new to forum what to build?

[borzie]

Hello to all fellow Porschephiles!
I must admit I've been a closet Pelicanite for a while but today have come out. I've been a Porsche freak for some time and didn't realize there were so many others as fascinated by these cars as me. I have been reading the posts for some months and am just overwhelmed at the information exchange, opinions, facts, help, and just such a focused group with one interest....how to make the Pcar better! I've had a bunch of Porsches, including a 944S2, (ya, it had a rad) fantastic car, high maintenance, came back to a 911 for the joy of doing stuff myself. I have so many questions to ask all the experts, my SC is looking at a rebuild....the first silly question, What is the big deal with the JE 98's, why did Porsche go with stroke increase rather than bore, (3.2 Carrera) is increasing both the way to go (3.4)? I'm looking to build a real torquer hot rod, have the cams and 3.2 clys, looking for opinions from anyone who has done either.
many thanks!

in Ferdinand we trust!

thanks Wayne for all you do

[Grady Clay]

Welcome to the Forum. I won’t ask for an image because I might be chastised for being critical. Aagh, post a cool picture of your 911. We will all say WOW.

Your SC can be made as large as 3.5L – well, perhaps a bit more. The Mahle Nikasil 100x74.4 work just fine. It should be twin plug. It can use carbs, EFI (Motronic and other), or MFI for high performance. CIS works OK if it is a street daily, many may argue that point, that's OK. The compression ratio is determined by your availability of high octane fuel, cams, and intended use. Cams are determined by your intended use, induction system, and some RPM restrictions.

The basic questions you need to ask yourself are:
What is the intend use?
What fuel is available or how much effort am I willing to go to in order to have access to high octane fuel?
What is my budget?

A BIG SC is great fun.

Best,
Grady

[geof33]

Now Grady, coreect me if I am wrong... but the 3.0 case requires the RSR distributor for the twin plug set-up. A 964 dist doesn't work. That's why I chose not to twin plug mine... BIG $$$$!!

Hopefully we can meet one day soon. My RSR project gets it's roll cage and the drivetrain back in next week... See you at the track...

Let's not be steering a newbie astray...

[Elombard]

I think he was talking about crank fired??? Thats interesting I thought I had seen some 964 dizzies in SC cases, maybe they were carrera based. Is that because of the direction of spin or someting else? If you are doing a full build cant you change the gears to carrera for the right spin direction??

[mtelliott]

Wouldn't going with a bigger bore create greater heat as compared to a longer stroke? If the cylinders can't get any wider, creating a bigger bore will thin the walls making heat dispertion less efficient and reduce the strength of the cylinders? Or is it not enough to be concerned with?

Disclaimer: I'm not a metalurgist and don't play one on TV nor have I slept in a Holiday Inn Express.

[Grady Clay]

Here is part of an e-mail exchange with another Pelican a few days ago:

Question:
Ignition: Twin plug is a given but after reading about all the options on Pelican I am even more confused. I would like to do a real twin plug distributor with proper cap and rotor but am worried about initial cost of the distributor and ongoing availability of the cap and rotor. Found a twin plug distributor, 12 plug cap and rotor from a guy out east but am not sure what a fair price would be. Also have heard that there are a lot of 935 twin plug distributors out there that will not work with my application. Help!
So, if I go with a more modern crank fire set up what do I need to make it all work and look somewhat like a vintage twin plug? Any brand (MSD etc.) that you like better than another?


Answer:

I can understand the confusion. There are several different approaches: First decision is weather to use the old technology cap and rotor or to use the new technology individual coil, crank fired electronic systems.

Here are the pros & cons, as I see them:

Cap & rotor;
Pro;
Looks cool, all those wires and huge cap.
Is somewhat original, certainly original Porsche race car.
Works OK.

Con;
Very expensive to buy.
Very expensive to maintain. Remember ignition components are normal service items that need to be summarily replaced on a regular basis.
Probably less reliable.


Electronic version;
Pro;
Less expensive to buy
Less expensive to maintain.
Current technology.
Probably more reliable.

Con;
Not original.
Possibly less “cool factor”


There is a third choice. Given my penchant for “sleepers” you can hide the electronic ignition behind the engine on the shock cross-member. You can put a dummy 6-wire or 12-wire distributor in the original location. Even for the trick 12-wire, It can have a cracked cap and no rotor – almost free. Even the exhaust plug connectors can be hidden.
You can have a twin-plug 2.8S that appears original ‘69S 2.0.

End Answer.


mtelliott, the secret is using the 1.82:1 engine cooling fan, the larger piston squirters, largest oil pump, and a big front full-fin oil cooler. Additionally, for DE events in hot weather, the “Rubbermaid Solution” works well.

EW, the direction of rotation of the distributor is simply matching the correct drive gear on the crank to the matching distributor.

Best,
Grady

[mtelliott]

Can someone point me to a discussion on how the electronic version works? Do you not still need a distributor to monitor the rotation of the engine? I realize the plug firing can come from the electronics but how does the electronics know when to fire without a distributor?

Sorry for the ignorance. I know there is a simple solution.

Michael

[Grady Clay]

Michael,

Good question.

The simplest electronic “crank fired” ignition systems have three triggers in the pulley or flywheel located exactly 120 degrees apart. That is the basic sensor to trigger the spark process. Also they fire the sparkplug every revolution. Firing the plug at valve overlap usually has no effect. Ignition advance or retard is determined by the internal computer. It uses inputs like RPM, vacuum, etc. just like a conventional ignition system.

