TheViper

on desktop dyno i put in my engine combo with headers and it came up to 350hp. when i put in roller lifters it comes aout to 390hp. this seams like a lot, would roller lifters realy gine 40 more hp? if so can i use them with a flat tappet cam? i've heard you can't use roller lifters with a flat tappet cam. if i can't use them, why not?

ede

lifters have to match the cam, if it's a flat hydrolic you need hydrolic lifters, flat solid, solid lifters, you get the idea. you won't see 40hp by switching to rollers, all else being equall.

Vader

That Desktop Dyno likely presumes that you would use a roller cam with the roller lifters (as you should). The significant change in lobe profile made possible by a roller lifter can make quite a bit of difference in total power, and more importantly, torque curve.

Flat tappet camshafts are generally made of a softer, more open-grained material (typically cast) so that the surface will hold lubricant and not chew away at the lifters as they slide across the lobe face. The lobes are also formed or ground with a slight taper from front to back, which helps hold the camshaft against the front of the case and causes the lifters to spin slightly as they ride the lobe.

Roller camshafts are made of a harder, more closed-grained material, since they need to mate with the harder rollers of the lifters and transmit forces without beating up the surface of the lobes. These lobes are also ground flat (no taper) to provide a full contact patch with the roller.

Installing rollers on a flat tappet can will do several undesireable things:

1. Create a poor contact area for the lifter since the lifter will tend to ride only on the high side of the tapered face of the lobe;

2. The harder roller will literally roll the softer and larger grains of material on the lobe face flat until the pieces of material turn into thin flakes that break and fall off;

3. The roller has a smaller contact area, so the intended motion of the valve will be reduced to short durations with very high ramps.

If you analyze the contact or a roller design versus a flat tappet design, you can see that the lobe shapes would be dramatically different to achieve the same type of valve motion, ramps, duration, etc. The flat tappet has a contact face that is as wide as the cam lobe, so the ramp of the lobe profile has an immediate affect on the actuation of the valve. The roller type has a very narrow contact point (only at the apex of the roller) so the lobe must be ground differently to force valve motion at a given degree of rotation.


The two type cannot be mixed with successful results, even if the materials were compatible.

TheViper

what roller cam would you sugest to get that is about equal in the power/trq curves but will give it more power? i have a melling .422 .444 lift, 204/214 .050 duration and 278 288 adv duration.

do you know what the adv duration is on a comp XE262?

RB83L69

The advertised duration of the XE262 is {drum roll please} 262°. Comp measures their adv duration between the .006" lift points; there isn't a standard for this among mfrs though. Some mfrs use .005", some use .001"; so it's very hard to compare this particular spec from one mfr to another.

For a cam to give the same general "shape of the curve" of the power band, look for similar .050" duration, the same lobe separation, and the same intake lobe center. A roller cam that comes close to yours in those regards is the Comp XE258 (08-408-8); 206°/212°, .480"/.487", on 110° lobe separation. You could use a degree kit or a selectable timing set to install it at whatever intake center line you want; IIRC Comp sets the majority of theirs up with the intake center at 106°, which is probably 4° advanced compared to what you have now, although that would also depend on what timing set you used.

Obviously that roller cam opens the valves for quicker, and holds them open much farther for much longer, than your existing cam does. That's where the additional power comes from.

TheViper

for the current cam i put in where it asks IVC(ABDC) 71 and EVO(BBCD) 76 as it says on the grind sheet for my cam. then it cam up to 278 288 duration as it says on the sheet. what is the IVC and EVO for the XE252? when i put in the .480 and .487 and roller cam it went from 345 to 392. i left the duration the same though. does this sound right to you? if it is right i'm going to get a roller cam soon

BTW, when you get a roller cam you have to use a bronze or brass(always get them mixed up) distributer gear right? how hard is that to change?

SinthetikIroc

iTrader: (1)

when you enter the lsa and int exh durations and what not it'll fill that in for you

V8Astro Captain

iTrader: (1)

Any of the Comp roller cams part number beginning with 08 are designed to be used in the '87 later block with the OEM roller cam stuff. So you don't need to switch the dist gear.

That info is on Comp Cams website somewhere...

AJ_92RS

Just a side note...... you may want to read a little deeper into the instructions that came with DD2000. I suggests that you not use the 'roller' option unless the cam is quite aggressive.

Read "Making the Best Lifter Choice" on page 54 of the user's manual. That should help a lot.

TheViper

what does it mean exactly by a high performance grind. i want to use a comp 252 or a 264. the lift is about .480 on the 252 and the duration is about 206/218(something like that). is that i high performance grind? the lift seams pretty high for that duration. what would be the best choice?

rx7speed

don't know if it was said here or not

but don't roller cams have a faster open and close ramp

do to the roller design you can get away with that where on a flat tappet your lifter would dig into the cam correct?

SinthetikIroc

iTrader: (1)

is that a roller? that'd be a good street cam.