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I\m trying to learn more about cams. I have a 383 stroker with cam specs of..
Duration @ .050'' Lift: 229 Intake / 230 Exhaust Lift: .480'' Intake / .486'' Exhaust
For lack of a better term. How "extreme" is this cam above, and what would make it more or less extreme?
What might a stock 350 c.i. cam specs be?
I'm having a hard time getting my head wrapped around all the numbers. I know what some of this is, but putting them all together is where I'm failing.
Thanks
John
Modest CompCams flat tappet street cam "268": 224/230/.477”/.480”
Somewhat aggresive CompCams street cam "274": 230/236/.488/.491
So your cam is more aggressive than any of the factory hydralic flat tappets, and in the range of a good aftermarket "performance" cam without getting too aggressive. Should be a good, driveable cam for your 383.
In terms of wrapping your head around what all the numbers "mean," there are entire books written about that subject... But CompCams has some very good camshaft design & spec tutorials on their web site and in the front of their camshaft catalog, available online at their web site. Check it out...
Ahhh Thank you lars. A comparison is just what the doctor ordered. I haven't been able to find much for comparison online, and just happen to have a comp cam, and have been reading some of their material, but it gets a little overwhelming, especially at my age.This will help a lot. Thanks again.
Sometimes just having a "known baseline" for comparative purposes helps to put things into an understandable relative perspective, so I'm glad the info achieved that for you.
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Look up the engine masters on you tube
. You might find some of the old shows if you dont subscribe to motor trend on demand. They give a good basic description
Lift is obvious for lift of the valve off off the seat, anything below .500 is considered mild now a days.
Duration is the big number. That's how long it says open. The longer it's open, the more air/ fuel you get and the more overlap you get from intake to exhaust. That's where you get into the old school racing motors that really thump and burp.
That's really basic but thats it in a nutshell. The center angle is also openning closing overlaps that tend to favor different styles of motors like normal aspiration, blown, turbo, racing vs stock etc....Comp cams likes 110*
The cam you describe was similar to my Comp cams solid lifter and with 10.5:1 compression I was around 350hp at the crank in my 327. It is a nice smooth cam with a little thump at idle
Last edited by Rescue Rogers; 03-12-2019 at 11:32 AM.
I had the same problem you did when I started. So I outlined all the articles I read. Attached is that outline- spelling mistakes and all. Hope this helps
.
Its a mild cam...what can make it extreme or not is the seat timing, those specs dont tell the whole story.
Is the valve being yanked off the seat and bounced back off or is it more of a gentle lobe?
I dont believe in the whole fast ramp or "xe" theory it just kills parts early. Factory stuff is too lazy, something in between would be ideal
Noones driving these 100k mi anyways
. There is a lot more to take into account such as ramp rates (how fast the lobe goes from no lift to XYZ lift spec). More agressive ramp the longer a valve is held open at a more optimal position, but hella hard on the rest of the valvetrain components. But this gives you a good idea
I\m trying to learn more about cams. I have a 383 stroker with cam specs of..
Duration @ .050'' Lift: 229 Intake / 230 Exhaust Lift: .480'' Intake / .486'' Exhaust
For lack of a better term. How "extreme" is this cam above, and what would make it more or less extreme?
What might a stock 350 c.i. cam specs be?
<snip>
John
My 72 Vette's 350 had a basic "stock" cam it was close to this:194/205 duration at .050 .390/.410 I don't recall the LSA probably 110 or 112. It idled well, lots of vacuum and it lacked power.
Best advice I have on cams is make sure the carb is set up correctly and a good (no points) ignition system is on the car. I reached the point I hated my 72 with the ISKY Mega until the Lars prepped Q-jet went on the car.
