2edybrd

My mind is creaking along slower than usual tonight, but I was thinking about these cams with a real fast ramp rateand high lifts. So many of them make power at higher RPM's and it got me to thinking about the extra strain that might put on lifters and valves??

From what I've learned on this site over the past couple of years it seems that the enemy of any high revving engine is the inertia that builds up on the internals as the RPM's increase. This inertia increases by a certain ratio (I think). If every little gram of inertia counts, wouldn't a fast ramp rate cause that much more inertia not only as the lifters travel up the lobe but also when they start back down. That is to say if the ramp rate is as fast on the down side and the inertia has built up from the upside, isn't there a real danger that the lifter may come away from the cam? If you have to compensate for this possibility by installing stronger springs wouldn't that also cause more stress on the valve train??

If you want to spin your engine to, say 72-7500 rpms, wouldn't it be better to have a wider lobe seperation and slower ramp rates? Would the cam lift need to be less as well?

foff667

iTrader: (2)

in a word yes

Scott Turvey

You are correct in your assumption about the lifters coming away form the cam. This is what is more commonly referred to as "valve float". Another alternative to addressing the inertia issue is to install the conical or "beehive" style springs and retainers. Because of their reduced size nearer the top of the spring, and the resultant smaller retainer required, there is a reduction is mass that needs to be moved. A conical spring-style titanium retainer is as much as 70% lighter than the stock retainer, for instance. In addition, the springs may also be of an "ovate" design, meaning if you looked at across-section of the wire used to make the spring, you would see that is flattened or rather oval shaped rather than the round wire in a typical spring. Not only does this allow the spring to be compressed further (more space between windings); it allows a lower spring rate for a given lift than the round-wire spring.

BTW, Conical/beehive refers to the shape of the entire spring, with the bottom of the spring being wider, and a gentle "curve" tapering to the top. Think of the shape of a beehive, with less curve towards the bottom of the spring than towards the top. Ovate refers to the actual wire shape, as described above.

VINCE

iTrader: (1)

Valve Spring selection is VERY important. The last thing you want is a valve spring failure, valve drop and cracked shortblock. Many change cams like they change clothes. I went through several cams and I was warned by the tuner that sold me the cam that the cam I requested was pushing the envelope of the 918 springs specs, but I let my internet peers who WERE running a bigger cam and the 918's tell me it would work. It did work for 10 months. The week the valve spring failed I had just ordered a brand new set of 918's just because I had a feeling it was time to change my current ones because of the mileage I had on them and because I was tired of hearing Damian and 383LQ4SS asking when I was going to change the valve springs. <--Perfect example of a run on sentence. Anyway, my point is make sure you use a valvetrain recommended by the group recommending the cam. If they have no clue, purchase a cam from someone that does know what works with their setup.

Brian Tooley Racing

iTrader: (13)

Exactly!! This is what I have been saying all along. We have worked with many Competition level hyd roller cam setups and the way to get them to RPM is to run LESS lift and MORE duration, (but not neccesarily wider lobe separation).

For example there is a NMRA racing class that mandates .500" lift cam, stock lifters, 306 cu in and no power adders. The springs are set up at alot more pressure then what you would think, 170 seat and 400 open, and with a slow ramp speed will turn 8000 RPM on my dyno (108 LSA). With the same lift and slightly faster ramp speed cam by a competitor the engine floated the valves by 7000.

Faster ramp speed is only harder on components if the engine is allowed to get into valve float. The lighter the components on the valve side of the rocker, the less the valve float. Most street car guys are not going to spin their LS1 past 6800, so the current cam offerings are OK. If you want something that will turn 7500+ then it requires more duration, less lift, and slower ramp speeds.

You can approximate the ramp speed a cam lobe has by comparing the gross duration, .050" duration, and .200" duration. The lower the .200" duration with comparable .050" duration, the slower the ramp speed. Hope this helps.

2edybrd

Vince, and Brian that's exactley my concern as well. The cam I have right now is a split pattern with .5790 lift on the exhaust and a very aggressive ramp rate. I also have 918 springs waiting to go in. The cam is supposed to make it's best power between 6500 and 6800 rpm. The 918 springs were recommended with the cam, but they were also recommended with the other 15 cam packages on the web site. So I'm a little sceptical about taking advice on springs from a supplier who is getting a great bulk purchase deal on those springs.

