Thread: Cam recommendations for 355 SBC

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I've got a 355 that is just too rough for the street where it will be spending all of its time. Vacuum is only 5-6 Hg at idle and is very rough & don't even ask how the power brakes work. Engine has 2.02 double hump heads, flat top pistons & 1.6 ratio needle roller rocker arms which I'd like to keep. Compression ratio is in the 9-9.5 range. What i'd like is a cam that will smooth things out & give me 15 about Hg vacuum at idle.

Thanks in advance for your opinions,

Dave

Need more information. What kind of vehicle and what is its intended use? Automatic or manual transmission?

Info .... heads intake... gearing... vehicle weight...ect would help.

Car is '72 Chevelle.
Gears are 3.42
Has Edelbrock RPM performer intake w/ 1405 Edelbrock 600 CFM carb.
350 automatic transmission

Car will be strickly a cruiser, no racing.
Just looking for a nice tame cam that will give me good idle & vacuum.

Lunati 60101 would work well for you. Duration: 213/219 @ .050 ; .454/.468 inch lift. It is relatively tame but would give you decent vacuum and good performance, and you could use a stock converter in your transmission. It would also be a good match for the parts you already have.

hey rumrumm what kinda cam would use in a 350 that is bored 30 over and its going in a 85 chevy 1/2 ton truck iam trying to make around 400 horse and also was woundering if a set of pistons with any dome on them would run any good on the street i was told it wouldn't but i thought i would ask i was thinking about running a 280 duration cam with a 480 lift the gears in the truck are 373's and the transmission is a 700 R 4
the heads iam going to use is has the 205combustion chamber

You cannot reach out into thin air and choose a camshaft for a motor. The cam is not a stand-alone piece, it must be matched to the static compression ratio of the motor in order to close the intake valve at the proper time to make the proper amount of cylinder pressure that will work with the fuel you plan to use. The first question that any cam tech at any cam grinder you talk with will be "what's the static compression ratio of the motor"?

The scenario can go wrong either way:
1. You have a low compression ratio motor and choose a killer cam, long duration and high lift. You're looking for that Ricky Racer rump-rump to impress the geeks down at the Sonic. The intake valve closing is extended to a point where the piston has pushed most of the intake charge back up the intake tract by the time the intake valve closes to begin compression and you are left with low cylinder pressure and a weak motor that won't pull the hat off your head.

2. You have a high compression motor and choose a wimpy cam that you think will be just about right for a daily driver. The intake valve closes too early, creating more cylinder pressure than you can use with pump gas. The motor rattles like a can full of marbles from detonation and pretty soon, you've broken all the ring lands off the pistons.

One more time....YOU MUST KNOW THE STATIC COMPRESSION RATIO OF THE MOTOR IN ORDER TO INTELLIGENTLY CHOOSE A CAM FOR THE MOTOR.

the motor is running 10 to 1 compression now is there anything else you need to know about the motor anything at all well if there is just let me know ok no you know what here you go one more time its a 350 bored 30 over with a air gap intake on it with a holley 750 double pumper with Summit Racing SUM-152123 - Summit Racing® Cast Iron Cylinder Heads puting some eagle rods and bearings and pistons in it and iam going to have everything else balanced such as the Harmonica balancer etc.... so now i would think if your a real tech you could tell me what cam to put in their but if you cant i will know the truth

hahahahahahahahahahahahahahahahahahaha

Originally Posted by Southernboss84

the motor is running 10 to 1 compression now is there anything else you need to know about the motor anything at all well if there is just let me know ok no you know what here you go one more time its a 350 bored 30 over with a air gap intake on it with a holley 750 double pumper with Summit Racing SUM-152123 - Summit Racing® Cast Iron Cylinder Heads puting some eagle rods and bearings and pistons in it and iam going to have everything else balanced such as the Harmonica balancer etc.... so now i would think if your a real tech you could tell me what cam to put in their but if you cant i will know the truth

SouthernBoss84,
You likely won't believe it but truth be known you just insulted one of the most knowledgeable guys around on how the various pieces and parts of an engine work together (or fight each other) to make optimum power and efficiency. Tech's tools to analyze and predict performance are top notch, and he knows how to use them. Others can give you guidelines, but Tech gets into the why, and explains how to make it work. Best of luck to you in your search for your answer.

