Rockers: 1.5 vs 1.6

[Ironmike]

don't think this has ever come up, so I figured I'd ask.

so you're building a new engine and you want, say .670 lift intake and exhaust, camwise. is it better to order a cam with .446 valve lift and use 1.5 ratio rockers, OR get your cam with .419 valve lift and use 1.6 ratio rockers.

Might be a moot point, but I was wondering which way would be best.

 

[hangn0ut]

In theory the 1.6 would be better as the lifter and pushrod dont move as much. But in practice no difference. However with 1.5 you can always upgrade to 1.6.

 

[pishta]

1.5 offers less stress on the rocker itself. You are going to run a pretty small base circle for a .446 lift at 1.5. 1.6 is going to give you a faster lift rate too all things equal. Is this a roller?

 

[JBurch]

Excellent question! Wished I knew.

What type of cam, FT or roller?

 

[Ironmike]

1.5 offers less stress on the rocker itself. You are going to run a pretty small base circle for a .446 lift at 1.5. 1.6 is going to give you a faster lift rate too all things equal. Is this a roller?

Yeah. but I'm talking .446 VALVE lift here, so hence would be .670 intake/.670 exhaust cam, with 1.5 rockers. ....I don't see what the base circle has to do with this.

 

[Ironmike]

Ok for example. The cam I run now is a Lunati solid roller with .400 valve lift, intake and exhaust. I'm running 1.6 rockers so my lift is .640.640...I COULD have them grind me a cam with .427 valve lift , run 1.5 rockers and have the same .640/.640 cam. My question is which would be the best option?

 

[xLURKxDOGx]

Ok for example. The cam I run now is a Lunati solid roller with .400 valve lift, intake and exhaust. I'm running 1.6 rockers so my lift is .640.640...I COULD have them grind me a cam with .427 valve lift , run 1.5 rockers and have the same .640/.640 cam. My question is which would be the best option?

Huh??? Is your valve lift .400 or .640?? How can regrinding .427 and using a smaller 1.5 ration equal .640??? From what ive seen going from 1.5 to 1.6 cant add that much lift on flat tappet, but it can on roller?

Jake

 

[Ironmike]

ok my bad. I guess in my first post, I should have used the term LOBE lift, first. For example here's my cam card. I am running 1.6 rockers, so it has .640 valve lift. IF I were using the 1.5 it would have .600 valve lift.

The cam is ground with .400 LOBE lift. LOBE lift X rocker ratio = VALVE lift. Simple math.

SO I'll make it simple and just say hey, I'm building a back up motor that I want to have around .670 lift. Is it better to get there using 1.5 or 1.6 rockers?

 

[TrailBeast]

besides the speed of the lift I don't see that it matter one little bit (except) if you used a fast ramp rate cam AND the 1.6 rockers you might be able to use a little more duration.

 

[Ironmike]

Gotcha. I do plan to use another 10 degrees duration or so on this little back up motor I'm doing. V to P clearance always a concern, though.

Thanks guys!

 

[AJ/FormS]

The difference in lift is 6.7% gross. That is 1.6/1.5 =1.0666666666666666666666666666lol
So at .640 x 1.0667 = .682
But a funny thing happens to the curve. Yeah it opens faster and higher, but it also balloons the curve over the nose to increase the dwell time there. That's extra hang-time, your engine might be able to take advantage of.

 

[pishta]

Yeah. but I'm talking .446 VALVE lift here, so hence would be .670 intake/.670 exhaust cam, with 1.5 rockers. ....I don't see what the base circle has to do with this.

I know what your talking about, .446 lobe lift. You cant raise the lift or it wont fit through the cam bearings, so you have to lower the floor, ie base circle. On a roller, its not an issue, on a FT cam the lobes start looking like roller lobes, very fast rate ramps.