I would have to do some searching but the more sophisticated systems can use inputs from throttle position, temperature, knock sensing, atmospheric conditions, boost pressure, and more. Some can have computer logic or cam driven (1/2 speed) timing that doesn’t fire the plug every revolution.

The high end features are usually found with the combined EFI and ignition systems.

Another important feature is a “soft” rev-limiter where the engine just feels like it looses power rather than ignition missing or total fuel shut-off.

Best,
Grady

[mtelliott]

Next questions then would be:

How hard is it to retrofit? I'm sure there is excellent information somewhere on how this is done. Guess I need to use the search function.

[Grady Clay]

Now that we successfully hijacked your thread for a while discussing the vagaries of ignition systems (much has been posted on the Forum) lets discuss your actual questions some more.

There is no substitute for displacement, however you get it. All modern engines are "over-square" meaning the bore diameter is larger than the stroke length. That makes for high revving, high horsepower - but there is a limit. The other issue is rod length compared to stroke length. Remember this was an engine that was originally 80 mm bore and 66 mm stroke providing 1991 cc. With the longer strokes the heads have not moved farther apart. That means shorter rods and greater rod angularity - not necessarily good at the extreme.

When Porsche increased stroke from 66 mm to 70.4 (2.2-->2.4) they kept the bore the same 84 mm. The same was true from 70.4 mm to 74.4 mm (3.0-->3.2) with 95 mm bore. Of course they had already "experimented" with the 3.3 Turbo (97x74.4.)

A general rule of thumb is; increasing the stroke, everything else the same, increases low end torque. Increasing bore, everything else the same, increases high end power. Doing both results in increased displacement and increases both torque and HP.

I'm sure someone is (or has) building a 4.0 - just not out of a 3.0SC

When you say you want to "...build a real torquer hot rod...." Keep in mind air cooled 911s like revs. I am very comfortable buzzing around at 3500-4500. I am uncomfortable at 2500. It is all about air and oil flow. Of course when you stab the loud pedal at 4000, things happen right now.

A 3.5 (100x74.4) is a reasonable mod. I think we built our first one in '79.


Best,
Grady

[Rob 930]

To continue on the hijack, let me suggest yet one more twin plug option that seems to have been dismissed earlier in the thread: a 964 twin distributor. I believe they can be retrofitted and made to work, both in 911s and 930s (if you're willing to modify the turbo up-pipe). I have a picture of one that's in a 930, so I'm assuming they can be made to work anywhere. Please correct me if I'm wroing. The advantage would be cost; one can often be bought for a few hundred dollars (plus modification costs), and the replacement caps and rotors are readily available and not too expensive. Another general benefit to a distributor (or pair of distributors), is that you get sequential ignition (not wasted spark, as with most crank-fire setups) and you have the advantage of being able to run with only two coils and a two channel CD ignition, if you want to run CD. I don't think that a multi-coil wasted spark system is necessarily a bad thing, but if you try to run CD with a multi-coil system, you need lots of CD channels, which can be problematic and expensive.

[Grady Clay]

Rob,

I didn’t mean to slight the 964 twin cap system. Yes, there all sorts of advantages there, cost being the most significant.

Who can shed some light on the reliability issue?

From a technical perspective, two 6-plug caps are far better than the 12-plug cap because of reducing the possibility of cross-firing. Remember, the 4-cam Carreras had two distributors and so did 917s. How about an engine with two 16-plug caps that Porsche made


Yes, you are correct. Each sparkplug has its own CDI; such is the diminishing cost of electronic systems.

Best,
Grady

[geof33]

Originally posted by Rob 930
To continue on the hijack, let me suggest yet one more twin plug option that seems to have been dismissed earlier in the thread: a 964 twin distributor. I believe they can be retrofitted and made to work, both in 911s and 930s (if you're willing to modify the turbo up-pipe). I have a picture of one that's in a 930, so I'm assuming they can be made to work anywhere. Please correct me if I'm wroing. The advantage would be cost; one can often be bought for a few hundred dollars (plus modification costs), and the replacement caps and rotors are readily available and not too expensive. Another general benefit to a distributor (or pair of distributors), is that you get sequential ignition (not wasted spark, as with most crank-fire setups) and you have the advantage of being able to run with only two coils and a two channel CD ignition, if you want to run CD. I don't think that a multi-coil wasted spark system is necessarily a bad thing, but if you try to run CD with a multi-coil system, you need lots of CD channels, which can be problematic and expensive.

From what I understand on the engine forum, is the 964 dist will NOT work with the 3.0 case... If it were a simple mod, I would have been all over it... So far there has not been anyone I have spoken to that suggests it is a reasonable option on the 3.0 case... ?????

[borzie]

this is fantantic, I want both, lots of low end torque(what you feel) and high revs speed (fun at da track) thanks Grady for that simple explanation Twin plugging never crossed my mind, I'm keeping the CR at 9.5:1 and was planning on having 98mm pistons and possibly a crank and rod change to get the stroke to 74 to make a 3.4 (+or-), what the fuch is an "up pipe"? Can I stay with the CIS if I went this big?. This is supposed to be a reasonably priced upgrade, if not, might as well try to find a decent 930

[Rob 930]

The up pipe is the charge air pipe between the turbocharger and the intercooler, such as you'd find on a 930. There's no up pipe on a normally aspirated engine like a 911.