360 head porting for big power (500HP ?)

[skrews]

Thought I'd share my head porting project. 308 castings destined to go on my Left over parts 360 engine build http://www.forabodiesonly.com/mopar/showthread.php?t=198914&highlight=left+parts+360 . Got 442HP outta that thing. Looking to bump it up to around 500HP. The plan is swapping in these heads, replacing the the ol' .484 cam with a 248*/248* @ .050 106 lsa .563" Hughes solid cam, Moroso deep pan running 6 qts. with Milodon windage screen, and a crank case evac system. Pretty much all stuff I got kicking around. Also replacing the 4300-4500ish verter for a 5500-5600 unit ( horse tradin deal ). The ultimate goal is low 11s, on pump gas, using as many left over or scrounged parts as possible. Low buck as possible.

I will update this post as things come together.

 

[skrews]

Out of the box 308 castings. 1.88 OEM valve. tested at 28" SuperFlo 1020 bench.
.050--26
.100--54
.150--80
.200--117
.250--150
.300--164
.350--183
.400--195
.450--205
.500--207
.550--207
.600--202

What was the factory thinking when they came up with these ridiculous port choking flow killing guides anyway.

Looks like this after being drilled out for bronze guides and profiled to a good shape. Note trailing vein behind guide. V V V

 

[skrews]

Pushrod pinch on 308 heads much like the Magnum heads sucks as the hyd. roller cam required more pushrod clearance. The factory fix was to drill a bigger hole, which required more meat in the pinch area. Heaven forbid they slot the hole, but that may have cost 50 cents more per head. Out of the box min. width is .750 by 2.25 height. I was able to open the width to .910 while maintaining .050" thickness (measured with E-tool). Older heads can usually open up to around 1". Might try tubing the holes to gain more area here, got a few cracked cores to experiment with.

 

[skrews]

pic of windage screen mentioned earlier

 

[skrews]

Valve guides installed and pushrod pinch blended in and port entrance gasket matched.

 

[skrews]

On to the valve job. I got to play guinea pig, helping out one of the other shops in town figure out their seat and guide machine. Not as nice as the machine at the shop I work at, but it get the job done. Used a Serdi 3D seat cutter with 35* 45* 65* angles. Followed by an 80* bowl cut to within .100 from the bottom of the seat. Finalized with a deshrouding cut 20* bottom (horizontal) to .125 radius to 90* side (vertical).
Quite the difference in size there.

close up before deshroud cut

with deshrouding cut

Pic of chamber after all machine cuts. Exhaust info is coming.

 

[skrews]

Pics of finished chamber. Deshrouding cuts blended in, bowl blended in, and short side radius profiled.

short turn pic

 

[gliderider06]

That's awesome! I should have gotten you do do a set of heads for me when I was building my motor.
Great post. Keep it coming.

 

[skrews]

Pic of valve. Ferrea severe duty hollow stem stainless. 2.02 diameter 33* back cut to within .010 of lap mark of seat. One of the best flowing valves I've tested. These are circle track motor take outs (one season). They are about $40 apiece, gotta love them high dollar guys throwing out stuff thats better than what a lot of us start with.

 

[skrews]

Final flow #s
........int-1..........int2..........int3..........int4
.050--26..............29............29............29
.100--54..............64............64............60
.150--80.............115...........106...........97
.200--117...........157...........144...........143
.250--150...........180...........169...........168
.300--164...........205...........195...........196
.350--183...........222...........216...........219
.400--195...........242...........237...........237
.450--205...........261...........255...........254
.500--207...........271...........271...........270
.550--207...........265...........277...........281
.600--202...........261...........270...........276

int1-stock port 1.88 OEM valve
int2-ported as seen above with 2.02 Ferrea valve 33* back cut (best over all test)
int3-same as int2 but with 22* back cut added to 33* back cut
int4-Milodon Mega Flo valve

Thought I'd share what did and didn't work. Test int2 is the best IMO. Although the peak flow #s are not as high as the others, it has the best area under the curve. I feel this is far more important. Let the bench racers go off of peak #s I always tell people. The motor will have about .520 lift at the valve after lash and the lifter angle loss is factored in, so #s above that don't realy matter anyway. Test int3 didn't work the way I thought it would. I never tried double back cutting a valve and I don't think I ever will agian looking at the results. Test int4 is your more average run of the mill valve. Again poor area under the curve, but bigger peak #s.

Exhaust results coming soon.

 

[rumblefish360]

Thanks for sharing skews. Nice work and a good bit of it I have to add. Test #1 certainly is the one I would want to run. I was surprised to see the peak flow on test 3. 281 from a 308 head?!?! WOW!

Have you ever done and tested this kind of work on a 1.88 valve?

I think, IMO at least, possibly, those designed ports were something to do with the era of the head and the swirl effect the factory was trying for. The 308 head was being made in an era where HP was still down, emissions were standards were high and computers were still poor for the automotive market.

Also funny you post this because I also have a spare parts 360 build on the horizon. The cam is much smaller to start with and a dual plane intake will be employed.

 

[skrews]

Thanks for sharing skews. Nice work and a good bit of it I have to add. Test #1 certainly is the one I would want to run. I was surprised to see the peak flow on test 3. 281 from a 308 head?!?! WOW!

Have you ever done and tested this kind of work on a 1.88 valve?

