What would you do?
 

I've got an 81'sc . I had so much fun building my 66' 2.0 that I would like to get into the sc motor, and with that, I'd like your thoughts. If you were in the same position, had an extra set of 40 ida's, and a budget of $5500, what would you build? Keep in mind that this is a driver, and yes, it's running well right now. Thanks in advance!

Jon,
Does the SC need to pass smog in Oahu?

No smog! Thanks Doug, I forgot to mention that. No track, and no smog. I guess you can't have everything.

Jon,
Lucky you. Most of us have the old smog nazi's hanging over our heads.
I like what I did to my 2.7.
No reason you can't do the same to your SC.
If you already have the webers, I would talk to John Dougherty about the best cam and piston combination for tooling around the island.
Get whatever additional carb parts you need from PMO, great people.
If you can get fuel over 91 octane for a reasonable price then a higher compression piston from your stock 9.3:1 is possible.
The euro version was 9.8:1 and made 204 hp.
Going to a '72 915 transaxle with a 7:31 ring and pinion gear made a big difference in my car on the track.
Since you usually don't see the high cruising speeds on the highway's like we get in New Mexico, I'd recommend going with the '71/'72 transaxle if you can find one.
I did the complete transaxle change, rather than getting the parts to change my original trans.
The labor plus the parts would cost as much or more than the $1500 I paid for the '72 transaxle, and I still have my original 915 in great shape. Maybe sell it sometime.
Yes, get a cam and pistons, freshen up the top end, maybe a new clutch to go with the transaxle, and let the fun begin.

You would be plenny happy with some dakine exhaust too, brah. Try get rid of dakine cat & free da bugga up some.

$5500? ARP rod bolts and Mod-S cams and maybe some better than stock valve springs, which is way cheaper than $5500. Are your heads big valve SC? If so, you are good to go. If not, I'd find a set.

That's all you need for a super torquey 7200 RPM rev monster. If you have to go further, you can bump the CR with new pistons, but the cost/performance benefit just doesn't warrant that move. I'd just cut your current pistons to clear the new cams.

Doug, It just so happens that I've got a 71' trans. , but I don't know the ring and pinion--I'll check it out. Makes sense, since freeway driving is minimal.

SWW914 "shoooots" Already running 1" 1/2 headers

Kenikh-- 81' heads, so small port, but I was thinking that they could be opened-up. ?? Your other mods leave cash on the table. Not that I'm opposed to that, but "s" cams with the cis pistons??
Thanks again!

S cams with CIS pistons can be done if you machine valve pockets into the swirled domes to clear the valves. You can have those heads opened up by the usual suspects, too. I would probably just spend $900 on JEs, though.

One of our spec racers opened up his own 81 SC heads with an air powered dremel like tool. He found a socket with an outer diameter of 39mm and cut away until the socket fit into the port. It was a very crude operation but it worked great. He has as much power as any of us.

If it were me I'd port the heads to 39mm or have them done and put a 964 cam in. I'm using stock rod bolts as I think they are plenty strong in this application. With no other mods and an early exhaust you'll get over 230 HP. You can get a little more by going to bigger carbs but why waste your money. I believe you'll also need to change the distributor to a 78-79 or get yours recurved for more advance.

One more suggestion would be to put racing valve springs in. That way you can rev to 7200 or so. With the more open intake and exhuast the peak power is at the higher RPMs.

-Andy

Thanks for the replys! I think enlarging the ports, springs, retainers and distributor work is for sure. Pistons and or cams seem to be the puzzle for me at the moment.
Andy-- the work that you described--did it include changing the pistons, or leaving the cis ones in?

Our spec class requires stock CIS pistons so that is what he has and what I have. Your CIS pistons are 9.3 to 1 so I don't think you'll gain much by changing them. If you use the 964 cam profile you won't need to change pistons. This makes a great motor with good torque and pulls all the way to 7000 RPM. I don't think you can do much better unless you put aggressive cams in and spin it to 7500 plus. A motor like that won't last as long as the one we've been talking about.

-Andy

Clean up the exhaust , early or SSI, headers if you don't need heat.
If the pistons are good, put valve pockets in them. You won't need much and the compression change is minimal.
DC 40 cams stock valve springs are fine.
Port intakes to 38 mm.
38 x 40 mm PMO manifolds.
Sachs sport clutch (aluminum so the engine spins up)
3.0 SC engine use 10mm rod bolts so stock bolts are fine.
220-230 hp and wqay under your target price.
If the budget allows, by JE 9.5 :1 compression.
Now for the self promotion:
Get rid of the Diliavar studs and install Supertec heads studs.

Thanks Henry. I've got to try and plug-n-play. We don't have a machine shop that would know what to do, to the pistons. Maybe better off just going with the 9.5:1's. How about the distributor? Can I have mine re-done, or should I look at something else?

Send us the pistons and the distributor.

http://forums.pelicanparts.com/uploa...1161183731.jpg

Thank you!

Thanks for the photo, Henry. I have heard of, but never seen the results. Very cool.

Agreed with above...

GE40 or similar cam, webers, p&c's, and rod bolts...

Might be tough to fit in at $5500 but it's worth a shot and about 60-75 BHP conservatively....

Why does he need cylinders? If he was going the JE/Nickie route, it would indeed be diffficult to fit the budget, but his CIS pistons, cut and reinstalled will not only be adequate, but very enjoyable.

