What cam should I get?

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mullinax95

mullinax95

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I bought a 67 Barracuda about a week ago with the 273. The motor was installed in July and is a fresh rebuild. The cam however seems to be to mild for me and I have a 4-speed so I can to a bigger cam without no problems. I know that I don't want to go to big because of the (far as I know) stock valve springs might not be able to handle the cam. I like the Mopar purple shafts cams since I had one in a 68 Charger and it sounded and performed great. Would a 484 lift be ok with stock valve springs or can I get away with a low 500 lift?
 
I think bolth of the cams are to big for a 273. I dont think I would go much bigger then the stock 340 cam. Is this a 273 4bbl or 2bbl ? 4bbl motors have solid cams from the factory.
 
It is 4bbl now and I don't know what it had factory. The guy I bought the car from wouldn't know what cam size is in it either. I have the paper work of the engine rebuild but it just says cam and gives the price but not the size. I was looking at Summit and Mopar performance has bigger cams than that for the 273 only. So I figure they must have tested these cams to be alright for the 273. When I had the Charger I told my buds about what cam I was going to run and some said thats to big and others said that would be fine. So I installed it myself and man did that car get up a go! It had a good take off and pulled alway through the run. But I'm opened ears for all comments.
 
This the cam I have in mind. It has a operating range of 2,600-6,000. I'm sure I will be above 2,600 when I dump the clutch.



DCC-4120231 $169.88
Estimated Ship Date: Monday
Warnings Application Suggested Parts Warranty Show All

Brand: Mopar Performance Parts
Product Line: Mopar Performance Purple Camshaft Kits
Cam Style: Hydraulic flat tappet
Basic Operating RPM Range: 2,600-6,000 RPM
Intake Duration at 050 inch Lift: 241
Exhaust Duration at 050 inch Lift: 241
Duration at 050 inch Lift: 241 int./241 exh.
Advertised Intake Duration: 284
Advertised Exhaust Duration: 284
Advertised Duration: 284 int./284 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.484 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.484 in.
Valve Lift with Factory Rocker Arm Ratio: 0.484 int./0.484 exh. lift
Lobe Separation (degrees): 108
Intake Valve Lash: 0.000 in.
Exhaust Valve Lash: 0.000 in.
Computer Controlled Compatible: No
Lifters Included: Yes
Lifter Style: Hydraulic flat tappet
Valve Springs Included: No
Retainers Included: No
Locks Included: No
Valve Stem Seals Included: No
Timing Chain and Gears Included: No
Assembly Lubricant Included: Yes
Pushrods Included: No
Rocker Arms Included: No
Gaskets Included: No
Quantity: Sold as a kit.

Cam and Lifters, Hydraulic Flat Tappet, Advertised Duration 284/284, Lift .484/.484, Mopar, Small Block, Kit
 
That cam is going to be a pig ina 273. What was in your Charger a 440 ? More cubes needs more cam. It wont take anyweres near as much duration to make a 273 lope like a 440 would with that cam.
 
It was a .30 over 383. Well I would like to know then why they have cams for the 273 with 484, 508, lifts if they are going to be to big?
 
It's more of the duration that will kill the engines performance.
Tell us your set up and the intended goal of the car.
We'll also need to know the rear gear ratio and tire size. Weight would be helpful in the cam choice.

Anytime you change a cam, more so from stock to a performance cam, you need to get the valve springs to go with it. It is sooooooo worth the cost to do so when you change from a stock cam to a performance cam. Not doing so can be engine damaging.
 
mullinax95 said:
It was a .30 over 383. Well I would like to know then why they have cams for the 273 with 484, 508, lifts if they are going to be to big?
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Just because the cam fits the engine doesnt mean it will perform right. If you run to much duration you'll end up with a motor that makes no torque and wants to rev to 7500 rpms. That fine if your seting the rest of the car to use it and if your building a race car.

273 heads wont flow enough air to use that cam, with your small bore and stroke you'll need 4.10 gears or lower. Its also going to want at least 10:1 compression. Even then I wouldnt run that cam in a 273.

If the car is a stock 273 with a small 4bbl, a 4 speed and gearing around 3.23s I would run something small like a CompCams XE262 or the Mopars 340 replacement. Either of these cams although small are still much bigger then the stock 273 2bbl cam.

If you rally want to run the 484 in your 273 by all means go ahead but you asked for opinions and mine opinion is that is the wrong cam for 99% of the 273s out there. Asl member Bill Paynter how is 273 runs with the 508 cam in it. He will tell you its a pig.
 