ISKY Mega Cam 270, same 350 it was more aggressive, less vacuum rougher idle. My Q-jet was exactly right so it stalled on occasion. After getting a 2rd hand Lars rebuilt Q-jet it ran very well and didn't stall. Per ISKY it was 9 hp stronger than the GM 222/222 factory cam in their testingFlat tappet ISKY Mega Cam 270 Specs 221/221 .465/.465 on 108383 with Doug Herbert hydraulic roller 240/250 .500/.500 on 110 LSA, had vacuum issues power brakes, vacuum headlights & windshield wiper door didn't work correctly until car ran for a while. TH400 with 3.08 gears it was the wrong cam for my set up - thank to Doug Herbert team ignoring everything I told them for the engine build.Dart 400 w / hydraulic roller Comp Cams XE 230/236 .510/.510 lift on 110 LSA, Great vacuum, drives like stock. Probably a little too small. Can get 19.5 mpg on interstate GPS confirmation.The Herbert cam would likely have been about right for the Dart 400.For small block Chevy 350's from what I've seen of other set ups a 220/230 works well, 224/230's also and off course the classic 222/222 Going hydraulic roller helps with power etc. Definitely a hydraulic roller fan here.
LSA (Lobe separation angle) is also an indicator of how "aggressive" a cam is but mostly only by sound.
Your cam is very similar to the old 280h Magnum Comp cam......which is fairly aggressive but not terribly so.
I'll be running a Crane hydraulic roller in my 496.
@ .050" its at 230/236 with .598/.610 gross lift and 114 degrees lobe separation.
What is the most important for me is that the engine will make good vacuum at idle and most of all is the RPM power range of 2000-6000.
Basically it is a good street cam that will produce optimum power in the areas where I will be operating the engine most of the time.
Higher lift, longer duration cams generally make peak power at a higher rpm, so depending on what you plan to use your car for is how you want to pick your cam.
Big lift cams sound cool, are good for drag racing, but are really useless in a car that you generally cruise on the highway or around town.
Choosing the proper cam generally starts with how you drive and how you plan to drive your car.
Everything throughout the drive train must work together to give optimum all around performance, starting with the rear end gearing all the way up through the carb.
Are you considering roller cams or flat-tappet only?
As you probably know, roller cam can give you more lift for less/same duration, yield better idle and require less stall and rear gearing.
Knowing this is not an equal comparison, my 218/224 @ .050" Xtreme Energy roller cam produces greater intake/exhaust lift. It is pretty mild. For your 383, you could go two steps beyond this and be in the .525" lift range. I went with my grind as I was looking to keep the same manners/duration but increase lift.
Thank you all for your information, and references. I guess I should have asked this question well before yesterday. I feel I have a pretty good grasp on it now.
For those who asked, I already have this Comp cam installed. The cam is a Hydraulic flat tappet cam, and HEI distributor, with 2400 stall convertor.
Thanks again all!
Oh, for the record, it's a street machine, with an occasional street confrontation.
Last edited by John Swift; 03-13-2019 at 02:38 PM.
LSA (Lobe separation angle) is also an indicator of how "aggressive" a cam is but mostly only by sound.
Your cam is very similar to the old 280h Magnum Comp cam......which is fairly aggressive but not terribly so.
Jebby
Thank you for all your time on this. It's very much appreciated !
I was told the cam is Comp cam 12-246-3
Last edited by John Swift; 03-14-2019 at 01:48 PM.
Its a mild cam...what can make it extreme or not is the seat timing, those specs dont tell the whole story.
Is the valve being yanked off the seat and bounced back off or is it more of a gentle lobe?
I dont believe in the whole fast ramp or "xe" theory it just kills parts early. Factory stuff is too lazy, something in between would be ideal
Noones driving these 100k mi anyways
I'm going to push back on this a little bit: The Comp XE series kills parts and sounds like a sewing machine because of the CLOSE RATE, not the open rate. It kills parts because it's a FLAWED "aggressive lobe" design, not because it's an "Aggressive lobe" design.
If you're willing to spend a little more on better springs, a more aggressive HYDRAULIC ROLLER lobe will get you more power under the curve- you can get more RPM from having higher lift and larger durations at higher lift, and still have great torque by having a shorter seat-to-seat duration vs. less aggressive lobes (because your valve open and close events are more like a cam with smaller durations). This also decreases your overlap and lets you have more MPG.
Flat tappet cams moved to being more "hydraulic roller like" over time (compare Comp XE Flat Tappet and Hydraulic Roller lobes- they're both called "XE" for a reason) and reliability DIED because flat tappets and modern oils and big spring pressures required to control those ramps just don't mix well.
