All B heads are not created equal

[na svt]

All B heads castings are not the same. The combustion chambers of the earlier castings, 93-95, do not have the same potential when used in stock form.

Many people buy B heads with the thought they all make the same power making potential. Also, there is always someone trying to pass off Mark 8 heads as Cobra heads. Looking at the combustion chamber is the easiest way to tell the two apart.See the pics below:

I only show two part numbers below but will start a "good" and "bad" list.

[me32]

nice pics, great info. while your add it can you give the cam info of both heads too

[na svt]

Originally Posted by me32

nice pics, great info. while your add it can you give the cam info of both heads too

Mark:
intake 184 deg dur
exhaust 196 deg dur

Cobra:
Intake 204 deg dur
Exhaust 196 dur

[metalman302]

The older Mark 8 heads also had crappy springs while the newr ones had beehives.

I have a 97 Mark 8 motor and it has the AD heads.

I also have a 95 Mark 8 motor and it has beehives and has AA heads. I may pull these and be able to take a peek, not sure yet. Maybe someone else can verify.

[Erich]

Can the older heads be reshaped to resemble the newer ones?
Erich

[na svt]

Originally Posted by Erich

Can the older heads be reshaped to resemble the newer ones?
Erich

Yup, I'm in the process of doing that to a set right now.

[Erich]

Here are some shots of my heads before and after I had work done to them. they are 93 Mark VIII heads. Does it look like I had improvements made as far as that shrouding?


Erich

[na svt]

nope, they are still shrouded

[Erich]

This is pretty irritating. I totally did not know there was a difference till recently. I could have easily swapped these for later heads.
Erich

[metalman302]

na svt, I think I may have posted this in the other thread...

Is there any truth to mark 8 heads using different diameter valves and valveseals than cobra? THe SHM book said this but there was a few errors in that book.

These are beehive springs correct? These are the AA heads on my 95 motor:

[na svt]

Those are Beeehives. Also, the Cobra heads have a "Z" in the part number.

[Erich]

I got my info that the heads were the same from that hyland book. I knew about the springs and had them changed to beehive.
Erich

[metalman302]

I blame Hyland. He even said Mark 8s had 8 bolt cranks.

[assasinator]

i removed the shrouding when i ported mine. if you remember.

[assasinator]

its difficult to quantify how much the shrouding hurts, but on 3v heads, the shrouding is the majority of the flow gains in ported 3v heads.

[Erich]

I was wondering how much that shrouding hurts. I thought the transition and bowls were the worst part of those heads.
Erich

[na svt]

Originally Posted by Erich

I was wondering how much that shrouding hurts. I thought the transition and bowls were the worst part of those heads.
Erich

The short turns are the worst part but the only way you can fix them is to raise the port floors. Raising them would also increase velocity by reducing the port volume.

[ModularSpeed]

Originally Posted by assasinator

its difficult to quantify how much the shrouding hurts, but on 3v heads, the shrouding is the majority of the flow gains in ported 3v heads.

Yes, but unshrouding valves on any application helps.

[metalman302]

Originally Posted by na svt

The short turns are the worst part but the only way you can fix them is to raise the port floors. Raising them would also increase velocity by reducing the port volume.

Do you mean you are adding material to the port in that spot?

How much hp do you think the shrouding costs on a mild na car? A few hp maybe 3-5?

[ModularSpeed]

^Yes. You basically re-shape the runner by adding material to raise the floor, and remove material in other areas when reshaping/porting.

[metalman302]

Originally Posted by ModularSpeed

^Yes. You basically re-shape the runner by adding material to raise the floor, and remove material in other areas when reshaping/porting.

How much does this typically cost for that? Would it make the low end of a NA B combo comparable to a C head?

Thanks

[Erich]

Can't you just grind down the short side to make the transition smoother?
Erich

[na svt]

Originally Posted by Erich

Can't you just grind down the short side to make the transition smoother? Erich

It's not an issues of it needing to be smoothed. A good short turn radius is not sharp. The B head radius is very sharp and grinding on it will only make it worse. In order to make the short turn radius larger you have to add material to the port floor.

[assasinator]

imo all you can really do to the primary is add a little flow. there is a shelf and not a turn from the factory. i added better flowing valves, and deshrouded the primary. its going to add some to it. but thats all intuitive. the flow bench guys are the only ones who know exactly how to get more. raising the roof a tiny bit and altering the roof of the bowl to turn the air more perpendicular to the valve should help some also. it should have the effect of compressing the airflow near the valve and helping the short turn indirectly.

too bad the primary sucks so bad. my heads are comin off soon enough. maybe i can flow bench the stupid things this time. maybe.

[46callaway]

My 98 Mark VIII heads are RF-F6ZE...

[metalman302]

Originally Posted by 46callaway

My 98 Mark VIII heads are RF-F6ZE...

Same here on my 97 Mark 8

[na svt]

Originally Posted by assasinator

imo all you can really do to the primary is add a little flow. there is a shelf and not a turn from the factory. i added better flowing valves, and deshrouded the primary. its going to add some to it. but thats all intuitive. the flow bench guys are the only ones who know exactly how to get more. raising the roof a tiny bit and altering the roof of the bowl to turn the air more perpendicular to the valve should help some also. it should have the effect of compressing the airflow near the valve and helping the short turn indirectly.

Raising the roof will increase the port volume and further reduce velocity and that (velocity) is just as, if not more important than flow.

[570cobra96svt]

Is it true another difference you cant tell, is the the intake ports/IMRC's?
The cobra has a square port & a round port, and the Mark8 has 2 oval/round ports.
Also the IMRC'S in the cobra are electricaly controlled by the ecu, were as the mark8 is vaccum.???

[assasinator]

the primary port is the same as the cobra. one square entry, one round.

[assasinator]

the imrc's for 97-98 mark viii is the same part.