Think about the operating range on the .484" cam for a moment. With a 2,600 up operating range, this means that the engine will not pull the car and rpm under this starting rpm. It will move the car but without building rpm's rapidly and the torque #'s will also be slow to build. On the stock 273 4bbl cam, the operating range is about 600 to probably 5,000 rpms. This means that the car will launch or take off hard from 600 rpms and will build torque quickly and accelerate quickly. If for example, you had a 3,200 stall converter and 4.11:1 gears, you probably could get the .484" cam to work with the proper intake, headers and decent flowing heads. Incidentally, 2.02" intake valve heads will not work on 273 engines without notching the top of the cylinder bores. You should find out what gears you have and what transmission you have. The engine could have the 10.5:1 pistons or the 2 bbl 9.2:1 pistons and this is important info to know when selecting a cam. Aslo '67 was the last year of the closed chamber LA heads and adjustable rocker arms/mechanical lifters, requiring different length pushrods(7.342" changed to 7.16 to 7.23" for hydraulic lifters. So it is a really good idea to get some positive feedback from these guys about a good game plan for your engine/parts swap or you might waste time and money which I know I do not like to do myself, David.
 
The mopar purple shaft cams are old tech designs, not bad cams but there are many better designs out there now. The smaller cams from the Comp Extreme Energy, Lunati Voodoo or Hughes will be a much better choice.

Also, remember a 273 is a small engine and it is not going to have a lot of power. The base 318 2bbl had more power than the 273 Commando motor.

BTW, you would defineately need to cahnge the stock valve springs to use the .484 purple shaft cam. Unless the cam manufacturer states that the cam will work with stock springs you really need to swap the springs to what the cam manufacturer recomends.
 
OK I don't know what the gear ratio is exactly, I don't know the wieght of the car, I will eventually change the wheels but I think I will try to run the 235/70/15s on the rear. I probably go with a 275/60/15 latter on. The car will see only street use. I might take it down to the drag strip once or twice.

The valve train is the basic Mopar design with the none adjustable rocker arms. I took the valve covers off and checked that out.
I might be just better off now that read these posts to leave well enough alone. It performs well but dosn't have that big cam sound that I like. It does however have a little lope to her.
 
mullinax95, help us out here a little bit.

Whats the intended goal?
Are you just looking for a "Big Cam" sound. rumpity idle and such?
Are you looking to run 14's with the car?
 
It's a 273 with non-adjustable rockers?
Pay close attention to what everyone has been telling you about the .484 Purple Shaft cam, because it will make your car a total pig off the line. That's not just a guess, that's the reality of installing a cam that's WAY too big for that size engine.
That cam will bleed off way too much of your compression, effectively killing the bottom end. Just because the cam physically fits in the block doesn't mean it's right for your particular combination, and in this instance, it's all wrong. If you know which shop built the engine, why not go see, or call them, and try to determine exactly what the specs are on your current cam. Once you have the specs, then we can make some informed recommendations for any changes.
I, for one, believe that there have been more nice street machines ruined because of over-camming than for any other single reason.
 
rumblefish360 said:
mullinax95, help us out here a little bit.

Whats the intended goal?
Are you just looking for a "Big Cam" sound. rumpity idle and such?
Are you looking to run 14's with the car?
Click to expand...

The intended goal of the car is to have a good soild ride to just jump in and go up the road and also when I take care of some miner details take it to the shows around town and pop the hood. I would like to take it down the track once or twice however.

I like the "Big Cam" sound and the cam that is in it is a little quiet for my tastes.
 
Big cam sound is contrary to your goal of "to just jump in and go up the road ". The big cam sound comes from a lot of over lap and duration. This makes for very inefficient cylinder filling at low rpms resulting in loss of power. Throw relatively low compression and small displacement into the mix and you make it even worse to the point the car is not driveable in traffic.

For your intended goal the Comp XE256H is likley the best choice and the XE262H would be the biggest you should go. Remember like carburators it's better to error on the small side than the big side.
 
I had the same setup as you but I had a automatic. I called Hughed cam and bought a cam with 208\214 duration at .050. You could get away with a little more with a 4 speed, but not much. Get a cam with the biggest lift you can get with the short duration. Lift is all good, unless the valve hits the piston. That should not be a problem with a low compression 273. In my opinion, Hughes makes the best cams for your engine. Bob
 
hi, for a cam in a 273, the isky E 4 grind works very well in a 273 motor.
I use to drive and race a 273 dart in stock elim, and brackets, plus drove it.
the E 4 is a solid cam. 260/ 216 @ .060, .425 lift, 108 LCA. the comp extreme energy 256 or 262 will be very comparable to it. as for RPM range?
with stock single springs, they will rev to 6000 RPM easily. add a little stronger spring, 7000 RPM will not be a problem. a short duration cam with tight lobe centers work very well in stick motors. especially in a 273 motor,
it will pick up the gear change faster and will accelerate quicker. this is from an older stick shift stocker racer.
 
