I'm sure this subject has been covered, but I could use some help finding headers to fit a 351w in an 84 f1fitty. It was originally a 302 and I tried to scab in an extension in the "Y". That didn't work worth a shoot. I'd like something that is'nt going to cost my wife's arm and leg. Also someone wrote in about the differences in a 302 and 351w flexplate. I had not heard of this before and may have the wrong plate in, if anyone has more info let me know. I also replaced the pitman arm seal and screwed the stearing adjustment all up, if more advice please respond.

 

I used Doug Thorley full length tri-y's on my '82. The fit perfect!! You need to have an exhaust shop to bend a crossover pipe, or just go with true duals all the way back. I went duals and put in a cat (short, hi-flow DynaMax) on each pipe.

The flexplates depend on the year and I cannot remember the breakdown, however, most 302s have the 50 oz counterbalance on the flexplate while the 351Ws use a 28 1/2 oz counterbalance.


'82 F150 2WD w/351W (orig 300 I6)
Slik

 

Somewhere in the 80's (1985 comes to mind but not sure) Ford went to external balance on the 302 and 351. I had a 78 F150 that I put an 88 302 HO into. I had a 3 speed W/OD from an 82 behind it and used the original flywheel and balancer from the 92. I kept it that way for about 2 days until I could figure out what was wrong and within that time it tore out the rear main and bent the crank. Is your truck have a vibration? if so then probably the wrong flexplate was installed. Hope this helps.

Brad Godkin
1986 F350 CC/SRW
6.9liter/C6

 

I tried to research the flywheel issue and can't find any info
on late model 351W. This is what I did find out:
All 221,260,289,302,351 are externally balanced.
Engines prior to 1985 are 28.5 ounce balanced-85 up=50 ounce
Ford part# for 289/302/351W 1966-69 Truck flywheel =C6TZ-C
casting# C7TE-A Ford part# for 289/302/351W 1965-69 Full
size flexplate =C5AZ-T
This tells me at least back then 302 and 351w flywheels were the
same. I am in the exact same situation that you are in. I put
a 1978 351w in my 1980 150 4x4. I had the original 351w flywheel
and kept it. After doing the oil pan thing I tried to bend my 302 y-pipe to make it fit. Ended up cutting it in half and putting a piece in the middle but it still leaks.
I thought about the header solution but have some problems with
it. First, I would have to buy the $89.00 type from Jegs. I have to save my wife's arm and leg too. These things are pretty thin and you end up replacing gaskets all the time. Second, how to you make the 90 degree turn on the drivers side to crossover? True duals are out of the question-I have to
pass inspection. I figure to crossover you are going to have to
have the pipe hanging real low under the trans. I think I am
going to the local muffler shop and get them to make me a y-pipe
to mate to the 302 manifolds. They have a flaring tool on their
machine to mate the pipe to the manifolds.

 

appreciate the info. forgot to mention that my truck is 2wd. I have all but decided to go with headers and straight pipes. Seems people aren't to concerned about emmissions in North Dakota yet. I thought that I looked over the flexplates pretty good when I reinstalled the motor. Don't remember seeing any major differences, but could have missed balances. The 351w is old, I was told about 1970 or so. It had the large size spark plug holes. And the 302 was 1984. I had the 351w bored and then I reassembled it myself. I've got about 30 miles on it right now. Haven't spent much time on it recently. "My garage isn't heated!" Looking forward to warmer temps. thanks again

 

My local shop crossed the pipe over to the passenger side on my true duals to avoid my 2nd gas tank. He took it across in front of the tranny cross member just under the tail shaft and I don't have a clearance problem at all. I built my duals to be emissions legal and it has passed for the last 3 years.

'82 F150 2WD w/351W (orig 300 I6)
Slik