Helmuth Bott?
 

I am a big fan of Paul Frere's book, "Porsche 911 Story".

Twice in the book Frere mentions Bott's 1975 CIS 3.5L, 911.

The first time is on page 80/81.
" There was thus no technical reason why the atmospheric 911 could not be stretched to th same capacity or to the even larger
size of the Turbo, (3.3) of which the bore is 2mm larger: in fact, back in 1976, a couple of experimental engines with 100 mmm bores and the capacity of 3.5 liters were successfully built, Development Chief Helmuth Bott using one for many years in his own 911."

The second is even more revealing from page 302:
"But as early as 1975 Development Chief Helmuth Bott operated a Sportomatic coupe protected by an ugly, chip-proof grass green
vinyl paint, which had an experimental 3.5-liter K-Jetronic engine developing an impressive torque. I drove it about 2000km. The car had a long life so it could be done."

Does anyone have any info on these early 3.5 naturally aspirated street engines?

What we do know is it was CIS and 3.5 liters. I suspect it had a flat piston ala pre-Max Moritz (love to know that developmental story) and was single plugged, 9.8:1 and 98 ron fuel. No question the torque curve is there if my 3.4 is any example.

If you followed the mid '70s to mid '80s 911 story you quickly realise that what is being done today on the street cars owes much of the research to those years. The performance of the naturally aspirated cars could easily have surpassed the street turbo engines if they had cared too. But the marketing department wouldn't let the 911 thump the other cars so easily.

What other engines did Porsche test so throughly and not market?

Once upon a time ... Herr Piech envisioned a line of 4, 6, and 8 cylinder DOHC engines for the street based on the 916 [908 development mule] experimental engine built and developed for use in the 911R in both endurance races and rallies. We know about a couple of 914/8 cars used on the street for several years with street versions of the 908 ... a direct descendant of the 916 engine. The 908 engine was designed for possible production use as a street engine, hence it's similarity to the MFI street engines of 1969 - 1976!

By extrapolation of the 6-cylinder 3.5 engine, a 908 of 4.66 liter capacity was possible ... so an immensely powerful street flat-8 was possible ... with much less complexity than the Turbo plumbing & thermal nightmare ... a DME version would have been quite economical to produce!

One can only imagine if the alternate path had been taken rather than turbocharging ... would there have been a 908-based engine in a 914 decendent [not based on VW parts] ... and other supercars along the lines of 911 SCRS, but not limited-production ... mid-engined 911 descendants with air-cooled flat-8 engines, etc.??? A price-leader 1984 914 might have had a 2.4 liter 4-cylinder variant of the 916 engine with DME and 200 hp ... with bigger-brother models called the 916 and 918???

Guys,

Starting in about ’79, we built several 3.5 engines using Factory parts left over from these experimental engines. They were 74.4x100 built on 3.0SC cores. Great street engines, I wonder where they are today?

Frau Baer was great at finding us “deals” on all sorts of cool stuff.

Best,
Grady

You guys are killing me :) Great info!

"a 908 of 4.66 liter capacity was possible ... so an immensely powerful street flat-8 was possible" This for example.

But Grady don't be so tight lipped tell us more? Where the originals and your street engiens single plug? Compression? Wedge shaped pistons?

Details! Come on give us the details :)

These 3.5s were remarkably similar to what is easily available today.

I think the first one was built on a 3.0 Carrera (’75?) with MFI. It took buying a couple of different sets of parts (~4) to get it right. We ended up using everything as it would fit SC and 930 Turbo cases. We are talking about crank, rods, P&C, bearings and machining heads.
We built a couple of others with MFI but there weren’t any MFI custom shops that could provide service and Porsche wanted an arm and both legs ($7K++) for a custom pump, we settled on Webber carburetors. We built one using 2.4S MFI but were worried it couldn’t handle sea level fuel requirements (later it turned out it would have been OK.)
Basically they were 74.4x100, S cams, modified heads, Factory rods and bearings, Mahle Nikasil conventional bump pistons with modest valve pockets, and whatever best was available at the time. None were twin plug because of the outrageous cost at the time. The CR was 10.3:1 or lower. There was higher octane pump fuel regularly available.

Other than more parts, there isn’t much difference compared to turning a 2.4S into a 2.8S.

Today, I wouldn’t hesitate to build a 74.4x102 at 10.5:1, S cams, MFI, twin plug as a cool street-track lightweight. Sorry, I retired 17 years ago. I’ll be glad to advise since there are several good shops in Denver staffed or owned by many of my former mechanics – good guys all. The current builders (Jerry Woods Ent, Andial, TRE, Supertec, and many more) have much more current knowledge than I. The principles are all the same.

Best,
Grady

Great information Grady, You always have the best stories and information. Thank you.

I have one question. Were the 74.4mm cranks available then (75?). I know they didn't come out in production until the Carerra almost a decade later.

The engine you describe sounds like a whole lot of fun.

I calculate that 102mm cylinders give almost a 3.7 and that a 70.4 crank with 102 cylinders gives a 3.5 (3.45).

