391 buildup
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Posting Guru
Joined: Jun 1999
Posts: 1,172
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From: SW Missouri
391 buildup
I have a great running 391, in a bus conversion. this winter I want to bump up the compression to 9:1. I am pretty sure that 390 pistons will work, and I want full-floating pins, anybody recommend a brand and part#?
I also might install a mild RV cam. the bus has a 5-sp, and 6.14 gears on 9:00 20 wheels. might upgrade to 22.5s for more road speed, better ride. I also have 5.86 gears that will likely get installed also.
the current 7.4 to 1 compression works ok, and the bus will do 70 if pushed, but I need more power for the mountains.
I also might install a mild RV cam. the bus has a 5-sp, and 6.14 gears on 9:00 20 wheels. might upgrade to 22.5s for more road speed, better ride. I also have 5.86 gears that will likely get installed also.
the current 7.4 to 1 compression works ok, and the bus will do 70 if pushed, but I need more power for the mountains.
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Posting Guru
Joined: Jun 1999
Posts: 1,172
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From: SW Missouri
391 buildup
no FE heads in the future for this beast. I am going to just clean up the FT heads, as I dont want to change the rest of the top end. I could go either way with the cam, as the engine is acceptable right now, I just want more torque.
does anybody have the stock cam specs for a 391?
does anybody have the stock cam specs for a 391?
Logistics Pro
Joined: Feb 2000
Posts: 3,565
Likes: 9
From: Sun River St. George
391 buildup
I'd do the 1130 Silvolite pistons, 30 over with moly rings, new bearings, balance the crank-rods-pistons, and do the oil modifications. Do a valve job and install hardened exhaust valve seats (you may already have them). Install oil flow restrictors in the heads. If the cam is in good shape I'd leave it, if not try Crane 343901. You always have the option of changing it later. My guess is upping the compression and a good overhaul is all that is needed. High volumn oil pump, roller timing chain, ARP fasteners. Figure about 1.5K$.
William in Atlanta
William in Atlanta
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Cargo Master
Joined: Aug 2000
Posts: 2,931
Likes: 12
From: SW Michigan
391 buildup
Whd, if the engine runs well now, how much effort are you willing to put into it to get some more snort ? I'm thinking it probably doesn't have enough valvespring to get much rpm, and the lift is only .424, and the duration is not much. Would you consider milling the heads ? You could gain some compression from that......Does your chassis have room for some headers ? Do you have an electronic ignition ? What is your maximum rpm as it is now ? DF
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Posting Guru
Joined: Jun 1999
Posts: 1,172
Likes: 2
From: SW Missouri
391 buildup
well, I took the 391 on its first international trip (to mexico) and it really ran well. I may reconsider the upped compression for a while. I replaced the governed Holley 4v carb for an edelbrock/AFB, and the difference was astounding. 7 mpg average@70 mph, in a 17,000 lb school bus conversion without overdrive.
hit the grapevine on I-5 shifted down to third, maintained 35-40 all the way up. much better than I expected.
one leg of the trip in Mexico I averaged a hair better than 10 mpg!
I upgraded to electronic ignition last year, now the carb, its a lot more fun to drive now...
hit the grapevine on I-5 shifted down to third, maintained 35-40 all the way up. much better than I expected.
one leg of the trip in Mexico I averaged a hair better than 10 mpg!
I upgraded to electronic ignition last year, now the carb, its a lot more fun to drive now...
Post Fiend
Joined: Jun 2003
Posts: 8,209
Likes: 12
From: Black Hills of SD
391 buildup
Most of the Ford truck engines had sodium filled valves and I believe hard seats. They are expensive to replce. If you choose not to abandon the FT top end then do a good clean up and gasket match porting job when you have it down.
