Swirl Port 308 302 info

I just wanted to say how impressed I am with everyone here at FABO. So to do what I can to improve this site I am offering my 2 cents on the 308 swirl port 360 heads and pre-magnum hydraulic roller motors.

I currently have a 1990 360 from a 1 ton van with low miles that was wrecked, in my 68 Barracuda Fast Back. Changed oil pans, pick ups, oil pump, plugged the air ports in the exhaust, added a mopar performance dual plane intake, MSD distributor and 6AL box, holley 650 double pumper. Original cam was 410 lift, currently have comp cams CCA-20-614-9 hydraulic roller 480/480 with long snout and matching springs. Other than checking rod and main bearing tolerances, heads have never been off, rotating assembly is stock.

Best time with the 410 cam, 600 holley 727/3.91’s was high 14.40’s. This is with a full exhaust 2 ½” and H pipe and slight wheel spin off the line and into 2nd. I have yet to get the car out there with the new cam and carb set up. I hope to do so in October before the snow flies.

I had probably 100+ runs with the 410 cam/600 carb, very consistent, best was a second place(air got cooler, car got faster, broke out). Took me a while to get reaction time down and consistent too. Wanting to go faster, cam change was only natural and within my budget. This is when the learning curve began.

Read the instructions on spring bind, quickly found out that all the exhausts spring were too tight. Intake was fine. I had a set of titanium retainers that solved that problem. Next thing I knew, oil smoke out the tail pipe. Pulled the valve cover figuring valve stem seals were gone since they were original too. I noticed these little silver springs lying on the head. 4 per side, by the exhaust, yes I know, very lucky. They are a Viton style seal. The retainers smashed everyone of them. Figuring it was the cam, I called Comp…they never heard of the problem. Quickly realized the springs for the exhaust measure out at about 1.4”. Intake measures out to 1.6.(not exact but close)

After some measuring and figuring, I had the exhaust retainers cut down .195. That problem soleved. The car is driven once or twice a week with limited highway and pretty regular 5000rpm 1st gear hole shots. So far so good.

Now, my brother, a chevy fan( yes there is a brother and brand competition, he is all about speed, me consistency) was into the low 13’s, knocking on 12’s door. So I went to the local yard looking for a 360, figuring stuff a big cam, solid tappets, in there with a set of 2.02’s adjustable rockers, single plane and 750 from the shelf. As long as I beat him, who cares. Motor was from a box van, date code was 7/3/88. Block, 4179930, rods 3418648, crank 3418640 heads 4027596. Flat tappet, non-roller motor. Originally was looking for swirl port motor but this is all they had. Cheap cam compared to the rollers is what I was thinking. I pulled the heads, gauged the crank and rods, inspected the cylinder walls, everything looked good.

While compiling a parts list, on a shoe string budget, my brother blows his motor. So now I am in no hurry to finish the motor. I have a trophy and mine is now faster.

I started writing down numbers as you can see but I noticed the heads looked very open on the exhaust side. I have 587 and other 596 heads on the shelf but these looked different. I originally thought they were my 2.02’s. I pulled out the slide calipers, my hypothesis was these were early 308 heads. Spring seats measured the exact same as the 1990 360’s. The Exhaust shorter than the Intakes. They look to be exactly the same as the 308’s but they have the smaller push rod holes.

As I was shuffling my parts around, spraying and wiping another coat of oil on anything metal, I decided to write down numbers from a complete running 318 I pulled out of my ’85 ½ ton. I had put a 30000 mile 318 in there that was given to me. Curious as to the head casting numbers, I pulled the valve covers, 4323302. Block is stamped 10/29/84. Now I was even more curious. This 318 ran just as strong as the 30000 mile 318 which I think was an 82. (The truck was sold a long time ago.) The 85 318 had 100000+ miles on it and let out a quick puff of oil smoke every time it started after sitting for a few minutes. Block casting on the 85 is 4323330. Referencing mopar1.us/casting, This 318 should have had the roller cam.

I pulled the intake, 2Bbl carbureted. There was a ton of crud. It had flat tappets but the lifter bosses were exactly the same as the 1990 360 roller motor. It even had the 3 bolt holes for the lifter yoke retainer. The bosses were machined for the yokes. I can not be sure how many owners my 85 had but I do believe, the roller cam was pulled out and a flat tappet was put in.