Cylinder Heads 101

-
BJR, what is your thoughts on the 308 heads? I am planning on a decent 360 for my Dart. Block and crank are a '72 vintage, want 9.0-9.25 CR, and a cam about 1 step above a '68 340 stick cam. The tranny is an A-999, the rear is an 8 3/4 with 3.55 sure grip(489 case). I have heard that the 308 heads are very effecient and require only minor work to get them to flow well, while "Going to town" on these castings is a mistake. What would you recommend :notworth: ? This engine will get proper machining done (including deck plating and balancing), but nothing too exotic that is only useful in such applications as drag or road racing.
 
6t8 Dart,
The 308 heads have a small window opening because of the big hole for the pushrod, and a larger bowl area. The larger bowl area is where the flow comes from, but this is very misleading as the bigger the bowl gets the slower the velocity will get even though the head will flow more air with a larger bowl. This is the same thing that Indy cyl.heads had done with the 440-1s, with these heads on a 446 engine you would have to turn the engine up to 8000 rpms to make them work. The 308s don't really flow that much better than that of the older counterparts when done properly. For the street engine that your talking about I would just do a bowl cut with a 75R7 cutter and leave about .060 before the valve seat for a additional angle to be put in of your choice. I would square deck the block a minimum amount and deck the heads a minimum amount, then run the .022 gasket from mopar, this should give you your 9.0-9.25:1 compression ratio. Most blocks will take .015-.020 to clean them up just as the heads will, just this difference will increase your compression ratio about 1 point and as the 360s were 8.5:1 or so from the factory this should put you where you want.
Then I would use a .484 from mopar or equiviliant cam, this may not sound like much but the difference is in the duration @ .050, and if you want a mech. cam the use the mopar .528 or equiviliant from who ever. But keep your centerlines and duration @ .050 similar or the driveability will be lost.
How much converter will you be running? If your not going to a stall converter then the .528 is out. As this cam will need at least a 3000 stall. Then I would use the .484 cam profile with a stock converter as the duration at .050 is a good bit less and more compatiable with the lesser converter.
Hope this helps you in your decisions.



BJR Racing
 
Hey BJR, again excellent post. I have had better results with the .528 over the .484 cams. The .528 has 60 degrees of overlap and the .484 has 68 degrees. I always have better vacuum with the solid .528 than the .484 hyd cam. Everthing else being equal. My compression is on the low side @ 9.02 to 1. That .484 cam is too soft on the bottom. JMHO. Anyway ..keep up the great posts. Terry.
 
Hello all,
Ok this is my first post here but this thread has realy got me interested. I have never ported a head and realy an not sure how to go about it.

BJR, you said this to 64Ragtop;
Mr.64, What you have asked about the smoothing and the gasket matching. First DON"T SMOOTH THE PORTS, leave them as rough as you can as this helps atomization and doesn't hurt flow. Actually super flow says it has no effect on flow, but smoothing the ports will cause the fuel to puddle and cling on the port walls on the intake side. Causing a rich condition in the engine. But gasket matching and doing a good bowl blending will pick up the air flow greatly and HP, this will give you 80-85% of a fully ported head when done properly with a good valve job. So yes it's well worth it.

Can you or anyone for that matter please tell me, or post a link on how to carry out a mild port job to a set of 360 or 318 head's,please? Im in the same boat as 64ragtop. By the way I have a '69 right hand drive Barracuda and live in Scotland. Thanks.
 
Trigger andy,
The main thing is to get the work done by a shop that can do performance, first and formost. If, and I mean IF YOUR DOING THIS YOUR SELF I can send you some shots,-pics. of how it should look. My E-mail is [email protected] or IM me here, and leave your e-mail address so to send pics.


BJR Racing
 
Andy, What they are talking about is a thing called a "boundry layer". any material flowing donw a tube has friction from the sides of the tube. In a port's case, the material is air, carrying fuel in peices as small as molecules, and as large as visible drops. The fuel is heavier, and tends to want to "fall out" of the air stream. By leaving the rough surfaces, you create all kinds of tiny turbulence along the walls. These tiny eddies and stuff makes it harder for fuel drops to attach to the walls. Also, you reduce the surface area for heat transfer from the port wall to the mixture by a bit, which can also lead to fuel puddling at low engine speeds and larger overlap cams. Really, there is always a boundry layer of some size, and a rough surface vs smooth makes a very small difference in the thickness of the layer. On the exh side, smooth surfaces are harder for the carbon and stuff to attach to, so usually you want a nice smooth exh side. In intkae ports, I dont even touch the floor. The majority of the flow ina stock port is along the top and the shorter side wall (the "inside" port wall) until you get to about an inch upstream of the sort side radius into the bowl. If you've ever looked into a clean intake port, you can see the fuel stains where the air is moving slowly. The goal of a head porter is to keep the port as small as possible for the given engine, to keep the port stable and fast. Not to straighten every bend, and enlarge everything to the max.
 
