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"308 Heads"


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11 replies to this topic

#1 mountainrich

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Posted November 27, 2009 at 07:57 pm

Are 5.2 and 5.9 "308" heads the same? (Thanks again Rodger) I,ve seen some 318 heads w/ larger intake valves than 360 and want to be sure.

#2 dana44

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Posted November 27, 2009 at 08:57 pm

Are 5.2 and 5.9 "308" heads the same? (Thanks again Rodger) I,ve seen some 318 heads w/ larger intake valves than 360 and want to be sure.



The 308s was the beginning of the 318/360 engines sharing the same heads, intakes and exhaust manifolds. There have been a couple sizes of valves over the years, 1.78 (273/318), 1.88(340/360) 1.92 (Magnum engine V6 and V8) and the rare 2.02 intakes for 340s. The only things that have never been was a 1.88 or 2.02 on a 273 or 318 (until the 308 heads) the 360 never had a valve smaller than the 1.88.

#3 TWX

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Posted November 28, 2009 at 12:21 am

According to my interchange book, the 4448308 head was basically the last casting in the '89+ LA era engine, on the 5.9/360, while the 4323302 head is the 5.2/318 equivalent. These heads have smaller chambers and better ports than the other factory heads. The 308 was not the only head used on the later 360s though, so you have to pull them and look at the casting number on the bottom of the intake runner to see what they were. I found vans to be a good source because people don't scavenge them as much as trucks. I do not think these were used on any 318 engines, but I will not swear 100%. At this point, remember, there weren't really any cars left to install V8 engines in, so there weren't any police high performance packages. There was a "576" number I've seen associated with these 308 heads, possibly as a dealer-parts-aftermarket head, but there was previously a 576 head that isn't high performance, so don't assume that a "576" head is just as good.

The chamber on the 308 is much bigger than on the 302. If I remember correctly, the 308 still has 1.88/1.60 valves.

Some people erroneously think there's a 4323308, but I have never seen them and I've taken apart several engines looking for the heads, and that number isn't references in the buildup book that I have either.

#4 mountainrich

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Posted November 28, 2009 at 09:58 am

Would there be any benefit in putting 302 heads on a 360 if you want torque?

#5 dana44

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Posted November 28, 2009 at 08:23 pm

Would there be any benefit in putting 302 heads on a 360 if you want torque?



There is room for major improvement in the design of the quench area valve bowl in the head, it is both very restrictive, but fixable. Higher compression will result in more hp and torque, but it doesn't do as much as it could if the chamber remains the way it is. The guys have named it "edging" of the chamber, TWX has some pictures of a set of Edelbrock heads I ported for him, the 302/308 heads have a taller lip that deters the proper flow to make more power, that's all. This lip keeps the flame within a four inch by two inch area, forcing the flame to kick back into itself too early in the flame travel and piston location, essentially making the engine a small oval of fire instead of the full 3.91 or 4.0 inch bore higher up.

#6 mountainrich

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Posted November 28, 2009 at 11:01 pm

So the valve edge is too close to the chamber head making the cone break up w/o the edging?

#7 dana44

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Posted November 29, 2009 at 01:28 am

So the valve edge is too close to the chamber head making the cone break up w/o the edging?


Not sure what you mean by the "cone". Picture this: A four inch bore with a piston going all the way up to the face of the cylinder, the combustion chamber and quench pads close the area of the cylinder explosion down to the size of that valve pocket, the explosion is a controlled blast against the top of the piston, and the speed of the piston pushes the fuel/air into that valve pocket and causes a swirl at the lip of the valve pocket from the quench area of the head. Picture this: drop something flat, like a board, against a mud buddle, you get a slap and a forced "blow" into the outer sides of the board, splash curls and wets the top of the board, totally uncontrolled. Now, drop a barrel against the same in the puddle and you get a wave, which is controlled and simply goes outward. This is one direction of force, now look at the other side of this. A spark starts a flame wall explosion inside this pocket. With a sharp edge the way it is, the flame slaps the raised lip/edge and turns back on itself (already burned, so worthless to do this), along with a curl of the explosion, doesn't go into the quench area, until the piston is down and the area opens, but it is already a vacuum area, waste of energy there. This is similar to the kinetic energy of hitting the piston with a hammer...you can hit it faster and as hard as you want, you will get the work done. Cut that lip so it is at the same angle as the valves themselves (the plane they are on), and when the piston comes up, you now have a controlled compression of the fuel/air, not a woosh, and on the other side of this, when the spark starts, it goes out and wedges itself into the top of the piston and quench area all the way to the outside of the piston to the cylinder wall, burns cleaner and has more torque and hp (force overall) at a higher compression, thus more work done at a higher compression, thus cleaner, faster, more efficient burn overall. This is equivalent to hitting the piston with a larger hammer. The bigger the hammer, the more work gets accomplished with each swing (compared to the smaller hammer earlier), and if you increase the speed of the bigger hammer, even more work is being done. If you put a domed piston in this engine, the top of the piston also needs to be altered so there isn't a flat wall, rounded, no dishes, lots of curves to allow the flame to travel farther than the reverberation of the flat against the spark plug side, over the top and to the other side without the curls and walls to redirect the started spark. Why do you think high compression domed pistons work well at high rpm, poor at low rpm? Everyone is getting the compression up, but not properly controlling the flame itself, the higher compression works better at the upper rpm because a smaller amount of the piston is being used and doesn't work well at low rpm from lack of burn.

