Convert 3 Litre turbo into Naturally Aspirated

Mark Crowe · 03-25-2008, 11:34 AM

I have a 1977 3 lite Turbo, and am considering going the naturally aspirated route for various reasons.

My motor was rebuilt about 10 000 km ago, bearings, rings etc, pistons and liners were ok.

I believe I should be looking at bumping capacity up towards 3.4 or 3.5, I want to try and avoid machining casings if possible, and I understand going to 100 mm requires some work on the casings.

I also want to have a fairly high CR, but not to the point that detonation on lousy fuel becomes an issue. I am junking the K Jetronic, and have a good programable EFI system available, can handle up to 800 hp, single or twin plugs

Questions are, will stock turbo heads work, should I open ports up, or go 3.2 head route? Twin plugging if less than 100mm- worth it?

I have a set of SC cams, will they work or do I need to look at some thing else, (mainly street use)

What pistons set can be recommended in line with goals above?

Any ideas on HP and driveabilty? I have the 4 speed turbo box but can change to G 50.

Look forward to hearing from those that have been down this road before!

Thanks

Mark

WERK I · WERK I's Garage

Have you considered maybe getting a used NA engine and selling your turbo engine instead of modding a turbo engine? Might be cheaper in the long run. Maybe a 3.2 or 964 engine as a baseline?

Mark Crowe · 03-25-2008, 01:02 PM

I had considered it, but they are a bit scare on the ground here, plus I have to do some stuff to my Turbo engine in any event, ( EFI, inlet manifold etc), so I had thought going the piston and liner route might have been more cost effective.

If anyone has a decent 964 or 3.2 engine and box though I am happy to look at it as an option.

kenikh · 03-25-2008, 01:21 PM

With a 3 liter turbo case, you could build a short stroke 2.8. This is arguably the most interesting and fun motor you can put in a 911. search 2.8 short stroke or 2.8ss on this forum to see what I mean. TONS of power and character: 8000RPM redline, good torque and over 100HP/liter.

boba · 03-25-2008, 02:27 PM

+1 for a 2.8ss.

If you want to do a 3.4 or 3.5 start with a 3.2 or just start with a 3.6.

As the 3.0 turbo case is in high demand by folks looking to do a 2.8ss you could swap or at least sell it quite easly. You may already have offers in your PM box.

As advised above search 2.8ss.

Aurel · Aurel's Garage

Is a 3.0 turbo case any different than a 3.0 NA case? I thought they were identical.

Aurel

boba · 03-26-2008, 08:07 AM

The 3.0 turbo and the 3.0 euro carrera are the same case and will take the 66mm crank. This crank + 95mm P&C get you a 2.8ss.

The rest of the 3.0 cases will not work unless you find a 956/962 crank.

jpnovak · 03-26-2008, 08:25 AM

Yep, 2.8SS would be fun indeed.

Why not 98x66mm? 3.0SS?

the issue I see is that he lists "Mostly Street" applications. I am not sure a 2.8SS with 8K rpm would be the optimal daily driver.

kenikh · 03-26-2008, 09:56 AM

Quote:

Originally Posted by jpnovak

Yep, 2.8SS would be fun indeed.

Why not 98x66mm? 3.0SS?

the issue I see is that he lists "Mostly Street" applications. I am not sure a 2.8SS with 8K rpm would be the optimal daily driver.

Having driven one, this is absolutely not true; they are a supremely tractable daily driver on RSR cams. They run very well on 46 PMOs, even better on EFI/MFI.

Why not a 3.0SS (or a 3.1SS for that matter)? That much displacement takes the air requirements into territory the ports and valves have difficulty supporting at 8000 RPM. At lower revs it is fine, but if you aren't going to spin it, why build it?