Thread: Cam opinion

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I have this carbed Chevy 350 c.i.d. L31-R 4-bolt main with one-piece rear main seals. nodular-iron crankshaft, powdered-metal connecting rods, and hypereutectic aluminum pistons.Vortec cylinder heads with 1.94 in. intake valves and 1.50 in. exhausts, and 64cc combustion chambers 9.4:1 compression ratio. roller cam that has 0.414 in. of intake lift and 0.428 in. for the exhausts. Duration at 0.050 in. of lift is 191 degrees for the intakes and 196 for the exhausts, with 111 degrees of lobe separation.

I have this roller cam on hand from Lunati, total lift @.050 .503 in. .503 ex. with 1.5 rockers. Duration @ .050 is 219 in. 229 ex. lobe separation is 112.

Since I have this new cam on hand for pennies. Any reasons why this wouldn't be and improvement. Of course will be changing springs/ retainers. car is a 56 with a 700r4 with 373 rear gear, 2200 convertor.

Excellent mid range torque and HP, good idle, moderate performance usage, crate motor upgrade, mild bracket racing, 1800-5300 rpm operating range, auto trans w/2000+ converter, marine applications: for 350 cu.in. modified engines with free-flowing, above water exhaust systems for performance applications in light pleasure and ski boats, including jet boats, 2800-3600 cruise RPM, 9.0 to 11.0 compression ratio advised.

Advise checking pushrod to hole clearance in heads through entire lift range. Use either rail rockers or pushrod guide plates, but not both. Low rpm's will be a little soggy, so I would use a 10", 2500 stall converter with this cam, giving me a 700 rpm stall lead on the low operating range of 1800 rpm's. This cam will give neither good fuel mileage nor good performance with overdrive trans. Advise 3.73 rear gears with 3-speed auto trans or 3-speed or 4-speed manual with 1:1 top gear.

Maintain minimum 0.050" retainer to guide seal clearance throughout lift. Maintain minimum 0.010" clearance between valve spring coils at max lift, for total clearance of 0.050" for 5 coils. Check rocker arm to stud for binding at full lift. (pinch a length of solder between them to find clearance). Check valve to piston clearance, advise minimum 0.080" intake and 0.100" exhaust clearance. Advise 1 5/8" diameter, equal-length headers with X or H pipe installed immediately after the collectors and dual pipes through mufflers of your choice all the way to the rear of the vehicle. Terminating pipes under the vehicle sounds Mickey Mouse. Advise minimum 3/8" header flange thickness. Thinner flanges will warp up like a strip of bacon under heat and spit out the gaskets. If someone would tool up on headers with a 1/2" flange thickness and 14 gauge tubes, I would buy them.

Use initial 18 degrees spark lead at the crank, with 16 degrees centrifugal advance for a total of 34 degrees. Crane makes an adjustable vacuum advance cannister that you could experiment with.

Your take on this cam may vary from my take on it, but that's what I would look for, based on my experience. Should make a very snappy street driver.
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I too like this cam - however, if your heads are stock you'll have problems with the lift. Here's a link to a good article that's pretty detailed but the take away is,
" The factory Vortec heads use a light, single-wire valvespring with a damper that generates between 70 and 80 pounds of load on the seat. Because these heads are meant to work with a 1.5:1 rocker, their tall valve guides can only handle maximum valve lifts of around 0.420 inch." As such, a bit of machining is required along with the new springs.

Vortec Cylinder Heads Valve Lift - Tech Article - Chevy High Performance Magazine

I think the low 1st in the 700R4 (3.06) would give a real kick in the pants at about 3500 and you'd probably see God when you hit second at WOT with those 3:73 gears

Could be fun!
Glenn

techinspector1, thanks for that detailed post. I appreciate the time you took to post this.

Glenn thanks for the post. And I have read up on the problems with lift on the stock vortec heads. after reading several articles on this matter including the article in your post. have found that some of these articles are not quite factual. The article you posted refers the the max lift on these vortec heads is .420, when that is not the case. The stock cam that comes in the L31 350 vortec has a .428 valve lift on the ex side. Here is one article that I have read about on how to install a larger lift cam without head removal on the vortec head.
https://www.thirdgen.org/forums/tech...ortec-lt4.html

The fact is that anyone who says that you can operate an L31 with stock components and a 0.470"/0.480" lift lobe, simply has not taken running clearance into consideration. You will need 0.050" to 0.060" clearance between the bottom of the retainer and the top of the valve guide seal as a safety clearance. The guys who run with no safety clearance are just newbies who have not seen the havok that can be wrought and are just asking for trouble. They will learn their expensive lessons sooner or later, just like the rest of us did.
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Originally Posted by glennsexton

