Thoughts on some different engine configurations

[350HP930]

Yet another reminder that the need for twin plug conversions is highly overrated.

[Wayne 962]

Originally posted by rdane
You certainly have a sense of humor Wayne. Bring your Ferrari or a Jetta along for a drive with us. My point is a more agressive cam is fine many places...like a track for example. On a street car, aggressive cams aren't all that practical. Fun, yes but practical..no.

CIS continues to get a bum rap no matter the evidence to the contrary. Perfect? No. Decent? You bet for a street car. We can continue to disagree but then I have both a 911 and a 3.4 Wayne, and you don't

Any flat six 911 that gets 275 to 300 hp is pretty fun no matter what induction you have. You can do that with CIS or Motronic.

First of all, I have a 914-6 with a 3.2, and have written two books on Porsche 911s, so I would guess that I know what I'm talking about. Secondly, I'm building a short-stroke 3.2 with mod-S cams that I would never dream of putting CIS on. Third, there's plenty of "proof" that CIS is not a high performance system - heck it was never designed to be one.

Since you referenced the Ferrari, when they went to CIS, the HP dropped by about 20% due to the lack of performance of the CIS cams and system. That is why I specifically bought a carbureted version with independent throttle boddies. Likewise, the 911SC engine produces 180 HP, compared to the 210 of the MFI RS motor that proceeded it. This is even despite the low compression of the stock RS engine, and the increased displacement of the 3.0L.

Yes, you can increase displacement to overcome and overcompensate for any handicap with the CIS system. CIS is old technology (1970s), it doesn't perform pulsed metering, requires intake plenums and sensor plates that are affected by fuel reversion, and thus, you can only use relatively mild camshafts with them. Heck, the early CIS systems weren't even closed loop (exhaust gas sensor) systems.

As for an agressive cam in a 3.4 motor - it would be very driveable on the street, with gobs of low end torque. As I discuss in Chapter Four of my book, the increase in displacement eases the low-end torque problem that is common in motors like the early 'S' 2.0.

CIS is a good, reliable system that produces less emissions, and enables cars to pass smog tests. If building a big bore, high performance engine, it would not be at the top of my list. A fuel system that would supply individual throttle boddies would be first (TWM EFI, MFI, carbs). Then would come the closed-loop Motronic system with the common plenum. Then would be CIS.

Sorry to have offended you...

-Wayne

[rdane]

"First of all, I have a 914-6 with a 3.2, and have written two books on Porsche 911s, so I would guess that I know what I'm talking about"

You're kidding me right?

Ok, but I wasn't offended. Guess you missed the smiley face.

I never claimed that CIS was a performance induction, just a reliable one, made for passing emissions and cheap for those of us with CIS cars.

I could have used any induction I wanted. For now I wanted CIS for no other reason than to put CIS into perspective. I'll let the guys who drive my car make up their own minds.

There were so many changes beside the MFI (still one of the best induction sysetms available for HP) between '74 and '78 that your 210/180 comparison is moot.

More so when you do a little work on CIS (exhaust and cam which still make emissions) and get 215.

Dane

[Porschekid962]

CIS CIS CIS, its great dont get me wrong, fires up in the morning without complaints, runs nicely throughout the day, emissions well those are decent i suspect. I have a 78 3.0 SC with the CIS and SSI's and also 20/21 cams. The engine makes very good power but I just cant wait to go wilder on the cams change to MFI and move up a little in displacement.

Hey wayne, I drive a jetta only because dad made the porsche his daily driver, I love hucking that thing around all the ricers here in pasadena, I just love the look on their faces.

[Porschekid962]

quick question here. this summer my dad and i are rebuilding the engine with the max moritz kit but have decided on higher comp. pistons. as long as the engine is apart is it worth the extra money to throw in a 3.2 crank and rods to make it a 3.4??

[rdane]

rebuilding the engine with the max moritz kit but have decided on higher comp. pistons. as long as the engine is apart is it worth the extra money to throw in a 3.2 crank and rods to make it a 3.4?? [/B]

I wouldn't get in a big hurry to up the compression past 9.8:1 as the Max Moritz pistons come. Eliminates the need for twin plug (if you are twin plugging I would go even larger MM style P&Cs) and there is more power than you might expect because of the improved piston design and combustion chamber @9:8:1.

Yes, the crank and rods are worth every penny and then some IMO. I'll have a dyno posted in the next few weeks to give you an idea of what is possible from CIS and a 3.4. The driving experience in unbelievable to this point.

Helmet Bott ran a 3.5 for many years in his personal car.

My response when asked is, "almost, scary fast" for my 3.4 CIS.
My mileage has gone up BTW and not down, even the harsh way I have been driving it on breakin.

I have a 78 3.0 SC with the CIS and SSI's and also 20/21 cams.

Same set up I built to specifially. I wanted to pay for my engine in installements so the cams and SSIs came first. You can build a very inexpensive and extremely strong engine by adding a set of 98 P&Cs and the 3.2 crank to just what you have now while doing a valve job.

