Ok guys, I've had my 68 F250 CS with a 390 4v for a couple years now and I love the truck. I bought it primarily to tow my car on a car trailer. Well It's gotten to the point that I just need more grunt, I would be happy with my 6.5mpg towing if I could pull up the big hills. I live in Maryland which has tons of mountians and I tow through PA a lot. What would you guys recomend to build a towing motor? Right now I have (at least as far as I know) a stock 390 with a 600 cfm Holley 4160 carb, Mallory dist, MSD 6AL box, and 2.25" pipes true dual's with 3 chamber flowmasters. It runs well and is not sick at all. I was thinking about a cam change and maybe bring the compression up a little because I might be able to get better milage out of it. I don't think headers or intake are going to do much in the 2500-3000 rpm range that I'm looking at; I could be wrong. I already have 4.10's in the truck and don't want anymore revs on the highway. Also with the upgraded power will the two piece drive shaft take it? It looks pretty wimpy.
I think the 2 piece shaft is up to the task. They put them in 3/4 trucks, between C6 trannies and Dana 60 axles, must be pretty tough. They are probably in 1 tons as well, although I don't know that personally. Also, I've never heard of any failures.
I know some of the guys will disagree with me, but I think that most mods don't help with your problem. Big cams, carbs, exhaust etc. They may make more torque, but it comes at higher revs. Still, a reasonably mild newer cam may compliment your mods.
In your case, I'd consider a longer stroke and/or higher compression.
You can do a lot of other mods for HP, but I don't think the gains will show up where you need them.
I will second that the 2-piece driveshafts are stronger than they look. The '70 F350 at work had a long wheelbase 12ft bed and the 2-piece with 2 1/2" diameter tubes on both ends. The truck is used, among other things, to pull a 580C Case backhoe on a 5000# gooseneck trailer. Lots of granny-gear, full-throttle takeoffs to get the load moving. Never had any driveline problems with it.
We also have a '70 F250 CS. It has over 370,000 miles on it, and it still has the original u-joints in its 2-pc driveline.
Phil, headers are the next step. Even at only 2500 rpm, they will help, because the stock FE exhasut manifolds are SO bad. I think the 390 likes a dual 3 inch exhaust setup, how new are your 2 1/4 pipes ? Are they close to replacement ? Next you might consider a bigger cam/lifters/springs the stock set is pretty wimpy. How about a new intake manifold under that holley 600 you already have ? Do you have an auto or manual tranny ? DF
I have a C6 auto. I'm guessing I want some shorty headers for the low end torque. Any segestions on what works and fits well for the truck? I may want to ask that in the truck forum, I have PS and PB if that makes a difference. This is my first FE so what cam's have you guys tried? I've heard that you can pick up a good bit of low end through the cam. More modern lobe shapes and higher lift with out to much more deration can help over a small 40 year old cam design. The pipes are small, but I don't think they are robbing me of anything with the stock motor. A few bolt on's might change that.
Phil, I ask about the tranny because the C6 has only 3 ratios 2.48, 1.48, and 1 to 1. That is not the friendlyest for towing. A shift kit will recuce overlap on shifting and help a little. But you might find big gains to be had if you added a GV over/underdrive splitter. Yes, you can tow in overdrive, so your fuel mileage over flat ground will improve. But you also get the benefit of being able to split 1st and 2nd gears. This should be a huge improvement. I'm guessing right now when you climb a steep hill, your engine is either lugging at too low of an rpm, in 3rd, or screaming higher than you want in 2nd. The GV would let you run 2nd and over, right where you need to be. The GV might be a bigger improvement than anything you do to the engine. But the engine, that wonderfull FE, is why we are here in this room on the site ain't it ? Don't raise the compression. If you're hauling heavy loads, more compression might lead to detonation, and you don't want any of that. Now, that Mallory dizzy you have.....does it have vacuum advance ? You need to have it if you do anything other than drag race only. If the mallory doesn't have it, get something that does. You might find some more mileage right there. As for the headers, tri-Ys would be your best bet. Carrol Shelby did some testing in the mid 60s and found that tri-Ys gave better torque under 5500, where his engines spent most of their time. Stan's makes some really nice ones to fit your truck. Shorties, if the pipes are sized correctly, work best at higher rpms....I'll try and come up with a cam suggestion later today. Towing cams are hard for me to think about, the small cammed engine in one of my two trucks is a 343801 ( Crane ) and that is probably too big for what yer wantin ta do. DF
Tall69, yes, exhaust sizing affects power, and where that power occurs. But there seems to be a big amount of confusion about what size we are talking about, and what it does to power. There is the common idea (old wives tale ) that too big of an exhast system will hurt low rpm power. It isn't so. Headers, of any shape and size,will outperform the factory ex. manifolds for the FE. If you choose a set of headers with 2 1/4 primarys instead of 1 7/8ths primary, the bigger pipes will have less low end power. But both will be ahead of the factory manifolds. The length of the primary tubes is a concern as well, longer is better for low rpm power. Once you gett past the collectors, it is almost impossible to get to big. A dual 3 inch setup will do fine on a 390 and will not hurt low speed pulling power. Most of this is an academic discussion however, because we are limited in how many choices are available for an FE in the chassis we have. Fit, quality of construction and how close are you the the starter become more important than primary pipe size. For Phil's towing duty, some Stan's tri-Ys are probably the best choice. DF
I totally agree with you regarding the headers vs. log manifolds. Regarding exhaust size, for his situation, there's absolutely no reason to spend the money upgrading the exhaust to 3 inch all the way back. I also re-read your post, I see where you asked how old the current exhaust setup is. If it's needs to be replaced anyway, I'd go 2.5" over 2.25" all the way back.
