Rocker arm ratio

[Joey120373]

My 520 BBM - FEPower build is finally starting to move forward.

Jay is hard at work getting the heads into production,
Pistons arrived last week ( thanks Jay ). I’ve been so busy at work though I haven’t even put my hands on them yet, but my buddy who I had open the box to snap a pic tells me they are not only beautiful but insanely light weight.

I’ve talked with Brent Lykins about a cam, and I’ll be getting in touch with him again soon to get it ordered.

Jay will be offering 1.75, 1.85 and 1.95 rocker arm ratios.

My question to the FE hive mind, is there any reason to not use the 1.95 rockers?
The cam Brent spec-ed out is relatively mild, I don’t recall the exact numbers off the top of my head, but it should peak power at about 6000rpm and have good street manners.
Edit, found the cam numbers:

 255/265 @. 050", 115 LSA, 107 ICL, .680" lift. 

However, I may decide to hop this engine up down the road with a bigger cam.
To me it seems like a good idea, given the lift limitation of FE cam cores, to get the 1.95 rockers.

The only downside I can see, if you wanna call it that, is that it may require a little more spring...

Engine specs ( for now )
BBM block, 4.35 bore
Scat 4.375 crank
CP pistons, 10.8 to 1 CR
255/265 @. 050", 115 LSA, 107 ICL, .680" lift.  Hyd roller
FE power top end with the SA exhaust port
Intake TBA ( cross ram most likely )

Going in a 4500-5000 pound truck, c6 and 3.73 gears for now, may do a 6R80 swap down the road.

[Sand hauler]

Piston to valve clearance to me could be a problem. Perhaps the more knowledgeable folks here will chime in on this though.

[blykins]

Piston to valve clearance can be a problem, unless specific instructions, cam specs, and gross valve lift were given to the piston manufacturer at the time of ordering.  I have had engines with an inch of valve lift, but that information was given to the piston manufacturer.  I had plenty of clearance. 

Another issue is spring pressure.   It takes more spring pressure to control a valve that's opening further.  An "old school" rule of thumb is that your open pressure needs to be close to the gross lift.  Obviously that's a very rough rule of thumb and different things play into that, but if you're looking at .800-.900" valve lift, unless you're running titanium valves, expect the seat and open spring pressures to be up there too. 

I made more power with less lift on Jay's heads than the previous cam grinder's choices, so I don't think you're going to be at a detriment with a more "do-able" valve lift.  It's totally up to you though.  If you wanted an inch lift and the heads didn't back up there, I'd be game. 

[Joey120373]

Piston to valve clearance should not be an issue,
The pistons I have should have the same valve clearance that Jays dyno mule has.
Not sure I can even get that much lift with any cam I am likely to run.

 .680 lift at 1.73
Should be
 .766 1.95

Pistons should be good to over .800 lift.

[blykins]

I have access to many different lobes and the ones I picked for you were geared for a 1.76 ratio.  However, that doesn't mean that we can't creep on up on the lift with a 1.95 ratio if that's what you want. 

Check with Jay, but he was getting close on PV clearance with around .900" lift and if it weren't for the fact that he lost some lift due to spring pressure/pushrod deflection, I think he was ready to start fly cutting.

However, that cam he had originally had a stupid amount of overlap, and overlap is the piston to valve clearance killer.

With that being said, .750-.800" lift should be do-able if you're willing to run the spring pressure for it.

[Joey120373]

I have access to many different lobes and the ones I picked for you were geared for a 1.76 ratio.  However, that doesn't mean that we can't creep on up on the lift with a 1.95 ratio if that's what you want. 

Check with Jay, but he was getting close on PV clearance with around .900" lift and if it weren't for the fact that he lost some lift due to spring pressure/pushrod deflection, I think he was ready to start fly cutting.

However, that cam he had originally had a stupid amount of overlap, and overlap is the piston to valve clearance killer.

With that being said, .750-.800" lift should be do-able if you're willing to run the spring pressure for it.

Thanks Brent, that’s kinda what I was thinking. I don’t foresee ever needing .900 or an inch lift, .800 might be in the cards for a future, bigger cam.

I do t mind spending a bit more on springs or even Ti retainers, just seems to starting with the higher ratio gives gives me more options down the road if I decide I want to spice it up a bit.

[blykins]

I have access to many different lobes and the ones I picked for you were geared for a 1.76 ratio.  However, that doesn't mean that we can't creep on up on the lift with a 1.95 ratio if that's what you want. 

