tapio

I´m in a process of upgrading my 64 327 engine with new XE262 cam and springs. Since I also need new rocker arms, I´m considering the roller rockers.

Do roller / roller tip rockers give more HP and how much? Are they worth the investment? Another issue is clearance with aluminum Corvette valve covers. Comments and experiences?

Thanks in advance.

gkull

The comp cams roller tips are very strong and function without failure to over 7000 rpm. The roller tip by it's self doesn't add power. They claim the increased is caused by the additional lift and lack of deflection. I used the 1.6 under the stock L-82 cast aluminum covers. I did have to remove the little oil tabs because they hit.

Full roller I believe add power just because of less friction in the pivit point. You also need screw in studs and pushrod guide plates.

1.6 ratio is would help out your little cam.

mountainmotor

The roller tipped 1.52's from Comp Cams is really all you need.Save the bucks for something else on the motor.That cam was designed for 1.5 rockers.Unless you would have a specific reason for needing added 3 or 4 more degrees of duration and approximately .030 more lift I would stay with the 1.52.The lift rates on that cam are pretty aggressive as is and the rocker geometry will be better also.Gkull is right about the deflection over stock.They are good quality part.Plus the stock rockers mostly came in at 1.47 or so because of quality problems.

JAKE

Dyno test after dyno test posted in most of the mags give the same results.

Rollers of the same ratio as stock sled type rockers increase power in the mid single digit range (5 to 6 HP). So all you do is pull off you sled type 1.5s and install full roller 1.5s - 5/6 HP.

Then when you go up one full ratio (1.5 sled to 1.6 full roller) power increases are in the 12 to 15 hp range over stock sled type 1.5s.

One of the mags ran an extensive article on rocker arms and ratio changes not too long ago and full rollers won out hands down in every dyno run. These power increases my not be felt SOTP or even show up in your time slip due to all the other variables involved (launch, traction, shift point, temps, etc)but the power increase is there.

All you need is to learn how to take advantage of it.

Hope this helps.

Jake


[Modified by JAKE, 4:17 PM 1/8/2002]

tapio

Thanks. I think I´ll go Comp Cams roller tipped 1.52´s.

bungoo2u

Which is a better choice if you were buying a new valvetrain to reach a certain valve lift and duration?
A smaller cam with 1.6 rockers or a slightly larger cam with 1.5 rockers (say XE262 with 1.6 or XE268 with 1.5)

mountainmotor

When you put a 1.6 rocker on the intake only of a dual pattern cam it becomes very close to a single pattern cam in respect to total duration.If that was the duration needed the correct cam for the motor should have been bought in the first place.So to answer your question yes a larger cam should have been chosen but LSA and other things need to be taken into consideration"intake manifold,carb exhaust" ect.Just to many variables to type!
However there are cams that have lobe designs specifically for use with higher ratio rockers.Some of Engles for the air cooled horizontally opposed VW motors in an example.
Correct rocker geometry which includes pushrod lenght ect is important for longetivity and effectiveness of the timing events.
Hope this helps some.

JAKE

Interesting question. I've kicked this around with some guys from time to time and, like with most things, there are differing views.

Mathematically, you can't get the same duration with just a 1.5 to 1.6 rocker ratio change.

Changing from 1.5 to 1.6 gives about 3 degrees of additonal duration (+/- depending on which cam company you reference), so a 262 with a 1.6 still won't equal a 268 with a 1.5 in duration, assuming cams from the same company and from the same 'family'.

Valve lift, however, will be very simlar and a 262 with a 1.6 rocker may even slightly exceed the lift of a 268 with a 1.5. It would depend on the camshaft family itself.

Most engine builders who build for endurance opt to put the duration and lift in the lobe rather than using the rocker. Using the rocker to gain duration and lift increases the opening and closing rates of the valve; meaning the valve is accelerated and decelerated faster. This can be a problem with endurance engines and works the valvetain (especially the springs) harder.

Engineers who design performance camshaft lobes work within some pretty narrow acceleration and deceleration parameters. Too aggressive and you sacrifice valve control and kill springs; too conservative and the engine is lazy. Really fast rate cam lobes call for more spring too.

Engines designed for sustained high rpms generally have more gentle ramps with slower/gentler acceleration/deceleration rates that serve to limit sudden shocks to the valve train which causes unwanted harmonics.

Drag engines, which only run for very short periods of time, use much more aggressive ramps to open and close the valves more quickly resulting in a greater area under the curve. This fast valve action is harder on the springs though.

The science involved in proper camshaft design is very complex and requires some extremely expensive equipment to test the lobes' dynamics.

Builders of short burst engines, like 1/4 mile drag engines, sometimes exceed rocker ratios of 2.0, but I believe that the long track Winston Cup guys stick much closer to stock ratios.

