F250 390 Cam Selection

[sparky72]

Howdy folks,

Well, I finally have my engine torn down and sent off to the machine shop. They’ve already tanked and magnafluxed the C8AE-H heads, and...they’re cracked. Both of them. Into every single spark plug hole...

Oh well. Time for a more fun topic. I was chatting with the guy and he was saying he probably wouldn’t go bigger than a 204/214 @ 0.050 cam in this motor. I had my heart set on something like a Comp 268H, which is 218/218 @ 0.050 (0.494 lift with the stocker rocker assemblies). Is this a big difference? I’m pretty green to engine building so I’m not entirely sure what to expect. Like I said, it’s going into an F250 so I want good low end, but I also want a hint of lope (not a lot, just enough to make me grin ). I do have power brakes but I don’t think a 268H would be big enough to rob me of that much vacuum.

What say you? Another quick thing, he usually uses cams from Melling or someone like that; says they’re pretty much the same as, say, a Comp, which I can see if the grind is the same. So is it stupid to still want a Comp, or a Lunati, or something...name brand...like that? If only for the stickers

Appreciate the help!!

Edit: Some more info...
See sig. 3.73 rear end, 235/85r16 tires (may change to 265/75r16, but they’re pretty much the same diameter), T18 transmission (may swap in a TKO-500 or 600 eventually, as shekels allow), will have an Eddy intake manifold and a 4bbl when all is said and done (carb size TBD; thinking a 600 w/ vacuum secondaries would be fine). Will rarely, if ever, use it to seriously tow, despite the 8100lb GVW; will primarily be a cruisin’ and bruisin’ truck.

[DuckRyder]

Comp 268H will be fine assuming you have compression in the range Comp wants. I’d rather run a split pattern cam in a Ford as generally they are weak on the exhaust side flow. (Crane 343941, Comp XE262, and similar from Lunati, Crower...)

I sorta doubt any of them (including the 268H) are going to have much lope.

Now this is opinion, and I have used some melling small block cams with decent results, just because the grind appears the same does not mean the cam is the same... is the metallurgy the same, quality control, tech support.... ?

Whats your piston/compression choice...

I’ve said it more than once, if you have to put much into the heads - edelbrock...

[sparky72]

Comp 268H will be fine assuming you have compression in the range Comp wants. I’d rather run a split pattern cam in a Ford as generally they are weak on the exhaust side flow. (Crane 343941, Comp XE262, and similar from Lunati, Crower...)

I sorta doubt any of them (including the 268H) are going to have much lope.

Now this is opinion, and I have used some melling small block cams with decent results, just because the grind appears the same does not mean the cam is the same... is the metallurgy the same, quality control, tech support.... ?

Whats your piston/compression choice...

I’ve said it more than once, if you have to put much into the heads - edelbrock...

I'm looking to have compression between 9 and 9.5:1. We haven't measured the bores yet but the block is already .030 over and will certainly need at least a hone. Once we know the required final bore, we'll choose the pistons to hit that CR goal.

[DuckRyder]

Sounds like you got it covered.

I think a 268H will work fine, I’d still prefer a dual pattern though.

[sparky72]

Sounds like you got it covered.

I think a 268H will work fine, I’d still prefer a dual pattern though.

Yeah, I'm looking at a Lunati 256/262 now. 213/219 @ 0.050", 0.524"/0.540" int/exh, 112 LSA. Sounds like a winner, but I'm wondering about how much lift the stock rocker arms and shafts can take I've read that over 0.500" is asking for trouble with stock non-adjustable rocker arms.

[sparky72]

Any advice on how much lift the stock rocker assemblies can take? I’m looking at this Lunati 250/256 cam, 0.503/0.524 valve lift: https://www.lunatipower.com/voodoo-hydr ... 0-256.html

Would this require adjustable roller rockers??

[sparky72]

double post

[DuckRyder]

FWIW, I ran a Crane 801 (278/290, Lift .548/.580) for a while with stock rockers.

I’d figure out the DCR with that cam, I can’t find the cam card, but the short duration and the VooDoo line suggest it might build high cylinder pressures. 9-9.5 may be to high SCR for it.

(ETA) If the DCR is in line, that’s a nice cam.

[sparky72]

FWIW, I ran a Crane 801 (278/290, Lift .548/.580) for a while with stock rockers.

I’d figure out the DCR with that cam, I can’t find the cam card, but the short duration and the VooDoo line suggest it might build high cylinder pressures. 9-9.5 may be to high SCR for it.

(ETA) If the DCR is in line, that’s a nice cam.