I think, IMO at least, possibly, those designed ports were something to do with the era of the head and the swirl effect the factory was trying for. The 308 head was being made in an era where HP was still down, emissions were standards were high and computers were still poor for the automotive market.

Also funny you post this because I also have a spare parts 360 build on the horizon. The cam is much smaller to start with and a dual plane intake will be employed.

Ya as far as peak #s 281 out of a 308 head is smoking. I think if I tube the pushrod holes it will pick up 5 to 10 cfm. Hell my cnc ported IndyBrocks peak at 292. I've done a set of 596 castings on this level of porting with 1.88s. They are on the left over parts 360 currently.

.........int.........exh
.100...61...........48
.150...113.........84
.200...150.........114
.250...172.........134
.300...197.........148
.350...212.........159
.400...225.........165
.450...234.........169
.500...231.........172
.550...231.........173
.600...228.........175
exh tested with 1.75 pipe
MP 1.88 stainless 33* back cut to within .010 of seat
MP 1.6 stainless tulip no back cut

 

[rmchrgr]

.250--150...........180
.300--164...........205
.350--183...........222
.400--195...........242
.450--205...........261

These low lift numbers look pretty good, especially .450".

Good to see someone working on these parts since they're essentially obsolete with the availability of aluminum head castings. I have 2 sets of 308s myself plus a set of MP 576 heads which were based on the 308. IMO they were some of the best factory iron offerings.

These would make a pretty decent street/strip head. Low 11s should be no problem with the right chassis set up.

Did you use the porting templates for these heads?

 

[goldmember]

I think Larry Meaux had a hand in the design of the 308 castings. The trouble was after he gave Ma the proper ports they forgot to include the intake port design.LOL At one time he had a pile of 308's with no pushrod holes machined. He did lot's of port testing years ago for SS and is one of the brightest guys I've ever met.

 

[goldmember]

These low lift numbers look pretty good, especially .450".

Good to see someone working on these parts since they're essentially obsolete with the availability of aluminum head castings. I have 2 sets of 308s myself plus a set of MP 576 heads which were based on the 308. IMO they were some of the best factory iron offerings.

These would make a pretty decent street/strip head. Low 11s should be no problem with the right chassis set up.

Did you use the porting templates for these heads?

Low 11's is cake. We ran mid 10's many years ago with home ported factory heads. High 9's is doable in the right hands with a well thought out combo.

 

[jimjimjimmy]

have been using 308 heads for a while. a friend of mine has been porting 308s for almost 20 years now with great results. one guy runs a 73 cuda with a 308 headed 340 the car is over 3500lbs he was running 10.86 consistently and thats with 273 stock rockers and a comp cam around 540 and 555 lift and 255 and 260@50. we were never lucky enough to have access to a flow bench and probaly not as good #s as yours but one thing we learned is 308s work.

 

[rmchrgr]

How was the de-shrouding accomplished?

 

[mopartom340]

Awesome port work! What's your thinking on a set of 308's from a 360 Commando Crate engine? They came with the 2.02 intake valves. I scored a set about 10 years ago for my 340.

 

[Dusterguy]

What is intake troat diameter in this head, how big you ported it? Like they say it should be 90-93% of the intake valve diameter. I think my own head i maybe should port the troat like you did.

 

[skrews]

Did you use the porting templates for these heads?

Made my own template for the short side. I've got a set of the MP templates, but most of them become obsolete when you virtually eliminate the guide and cut the bowl at 75 to 80 degrees.

 

[skrews]

How was the de-shrouding accomplished?

Deshrouding cut is made on the seat and guide machine.

 

[skrews]

Awesome port work! What's your thinking on a set of 308's from a 360 Commando Crate engine? They came with the 2.02 intake valves. I scored a set about 10 years ago for my 340.

I think those motors were just production line engines with a cam, intake, and pass car oil pan. If thats the case the heads would be exactly the same as these, aside from the 2.02 intake valve. Honestly like most factory iron the valve job is probably lacking, and the OEM valves aren't so good. The possibility of cracks is a lot less likely as they probably weren't being run hot in a heavy rig.

 

[skrews]

What is intake troat diameter in this head, how big you ported it? Like they say it should be 90-93% of the intake valve diameter. I think my own head i maybe should port the troat like you did.

The way I size it is by running the 80* bowl cut to within .100" of the bottom of the seat. Don't know the exact diameter percentage off hand, but it always works. You can see the ink marks in the bowl.

 

[Woods74]

Now that's some work! Breaking a sweat just looking at it.

 

[skrews]

Now the exhaust side. This is where the 308 shines. From what I've read over the years is that the 308 ex. port was inspired by the W-2. The port is a drastic departure from the older designs. The floor is raised up into a proper shape, yielding an excellent broad short side. Even though the port exit looks small it flat out works. I can tell you from personal experience that opening up the port at the exit to gasket size will kill the flow.
.......ex1.......ex2
.050--21.........21
.100--46.........45
.150--73.........70
.200--92.........87
.250--117.......108
.300--137.......126
.350--156.......139
.400--169.......150
.450--178.......159
.500--182.......162
.550--184.......163
.600--184.......164

ex1-out of the box with OEM valve flowed with 1.75 pipe
ex2-out of the box with OEM valve flowed with out pipe

guide ground flush with roof