Tweet
This post is about a simple rebuild on a late model low compression 360 to get the most bang for the buck. The idea is to use off the shelf 343 flat top pistons to boost the compression ratio along with an inexpensive cam, intake and carb. The goal is to maximize the compression ratio but to keep it below the magical number of 10.0:1 to be able to run on regular old pump gas.
The first thing I did was go through some measurements and calculations to figure out what the compression ratio will be. The engine I am working with is a 1978 (and latter) 360 with 8.3:1 compression and late model bridge-rocker heads. I measured the heads along with a couple of earlier model heads to get the data.
According to the information I can find and have backed up with measurements, here is the list of 360/401 cylinder heads per years and their respective combustion chamber sizes.
51cc - 1970 & early 1971 #3196291C
58cc ? 1971 through 1974 #3212993, #3213948, #3220502
60cc ? 1975 through 1977 #3220503
63cc ? 1978 and up.
Here are some photos of the combusction chambers.
I checked the cc's on the heads that I am going to use which checked out at 62/63cc.
The next thing I did was measure the dish and valve reliefs in the pistons.
The replacement dished 360 piston measured at 23cc and the valve reliefs in the 343 piston measured 6cc total. The compression height (centerline of pin to top of piston) is 0.001" difference so, it is a wash.
Once I measured everything, I plugged it all in to Diamond Pistons's Compression Ratio Calculator and liked the bottom line!
The first thing I did was go through some measurements and calculations to figure out what the compression ratio will be. The engine I am working with is a 1978 (and latter) 360 with 8.3:1 compression and late model bridge-rocker heads. I measured the heads along with a couple of earlier model heads to get the data.
According to the information I can find and have backed up with measurements, here is the list of 360/401 cylinder heads per years and their respective combustion chamber sizes.
51cc - 1970 & early 1971 #3196291C
58cc ? 1971 through 1974 #3212993, #3213948, #3220502
60cc ? 1975 through 1977 #3220503
63cc ? 1978 and up.
Here are some photos of the combusction chambers.
I checked the cc's on the heads that I am going to use which checked out at 62/63cc.
The next thing I did was measure the dish and valve reliefs in the pistons.
The replacement dished 360 piston measured at 23cc and the valve reliefs in the 343 piston measured 6cc total. The compression height (centerline of pin to top of piston) is 0.001" difference so, it is a wash.
Once I measured everything, I plugged it all in to Diamond Pistons's Compression Ratio Calculator and liked the bottom line!
Jeep gauges are for amusement only. Any correlation between them and reality is purely coincidental.
Comment