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 Post subject: Re: Wide Lobe Cams
PostPosted: Wed Dec 13, 2017 6:03 pm 
356 Fan

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DonCichocki wrote:
Ahhh, here we go again. The lift on my worn stock '65 "C" cam was .295" @ the lobe for both intake and exhaust. It was NOT a wide lobe cam. I recently sent it to Web Cams for an evaluation and they reground it to their 1187 grind. The lobe lifts are: intake .302", exhaust .293" @ lobe. The duration is still suspect as I'm waiting until I have the engine out and can verify the cam timing #'s. Why somebody can't duplicate the stock '64-'65 "C" cam to the book specs is a mystery.


...the 2 "C" cam cores in my holdings, are the narrow lobe style, as well...

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 Post subject: Re: Wide Lobe Cams
PostPosted: Wed Dec 13, 2017 6:09 pm 
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IIRC, the original Normal cam, was on a ...103 cam blank P/N, and the C cam, is on the ...102 blank P/N ?

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 Post subject: Re: Wide Lobe Cams
PostPosted: Wed Dec 13, 2017 6:13 pm 
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Does anyone know the difference in a 616-105-102, and the 616-105-105, the later, a wide lobe 912 ?

I've been studying this subject since '64, and the more I read, the less I'm certain...

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 Post subject: Re: Wide Lobe Cams
PostPosted: Wed Dec 13, 2017 6:41 pm 
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Unless somebody can absolutely prove me wrong I stick with my assertion that 616 series engines all had 1 of 2 grinds, Normal/C or Super/Super 90/SC/912. There were also iron low ratio rocker arms and alloy high ratio rocker arms. Both of the 2 cam grinds were at one time or another used with both of the rocker ratios. The Porsche spec book gives the timing and lift measurements at the valve, not the cam/lifter, and that is why you see so many different specs.

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 Post subject: Re: Wide Lobe Cams
PostPosted: Wed Dec 13, 2017 8:37 pm 
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Hi CJ
i believe that the Normal and C cams are different. the specs seem to confirm that the C has more exh lift and about the same duration. i beleive all cams are singe pattern that is the intake and exh are identical at the lobe. also from the spec book the alloy exh ration is smaller than the iron so the C having more lift(8.6 vs 8.2 N) is not a ratio issue. if this still is an important issue i will take a C and a normal cam and do a cam doctor plot. Also i contend that C and Normals do not produce more torque just that the torque peak occurs at a lower RPM and falls off faster at higher RPMs giving a seat of the pants feeling of greater torque and depending on the gear box could produce different 0-60 times.
KTF
j

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 Post subject: Re: Wide Lobe Cams
PostPosted: Thu Dec 14, 2017 8:45 am 
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"i believe that the Normal and C cams are different"
+1
I have NOT seen a difference in the exhaust rocker arm ratios.

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 Post subject: Re: Wide Lobe Cams
PostPosted: Thu Dec 14, 2017 9:45 am 
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Jacques,
If you do a "cam doctor" plot of the "normal" and a "C" please post it here as that will settle a lot of speculation. Thanks!
DC


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 Post subject: Re: Wide Lobe Cams
PostPosted: Thu Dec 14, 2017 9:55 am 
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I'm with Jacques and Vic here. My first A T1 N coupe, with the 32 single barrel Solexes, BBBC gearing, to take advantage of the torque at the lower revs, smaller ports, 56,000 mi. from new, & bias ply tires, consistently got 33.5 mpg @80 mph, on TX highways, a concept Porsche returned to with the 914, high torque T4 engine.

As well, with the introduction of the C, we got bigger intake ports, matched and contoured manifolds and slightly different calibration on the Zeniths. I never had a C car, but the late 741A, T6 gear boxes I have, IIRC, were geared BBBD, to better match the higher torque range of the paired engines, at higher road speeds, anyone?

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 Post subject: Re: Wide Lobe Cams
PostPosted: Thu Dec 14, 2017 10:08 am 
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I think I also plotted the revs at highway speeds between the late B S90, SC, and my 912, in top gear, to yield the near same cruise revs, and legal road speeds, per the charts in the owner's/driver's manuals, all with the same spec book cam specs, as Cliff states.