#8 mountainrich

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Posted November 29, 2009 at 08:20 am

Thanks- I understand this. Have seen this before. This technique allows quicker and more "explosive" flame propagation-more even and quicker pressures to the piston. Some grooves are suppose to help this also. Initially I thought there was an obstruction to the fuel mix's "cone" flow around the valve- causing this to break up along the edge. I get what you're saying but obviously I need to seen the head and/or pictures. I'll do some searching-thanks.

#9 dana44

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Posted November 29, 2009 at 03:36 pm

Thanks- I understand this. Have seen this before. This technique allows quicker and more "explosive" flame propagation-more even and quicker pressures to the piston. Some grooves are suppose to help this also. Initially I thought there was an obstruction to the fuel mix's "cone" flow around the valve- causing this to break up along the edge. I get what you're saying but obviously I need to seen the head and/or pictures. I'll do some searching-thanks.



These pictures give an idea what is involved, the 308 heads just have a larger lip.

http://www.allpar.co...howtopic=119060

With the edging, grooves aren't needed, and I look at it as being akin to using a pick instead of a wedge to get the explosion focused in the right direction. The cone you are talking about is the bowl under the valve itself. It is best to blend from the valve seat to the valve stem guide, open the sides of the bowl and keep a curve from the valve guide to the valve seat, don't do a straight wall from the guide to the valve seat ( it causes an eddy at low rpm). Think tulip, where it flares outward to the valve seat, not a vertical vase, because the flow expands as it travels, straight sides fill and stall, which is not what you want. You aren't going to find too many pictures other than these, very few people truly understand what is going on with the flow or don't feel it is necessary.

My mentor and I discovered this problem when I had the 283 in my 39 Nash have the rings slack in it from not running. When we pulled the heads because she was smoking, we saw the cylinders weren't burning clean or complete. He located the reason, the lip at the center of the combustion chamber causing a curl that was not allowing flame to travel all the way across the piston top. We removed the lip, put rocker studs into the heads to keep the rockers in place, and needless to say, it made so much power and changed the tone of the engine that his mom called down after breaking the engine back in to shut the car off (open headers at the time) because at two hundred yards away, dishes were rattling on the shelves of the house, just like his big block Dodge would do! Been doing it since 1979 with improved mileage, performance, cleaner burning engines, 13.3:1 compression on 87octane, and the slight drop in compression on stock engines (a 4.9 Cadillac V8) that was actually dyno'd as 275lb-ft torque at the flywheel increase to 349.7lb-ft torque at the wheels (there was a 4800rpm rev limiter that prevented the hp number, stock 200 at the flywheel, estimated to be above 300hp after three pulls, but it knocked 1.2seconds off the 1/8th mile times, 9.335 consistently compared to 10.6s, which prompted the head job to start with). We played with engine dyno builds for weeks before I got to do the actual work, we were going to be happy with 275hp and 300lb-ft torque, but the dyno models did not pick up the flow/flame travel efficiency ability of edging under any and all attempts to depict them.

#10 Rodger

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Posted November 29, 2009 at 06:04 pm

Rich

All 273 and 318 Heads have a smaller port size at the
Intake Manifold, the in-let to the heads and the out-let
from the heads than 360's.

The 360 has 42 more cubes than a 318 and needs some air
vol to feed the cubes.


Rodger & Gabby
COS

#11 mountainrich

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Posted November 29, 2009 at 07:06 pm

Really thinking of the 302's. If the engine runs out at 5K, I don't care. The higher velocity (and hopefully mix) is what I'm after. MPGMIKE has given me some ideas about keeping the flow turbulent- I mean mixed well. Plus I've got other ideas about mpg's. I'm also gonna keep my 318 SP2P intake.

Edited by mountainrich, November 29, 2009 at 07:07 pm.


#12 TWX

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Posted November 29, 2009 at 10:47 pm

I personally wouldn't put 302 heads on a 360, at least not without significant modifications, like increasing the valve size and enlarging the ports.


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