It’s my turn to choose pistons and cams for an SC

[Porchdog]

This all started with a broken head stud...

My car is a 1981 SC that has given me 30 years of faithful service. When I found the broken stud, I figured it was time to fulfil a long-time goal of “More Power”.

Thanks to the Classifieds here on Pelican, I now have a rebuilt long block and heads (1981). The heads are small port with single plug – but they are fully assembled, so I’m not too eager to pull them apart for porting or twin plugging. I also have SSI’s and a full X-Factory / Rasant ITB and crank trigger ignition.

My goal is to have a lively, reliable street motor on pump gas. Since I’m buying pistons and cylinders, I’m thinking I might as well go 3.2 SS with 98mm cylinders. I won’t have the constraint of CIS, so camshaft options are pretty much wide open.

For pistons and cylinders I’m thinking the Mahle PP98-015 set is the obvious choice – 98mm, drop in 3.0-3.2 and 10:1 compression. I’m assuming that I will need to use a thicker base gasket to drop that compression a bit with single plugs.

When I was planning to rebuild my existing motor I was leaning to reusing my current cylinders with higher compression pistons, but since I’m buying cylinders anyway – 3.2 seems like the way to go.

Mahle used to offer PP98-005 for non-CIS applications – but that seems to be obsolete? Fred Apgar’s pistons look interesting, but I’m assuming there’s no advantage if I’m not using CIS. Are there better options for street use that I’m missing?

For camshafts – E cams or GE-40’s seem to be the thing for a street application with ITB’s – unless there’s something better I’m missing?

Thanks for any input!

[fred cook]

When I rebuilt my 3.0 SC engine in 2013 I went thru the same decision process. I decided to go whole hog with twin plug Carrera heads, 100mm Mahle 11:1 pistons, LN Engineering cylinders, 964 cams, large port early SC airbox, SSI exhausts and some CSI mods. The 100mm pistons give a 3.3L displacement and the large ports let more air flow. I used the Electromotive Xdi ignition system to fire the plugs. This allowed me to delete the distributor and not have to buy expensive dizzy caps and rotors. After assembly, I ran compression tests on all cylinders and found the actual compression to be 10.85:1. Close enough! I have not had this engine on a dyno, but seat of the pants estimate of HP seems to be over 250, maybe as much as 275. With the twin plug system it runs quite well on 91 octane pump gas. One of the mods I made to the CIS was to wire the cold start valve so that it would engage when at full throttle. My reasoning was that the extra gas would help prevent a burned valve or piston. Happy building!

[Porchdog]

I was under the impression that the cylinder walls were getting questionable with the 100mm bores and the standard case spigot diameter - but I see that LN offers that set as "Slip In".

Since my "new to me" long block and heads are all freshly assembled I'm reluctant to do more work on them. I'm guessing that the single plugs would be ok in 100 mmm bores with low enough compression - but how to figure out what's "Low enough"?

I'm further guessing that a serviceable set of 964 cams would save some money over the GE-40's. I'm curious how you chose those. I figured that one advantage of the ITB's was that my cams could have more overlap.

Thank You!

[fred cook]

I strongly encourage you to go twin plug with the Xdi 2 ignition system. You will be giving up a lot of hp otherwise. Being able to make adjustments to the timing is quite handy! The difference between 8.:1 and 11:1 is pretty large! Also, think about selling the small port heads and get a set with larger ports. Again, makes a big difference. The small port heads will likely start to poop out around 5500 rpms while a large port assembly will still be making power at 7500, especially if you use the afore mentioned ITBs.

To answer your question about picking the 964 cams, the timing overlap and the valve lift is just a bit more aggressive than the SC cams. I didn't want a real "rump rump" idle.

[Dpmulvan]

How much money do you have?

[Porchdog]

I think the question is actually how much am I willing to spend on this project.

I have already spent more than my wife thinks is reasonable - but she has spent three decades thinking the 911 is a noisy uncomfortable car that doesn't cost very much.

From where I am right now - I looks to me like pistons and cylinders will be $5,000 - $8,000. Cams $600 - $1500. All the other stuff to put the motor together - at least a couple thousand.

If I change direction to take Fred's advice - several more months - maybe another $10K?

In my head I'm thinking I will have this motor together for another $8K. My joy would be dampened if it's another $20K.