Hook up with Andial and beg a ride in one of their CIS big bore cars. That will answer a lot for you I suspect.

[Wayne 962]

Originally posted by rdane
Ok, but I wasn't offended. Guess you missed the smiley face.

Hmm, I guess I did. Chalk it up to multiple nights of 5-hrs sleep.

There were so many changes beside the MFI (still one of the best induction sysetms available for HP) between '74 and '78 that your 210/180 comparison is moot.

Hmm, this I will respectfully disagree with. The 1975 Euro Carrera had the 2.7 engine, the 1976 Euro Carrera had the SC engine - each one year apart. The CIS motor replaced the RS motor in Europe.

- The two motors basically share the same crankshaft.
- The two cases are very similar, except that one is aluminum and one is magnesium (doesn't affect power).
- The pistons on the RS are shaped with higher domes to work with the 'S' camshaft. The 3.0 pistons are specifically shaped to work with the mild-profile CIS camshaft. Both engines had 8.5: compression
- The Euro Carrera was a 3.0L displacement, the RS engine was a 2.7 displacement
- The Euro Carrera had much bigger ports than the RS engine (39/35 vs. 36/35)
- They had the same sized valves

Looking at the specs for the Carrera 3.0, you'd think that the larger ports and larger displacement would generate an engine with significantly more power. Yet power per liter was down significantly from the previous year's system due to the switch to CIS and the mild CIS cam.

As I mentioned previously, the same thing happened to the Ferraris when they made a similar move to CIS - power was significantly down.

For an idea of what the 911SC could have been had it been sold with MFI, you have to look at the 911SCRS with 255 HP (although arguably, in a street car it would be lower, as you would want to drop the compression from 10.3:1 to about 9.8:1). A good individual throttle-body EFI system should be able to achieve at least that, if not more, using closed-loop monitoring of the mixture.

CIS is a very reliable, simple system that is good for emissions and everyday driving. I'm not knocking it - I'm simply saying that the other systems deliver better performance. I can't say for sure, but I would guess that the reason why Andial builds so many CIS big bore engines is so that they will pass smog. A friend of mine bought their experimental 3.7 CIS engine a few years ago (Steve Lee). I believe that car was left with the CIS system on it soley to avoid smog problems.

I suppose if I were going to spend a lot of money on a big bore upgrade, I would probably want to go with an EFI system to extract the maximum HP per dollar. However, if you're trying to keep the car smog legal, I can certainly see a very good argument for keeping and tweaking the existing CIS system.

-Wayne

[rdane]

Hmm, this I will respectfully disagree with

Fair enough, how about this?

'74 2.7 MFI @ 210hp @ 6300k and 255@4500
'83 3.0 CIS @ 204hp @ 5900k and 267@4300

The 3.0 CIS SC ran at lower revs, with more torque, had a longer engine life by far, certainly was/is more reliable and passed some pretty strict emmissions.

Now add to that data a '78 or '79 with a good CIS cam and a set of SSIs makes 215hp no problem (with the same lower 8.5:1 compression), as many Pelicanites can atest. This while getting some of the best mileage seen in a 911 to date in '83. All things I really value in a street car.

I would hope any modern EFI system would better all of that. But at what cost? You have discouraged a 3.2 crank @ $1500 as too expensive, but figure a EFI @ $1500 plus labor is a good investment? No one is going to argue "there is no replacement for displacement" here, right?

CIS isn't the best performance induction available today or yesterday. We both agree on that. But from my many phone conversations with Pete and Deiter @ Andial, I was under the impression that they used CIS and Motronic for convenience, price and a nod to emissions, in that order. If CIS or Motronic were so limited I doubt they would have built as many performance engines with either induction.

Your points are well taken Wayne, I just don't agree with all your conclusions. But that is what makes a horse race, eh?

[Wayne 962]

This is sortof a silly argument, because on some level, we're both agreeing with each other.

Originally posted by rdane
CIS isn't the best performance induction available today or yesterday. We both agree on that. But from my many phone conversations with Pete and Deiter @ Andial, I was under the impression that they used CIS and Motronic for convenience, price and a nod to emissions, in that order. If CIS or Motronic were so limited I doubt they would have built as many performance engines with either induction.

That's my whole point:

"convenience, price and a nod to emissions, in that order. "

Nowhere in that sentence is the word "performance", which was my original statement and point here.

Just to refresh:

Originally posted by Wayne at Pelican Parts
It would most certainly be quite a bit better without the CIS, as that would allow you to run a more aggressive cam. CIS is just not a performance injection system.

I guess we're arguing over exactly what I meant by the word "better." In that sentence, I meant better as being "squeezing more horsepower out of the engine", not necessarily economical.

You did touch on a good point with the cost of an EFI system versus a 3.2 crankshaft. It's personal preference there. I would rather have an EFI system on a 3.2 than a CIS system on a 3.4 with a Carrera crank. In my opinion, the EFI system allows you a lot more freedom and flexibility, and also allows you to grow with the engine as you make changes. I'm a big fan of EFI...

