Can anyone recommend an ignition cam curve to get me close to the sweet spot for the igintion advance?

How about some real world experience using cams similar to these?

Does anybody have real world experience on how these cams idel and actually work?


I'm working on putting a fresh 460 with the good stuff (ported DOVE heads with CJ valves, DOVE block, CJ intake, headers, F2404 pistons, CJ rods, 5spd overdrive) into my 86 F250 4x4 Supercab with 3.55 gears.

I use the truck mostly for highway towing (40%), some offroad driving (20%), and as a work truck (40%). Of course I want the best power/torque/ and MILEAGE that I can get.

I was thinking of using one of two cams:

Cam A:
252/260 duration (I/E) 206/212 at 0.05 in.
110 Lobe Speration
106 Intake Centerline
0.467/0.484 lift (I/E)

Cam B:
270/280 duration (I/E) 214/224 at 0.05 in
112 Lobe Seperation
112 Intake Centerline
0.510/0.530 lift (I/E)

Any thoughts on what would be the best all around cam for this application.

My engine simulation gives me these numbers for these combinations:

Cam A: (-4 degrees)
Rpm HP TQ
2000 / 209/ 548
2500 / 254/ 533
3000 / 297/ 519
3500 / 333/ 499
4000 / 357/ 469
4500 / 358/ 418
5000 / 336/ 353
5500 / 302/ 288
6000 / 253/ 222
6500 / 201/ 162

Cam B: (straight up)
Rpm HP TQ
2000 / 193/ 507
2500 / 244/ 512
3000 / 290/ 507
3500 / 336/ 505
4000 / 376/ 493
4500 / 402/ 469
5000 / 403/ 423
5500 / 385/ 367
6000 / 344/ 301
6500 / 299/ 242

The gears (3.55) and tires (215/85/16) and transmission will put the engine speed at:

3350/65 mph 4th gear
3850/75 mph 4th gear

2550/65 mph 5th gear
2950/75 mph 5th gear

I do want some reserve for pulling moutains in case I need to down shift.

At 75 mph Cam A is past the peak torque curve.
At 75 mph Cam B is almost right on the peak torque curve.

A down shift at 75 mph will give me more power and less torque on both cams:

Cam A:
3000 to 4000 down shift +60 HP - 50 lbft
Cam B:
3000 to 4000 down shift +86 HP -14 lbft

The differences of the cams at 3000 and 4000 are:

Cam B-Cam A

3000 rpm -7 HP -12 lbft
4000 rpm +19 HP +24 lbft

 

bump to top

 

anybody want to reply to this?

 

Tough call - your engine setup is really better suited to a lighter, streed rod type vehicle. The large-port CJ heads and intake would not have been my first choice for a towing rig.

In terms of total power, the second cam would be a better compliment to the rest of your parts selection. The problem is that the power package would make for sluggish off-idle performance, especially in a heavy vehicle with a big tow load. Throw in the manual tranny and low-end becomes even more problematic. You would have been better off with a locking overdrive that had a slightly higher stall to take advantage of the more midrange-ish power characterisics your combo and cam 2 would produce. As it is you definitely will have to keep it above 2500 RPM for the best performance, and getting a heavy load rolling from a dead stop will involve a lot of tricky clutch work unless you have a really deep first gear.

Brad

 

I agree with Brad, totally wrong parts for towing. Cam "A" is better for towing. What you really need is stock heads with a cam with "A"s duration and "B"s lift. Towing requires shorter duration and the extra lift helps the top end without penalizing the bottom end. Little holes (ports in the heads and carburator) keep air velocity up at lower speeds which helps torque, which is what towing is about; not peak horsepower. You don't mention what you are using for a carb, but bigger is not better for towing.

 

Let me clarify. I'm not using CJ heads or PI heads. I'm using the stock DOVE-A closed chamber heads. The stock heads have been worked. The intake port has been ported to match the stock CJ intake. Not ported the entire intake track. I installed hard seats and larger intake and exhaust valves (2.10 intake and 1.76; the were 2.19 CJ intakes but were cut down to 2.10). The exhausts have been ported to remove the bumps and humps. The low rpm velocity should be good since it is a stock small port head.

I think Cam A would take the pick if I wasn't towing at 2500 or 3000 rpm.

It looks like Cam B may be better suited for that rpm range even if it is down on power a little.

The both offer much improved power and torque over stock. It seems like the trade-off of some torque for improved top end is fair. I'm thinking I would like there to be some power when I down shift and pull a high moutain pass.

The way I looked at low torque was this:

The 5 speed zf S452 S457 gear ratios are: (1) 5.72 (2) 2.94 (3) 1.61 (4) 1 (5) 0.76
Rear gear ratio 3.55
Crawl ratio is 20.3

Cam "A" at 2000 has 548 lb-ft that gives 11,124 lb-ft (200# guy on a 55.6 foot cheater bar hooked to the center of the wheel)
Cam "B" at 2000 has 507 lb-ft that gives 10,292 lb-ft (200# on a 51 foot cheater bar hooked to the center of the wheel)

The difference is 832.4 lb-ft. That is the equivalent of a 200# guy standing on a 4 foot cheater bar to the center of the wheel.

