quick question for those of you that know...

two camshafts, both identical with the exception of lift as that one has about 10% more (let's say .500" vs .550"). how would the power-curves differ in the same engine?

thanks in advance!

jay

 

Just adding 10% lift would be like increasing rocker arm ratio from 1.5 to 1.65 without changing the cam.

Generally this should improve torque and power a little. However, if the engine was already "overcammed", you could lose some low-mid torque and power.

So it all depends.

 

Since were talking theory, how about this? The cc306 is bigger than the 305 in both lift and duration. Obviously the lift is more than a stock headed camaro needs, or can use. What would the end result be if you used the duration from the cc306 with the lift from the cc305? Either a 114 or 112 LSA, probably the 112, as that would keep the power lower in the rpm range right? Wouldn't a combo like this make more power than either the 305 or 306 in a stock headed car? Where is the extra power made in the 306? Wouldn't it have to be from the duration, otherwise you wouldn't need ported heads to run more lift than say .550. Isn't that why some of the "stock" classes let guys run whatever duration they want, and regulate a stock lift cam? I could have sworn there was a guy here trapping 118+ on stock heads and stock lift cam. Am I on the right track here? If so, what is a downside to doing this?

 

Agree with this but would add that, in general, more lift is better. The exceptions first concern limitations related to springs. You will wear the springs out sooner with a higher lift cam (though 0.500 to 0.550" shouldn't be a major issue) and you will experience valve float sooner with a steeper lobe. This may or may not be a problem depending on how high you are going to rev it. The other thing to consider is the heads. If the heads reach their "choke point" at a much lower lift (say 0.450" in this case) there will be very little gain. There will still be some gain, since with steeper lobes you will reach higher lift sooner at every point, but not as much as you might think.

I am a big fan of high lift/degree cams. For example, the CC 3100 series XE lobes really kick but, provided the limitations are understood.

Rich Krause

 

So are we. Think "aggressive".

Rich, what do you think about asymmetrical lobes with a steeper closing than opening flank? The valve comes screaming down, and then is slowed down just enough to keep the seat bounce to an acceptable level. Think about a 3196 with 3190 duration.

We've discussed this, but haven't tried it yet. Others have, but they aren't saying much.

Jon

 

thanks for the info... the cam would be a very mild street grind so i don't think the motor would be overcammed or that the heads wouldn't be able to use it (ls1 w/ ls6 valve springs). would the higher lift cam pick up more power in the low, mid or high rpms?

thanks again!

jay

 

more lift will pick up power basically everywhere.

you can ALMOST never have too much lift. aside from stablity problems, and if for some reason the port actually goes super turbulet and loses a lot of flow.

 

Jon: the concept of a very steep closing ramp is appealing. The problem is in finding the limits. What I assume is the limiting factor is spring pressure. Wouldn't the opposite of valve float have the potential to occur? What I mean is that the closing ramp being so steep that the roller loses contact with the lobe. Obviously, a solid roller can use more spring than hydraulic and could utilize a steeper closing ramp. Of course, the rev range will also play a factor. If I had an engine dyno and a way to grind my own cams, I'd be up for trying!

It's worth noting that the 3100 series are actually as steep as milder solid roller lobes, so I am guessing that they are pretty close to the practical limit for hydraulic rollers.

Rich Krause

 

Rich,

Jon and I talked with Comp Cams about such a cam, in fact the engineer there said he could make one. They need to be desinged and run with more spring rate, to prevent what you have said, but with the right lifters (a semi soild) these lobes could give you some interesting valve closing points with the lift, duration Inche Deg of area. Yeah they would be at the MAX rpm 7000, but I would not run them that high! The seat bounce is the hard thing to control, but light weight valves would HELP A TON!



There are even higher lift hyd roller lobes in the Comp range.
The lobes are numbered 4639, 4640. They are 230 and 232 .050 duration, .407 and .412 lift. Your not going to find those in the book. I doubt the phone techs know about them either, but you never know. The 3190 series is aggressive, but you can do more. The low end of that range 206,214,224 duration is pretty aggressive, but I'm sure you could push the limits more.

Bret

 

Hey guys, what is the book that was mentioned? Comp's catalog? Does it list lobe options? The comp cams tech was not very willing to help a new member of the hobby with his first engine build up so I need to do some reading.

I have pretty much decided on my cam (XE 230/236) but I think there is potential to increase power by increasing the lift from the .510/.520 the cam is listed at. I would like to take more advantage of my flow numbers at .550. Perhaps lift of .550/.560 with 1.5 rockers (.587/.597/w1.6). But I need to understand the consequences/longevity concerns by increasing the lift.

 

Faster acceleration is all good and fine but it's always harder on the springs. Yeah, it gets the cam closer to the theoretically correct 'square lobe'.
Considering that you can get upwards of 600 crank hp out of an n/a 350 with a 260 @.050 cam and .600 lift I don't really see the point in subjecting the valvetrain to any additional stress. Especially if you have a set of heads that stall in the .6 region.
Now, if you're in some type of motorsports competition where everyone has to run a similiar duration, compression, induction etc., there you'd need to squeek out as much extra hp as you can to get an edge. I can see it being of benefit in that type of situation.
Anyhoot, just my opinion, and we all know what they say about those.

-Mindgame

 

From the people who I have talked too the fast acceleration lobes need more spring rate to control the valve but they do not cause more wear on the springs, lift is the sole reason that springs are stressed. So yes those lobes will wear out the springs more because they always have more lift than a same duration cam. The other side of that is if you had two cams, both with .600 of lift, one with 224 deg of Duration and one with 260, they will both be equally hard on the springs life. If it was two 224 duration cams and one had .500 of lift and the other with .600 of lift, the high lift one will work the spring harder.

Bret

 

A more aggressive lobe will need more spring to control the valve (at the same rpm) compared to a lobe w/ shallower ramps. A steep closing ramp will put much more load on your valve seats, as the valve hammers shut every time. On a hydraulic roller, I'd say you've got nothing to worry about since the hydraulic lifter would collapse (from too much spring or ramp acceleration) before the valvetrain gets too hammered. To keep the roller onto the cam's closing ramp, you might want to consider running a Hydra-Rev kit on the lifters, so you don't need to bump up spring pressures. Once you start getting into solid roller spring pressures, then I would assume valvetrain wear would be a more valid concern.

A.

 

Comp cCams catalog is online.

http://www.compcams.com/

select 'online catalog' from the lower left menu

select 'PDF Version Here' from top center.

select Camshsft Lobes 226-248, and you'll get the lobe pages.