Hydraulic rollers CAN and IMHO, SHOULD move to being more solid roller like and more aggressive. -The LS cams, hydraulic rollers, and spring packages show the recipe to making more average power with this strategy. (You get a more aggressive lobed cam for the aforementioned reasons, you get a lighter weight retainer / spring (beehives) and or lighter valves, and you use a short travel/low leak-down hydraulic roller tappet that can support your RPM and spring pressures
A modern SBC build can take advantage of the combo of more aggressive hydraulic roller lobes, beehive or conical springs, lighter weight valve train, and slow leak-down roller tappets and can be PERFECTLY RELIABLE with more average torque, HP and MPG. (It just takes more $$$ to spend on good springs and good retro hydraulic roller tappets.)
If you DON'T go with a more aggressive lobe, you're simply stealing from Peter (low-end torque) to pay Paul (higher-RPM HP). The more aggressive lobe and lightweight valvetrain strategy gives you both, in exchange for more of your $$$$.
Adam
Last edited by NewbVetteGuy; 03-14-2019 at 04:15 PM.
When building flat tappet stuff....I stick with old grinds because of the break-in.....I just have better luck with the Magnum series and Howards grinds than the XE Comp......
I seriously doubt that a person could tell the difference in power without a dyno....and they are easier on springs in the long run......
If a person wants to make real power then install a HR......splitting hairs on Flat Tappet stuff is redundant to me. I run a Magnum 292H in my own 406 and I love it.....would it make another 30hp with a HR? Yes, it would....but the darn thing makes enough power to get arrested quickly as it is!
OP: Hopefully you're catching that the term "Aggressive" can mean different things -so you'll get different answers.
"Aggressive Cam" Definitions:
1. Typical Def: Large duration cam that moves the peak HP RPM high up in RPM and results in poor vacuum, reduced low RPM torque, and a choppy "potatoe potatoe" idle (greater durations require higher static compression to not have a completely soggy bottom-end and should be combined with higher rear gear ratios to keep you in the power band of the cam).
1b. More moderate duration cam with a "tight" lobe separation which gives you a big overlap which reduces vacuum and produces a choppy "potatoe potatoe" idle
2. Cam with "aggressive lobes"; the "ramp" of the lobe itself goes from closed to max lift as quickly as possible and gets to higher lifts; the cam quickly gets up into "good air" / higher lifts and has more durations at higher lifts than less aggressively lobed cams. You can tell how aggressive the lobe is by looking at the difference in duration seat-to-seat, 0.002", 0.006", 0.050", and other lifts in the range up to max lift. (The difference between the seat to seat duration and the 0.050" duration and 0.200" duration will be LOWER for cams with more aggressive ramps.) -A flat tappet cam with an aggressive lobe will have duration differences that look more like a hydraulic roller cam, an aggressive hydraulic roller cam will have duration differences that get closer to solid roller cams. "Aggressive lobes" can be implemented for most any duration range. They require more spring pressure or lighter valve train weights or both and the extra spring pressure causes hydraulic roller lifters to bleed down / collapse at lower RPMs so you have to watch the combination of RPM and the aggressiveness of the lobe. (Most short travel roller lifters are also low bleed-down lifters and work well with aggressive lobes. With typical modern ramp rates LS hydraulic roller lifters and short travel Johnson lifters and Morel lifters advertise supporting up to 7,000 RPM; really aggressive lobes bring that max RPM potential down.)
The rollers from that line arent any better either.
I will give up a few lbs tq and maybe an inch of vacuum all day long for some longevity; too many cams with catchy names aimed at beginners & cheapskates that simply dont know any better.
After a few FT and 3 rollers from that same co I learned my lesson failures were quick and cost thousands to fix.
The numbers we see posted a lot dont tell the whole story, meaning duration at 050,. lsa etc. Plenty of tight lsa cams that make ok vacuum and wider ones that dont sound like youd think telling someone a splt duration cam is only good for poor exh ports is not always true either. .
W/Jebby....the magnum series and Isky Mega cams ran great while having some longevity also. Crower & schneider make some neat stuff also
03-11-2019, 03:31 PM
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