906 valve lift? And pistons

[salteen_dude]

What's the most lift I can get out of my 906 heads? Will changing springs help any and what else can I do?

Wanting to run a piston with a good valve relief. Trying to keep it between 10 and 10.5:1. I brought the heads to work, I'm going to cc all the chambers later once it's cleaned up.

I've been weighing the pros and cons and I think I'm going to pull the trigger on a Hyd roller cam. I want something big enough to give me a lopey idle, but also something that will remain streetable (6 pack, and 440 should help plenty there).

May consider a flat tappet cam though. Unsure of the hydraulic roller conversion. I have 0 experience with linked lifters and they look like a failing design imo.

TIA -Paul

 

[Lefty71]

Spring change is to match the cam profile. You typically get more lift on '906's by cutting the guides down and using the proper keeper/retainer combo.

I've been reading some of your recent posts....... just a word to the wise here, I'd do a lot more reading before pulling any triggers if i were in your shoes.

Best of luck, Lefty71

 

[zyzzyx]

You didn't mention if you have power brakes or manual. If you have Power brakes, your first
responsibility is having enough vacuum to operate the booster. if not, it'll sound real kool as
you slam into the car in front of you! Deck height matters too. You can only get so much lift
out of 906's before the retainer bottoms out on the top of the guide as mentioned before. Not
as easy as you think.

 

[salteen_dude]

You didn't mention if you have power brakes or manual. If you have Power brakes, your first
responsibility is having enough vacuum to operate the booster. if not, it'll sound real kool as
you slam into the car in front of you! Deck height matters too. You can only get so much lift
out of 906's before the retainer bottoms out on the top of the guide as mentioned before. Not
as easy as you think.

I do have power brakes, and power steering, air conditioning.

 

[lewtot184]

.480 lift is pretty safe with a stock guide boss. Rocker ratio and aftermarket retainers play a big factor in retainer to seal/guide boss clearance. Stock magnum springs will coil bind quickly and won't take much if any lift more than a stock cam. With power brakes don't chase some lumpy cam.
.

 

[HawkRod]

What's the most lift I can get out of my 906 heads? Will changing springs help any and what else can I do?

Wanting to run a piston with a good valve relief. Trying to keep it between 10 and 10.5:1. I brought the heads to work, I'm going to cc all the chambers later once it's cleaned up.

I've been weighing the pros and cons and I think I'm going to pull the trigger on a Hyd roller cam. I want something big enough to give me a lopey idle, but also something that will remain streetable (6 pack, and 440 should help plenty there).

May consider a flat tappet cam though. Unsure of the hydraulic roller conversion. I have 0 experience with linked lifters and they look like a failing design imo.

TIA -Paul

The only way you really know is to mock up the engine and check the actual combination. There are so many variables: Deck height, piston height at TDC, valve reliefs, heads, valve size, cam lift, cam overlap, etc.

The compression stroke doesn't matter since both the valves are obviously closed. The concern is overlap; roughly 10* BTDC until 10* ATDC. Cams with overlap will have both valves open at this time. It you want to go with an aggressive lift you need to mock it all up to be 100% certain.

 

[Cranky]

"I want a lumpy idle....." I've heard that so much over the years. Heck, I can make a stock cam sound lumpy. Do your homework grasshopper. It took many of us years to gather knowledge before the internet became available in your pocket. Btw, do you know why a cam will give you a 'lumpy' idle? You can also take a cam that's a bit lumpy sounding and advance it a bit and it'll do two things....the idle will get a bit more smooth and it will move the power band into a lower rpm range. Learn what advancing or retarding a cam does and NEVER EVER install a cam using the dot method!

 

[Rusty34]

Cranky is on the money here. In order to change your cam you will need to get up to speed on the many variables involved with changing cam timing, any of which can get real expensive in a hurry and ruin your day. Assuming your new cam is installed you will need a good large diameter degree wheel attached securely to the c/shaft front snout and with a pointer attached to reach the OD of the degree wheel know and have the proper tools to find exact TDC with your pointer on 0°. This is a very critical step. Make sure you have TDC and it will repeat several times. Now with light pressure checking springs installed on the Int and Exh of #1, rocker arms installed and lash adjusted to zero lash position your 0 to 1" dial indicator stem over the #1 Int. spring retainer and adjust its angle of travel so that it closely lines up with the intake valve stem angle of travel. Now go through a couple of revolutions to check for clearance between the bottom of the spring retainer and the top of the valve guide and make sure the rocker arm's travel does not interfere with the dial indicator stem's travel and you don't run out of dial indicator range as you approach full lift. Now zero the indicator and get a long wrench on the cam gear bolt to pull back on it while pushing forward on the long c/shaft wrench and as you approach .050" before full lift, get a degree wheel reading. You want to push the two wrenches apart while taking your readings to eliminate backlash in the gears and chain for accuracy. Now go through full lift and take a second degree wheel reading at exactly .050" after full lift. Add the two together and divide by two to get your exact Intake Centerline angle. Now compare this reading to the cam card spec for lobe separation angle. the best compromise place to be is about 2° advanced which means your Intake Centerline angle will be 2° less than the lobe separation angle.

 

[HawkRod]

Now with light pressure checking springs installed...

Just one thing to add. The actual engine springs should really be used. The higher rate springs will change timing, so conversely using really light springs is not ideal. As a matter of fact, if we were really were to do it right we would spin the engine at RPM to check all this, because the dynamics of the valvetrain in motion again change things. But must of us cannot do this (really high end engines do this, like NHRA and NASCAR). But at least using actual spring rates will get us close(er).

 

[eldubb440]

. Heck, I can make a stock cam sound lumpy

just pull one of the plug wires

 

[Rusty34]

The actual engine springs should really be used. The higher rate springs will change timing, so conversely using really light springs is not ideal

I was trying not to complicate it by splitting atoms for someone who has not done much like this before. What you are saying is technically correct about cam timing being affected by Light Checking Springs in place of the Final Assembly Springs ONLY because the normal load placed upon the timing chain takes up any slack in the system. This is why I advised placing a long wrench on the cam bolt to use as a handle to push down on at exactly the same time you are pushing down on the long handle on the c/shaft front snout just as you are arriving at a checkpoint on the degree wheel. This method also takes slack out of the system to get accurate readings. The ONLY difference using Light Checking springs is what ever numbers you get for V to P clearance you can add about .010 to both for actual clearance numbers.

The main purpose for Light Checking Springs is to make it easier to check Piston to Valve clearance while turning the engine over. The place where you want to check Piston to Valve clearance is in the Split Overlap Position where both valves are open at the same time. This point will be around TDC as the Intake has already started opening and the Exhaust is almost closed. The Intake Valve will be closest to the piston at around 10° ATDC while the Exhaust will be closest to the piston at around 10° BTDC. Easy to push down on Light Checking Springs to get dial indicator readings. The 10° BTDC and 10° ATDC is approximately where you want to begin checking. You should check both sides of the TDC Split Overlap in small increments between about 9° to 11°. The actual closest point will be close to 10°

 

[Cranky]

just pull one of the plug wires

That and pulling a vacuum hose or both