Thanks guys.

Ok first thing I want to do is try to find out how much compression I am running in the 273. I don't know if the motor is bored over or not. I am trying to get into contact with the previous owner just to find out but he does not appear to know much about the car. He is like he got everyone else to work on the car but I try to do everything myself to save money. If I borrow a compression test tool would that let me know somehow what compression I am running? 9:1, 10:1 ?
 
My 273 had between 135 to 144 lbs. with the warm cranking check. I measured everything and it worked out to be a 8.5 to 1 motor. If yours is stock low comp. its around 8.0 to 1. Bob
 
bobscuda67 said:
My 273 had between 135 to 144 lbs. with the warm cranking check. I measured everything and it worked out to be a 8.5 to 1 motor. If yours is stock low comp. its around 8.0 to 1. Bob
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If I do the readings on each cylinder then what math do I do to work out what compression ratio I have. This next question is how do I find out what gear ratio I have without going in the rear end? I know that I can put a strip of tape on the drive shaft and count how many revolutions it turns as I turn the wheel one revolution but I don't know if that would be right.
 
The cylinder compression test gives you the pressure value, in pounds per square inch, that is built up in the cylinder after a couple of sweeps of the piston in the cylinder bore - ie, cranking compression. This info is used to determine basically how well your piston rings and valves are sealing in your engine, and really has nothing to do with the actual final "compression ratio" of your particular combination.
The actual final compression ration of an engine is determined by careful measurement of several areas, including cylinder head volume (measured in cc's), depth of the top of the piston below (or above) the deck, head gasket thickness, deck height, etc. etc. Without knowing all of the variables involved, you can't determine your actual final compression ratio.
If you look on one of the bolts on the rear end housing, you should find a small metal tag with the gear ratio stamped into it. If the diffy has been apart before, the tag will probably be missing and you can do the driveshaft turns thingie to get a very close guess on the ratio. Hope this helps.
 
Well, stock, there should be a tag bolted on the rear end with the ratio on it.
However, I have been there, like you, and did not have a tag. So, I errored on the side of caution and did a gear oil change since who knows when the last time that cover was off, if ever. The ratio as you may allready know is stamped on the ring gear.

The driveshaft method is not to accurate, but close enuff to get close enuff to make a good stab at it.
 
OldVart said:
The cylinder compression test gives you the pressure value, in pounds per square inch, that is built up in the cylinder after a couple of sweeps of the piston in the cylinder bore - ie, cranking compression. This info is used to determine basically how well your piston rings and valves are sealing in your engine, and really has nothing to do with the actual final "compression ratio" of your particular combination.
The actual final compression ration of an engine is determined by careful measurement of several areas, including cylinder head volume (measured in cc's), depth of the top of the piston below (or above) the deck, head gasket thickness, deck height, etc. etc. Without knowing all of the variables involved, you can't determine your actual final compression ratio.
If you look on one of the bolts on the rear end housing, you should find a small metal tag with the gear ratio stamped into it. If the diffy has been apart before, the tag will probably be missing and you can do the driveshaft turns thingie to get a very close guess on the ratio. Hope this helps.
Click to expand...

Yeah I didn't think that I could find the compression ratio just by the cranking compression alone. I knew that there was to many factors to concider. It was worth checking into. I however got the phone number of the fellow that bulit the motor from the one I bought the car from. His name is Bob and he builds motors for the guys who drag race and such up in NY. I tried calling him yesterday after I got off work and got no answer so I better try calling him on regular businsess hours. The previous owner told me that he can tell me everything I need to know about the little 273.

I had already looked at the rearend and could tell that someone has been in there before. It feels like a 4.10 but I'm not exactly sure. It dose not take long to go through the gears to get to speed I know that. I need to break down and get me a good tach. I will eventually pull the chunk out and find out the gear size.

Once I find out as much as I can about the motor and get the stuff wrote down I believe that everyone that has helped me so far will have a better knowledge of the car and make a better decsion on what cam size I can run. I do admit that I was going to throw to big of a cam in there and it would have been slow on take off. So I would like to have the"big cam" sound but I much rather have power over sound. Maybe I can get a happy medium.
 
There is now way to tell what static compression ratio you have with a compression tester. You need to pull a head and measure some stuff. MUllin, you will want to keep the cam coice mild until you do some digging. You cant run stock springs with a lot of cams. Even the milder ones I install. They get matching springs. That 484 is so wrong for your car, you need to stop reading magazines, and start reading tech books. YOu said in another post the car tried to come around on you when you drove it recently..Too big a cam will give the sound you want, but you wont need to worry about it ever coming around unless it's raining. The less you knwo about your exact engine, the less likely any choice will give you what you want. And the more likely a change will hurt you.
 
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