The goal of a head porter is to keep the port as small as possible for the given engine, to keep the port stable and fast. Not to straighten every bend, and enlarge everything to the max.
Click to expand...
And with that "Money quote" well said, it is amazing to me how offten someone will say the 2.02 - 1.60 360 heads made there stock 318 pull like a feight train as there only mod or with headers as the only other mod.
Balance in a package is were it's at!
Velocity is whats need. Even more so for the street.
 
Hi trigger Andy, nice to see you got over to this site. The only porting i've had to my 'new' 360 heads is in the bowl area. as i understand this area if ported correctly is a win/win modification. I'm not running deep gears or high lift cam to require the heads to be big valve/big ports.
 
Well said Rumblefish. 'The most flow with the smallest port'. Rumblefish, Moper, BJR..lead on gentlemen. That is what this board is all about. Terry.
 
Hi All ! Trying to sort out the last of details on my motor project for my 66 dart vert.

I need some advice from experienced folks with porting the #302 cast late 318 head.

Heres where I am. 1.88/1.60 valves installed, un-shrouded the valves somewhat, hard seats on the exhaust. Bowls ported, intake port gasket matched.

Looking at the intake ports - these have a narrow point where the pushrod goes thru the casting. It also looks like that area is kind of tapered on one end the port. I assume this might be to induce "swirl" action ?

My questions:

1) Should I remove as much of the pushrod pinch point as possible or, clean it up some and leave it. If I am to remove material, about how much is a safe bet ?

2) I also noticed there is fair amount of the port taken up by the casting boss for the valve cover bolt, should this be taken out as well ? I assume if I grind it out and get into the threads that a thread locked stud would solve any leakage issues.

3) Is there an effective backyard mechanic way of measuring the pushrod wall thickness while doing this ?

Thanks !

:salut: :notworth:
 
66dartgt,
Remove as much of the pushrod pinch as you can and make it as straight as you can this will help greatly with the flow.
You can safely remove the boss from the valve cover retaining bolt and use a sealer when installing the bolt back in the head.
What I would do is use a straight edge and a sharp marking pen, make a mark at the top and bottom of the pushrod hole on the intake face, use this as a guide to keep the wall of the port as straight as you can. You will want to leave about .030 of material to be safe. This can be measured from the straight edge to where your grinding with a thin piece of material thats .030 thick or a feeler gauge. Usually the factory port opening is close to the point where you would have to stop grinding, if this hasn't been opened up yet. You can usually go straight in from the original opening and be safe, then match the port to the gasket, this is just another way of doing it.


BJR Racing
 
BJR; thanks for the advice! I will get after these heads sometime this weekend. I have to finish screwing with the intake manifold first.

I assume what you mean by making a mark with a sharpie, is to eyeball it and transfer the imaginary line for the inside of the pushrod hole to the inside of the port and then grind almost down to the mark. This will be a little hard since the ports are already gasket matched and nothing is left to directly mark on to, but I understand what you are saying. This looks like its gonna be alot of material !

Is there a way to repair a hole should one occur in the pushrod passage ? I assume JB weld or something like that would work ?

Thanks again !

:notworth:
 
I read through this thread, was wanting to know, what brand of flow bench you test on? what computer program is in your flow bench? what test pressure do you flow at? Is your bench a pressure drop style or a laminar flow unit? just asking,
 
perfacar,
It's a Superflow bench, I flow at 28" and it's a pressure drop style. As for the computer program it is seperate from the bench, it's a PerformanceTrends Pro it was about $1000.00 when I bought it a few years ago. I have been looking into a new program that should make this look ancient, but it's $1400.00. I should have it soon.


BJR Racing
 
BJR good to see you on here again. Yes I use the same method. The push rod pinch can be safely removed up to the original port dimension, if not gasket matched. I also use a Helguson 'E' tool to directly measure the wall thickness at the pinch. I use both to be safe. I try to leave .060 on street work and .030 on race work. Hope to be down your way real soon BJR. Work hasn't let up much, will call you then. Terry.
 
You must log in or register to reply here.
-

Back
Top