Bakerlite
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1967 273 cam suggestions
- Thread starter Pebble beach
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Good to be known for something !
There are still a couple important unknowns like lifter style and compression ratio. Some good choices have been given, but until we know the rest, we are kinda shootin in the dark.
Dang right and don't you forget it.
Bakerlite
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My 67 Dart was solid lifter, before I added 199 cubes to it.
Nice! You went from a Cessna to an F16!
Ultralight then. With a misfiring Briggs.
To the OP… what cams did summit suggest for it? Also, what head gaskets were used in the changeover? If it’s not something close to the factory steel shim head gaskets with the usual stock 68cc or more actual open chamber 318 head volume, a cam larger than a stock 318 hydraulic flat tappet is probably not going to be any help. Anyone know how far the pistons are below deck on a stock 273 2 barrel? We can come up with some compression figures to get an idea of what it’s starting with.
The 270S Comp Cams I quoted earlier is a solid lifter cam. Because my understanding is this engine used a sol lifter cam....
Somebody else recommended the XE 256 cam. That is a hyd cam, 212/218 @ 050.
According to Crane Cams, to get a rough comparison of a sol to a hyd cam, you need to ADD 8-15* to the 050 duration. 8* if it is tight lash, 15* if it is wide lash.
The 270S has variable lash. If you lashed it at 0.030" lash, the duration is reduced 10*, now a 260 degree cam & a reduction in the 050 number as well. Power range listed as 1500-5500 rpm. So I do not see how it could be too big, considering what the OP is seeking.
Somebody else recommended the XE 256 cam. That is a hyd cam, 212/218 @ 050.
According to Crane Cams, to get a rough comparison of a sol to a hyd cam, you need to ADD 8-15* to the 050 duration. 8* if it is tight lash, 15* if it is wide lash.
The 270S has variable lash. If you lashed it at 0.030" lash, the duration is reduced 10*, now a 260 degree cam & a reduction in the 050 number as well. Power range listed as 1500-5500 rpm. So I do not see how it could be too big, considering what the OP is seeking.
I remember way back when comp was marketing variable duration solid lash cams back in the early mid eighties. I did not realize that they had continued to carry any of those designs forward to the present day. Do you know of any other of their magnum solid grinds that have that capability?
Bakerlite
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Then you are blind.
What ever Camshaft you pick I myself would stay away from Hydraulic lifters . The common tick is a problem with all hydraulic lifters lately. A solid lift cam is something you may want to consider. I won't install another Hydraulic cam in my engines . Just buy some adjustable rockers. You'll be a happy person. Why chase a tick.
We installed the 270S in our 273. 2 barrel pistons. Too much cam for the heads and compression. Stock TC and 323 SG, LD4B.
I even did a mild port job, not near enough head for that cam.
Sounds great, lol. It will get the Commando pistons in near future hopefully.
I even did a mild port job, not near enough head for that cam.
Sounds great, lol. It will get the Commando pistons in near future hopefully.
Bakerlite
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Bewy will be along in a moment to tell you that you should have just kept adding valve lash until it purred like a kitten. That dodgy trick is so 1980's... lol.
273 two barrel pistons are about .020 down in the hole. You should have run 273 heads, which are the best, or since you have a 67 car, 302 heads at least for compression. To make the best of what you have now, if you have a hydraulic cam, something around 260 duration and around .450 lift using 340 valve springs or equivalent. If you still have the solid lifter rockers, shafts, and pushrods that is the way to go. I'd second the Racer Brown recommendation. Jim is easy to talk to and the higher cost is nothing to have a cam that will do what you want for the next 10 years. He knows MOPAR and 273 engines.
I figured that variable duration didn’t last long. Seems like there were a lot of failures involving hammering the valve train when set loose and wiping lifters out when set tight. IIRC, solid don’t work too well when they run completely out of lash. Don’t contend too well holding back combustion pressure at TDC. I’ve seen detonation go to pre ignition and wipe out a hydraulic in stout build before.
It’s worth posting to this thread just to see how to build a base 273 properly. There’s hope for the base 273 B & C bodies after all.
On hydraulic lifters, I know one member who runs the Rhoades lifters without any problems. The variable duration may work pretty well, but I still would prefer a solid.
The op still hasn't given us any specifics on the engine other than it is a low mile original. 67 could have a 10.5/1 in it which would be a good thing. Depending on which 318 heads are on it the compression could be in the 9's and with that info the right cam would be easier to pick. If the 273 started out as a low compression 2 barrel and someone added open chambered 318 heads, the compression could be down in the lower 8.0 range
(or even in the 7's) and picking the right cam will be quite a chore. We also don't know if he has a solid or hydraulic in there now. If the OP contacts a cam company for their recommendation he will need to know all those variables. If we suggest a cam for him we are simply guessing. Way too many unknown variables!
(or even in the 7's) and picking the right cam will be quite a chore. We also don't know if he has a solid or hydraulic in there now. If the OP contacts a cam company for their recommendation he will need to know all those variables. If we suggest a cam for him we are simply guessing. Way too many unknown variables!
Dave999
Well-Known Member
I asked this question when building my current motor
I got lots of great advice with lots of varying views
I learnt a lot about cam timing, but i'll admit not enough.
