What would you do?

[shbop]

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.

[Henry Schmidt]

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

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.

[mb911]

Originally posted by Henry Schmidt
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.

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

[cstreit]

Originally posted by Henry Schmidt
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.

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.

[kenikh]

Originally posted by cstreit
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.

[shbop]

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?

[Henry Schmidt]

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

[shbop]

Thanks Henry!

[Eagledriver]

quote:
--------------------------------------------------------------------------------
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
--------------------------------------------------------------------------------


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

[Wayne 962]

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

[shbop]

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!