356 top cruising speed critically viewed.

[Mike Smith]

Kneeslider Quote -

Is my car in any way typical?

I think that a higher top gear or diff ratio would be beneficial. Some folk in the USA are making 5 speed conversions using VW bits. That might be the way ahead.

@@@@


Your car is typical in that we are carrying out more engine upgrades these days and the spec looks good, although (in my opinion) it would benefit from Late Heads or maybe (?) Zenith Carbs.

The crank is interesting, the rumour on the street is that they always fail – although I have little experience of them, Bob Garretson always said that the fault lay in the width across the Little End – there is insufficient clearance between the rod and the Piston. This is something that is easily rectified and maybe yours was already modified in The States

As for Gears - I run a high top in my (Bog Standard) `C` and it is a great motorway gear. The only problem is that it is a little noisy and you have to suffer the longer drop from 3rd to 4th. I do not worry too much about these things and anyway I deaf.

To set the correct Toe-in on the rear of a 356 (which is mega important) requires the Transmission to be of the correct length from the Output Shafts to the face of the Front Mounts. The 5-speed boxes in The States use their own case so this point would need to be checked. I know of no way that you can get another gear inside a 356 Case without a different Syncro. system or the use of Dog Rings

In my opinion the better way to alter the gearing is by fitting a higher ratio Crown-wheel and Pinion. This raises 4th and 1st which are both a little too low and, of course it does this without altering any of the drops between the other gears. I have a transmission built but have yet to find the time to fit and trial it.

As for Max Speeds – I am sure that Will, will correct me but I believe that the Bill/Will Stephens Speedster is touching around 130 mph before they brake for the 2nd chicane on Mulsanne.

As for me – In the Tour Auto, on a French Auto Route, I saw 140mph (slight downhill with the wind behind me) in my 356 Carrera GT (that was approx. 7,600 rpm) - I was then blown away by a GT 40 who must have been doing 200 +

By todays standards the cars are noisy at speed but a lot of it is wind noise

[Kneeslider]

Hi Mike, thanks for the input.

When I had my engine stripped down to a long block about this time last year, I knew that I needed a replacement piston and cylinder kit. The pistons that were in were forged, and had a very large dome on the top with a large cut out for the exhaust valve. Goodness knows what the compression spec was, but they had a massive 0.008" clearance between the piston and the cylinder with oil burning to match, so any increase in CR was definitely being blown back into the crank case. Don't you just love American engine builders?

Because its a bitsa, I'm not precious about the engine, if I run it and it works, fine, but if the crank lets go and it destroys the case, then so be it.

I found the crank inside the case, and was concerned that there would be too little clearance between the pressed up crank webs and the base of the new piston skirts at BDC. I chucked the engine into the car and drove from Yorkshire to Essex to consult with Paul at PRS, and we were able to establish that the AA piston kit would work with my crank, and that my heads would match with the 22° piston tops on the AA kit, so that is what I bought. It was great to talk to someone who has been there and done that with engine rebuilds rather than just taking pot luck and buying something unseen from the other side of the world.

I am thinking that Mike is right, and that the cam and carbs I have will work much better at higher RPMs with bigger valve heads, but the performance I have now seems adequate, and I feel as though I am thrashing the engine somewhat by running it near to 5000rpm, the better heads will unleash some performance above this figure, but the car feels like there is enough torque to run a higher gear. If some big valve heads were available and I had the engine out in the near future, it might be interesting to compare. If it involves spending a couple of thousand £, then I will probably leave it as is.

When I said that the noise and vibration were an issue, I really meant the wind noise induced vibration rather than vibration from the engine or transmission. The engine itself seems really smooth.

I have used roller cranks in many different motorcycles, and never had an issue with them, including racing two strokes, so in spite of the doom mongers, I'm going to use this crank, and see what happens! It looks to me to be suitable for the job, and I like to be a contrarian.