[shoooo32]

Mahle PP98-015 are on sale all over ($3500). Combine that with a set of M1 cams and you have a very nice engine that will still make torque from a stoplight and pull hard to 6500. With small heads, I think that's all you can ask for. Financially, there are diminishing returns beyond this setup - it costs a lot more to make more HP and that HP will be higher up in the rev range, which isn't always where you want it in a street car.

[911MANN]

I agree with Shoooo32, as I completed a similar project late last year and am very happy with the result. Take a look at my thread in the Engine Rebuilding Forum entitled "The 'Prodified' 3.2SS". I have the ROW version, and I made a few other improvements and expenditures that were likely unnecessary, but I won't complain. With this path, you will need to improve fuel delivery with your Fuel Distributor and WUR. I also recommend getting a nice valve job and head flow improvements (not porting) from an expert. And getting SSI heat exchangers with properly sized muffler. I cannot say if the larger 41mm SSIs are better with the smaller US heads, but hopefully, someone will chime in.

The only minor comments I experienced: My engine now likes to idle a touch high, at around 1050RPM, and I need to nurse the throttle with my foot for the first three minutes on cold start. After that, it runs as normally. If you want it to start and idle exactly as original stock did, I think the 964 cams would permit that, but I've been told they won't deliver quite as much torque and HP, and they also roll off a bit earlier in the revs. I do not have comparative dyno results to share. Speaking for myself, I am very willing to accommodate these 2 caveats for the performance I now have. Hope this helps.

[Porchdog]

Shooo and 911Mann - after looking at a variety of the builds documented on Pelican, I was thinking that I should be OK for my intended use with small ports and single plugs. I'm mostly zipping about on country roads - here that means mostly 2nd & 3rd. I already have SSI's and an M&K muffler. As mentioned above, I'll be using a full X-factory setup for ITB's & spark. I did hear from Al today and he endorsed the Mahle 3.2 kit with E-cams and small ports.

I'm bit intimidated by the anticipated tuning process with ITB's - but I expect I've gotten past tougher challenges. Plus, Al seems to have already worked through similar builds.

$3500 for the pistons and cylinders is less than I have seen - but I haven't looked hard yet.

Thanks

[targa72e]

A well flowing head can make more power everywhere. Below is some flow information comparing Stock 3.2 head to 3.2 heads ported with bigger valves by Xtreme.




I had Xtreme do the full workup on my 3.0 heads and had them flow tested afterwards. The Intake flow was almost identical to the 3.2 XTR above and the exhaust was just slightly less. I keep the port size close to stock 3.2 as it will be a street engine. My heads needed everything as the seats, guides and sealing surface were toast so easy decision to CNC port, add big valves (53mm, 42.5mm), head surfaced, and twin plugged.

john

[shoooo32]

Coming from a bone stock SC, a small port, single plug 3.2ss with a mild cam, SSIs and ITBs will feel like a rocketship. Head work seems like a bridge too far for a cost conscious build.

[PeteKz]

10:1 is the commonly accepted limit on CR for a single plug head, and that's using 92+ octane gas. However, the advertised CR's notoriously are higher than the actual CR in an assembled engine. If you buy the "10:1" p/c's you should be okay.

Next, if you have a recently rebuilt engine, Why start down the slippery slope of changing the pistons and cylinders to get 3.2? If you do that, and you want to change the cams, then you will probably slide down the slope to either porting your current heads or buying the larger port heads, otherwise, you are limiting what the new cam and ITB FI can do.

Like the broken head stud, if you open the new motor, you will rapidly end up at $10,000 plus if you pursue more power. Because, while you're in there...

[Porchdog]

I'm not starting with my original, complete engine which is still assembled.

I bought another rebuilt engine, minus pistons, cylinders and cams (same year). So the case is complete and the heads are completely redone and assembled.

Similarly, I already bought the ITB and ignition setup. This will be a complete replacement for my stock engine.

[PeteKz]

Okay, that makes more sense. You said you bought a "long block" which includes p/c's and heads and cam housings, assembled. What you have is a "short block" (case and internals) plus heads, etc.

Anyway, now the fun begins.

