Mahle 80mm piston set

Bill, I have a very neat way of making higher compression 1.6L or even 1.7L pistons.

As you are probably aware, the 1.5(short stroke), 1.6L, and 1.7L engines all shared a common block, as well as rods, and bore. When VW went from 1.5 to 1.6 and then to 1.7 litres, they changed the stroke, and the piston pin height to keep the compression low. So, if you were to drop in a 1.5L piston onto a 1.6L crank, you would end up with a piston that was sticking up above the deck surface. One would then machine the crown of the piston, to lower the compression ratio. You would lose a bit of the squench area of the piston, but the gains from the compression are huge, as you probably know.

When I made my 1.5L pistons into higher compression 1.6L pistons, I removed material off of the crown, but it still left a TINY amount of the dish in the center of the piston. To figure out exactly how much, I think you will have to do some experimenting. It might take you a few visits back and forth to your (newly found friendly) machinist, but it will be well worth it. I revved mine well past 6500 RPM, with no ill effects. There is plenty of material available to machine away, so no reliability issues ever came up.

I also had a neat way of getting a big intake valve into the 1.5/1.6/1.7L head, and if you are curious, we can talk more.

Hope this helps.

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Pete Mills
 
This is a very common "trick" and I bet more than a few ITC VW's have had this "improvement" done to them.
wink.gif


Obviously it's not legal for ITC but a cheap way to get higher compression pistons for an limited prep engine for example.

Two things to be careful of when doing this modification:

1. Remember that the ring package will now be higher, so if you're putting this into an existing block make sure you remove any ridge at the top of the bore or you're likely to crack the top compression ring.

2. The machining of the top of the piston also effectively moves the top compression ring closer to the piston deck, which can lead to higher operating temperatures and warp the top compression ring land, resulting in a top compression ring failure. This obviously depends on the final compression ratio, advance, mixture, etc.

Just a couple of things to think about!

MC
 
Pete and Mark,

I'm aware of this 'trick'. Similar to using 16v pistons in a 1.8 8v to get higher compression. I've never had a set done, but I'm curious as to what it usually costs to have a set done. The other question, is what's the current availability of 1.5 liter pistons in 80.0mm and 80.5mm? With the machine work and all, I would wonder if they'd be any cheaper than custom, forged (not even gonna go there) pistons. And, you wouldn't have the issue w/ the upper ring.

Thanks for the info guys!

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MARRS #25 ITB Rabbit GTI
SCCA 279608
 
Bill, that's what I did on my Limited Prep 1.8 GP motor. Had my local machine shop match the deck height on my 16v 1.8 pistons (Got on eBay) to the 8v 1.8 piston. That, and along with prepping/balancing the stock rods, and installing ARP bolts was around $425.



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Tim Linerud
San Francisco Region SCCA
#95 LP GP Wabbit
http://linerud.myvnc.com/racing/index.html
 
Hello Bill, about 15 years go when I needed a new engine in my 75 Autocross Rabbit. I built the 1.6 engine using the piston from the 1.5. It worked great. The piston set was pretty cheap, and the machine shop only charged me $40.00 to cut 0.040" of the top. However, I'm not sure if these pistons are still available, but I will check with my two sources tomorrow. If we can't fine the pistons and the only choice we have is to go with forged, I can have them made by Wiseco. The sets come complete, and the cheapest I can let them go for is $400 a set. We can make them to any spec you want. The down side it will take 4-5 weeks.

Thank you,
Jose Rotger
www.porttuning.com
 
Tim:

What CR are you running in the motor? I'd like to do this with a 1.8 GTI engine being prepped for ClubRally, and would like to run about 11.5:1. Do you know how much I would have to mill to get that ratio?

Thanks,

Wilson


Originally posted by racer_tim:
Bill, that's what I did on my Limited Prep 1.8 GP motor. Had my local machine shop match the deck height on my 16v 1.8 pistons (Got on eBay) to the 8v 1.8 piston. That, and along with prepping/balancing the stock rods, and installing ARP bolts was around $425.
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