1980 US 911SC - engine rebuild/upgrade

[Glenfield]

All,

I’m up for an engine rebuild on an ‘80 US spec 911SC. The “how I got here” makes for painful writing and (potentially) interesting reading but will spare you that backstory here (since I’ve done it to death on another thread). Thanks to all who have already weighed in there!

I’m resigned to my fate and have cried myself to sleep while reading Wayne’s book on engine rebuilding and these here forums (incredible resources!). I believe I now have a good game plan for setting this car right. I do have lingering questions that I haven’t been able to answer and would also like to get your collective opinion / sense check on a list (to come):

Pistons and cylinders: intention is to re-plate and re-use my existing P/Cs since they do appear to be close enough to spec (being determined). Fortunate also to have Mahle 9.3:1 in the car so a good base to work from. Had some questions should I not be so lucky on re-using the existing:
1. How are folks replacing 95mm ~9.3:1 P/C in the new aftermarket? Without other changes, I don’t want to go to 9.8:1 Mahle if I can avoid it and 9.5:1 Nickies are overkill for my stock engine

2. Excellent debate going on in various threads around re-plating at Millennium (via EBS) ... My takeaway is that Millennium (still) do an excellent service that can be relied upon, provided you send them your pistons with your cylinder and clearly specify dimensions and Ra? I admit, I still don’t know which camp I’m in on the Ra debate and have more to learn there ...

Performance upgrades and “stock”: outside of engine, car is an otherwise excellent stock car of relatively low mileage (~70k). I want to remain faithful to that DNA, while future proofing the rebuild slightly i.e. me 10yrs from now won’t want to re-open the engine, but may dislike present self for not doing [insert upgrade] now when I had the chance. Will only see street driving and currently dines out on 93 octane in Illinois but may accompany me West on my way back ‘down under’ to Australia.

So my philosophical question is, at what point do engine performance upgrades turn a stock car into a “modified” car / “hot rod”? Having not enjoyed stock guise for long enough, I don’t want to get the cart before the horse (or horsepower before the car) but am considering:
- P/C: if I have to replace, is a bump to 9.8:1 of itself enough to earn the “modified” moniker in a US ‘80 SC? I probably would look at it that way but Mahle 9.8:1 seems to be the most readily available (albeit, not my preference for a range of reasons)
- New cam: mine has pitting and so am thinking DC15 (if I keep 9.3:1 compression) or 964 (if I increase to 9.8:1) ... shout out to John Dougherty / cam grinder for his time on this topic earlier today! Cams and small v big port SC motors is a fun rabbit hole to go down

I am compiling a list of reliability upgrades and pre-emptive leak-prevention work that I’d greatly appreciate folks opinions on. It’s more important to me in this rebuild than the above but is still coming together (and less fun to dream about). It’s a synthesis of all the threads I’ve digested and Wayne’s very comprehensive guide in “Engine Rebuilding” and “101 Projects” (again, shout out to those books).

Cheers,
Tom

[Mike Andrew]

Subbed

[Flat6pac]

70k miles, you’re just broke in on the cylinders. Mahle is nikisil. Clean up, glaze break and run.
Weak spot is always the heads, do a valve job because your guides are failing, change bottom studs and you’ll be good for the next 70k over 40 years.
Bruce

[Glenfield]

Thanks Mike and Bruce.

Agree on the P/Cs, Bruce. Presume you mean re-plate those out of spec and just clean up others? At least one is out of spec on ovality (#4 and probably #5). I presume Ok to mix and match OG and re-plated cylinders if balanced. Pistons have slight wear on skirts but are otherwise Ok and plan to reuse.

I’ll also change out exhaust studs with steel and do valve job when head is being cleaned up.

This the list of leak prevention R/R I’m planning on. Hopefully I’ve caught them all:
1. Crank case breather hose and gasket
2. Oil cooler thermostats ring
3. Oil cooler seals
4. Oil tank level sender
5. Oil pressure switch
6. Replace oil return tubes
7. Rocker arm seals
8. Oil pressure sending unit
9. Cam housing gaskets
10. Flywheel seal/pulley seal
11. Distributor O-ring
12. Check and clean all oil ports and oil squirters and oil lines. Pressure check pump
13. Replace oil pressure relief springs and pistons

In terms of preventative maintenance, will probably only do clutch.

[Mike Andrew]

Tom;
I assume the shop is still doing the rebuild. If so, most of these seals should be included in the gasket kit. Since there were aluminum (aluminium to you) bits found during disassembly, I think # 12 is critical. You might give the oil tubes to tank and engine looked at and the fuel lines in the engine bay.
Clutch kit is a no brainer since it is a bolt on during assembly and far cheaper than doing it as a stand alone.
While this is painful now, the joy and carefree driving for years will offset the discomfort. If values continue increasing, the overall cost may be significantly offset. Plus being able to have a smile on your face every time you look at it and drive it.
Should be done in time to drive it up to Road America and show it off at the historics or IMSA races.

