Building a new engine - qns
 

Planning a new donk for the race car, have a couple of prelim questions.

1 - what is the max capacity you can reliably get from a 7R case? 2.9??

2 - can you increase the comp ratio for standard (8.5:1) 2.7RS pistons?

Cheers - Ryan

Ryan,

I sold the 7R crankcase (which was apparently cactus) from my previous 911 to my mechanic who used it to build a 320bhp 2.9 for Jeff Beaumont. It was the last engine my mechanic built, and it was his masterpiece.

I have 11.3:1, 90mm JE pistons in my 2.7 . I've now done over thirty trouble-free tours of Calder since the rebuild.


Matt Holcomb
MFIWDP
<b>PRVC</b>
<b>BOHICA</b>
1974 911 Carrera 2.7 RoW<a href="http://www.holscope.com/74Carrera2.7" TARGET="_blank"></a>
1974 Ford Falcon GT coupe
<a href="http://www.holscope.com/74Carrera2.7" TARGET="_blank">Dedicated Homepage</a>
<a href="http://www.holscope.com/74Carrera2.7/rebuild" TARGET="_blank">Engine Rebuild Homepage</a>
<a href="http://www.cheaterswayside.com/911/gallery.asp?sort=0&userid=127" TARGET="_blank">Porsche Owners Gallery Profile</a>
<a href="http://www.pelicanparts.com/cgi-bin/pmpre/pm.cgi?action=display&login=Matt_Holcomb" TARGET="_blank">Pelican Gallery Profile</a>

I am currently running 10 1/2:1 compression in my 7R case with no problems.REMEMBER that you CANNOT use the ALUSIL cylinders with JE pistons.

Ryan,

Shouldn't be any problems at all (as demonstrated by Matt's engine) with raising the compression ratio quite significantly, you might have to go to twin plugs just to be safe though, especially if you are going to be running the car in events like Targa Tassie where you can't access super-high octane fuel.

My mechanic had forty years of experience to drawn on when he rebuilt my engine, which is why I can get away with 11.3:1 pistons and single-plug heads.

The theory is that as long as the high compression pistons don't have any sharp edges, you can safely use 98-octane fuel with a single-plug ignition system. You'll also have to lower your distributor advance to 27 or 28.

But I'm not sure that's the whole story.


Matt Holcomb
MFIWDP
<b>PRVC</b>
<b>BOHICA</b>
1974 911 Carrera 2.7 RoW<a href="http://www.holscope.com/74Carrera2.7" TARGET="_blank"></a>
1974 Ford Falcon GT coupe
<a href="http://www.holscope.com/74Carrera2.7" TARGET="_blank">Dedicated Homepage</a>
<a href="http://www.holscope.com/74Carrera2.7/rebuild" TARGET="_blank">Engine Rebuild Homepage</a>
<a href="http://www.cheaterswayside.com/911/gallery.asp?sort=0&userid=127" TARGET="_blank">Porsche Owners Gallery Profile</a>
<a href="http://www.pelicanparts.com/cgi-bin/pmpre/pm.cgi?action=display&login=Matt_Holcomb" TARGET="_blank">Pelican Gallery Profile</a>