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Mike D'Silva

WTD - Pistons suit 3.0 SC

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Is anyone sitting on a set of aus/Euro spec pistons to suit a 3.0 SC?

I'm after something with higher compression than the stock 8.5 compression pistons in my C3 motor...

I recently missed out on a set for $100 on facebook.. but yes, I am prepared to pay a little more !!

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8 hours ago, Mike D'Silva said:

Is anyone sitting on a set of aus/Euro spec pistons to suit a 3.0 SC?

I'm after something with higher compression than the stock 8.5 compression pistons in my C3 motor...

I recently missed out on a set for $100 on facebook.. but yes, I am prepared to pay a little more !!

You wanna pull it apart again?

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I have some new cams to try.. if I can get some suitable pistons and cylinders at the same time, I'll make the effort.

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Mike,

How wild are your cams?  Will they stop you fitting the standard CIS style pistons?

 

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28 minutes ago, Peter M said:

Mike,

How wild are your cams?  Will they stop you fitting the standard CIS style pistons?

 

Just 964 cams. 

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On 8/9/2018 at 2:35 PM, Mike D'Silva said:

Is anyone sitting on a set of aus/Euro spec pistons to suit a 3.0 SC?

I'm after something with higher compression than the stock 8.5 compression pistons in my C3 motor...

I recently missed out on a set for $100 on facebook.. but yes, I am prepared to pay a little more !!

I checked my stash & sorry, I only have a spare set of 93L7++ pistons.

They are ex UK so I suppose they came out of a Carerra 3.0 ???

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Thanks.. the 93L7 is a Mahle 8.5 compression from SC and C3.. which is what I have already, but thanks for looking,

Apparently, I need either 95L67 for 9.3  or 95L70 for 9.8.

I dont think I will find a set in time so will likely end up just leaving as is. Once I put the cams in and put the motor back in the car, I am sure a set will turn up !

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16 hours ago, Mike D'Silva said:

Thanks.. the 93L7 is a Mahle 8.5 compression from SC and C3.. which is what I have already, but thanks for looking,

Apparently, I need either 95L67 for 9.3  or 95L70 for 9.8.

I dont think I will find a set in time so will likely end up just leaving as is. Once I put the cams in and put the motor back in the car, I am sure a set will turn up !

I think the comp increase would have a much larger effect than the cams...would be worth waiting to find some nice pistons. 8.5 is very low for an N/A!

Is there any machining of the heads/barrels that can be done to raise compression?

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I'm no expert, but my understanding is that the piston dome shape lends itself to hitting valves if you machine the head/cylinder mating surfaces. To go any higher I think you need pistons with cutouts for the valves.

The stock CIS pistons have a nice curvy surface which was something to do with swirling the intake charge with the CIS systems. The 964 cam I understand, works well with CIS systems and is about as far as you can reliably go, if keeping CIS.

With my EFI, it seems silly not to go nuts and buy new cams and new piston and cylinders and aim for 10.5:1 or something like that! But SO MUCH MONEY. Also, the cams were the right price (a very generous nice fella gave them to me). 

At the moment, the cost ahead of me is just my time and some new gaskets (I hope).

 

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2 hours ago, Mike D'Silva said:

Now we're talking! 10.5:1 comp will totally transform that engine. After all the effort you've gone through, particularly with the ITB EFI conversion, that engine really deserves to have some proper compression.

 

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But is it as simple as simply buying a set of pistons and installing them?

The Mahle pistons and cylinders are all matched to tolerance groups.. and the piston pins in my pistons are perfecly matched to each conrod bushing. If we are talking complete engine rebuild and machine work again, then no.. I don't think so. The next person can do that. 

https://www.ebay.com/itm/JE-Forged-pistons-95mm-STD-10-5-1-Porsche-911-3-0L-274049/291657929423?epid=1623390555&hash=item43e82ad2cf:g:gMAAAOSwFSxZ5YZl

 

 

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3 hours ago, Mike D'Silva said:

But is it as simple as simply buying a set of pistons and installing them?

Could be depending on what you have done to your existing cylinders.

Assuming you have honed them in preparation for your new rings (on you old pistons) and they have measured up still within spec, installing new pistons wouldn't incur any more cost.

With the gudgeon pins, assuming the old ones were still within spec, you would just mix and match the new ones to best fit the conrods.  At worst you may have to rehone the tight ones but that wouldn't mean splitting the crankcases.

  

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