Boredom 391FT thoughts

[Fordman]

I have never looked at a 391FT from any performance angle but even from a stock utilitatuan standpoint (F500/600) why on earth such low compression?(stock is like 7.5-1?). That being said, with today's fuel being worse than yesterday's,  would there be any advantages to upping the compression , like a
Swapping out the head gasket from the stock to regular FE gaskets?. What about to regular FE heads which much flow a world above FT heads.  I realize these engines are built for torque  but we must be able to build a better tourqe  monster today!??. Any thoughts on an improved FT engine?

[GerryP]

What's the application?  How you use it will determine what build options you'll want to explore.

[gdaddy01]

I would want one to pull a 28 foot car hauler with drag car , or a 24 foot camper trailer , with something like a 1949 F-5 with a c-6 with gear vendors od , 4.11 gears , 32 inch tall tires .

[TomP]

They were made for lugging. And the trucks they came in had some pretty wide drops between gears so going up a several mile hill grunting away and not being able to upshift was a common thing. If you raised the compression and used a transmission that didn't have terrible gear ratios it would make more power, better mileage and wouldn't lug.

[Lowrider]

Picked up a 61 Starliner a few years ago where the guy made a 406 out of a 391. Never ran very good even after I repaired a few problems. Finally decided to go through the engine even though the PO said he had just rebuilt it. After I got the heads off I could see the pistons were waaay in the hole but don't recall how much. Sent the block out to have it decked. Don't recall where I saw the spec but 427's were supposed to be 0.023 in the hole. When I got it back and reassembled that's where the pistons ended up. Runs a lot better now. If nothing else l have the satisfaction of having an engine I put together and not having to trust one put together by someone I don't know.

[Dr Mabuse]

... why on earth such low compression?(stock is like 7.5-1?) ... would there be any advantages to upping the compression ... What about to regular FE heads which much flow a world above FT heads ... Any thoughts on an improved FT engine?

I also would like to have answers to Fordman's questions.

I have always assumed the low compression was mostly related to TomP's response "They were made for lugging", and to avoid detonation from the heat generated in heavy work load use.

In 1976, I crossed the 7,834 foot Raton Pass on the Colorado-New Mexico border in a loaded 330XD V8 DRW 14' U-Haul. Ascending the pass my speed was dropping, requiring me to downshift from 4th to 3rd in the NP-435 "4 speed". "OK" I thought, "it's starting to lug in 3rd, I need to downshift to 2nd now, and that should get me over the top". Nope - my speed slowed and I started to think I wasn't going to make the pass.

The New Process 435 has a 6.68/1 first gear (2nd is 3.34/1, which is much "lower" than the Ford Toploader's wide ratio 2.78 1st gear). So, 1st gear it was, and I creeped over the pass at what seemed like walking speed. I suspect the engine's governor was maxed out.

I have a rust-free 1979 14' U-Haul with the same 330XD and NP-435 (minus the governor on it's Ford 2V). I think the rear axle is a Dana 70 4.11. With 2 spare FE blocks and 3 pairs of FE heads, I have thought of building a 390 stroker for it. Anyone care to speculate on a 445 cu in build for it?

[cammerfe]

Hello Dr.---

And welcome! Long time no hear. Glad you're here.

KS

[TomP]

Yes, same. Long time, no see.

A 445 stroker with low compression, like under 9, should do OK.
 I drove an old F600 lightly loaded moving van with a 330 to Horsefly BC, that is 250 miles of uphill all the way and even the downhill coming back was slow because what seems like flat ground to every other car or bicycle on the road is a steep hill to that pig. It was in granny low and going walking speed for 15 minutes up every mile long hill that even a four cylinder car goes up at 50mph in a minute or less.

Sign would say "Spence's Bridge 20 miles" and in an hour we wouldn't be there yet. I think the four way flashers were going for half the trip.  I remember 500 miles return with less than an hour stop in Horsefly taking us something like 18 hours.

[Fordman]

What about adding a turbo. It seems to have the right compression for that application or is the rotating assembly to heavy?.

