View Single Post
Outlaw 911 Outlaw 911 is offline
Outlaw 911
 
Join Date: Apr 2008
Location: Northern Colorado
Posts: 66
Opinions Wanted - 77 3L Rebuild/Upgrade

I placed this in the "911 Engine Rebuild" section too....

I am looking for the 911 Engine Rebuild Experts - opinions, thoughts and general chit chat is welcome. If you see something that does not make sense or I need to reconsider - please let me know.

Here is the background:

I have a 80 Euro SC Coupe with no sunroof, no AC, and about 3 months ago I bought a 1977 vintage 930 3.0L Turbo motor complete. The plan is to build a narrow body track beast. The engine is pretty original. The exceptions are the eliminated thermal reactors and the missing air pump.

The motor was disassembled when purchased and after a few hours of inventory – it appears to be all there from the fly wheel to the muffler, including electrical harness, injection, engine tin, AC compressor. The only exceptions are the driver’s side chain tensioner oil line and some of the cylinder cooling air guides.

The Good –

77K mile engine – appears to have had a top-end rebuild recently.
WebCams – stock grind? Has the number 150 under the Webcams stamp.
No broken rings or damaged pistons.
Crank and rod bearings in good shape.
Updated to Carerra tensioners.
Heads rebuilt with new guides.
Heads professionally ported to 36-38mm size – very well done.
Rockers appeared to rebushed.

The Bad –

2 broken head studs - but typical for this vintage.
2 of the cam lobs on the same cylinder are rough. Looks like someone ran it with valves misadjusted - way too tight?
2 of the rocker arm shafts were stuck in their bores – and it took a little work to get them out their bores – and those bores were slightly scored – is this OK?
And in general the it is an oily, stinky mess - the thermostat was leaking pretty darn good - dumping junk all over the backside of the engine.

I pulled the engine apart over the past few days and have observed the following:

1 The ring to piston gap is .004 - below the wear spec - so I am hoping I can use my existing pistons with new rings - a good sign.
2 The cylinders bores are in great shape - no scuffing.
3 The pistons are in great shape - no scuffing.
4 No broken rings - a good sign.
5 2 broken head studs - typical.

I cracked the case last night and ...

6 Dirty, dirty, dirty, yucky, dirty, stinky.
7 Timing chain - at one time - it appears the chain tensioner failed - because I can see chain groves in the timing chain boxes. It was repaired and pressure tensioner where added. There is also a master link chain in place. There was a small piece of a failed plastic chain ramp in the bottom of the case.
8 I removed the intermediate shaft, pump, chains and crank. The main bearings look to be in good shape - not worn out in any specific area, no big scratches, no spun bearings, very consistent wear across all of them. How can I tell if these are undersized bearings? PN on the bearings - 911.133.00
9 The crank looks good, but there are very light scratches across the bearing surfaces - here is my guess - based on research on this site (1) turbo engine put alot of burn oil junk (coke) back into the oil which is hard on stuff (2) the failed tensioner and chain ramp- put junk into the oil too (3) this was not a loved engine, but was not run too hard.
10 The clutch side main bearing is in good shape.
11 The intermediate shaft bearings are in good shape.
12 There is some sludge in the bottom of the case.
13 This is an early turbo engine - so it has the 2.7L crank and oil pump.

I will be rebuilding/upgrading the long block in next few months and add the following:

Install late model Carerra intake.
Swap over to electronic engine management.
Run crank fired distributorless ignition.
Install an intercooler.
Upgrade the cams (SC or 964)
Use a modern turbo header/exhaust.
Use a modern turbo (a K27 version).
Low restriction exhaust - loud and bad.
Use a modern blow off valve or recirculation valve.
Use a modern waste gate.
Run either a short G50 or re-geared 930 transaxle.

The goal is a 350hp to 400 hp engine that is happy on the street, but can handle track duty, with a useful power band from 2500 to 6500. I am NOT interested in a dyno queen with big numbers - this 911 will be used for DEs, autox, fun rallies and OLOA.

I need some help deciding a few items:

1 What sort of compression ratio should I aim for? Currently, it is at 6.5 to 1. I will run 10 psi of boost and would like a peppy off boost engine.

2 What is the cost effective way to increase the CR? I have heard of folks machining the heads to allow the cylinders to fit in deeper (1.0mm) to get a CR bump. Another option is offset wrist pin bushing. Is this a good way to do this? I would rather not have to purchase new pistons.

3 What cam shaft grind should I run? Since this is a 3.0L – is the 964 cam with ported heads too much?

4 Any reason to upgrade to a later 930 or 964/933 oil pump - (this engine is an early turbo so it is the Euro Carrera based 3.0L that used the 2.7L pump and crank).? Not alot of info out there on that.

5 Should I replace the chain and sprockets?

Any other input would be more than welcome.

I will post images in the next few days.
Old 07-09-2010, 08:15 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)