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Old 21 Apr 2010, 09:44 (Ref:2677163)   #16
phoenix
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Thanks Rob
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Old 21 Apr 2010, 22:29 (Ref:2677565)   #17
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All the cranks I have are marked "Laystall" and dated. The 1964 cranks appear to be modified MAE cranks, in that the snout is to SCA dimensions to mount the gear for the cam drive, but part of the keyway for the standard snout and pulley remains. The cranks that are dated 1965 do not have evidence of the keyway, so I assume they were purpose built for the SCA. By the way, the SCA has a rather unusual method of driving the crank gear. The gear itself floats on the snout on a bronze bushing and is connected to the crank via a small shaft that presses into the crank snout and the forward end of the crank gear. There are two pins sticking out the front of the crank that engage with slots in the rear edge of the gear. This setup allows the crank gear to rotate slightly as the shaft torques. I am guessing that this allows for absorbing some torsional shock and vibration in order to prolong the life of the geartrain for the cam drive. I am told the FVA used a similar arrangement but the DFV instead used a compound drive gear futher up the drivetrain that had similar shock absorption features. If anyone is interested in any of this I will see if I can take some photos and post them.

Rob
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Old 22 Apr 2010, 08:46 (Ref:2677713)   #18
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Interesting thread.

Yes i would like to see some photos.
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Old 23 Apr 2010, 06:52 (Ref:2678227)   #19
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photos of crank gear drive

Robyn,

I have tried to attach some low res photos of the crank gear drive set up, as well as a shot of teh other gears in the cam drivetrain. You can see the short quill that presses into the nose of the crank and then gets the gear pressed onto it. In the last photo you can see the crank gear sitting in place on the snout with the two pins lined up in the slots in the gear. I am still trying to figure out how I am going to make sure it is all lined up before I press it together.

I should have some photos of the geartrain mocked up on the front of the engine next week, as I am going to have to figure out how to shim everything so that the backlash between all the gears is correct when I bolt the cylinder head on and install the cam. There are shims under the cam carrier to allow for adjustment there, but it is the head gasket thickness that will set the backlash for that particular pair of gears.

Rob
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Old 23 Apr 2010, 06:55 (Ref:2678228)   #20
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I'd be interested to see some photo of the head too as I have never seen one. A shot of the combustion chambers/valves, one of the cam and valve operating arrangement, one of the inlet ports and one of the exhaust ports would be fantastic.
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Old 23 Apr 2010, 16:38 (Ref:2678508)   #21
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Phoenix,

All four of my cylinder heads are at the cylinder head shop being rebuilt. I will have to pick up one next week in order to mock up the cam geartrain and see how the backlash is going to work out. The head will likely have no valve in it, but I can get some pictures then. It is kind of interesting because the ports and valves seem small for the claimed output, but my cylinder head guy said it is all about making it work with high velocity flow. As someone pointed out earlier in this thread, they actually reduced the exhaust port size in 1965 to improve performance.

In the meantime, I have attached a scan of the cutaway drawing from Autocar magazine 16 April 1965 edition. They did an article on the SCA that included some really good information and photos.

Regards,

Rob
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Old 24 Apr 2010, 13:03 (Ref:2678957)   #22
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Thanks once again Rob.

That's really interesting.

I read that one of the final developments of the FJ engines was the XVII for which Cosworth converted the head to 'downdraught' from sidedraught by boring the head and brazing in more vertical replacement inlet ports. This was the first Cosworth to develop over 100 BHP/Litre and it looks like the SCA-C engines were a further development of the ideas explore with that engine.

Downdraughting the ports to the vertically installed inlet valve shallows the angle between the valve and the port and in doing so opens up the 'short side radius' which will improve flow through the port, delaying the onset of turbulence in the port and allowing higher inlet gas speeds to be achieved. The inlet valve size (1.45") in a sidedraught head would flow a maximum of about 128 BHP. In a 'hemi' style crossflow head the same sized valves would flow closer to 142 BHP due to the better port/valve angle and the better position of the valve exit relative to the cylinder wall. It would appear that on the SC engines the head can flow 5-8% more than the best side draught port arrangement could achieve.

I imagine the inlet port sizes are quite large due to peak torque being at 8000 rpm in the 997 cc engine. If this is the case it might have made it necessary to reduce the exhaust port diameter as a compromise in order to fit the large inlet ports into the space available. The plus side of this might have been improved scavenging; the peak torque of 76 lb/ft suggests a VE of around 114% was achieved, and that would not be possible without excellent inlet and exhaust manifold tuning.

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Old 25 Apr 2010, 17:00 (Ref:2679412)   #23
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Phoenix,

The bottom of the cylinder head is completely flat, so the only combustion chamber is the dish on top of the piston. The picture below shows an SCA piston on the left and an SCC piston on the left. The Autocar article mentions that the '64 SCA pistons had the offset chamber like the one on the left and that the '65 SCA engines went to a shape more like the piston on the right. I assume that the SCC was a '65 engine and hence had the later chamber shape.

