On the exact same engine with As close as possible cam specs.

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Black 89 IROC...Mods: 355, 10.5:1 comp, Big Solid Crower Cam, TFS heads, Victor Jr, Holley, and a 5 spd...

 

It really depends on the max recommended rpm level. Also depends on the cam shaft. Some examples: You may gain 10hp and more torque if you redline at say 6500 and have a cam with duration of say 220/230 and lift of .46"/.53". Or you may gain almost no hp if the cam is really small like stock l03 engines. The best thing about roller is the free hp. They'll give you more hp no matter what engine they're used in. They really just free up the hp with the same kind of intake. Also roller is the only way to make the crazy hp numbers because the flat lifters actually start to almost jam (lifted by their sides which is a point off center). Search the board and you should find some really good posts and explinations.

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, Jon (91 RS too many mods to list), getting new engine in summer

 

With the same cam specs, you wont see much difference at all. The contact point with a flat tappet is pretty small initially, so the minor advantage of the roller setup wont really show up until the higher RPM's.
Where a roller is better is that the cam profile can be just about anything (within realistic limits), and also it doesnt wear very much over time. The flat tappet is very limited in what the shape can be just because of the way it works, and they do wear out over time, especially with radical cams since the spring pressure needed presses the lifter on the cam harder and wears it out faster.

 

I agree with madmax, it is the lobe profile that has more to do with HP differences between identical duration and lift numbers @ .050. Generally, a hyd roller cam has steeper ramps and opens the valve more quickly, thus you get more air flowing while the valve is opened.

 

Very big difference.
The camshafts can have the same measured lift and duration, but the hydraulic roller can have a vastly different lobe profle. It is the lobe profile that gives the huge performance advantage, namely more open valve time at the higher lift while utilizing the same overall duration. This why my camshaft works so well and still acts extremely mild.

ODB



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*I do custom performance mods on Edlebrock Performer carburetors (dualplane intake mods in the works),
White 1986 Irocz, 305 with iron #416 heads,
383 with aluminum TFS heads,
Edlebrock Performer-RPM intake and Performer #1407 carburetor, +110hp shot of crack, 700R-4 tranny, Vigilante 2400 lockup converter, 3.25:1 Ford 9" rear, Mcreary Road-Stars, SLP-stainless 1.75" shortie headers & Y-pipe, single 3" Borla exhaust, Linginfelter-TPI camshaft part number 74216 pulls 17" vacuum solid. Cam specs 213/219 @.050 114-LSA, sometimes advertised at 216/219 @.050 112-LSA .462/.470 lift @1.5:1 ratio. Using Harland Sharp 1.65:1 roller rockers. MSD-6AL, billet distributor, multi-retard, blaster-3 coil, and RPM switch. SouthSide machine subframe connectors, SSM lift-bars, Moroso 4" underdrive crank pulley.

N/A runs 10.9 @124,
Crack-runs 10.3 @135
haven't run at track since Oct-99