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TurboKraft TurboKraft is offline
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Join Date: Mar 2005
Location: Phoenix, AZ
Posts: 2,764
Originally Posted by Mick_D View Post
You win
I'm guessing a 4.0 motor from you would be a lotta scratch- at least as much as a turbo, eh?
High power naturally aspirated engines make turbo engines look inexpensive.

Building a 3.8L non-turbo is easy: a set of big bore 102mm P&Cs, and you can reuse and modify your rods and cylinder heads, plus your factory Motronic ECU with a chip.
With a little head work and cams, and a decent exhaust, you have a really nice, responsive street/track driver with about 300hp.
Think 993RS or a little better.

Add ITBs and programmable engine and now you have throttle response like a GT3, a wider torque band, increased redline.
With better cams she'll make power to 7,500rpm.
Oiling mods to crank & bearings highly recommended.
About 350hp on good fuel.
Total blast to drive on the street, great track weapon.

But now you've likely spent as much as one of our really responsive Turbo engines, and those usually start life at 500whp on plain 91-octane pump gas. Recently dynos: 3.6L made 555whp on plain pump gas, 3.8L did 575whp/550wtq.

Once you get past 3.8L, the list of things that have to be changed out expensive. There's no cost cutting when building a 4.0L:
* lightweight billet crankshaft, lightweight forged rods, lightweight pistons & pins, high strength rings, machine-in cylinders, special gaskets, billet pulley
* Xtreme Cylinder Heads -- even modified 964/993 heds become a limiting factor, Xtreme's let you get everything possible out of the 4.0L displacement
* ITBs required -- without them, performance is choked by the single throttle intake, hardly better than a 3.8L
Starting with a plain 964/993 engine, it's easy to have a parts bill of $60k for all rebuild parts, rotating assembly, exhaust, intake, and flywheel+clutch package. Plus labor and tuning. 380-415hp, depending on camshafts, tuning, and fuel quality. That's our 993RS4.0 engine.

But again, at that price point, you would have had a really punchy Turbo engine that felt like a turbocharged GT3: snappy throttle, instant-on torque, 600whp or more on pump gas -- and money left over.

Want over 400whp naturally aspirated? BTDT, dynos of 450whp on high test fuel. Be prepared to spend Motorsports level money.
Chris Carroll
TurboKraft, Inc.
Tel. 480.969.0911
email: -
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