I know this goes against manufacturers suggestions and all, but here's hte deal. I have a comp 280H cam, that has .480/.480 lift. I am using the correct valve springs for that cam. I want to change my exhaust rockers to 1.6 ratio. This will bring my total lift up to .512. I REALLY don't want to buy new valve springs, or have to spend half a day putting them in. Does anyone think there's a margin in which I can exceed the reccomended lift of valve springs by a hair? I mean .012 isn't all that much. Has anyone tried this? Is the only way to tell if it will work to see of the coils contact each other when the valve is open? Thanks

 

Exactly what spring are you useing at how is it installed.
(installed height)
Most will work with minor adjustment to the installed height.
You can increase the installed height by .030" by removeing
the stock oil shield caps from your valve spring assembly.
this will only reduce your seat spring pressure a little and allow .030" more lift.
You will also need to check that there is enough extra clearance between the bottom of the retainer and valve seal at full lift.
and that the pushrod is not contacting the edge of the pushrod slot or guideplate on the head during rotation of the motor.
the interferance may not be at full lift.

 

I'm running a Comp XE268 cam (.477/.480 lift) with stock length pushrods and stock rockers (I'm replacing the heads, soon, so I'm not THAT worried about rockers and studs and stuff). This is all on a 416 casting head 305 head. I know the springs included in the kit are gonna be good, but I'm not gonna have issues with the valve guide boss, am I? I'm thinking that the stock rockers are a bit flexed, so I'm not getting full lift, so I should be fine.

 

You know thats a good question. I don't have my cam build sheet here or I'd look. I bought the Comp 280H cam as a "K-kit", included springs. The guy who built my heads that are on their way to me put .500 springs in them, so we arent even really talking about the same springs. He is positive they are .500 springs that are supposed to match my cam though, but I don't know the part number. Whats the verdict? If there's not an extremly good chance they will work with .512 lift, I might as well forget about getting 1.6's because I don't want another set of springs sitting around.

 

Oh, maybe once or twice... how much do you like your short block? Remember, valve fragments are essentially incompressible...

The springs that will come in that kit are 981s, only 1.25" diameter, not safe above .500" lift. But who knows, you might be the guy that gets lucky. How lucky do you feel?

 

Your problem's going to be that there's just a point where the coils of the spring hit each other. As you can problably see, the springs are taller uninstalled than they are installed. If you can make your installed height taller, then you'll be fine, although sacrificing a tiny bit of spring pressure with the valves closed (higher spring pressure is good, to a point, because it helps close the valve and prevents valve float). One way to change spring height would be with a taller valve stem. You could also machine the valve seat. I think somebody also makes a spring retainer with a different height (which I think they should make a set EXPLICITELY for replacing heads cut for the exhaust rotator).

 

sounds like I'm getting 1.5 rockers. I don't have anything I can take off between the spring and the retainer. Oh well

 

The "K kit" for that cam should have included comp's
#981 spring. That spring coil binds at 1.13" so if it is installed
at 1.70" you would have just enough clearance for .512 lift.
If you have stock retainers and keepers and used the stock oil shield, you should be right at 1.7" installed height.
you can increase your installed height by .030" by removing the oil shield caps. then you should be at 1.73"
" The guy" may be useing something quite different.
If you're going to use his springs, check 'em.

If you're not willing to check these clearances your self than just leave it at 1.5rr. Not enough performace gain to warrant
the 1.6's and then F&^%k up the motor 'cause you won't check.
Never assume any thing.

 

makes an a$$ out of u m e.

The kit also included comp's retainers, and I called comp and they say not to use the oil shields. So do the signs point to a 1.73" installed height? I can only measure the installed height, but I have no way to compress the spring when the head isn't onthe engine.

 

GilmourD:
You have a strange sense of engineering ... Ha Haa hhaa.
You would get just as much "full lift" wether your rocker studs were a little flexed (bent) or not. As long as your lash is the same.
The 416 heads have a deeper exhaust spring seat.
If you don't run the stock rotator style exhaust retainer you'll need a stack of shims equal to .105" to correct the installed height.
that would be a .060+.030+.015" shim under each exhaust spring seat. then your springs would have equal installed height
with stock retainers.

 

You can compress the springs in a vise and check the coil bind height with a caliper.

Don't ask CHECK!!!!

 

hey you know what I remember that my exhaust retainers WERE larger than my intake ones when I took them off. So it's safe for me to run 1.6's on the exhaust side, it would almost correct it. Am I in la la land or does this make sense?