Check with Jay, but he was getting close on PV clearance with around .900" lift and if it weren't for the fact that he lost some lift due to spring pressure/pushrod deflection, I think he was ready to start fly cutting.

However, that cam he had originally had a stupid amount of overlap, and overlap is the piston to valve clearance killer.

With that being said, .750-.800" lift should be do-able if you're willing to run the spring pressure for it.

Thanks Brent, that’s kinda what I was thinking. I don’t foresee ever needing .900 or an inch lift, .800 might be in the cards for a future, bigger cam.

I do t mind spending a bit more on springs or even Ti retainers, just seems to starting with the higher ratio gives gives me more options down the road if I decide I want to spice it up a bit.

Also keep in mind that a hydraulic lifter, even a short travel race lifter will only handle so much spring pressure before they start giving up.

[Joey120373]

Brent, I’ll be getting in touch with you soon on this.

I will be getting the valves from Jay, and I think he will be offering hollow stem intakes.

[Joey120373]

The hydraulic lifter limitation is one thing I was worried about, if it turns out that the higher ratio will start messing with the lifter, then maybe it’s a better plan to just get 2 sets of rocker arms.

1.75 for the mild hydraulic grind and
If I decide to go with a bigger solid roller down the road just plan on getting a set of the 1.95s.

[Joey120373]

Wonder if I’ve got enough info now to get the gonkulator involved ?

[Nightmist66]

It should be noted that a higher ratio rocker is not free lunch. Going from say a 1.75/6 to something like a 1.95 will be a little harder on parts, especially a solid roller with decent lift and/or spring pressure. The rocker will become weaker as you move the pushrod cup closer to the trunnion to increase the ratio. The whole side of the valvetrain on the pushrod side has to work harder. Pushrods will deflect more, needle bearings may not last as long, cam bearings will see more load, etc. If you were going to do a high lift/spring pressure deal, go with bushed lifters. The load bearing area is dramatically increased and no parts to come loose like the needles.

Going with an inch lift may sound good, but is it best? Just because it will clear, you have to consider how much shrouding will be at the cylinder wall. In my case, I have a 4.085" bore, Ed heads with 2.200/1.65" valves. My heads were milled to death(no angle) to get me some compression with a flat top piston. So, at around .730"ish lift, the valves will touch the walls. I mocked up with a couple sets of rocker arms ,degreed, and checked PTV and valve to wall. The Erson rockers I am using come up short on the lift, but plenty on the safe side for valve to wall. I could have run the Harland Sharp and been "ok" with the actual valvesprings on(it was close to touching with checker springs). I feel the slightly lower lift is worth more with the valve unshrouded than jammed into the wall. Longevity of valvetrain parts with an inch lift cam and springs, etc. will pretty much be out the window if it is going to be a driver. JMO

[Joey120373]

I will be no where near 1 inch of lift!

[Gaugster]

While it might be nonsense ...I had asked Jay if mixing ratios between intake and exhaust was possible. It seems possible to use different ratios and just have a compromise on the actual rocker to valve stem geometry. No need for it initially but might end up being a trick to optimize a build??? Just a neat thing to ponder I guess.

[blykins]

There are many instances where I'd use a different ratio between the intake and exhaust.   It would be a smart plan to be able to do that if need be.

Sometimes we get into situations where we want the intake valve to snap open.  Some of that is in the lobe design itself, but a higher ratio rocker can result in quicker valve action as well. 

I've also been in situations where I didn't do as much mock-up as I should have and found myself with plenty of intake valve room, but the exhaust valve touched the cylinder wall.  Dropping to less ratio on the exhaust rocker got me through that mess.

[Gaugster]

There are many instances where I'd use a different ratio between the intake and exhaust.   It would be a smart plan to be able to do that if need be.

Sometimes we get into situations where we want the intake valve to snap open.  Some of that is in the lobe design itself, but a higher ratio rocker can result in quicker valve action as well. 

I've also been in situations where I didn't do as much mock-up as I should have and found myself with plenty of intake valve room, but the exhaust valve touched the cylinder wall.  Dropping to less ratio on the exhaust rocker got me through that mess.

Cool. I know it's an option for individual rocker systems but was unsure how it could work with paired sets.  Many of these first builds with Jay's new products are going to be a learning experience for all. Good to know there will be some "wiggle" room in the efforts.