I personally feel that rocker ratio changes are a fine tuning tool. The best thing to do is to select the"right" camshaft up front; then play with rocker ratios somewhere down the road, if you feel the need.

Remember, it's a lot easier to change rocker arms than to change camshafts.

Just my thoughts and your mileage may vary.

Jake




[Modified by JAKE, 10:37 AM 1/9/2002]

mountainmotor

Bungoo2u,
As you can see by Jakes post there are many variables that he only breifley touched on .I agree with Jake that rockers can be used in an effective way.

Take say a 1988 TPI motor that has had headers good exhaust and throttle body mods but the owner does not want to change cams yet.The use of 1.6 rockers will help .A costly 8-10 hp.But yet works.
A well thought out engine combination with an outright goal is always best in my opinion.Although some prefer to bolt on and go for now.

tapio

"Most engine builders who build for endurance opt to put the duration and lift in the lobe rather than using the rocker. Using the rocker to gain duration and lift increases the opening and closing rates of the valve; meaning the valve is accelerated and decelerated faster. This can be a problem with endurance engines and works the valvetain (especially the springs) harder."

Yeah, somebody said something similar in another thread on cam selection. I think that in the long run it would be wiser to stick with 1.5´s on fast rate lobes.

JAKE

Yea, probably me.

I seem to respond to these kinds of questions on this and other boards pretty often. I've always had a special interest in camshafts since they pretty much define the characteristics of the engine.

Jake

JAKE

Here are some more thoughts to add fuel to the fire.

Most folks researching camshafts primarily look at four things (other than hydraulic vs mechanical and flat tappet vs roller):

Advertised Duration
Duration at .050
Lift
Lobe Seperation Angle, sometimes referred to as Lobe Centers or Lobe Center Angle

All of these show up on the cam card and are usually listed in the cam company's catalog.

The one thing that doesn't show up, though, are the ramp ratings. Ramps are very important because they determine how quickly the valve is accelerated or decelerated.

There are basically two types, symmetrical and asymmetrical.

(There's an inverted flank type, but it's generally considered to be non-streetable because it's so hard on springs. There may even be some other types - proprietary stuff - like what the Winston Cup boys run, etc.)

Symmetrical lobes have the same opening rates on both opening and closing sides of the lobe.

Asymmetrical lobes have different rates, usually the opening rate is faster and the closing rate is slower, more gentle. This allows for air flow to begin quickly as the valve opens, but allows a slower, more gentle closing so the valve sets down on the seat without bouncing.

The cam cards, however, don't show the ramp rates. These rates can only be deduced (inferred) from comparisons. Maybe not particularly scientific, but I've found that using a little trick can give you an idea of how fast/slow the ramps are.

It won't show you the actual speed (aggressiveness) of the ramp, but helps in doing comparisons between similar camshafts.

In order for it to work, though, both cames must have their advertised duration measured at the same point, something like .006, .020 or whatever. Just as long as they are the same.

Take two cams with the same advertised duration, measured at the same point. Then subtract the .050 duration figure. The smaller the difference, the faster (more aggressive) the ramp.

Example: Take a look at some of CompCams custom roller options. They have one series called the "Hi-Tech .440" series of grinds. All 8 cams in that series have a lobe lift of .440, but the duration of the cams spans a range of 260 @ .050 to 287 @ .050. All of these cams, however, lift the valve the exact same amount.

So you'd have to conclude that for cam lobe to lift the valve (in this case .660 with a 1.5 rocker) .660 yet keep duration at only 260 its ramps must be more aggressive than a cam that lifts the valve the same amount (.660) but has 287 degrees of duration @ .050.

So if you plug in the numbers, the 260 cam checks out at 36 (296 advertised and 260 @ .050) while the 287 cam checks out at 38 (325 advertised and 287 @ .050).

The real beauty of this little trick is when you compare two cams that have the SAME .050 duration and lobe lift.

So lets look at another of CompCams offerings that has the same .050 duration as our Hi-Tech .440; 260 degrees @ .050. The "High-Torque .440" is a good example. It has an advertised duration of 288 and a .050 duration of 260; lobe lift is .440.

Using the little trick, the "Hi-Tech .440" checks out a 36, while the "High-Torque .440" checks out at 28. Now you can really see the difference!

Anyway, it's something you might want to keep in the back of your head for later use when comparing camshafts.

Hope this helps.

Jake




[Modified by JAKE, 11:10 AM 1/12/2002]

LT401Vette

As Jake said you will really get a faster open/close rate with a higher rate rocker.

As for longevity on your setup, I wouldn't worry with a 1.6 ratio. If you have heads that can take advantage of the extra lift I would go with the 1.6's. This allows you to get more lift and open time within almost the same duration. Adding duration is where your streetability begins to degrade, so high rate rockers work well. All the computer simulations keep showing faster rates makes more power. This is why GM took the LT4 to 1.6's and they designed the LS1 heads to use 1.7's from the start. The valve over-lap can remain smaller and the intake valve can close sooner to start building cyl pressure, yet there is still as much time with the valve open enough for effective flow to fill the cyl.

