only problem i can see is finding out how much boost it can take, its not like you can keep uping it, then go ooops too much, back it off a bit!!!!!

[IbiVR 0]

Hehe, i think they'll take a fair bit. If they crack i'll put some other ones in and back it off a bit...

[FishWick 21]

Nice one. Although why not just offset bush the small ends? Cheaper, easier and you leave the meat on the piston crown ;-)

More than one way to skin a cat I suppose, good effort.

Is it a pain in the arse sliding the head down the ARPs? I bet the head binds on the bolts? Any tips? Will be doing that myself next week.

[cadguy77 0]

Hats off to ya Tom for your balls out methodology. I look forward to seeinghow she's holding on after a month or twos hard driving

[IbiVR 0]

Nice one. Although why not just offset bush the small ends? Cheaper' date=' easier and you leave the meat on the piston crown ;-)

More than one way to skin a cat I suppose, good effort.

Is it a pain in the arse sliding the head down the ARPs? I bet the head binds on the bolts? Any tips? Will be doing that myself next week.

[/quote']

Yeah, just something different to try, this was free so worth a go. :-p

Offseting is ok, but to get that cr they'd have to go down ~2mm. This way the compression is reduced while still maintaining a good squish gap. This keeps good turbulance in the combustion chamber just prior to ignition.

Theres no problems running a small spacer to drop cr as i was running before, but even lower compresion means a thicker spacer and theres a limit. Offsetting the small ends instead effectivly gives the same result. Also the std vr6 rods are proven to take 600 bhp with ARP rod bolts, I dont want to confuse the matter by possibly weakening a ~known factor.

The last thing to consider with rebushing is that the pistons and there rings would be coming down ~2mm or so further than they have done for the last 80,000 miles, and into an area of the bore with no wear in it. This might not be such a good idea without boreing the block slightly, again with a cost attached.

Both ways work, in theory this way will make more power than doing the small ends.

The time will come eventually for forged ones, but in the meantime its useful to know what a fettled std bottom end can take.

Head goes on fine. Line up the middle left and middle right, and she slides right on Only tip really is have something long and thin to hand, getting a greased up nut and washer onto some of the studs can be tricky. Grease them up, slide them onto your "stick", put that on the end of the stud and they just drop on first time.

Tom.

[GVK 1]

Good work Tom, test drive me up!! )

[VR6Will 0]

nice work tommy!

[FishWick 21]

All good points regarding offset bushing Tom! I suppose it's probably better to do it with an engine rebuild, but then you might aswell use Forgeds! I reckon your pistons will work well!

Cheers for the ARP tips, very hand indeed, thanks mate!

[IbiVR 0]

Good work Tom' date=' test drive me up!! )

[/quote']

Hehe no probs gary - just let me run it in and you can "borrow" it for a healthy dose of boost :-p

Tom.

[Petesvw 0]

Smart tom ; )