Here's what I came up with, using the calculator at: https://www.rbracing-rsr.com/comprAdvHD.htm

For this cam (Lunati 10330700), we have:
Advertised duration: 250/256
Intake duration /2 = 125 degrees
Lobe separation = 112 degrees
125+112 = 237 degrees
Intake centerline = 108 degrees (therefore, 4 degrees ground-in advance [112-108])
237-4 = 233 degrees
233 degrees -180 = 53 degrees (intake closes at 53 degrees ABDC)

Now, for the following 390 stats:
Bore: 4.090"
Stroke: 3.75"
Connecting Rod Length: 6.488"
SCR: 9:1
Boost pressure: 0psi (haha)
Target altitude: 0' (assuming a "worst case," a nice drive to the beach )

This gives a DCR of 7.78:1.

If we go with a 9.5:1 SCR, holding all other quantities the same, we get a DCR of 8.21.

The above results are the same whether the engine is 40 over (4.090) or 60 over (4.110).

This seems to be a fairly safe DCR, even at 9.5:1, yes? It should be mentioned that the highest pump gas I can get around here in the PRK is 91.

Thank you for all your help

[DuckRyder]

Again, it seems like you are on top of it...

Assuming the numbers are right that should work. Watch your quench...

You might run the numbers through the pkelley calculator

http://www.empirenet.com/pkelley2/DynamicCR.html

Since they don’t all give the same numbers.

[WhitsEnd]

Cam selection questions generally get more opinions than you can handle, so I’ll not jump on that, other than to strongly suggest a hydraulic roller.

Also, you commented on using stock rockers...I hope you don’t mean original. Most of these old FEs have excessive wear at the rocker and shaft clearances. This leads to poor oil pressure, flooded valve covers and lack of oil at the valve tip and pushrod where you need it.

You can buy new, original style rockers and shafts. If you’re going to bump the specs on the cam and stiffen up the springs, I would get heavy duty shafts from Precision Oil Pumps. You may have to hone the rockers in to size.

Worn out rockers have created a lot of myths for the FE, including having to excessively restrict the oil feed to the heads and pushrod bending.

[sparky72]

Cam selection questions generally get more opinions than you can handle, so I’ll not jump on that, other than to strongly suggest a hydraulic roller.

Also, you commented on using stock rockers...I hope you don’t mean original. Most of these old FEs have excessive wear at the rocker and shaft clearances. This leads to poor oil pressure, flooded valve covers and lack of oil at the valve tip and pushrod where you need it.

You can buy new, original style rockers and shafts. If you’re going to bump the specs on the cam and stiffen up the springs, I would get heavy duty shafts from Precision Oil Pumps. You may have to hone the rockers in to size.

Worn out rockers have created a lot of myths for the FE, including having to excessively restrict the oil feed to the heads and pushrod bending.

I had the machine shop work over the rocker assemblies. They said the shafts looked good. I know the engine has been rebuilt before at some point so it’s possible the shafts aren’t original.

I will be buying some end stands from Precision Oil Pumps this week.

[sparky72]

Just a quick update for you guys - I ended up picking a Comp 270H, or at least I tried to... the first one was bent about 7 thousandths, and the second (replacement) was bent 5 thou I suspect it was a shipping issue on at least one occasion, but still... I decided to take the opportunity to go hydraulic roller instead.

So what I have ordered now is this Howards cam kit: https://www.howardscams.com/hydraulic-r ... l250705-12

272/278 advertised, 219/225 @ 0.050, .525/.525 lift, 112 LSA and 108 ICL. Very similar to the 270H, but with a wider LSA, split pattern, and a dash more lift. I think this will work better in my application, since it will produce a slightly lower DCR compared (7.83) to the 270H (about 8.00), along with all the positives of being a roller. If you've seen my other thread on Compression Ratio Help, you'll see that my actual SCR is on the high side of 9, 9.77 or a bit more. This is what pushed me towards the 270H vs a 268H or similar. I think the Howards will be even better, its profile is sort of a split-profile hybrid betwen the 268 and 270, with a wider LSA than either.

I don't see very many (if any) experiences with this cam in an FE on the net, so I'll be sure to report back on how it performs! Not cheap, but I think the peace of mind of not having to worry about flattening a lobe on a flat tappet will be worth it.

[DuckRyder]

Let us know how that works, I think its a better choice than a 270H...

Interesting it says it requires adjustable valve train, as I see that as the main benefit of HR vs SR, bolt the rockers down and forget it. Lykins is even cranking out non adjustable roller rockers...

[sparky72]

Let us know how that works, I think its a better choice than a 270H...

Interesting it says it requires adjustable valve train, as I see that as the main benefit of HR vs SR, bolt the rockers down and forget it. Lykins is even cranking out non adjustable roller rockers...

Yeah, I'm not too sure why it says that. I spoke with Ross (my427stang) briefly via email about it and he said adjustable rockers wouldn't be needed, just correct pushrod lengths. There is some temptation to get a Precision Oil Pumps adjustable rocker setup as well, though...