427zm

iTrader: (9)

As my title says, I'd like to understand cam ramp rates and ratios better. Specifically, how do they effect the top end; what is to disturbing to valve events, what effects they have on springs, what long term effect they have for the motor, and any other thoughts any gurus may have. I would assume faster rates and higher ratios typically product more power, but then have short life spans. Any relevant discussion would be appreciated.

2000PewterT/A

This should cover most of your questions.

https://ls1tech.com/forums/generatio...-me-first.html

427zm

iTrader: (9)

Thanks. I have looked over Pat G's full assortment of links, they're great, but I didn't see anything explaining cam ramp rates and ratios.

JakeFusion

iTrader: (7)

More aggressive ramp rates make more power and also idle and drive better.

The downside is they require more to control them. More spring pressure, more pushrod robustness, less valvetrain weight over the valve (springs, valves, and rockers), and the right combination to control the harmonics/weight. As you get more aggressive with your lobe, you generally need more spring pressure to control the lobes especially when combined with heavier valves/rockers for example. In those instances, you need more robust lifters and pushrods to take the force of the springs and keep the lifter from bouncing off the cam or having valvefloat.

Another thing to look at is the lobe itself. Some aggressive lobes have been designed for stability at higher RPM. The Comp LSL lobes are one such design as well as the LXL, RPM, and the EPS LSG lobes. Any of the "endurance" type lobes usually trade a little aggressiveness for better stability. They don't have the sharp ramp-up or ramp-down but are more easy on and off the seat and then ramp quickly.

Best bet is to get the best lifters you can afford, stoutest pushrods that will fit, best springs (whole other discussion - but go for the lightest option whether it's beehive or duals with Ti retainers), lightest valves, and lightest rockers.

427zm

iTrader: (9)

Thanks for the explanation! I have a Pat G spec'd cam that I believe is running on the comp XER lobes, but I'm not positive about that. It's stats are .230/.230 .598/.608 on a 112 LSA. It has been a great cam for drivability and even with the more aggressive LSA, it still idles pretty dang smoothly (doesn't shake the car), and sounds mean! I just added TSP stage 2.5 LS6's to it (I'm aware Mr. fusion you're a pretty strong AI advocate) stock chambers w/ Cometic .040 gaskets, and since adding the heads it's become smoother while putting down 422/391. I know tuning has to do with the street manners as well as how smooth the engine is, but I know this cam was most like built for good street manners while being lopey. As it sounds, I bought the car with the cam already in place, and have to say, I'm happy with it.

All this aside, I'm guessing the comp XER lobes are less aggressive than others available now, but it has suited me well.

So, for further discussion and understanding, what is considered a fast ramp?

JakeFusion

iTrader: (7)

XE-R are aggressive. The 598 lift looks like XE-R and the 608 looks like an XFI lobe. LSL and LSK are more aggressive .050 to .200" but less so .006" to .050", XE-R is a square lobe, so you get a lot of jerk with it that can cause instability. LSK's ramp is really aggressive and with huge lift beats the **** out of springs.

I do advocate for Ai but I bought TEA heads.

427zm

iTrader: (9)

When you say Jerk do you mean torque? Just want to clarify. And when you say square, what exactly do you mean? and what does this do to the valve event? Also, how do you know what lobe profile the lifts bring?

That's right, I did see you picked up TEA's!

JakeFusion

iTrader: (7)

It's shaped like a square. Means it ramps up flattens out then ramps back down really quick. An oval or rounded triangle would be easier on the valvetrain but obviously doesn't make the same kind of power since it takes longer to open the valve for a given lift/duration.

Jerk is just that. How the lifter follows the cam profile. Jerk means it aggressively follows the cam lobe shape. Less jerk = more stability at the cost of some power.

I have an EPS cam with LSG intake and LSL exhaust because they come off the seat relatively quickly the .006" to .050" number and have good jerk properties for high RPM stability and also, in the case of the LSL lobe, sets the valve closed nicely to reduce the sewing machine noise inherent to LS1s (mostly the exhaust valve snapping shut and reverberating in the exhaust manifold/header).

427zm

iTrader: (9)

Again, thanks for the explaination. So jerk is good for higher RPM pulling, accompanied with my 112 LSA, makes complete sense why my dyno was what it was. I am currently spinning mine to 6800, which is where the power flattened out. Also, my setup doesn't create the double "hump" torque curve many here have spoken of. My torque curve is flat from 3k-6k. HP peaks @ 6500, torque @4800? Interestingly though, my top side is basically silent, like a stock Z, since installing the new heads.

Where does the overlap play its part in the whole valve event here, and what benefit does it add with a fast intake ramp? In my mind, overlap with a fast intake ramp would be most beneficial with an even faster exhaust ramp, high lift with longer duration. Am I correct in my assessment?

What can you spin yours too and what do you spin it to? Where is the power band with your cam? Also, have you installed your heads yet? If so, what did it dyno at?

.

JakeFusion

iTrader: (7)

No jerk is bad. It means it's harder to control as the lifter wants to jump off the cam lobe.

Your cam's power and is more of a function of the profile. Lobes can make more power or increase high RPM stability but the difference between an XFI or LSL is a few HP for a given profile.

Your cam flattens out on torque due to the valve events. Earlier opening of the valve and later closing creates tabletop torque. A high valve closing event carries the peak higher - longer exhaust duration does the same thing with an earlier intake valve closing event. My cam is designed with a late valve closing, minimal exh duration, and lower overlap. Overlap is power, but efficient heads need less overlap to make comparable power. Also a late intake valve closing kills power unless you up compression. I have compression. So I don't need more exhaust duration because I'm looking to keep overlap under control, create torque through compression, and create a peak rpm with my late intake valve closing point.

427zm

iTrader: (9)

Ok, so I think I have it, fast ramps are good for power, but tough on valve train, while slower ramps will require higher lifts, or longer duration to create similar power, but will better for the valve train. Now, this is making me want a different cam! I have good flow from my heads, a different cam with less overlap and different lobes to push more air with more stability would be more fun!

JakeFusion

iTrader: (7)

I have an EPS 230/234 114+2. It has LSG intake lobes (the EPS proprietary lobes) and LSL exhaust. Stability with decent lobes profiles and an overall cam profile that creates the valve events I want to make use of my ported/milled heads without sacrificing drivability with a ton overlap.

427zm

iTrader: (9)

Are you still stock displacement? And are you running a fast? Also, what CC is your chamber and what head gasket are you running? What lifters are you running?

I will say, the drivability of my cam is nice. I can let out the clutch and let it pull me along if I'd like too. It's smooth in parking lots, and nice around town. As you can see the cam has 6* of overlap in it. Is yours running less?

JakeFusion

iTrader: (7)

4 degrees of overlap in a stock 02 shortblock.

Ported FAST 102, 62cc chambers with TEA Stage 2 LS6 heads, .040" Cometics, Morel 5206 Link-Bar lifters, and Manton 11/32nd pushrods. Stock rockers w/ Comp Trunion upgrade.

Don't have it together yet. Waiting on parts still.

427zm

iTrader: (9)

Nice setup. I have the Fast 92 unported, 64cc chambers w/ the .040 Cometic gaskets as well. Should have gone Morel's after this discussion, but I went LS7's (now I'll pray), and the comp trunnion upgraded rockers as well. Think I need to port my LS2 TB and my Fast now.

Will you need to fly cut with the setup? Also, did you go with the 2.04 intake valves and the 1.60 exhaust valves? Also, are you waiting on the 102 TB? Should be ~440-450 whp correct? Is that the goal?