Guys, I have been messing around with Desktop dyno lately and have recreated my combination pretty closely. DD says 302hp and 350tq, my chassis dyno numbers with the old automtic trans were 235hp/280tq repeated in a total of 3 runs. I have been goofing around with different cam profiles and have subsequently become a bit confused. I have tried many different Hyd flat tappet cams with my combo, from my curent 214/224 .442/.465, to numerous other flat tappet cams with durations from 206 to 219. All of the flat tappet cams deliver about the same power 290-310hp and 340-355tq. When I switch to a roller cam of similar duration my horsepower goes up by a few but torque jumps up by about 40ft lbs. Is this really true? Do roller cams really add this much torque over hydraulic flat tappet cams or is DD just messing with my head? I have tried these cam comparisons on TPI and carburated v8s and the results are the same, anyone got any insight? I feel somewhat juvenile asking this, I thought I understood cams better than this, but this really has me curious. Thanks for the help guys.

 

A non-trivial part of that increase is the fact that the roller cam design reduces friction. In addition, the roller cam allows the use of more-aggressive ramps* which means more lift/area "under the curve" - so yeah, 40 lb./ft. is possible...



*(According to this book, flat tappet cams can actually give a more-aggressive initial ramp entry - something that I'm not entirely sure I agree with. Regardless, the author states that this advantage "peters out" by around .460 or .470 lift {can't remember the exact number right now, but it was something fairly mellow...})

 

A roller cam gets the valve from closed to open alot faster, that means that you can pack the same .050" duration into alot shorter advertised duration. The closer .050 is to .008 duration, the more aggressive the ramps. When you can get the valve fully open faster, hold it there a certain period of time, then bring it down quicker, you will keep more cylinder pressure and make more HP/TQ. A roller cam will really boost the mid-range torque of an engine. Then add in the roller lifters to reduce the friction and you really have something.

 

This is interesting information. I knew that obviously there is less friciton with a roller cam, and I knew you can run a way more agressive ramp with a roller as evidence of the lift numbers on a roller cam vs a flat tappet cam of similar duration. I just didnt realize that kind of torque increase was possible. I tried installing the profiles of some of the Lunati Voodoo cams which have aggressive ramps and high lift for a flat tappet cam and they give me no noticeable gain in Desktop Dyno. I figured if the roller cam thing was true a Voodoo cam should give me a gain and it does not. Does anyone have any power numbers to support our thoughts? It will cost me like $700 to get new roller lifters and a roller cam for my LB9 but 40ftlbs is substantial.

 

I would guess the effect is because not only more lift under the curve but typically a roller cam specifically for fuel injection use will have more lobe seperation which allows more cylinder pressure because the intake and exhaust valves are open together at a much shorter amount of time. More cylinder pressure (assuming octane level is correct) always means more torque.

 

a wider LSA will broaden the power curve, whereas a cam with a narrow LSA (108* for example) will make more peak horsepower but also have a peaky power curve. for this reason many pulling trucks and tractors run a very narrow LSA because they are sustained rpm the whole time. They dont shift gears or anything, the clutch comes out and they are runnin. LSA does have a pretty major effect on power peak and area under the power curve, even a few degrees will make a noticeable difference from what I've seen. I just couldn't get over the 40ftlb increase in torque, thats like bolting on a set of cylinder heads!

 

The program is messing with your head. With that short of duration,,, going from a slow rate of rise flat-tappet to a fast rate of rise hydraulic roller with similar specs at .050 lift will not give you any where close to 40lb/ft. From my own experiences and running the scenario through EAPro (that takes into account the rate of rise of the cam),,, you're looking at maybe 15 horses on the top-end and a gradual rise in torque in the midrange to maybe 15 - 20lb/ft (on a 400fwhp engine) and that's if you take advantange of typical lift increases for the similar duration. If you keep the lift the same, it'll be less.

Now,,, on the larger duration cams running aggressive ramps and taking advantage of near solid roller cam lifts,,, depending on how good the heads are,,, sure,, I've seen more than 40lb/ft at the rear wheels from one hydraulic roller to the next.

 

BadSS, thanks for your post. This is the kind of information I was looking for. I just couldn't swallow a 40hp increase by swapping to a roller cam with similar duration and more lift than my current flatt tappet cam. In DD2000 I put a voodoo cam from Lunati in it. Those cams have huge lift for flat tappet cams and it gave me like 5 hp maybe. Then when I put in a typical Comp Cams roller cam that is mild and for use with EFI with a 114 LSA the torque goes way way up. It even did this for a carb motor I tried. I figured it was all too good to be true. Thanks for the insight. If anyone else has some info give a shout. I cant believe with as many DD2000 users as there are that no one has ever asked this before.

 

It also depends on the lift, if the lift is the same then yes the torq will not be 40 more but could be if the lift is like .05 or greater it could be depending on the head flow #'s