Carrera 3.0 to 2.8 Short Stroke Questions
 

I have another thread for my rebuild of a 1976 Carrera 3.0 (http://forums.pelicanparts.com/911-engine-rebuilding-forum/799309-engine-rebuild-diy-project-1976-carrera-3-0-a.html), but I have come to a crossroad and thought it best to start a new thread concerning the details of going 2.8SS rather than staying stock.

I understand that a Carrera 3.0 case, a 2.0/2.2 crank, and stock 3.0 pistons/cylinders make a 2.8 short stroke, but I have the following questions to clarify some specifics:

Does it matter what type of 2.0/2.2 engine the crank comes from? I have noticed that many of the builds here on the forum used S cranks. Is this necessary?

Are all 95mm MAHLE piston & cylinder sets the same? In other words, can I use a set from/designed for a different 911 (3.2 Carrera or SC)? Mine have some corrosion that has eaten into the Nikasil.

Is it worth making this change without taking the mod list any further? While I understand that twin plugs, larger valves, and a custom mfi setup can squeak out extra ponies, I'm not really interested in taking this engine to that extreme. I am planning to run 964 grind cams, PMO carbs, SSIs, and an aftermarket muffler.

The Carrera 3.0 uses the 2.4 liter 70.4mm crank not the 2.2 liter 66mm crank

All the 2.4 and 2.7 cranks are the same

Yes, the stock 3.0 liter uses a 2.4/2.7 70.4mm crank, but a short stroke 2.8 built on the Carrera 3.0 case requires a 2.0/2.2 66mm crank. I am asking whether this replacement needs to be an 'S' crank.

Are you asking about the acceptability of the 66mm counter balanced (E & S) or non-counterbalanced (68-71 T's)? I'm no expert here but reading a lot of threads, I gather the non-counterbalanced cranks are coveted for race applications because they are lighter and spin up faster. Don't know about the suitability for your 2.8. I can say that like all things long hood, it's getting harder to find parts that aren't knackered. Good luck whichever direction you go.

To quote Wayne:

FYI, for everyone else:

- 66mm crank & rods
- 3.0L pistons
- 3.0 1976-77 Euro Carrera or 911 Turbo Case

= 2.8 short stroke...

-Wayne

If you are not planning to spin above 7000 rpm I would not travel down that road.

I would keep the crank and get a set of aftermarket 98mm P/C and run a Mod S cam.

The stroke
 

From my point of view this is not the way to go.

You loose some static compression, you loose power and you loose torque.

To compensate all this you need a suitable valve train, some correct engineered pistons, the right conrods etc, etc....

There is a good reason why Porsche went the other way - these engines like the most possible stroke.

Most of the std. ports are too big anyhow, so let the stroke pull the port as we say.

It is also not true that the longer strokes are not spinning - if everything is alright we rev 9000 plus also with our 80,4 mm, 82mm or even 84 mm stroker cranks.

Best reg.

Dirk

https://de-de.facebook.com/edelweissmotorsport

I don't think anyone is stating you cannot "spin" longer stroke cranks. We are talking about factory cranks...in particular the 2.4/2.7.

...In the real world, factory 2.4/2.7 cranks are not stable above 7500 rpm. To do so generates harmonics that shed flywheels,pulleys, damage bearings,cases etc...

I recently seen a 2.9 out of a 910 with counterweight marks on the case webs and chunks of babbit missing from the main bearings. Not to mention the flywheel making contact with the case. All due to excessive RPMs

9 bolt cranks are stable and can achieve higher rpms as long as reciprocating weights remain well below 700 grams....something hard to do with a 90cc combustion chamber.

Thanks for the helpful responses!

Any recommendations on which aftermarket options are best/most economical? I was under the impression that the stock 3.0 had 95mm cylinders, identical to the SC and Carrera. Sounds like I might be incorrect about that - could you shed some light here?

The most economical approach is

used 3.2 cylinders bored and nikasil coated.

If you choose 9.5/1 get off the shelf J.E. pistons

The Mod S cam will be happy with the PMO's and you don't have to port the heads. If you want a little more torque, you can try the DC30 which is a Mod Solex

You can get and about 275 hp with a low back pressure muffler and it will pull well to 7000 rpm. And you get to keep the SSI's.

ARP's on the rod bolts for insurance.

Yes and no.

Both the SC 3.0 and 3.2 Carrera used 95mm with nikasil and alusil finishes.

The SC 3.0, like your 3.0 Carrera, have a groove for a CE ring where the head meets the cylinder. The 3.2 Carrera cylinder does not.

You can use SC 3.0 cylinders on the 3.2 Carrera, and vice versa, as long as you use the correct piston for the cylinder type (nikasil or alusil. They are different)

Both nikasil and alusil cylinders can be replated with nikasil.

Only 3.2 Carrera cylinders can be bored to 98mm because they don't have the CE ring groove on top.

Your least expensive option is to have your original cylinders re-plated and use 9.5:1 95mm JE pistons. If you stick with CIS FI, DC20, 964, and 20/21 are good cam choices.

If you are going carbs or ITB FI, There are better cam choices.

If you choose a 3.2 SS, you'll need some 3.2 Carrera cylinders for cores to have bored and plated in nikasil, or by new cylinders.

The stroke
 

This is 100 % right !

