Chevrolet Nova Forum banner
1 - 6 of 6 Posts

·
Registered
Joined
·
5,249 Posts
Discussion Starter · #1 ·
Anyone running these heads?

Have a set on a 408, 6" rod motor 2 valve relief flat tops. XE 284H cam .501/.510.

Springs are 1.55 and good for .700 lift. Is this too much spring for a hydraulic lifter of the non roller type?

valve length is 5.060 which is about .140 longer than stock, should i use a .100 longer push rod.

Bonus :)) In a 71 Nova, sub frame connectors, 4:88 gear 12 bolt, 750 holley, team g intake, compression should be 11:1 - 11:3, turb 350 highly modified, 3000 stahl, lift bars.....How fast will it go ?????????????
 

·
Premium Member
Joined
·
17,540 Posts
Heads are in the ball park for the size of motor assuming you are going to rev it up to enjoy those heads; other wise I would look for about 180 cc sized ports if you don't intend to let it rip.

Springs designed to control 0.700 inch valve lift will generally collapse a hydraulic flat tappet lifter. Need to verify with manufacture the maximum spring pressure recommended (don't forget that springs are rated at a linear rate in pounds per inch of compression). You will have to figure the spring pressure on your lifter from your maximum lift for the ratio of your rocker arm (standard is 1.5:1 for SBC) times the spring rate to determine open pressure. If you are not using but half of that 0.700 max lift spring the pressure may still be tolerable.

The correct length of your valve is determined by the head you choose. Thicker head decks with raised ports frequently require a longer valve stem (usually noted with an asterisk in the fine print). The manufacture of the head will tell you on their web site technical info portion the correct valve to use. You may also have to change your pushrod length to match the changed valve geometry. That is best measured after assembling the heads to the block with the correct thickness head gasket; rather than calculating what the value should be. Pushrods can be easily custom made to any length you want, based upon a final measurement with a pushrod length checking tool.

How fast will it go, no one now knows. But once you get it together and try it out, I'm sure we can make it go faster, by correctly tuning it, and making adjustments to the suspension as needed.


Big Dave
 

·
Registered
Joined
·
9 Posts
Comp Cams recommends that you use their 986-16 valvespring (132lbs seat psi / 322 rate) with the XE284 camshaft.

At .507" lift the 986-16 spring has an open psi of 295lbs.

The springs on the 215cc R head have 138lbs seat psi / 420 rate. Which means at .507" lift the spring has an open psi of 350lbs.

Are you using a 1.5 or 1.6 ratio rocker arm?
Is this a nitrous engine? If so, How much nitrous are you using?

The ports of our 215cc head are not raised, They are in the stock GM location. We redesigned the waterjackets to allow for the thicker deck.

We used a longer valve so as to facilitate a taller installed height on the valvesprings (The 215cc heads feature a 1.950" installed height whereas a stock SBC GM head has a 1.700" installed height).

When dealing with pushrod length there are a multitude of things to keep in mind that will affect the required pushrod length, They are:

1) Deck height
2) Gasket thickness
3) Camshaft base circle
4) Rocker arm ratio
5) Rocker arm design (Not all rockers are made the same)
6) Machining tolerance stack up.

Not all rockers maintain the factory GM dimension from the rocker stud to the valve tip. This affects pushrod length.

The "unknown" determining factor in pushrod length is "Machining tolerance stack up". Every part that is machined has a working tolerance of +/- a certain amount (As an example, If something has a .005" tolerance and is supposed to be 2.40" it can be anywhere from 2.35"-2.45"). Now consider how many machining operations are involved in the cylinder head itself & all of the individual components in the valvetrain.

Because of this, There is no way to give out pushrod lengths with 100% accuracy. You will need to get an adjustable checking pushrod & verify the wear pattern on the tip of the valve. You want the wear pattern to be in the center of the valve tip & you want to minimize the tip travel (.080" or less total tip travel).

If you do not know how to verify the rocker arm geometry, Email me & I will send you a file that outlines how to do so...
 

·
Registered
Joined
·
5,249 Posts
Discussion Starter · #4 ·
I got your email on the RPM air gap manifold. I was using a Team G part #3501 and actually found a manufature flaw that in my opinion is fairly signifcant. the thickness between the intak runners on all of the adjoining ports are 5mm, one set of adjoing ports it is 9mm. also on the same side of manifold, the bolt holes dont match up to the gasket from front to rear, but match perfectly on the other side of the manifold. this is real nice for a brand new manifold.

since you recommend the rpm airgap, the r-215 head in your add states use a 1206 or 1266 intake gasket. the rpm manifold manufacture reccomends a 1205 gasket. should i enlarge the ports on the rpm manifold, or leave as is?



I understand all the machining variables. deck height is stock
gasket thickness .038
stock base circle cam
rocker arm ratio 1.52
scorpion roller rockers (i understand holley red vs gold rockers are different)
i know if you have correct valve train geometry that the tip of the rocker should be in the center 1/3 of the valve tip and should not move out of the range during the entire movement of opening and closing of the valve.
 
1 - 6 of 6 Posts
Top