In any case these numbers should move most things.

Gas milage is the other issue. With either cam the city milage will be poor. Just to much ideling. Milage towing on the freeway is best when close to peak torque. So I was thinking that overall milage would be better with Cam "B".

 

Split the difference.

After a couple of runs in a friends truck and a build for my brother's work rig, I've become a big fan of the Comp 262H. Idle has some chop bit is still acceptably smooth for what it is. Off-idle and midrange power and response is just stunning, especially for his otherwise stock-headed work rig.

Comp Cams 262H (part number 34-235-4)
Adv duration (seat-to-seat) 262/270
Overlap - 44.0
Int/Exh - .514 / .524
IVO/IVC - 24 BTDC / 58 ABDC
EVO/EVC - 70 BBDC / 20 ATDC
Intake centers - 107.0
Lobe sep - 111.0

Plug that into your sim - I bet you'll like the results

Brad

 

With that set up I would go with a full roller hyd that crane has. Dont remember the exat specks but it was around 220 duration at .050 Lift was around .550. It is one of there broadest range cams for a 460. Next to get economy from those big heads you would actualy need lower gears to get the RPMs up were the air speed through the engine is up high enough that the fuel stays suspended better. I woud say your 4 gear RPMs would be better suited to 5th gear. So somethig lower than 4:11 would be needed.

 

As for timing start with 20 degrees inital and a total of 32 to 36 degrees. It should all be in by around 3000 RPM. Each engine is a bit different but its a good starting point. Most distributors factory or after market wont get you these timing curves with out modifing ther einternals beyound what they are sesignd for. A ford distributor will need the advane plate slots welded up. A MSD will need a custom made advance bushing the black one is too small.

 

Okay Cam C: (straight up)

Rpm HP TQ
2000 / 203 /534
2500 / 253/ 531
3000 / 301/ 526
3500 / 345/ 518
4000 / 378/ 497
4500 / 394/ 460
5000 / 387/ 407
5500 / 357/ 341
6000 / 310/ 271
6500 / 299/ 242

So at 75 highway cruse speed: HP 301, TQ is 526 at the end of the torque curve.

A downshift to give 4000 rpm gives: HP 378, TQ 487

The downshift increase HP by 77 and looses TQ -39.

where:

Cam A:
3000 to 4000 down shift +60 HP - 50 lbft
Cam B:
3000 to 4000 down shift +86 HP -14 lbft

So this cam is definately in between the other two.

Cam C gives up 14 lb-ft at 2000 for a max gain of 55 at 5500 rpm
Cam B gives up 41 for at 2000 for a max gain of 83 at 5500 rpm

The payback on percent basis is that Cam C gains almost 4 times the HP that it loses in torque. Cam B gains only 2 times the torque loss.

If I retard the cam -4 degress it becomes:

Rpm HP TQ
2000 / 201 /529
2500 / 251/ 527
3000 / 299/ 523
3500 / 343/ 515
4000 / 381/ 500
4500 / 403/ 470
5000 / 402/ 423
5500 / 383/ 365
6000 / 340/ 297
6500 / 294/ 238

Which is almost the exact HP curve of Cam B and it beats the torque of Cam A at 3000 rpm and 4000 rpms (519 to 523 and 469 to 500). The payback is loose 19 Torque at 2000 and gain 81 HP at 5500 rpm which is a 4.2 factor and a very good trade off factor (in my opinion).

The question still remains is Cam B more efficient (mpg) at towing at 75 mph because the torque curve peaks at 2500 vs Cam C which peaks at 2000?

 

Here is the cam I sugest Crane HR-200/311-25-12


Dur at .050 200/212
Adv 262/274
Sep 112
Lift .532/.568

Open close at .050
(7) 27
43 (11)

Best to go with rollers these days fewer oils support flat tappets.

You wont get quite that lift most roller rockers for 460s are only 1.7

 

Here is the cam I sugest Crane HR-200/311-25-12


Dur at .050 200/212
Adv 262/274
Sep 112
Lift .532/.568

Open close at .050
(7) 27
43 (11)

Best to go with rollers these days fewer oils support flat tappets.

You wont get quite that lift most roller rockers for 460s are only 1.7

 

Are you insane? You can't run an advance curve like that if you are towing, in a car maybe or a truck that never tows but not towing. You will burn holes in pistons and overheat the motor. He says 40% towing and 40% work with the truck. Better off to start with 10 to 12° initial and end up with 32 to 34° in not sooner than 3500 rpm.

 

Hydraulic rollers are great, but they cost lots of bucks. The HR cam is running $413 and the lifter are $550. I didn't price the pushrods, but those are special order as well.

I have bought some lifters that have an EDM hole in the center for improved oiling, and have also bought API Grade H Rotella T SAE 30 for the break in of the hydraulic cam.

 

The lower torque peak of cam C should give you better overall efficiency in addition to being more tow-friendly than cam B. Plus, it will give you better non-towing performance where you need it most in your heavier vehicle without sacrificing upper RPM HP.

Brad