Better stay with the 70,4 mm crank and use a set of pistons to achieve a higher static compression to go with a nice cam - TDC lift, depending on inlet and exhaust plenum / configuration 2,5 to 3,5 mm and upwards.

This with 95 or 98 mm bore makes an elastic allrounder.

Best reg.

Dirk

I'll have to show this to my wife as confirmation that I'm NOT 100% wrong most of the time........:D

The wife
 

Yes for sure - we are all members of the same club !

Feel free to use it wherever it fits in....:)

Yours in sport

Dirk

3.0 - isn't the old adage: there is no replacement for displacement?

For a street car, or even a street car you will DE or AutoX, the 2.8 motor, be it short stroke or long stroke, is not the way to go when you start with a perfectly good 3.0 liter motor.

I like my long stroke 2.8 clone. No problems shifting at 8,200 RPM. With the right approach, the flywheels stay put (see discussions of that issue on the 70.4). Great race motor. But all that is wasted on the street. How often do you get above 4,000, occasionally 5,000, RPM? A 2.8 fits nicely into the racing class I run in.

Some engine builders say the 2.8 short stroke is even better. Mine pulled a piston in half on the chassis dyno, so I can't yet say from personal experience.

I'm glad I followed this discussion, because I had forgotten the CE ring groove problem with boring a 95mm cylinder out, so that is not an economical approach.

Your pistons are low compression, so if you want a boost in torque beyond what you will get in power with a more aggressive cam and an induction which isn't CIS, you need more squeeze. However, you can probably find a set of good used designed for Nikasil 95mm 9.3:1 pistons from an 80-83 SC.

Thanks again to everybody for all of the education... Perhaps I can learn enough to one day return the favor and convince my wife that I'm occasionally correct about something as well.

So I already have cams regrouped to 964 spec (Webcams believed that S cams would cause clearance issues), and I am planning on SSIs and PMOs (need to have heat in the car). From what I am reading above, I'm thoroughly convinced that keeping the 70.4mm crank is the way to go.

I have the stock MAHLE pistons and cylinders, but the Nikasil is worn away in a few spots due to the car sitting. I see my options as follows, and would appreciate any advice on which is best for my street car application:

1) Replate the stock cylinders and reuse the stock pistons. Cheapest option at $950 or so for replating and new rings.

2) Replate the stock cylinders and buy JE pistons to increase compression to 9:5:1. This option prices out at around $1800 for replating, pistons, and rings. Is the higher compression worth the additional expense?

3) Buy used 3.2 pistons and cylinders, and have the cylinders bored and replated. Is this what is being referred to as a "3.2 SS"? I assume that this would require the purchase of new pistons? The used set will be $800 (give or take), new pistons are another $1,000, and replating is around $800, so I think I am looking at around $2,600 to go this route. Do those numbers sound right/could I reuse the used 3.2 pistons instead of buying new? Is the additional expense of this option that much better than options 1 or 2?

1) Cheapest option, but not a good option with the 964 cam. The bigger cam will need more compression or your motor will be a real dog at lower revs

2) A good option. No real downside other than not getting the benefits of the increased displacement. Will work well with your 964 cams

3) best bang for the buck power wise, but can be the most expensive. It really depends on if you can score some 3.2 cylinders cheap. To bore and plate is about $900. Add the cost of a set of used cylinders to that. I believe the cost of 98mm JE is the same as 95mm JE, so that is a wash.

Just for a point of reference, and something to think about, if you are patient and able to jump in quick, 98mm pistons do show up for sale from time to time. I scored a set of Mahle Max Moritz 9.3:1 98mm wedge pistons for $525 shipped. Then a couple days later jumped on a set of 3.2 cylinders that I got for $465 shipped. Once I get these bored and plated and add rings, I'll be into a set of 98mm P&C's @ 9.3:1 CR for right at $2K.

Best motor I've ever driven is a 2.8SS, using 66mm CW crank, 95mm JE pistons @ 11:1 CR, RSR sprint cams and twin plug ignition. This combo nets an 8500RPM motor with solid low end torque and a top end unlike anything you ever felt...and it sounds ridiculous, like a 911R with a baritone wail a small motor can't match.

But with low compression, stock pistons, stick with stock specs.

So I was all ready to go for option #2, above (replate cylinders and purchase new 9.5:1 JE pistons for higher compression.

After receiving my parts/request, US Chrome called me back about piston options. They are recommending a Wossner 10.5:1 piston in lieu of the JE 9.5:1, citing higher quality and greater compression with the Wossners. My questions are:

1) What am I giving up by going with higher compression? I understand that the higher compression is going to boost low end torque, but is this more than I need? Premium gas is not hard to come by in my area, and there is no emissions testing in my state. The engine is going to run PMO carbs and SSIs. That said, this is a street application.

2) Is Wossner any better or worse than JE? From what I can find on the forum, there is not much experience with Wossner in 74-89 cars, but they are a respected piston manufacturer in other applications. US Chrome quoted a price that is about the same as their price for JE, but both prices were higher than expected (+/- $200 more than numerous suppliers online).

Wossner are very, very well made. But at 10.5:1 CR, you will need a twin plug distributor for the Wossner pistons. Premium gas isn't enough, unless you are running low dynamic compression (e.g. race) cams, knock control and computer controlled timing control.