Ford Muscle Cars Tech Forum banner

1 - 20 of 39 Posts

·
Registered
Joined
·
865 Posts
Discussion Starter #1
A few days ago I ran a SB Chevy where we tested camshafts-- The same duration at 050 and 200 lift-- The roller camshaft made 57 MORE HP at the peak, and 33 pounds more torque at the peak- I am showing this for any of you who think than a flat tappet is sort of close to a roller ---WRONG-- The only time a flat tappet is close to a roller is when it has 25 or 30 degrees more duration

JOE SHERMAN RACING ENGINES
 

·
Registered
Joined
·
1,892 Posts
Wow! That much of a gain is pretty shocking. Do you have a few more details on the combo? What was the max lift on each cam? What was peak hp rpm on each? What core material on each?
 

·
Registered
Joined
·
7,408 Posts
Joe, you care to share the rest of the details about the engine combo?

I know of two people that went from solid flat tappet to roller who didn't pick up hardly anything at the track. BOTH had fairly large sized heads for their combos, already. One was a 4bbl 351C.

I figured they had about all the flow they needed for their combo already, and couldn't REALLY take advantage of the added open area of the roller.

I'd -think- that an engine with a limited cylinder head would take better advantage of a roller, as it would better maximize the "bottleneck" in the combination.

Of course, that's just my theory.

Thanks!
 

·
Registered
Joined
·
865 Posts
Discussion Starter #5
The engine is a 355 with a stock GM block- 13 to one compression-modified 850 Holley on a super victor- the two cams were 276-286 at o50, both on 106 centers- Roller cam made 616 at 7700. flat tappet made 559 at 7600- AFR 210 heads ( ported ) two inch headers- That is all I can say about it

JOE SHERMAN RACING ENGINES
 

·
Registered
Joined
·
1,477 Posts
I'm with ya Joe. When comparing a solid flat to a solid roller for an all out application, I am not surprised to see a significant difference. Solid roller is as aggressive as a cam gets.

For street apps, comparing a solid flat to a hydraulic roller for durations below 240 would be very interesting. My gut tells me that the difference would not be as dramatic and the cost to retrofit to a hydraulic roller may not justify the cost in many cases.

By the way, besides the cam and lifters, did the springs get changed too or the same springs for both cams?
 

·
Registered
Joined
·
1,892 Posts
Tracy, I sure as heck hope the springs got changed. Why not compare the solid flat to a tight lash solid roller instead of a hydraulic?

I'll go out on a limb and guess the solid roller had a good bit more lift. Valve open longer at an amount / lift that really moves some air with those nice cylinder heads.

There was an interesting topic on speedtalk that was discussing flat tappet cams to rollers and how each moves the valve. Seems the point of interest was that the flat tappet cams would actually move the valve faster than the lobe appears to due to the fact that the lobe is ground at an angle and the lifter (slightly convex I believe) travels along the base circle of the lobe near center and then shifts off of center as it move and spins over the lobe. You can see this wear pattern on any used flat tappet cam. Roller does not have that characteristic. So some may argue very convincingly that the solid roller in Joe's cam test was a fair bit slower at the valve from .050-.200" lift since they measured the same at the lobe.

Log inSpeed Talk
 

·
Registered
Joined
·
7,408 Posts
There was an interesting topic on speedtalk that was discussing flat tappet cams to rollers and how each moves the valve.
I believe it was that a flat tappet moves the lifter more quickly at the beginning of the lift cycle, but the roller can move it faster after that.

Most will say, and it makes sense to me, that the larger the duration, the more of an advantage the roller has.

If you can visualize a roller lifter on a flat tappet lobe, it would be incredibly slow, as the roller relies on a point contact in the center of the lifter, where the flat tappet can work all the way against the edge if it has to. The larger the lifter diameter, the sooner it can be designed to work.
 

·
Registered
Joined
·
1,892 Posts
After reading that it seems a flat tappet can have a higher acceleration rate while a roller can have higher peak velocity and run more lift.

I'm curious about the duration comment Mike as I've heard that before. I think with similar .050 duration a roller cam can still have a significant advantage since it can have significantly more lift. Take away the ability to use more lift and the roller advantage is crippled IMHO. The duration at higher points of lift should be more on the roller lobe with more lift as well. How much of that could possibly be made up by a flat tappet lifter at the valve where it counts I couldn't say???
 

·
Registered
Joined
·
1 Posts
No mention of seat timing here. No mention of lift or amount of dwell over the cam nose. No mention of rocker ratio either. Comparing cams based strictly on.050/.200 numbers is near meaningless.(at best an indication of ramp rate). Seldom discussed but seat timing has huge impact on an engines power curve. While there is very little actual flow at very low valvelifts, pressure differential changes begin as soon as the valve cracks open. (anyone who has fooled with lash should know this) IMO duration at .050 cam lift is best used for cam timing and checking purposes. Also keep in mind LSA is merely the coincidental centerlines of the intake and exhaust lobes or ICL the intake centerline. When a cam is designed you strive to obtain the optimum opening and closing points for the application(as well as rate of lift and total lift required). The end result of that then gives you the LSA and ICL.

Its the entire cam design that matters not just a few numbers at .050" or .200" cam lift. To see a truer comparison of how the two cams you just tested look to the engine get out your graph paper. Check net duration at the valve after lash starting at say .005" net valve lift then.010, .020, .075, .150 inch etc.. Tie that to a graph of piston position (depth) relative to crank degrees obtained at the various valve height duration checks, then to your flowbench numbers as well. Its a ton of work but it will reveal plenty clues to what really is going on.
 

·
Registered
Joined
·
865 Posts
Discussion Starter #13
A hyd roller is one step up from a hyd flat tappet, then a solid flat tappet, and finnally , a solid roller-- Hyd rollers are for girls


JOE SHERMAN RACING ENGINES
 

·
Registered
Joined
·
3,233 Posts
A hyd roller is one step up from a hyd flat tappet, then a solid flat tappet, and finnally , a solid roller-- Hyd rollers are for girls


JOE SHERMAN RACING ENGINES
LOL he said "Hyd rollers are for girls" HAaaaaaaa!!!
 

·
Premium Member
Joined
·
317 Posts
Je pensais que c'était lié aux poussoirs et à des modifs à faire sur le bloc pour installer ça.
Si tu veux installer des poussoirs à rouleaux OEM non liés, il faut effectivement installer un Spyder et faire des perçages sur la partie centrale du bloc.
Mais si tu optes pour des poussoirs liés, çà se monte sur n'importe quel bloc sans modifs, du 289 au dernier 5.0..
Ces derniers sont plus chers (entre 450 et 550$ le kit), mais bon, tu n'es plus à çà près ;)
 
1 - 20 of 39 Posts
Top