Widening CIS to work with big bore heads - a question or two
 

I believe I may either have a line on some Carrera 3 heads, or will extrude hone my own 34mm cylinder heads. My eventual goal is to get to 38 - 39mm in diameter, and would need CIS fuel injection to work in compliance with these newly-bored heads.

My options are to either adapt an early-style CIS system (I have a late-style CIS), or possibly hone out my own existing CIS. I do not want to go to Webers as that would entail changing my current pistons, which I already like.

My question is can my CIS be honed-out in any way to work with these heads, or should I look for an early CIS system, say 78-79?

Also, will I need to change the fuel distributor, or any other parts?

Tyson, Dave and I have been discussing this, but I'd like to see what others think as well.

Thank you.

When you talked about enlarging your cylinder heads, are you refering to the ports? If so, i believe boring is what you need there and extrudhoning would be usefull for the CIS intake runners. Extrudhoning is a process where they force an abrasive paste through an intake and it removes an even amount of material off of a surface.

Paul

Yes, Paul. That is what I mean. I'm sorry about the clarity of my post. I'm on Tylenol Allergy medicine at the time being - the smoke around here has finally gotten to me.

So it is possible to extrudehone the CIS? What would that process be/how does one do it? Boring the cylinders I think I understand. The CIS is a different story. And, will I need a new fuel pump/distributor, etc?

Thanks.

What is the current engine?
What is the current system?

Early SC intake systems are completely different. Not only are the intake runners and intake ports bigger, but the air flow sensor plate is bigger the FD is different, etc. You'd be better off finding a complete early SC system and either use those heads, or machine yours. You're looking at a fair amount of expense and trouble for a limited amount of power gain. And the 'new' engine will have poorer low-end torque characteristics than when you started.

David, why would you have to change your piston to use carburetors? You can use your CIS pistons with carbs.

William: my engine is an '83 3.0 stock with CIS and backdated exhaust and a Triad muffler.

Supes: yes, I'm starting to realize the "minimal gain" of an otherwise $4-5K project. Jeez, there's no winning this game, which makes me wonder if it's a game at all.

Souk: Yes, I realize it is possible to use carbs with CIS pistons, but not optimal.

In the end, I'm starting to think none of this is worth it. The engine runs fine and that's all I really should ask of it. But I say that now. In about two hours I'm sure I'll post a question about head porting, crankshafts, pistons, carbs, supercharging, V8 transplants...you know...LOL. :)

The 3.2L upgrade with 9.8:1 pistons would be a nice improvement, when and if you need P&Cs. Horsepower is not easy to get from an existing German-engineered performance engine. Your engine already makes 1 hp per c.i. It's a 182 c.i. engine, you know.

Performance gains through seat time are by far your best bet. After that, tires. Then suspension and weight loss. Engine mods are way down the list.

Is it a US engine? 930/16 or Euro 930/10?
Just checking!

You're right, Jim. Fortunately I'm realizing that before plunking down the equivalent of a lot of Maui getaways...

William: U.S. motor. I forget the designation # for '83 3.0s.

All good points, Noah. Would you care to become my new financial advisor? :)

dd74-- I asked about the engine model because I have an 83 Euro SC with the US 930/16 engine that I just rebuilt.
The Airbox and the runners are of the larger diameter. Same as the 79 USA parts except I don't think the 79 US airbox has the interior metal manifold for the cold start valve. When rebuilding I noticed that the intake ports on the heads are smaller than the intake runners so I bored them out to the same diameter eliminating the step that the air would have to flow past. I assumed that the Euro heads would have done this but last night I was looking up some specifications in Andersons book and noticed that the intake port size was reduced just like the US heads of those years. 81-83. Is this correct? This would mean that the 930/10 was produced with the larger runners that were choked down to the smaller diameter. Why would they do that?

I agree that the benifits of the lambda control system are probably more valuable than any small power gain acheived by swopping it out, unless of course it was for carbs with all the other modifications.

The k-basic can run pretty smooth if it is set up right, maintained and kept in tune. So I really don't see much benifit in going the other way either.

William: for what it's worth, as my engine stands now, it has gobs of torque that remains pretty flat to 4,800 RPMs. This has proven very useful in daily comuting when in traffic, allowing me to "squirt" through gaps and such. As Superman stated, there stands to be a loss of torque if I open up the heads. Sure, opening up the CIS will give the engine more gas and air flow, and there would be the added benefit of "hotter" 20/21 or 964 cams, but who knows...