Not enough becasue like many i build an engine once every 10 years or so,i make changes rarely, got teenage kids and a house to maintain, work a 40 hour week so i'm never in a position to try try try again, comparisons back to back are not really that possible.
i need it to be an improvement over what i had.....so i have to make the best of it
Also until its in bits and you can measure, you are not fully availed of all the facts
i found it easier to take all the suggested cams
and run them along with the measurements i had taken or had got from the manaul
in this software
http://cochise.uia.net/pkelley2/dcrvb6.zip
it should run on old PCs xp win7 win 8 and will run, or run in, "compatibility mode" on win 10 and win 11 provided your windows allows you to install any softwre you like. not just stuff from the microsoft app store (usualy cheap lap tops and tablets are stuck with that)
it does everything for you, so you don't have to manully do the maths
discussed here
Dynamic CR
with your rod length, your stroke (rod ratio) your bore your combustion chamber CC and the deck height.... the bore of your gasket and its compressed thickness the cc of the valve relief in the piston etc.
you can plumb in the cam figures to check DCR, fill first tab, use answer from first tab in the second tab and repeat the process again in the 3rd tab
look for a cam that gives a DCR in the 7.5 to 9.1 range 9 with good manifold and distrinbution, and high octane fule closer to 7.5 for a street engine running standard octane fuel. for the 8.5 to 9 range as i had upgraded carburation and nice set of headers
it aint a magic bullet but it gives you an idea of the cam needed to produce a motor with decent cylinder pressure, decent torque and that will run ok on the gas you intend to feed it without pinging.
the actual cam spec you come away with might be slightly off what you expect, becasue most talk in the realms of static CR and its dynamic CR that counts, but if you put in the cam figuers as specified and put the chosen cam in te motor straight up that motor will run nicely, provided that its a quality assembly, correct advance curve and decent tune
its very good if you don't want to buy anything more, have to work with what you have and just need to home in on a cam spec.
in the right hands you can use this as the centre of a build and adjust stroke rod ratio static CR etc but thats for the guys who do this every day or race rather than play at the track. But it works very well the other way as well. everything fixed (no more money to spend) apart from the cam n lifters....
its a tool to help with the math. A person builds a nice motor, not a computer program. but i sure found it a great help.
It might help in your quest.....
Dave
I got lots of great advice with lots of varying views
I learnt a lot about cam timing, but i'll admit not enough.
Not enough becasue like many i build an engine once every 10 years or so,i make changes rarely, got teenage kids and a house to maintain, work a 40 hour week so i'm never in a position to try try try again, comparisons back to back are not really that possible.
i need it to be an improvement over what i had.....so i have to make the best of it
Also until its in bits and you can measure, you are not fully availed of all the facts
i found it easier to take all the suggested cams
and run them along with the measurements i had taken or had got from the manaul
in this software
http://cochise.uia.net/pkelley2/dcrvb6.zip
it should run on old PCs xp win7 win 8 and will run, or run in, "compatibility mode" on win 10 and win 11 provided your windows allows you to install any softwre you like. not just stuff from the microsoft app store (usualy cheap lap tops and tablets are stuck with that)
it does everything for you, so you don't have to manully do the maths
discussed here
Dynamic CR
with your rod length, your stroke (rod ratio) your bore your combustion chamber CC and the deck height.... the bore of your gasket and its compressed thickness the cc of the valve relief in the piston etc.
you can plumb in the cam figures to check DCR, fill first tab, use answer from first tab in the second tab and repeat the process again in the 3rd tab
look for a cam that gives a DCR in the 7.5 to 9.1 range 9 with good manifold and distrinbution, and high octane fule closer to 7.5 for a street engine running standard octane fuel. for the 8.5 to 9 range as i had upgraded carburation and nice set of headers
it aint a magic bullet but it gives you an idea of the cam needed to produce a motor with decent cylinder pressure, decent torque and that will run ok on the gas you intend to feed it without pinging.
the actual cam spec you come away with might be slightly off what you expect, becasue most talk in the realms of static CR and its dynamic CR that counts, but if you put in the cam figuers as specified and put the chosen cam in te motor straight up that motor will run nicely, provided that its a quality assembly, correct advance curve and decent tune
its very good if you don't want to buy anything more, have to work with what you have and just need to home in on a cam spec.
in the right hands you can use this as the centre of a build and adjust stroke rod ratio static CR etc but thats for the guys who do this every day or race rather than play at the track. But it works very well the other way as well. everything fixed (no more money to spend) apart from the cam n lifters....
its a tool to help with the math. A person builds a nice motor, not a computer program. but i sure found it a great help.
It might help in your quest.....
Dave
Last edited:
http://cochise.uia.net/pkelley2/dcrvb6.zip My security software tells me there is a Trojan Horse in that website.
Rat Bastid
Dunamis Metron
You’d be much better served to forget you ever heard “dynamic” compression ratio and spend your time understanding EFFECTIVE compression ratio.
They aren’t the same and the one matters and the other doesn’t.
Think of it this way. What’s the quickest way to gain (or reduce) static compression ratio?
Once you understand that you’ll be much further down the road to understanding cam timing and compression ratio.
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