[neilbardsley]

I'm glad Mike contributed. Some Registry discussion on SPG cranks

http://forum.porsche356registry.org/vie ... pg#p285797

[Ashley James]

Suzuki and Kawasaki roller bearing cranks never wore out, they were as good as new after 100,000 miles but the BMW Bikes before 1970 were very hit or miss.

[Mike Smith]

Jacques seem to agree with Bob Garretson

Jacques Lefriant
Post subject: Re: Who made this crank ?
Posted: Fri Mar 31, 2017 10:30 am
356 Fan


Joined: Mon Dec 06, 2010 1:50 pm
Posts: 3302
Location: National City Ca
Hi Cliff
i think they are trying to get oil to the pin bushing. When using the SPG crank you have to ensure that the piston will have enough clearance for the little end of the rod.
j

[jjeffries]

I'm not a 356 owner, but I bought the Brooklands 356 roadtest collection in the mid-80's and also have Denis Jenkinson's book in which he details his early Porsche motoring (lovely writing), so may have read the same old articles as referenced here.

My two penneth: I believe these old roadtests need to be taken with a big grain of salt; much gung-ho and false bravado was written by these fellows in period (as now). Also, Jenks excepted, these guys weren't owners of the cars they were testing, aka flogging. Did they care if their high-speed "testing" caused any harm? Likely not.

My 74 Alfa GTV 2000 has a five speed gearbox but a 4:55 final drive, so at 70-80 mph it is really singing. A few years back I substituted a 4:10 axle from a later Spider, in my (ultimately vain) efforts to turn the car into a more long-legged highway cruiser. In doing so, however, I thoroughly dulled it's accelerative capabilities, part of the car's charm, so the 4:55 went back in. You guys are all correct in how our senses have been retuned by today's cars with the tall gearing and engine management systems that make them so effective. John.

[neilbardsley]

Jacques seem to agree with Bob Garretson

Jacques Lefriant
Post subject: Re: Who made this crank ?
Posted: Fri Mar 31, 2017 10:30 am
356 Fan


Joined: Mon Dec 06, 2010 1:50 pm
Posts: 3302
Location: National City Ca
Hi Cliff
i think they are trying to get oil to the pin bushing. When using the SPG crank you have to ensure that the piston will have enough clearance for the little end of the rod.
j

I always play more attention to Jacques comments. He seems several steps a head of even very component engine builders.

[Ashley James]

I'm not a 356 owner, but I bought the Brooklands 356 roadtest collection in the mid-80's and also have Denis Jenkinson's book in which he details his early Porsche motoring (lovely writing), so may have read the same old articles as referenced here.

My two penneth: I believe these old roadtests need to be taken with a big grain of salt; much gung-ho and false bravado was written by these fellows in period (as now). Also, Jenks excepted, these guys weren't owners of the cars they were testing, aka flogging. Did they care if their high-speed "testing" caused any harm? Likely not.

My 74 Alfa GTV 2000 has a five speed gearbox but a 4:55 final drive, so at 70-80 mph it is really singing. A few years back I substituted a 4:10 axle from a later Spider, in my (ultimately vain) efforts to turn the car into a more long-legged highway cruiser. In doing so, however, I thoroughly dulled it's accelerative capabilities, part of the car's charm, so the 4:55 went back in. You guys are all correct in how our senses have been retuned by today's cars with the tall gearing and engine management systems that make them so effective. John.

I’m surprised, I thought the 2000 Alfa was a torquey engine because torquey engines usually benefit from a higher overal ratio. My MK VI Bentley did and so do Healey 3000s.

The ones that don’t are the high revers.

[Kneeslider]

Just as a post script to this...

There appeared to be no problems with the little end to piston clearance when I built the engine.

My SPG crank runs with a hot oil pressure of approx. 2.5bar. 3.0+ bar cold on start up. At idle, hot it is always above 2 bar.

This leads me to believe that the main bearings have been fettled as described in the Registry thread to bleed off some pressure to splash lubricate the big ends.

