Advertised cam rpms

[2233]

Can anyone answer the following question.............Why is it that when putting a cam in a stroker with an advertised rpm range of 2500 - 6500 that it always falls short to the tune of 500 - 1000 rpms when installed and running? Example Heven's dyno shows a 5700rpm peak with a cam with an advertised peak of 6500?

Is it timing?

Heads restriction? (In hevens case not possible)
Manifold restriction? (As above)
Carb to small? (as above)

Suggestions?

[shaunp]

Optimistic advertising perhaps! But really they can only give a ball park figure as every engine is different, some heads will flow less with more lift etc, carb jetting not exact, ignition advance not perfect for the set up, which is often the case, who knows, engine being fresh. The other thing is most grinders build advance into the cam, sometimes you need to retard the cam to push up the top end power, but this will knock out some low torque. If you advance the cam more it will knock the top end and build the low end, but this normally makes them feel like they come on harder as well. Another problem can be lifter leak down at high rpm when using hydraulics particulary if the springs are to strong. This is how Roades lifters work to build torque, they leak down, which changes lift and duration effectivly making the cam quieter.

[HEVEN67]

In this case its the hydraulic cam, with the same grind cam in solid grind he said an easy 100 + hp

[shaunp]

It's just because you loose lift and duration with a hydraulic lifter, being a roller makes no differance to this, it does allow for a better profile because a the flat tappet doesn't have to climb the ramps. Hydraulics don't belt the rest of the valve gear around as much either due to the cusioning effect, they give a little in this respect but loose ultimatly in opening and closeing the valves when they should. The leak down of the lifter is an issue here. Anti pump ups are a compromise, sure they don't pump up at high revs but the also leak down more. In Holden engines they made more power with factory GM lifters as they were really good quality, as long as the valve springs were strong enough to stop them pumping up.  They lost power using  after market anti pump ups.
Of course there is some compensation in the profile, but it's never the same as direct action metal to metal you get with a solid cam roller or flat tappet. I used to use solid cams in holden engines years ago, they were great  for making power while the valve train lasted  but they used to hammer stuff to pieces. In a daily driver they ended up becoming a pain.

[418mach]

if you put the cam in a motor the same as whats advertised ie a mild 302 cam into a mild 302 or a wild 302 cam into a wild 302 it will probably do what is advertised. but here we are talking about a stroker which changes all the dynamics and the extra cubes pulls it all back my cam for example is  a solid flat tappet power range 3500-6500 and redline 7000 plus for a 351 i have just increased to a 6800 chip for the low gears but i dont think it will never see the other side  of 6500 in the high gears. also my experience not a lot of people are all that clued up on strokers even though they are more common now.  

[shaunp]

347 stroker should behave almost the same as a 351 windsor with respect to the cam, they have the same nominal bore & capacity is similar.
 Makes no differance that it used to be a 302.  It's really about  overall capacity. General rule is for every 10cui increase you need 1* extra duration at 50 thou lift, and as the capacity increases you tighten the lobe centres as well. Same applies to high head flow, tighter lobe centres are needed to be to get the benift of the increased flow. It's just about the abillity to fill the cylinder volume, more volume needs more duration.  For example if you had a 393 stroker it would need 3-4* more duration to get a similar rpm band as a 351 in thoery and a 347 can use 5*or so more than a 302 at 50. This gives the same effective duration.

[2233]

From memory Hevens cam is a 351 grind..........Heven is this correct?

[shaunp]

Yeah but is it a 351 grind in that is just 351 firing order but timing is the same? Lots  351 cams are just different firing order only.

[HEVEN67]

Ned said its a similar grind the the Cleveland GTHO cam, and yes I wanted a Hydraulic cam so as the valve train stays in one peice longer, Like 418mac said "not a lot of people are all that clued up on strokers even though they are more common now. " and this is what Ive heard alot of others suggest, but it goes to show that the engine gooroo did afterall know what he was doing with the selection, cause thats a pretty good figure for a hydraulic cam, maybe the torque curve would have been a little different if i would have used the 195 heads but its more up my sleeve for later without being wild.

[shaunp]

Originally posted by HEVEN67
torque curve would have been a little different if i would have used the 195 heads but its more up my sleeve for later without being wild.
 

Or got a custom cam with a tighter lobe centre to use up the bigger heads, but hell it's probably got enough power to pull christ off the cross anyway.

[HEVEN67]

And the valve train will then outlast christiaity!

[shaunp]

Dean Tighe will always purpose grind a cam, particulary for a V8, he is normaly happy to move the lobe centres around etc for different needs particulaly if give him the head flow figures and what you want it to do.

[418mach]

so heven are you happy with the numbers and the outcome is the car fun to drive. have you been back to the track to see the improved et.
the more radical you go the more it will become more tempermental.
with my build i did not pick the cam and entrusted that to my engine builder as i am no expert but i will say that it has 105 lobe centre which agrees with what shaunp is saying and i am not running the biggest heads or lift but they are at max. output for the head size.