I thinking of dropping a Crane Powermax cam 204/216 duration with .427/.454 lift (1.5) into my LG4. My question is, I want to use 1.6 roller-rockers and I think this pumps the lift to .455/.484. Is this possible without machining the heads for larger valvesprings? I've heard that conical valvesprings like the ones from Comp fit in the stock seats and support upto .520 lift, but I am not sure. Is this lift even possible at all? Any help/info would be great.

 

you should be ok. run the springs your cam grinder says to run, or a similar spring. stay away from gmpp springs and k motions, crane, comp, and lunati all make good stuff. if you need larger spring seats, and i doubt you do, it only cost around 2 dollars a seat and springs for your cam should be in the 60 dollar range. even if you can should run with your stock springs considering how cheap they are it'd be a good idea to replace them. springs get weak and tired over time.

 

When F-Bird'88 did a dyno simulation for me, using Performance Trends Engine Analyzer, he found that 1.6 rockers with this exact cam would work fine on the intake valves, but were worthless on the exhaust side. You just can't really improve the exhaust flow on a 305 without some porting and polishing to the head.

So that solves any problem you might have had quite nicely!

Just get 8 of the 1.6 rocker arms and reuse your best 1.5 rockers on the exhaust.

 

The roller rockers I want to use, SUM-6906 3/8 stud, only come in sets of 16 so i can't buy just eight. They will still improve power because they're roller right? Oh, do I need self-aligning rockers,or the normal kind with guideplates? Thanks for your help guys.

 

I think if you phone Summit, they will fill your order the way you want. If you choice to got this route. The 1.5 and 1.6 rockers cost the same.

At any rate, you'll have to look at your heads to see wether they are designed for self aligning rockers or not.

If they have a machined slot that the pushrod is guided by
or guideplates, then use conventional rockers.
If your heads have a larger round hole where the pushrod comes through the head and no guideplates then you will need to use self aligning type rockers or install guideplates.
If you have the machined slots in the heads you may have to lengthen the slot towards the stud to accomodate the 1.6 rockers. The change in ratio is accomplished by moving the pushrod seat towards the rocker stud on the rocker.
I have a method of doing this without using a "LOUIS TOOL"
(drill guide). It involves a modifyed 5/16" rat tail file in a drill.
You can even do this while the heads are on the motor with a little creative housekeeping.

If you have guideplates you may have to loosen the rocker stud
and adjust the position of the guide plates.

 

Thanks for your help guys. I think I know what I'm doing now. Just for fun, how much do you think that powermax and 1.6 rollers is worth over the puny LG4 cam?

 

Without any head work? Maybe 25 hp or so.

 

25 HP or so, not bad. With a somewhat short duration cam such as this, and using Rhoads lifters, will there be a noticable loss in low-end torque (daily-driver)?

 

I can't say I've noticed any, though I've also replaced my stock 2.73 rear gears with 3.42s.

DD 2000 shows the torque and hp curves to be almost identical until you get out to 3500 rpm. Then the Crane 260 cammed engine just walks away from the peanut cammed one

 

Could you add some punctuation so we know where the "stay away" ends and "good stuff" begins?

I've got GMPP springs on the Camaro, they haven't floated yet with several excursions into the 6200-6300 range. However, I have 502 crate take-offs on the 396, I'd better be in the process of shifting by the time the tach reads 5500.

I spend a couple of hours at the Super Chevy show helping a fellow racer replace a broken K Motion spring on his 468. Of course, that SG car has about .765" lift...

 

This is a little off topic, but I've heard that with a high duration cam you can get some "free" EGR because of the increased time the exaush valve is open. Does this actually work, and would you pass a smog test?

 

They did with the ZZ4 conversion kit, apparently.

 

well five7 i understood exactily what i was saying. guess only i under stood the babble. what i meant was comp, crane and lunati make top of the line parts that shouldn't give you any problems