Jake, Most NASCAR Winston cup engines have actually run 2.0:1 on the intake and 1.9:1 on the exhaust for the past 5 yrs or so. This is because they are not allowed roller cams. With these wild ratios the flat tappet can give them nearly the same valve rate as a roller. The down side is that they basically shell the cam every race running these high ratios and springs heavy enough to control the valve with no roller on the lifter.

tapio

Thanks, JAKE. Yes, I´m familiar to this technique. That´s why I chose the new XE cam series over the more conventional stuff. I wanted to have more duration and lift and still to have good manners on the street. I´ll report my experiences after I got my car on the road again. The winter is not over yet and there´s still some snow on the streets, so it will take three or four months...

JAKE

[Jake, Most NASCAR Winston cup engines have actually run 2.0:1 on the intake and 1.9:1 on the exhaust for the past 5 yrs or so. This is because they are not allowed roller cams. With these wild ratios the flat tappet can give them nearly the same valve rate as a roller. The down side is that they basically shell the cam every race running these high ratios and springs heavy enough to control the valve with no roller on the lifter.[Snip]

That's really interesting. I suspected it would have been just the opposite. I'll bet that all the rotating and reciprocating parts - except maybe the crank - are replaced after every race.

I've read, too, that builders would de-stroke the crank and bore the block when bore wear shows up in order to keep the seasoned block. They'd rather keep the seasoned block and use a shorter stroke rather that a green block and the normal stroke.

On that point, some company in Indiana is supposed to have a procedure to "season" a green block. It involves heating and cooling the block to very precise temps and rates under tightly controlled conditions.

I sure would like to see the full setup specs of a Winston Cup engine, but all I can come across are bits and pieces.

I did learn some other info recently though, that they run .001 bearing clearances and Zero weight oil.

If you have any other numbers put 'em up.

Thanks

Jake

tapio

Btw, does anybody know the true ratios of the most popular rocker arms:

Comp Cams Magnum roller tip
Comp Cams Pro Magnum true roller
Crane Steel roller tip
Crane Gold Race true roller
etc.

I would appreciate any input.

Les

From what I've seen the advertised ratios are accurate for the namebrand aftermarket rockers. This is largely what gains you a few ponies vs. the inaccurate stamped rockers. I added 1.5 Crower full rollers to my smallblock years ago w/ no other changes and, between the accuracy in ratio & the loss of friction, the difference was about the same as putting a fresh tune-up on a motor that was badly in need of it....noticably quicker revving and it pulls harder on the top end.

JAKE

I agree, the rocker ratios are accurate from the aftermarket companies, but there's another variable that effects actual valve lift that often isn't considered.

It's deflection.

One way to really tell is to put a dial indicator on the valve stem tip and cycle the engine through one revolution. Because of deflection, you probably won't see the valve lift that the math formula says you should be getting. The heavier the spring the more the deflection too.

The best way is to do this with all 16 too. Some valves won't lift as much as its neighbors because of lobe location along the camshaft. Those lobes nearer the cam bearing deflect less than those farther away. This is one reason that the PRO boys have gone to the larger diameter (BB) cam size. With the super heavy springs they run deflection (bending) of the camshaft itself is a real problem and the larger (bigger diameter) cam helps a lot.

Although I've never seen a tech article on this point, I suspect that in a running engine the deflection increases and lift decreases even with good parts. Of course aluminum rockers will show up the worse and steel rockers the best due to the lesser amount of deflection; steel being more rigid and stiff than aluminum.

Your pushrod diameter, wall thickness and type of material factors in to this deflection situation too.

That's why it's always recommended to get the most rigid/stiff parts you can, consistent with low weight. There's a trade-off here. The stiffest puhrods will probably be 7/16" in diameter, but when filled with oil, these suckas weight a ton, so up top that additional weight really hurts valve control.

.080 wall 5/16" seems to be the most commonly used, but CompCams tests have shown a higher degree of harmonics with these in certain RPM ranges. In those cases, a .060 wall, 5/16" rod shows up better. Another example of bigger not always being better.

In a streetable comb, all this may not matter a whole lot, but when you begin to push the envelope this stuff makes a world of difference.

I'd follow my cam maker's recommendation on these parts since they've done all the specialized testing to know what works and what doesn't.

Hope this helps.

Jake




[Modified by JAKE, 9:32 PM 1/13/2002]

Aaron-74

i now have the same cam and rockers that you do. But before I got ported heads and all that, I just added Comp Cams 1.52:1 roller tip rockers. And though I really didn't feel much of a gain in power, I noticed that there was no smoke coming from my exhaust at full throttle anymore.