390 cam suggestion

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wilb68

wilb68

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First of all I want to thank you for taking the time to read my post. I'm in the middle of my engine rebuild. What I have is a 390 stroker kit from scat I beam rods icon pistons. I'm going to run the stock heads with some porting in the bowls.and 273 rockers and push rods.
I just freshend up my 727 with a 1900 to 2300 stall. I'm running 323 gears with 215/70r14 tires. I want to have some fun on the weekends but I have no ideas on a cam. Any help would be appreciated.

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Those appear to be Icon's version of the KB107 for the 318 so compression is probably around 10:1 or so. I'd use something like the Comp 270S, but let Ken Heard at Oregon Cams grind you his version on either your cam core or one he supplies. I wouldn't trust Comp any father than I could throw a one thousand pound turd.
 
It really depends on you, people could make arguments for a fairly large range of cams.
 
I would like to hear more about your combo. Im at just over 4k above sea level. Your head choice, valve size and did you CC them? The head gaskets your using?

Im also finishing my 318 to 392 with the zero deck IC846 pistons and am undecided on many things.
 
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wilb68 said:
First of all I want to thank you for taking the time to read my post. I'm in the middle of my engine rebuild. What I have is a 390 stroker kit from scat I beam rods icon pistons. I'm going to run the stock heads with some porting in the bowls.and 273 rockers and push rods.
I just freshend up my 727 with a 1900 to 2300 stall. I'm running 323 gears with 215/70r14 tires. I want to have some fun on the weekends but I have no ideas on a cam. Any help would be appreciated.

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View attachment 1716393213
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Looks good. I think we need more info.
What heads, intake, hyd. Flat/ solid flat/ roller?
What type of rpm, hp level are you looking for?

I'm actually still undecided with my 390 just because I need it to work with Sniper EFI and Power brakes. I've been on every forum and can't find what's the cam limit with power brakes.

If you have manual brakes and Carburated then skys the limit.

With those flat top pistons your probably be looking at a high 10 or 11:1 cr. so you can run a health cam 235<[email protected] lift..but the low stall and rear gears might not work with that.
They will probably keep you in the 220 or so int duration lower around 220<[email protected]" like a Comp XE268<XE274. I would just be concerned about how much compression with iron heads on pump gas.

I do have a few dyno builds that I have stored , so when you give more details about intake etc.
 
The intake valves are 1.780 and would like flat tappet. Rpm around 1800 to 5000
 
Jersey Devil said:
Looks good. I think we need more info.
What heads, intake, hyd. Flat/ solid flat/ roller?
What type of rpm, hp level are you looking for?

I'm actually still undecided with my 390 just because I need it to work with Sniper EFI and Power brakes. I've been on every forum and can't find what's the cam limit with power brakes.

If you have manual brakes and Carburated then skys the limit.

With those flat top pistons your probably be looking at a high 10 or 11:1 cr. so you can run a health cam 235<[email protected] lift..but the low stall and rear gears might not work with that.
They will probably keep you in the 220 or so int duration lower around 220<[email protected]" like a Comp XE268<XE274. I would just be concerned about how much compression with iron heads on pump gas.

I do have a few dyno builds that I have stored , so when you give more details about intake etc.
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My heads cc at 65 with 1.780 intake I'm going to use a .024 cosmetic head gasket I'm running manual brakes and I'm going to be carburetor.
 
With the compression charts I've found it's going to be around 10.1 or 11.1
 
wilb68 said:
The intake valves are 1.780 and would like flat tappet. Rpm around 1800 to 5000
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there is only one answer: 3/4 race cam!

all kidding aside, within those parameters i like something like the comp 270S but i would want more modern lobes than some old lazy ones on a wide LSA.

i'd say mid 220ish with lift in the 460~470's on a 110~112 LSA. something i'd love to see is a split pattern in that framework.
 
wilb68 said:
With the compression charts I've found it's going to be around 10.1 or 11.1
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wilb68 said:
My heads cc at 65 with 1.780 intake I'm going to use a .024 cosmetic head gasket I'm running manual brakes and I'm going to be carburetor.
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A 318 head is gonna limit your potential, you probably have too much cr cause you'll probably need a fair size cam to be able to run on pump gas but don't have enough stall to work with that cam.

I'd really look into a head and stall up grade.
 
390 cubic inches with those heads are going to really limit the rpm range that you can feed the engine, so I wouldn't get to carried away with a big cam.