HAVE JUST PULLED ENGINE AND TRANS OUT OF 68 F100 87K SHOWING ON ODO LOOKS ORIGINAL GREAT SHAPE TO RESTORE. WHERE I NEED HELP IS I WILL BE TAKING BLOCK INTO MACHINE SHOP IN A COUPLE DAYS BY THE WAY IT,S A 390 MY QUESTION IS HOW SHOULD I RAISE COMP ON THIS ENGINE WHAT I HAVE PLANNED NOW IS REBUILD KIT PLUS NEW EDEL CARB INTAKE CAM LIFTERS TIMING CHAINS AND GEARS PLUS HEADERS ALL THESE ADD ONS ARE GOING TO BE EDELBROCK PERFORMER PACKAGE 0-5500 RPM I DONT BELIEVE I WILL HAVE TO REPLACE PISTONS BUT IF I NEED TO TO GET COMPRESSION UP I CAN OR WOULD ANOTHER SET OF HEADS WORK FROM ANOTHER FE ENGINE ALSO WHAT CAN I DO AS FAR AS THE ROCKER ARMS ARE CONCERNED THEY ARE TUBE MOUNTED I,M NOT SURE WHERE TO GO REALLY NEED TO MAKE THIS A GOOD DAILY DRIVER HOWEVER A GOOD 1/4 MAKES ALL THE WORK WORTH WHILE IF YOU HAVE A REALLY GREAT 390 RECIPE PLEASE LET ME KNOW THANKS
Phil, you might be very happy with the Crane 343941 cam. It is bigger than stock, but not too much. The 343941 is one size bigger the the Cam recommended by Crane in their truck page, but is still considered a truck cam. I think sometimes the cam companies are a bit overly consrvative. The '941 cam has 272/284 (216/228 @ 050 ) duration with 533 and 563 lift, more than stock. The wide 112 LDA will give a nice smooth idle. I would also give the engine a fresh set of valvesprings, yours may be kinda tired. FWIW, I have the 343801 cam in my 2wd auto tranny 3.50 rear geared everyday truck. the '801 has 278/290 duration ( 222/234 @ 050 ), about the same as a 390GT or 428CJ cam, but with more lift-548/580, and a wider 114 LDA. I tow with this cam and have no trouble, but I am running the rhoads lifters (boy are they NOISY !) and don't mind a slight lope at idle. Pulling power I have no trouble with. But I like to buzz the engine to 6K everyday, and not everyone is like me. The '941 would be great for towing. DF
Thanks DF, I will get the tri-Y's and see how they do. I was looking at the Crane truck cam, but after your seggestion I may go for the 343941. I will change the valve springs because I don't know if they can take the lift of the cam. Do I need Cranes adjustable rocker's and push rods? I would like to get away with what I have unless I need them. The 2.25" exhaust was put on a year ago because I intended to keep the truck stock for the most part. When I started towing more then two hours away the short comings of the engine where really showing. I do have vacuum advance and I have the timing at 18 initail and 44 total, seems to like it there. Yes, I do get stuck between gears while pulling up hill and hear the engine sing in 2nd gear. What kind of gains should I expect from the cam?
I have been trying to choose between the Crane 343901 and 343941. I have been told by a few people that I like whimpy cams. Crane lists the 343941 under strong performance with gains from 50 - 65hp. Is this accurate? Maybe I should have been choosing between the Crane 343941 and 343801. I thought the 343801 to be a bit much for a daily driver 4x4 with 4:10 gears. I was also concerned about idle quality in Canadian winters.