[Glenfield]

Thanks Mike. That’s where my heads at also on clutch and oil routes and the ‘aluminium’ ... Will be back together before long and looking fwd to cruising up to Road America. Had been targeting Sister Bay over July 4 post break-in but that’s probably wishful thinking from here.

[Mike Andrew]

Update on progress????

[fred cook]

Your 1980 heads have the small ports so you might want to consider a porting job. Also, the airbox has the small ports so a swap to a 78/79 big port would help also. The best thing you can do for the exhaust would be a set of SSI headers or the equivalent. I used the 964 cams and am pleased with them thus far. They are just a notch hotter than the stock 1980 cams but you can feel the difference. As you have found out, this is a slippery slope process so you pretty much have to decide if you are willing to stay pretty stock or want more of the go fast goodies. Remember, all it takes is money!

[Glenfield]

Guys, thanks for checking in.

Mechanics back from life duties so clock has only just started on a replate of cylinders at Millenium and rebush and recondition of rockers. Three more weeks and then should be into the break-in.

Fred, I ended up going with the Web 20/21. Little bit of a “stock plus” decision to provide some future proofing. Was the result of a lot of existential soul searching on my behalf. Ultimately, I was swayed by a gentleman on here (Superman I believe) that was the world’s biggest advocate for small port, high compression and 964 or 20/21 cams (with backdated exhaust). The combination of higher fuel velocity from the ports and higher compression generated (surprisingly) considerable torque and HP in lower revs. Some really impressive dyno results relative to other configurations. Of course, then it dropped like a sack of spuds in the 6k range, which is probably fine for my intended use. I’ll dig out the thread as it was very interesting.

Last remaining outstanding points on my build:
- mechanic doesn’t seem concerned with magnafluxing crank and rods. Says they’re perfectly fine. Seems to be cheap insurance?
- engine balancing - I will probably not check crank balance since it hasn’t been damaged or touched since it rolled off the line I’m 1980. I’m very tempted to zero balance the rods and pistons etc ... mechanic says blue printing and matching based on stock weight classes is more than adequate at the revs I plan to live at. For an extra 300 and chance of a glass-smooth engine though, the race balance is on my mind big-time

Mike, PM me your email and I’ll send you a spreadsheet that will help your thinking around a build.

Cheers,
Tom

[fred cook]

[QUOTE=Glenfield;10915183]Of course, then it dropped like a sack of spuds in the 6k range, which is probably fine for my intended use. I’ll dig out the thread as it was very interesting.

For your described use, 6K should be plenty. My engine is a 3.3SS which is rev happy to begin with so I wanted it to make good power at least up to 7500. Turned out to do that and more! So, I set the ignition interrupt at 7500 to keep from blowing it up. You will probably be ok with the 1980 rods as they are some of the strongest stock rods you could use. A balance job or at least a balance check would be good insurance. You might want to use the ARP rod bolts though!

[Glenfield]

Your 3.3SS sounds like a hoot! Mainly track and DE or a hot street build?

On the slippery slope, when I thought I was up for a new set of P/Cs, the better (Porsche) angel of my nature had me thinking 3.2ss. I then thought of going the 930/10 route with higher compression and larger ports. In the end, I regained my senses and kept the limiter on myself. This is a good stock car and so stuck with the slightly hotter cam which as you say, will be plenty fine.

That is reassuring about the rods. I did end up going the ARP bolts and also upgraded the oil pump in case down the line, I get more expansive on the top end.

Good call on balance check. I will certainly do rods and pistons. Bit reluctant on the crank, as I don’t know of a machine shop in Chicago area that I’d trust to absolutely do a better job that Porsche did all those years back.

[fred cook]

Originally Posted by Glenfield

Your 3.3SS sounds like a hoot! Mainly track and DE or a hot street build?

On the slippery slope, when I thought I was up for a new set of P/Cs, the better (Porsche) angel of my nature had me thinking 3.2ss. I then thought of going the 930/10 route with higher compression and larger ports. In the end, I regained my senses and kept the limiter on myself. This is a good stock car and so stuck with the slightly hotter cam which as you say, will be plenty fine.

That is reassuring about the rods. I did end up going the ARP bolts and also upgraded the oil pump in case down the line, I get more expansive on the top end.

Good call on balance check. I will certainly do rods and pistons. Bit reluctant on the crank, as I don’t know of a machine shop in Chicago area that I’d trust to absolutely do a better job that Porsche did all those years back.

It is a hot street build. Unfortunately I don't have access to a track near my home. A few years ago I did make the trip out to Monteray and took one of the performance driving schools at Laguna Seca. Now that was a hoot and a half. We practiced driving techniques all day and then got about an hour on the track. Wish I could get my SC out there for a session!