You'll probably be out of cylinder head by 5000 rpms, so I would plan for that at maximum rpm. Not saying it won't rev higher, but it probably won't be making power above that.

Tom
 
273 said:
A 318 head is gonna limit your potential, you probably have too much cr cause you'll probably need a fair size cam to be able to run on pump gas but don't have enough stall to work with that cam.

I'd really look into a head and stall up grade.
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Yes the heads are going to be the weak link.
 
any reason you didn't use 360 heads if you wanted to stay with iron? they'd work much better with a 390 for sure.
neil.
edit.... to put it another way, would you try to feed a 1000hp v8 with a stock 5/16" fuel line? then why strangle that 390 with 318 ports?
 
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360 heads shroud the cylinder walls I don't want to machine reliefs in the cylinder walls.
 
wilb68 said:
360 heads shroud the cylinder walls I don't want to machine reliefs in the cylinder walls.
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have you been talking to 'dan the man'? :rofl:
we're not talking a 1/4" bore difference here, at stock bore on both blocks there's 90 thou difference, which of course is 45 though all round. so a spark plug gap difference, is that going to shroud your cylinder walls? oh, and that's without the overbore you have to get the 390 pistons in there. so that's only 60 thou smaller than a stock 360, which again is only 30 thou all round. you're worrying about something that doesn't exist. many sets of 360 heads have been fitted to stock bore 318's and improved performance. with the bigger ports and valves they have you'll gain much more than you think you'll lose with any 'shrouding', lol.
neil.
 
wilb68 said:
Yes the heads are going to be the weak link.
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I disagree, with a good porting job those heads with 1.78 intake valves should flow in the 200 cfm range. Your choke point is going to be your intake manifold. I agree you don't want to shroud the valves with a larger combustion chamber and let the static compression ratio be what it's going to be. You can bleed off some with your cam choice to lower the static ratio.
 
People use 2.02 valves in 318’s no problem. Even larger.

You got to look at the pros and cons, say you would lose some flow to valve shrouding so the solution is to put poorer flowing heads on ?

318 heads are really 273 heads they were designed to feed a 273 which they do very well, not designed to feed an engine over a 100 cid larger even with some bowl work.
 
If the intake manifold is not a 318 intake manifold, this is a no brainer. The 360 head in stock form flows 30 cfm more than the 318 in stock form. The shrouding of the smaller 318 bore will knock 5-7 cfm off parts of the curve but the gains will still be huge. Gains would be less if a 318 manifold is used.

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273 said:
People use 2.02 valves in 318’s no problem. Even larger.

You got to look at the pros and cons, say you would lose some flow to valve shrouding so the solution is to put poorer flowing heads on ?

318 heads are really 273 heads they were designed to feed a 273 which they do very well, not designed to feed an engine over a 100 cid larger even with some bowl work.
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While stock 273 closed chamber heads do not flow all that well, Charles Servedio ported a one chamber and got 200 cfm with 1.78 intake valves. He got 235 with 1.88 valves. After I sent him a sawn up chamber revealing water jacket thickness, said no doubt in his mind he would be able to get close to 270 cfm with 2.02 valves, no problem. It's all on his youtube channel. 340 x heads ported won't go over 300 cfm, for that you would have to go aftermarket.

Really, how much do you think you need for an engine with a 5000 rpm ceiling?
 
Put in perspective, a 273 and 340 have similar flow to cid ratios and port cc to cid ratios.
Both have a decent street power curve.

For a 390 to have similar it would need a head with about 250 cfm and 170 cc port to have similar ratio as a 340.

So even with a 340 cam it probably would rev similar but with 50 extra cid it make around 60 lbs-ft more torque which would obviously make more power across that rpm range.
 
ch1ll said:
While stock 273 closed chamber heads do not flow all that well, Charles Servedio ported a one chamber and got 200 cfm with 1.78 intake valves. He got 235 with 1.88 valves. After I sent him a sawn up chamber revealing water jacket thickness, said no doubt in his mind he would be able to get close to 270 cfm with 2.02 valves, no problem. It's all on his youtube channel. 340 x heads ported won't go over 300 cfm, for that you would have to go aftermarket.

Really, how much do you think you need for an engine with a 5000 rpm ceiling?
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Cfm is important but so is port volume, A 390 is in between a 383 and a 400 it’s basically a small big block it needs volume to even make power at 5000 rpm.

A 390 spinning 5000 rpm is similar to a 318 spinning 6200 rpm or a 273 spinning 7200 rpm. (At similar VE%)
 
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