questions about an engine rebuild 2.5 l

[martinW.911]

hello all,

ok, the first step is done, I found an excellent 911 t from 1971. after having totally stripped it, my rebuilding policy is to keep it as original as possible from the outside, but to upgrade it´s performance.

the performance upgrade should only comprehend steps which someone would have chosen, when upgrading the engine etc. in the seventies. I just don´t want to shift a modern engine into the car.

so I thought it would be a good idea to achieve the following characteristics:

- keep the original 2.2 block as it has matching num- bers, so I could achieve a fia-homologation later on for rallies etc.
- full rebuild of the engine
- engine should be reliable and able to be a daily driver in traffic situations
- an upgrade to (contemporary) 2.5 l would improve a bit of the bottom end power, i.e. there should not only be power between 5.500 to 7.500 rpm
- an output of > 200 hp would be my benchmark.
- a carburetored engine would be preferred, to have the “classic” feeling and to make it different from my 1989 carrera 3.2

my question about this project are:

- there is an LN engineering set of 2.5 l pistons and cyl. at pelican parts. Would this be a good basis to start with?
- Is the 2.2 block sufficient to get these in?
- do I need a 2.4 or better a 2.7 crankshaft?
- which compression ratio would be recommended?
- which cams do I need, 2.2 S or carrera 6?
- change conrods?
- any amendments to the heads, valves?
- would pmo carbs be a good choice? (40 or 46 mm?)
- which oilpump do I need?
- additional (which) oil cooler needed?
- anything else?

I know these are a lot of questions, but during the last months I learned that there is so much know how in this forum, why not just ask.

[cnavarro]

I'm not sure if the catalog is up to date or not with the Nickies, but with the 2.2/2.4 spigots most commonly I sell 87.5s, but as of late, I've done a bunch of slip fit 89s! Just ask them if you want a size you don't see.

[YTNUKLR]

2.2 original case is cool, but you might think about a stronger early aluminum (65-68) or later 2.7 magnesium case to build this engine. if you want it to go in traffic, do not put in the carrera 6 cams. I would go for 911S or DC40 (mod-s) most likely.

If you use a 2.7 case and you use Nickies cylinders, go for the standard 89-90mm, with JE pistons. If you keep the original 2.2 case or use an early aluminum case (not boring the case), the slip-fit 89mm that Charles mentioned above are good. This is to build a 90(or 89)mm x 66mm (stroke) 2.5L. This means you need a 2.0/2.2 crankshaft. If you want to build a 2.5L using a 2.4 crankshaft, the factory used 86.7mm Pistons and cylinders. You could use something like this, I imagine Charles would be happy to make whatever you want. Conrods--use 2.0 rods on a 2.0/2.2 crank, 2.4 rods on a 2.4 crank. Make sure they are balanced, rebuilt correctly and use ARP rod bolts if you rev it high (8k+). I would use 2.7 heads if building a standard 90x66 2.5L, with the head chamfer. Ports should be enlarged to 36/36 at least. 40mm carburetors sounds like the best choice. Use any upgraded oil pump--911SC 3.0, 3.2 Carrera, 3.6, 930 turbo . Sounds like you'll need better valve springs, like "sport". Use Carrera or brass (28-row) front oil cooler.

Let us know if you have more questions