Anyway, the thread seems to have strayed somewhat from its original purpose

[steve wright]

Although a race car and therefore noise isn't a primary concern (especially as we're running solid mounts and no carpets!) we're running the 356A Super with Solex P11's flat out for up to three hours at a stretch, never below 50mph and often well over 100. I've seen 135mph on the speedo on a couple of occasions down hanger straight at Silverstone, at which point it's pulling 6,500rpm in 4th. Can't recall what the ratio's are but they aren't super long. The car never (and I mean never) overheats, with the oil temperature rock solid on 85 degrees. We run no oil cooler in the fan shroud as it just heats the air to the cylinder heads and heats up the engine bay. Instead we're running an oil cooler in the front of the nearside front wing with a bit of ducting dropping a 1 inch lip into the airstream as well as taking air through the horn grill. Ian changes the oil after every race. Our average speed depending on the circuit is between 75-90mph (that's average speed...). The car ran for 3 seasons like this before being stripped for a refresh. We needn't have bothered! Other than new piston rings and valve guides as a precaution, Ian Clark put it back together with a little more porting and fettling. Even the crank didn't need a polish and we're regularly seeing 7,500rpm and sometimes 8,000rpm... They say a mile racing is the equivalent of a 100 on the road. We did 3,000 miles over those three seasons.

Just thought I would provide this as a contrary view. I'm not condoning speeding on the road, but it's all too often easy to think these are old cars and need to be treated gently, when in fact the engineering is as good today as it was when they were built. Don't forget they were built for Le Mans, Targa Florio, etc. These are tough little cars which if set up well will go all day flat out....

regards,
Steve

[Lightweight_911]

... I thought the 2000 Alfa was a torquey engine because torquey engines usually benefit from a higher overal ratio.

It's a US thing - std axle ratio for European-spec 2000 GTV's was 10/41 (4.1:1) whereas the equivalent US-spec models had a 9/41 (4.56:1) ratio - up to ~1980 from memory ...


- sorry for the diversion ...

[Ashley James]

Same applies to US model 356s, they have lower overall gearing too.

[Kneeslider]

So, has anyone access to data on the CWP assembly of a US sourced car compared to a European delivery car?

What the difference is, and is it worthwhile changing my ex-USA car? I suspect yes.

Any idea how much one might cost to procure?

[Ashley James]

The information is in the owners manual, the CW&P stays the same it’s top gear that changes I think.

[Mike Smith]

For road use the Crownwheel and Pinion were the same for all 356`s whatever side of the pond you were on
It was 7:31 ----- i.e. 7 x Teeth on the Pinion and 31 teeth on the Crownwheel , giving you a ratio of 4.42

However two other ratio`s were available to special order - 7:34 (4.86) and 6:29 (4.83)

After that everything depends on Tyre Size – Tyre manufacture – Tyre type and Gear ratio
Tyres – You need to know the distance that the tyre will roll at a set speed – Manufacturers quote it as the number of revolutions at 100 mph

Gears – For road use Porsche used 4 x different options for top (4th) Gear A, B, C and D (just to confuse you C is a higher than D).
In addition (for race use) Porsche also used 3rd gear in the 4th gear position for some tracks.
Speedsters were usually fitted with ratio`s of BBAB

We are usually only thinking about Ratios when calculating for race issues so I have never checked what the rolling distance is, for say, a standard 165 x 15” Michelin.

However, for a 5” x 15” Dunlop Racing Tyre with a `B` top gear the speed produced with the various final ratio`s at 5,000 rpm are :-
7:34 – 85.89 mph – (Hill Climb Option)
6:29 – 86.31 mph – Weak Option (too few Pinion Teeth)
7:31 – 94.20 mph – Standard Road Differential
8:31 – 107.66 mph – After-market Motorway Option

I hope I have calculated this correctly our board meeting was at the local pub this evening