Vic, my A, & T5 Normals came with the "C" top gear, my '63 N, the "D" gear, as I recall, what gear did the straight C 741As come with? Thanks! (my specs book is not here)

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 Post subject: Re: Wide Lobe Cams
PostPosted: Thu Dec 14, 2017 10:11 am 
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4D is lower than 4C; so higher revs at the same road speed.
American market cars had the 4D, Rest of World got the 4C.

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 Post subject: Re: Wide Lobe Cams
PostPosted: Thu Dec 14, 2017 12:02 pm 
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Hi Vic
yes the exhaust ratios are almost identical i was just commenting on the specs for 616/2 p15 in spec book the lift was 9.25 cast iron and 9.2 alloy. i have not measured any statistical meaningful sample to confirm this. also from the geometry the ratio is not a constant.
j

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 Post subject: Re: Wide Lobe Cams
PostPosted: Thu Dec 14, 2017 2:34 pm 
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I will attempt to blow a little smoke so that it doesn't look like I made a mistake on my previous hand written calculations, even though I did make a mistake.

I long ago noticed that the C cam was unique but the other night using my guess of the different rocker ratios I came up with the same lobe lift for the N and C cams, wrong. They are very close in function but the C has greater lift at the lobe and yet more intake valve lift due to the alloy rocker ratio.

Once again I wrote down some data but I have not done any of my own calculations that assume a rocker ratio number.

First, the respected sources cited do not always agree with each other.

Second, cam lift is different from valve lift.

Increased rocker ratios increase duration as well as lift.

Rocker ratio changes a little as the rocker sweeps through its range of motion.

Porsche provides a duration number at 1mm of valve lift. US cam grinders use seat, .020", or .050" duration numbers that could be measured at the cam or the valve and that makes a difference.

Trying to compare all this differing data is not going to get you a precise answer. That is where the Cam Doctor comes in, IF, the cams being compared are all brand new and measured with care.

Using the Porsche specs the N and C cams are the same duration but the C has a little more lift at the lobe. Add the alloy rocker ratio and you get significantly more intake valve lift in a C engine. Duration is the primary factor and that is what gives a C or N such nice manners at lower rpm.

We could look at the power curves for the 1963 Super and the 1964 C, both with the same peak power I think, and we should see that the C has stronger torque spread. Yes, there were some other differences but they are similar other than the cams. Now that I have said that without looking at the Porsche power graphs I wait to be corrected.
Attachment:
Cams.pdf [411.1 KiB]
Downloaded 29 times

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 Post subject: Re: Wide Lobe Cams
PostPosted: Thu Dec 14, 2017 2:56 pm 
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I wonder if somebody like Jon who has a deep library of Porsche bulletins might have more detailed information on cams and rockers.

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 Post subject: Re: Wide Lobe Cams
PostPosted: Thu Dec 14, 2017 6:07 pm 
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C J Murray wrote:
I wonder if somebody like Jon who has a deep library of Porsche bulletins might have more detailed information on cams and rockers.

Cliff, I rely on you and Jacques for all of my in-depth cam information & analysis ;-)
I was under the impression that the C camshaft was unique. It did have a different part number than the 1600 "normal" cam- 616.103.014.00 with 0 gear.

According to the 356A Workshop Manual, valve timing for 1300S and 1600S engines was 15°/50°/50°/15° with 1 mm valve clearance, and obviously with iron-stand rockers.
I think that the Specs Booklet, at least the 3rd edition, only lists 1600S valve timing numbers with the alloy-stand rockers.
Conradt's book mentions that all B engines were originally intended to have the alloy stands & new rockers, but that tests indicated a drop in acceleration when used in the 616/1 "Dame" engine.

I'll look through my bulletins to see if I can find any additional information.

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 Post subject: Re: Wide Lobe Cams
PostPosted: Thu Dec 14, 2017 7:08 pm 
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Thanks Jon,
I remember the Conradt book mentioning that internal Porsche memo. His book is full of great Porsche internal memos. I can imagine that the 24 mm venturis would be a mismatch with the higher lift. The general theory is that an intake valve "curtain" when opened can pass a certain amount of charge. Based on that and the rpm of the engine, at a certain rpm the charge will reach mach at the curtain and at that rpm the engine will produce peak torque. Increasing the lift or diameter of the intake valve will push peak torque to a higher rpm. The 24 mm venturis and lower lift apparently worked well together while the much higher intake lift of the C worked well with the 28 mm venturis. Makes sense.

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