From my knowledge, the CIS and intake manifold port sizes on the US and Euro-spec engines are the same. The major difference was the increase in compression (9.8:1 vs. 9.3:1) and a possible recurve of the distributor (advanced).

Of course, finding gasoline, especially in CA. to run an engine with that compression, may be challenging. As Steve Werner and Wayne Dempsey and others have said, a compression above 9.8:1 requires twin-plugging the engine. To be honest, I wouldn't be surprised that octane ratings in California decrease in the near future only because many modern high-compression engines can run on 89 octane.

The horsepower quote I received for the bottom end of an '83 3.0 mated with the top end of a '78-'79, has been anywhere from 215 hp to 240. All in all, there is some gamble with horsepower ratings. At the end of the day, however, there will be an increase in power.

My idea is early CIS, heads bored to 40mm, 20/21 cams while leaving in place the 9.3:1 pistons. But by that point, half the engine is torn into. Why not go the extra half-mile (and $5-6K more) and get big pistons and PMOs.

Noah's idea sounds better for a lot of performance reasons. Reliability may be another situation entirely.

I am not sure Bruce Anderson's book is correct. As I understand it the size of the intake runners changed to match the ports.

I looked up the part numbers for the intake runners for the US and ROW 911SCs. US cars had different numbers early and late, ROW engines had the same part numbers for intake runners from 78-83, except for #6, which changed in 1980, probably due to something that screwed to it.

Someone look in Wayne's book, and see what it shows for the port sizes of a type 930/10.

Quote:

The horsepower quote I received for the bottom end of an '83 3.0 mated with the top end of a '78-'79, has been anywhere from 215 hp to 240. All in all, there is some gamble with horsepower ratings. At the end of the day, however, there will be an increase in power.

I think whoever said 240HP for just that change was optomistic. Otherwise, a stock 3.2, with higher compression, larger ports, and more displacement would be higher than the factory 207/217.

Quote:

My idea is early CIS, heads bored to 40mm, 20/21 cams while leaving in place the 9.3:1 pistons. But by that point, half the engine is torn into. Why not go the extra half-mile (and $5-6K more) and get big pistons and PMOs.

Well you are in California, so passing smog will be an issue with carbs.

Quote:

Noah's idea sounds better for a lot of performance reasons. Reliability may be another situation entirely.

Economic reasons as well. The big problem would be having a way to revert to single plug every 2 years for smog. I don't see a reliablilty problem. Longevity possibly, some of the people I talked to say Mahle pistons will last longer than JE.

Tom

Just thought I'd say BA's book is wrong about the euro '80-'83 heads having the smaller 34mm intake ports. I have both '80 and '83 euro heads which do have 39mm intake ports.

Oh, and I have an extra set of the larger '4R' intake manifolds if anyone's interested.

-Rob
1980sc

!
 

Hello.

you don't need to "widen" CIS at all...it's a stupid system that just measures amount of air being drawn in and injects fuel accordingly. It doesn't know what kind of engine it sits on or if it's ported or not.

Cheers!

Last night I was reading Probst (Bosch Fuel Injection) about CIS. The cone shaped funnel that surrounds the air measurement plate is "tuned" to the motor it is on. In some cases, the bell isn't even a simple cone shape. Just making it bigger would seem to be a different problem than boring out a throttle body for example.
-Chris

Re: !
 

It doesn't make much sense to have 39mm ports if you have intake runners that are 34mm.

Cars that came with larger ports came with larger runners to match.

Tom

Re: Re: !
 

I'm talking about cone shaped "barn door" , intake runners are not part of CIS.

Rob- Is there any difference between the 2 Euro heads?
My heads are from a 82 US SC engine# 930/16
I bored the intake ports out to match the larger Euro intake runners.
Since this was a us 82 head is did not have the ports for air injection.
They did have the longer exhaust studs for the thick exhaust flanges.
My problem was that before I bored them out there was the step where the air flowed from the intake runners to the smaller diameter intake ports on the heads.

Thanks's for confirming this info. BA's spec.s must be wrong, I think Waynes book has the same number but I'm not sure at the moment.