[911MANN]

Porchdog- Sorry I didn't read your post carefully enough to realize you will be using ITBs- I always liked the look of the Rasant induction. I would be particularly interested to follow your project if you used the M1 cams along with 98mm P/C and the rest of your specification. I wouldn't be surprised if you squeezed out a bit more power than CIS would permit. Please let us know which path you take and the results you obtain. Thanks.

[Henry Schmidt]

DC 20 and 21 are reasonable choices.
My favorite is the Web 20/21 which is similar to the DC21

Porsche 911SC-Leistungsgesteigert Piston & Cylinder kit.

The 3.1 L Wedge

[flat6pilot]

Not sure if this will make you feel better or worse.

It sounds like you're assembling yourself? My breakdown includes assembly and machine shop labor.

This is for a 3.0SC--> 3.2, Turbo build. Does not include turbo components, EFI...etc. Just the Long Block.


$819.08 ARP 204-4206 Custom Age 625 Porsche 911 Head Stud Kit Inc. Nuts & Washers
$1,123.00 ARP 204-5405 Porsche 911 3.0, 3.2, & 3.3 Crankcase Thru-Bolt Kit
$550.00 Regrind SC CAMS (964?)
$594.00 Rocker refurbish
$265.50 Piston squirters - Turbo
$300.00 Refurbish Crank (machine out oil plugs, fit with larger?)
$250.00 Magnaflux Crank
$300.00 Siemens 60lbs Fuel Injectors
$1,000.00 Cylinder Head Rebuild
$2,400.00 Cylinder Head Rebuild option: New Valve Guids and Seats, AASCO Springs + Seats + Ti Retainers Package
$950.00 Cylinder Head Rebuild MACHINING: Ni-Resist Rings
$300.00 Cylinder Head Rebuild option: Twin Plug
$320.00 Twin Plug Valve Covers
$11,100.00 LABOR
$1,300.00 964 Oil Pump
$4.50 964 spacer shim
$84.91 964 Oil Pump driveshaft
$39.50 Restrictor Fitting for Camshaft Oil Line at Camshaft Housing
$4,541.60 Porsche® 930 TURBO 3.0L to 3.2L (1976-1977) 98mm 7.5:1 Mahle® Cylinder and Piston Set
$2,479.08 CP-Carrillo Connecting Rods Set for Porsche 3.0 Liter with 3/8 CARR Bolts
$351.72 Clevite 77 Tri-Metal Coated Performance Rod Bearing Set for 3.0
$3,748.00 BRISTOW'S PARTS
$1,603.00 MACHINE SHOP LABOR

[Black 993]

OP, it sounds like you've created a complicated set of circumstances for yourself. You've bought a bunch of different stuff that doesn't really work together (a rebuilt stock long block; small port heads; ITB's and ignition system) alongside your stock engine that needs to be rebuilt.

IMHO, the way to proceed is to start with what engine you want/can afford and work backwards from there. If you want a warmed-up SC engine, keep the stock CIS and ignition, install pistons/cams/SSI's, and you're done. If you want a hot 3.2, keep the ITB's/ignition, probably makes sense to sell the long block you bought, and then rebuild the engine that's in your car.

But trying to play mix-and-match with the assortment of parts you currently have is no way to go about this project, IMHO. If you're going with ITB's, hot cams, and 3.2 p/c's, for example, it seems unwise to then use small-port single plug SC heads, just because you happen have those heads on the shelf. If you're wedded to using those heads, then build the rest of the engine to complement 34mm intake ports. If you want to use ITB's and go larger displacement, then sell or modify the small-port heads. You get my drift.

[jac1976]

Originally Posted by 911MANN

Porchdog- Sorry I didn't read your post carefully enough to realize you will be using ITBs- I always liked the look of the Rasant induction. I would be particularly interested to follow your project if you used the M1 cams along with 98mm P/C and the rest of your specification. I wouldn't be surprised if you squeezed out a bit more power than CIS would permit. Please let us know which path you take and the results you obtain. Thanks.

I assumed that the M1 cam was geared toward CIS and that there may be preferable alternatives for ITB.

[PeteKz]

Yes. The M1 was designed to maximize lift and duration with the CIS and Carerra piston domes. If you are using pistons with deeper valve pockets, you can choose higher lift and longer duration cams. Those will increase and move torque and HP further up the RPM range.