Yeh, why new Ps&Cs?
Remember we're trying to stay within a limited budget.

Rods bolts (aftermarket) are not necessary under 7800 RPM.
The engine we're discussing will top out a high 6K low 7K.
911 SC rods are design to be stronger (perhaps the best Porsche rod design) and the stock bolts are more than adequate for this configuration.

You'll need to use stiffer valve springs or be very careful to keep the revs to 6700 or so. John Doherty sells a set of uprated springs for a very reasonable cost. That is what I'm using on my engine. You'll find that with the carbs you'll like reving the engine to 7200. The stiffer springs will give you some insurance incase you exceed your intended revs.

-Andy

Thanks everyone for the information! Can't wait to get started. There are a few family matters at hand ( kids in school), but this project should be well underway by January 1.

I totally disagree. The whole subject of aftermarket valve springs is out of control.
All Porsche 2 valve race engines from 1965 to 1989 ? or so used an inspected version of the stock spring. It's a very good quality spring. That means all 906, 910, RSR, 935 and 2 valve 962 used production springs (8000 rpm and 24 hr races)
The only reason to use an aftermarket spring is valve lift. The stock spring can only handle 490 lift safely. The problem is coil bind. High lift cams cause the stock spring to coil bind if spring height is set for reasonable seat pressure.
For 98% of all engines stock spring are the best choice.
High seat and over the top pressures are common with aftermarket springs and these high pressures cause unnecessary heat and wear.

I agree I was talking with someone the other day about the same thing and this is what I am going to do as well

All true... However he's looking for "ideas", not "idea". P&C suggested because depending on what his compression ratio is, he might bump it up a bit... ...and RE-rining Alusil CIS pistons with a lot of miles is a hit-or-miss IMHO.

Good point. On this note, Nikasil recaoting of Alusil cylinders is a good way to go, too.

Post tear-down, I'll certainly know more about the condition and type of p's & c's. I'm inclined to probably over-due things. It will be very difficult to resist the urge to inspect the insides of the case, and comming from the Chevy world, not replace crank and main bearings, just because. I know that even wioth 120K the bottom end could still have a lot of miles left, but it's a habit that's hard to break. It gets a little easier every time I order parts, as the cost of these sure gets your attention. I know I could probably look this up, but if it turns out that the c's are Alusil, and I decide to replate, does the re-plating add-to, or shrink the inside dimension of a cylinder?

Replating is generally done to size. That is 95mm cylinders are generally replaced to 95mm +or- .001.
If you have Alusil cylinders you are better of buying a set of good used Nikasil cylinders. They are generally less expensive than replating and the replating process varies in quality. I rarely see a replated cylinder that is as round as even a good used Mahle.
New Mahle cylinders are generally .0002" out of ovality.
My new QSC cylinders are less than .0004".
Good used cylinders can be as close as .001"
I have seen replated cylinders .002 out of round.
Whichever you choose, I suggest measuring them.
Cheers

Thanks Henry!

quote:
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Originally posted by Eagledriver
You'll need to use stiffer valve springs or be very careful to keep the revs to 6700 or so. John Doherty sells a set of uprated springs for a very reasonable cost. That is what I'm using on my engine. You'll find that with the carbs you'll like reving the engine to 7200. The stiffer springs will give you some insurance incase you exceed your intended revs.

-Andy
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Henry says...I totally disagree. The whole subject of aftermarket valve springs is out of control.
All Porsche 2 valve race engines from 1965 to 1989 ? or so used an inspected version of the stock spring. It's a very good quality spring. That means all 906, 910, RSR, 935 and 2 valve 962 used production springs (8000 rpm and 24 hr races)


Henry I very much value your opinion as do most of the other members of the board. This time however I believe you are just wrong. You will get valve float with stock SC cams at 6900 RPM as seen by some of our spec racers on an engine dyno. Factory cams for high RPM have very shallow ramps so as to not accelerate the valves too quickly for the springs to keep up. This is why you can do better with cams such as the DC 40,60 etc. You can accelerate the valves faster and get more torque and HP. The drawback is that you have to use stiffer springs or lighter valve train components. Stock springs are no problem on a 911S cam at 7300 RPM, try this with a "Mod S" cam (DC 40) and you'll drive the pistons into the valves. In short the RPM limit is not determined just by the valve springs but by the shape of the cam and the weight of the valve components as well. There are many engines that don't need aftermarket springs but if you are going to use an SC cam or 964 grind at over 6900 RPM and with stock valves/retainers then you need stiffer springs. John Doherty can back me up on this.

-Andy

Make it similar to the engine in my '72 RS clone, but with a bit more kick:

- 3.0L SC case, stock bottom end
- 3.2 Big bore pistons and cylinders
- Weber 40s with large venturis
- Mod 'S' cams
- 2.7 CIS distributor
- Stock 3.0 heads, or the larger port 78-79 heads

You would be *very* happy with this combination.

-Wayne

Well, the fickle hand of fate has not been kind. Turns-out, I've got Alusils. Well traveled at that, so now I need to ask another question. Since it's time for another set of p&c's; 95's or 98's? Is there a down-side to the 98's?
On the distributor issue: Aside from changing the crank gear, can someone tell me exactly what happens when you use a 2.7 distributor? Do they all need to be modified for use in this application, or just the "001" model? Is the only mod. the advance curve?
Thanks to all, and Merry Christmas!