Opinions Wanted - 1977 930 3L Rebuild/Upgrade

[Outlaw 911]

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.

[kenikh]

If you are running EFI, dump the pistons. Since it is a 3 liter you can't bump compression by going to a longer stroke crank and the most CR you can get decking the heads is an additional .5 pts. 7:1 blows.

You will be happy to know that 8:1 CR on EFI is now the norm. These early motors have really small ports, too. A port job, big port SC or 3.2 heads are really in order. If going EFI, you really should go twin plug, which is compulsory for 8:1 CR. 964 cams are a good choice, but a GT2 cam is the hot ticket. Also, consider a Garrett GT35R over the K27...same money, better turbo IMHO. Couple all of this with RarlyL8 headers and you'll have a BEAST. Scope creep? Maybe. But given your goals, this is the right way to go. If not, you'll still have a fun car, but will not realize the full potential of your planned upgrades.

If you stick with stock pistons, button it back up with SC cams and call it good.

[kenikh]

BTW, yes, upgrade the oil pump...stat!

[kenikh]

Another nice upgrade is a 66mm crank, reground to 70.4 mm stroke. Much stronger than the 6 bolt 70.4mm crank. Or even cooler, regrind the 66mm crank to 66mm stroke on SC journals and you get a 2.8 short stroke turbo with the optimal 130mm rod length. Requires custom moly or GT3 titanium rods, but hey, it's all academic right now, right?

[spuggy]

I would be careful about tuning a 3.0 930 too much for top-end performance with cams, ports etc. if it's not going to live entirely on a race track.

I found a RoW 3.3 turbo with SC cams, 8:1 C/R and stock ports/intercooler/3DLZ to be a fairly dispiriting experience off-boost in traffic - and with a 5 speed in a 2500 lb car, that was as nothing compared to a stock 930 (Note that small ports help low-end torque.)

With a K27 hybrid, Kokelyn and GHLs, it was a different beast altogether.

EFI will give more flexibility - but you want a 5-speed IMHO.

John "camgrinder" Doherty recommends SC cams for a street 930, as do many other people. More mid-range, slightly less at the top. On the street, you'll be using the mid-range much, much more than you'll ever manage to use anything near the red-line.

Don't use a blow-off valve. This will mess up any injection system by releasing metered air and screwing up the AFRs. Use a 964-style recirculation valve - there are billet replacements for the plastic Bosch item that last longer/tunable/rebuildable.

Why are you going down on stock boost? 12.5 PSI is .8 bar - all 930's used the same wastegates AFAIK. With an intercooler and EFI you should be able to run at least the same, if not higher.

Active knock sensing would also allow you to run significantly more advance off-boost. The difference between 25 degrees and 28 degrees in town driving on a 3.3? At least 3-4 mpg - because with the more retarded ignition you need to actually OPEN the throttle slightly to pick up speed. With good gas and 28 degrees advance, you hint at opening the throttle and you're already backing off...

With the money you're looking to spend, talk to Rarly about the twin-turbo headers he just fabbed. That should really get the most out of a small displacement motor - great flexibility as well as much power as you can use.

I trust you've allocated as much thought/funds to suspension, wheels, tires and brakes? Stock 930 rear TBs will squat horribly in that chassis - and SC brakes leave a little to be desired.

[Steve@Rennsport]

Food for thought,.....

We recently did a '78 3.3 930 engine for a client that came out quite well.

We used new OEM 97mm P/C's, SC cams, stock heads with new valves, guides, etc. We retained the stock CIS system and added a custom Garrett G35 turbo, bigger IC, modified B&B header/HE's, Powerhaus muffler, and a Tial wastegate since the OEM one couldn't control the boost.

At .8 bar, it made 426 BHP.

Surprised me, too but the results were repeatible on every pass as we worked on controlling the turbocharger.

Nothing fancy here, simply good construction practices along with using properly matched components to make a quick-responding street car with plenty of power that retains OEM durability. Its all about managing the details.

This wasn't cheap to do, however at .8 bar, it will last a VERY long time; something that cannot be said about many modified 930 engines and thats where the payback lies.


Spuggy offered good thoughts about suspension & brakes that are commensurate with the power and acceleration potential.

[930slant]

Steve,
I have a very tired 88 930 that i would like to refresh with an rebuilds similar to what you describe on the 78 3.3. You mentioned that the rebuild was expensive. Since everything about Porsches falls into the "expensive" range, I'm curious what the general cost of a rebuild as you describe costs. Thanks!

[Steve@Rennsport]

Originally Posted by 930slant

Steve,
I have a very tired 88 930 that i would like to refresh with an rebuilds similar to what you describe on the 78 3.3. You mentioned that the rebuild was expensive. Since everything about Porsches falls into the "expensive" range, I'm curious what the general cost of a rebuild as you describe costs. Thanks!

There are a lot of variables in rebuilding these engines due to the condition we find them in and what needs to be done.

Generally speaking, I don't post prices here since without all the details, its usually taken out of context.

Feel free to call me.

[930slant]

Thanks. I understand. I'll give you a call.
J.