 

It's not the studs that are flexed. It's the rockers themselves. These are 416s from an 83 TA. I'm sure I'd be running more like 1.4:1 ratio rather than the theoretical stock 1.52:1.

I'm unfortunately using the rotators for now, cuz I need to get the car done ASAP. It should've been done last month because my bro and sis have to wake up earlier now to walk to school cuz i need to rob the soccer mom van to get to work. I do plan on new heads soon (Pro Lightning 180s or Vortecs with intake)

 

NO!!! If your head has the deeper exhaust spring seat to accomadate the rotator spring retainer and you use standard retainers your spring installed height would be 1.84+"..

Your spring pressure would be reduced a lot.
You need to shim the spring seat up to correct this.
Spring shims are cheap.

Most all small blocks only respond to 1.6 rockers on the intake side, so putting them only on the exhaust side is a waste of time.

 

Don't ask CHECK!!!!

Of course I will check before I put anythin on the car. But I was hoping I'd get a somewhat definite opinion before I go make an order from scummit. That way it will save me from having to order twice. I really think that due to the fact that i am using 16 of the same retainers, as opposed to the bigger ones on the exhaust, I can put 1.6's on the exhaust side, which was my goal. These are 415 casting heads btw. Did they also have those thick retainers on the exhaust like the 416's have?

 

You're really assuming a lot there. Your rockers are not really that bad. Not as bad as the roller rocker manufactures would want you to believe. Ha Hha HHaa!!!
Note to self : By stock on a roller rocker company.

In a running engine at high rpm you very well may see
more than the gross lift, because of "valve loft".
This is when at high rpm then valve lifts a little higher at or just after full lift. This is because of kinetic momentium.
The cam companies actually design their grinds around and take advantage of this action.
When this valve loft becomes exessive, its called valve float.
Valve loft is good to a point, valve float is BAD!!
that's why they recomend a minimum .060" extra clearance
in the valve travel.

 

I see most of the dual pattern cams having more lift on the exhaust side, and since exhaust valves are smaller, it seemed logical to me. This guy is going through all this work building me a pair of heads for my cam I think I might just get some 1.5 ratio roller rockers and then I won't have to lose sleep about buying new springs, seals, shims, etc. I don't know if there is more power gain with the fact that a rocker is full roller, or with it being 1.6 ratio. But I know I will reduce friction with the 1.5 roller setup.

 

You have the 415's there, look for your self. I have the 416's here, They definatly are machined to accomadate the rotator style exhaust retainer.

If you want an opinion, yes you can make it work. IF.....

Putting the 1.6's on the exhaust side only is a waste of time.
It's the intake side that needs it.
As you increase the rocker ratio your required spring pressure becomes more critical ( faster valve action).
Thats why running the 1.6's on the exhaust side with out shimming up the spring to the proper installed height
is likely to result in decreased performance overall.
(Valve float)
No flame intended here but, you're really lookin' for a f&^*% up here.

 

415's are in the mail and haven't arrived yet. The heads I was talking about before when I mentioned the thicker exhaust retainers are my current "mexican" heads. I know anything can be made to work with anything, I just figured since I needed rockers I'd try to gain some lift as well. If I were to get the 1.6's I'd probably have to get the louis tool out and clearance the guides to make the rockers fit. I think my best approach to this is to listen to the guy who built the heads- and he put in those springs for that cam. So if I get the 1.5's I won't have to dick around with anything. I really do appriciate all the help, even though it took me a dozen posts to come to a conclusion. Thanks-Randy

 

I see most of the dual pattern cams having more lift on the exhaust side, and since exhaust valves are smaller, it seemed logical to me.

Trouble is, when it comes to an internal combustion engine,
what appears to be logical often is not.
Stock Small block exhaust ports don't usually need or benefit from more than about .480" lift.
Dual pattern cams have more lift on the exhaust side because
they have more duration ( bigger lobe)
It's the longer duration that they are after in their design.
The extra lift is only to make the lobe shape smooth. to control the valve motion with the least amount of spring pressure.
Speaking of pressure the exhaust valve is smaller mostly because the exhaust is under much more pressure than the intake side. in a running motor.
If you had access to a dyno you're assumtions about
what makes a motor make power or more power would be a lot different. A lot of engine builder s that want to get the most out of a stock or near stock head actually often end up with a cam
that has more intake duration than exhaust duration
and lift. You can emulate this by useing 1.6 rockers on a single pattern cam's intake side only.
I'm giving away too many secrets......

Try it..... have a good day