You seem to be keen on engine theory, so I would be interested in your opinion about the 1500cc SCB. I am currently building one of these engines as an SCB to fit in my Lola. Cosworth claimed to get 175hp, which would make it competitive against the Twincam powered cars I have to run against here. I have ordered a long stroke crank, shorter rods, and custom pistons. I have taken one of the large port heads and put in the biggest valves I can fit (1.60 in/1.35 ex). My cylinder head man is looking at things on the flowbench so I can get some data to select the cam profile, likely more lift and less duration than the original SCA cam. Do you think it is really possible to get 175hp out of such an engine? A friend of mine used to run against Brian Redman in F2 when he was using an SCB engine in '66 or '67 and he remembers Brian had more power than his Twincam but less than the FVAs. I assume that a Twincam probably made 150hp back in that time.

More later,

Rob
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Old 25 Apr 2010, 18:16 (Ref:2679459)   #24
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Hi Rob

Remembering this is only theory I think the Cosworth figure is a bit optimistic, as I get 169 BHP as your likely maximum with 115 ft/lb of torque.

My bet is that the Cosworth A8 cam profile will be similar to what you end up with as optimum, though the A6 may be enough for this engine as it isn't going to be making the revs of the 997/1099 shorter stroke engines.

I don't think you could expect to match a twincam with 1.625" inlet valves which they seem to run over here now, but would be pretty close, maybe 7-9 BHP down, but back in '66-'67 the SCB might well have produced more power than the twincam.

Any details you can let me have of the original cam profile would be a great addition to my library of engine data....

Did the SCB use 4.825" rods like the 1500 116E and the twincam engine?

As for the pistons, the larger engine would need a slightly larger combustion chamber for the same CR ratio, wouldn't it?

Thanks

Martin

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Old 25 Apr 2010, 19:29 (Ref:2679504)   #25
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I have taken one of the large port heads and put in the biggest valves I can fit (1.60 in/1.35 ex). My cylinder head man is looking at things on the flowbench so I can get some data to select the cam profile, likely more lift and less duration than the original SCA cam. Do you think it is really possible to get 175hp out of such an engine?
p.s. Let me know if your head man gets better than 166CFM @ 28"....
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Old 25 Apr 2010, 22:17 (Ref:2679618)   #26
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Martin,

The original cam for the SCA was the F1 profile. It has .402" lift and 324 deg. seat to seat. Like you, I was thinking I would end up using something more like 300 deg. seat to seat for the SCB, but I was waiting for the flow data to see if additional lift was going to be useful.

Since there is no data on the SCB (it appears Cosworth only built one) I am having to make up the specs as I go along. I am planning on using the 4.825" rods unless they don't leave me with enough room for the larger dish in the piston. The piston guy is supposed to get back to me next week about whether I have enough compression height. If not I will have to custom make some shorter rods.

I noticed that an earlier post to this thread noted that Keith Duckworth said the SCA needed too much ignition advance to be efficient. I am trying to figure out what I can do to the shape of the dish in the piston to make the chamber "faster". I am working with the piston guy on this, leaving large squish areas and such, but I don't know what else to do. Possibly this is why the "high swirl" intake ports were so important.

Regards,

Rob
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Old 26 Apr 2010, 01:53 (Ref:2679684)   #27
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Cosworth SCA F2 Spec sheets :

Capacity 997cc Bore 81.0mm Stroke 48.35mm

Gross HP : 115bhp minimum @ 8,700rpm, rev limit 9,500

Cam ; F1 - 102 degree

Inlet valve size : 1.45"
Ex " " : 1.25"

Note pistons are two ring suggesting slipper type .....

Copies of sheet available and get any components made .....
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Old 26 Apr 2010, 11:09 (Ref:2679802)   #28
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Cosworth SCA F2 Spec sheets :

Capacity 997cc Bore 81.0mm Stroke 48.35mm

Gross HP : 115bhp minimum @ 8,700rpm, rev limit 9,500

Cam ; F1 - 102 degree

Inlet valve size : 1.45"
Ex " " : 1.25"

Note pistons are two ring suggesting slipper type .....

Copies of sheet available and get any components made .....
Do you have a spec sheet for the SCC also? I found a reference on the web that these produced 135 BHP from 1099.6 cc (83.5 mm bore and 50.20 mm stroke) but with the same size inlet valve - so I'd like to find confirmation of that. Also Rob mentioned that some SCCs had 1.55" inlet valves.
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Old 26 Apr 2010, 11:16 (Ref:2679805)   #29
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Rob

Are you planning to use and 83.5 mm bore for your SCB? If you are free to do so you could find a 6% improvement on torque output from the 1593.5cc that would result in (same capacity as the FVA I believe) and more bore clearance for your 1.6" inlet valve.
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Old 26 Apr 2010, 18:13 (Ref:2680022)   #30
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Thanks for posting the photos Rob,
What is the purpose of the small dumbell shaped shaft that fits in the nose of the crank?

Pheonix, interesting you should mention the downdraught conversion as i've recently done this mod on my anglia engine.Also interested in the calcs to determine cam profile. Any suggestions where i can find info for further study?

Robyn
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