Some people's kids

A balanced harmonica balancer hmmmm......... Dang why didn't I think of that??

I was going to make a sarcastic comment on that...

But I remembered that a balancer can indeed get off balance: if the outer ring spins. I seem to recall that a particularly cherished or valuable balancer can actually ne rebuilt; with the rubber isolator replaced. However, I have neither seen a defective balancer, nor know anyone whom has had one rebuilt.

Maybe we are all lazy: simply buying new balancers if there is any doubt.

Originally Posted by Southernboss84

the motor is running 10 to 1 compression now is there anything else you need to know about the motor anything at all well if there is just let me know ok no you know what here you go one more time its a 350 bored 30 over with a air gap intake on it with a holley 750 double pumper with Summit Racing SUM-152123 - Summit Racing® Cast Iron Cylinder Heads puting some eagle rods and bearings and pistons in it and iam going to have everything else balanced such as the Harmonica balancer etc.... so now i would think if your a real tech you could tell me what cam to put in their but if you cant i will know the truth

If you LEARN anything at all,advertized compressions ratios are worthless on pistons.You need to know how to figure SCR/s and DCR's.

Originally Posted by firebird77clone

I was going to make a sarcastic comment on that...

But I remembered that a balancer can indeed get off balance: if the outer ring spins. I seem to recall that a particularly cherished or valuable balancer can actually ne rebuilt; with the rubber isolator replaced. However, I have neither seen a defective balancer, nor know anyone whom has had one rebuilt.

Maybe we are all lazy: simply buying new balancers if there is any doubt.

If the unit has an offset hunk of metal on the hub to aid in balancing the rotating assembly, like on a small block 400 or a big block 454, then the unit is called a damper/balancer. These units serve 2 purposes; to aid in balancing the rotating assembly and to cancel harmonics that were created by the springing back and forth (twisting) of the rod journals in relation to the centerline of the crankshaft. If the motor is balanced internally, like a 350, then the unit is called simply a harmonic damper and serves no purpose for balancing the rotating assembly.

The thing about dampers/damper-balancers is that the outer inertia ring is what we use to time the motor with a light. Age, ozone, lubricants and so forth can allow the inertia ring to slip circumferentially in relation to the hub due to degradation of the elastomeric material that separates them and the TDC notch on the ring no longer indicates TDC, so timing the motor with a light is fruitless.

Problem #2 is that you must use the timing tab that was meant to be used with that particular damper/damper-balancer assembly. Small block Chevies use 3 different combinations, 12 Noon, 2:00 O'Clock and 2:30 O'Clock, so unless you bought this motor new from the factory, you have no idea if it's the damper/damper-balancer that was meant to work with the timing tab that's on the timing cover now. Some other hot rodder may have changed either the damper or the cover or both during a rebuild and used the improper damper for the tab that's there or the improper cover for the damper that's there.

Problem #3 is that the company that manufactured that brand new whiz-bang damper that you just bought on the aftermarket may not have used the proper I.D. on the hub that will allow a close press fit. It may be too tight and you'll never get it onto the crank snout or it may be too loose and will not make the mechanical connection that will allow crankshaft harmonics to be transferred to the inertia ring to be eliminated. The damper/damper-balancer hub MUST-MUST-MUST be a press fit onto the crank snout.

Although there are well-respected members on this forum who don't exactly agree with me, I contend that the best unit to press onto the crank snout is an original OEM unit that has been rebuilt. The fact that it is an OEM unit means that the I.D. of the hub is the proper dimension because that particular unit left the factory on a running Chevy engine. Since the only thing that really goes wrong with a damper/damper-balancer is the elastomeric material that separates the hub from the inertia ring, it makes sense to me to pay someone to disassemble the unit, clock the hub to the ring and press in new elastomeric material. Sounds like a job for....
Damper Doctor Online - Your source for Harmonic Balancers, Motor Mounts, & Drive Shaft Supports
Once that's done and you clock the TDC notch on the ring to the TDC position of #1 piston by using a strap if you have a short block or with a piston stop tool if the heads are on and you use the proper timing tab for the ring, you're back in business same as the factory did it.

Here's some good information that I had a hand in writing....
http://www.crankshaftcoalition.com/w...op_dead_center