I think the low 1st in the 700R4 (3.06) would give a real kick in the pants at about 3500 and you'd probably see God when you hit second at WOT with those 3:73 gears
Could be fun!
Glenn

As I said in post #2, this cam is not a good choice for an overdrive transmission. Or put another way, an overdrive transmission is not a good choice for this cam. The purpose of an overdrive transmission is to help with fuel mileage. There is no other reason to use one. But the timing on this cam is too radical for use at 1800-2000 rpm's, where an overdrive motor runs. For an overdrive transmission, you need a cam that begins making power at just off idle, like 1000 rpm's, so that by the time the crank is turning 1800, the motor is "up on the cam" and running efficiently. This should be a very easy to understand concept, but I have made quite a few fellows mad when I have tried to explain it to them. I think they were just pissed that their combination was junk after spending all that money. COMBINATION/COMBINATION/COMBINATION.
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Originally Posted by techinspector1

The fact is that anyone who says that you can operate an L31 with stock components and a 0.470"/0.480" lift lobe, simply has not taken running clearance into consideration. You will need 0.050" to 0.060" clearance between the bottom of the retainer and the top of the valve guide seal as a safety clearance. The guys who run with no safety clearance are just newbies who have not seen the havok that can be wrought and are just asking for trouble. They will learn their expensive lessons sooner or later, just like the rest of us did.
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Cam won't be use with stock components. Will use LS1 beehive valve springs and Comp cams valve retainers.

Originally Posted by techinspector1

As I said in post #2, this cam is not a good choice for an overdrive transmission. Or put another way, an overdrive transmission is not a good choice for this cam. The purpose of an overdrive transmission is to help with fuel mileage. There is no other reason to use one. But the timing on this cam is too radical for use at 1800-2000 rpm's, where an overdrive motor runs. For an overdrive transmission, you need a cam that begins making power at just off idle, like 1000 rpm's, so that by the time the crank is turning 1800, the motor is "up on the cam" and running efficiently. This should be a very easy to understand concept, but I have made quite a few fellows mad when I have tried to explain it to them. I think they were just pissed that their combination was junk after spending all that money. COMBINATION/COMBINATION/COMBINATION.
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techinspector1, I appreciate your knowledge. Not trying to argue with you, and your not making me mad, trying to understand and sometimes for me it takes awhile. But I'm not running a 700r4 o/d trans for gas mileage. In fact around town I mostly don't use 4th gear stay in 3rd. When I get out on the freeway or open round i'll shift into 4th. and with a 2200 stall convertor, I don't understand why this cam wouldn't work.

It's not that this cam will not pull the car, it will, but a cam that is designed to begin making power at 1800 rpm's will not be as efficient at low rpm's as a cam that is designed to begin making power at 1000 rpm's. You're moving the effective range of the cam up by about 800 rpm's over a stock cam, so you need to move everything else in the powertrain up by 800 rpm's if you want the package to be efficient and pull well.

Bottom Line: Go ahead and use the cam. You will either like the way it behaves or you will not, and you will have learned something in the process.
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I have a similar lunati hydraulic voodoo roller cam similar to that one you posted that you got and I run mine in a chevy s10 with a turbo 350 and 3.42 rear gears and I cruise at about 2400 rpm at 55 mph.Mine is 219/227@50 510/515 lift 1.5 ratio and with dart shp heads with dual springs for hydraulic roller cams.

When I first got my chevy s10 I had 4.11 gears in the rear and a 700r4 transmission and I pulled the same rpm's at 55 mph. So depending on your rear gearing you can run it with a 700r4 but the key is the rpm range to keep the engine happy in.

That cam would not like to be cruising at 55 mph and only 2000 rpm and even though the cam I have is pretty mild and does not even have a lope at idle it does run good in a daily driver but the key is to have your engine in the proper rpm band or it will be a dog and no fun to drive and even worse in mileage.

Trust me I have been there and done that with cam stuff not being matched and ending up pulling it out and going smaller. You always want to have it matched up right the first time. Its better to be slightly on the smaller side then to have slightly too much on the bigger side. When I do my builds I try to leave a little on the table so as to not have a little to much to have a headache with. With aggressive cams on vortec heads its best to have them machined for screw in studs and good seals etc as the pressed in studs with cams having over 500 plus lift and fast ramp rates can pull them out over time.

Stock vortec heads don't work well with modern fast ramp rate cams without doing some changes to them and screw in studs are a good option or at least I have read you can get a tool and you can pin the studs as well.