-Wayne

[Wayne 962]

Let me add another thing - my whole argument against CIS (and Motronic too) is that they are throttle-body induction systems. In order to run a more aggressive cam, you need to have individual throttle boddies, like on the MFI system or Weber carbs.

However, I'm not a huge fan of simply bolting carburetors onto a CIS engine. You will get poor gas mileage, an emissions nightmare, and decreased performance, overall. You may get a bit better throttle response, but it's at a high price. The only time I really advocate ditching the CIS system and bolting on carburetors is if you're going to swap out your camshafts.

-Wayne

[JohnC]

Henry......For the 100mm cylinders are you boring the spigots on the case.......and if so how are you sealing tha case? "O-ringing" the spigot bores by cutting a groove in the bore perhaps?

[Shuie]

Originally posted by Shuie
Henry, that is spectacular. There was obviously a lot of thought that went into designing and building that engine. I have to ask why you guys didnt twin plug it or run engine management instead of the MFI? I thought the twin plugs were bascially required on anything that size.

Just saw that Henry was online and wanted to bump this to get some more input on his 3.5.

If I get into my 3.whateveritis and find the 100mm Mahles, I may spring for a 74mm crank and try something similar.

Also Henry, does your shop do the custom MFI setups?

Thanks Henry!

[Henry Schmidt]

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[Henry Schmidt]

Originally posted by JohnC
Henry......For the 100mm cylinders are you boring the spigots on the case.......and if so how are you sealing tha case? "O-ringing" the spigot bores by cutting a groove in the bore perhaps?

On this engine, the case was bored, in house and a special base gasket was made to seal it properly. On this engine as with all 911 /930 engines we build the cylinder base gasket was sealed with Ciril T.

[Tspringer]

Henry....

How about a group buy those 3.5 MFI engines! That sounds just incredible.... but im not sure my 901 could deal with it!

[jase007]

Terry:

We were told for YEARS that our 915s couldn't handle the 350+ hp we run through them. It has been 10+ years on multiple versions of twin-plugged 3.0L, 3.2L, 3.4L and 3.5L engines and the 915 box has NEVER been the problem.

Reading between the lines ... something else usually happens (race "rubbin", missed shifts, major and minor shunts, etc...)

Currently running 220+ hp through a 901 in a '68 2.0L ... no problems.

Jason

[Wayne 962]

John (Otto) has run 901s with 300 horses through them for ages. I think he reinforces the center plate though...

-Wayne

[daloff]

Anyone have any thoughts on a short stroke 3.8 ? Using a 3.6 case modified to take 102mm pistons and a 3.2 crank which has a shorter stroke than the 3.6. The thinking is a higher reving version of a 3.8. I know special pistons would have to be made, but does anyone think it is worth it or should I just use a 3.6 crank ?

[Henry Schmidt]

I like any thinking that leans towards shorter stroke 911s. I think a better way to go would be to destroke and lighten (knife edge) the 3.6 crank. This would require a custom rod but it is my opinion that the 3.2 crank and rod combo sucks, and the 3.6 rod is too short. By destroking the 3.6 you get a smaller ( less friction) rod journal and larger radius at the flyweight for great stability ( more strength). By using the stock 3.6 wrist pin location in the 3.8 piston the rod gets longer and the engine gets happier. Why? Because the rod length to stroke ratio gets better ( less rod angularity = less piston side loading ). It is also my understanding that cylinder filling is improved when a piston spends more time at TDC and this time is lengthened by smaller rod angles.

[KobaltBlau]

Originally posted by Henry Schmidt
I like any thinking that leans towards shorter stroke 911s.

First: love your subject line!

Henry, I have a specific question I'd like your opinion on, and that of anyone else interested:

3.0s can be built relatively easily in a couple of different configurations:

1. 70.4x95 (SC, 3.0 Carrera, 3.0RS, 3.0RSR)

2. 66x98 (bigger bore version of short stroke 2.8)

Note that the 3.0RSR made peak power at 8000rpm, with max. engine speed slightly above that. I don't think the factory was using any 98mm cylinders at the time, so #2 might not have been obvious.

Here's my question: If you built a #2 configuration race engine, what power peak RPM (or torque peak, whatever you prefer) would you be shooting for? would you try to use bigger cams to lift the power peak over 8000 rpm, perhaps 8500?

My point is, if the power peak is not any higher than 8000 or so as in the RSR, at least in a 3.0 it would probably make sense to use the #1 configuration, not least because it is much easier to create. I make no statements about the 3.2/3.6 since they have quite a longer stroke.

However, even longer stroke 911 engines are still very oversquare compared to many production engines. As an example, the original honda S2000 engine has an 84mm stroke, and a 9000 redline. No doubt the reciprocating assemblies are lighter (have you seen a honda rod lately), but I'm curious where the balance point is in 911 engines between stroke and comfortable RPM.

TIA