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Grady Clay Grady Clay is offline
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Join Date: Dec 2003
Location: Arapahoe County, Colorado, USA
Posts: 9,032
Derek,

There is no substitute for displacement.
2.7 is better than 2.4.
3.2 is better than 3.0.
And then you can get more for much more $.

If you have a 2.4 MFI, want to keep the MFI then 2.7 (or 2.8) is a logical choice. An advantage of the magnesium case is weight (or lack of it). The disadvantage is it isn’t as strong as the later aluminum cases. With the modern techniques that limitation can be overcome.

There are two other considerations when looking for more power – compression ratio and cams.

Compression ratio (CR) choice is almost 100% fuel dependent. The higher the CR higher fuel octane is required. Some who only drive <10K per year use 112 octane leaded race gasoline for 11.5:1 CR. For most the CR is limited by the fuel available at the pump. Twin plugs allows slightly higher CR with the same fuel.

The progression of cams somewhat trades off performance, fuel economy and drivability at low RPM for higher power at high RPM. This is the progression from CIS cams to T,E,S and on to race cams. Your MFI is eminently suitable for more aggressive cams than your T.

Along with more power comes the catch. You will need more cooling capacity. A substantial front oil cooler and a higher fan ratio usually suffice. Since you tend to go faster, you also need to stop – hence larger brakes. Since you tend to drive more aggressively, more suitable suspension is desirable. At some point tire size becomes an issue so you install flares and wider tires & wheels. At some point you are putting so much power through the transmission, it needs an oil cooler. On it goes.

This progression is known euphemistically as the “Slippery Slope.”


What to do?

If it were my choice I would recommend you opt for Mahle Nikasil 2.7 at about 10:1 CR. Have the MFI, heads and cams be to 911S specs. Current electronic twin ignition with knock sensing. Bring the crankcase up to current standards; shuffle pins, line bore, oil circuit mods, Turbo oil pump, large piston nozzles, clearance the case and cylinder spigots. It will need a higher ratio cooling fan and a substantial front oil cooler.
Otherwise I would add stiffer torsion bars, good serviceable shocks, lowered and cram as much tire & wheel under the stock fenders as possible.

There are several dozen significant “while you are there” projects that should be undertaken simultaneously on a 33 year old 911.

One thing to keep in mind is that a 911 isn’t just an engine, it is a well balanced system where things are sized appropriate to everything else.

This makes a stock appearing, very drivable and serviceable 911. With 200+ HP and good handling it is a fun “wolf in sheep’s clothing.” This is pretty expensive but much more and the slope gets very steep.


If I were building a 911 for myself I would tolerate a true lightweight – under 1800#. A lightweight to the extreme 2.8, 12+:1 CR. Not much more than SC flares. Single out OEM muffler.

Best,
Grady
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Old 08-15-2005, 09:28 AM
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