[cjshaker]

I have a 390 that I got from Blair that was originally intended for a fun heavy street car, and I use it in my '70 F350 dually to pull 9k+ lbs through some hills in Pennsylvania and Ohio. It's about 9.5 compression, C4 heads, Edel RPM intake, Holley 750 with an unknown spec cam that has a nice little rumble to it. I kept the performance timing curve that Faron put in it, used an MSD Blaster ignition to fire it, and with 93 octane it pulls fine with no hint of detonation. That's with the NP 435 and 4.11 gears with 29" tires. I DO keep the RPMs up though, and never lug it in anything but 1st gear. I'd never have to drop to first, and I'm confident that it would pull fine in 3rd up about any hill that I'd encounter in it. I've actually never had to drop a gear to get up a hill yet, although from a takeoff I've held it for all she's worth before going into 4th. I do wish there was an easy 5 spd to bolt into it, but it is what it is for now.

The 390 doesn't have any issues pulling up the hills, but I've still got a 445 that I'm about to drop in it. I went that route for the extra torque. It'll use the same type C4 heads and RPM intake, and about the same compression. Maybe a bit less at around 9.3. As long as I use good fuel and don't lug it, I don't expect any issues pulling with it either.

I just posted this to show that it is possible to tow with a stock type drivetrain. When pulling heavy loads with a gas engine, I think RPMs are your friend, to keep the engine load lighter and away from detonation. As long as the engine is built good, a good tune, timing and an eye on plugs is key to make sure you're in the safe zone.

[BigBlueIron]

Love seeing an old work horse still working. You need a Advance Adapters Road Ranger OD in that truck. Makes the split between 3rd and 4th into a very usable gear plus you gain an OD gear.

[pbf777]

     If you want to be really cool, how about an auxiliary transmission, or perhaps better known as a "Brownie-Box", thus creating a "Twin-Stick" arrangement for both over or under driving selection or as a "Splitter-Box" all the way up or down thru the gears?         
     
     Perhaps one of the most commonly encountered units might be the Spicer model 5831, which is reasonably sized for your light duty application, but probably big enough to tolerate the out put behind the primary transmissions' engine torque multiplication.  These are three speed manual units and there are several versions of available gearing; some are intended as a "splitter-box", some as "over-unders", and others are "double-unders";  this can be determined by the alfa suffix within the model designation, so one whats to investigate which unit that might be presented.

     I chose to use an older Watson under-direct-over box for my 1937 Diamond T truck as it was period correct for the truck, and which provides for the original gearing, and reduction gearing for heavy pulling or just creeping along slowly thereby saving the clutch, or an overdrive so I can drive at reasonable speeds on the road.  Watson was folded into Brown-Lippe (hence "Brownie-Box"), who latter went to Dana to become part of Spicer, who then sold to Tremec.           

     Scott.

   

[Dan859]

My Dad had several 66-67 F-750 Ford dump trucks (10 wheel).  They all had 391s with a 5 speed main and 3 speed splitter transmission.  They weren't the fastest trucks on the road, the 477 and 534s were noticeably quicker.  But, you could put 20 tons of blacktop or stone in them, and they'd haul it anywhere you wanted to go. 

[RustyCrankshaft]

534's might have been noticeably faster, but they are noticeably hungry too! I still have a Lousiville with a 534 and it gets about 4.5-5.2 all the time no matter what you're doing. The older F750 with a 391 will get 8-9 if I drive it easy, but it's just a flat bed so the truck itself is pretty light. Sadly both of them are mostly not roadworthy anymore but cool old trucks, waiting for their turn in the shop.

[BigBlueIron]

What about adding a turbo. It seems to have the right compression for that application or is the rotating assembly to heavy?.

I think it would be a great application, if designed correctly. Keep boost really low and use a large intercooler. Assembly weight is only a concern with higher RPM I would say 4k is the max.

Always wondered how much a swap to regular say D2 FE heads and T intake would wake one up. Ever looked at FT heads? They are horrible. Keep the FT exhaust manifolds by welding the heat crossover up. Like to find a 70 F650 or similar to make a ramp truck.