Thanks Grady. I was just looking for info on the original 3.5 engines and how they were built. Wondered why Bott used CIS instead of MFI myself. Test mule and not the end all of performance is my quess.

No question MFI would have ben a hoot compared to the CIS that Bott (or I) used on his. Appreciate your time.

How often did you geys get a chance to buy "one offs" from the factory on parts and cars?

Jamie, Grady will have the full answer for you I bet. The 74.4 cranks were available from the begining production of the 3.3 Turbos...what '76? (8/77 is first production dates of the 3.3 Turbo) I think Bott had a thing for N/A engines and saw an easy opening to bump the cars with the turbo crank.

Doh! I completely forgot about the 3.3T.

Jamie,

These weren’t stock parts at the time. A manufacturer like Porsche is always “stretching the envelope” in the research or race departments. That is how we get all these cool 911s. They may order up 40 of some configuration, use six, and go on to some other project. Rather than throw that stuff in the recycle bin (trash then), they shuffled those things off on us “dumb yanks” like Vasek Polak, Chuck Stoddard, and more. I was fortunate to be included.

102x74.4 = 3647 cc
102x70.4 = 3451 cc
100x74.4 = 3506 cc
100x70.4 = 3318 cc

Great Porsche engines all.

Best,
Grady

Fun thing for me is that Bott used the 100 P&Cs with a 74.4 crank and CIS as far back as 1975 according to Frere. My CIS 3.4 will spank an early turbo and keep up with a mid 80's Turbo. I bet Botts' car drove a few of the marketing guys at Porsche crazy. Wonder if they wanted to burn it just to keep the noise down from a naturally aspirated 911 car that would thump their own production Turbo in '77.

I gotta like how Bott thought to keep that car around so long and even allow Frere to take it for a 2000km spin ;) How many years past 1975 did it take for a n/a production 911 to make 260hp or 250# of torque?

C2 was close in 1990 with 247hp AND 228#.

Twenty years later...'95 993...270hp/247# of torque with a 100mm P&C and 76.6 crank.

I get the feeling Porsche is always holding out on us ;)

Of course Porsche holds back. The only way they can give us fully developed, reliable, fast, cool 911s that are legal to import into the US is through proper development. So what if a few experimental parts make out the “back door.” The trade off is Porsche had (has?) a large number of skilled people around the world giving them feedback in advance of production. This is similar to the software industry pre-beta testing.

Now, do you think that engine went into Herr Bott’s 911 and never came out for rebuilds, dyno tuning, up grades and more? Somehow I think that was a cool “test mule” that the chief drove.

Best,
Grady

I thought Herr Bott's wwould have had what he thought was the best available in his own car. When you own the the store you usually have the coolest stuff.

Always surprised me he had a CIS car with a sportomatic tranny when he had access to things like an RSR.

Street cars and race cars as thjey say are not the same thing.
Thanks for the insight Grady.

Grady, what exactly was your connection to Porsche to get all the cool stuff? It sounds as if you must have had a race team if you had mechanics working for you and had put 25 different engines into one car. Sorry if the question is too personal, but I'm sure many of us would like to know where you amassed all this knowledge!

This is great stuff!

Grady, next time you make it to Missouri, I may have to come tag along! (Kurt will have to hold back on his questions...I have lots!) :)

Does anyone know what happened to Herr Bott's 3.5 car, that would be an amazing find (sans the Spotomatic)?
j.p.

The talk about a 3.5 with a Sporto tranny got me thinking.

My 3.5 was built by Andial in the early 80's, driven for a while and sat for most of the 90's until i bought it in 98. It has MFI and when i got it, it had a very large (like .5") vacuum line coming out of the throttle body on #2. Didnt the sporto need vacuum for the clutch? The MFI system was from an RS and it had standard SSI heat exchangersand a twin plug RSR distributor on it.

When i changed cams recently, the guy that did it said that i dont need to worry about missing a shift because there is plenty of clearance (flat piston?).

Anyway there are lots of unknowns that will not be answered until i tear it down one day in search of more power. It runs very well, doesn't leak and moves along very well in my 2300#car.

Paul

Helmut Bott, father of the 959. Like Ferry Porsche he loved to drive various cars often registered in Switzerland for tax purposes.
Porsche built 2 914/8's with quad lights. I saw one at the factory a few years ago. Ferry put 60K kilometers on one, both were at his disposal.
Helmut Bott owned the only 959 with catalytic converter and drove it extensively. It met all US standards including CA.

Of the two 914/8's...one was slightly detuned and was run by Ferry. The other had the full ( 350 hp or so) race configuration 908 engine, but with silencer added...and was run by Ferdinand Piech.

As to hold outs....let's not forget it even involves cars like the 944/968. Porsche made some 968, 3 liter, DOHC 4 valve turbos too.....sounds like an interesting car!

---Wil

If you have access to Ludvigson the tests of the 3.5 are extensively described, vol3 pg 1133 - 1135. It's worth reading.

Thanks Bill. Good stuff on twin plugs from your referenece. A single paragraph on the 3.5 to 3.6 for the 964 and nothing that I can find on the early 3.5 Bott obviously had early on.

I had hoped there might be more in vol2.