I want to turbo the car this summer and, for the street, I see absolutely no need for a *****-to-the-wall cam spinning out of orbit to reach it's peak. Maybe I didn't really need to add this last part but it's a concern for me, especially since I really don't want to have to change the springs every 10- 15000 miles, or the lifters, or the rods, etc.

I wish someone made a cam to the ASA cam's specs, but with a 115 or 116 LSA.

Unaffliated Racing

iTrader: (15)

another thing about valve float is that, it being a hydraulic lifter...and at higher RPM's the hydraulics cant keep the slack taken of the valvetrain..therefore causing valve float

GrannySShifting

iTrader: (10)

hydraulics have been to 7500 in these motors

MNR-0

Hydraulic lifters are fine. They are safer than solid lifters in that they impose their own "rev limiter" by way of hydraulic flare. This would only happen at very high revs, say 6700+, and then only with crap springs.

If you still want to use that cam, advance the cam a few degrees so it peaks earlier on yet delivers more torque earlier in the rev range, right where you use it on street duties.

critter

iTrader: (9)

Lobe seperation and ramp rate are not closely coupled. What you really want is a certain amount of area under the lift curve and valve events (mainly IVC) at the proper times to get the desired performance characteristics. You can get the same area under the lift curve with longer duration and slower ramps or shorter duration and faster ramps. The advantage of the shorter duration is that you can get better valve event timing with the same area under the curve, but the disadvantage is the higher loads the faster ramps give. As noted, the faster ramps require stronger springs (and pushrods, rockers, and lifters too) and make it harder to run at high RPMS without valve float. Lobe seperation is really a fallout from choosing the valve events. Now, since HP = Torque * RPM/ 5252, it is obvious that higher RPM means more HP if you can maintain adequate torque. This is where the long duration, slow ramp, long lived component strategy can pay off - more peak HP. But once again, it is area under the curve that matters for most of us, because we shift (either manually or automagically) and RPM drops with the shift. This is not true if you run a 6000 RPM stall converter because your RPM doesn't drop much. I have heard cars make a pass where you couldn't hear much RPM change for the whole quarter mile. Those cars are not so particular about the width of your power band ...

There are so many trade offs it is a wonder that so many run so fast. And that is also one of the reasons some cars are slower - poor combination of trade offs.

GrannySShifting

iTrader: (10)

2EDYbrd... you can have any cam made if youd like, Pm me and ill show you some possible cams liek that

cooks 7

Anybody try the AFR Hydra-Rev to control valve float, it looks like a decent theory. I assume they fit LS1s?

GrannySShifting

iTrader: (10)

no it woudlnt work

cooks 7

no what wouldn't work, it won't work on LS1 or it doesn't work at all or what? according to the description controlling high rpm valve float is what it does

MyLS1Hauls

iTrader: (2)

There is only one rev kit for the LS1 and i believe it was a sponsor that had one custom made. I dont think they are readily available. The AFR kit wont work.

GrannySShifting

iTrader: (10)

It places load on the lifter body i bleeive, but traditional rev kits sit under the head in the lifter valley. LS1 heads seat over the lifters, not like a SBC where you can pull an intake and grab the lifter

2edybrd

Wow. Talk about rebirth of the dead thread. GrannySShifting, thanks for the offer. I just bought a six-speed GTO and I plan to bump the RPM limiter to around 68 - 7000 rpm eventually. The cam I would want doesn't need the highest lift in the world. I am definately NOT looking for a rough idle. I want to see a torque curve that is making within 20% max torque from 18-2000 rpm up to as close to red line as possible while being able to spin to around 7000 rpm. Maybe these are unrealistic hopes, but if I can get close that would be fine as well.

Maybe a larger base circle would help also. Who knows? I think I am kinda hampered in the Mod department right now until the ridiculously high prices for exhaust drops for these cars. I mean, really, 800 USD for a set of shorty headers?

GrannySShifting

iTrader: (10)

No way would I pay 800 for shorties! lol PM me about the headers!