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Teach me about camshafts


Phill

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18 minutes ago, Leicestershire said:

I was referring to the numbers quoted for the port sizes - 49mm inlets???

SC's 34,36,39mm - trying to clarify what year, model or market has what. 3.2 has (I think) 41mm - somebody please confirm

SCRS 41mm

 

Sorry, that was a labeling mistake. Corrected here:

Engine Model Intake valve [mm] Exhaust valve [mm] Intake port [mm] Exhaust port [mm]
930/03 911 SC 78-79 49 41.5 39 35
930/09 911 SC 80 49 41.5 34 35
930/10 911 SC 81-83 49 41.5 34 35
930/18 911 SC RS 49 41.5 43 43
930/20 911 Carrera 3.2 49 41.5 40 38
M64/01 964 Carrera 2/4 49 42.5 41.5 38
M64/03 964 Carrera RS 49 42.5 41.5 38
M64/05 993 94-95 49 42.5 43 39
M64/20 993 Carrera RS 51.5 43.5    
M64/21 993 96-97 50 43.5 43 39
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1 hour ago, Leicestershire said:

Don't believe everything you read!

 

I've just made some measurements on my MY80 SC which seem to contradict the value in Bruce Anderson's book for the intake port size of the 930/09 (MY80 SC RoW) engine.

Not sure if my car is exactly as it left the factory but the intake runner for cylinder 4 has part number 911.110.169.4R and has an outer diameter of about 48 mm. According to some threads on pelican this seems to indicate a large port engine. Engine number is 6302xxx which indicates it's a 930/09 engine, i.e. the one that corresponds to a MY80 SC.

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30 minutes ago, jehatwhitland said:

I know it doesn't say so in the Anderson book, but that's what I thought as well. It also feels logical given the power difference.

My own SC is an early ‘81 model year registered December ‘80. Fuel filter, side repeaters and the hard fuel lines on the original CIS confirm it’s an ‘81 model car. The original camshafts were retained with the large hex bolt and spring washer as fitted to early motors and the first batch of 204 bhp engines before changing over to the hex head bolt with thick washer. This engine has the large ports and valves. 

Possible reasons:

My engine was a parts bin special using up old stock heads - unlikely.

it had been meddled with at sometime in the 30 years before my ownership- possible.

the vast majority of information on the web originates from the US and is of questionable accuracy - ??

 

 

 

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8 hours ago, Leicestershire said:

...the vast majority of information on the web originates from the US and is of questionable accuracy - ??

This possibility had crossed my mind. 

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Anderson wasn't just some punter who wrote a book.  He ran a shop for decades and would have seen many US and ROW cars over that time with many being rebuilt for track/race.  I am not saying he is infallible, but I would start with the presumption he is correct.

Maybe Anderson is the only source for this small port "legend", but it has certainly been the accepted wisdom for decades. 

$0.02.

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50 minutes ago, Richard Bernau said:

Anderson wasn't just some punter who wrote a book.  He ran a shop for decades and would have seen many US and ROW cars over that time with many being rebuilt for track/race.  I am not saying he is infallible, but I would start with the presumption he is correct.

Maybe Anderson is the only source for this small port "legend", but it has certainly been the accepted wisdom for decades. 

$0.02.

Since there is probably a decent representation of RoW SCs in this forum, we could have our own survey to verify Bruce Anderson's claim that 80-83 RoW SCs have smaller intake ports. @Leicestershire's and my car seem to indicate that the claim is not totally accurate but that's a small sample...

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2 minutes ago, SP72 said:

Have you got the Bruce Anderson book? It’s not a build book specifically, however.

No, is it complimentary to the Dempsey one or repeating the same in a different way?

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On 8/22/2019 at 2:21 PM, WP0ZZZ said:

Since there is probably a decent representation of RoW SCs in this forum, we could have our own survey to verify Bruce Anderson's claim that 80-83 RoW SCs have smaller intake ports. @Leicestershire's and my car seem to indicate that the claim is not totally accurate but that's a small sample...

There is a good thread on port sizes here - http://forums.pelicanparts.com/911-engine-rebuilding-forum/519112-early-911-cylinder-head-cross-reference.html I suspect all, or mainly, US contributors but including some experienced engine builders. I've attached the OP's last table from the thread.

Also attached a pic of one of my 1982 US spec SC small port heads, part# ending ... 326.3R (you can see the 82 date on the casting). The heads I replaced them with were large port heads with part# ending ... 329.2R that have a 1979 date on the casting.

If anyone has a 1982 UK or ROW SC head off the car, we should be able to compare part numbers.

Picture21263551298.jpg

1-IMG_20190824_135519188.jpg

PS Looks like everything 76 onwards is based on the same casting, with the same valve sizes. It's just the port sizes that appear to vary.

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  • 2 weeks later...

Wayne's book was delivered the other day. I've started reading and I have to say I am very impressed with the way it's written. Plain and simple, expecting you to have some knowledge. I've already read the first 20 pages, he actually makes it interesting and understandable.

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