Chris Bennet

Hi Rennlisters,
Background: I recently converted my Eurospec 3.2L to a twinplug 3.4L with 10.5:1CR JE's. The exhaust consists of stock headers with a gutted cat and a freeflow (Fabspeed) muffler.
Question: Now the engine seems to rev very willingly - more like an SC than a Carrera. When I ran SSI's (a couple of years ago)it didn't rev this nicely. I'm curious as to what caused this change in character. Is it the lighter pistons or higher compression or what?
TIA, Chris

Bill Gregory

Chris,

Has to be that 964 oil pump - more oil, more slippery

Chris Bennet

Yeah, that's the ticket.

Bill Gregory

Chris,

Kidding aside, I noticed in the May 2001 Pano (p.90) that Bruce Anderson talked about twin plugging when responding to a question on MSD vs Bosch ignition. He said: "However, we have found that while adding a twin ignition to an engine will not provide a large increase in the horsepower as measured on a dyno, you will see better low end throttle response and better part throttle running."

aquabat911

The ratio of bore to stroke has alot to do with the "revyness"(hi-tech physics word originaly used by Einstein) of the motor. Engines with a larger bore than stroke tend to rev alot easier simply because the piston is not traveling as far during a crank rotation. People usualy dont think that if your motor is turning 7000RPMS your pistons are traveling up(in the cylinder), stopping, going back down, stopping, changing direction to do it all over again 7000 times in one minute. Just a few mm of stroke makes a huge difference. In engineering school we worked out the equations for the velocities and the acceleration of the pistons during the stroke and it is mind numbing!
Oh yeah you may have lighter pistons now which adds to the effect, recipricating mass, or basicaly anything moving up'ndown also has a huge effect. I hope I helped

Chris Bennet

I appreciate the effort but my curiousity is not satisfied. I've heard that "short stroke" motors like to rev but the stroke is unchanged so perhaps it is the bore to stroke ratio like you say. The bore went from 95 to 98mm. -Chris

[ 06-21-2001: Message edited by: Chris Bennet ]

87slant-nose-cabriolet

PLEASE EXPLAIN WHAT WAS INVOLVED WITH JUST
THE DISPLACEMENT INCREASE. WAS IT JUST NEW
PISTONS AND REBORED CYLINDERS, OR DID YOU
HAVE TO REPLACE THE JUGS AND BORE THE HEAD
MATEING SURFACE TOO. JUST DREAMING
KEITH

Chris Bennet

NO NEED TO YELL. :-)
To change the displacement I just changed the pistons and cylinders using bored stock cylnders that have been re-nicalcilled (sp?) and larger diameter (98vs95mm) JE pistons. This didn't require any modification of the head mating surfaces. -Chris