Seeking camshaft recommendations for a street performance Longchamp

Please let us know which heads the engine is equipped with; i.e. US 4V heads with bigger ports, Australian heads with smaller ports, or aftermarket heads.

The cams you've mentioned appear to be hydraulic flat tappet, is that correct? You may want to verify what "type" of camshaft you're interested in.

Do you know the engine's compression ratio, if so what is it?

Describe the Longchamp's exhaust system.

Finally what are the specs of the Comp Cams valve springs?

Greetings George.

The heads are Australian 2V open chamber (74cc) with 2.070in intake and 1.650in exhaust valves. I think the compression rate is 8.5:1. 

The camshafts listed are both retrofit hydraulic roller cams.

I'm considering switching to roller cams with roller lifters and roller rockers. I'm also considering the Rollmaster CS10065 Ford 351C billet roller timing set with torrington bearings and 9 keyway adjustable crank sprocket.

The exhaust is stock with front and rear mufflers:

The specs for the Comp Cams springs:

Number of Springs Per Valve:Dual with damper

Outside Diameter of Outer Spring (in): 1.509 in.

Coil Bind Height (in): 1.175 in.

Spring Rate (lbs/in): 347 lbs./in.

Inside Diameter of Outer Spring (in): 1.125 in.

Inside Diameter of Inner Spring (in): 0.697 in.

Cheers,

Robert

Robert thanks for responding.

You didn't mention the installed height of the valve spring, but assuming the factory installed height:

1.820 installed height
-1.175 coil bind
= 0.645
-0.100 standard clearance
= 0.545 max. lift

Based on that I'd warn that you'll need different valve springs. On top of that the spring rate (347 lbs/inch) is fairly anemic for a roller cam. For a hydraulic roller cam I'd look for a spring with 150 lbs on the seat and 400 to 440 lbs/inch spring rate. The Lunati cam has a very aggressive ramp rate (indicated by 51° hydraulic intensity) for a hydraulic roller, I'm not sure 150 lbs on the seat is enough spring for that cam. If you're going to select that cam you should investigate the specs of the spring Lunati recommends, and use a spring that has at least the same specs as their recommended spring. Its always better to have too much spring than not enough.

The Aussie heads plus stock flat top pistons will yield about 8.8:1 mechanical compression. The relatively low stock mechanical compression calls for the intake valve to close as early as possible to build as much dynamic compression as possible..

Small port heads are tuned about 1000 rpm lower than the 4V heads thus we need to make sure the engine has enough intake duration to build a "street performance" powerband. 

The stock exhaust system calls for a cam with long exhaust duration that opens the exhaust valve early.

The aspects which work against good drivability are too much overlap, opening the intake valve too early, narrow lobe center displacement, and opening the exhaust valve too late. I'm not enthusiastic about either of the off-the-shelf cams you've listed. If I were putting together a hydraulic roller cam for you for a reasonable street engine it would look something like this:

• Duration at 0.006 inch tappet lift = 274°/286°
• Duration at 0.050 inch tappet lift = 220°/232°
• LSA = 114°
• Seated Overlap = 52°
• ICL = 111° ATDC (indexed +3°)
• Seated EVO = 80° BBDC
• Seated IVO = 26° BTDC
• Seated IVC = 68° ABDC

That happens to be a spec I've recommended often in the past, but I didn't plan it that way. I put together each cam from scratch, this is just the way the numbers came together. You can consider it an old school cam, or something close to a production cam … but its not a hot rod cam by today's standards. The engine would run strong and do nothing wrong … guaranteed. It would run stronger with more mechanical compression. I can explain the reasoning behind the spec if necessary … just ask if you have questions.

Thank you very much for your advices George! I really appreciate it.

I'll bring the information to my engine builder. He may also understand the reasoning behind the spec if it's not to much work for you? (This is rocket science for me..)

Would I be able to use my springs if I order a custom made camshaft based on your data? The spring specs:

• Seat Load: 112@1.900
• Open Load: 355@1.200
• Coil Bind: 1.175
• Rate (lbs/in): 347

I understand it may be a issue using the Ford Racing M-6564-C351 roller rockers with standard 6/15" bolts with high spring rates. Do you think they will work well with the springs? I'm thinking about durability.

Is there any camshaft grinder you would recommend if it should come to this?

Thank you again for all your advices! 

With sincere thanks,

Robert

We can increase the seated force of the Comp Cams spring by reducing the installed height, but as we do that we are also decreasing the max. lift.  Installed at a height of 1.825 the seated force would be 138 pounds. I usually target 150 pounds, so that's a little lower. That installed height will accommodate up to 0.550 inch valve lift. But the "over the nose" force at 0.550 lift is only 329 pounds due to the spring rate (only 347 pounds per inch). Both the seated force and especially the force at maximum lift are lower than the application calls for. So I can't recommend using that spring with a hydraulic roller cam application, it would be OK for a flat tappet cam with a rev limit at 6200 rpm.   

I believe the Ford bolt-down (pedestal mount) rocker arms were supplied with heat treated/black oxide coated allen head cap screws (5/16 inch). With those cap screws the rocker arms should be good to 400 pounds spring force at maximum lift (over the nose). If you want a little more assurance you could substitute ARP chromoly cap screws.

The theoretical specification I penned above was based on lobes with 54° hydraulic intensity. When I get to the point of specifying a camshaft that can actually be ordered I select lobes from the Bullet Cams on-line catalog.  I was able to find a matching pair of lobes with 56° hydraulic intensity (gentler ramps) providing 0.554 inch gross lift in their catalog. The lobe numbers are:

Intake = HR278/320
Exhaust = HR286/320

The spec with those lobes would be:

• Duration at 0.006 inch tappet lift = 278°/286°
• Duration at 0.050 inch tappet lift = 222°/230°
• Gross valve lift = 0.554/0.554 inch
• LSA = 114°
• Seated Overlap = 54°
• ICL = 111° ATDC (indexed +3°)
• Seated EVO = 80° BBDC
• Seated IVO = 28° BTDC
• Seated IVC = 70° ABDC

Bullet Cams make excellent cams with top workmanship and good customer service. I can provide further details (springs, timing, compression, and ordering info) if this spec interests you. If you think the spec needs adjustment I can do that too.

Food for thought.

Crane Cams has an off-the-shelf hydraulic flat tappet cam that is basically identical to my spec, with 0.539/0.534 lift. It should be compatible with your valve spring. The grind number is H-278-2, (part number 523801).

278°/290° duration at 0.004 (advertised)
274°/286° “assumed” duration at 0.006 (assuming 52° hydraulic intensity)
222°/234° duration at 0.050
0.539/0.534 gross valve lift
LSA = 114°
Seated Overlap = 52° (based on the assumed duration)
Intake lobe centerline = 113° ATDC (install 2° advanced @ 111°)

I'm absolutely speechless.. Thank you so much George! 

Robert

If you were to decide to use the Crane Cams camshaft I would suggest installing the Comp Cams spring at a target height of 1.848 inches. This would give 130 pounds seated spring force and 317 pounds over the nose (at 0.539 inch lift). Maximum lift at that installed height would be 0.573 inch.