I am new to the forum don't know if this is the right place to post this.Ihave a 1985 ford f250 460 4 speed manual I pull a 30' fifth wheel toyhauler with it when fully loaded weights just over 12,000 lbs I am rebuilding the engine this winter need to know what I can do to improve horsepower and torque and im running a edelbrock 750 carb

 

First thing is your carb is to big. On the rebuild get yourself a straight up timing set, Just get an early 429 timing set like 1970 or so and that will be good. Stock compression is fine in my opinion but some will say you need to bump it up. Contact a couple cam companies and tell them what you want the truck to do, which sounds like to me you would just want low end torque more than high rpm horsies. You really need to get the exhaust side of the heads ported, nothing real major mainly just knock the smog(thermactor) bumps off, this will do wonders for you. Get a set of longtube headers and a 2 1/2" dual exhaust. I did this exact build for a friend of mine who pulls a 5th wheel camper and he loves it. He has an 86 and he just loves going up hills walking right by the new trucks with there big bad diesels, he claims they just stare at him like what the hell. He has even had some of them come up to him in rest areas wanting to know what he has in that thing. He tells them just a stock 460 then he......


Oh forgot to add....with all this I put on a Holley 670 and it is border line to big. Plugs say it run's just a tad on the rich side but I figure better a little rich than lean.

 

That carb you have should work ok. If you are in the ballpark they size themselves to the engine, they only open up as much as the engine will take, since they are vacuum secondary carbs. If the plugs are dark, put smaller jets in the primary.

I agree with the timing set.

Have you ever considered putting a zf 5 speed in it? With your 4 speed you really only get 3 useful gears out on the road. With the 5 speed you would have 2,3,4 like you have now, and on the flat land you could throw it up in overdrive. Check your rearend ratio. Are you running 4.10's?

 

Franklin2 if I remember right I am running 4:10 gears I have thought about the five speed I think it would do better than the four speed. Plowboy I have looked into headers its on my list I also have considered running fuel injection instead of a carb and my cam is a hydraulic flat tappet 280h from comp cams that im looking at.

 

Raised compression is not only a good thing, it is the byproduct of a very important thing.
Providing adequate quench in the combustion chamber.

D9TE blocks leave stock pistons over .030" in the hole.
Add a .042-.045 head gasket and you have a recipe for spark knock.

A tighter chamber creates turbulence, suppresses detonation and the increased compression helps torque.
I don't know the numbers on your cam but 9.5:1 is not unreasonable with iron heads.

I would suggest the full roller timing set from any '88 and later EFI 460.
They are straight up, just like the old 429 chain but don't wear nearly as fast.

 

Personally I think the cam you are looking at is to big. It seems to me you are wanting low end power and that cam does not kick in until 2K rpm. The 260H cam is real close to the one I put in my buddies truck and it pulls good right off idle and up to 5,200K rpm.


Ardwrkntrk is correct on the EFI engine timing set being straight up, I alway's forget that about the EFI engines. Also he is correct on the full roller set, I even make sure mine are all steel, no cast gears. You will pay more but they are worth it. If you want to really step it up get a double roller set...not a must but an improvement.


Another thing I did forget in my previous post is I also put in a recurved distributor, if you want to do this (I do recommend it but not a must) let me know and I will get the info on the guy who did it. He is great to work with and very reasonable on prices.


As I said some will say to raise compression, I am not against this cause it will add power. Just my opinion it is not always necessary, it's one of them personal opinion things to me. Neither way is wrong just a different approach.


Getting the smog bump knocked off the exhaust port on the heads will do you wonders I promise. If you have to have someone else do it tell them to just knock the smog bump off and that's it. Most people wanna go crazy and port the crap out of them. For what you want just knocking off smog bump will be sufficient.

 

A Comp 280h is no good for a tow pig, and the smog heads really benefit from a split duration cam. Here is my build which on paper is around 400 HP and 550 ft/lbs... It tows way better than my diesel, and is very torquey from just off idle through high RPM.

.030" over D9TE block
E6TE heads ported exhaust side, polished chambers
KB137 pistons (.020" in the hole... should have zero decked)
Comp XE4x4 262/268 cam
Summit brand double roller installed 4* advanced (which worked out to straight up)
Edelbrock Performer intake
Holley 750 double pumper... I want to say about 72/82 jetting
Duraspark II ignition, 10* initial, factory curve
Flowtech 12560 headers, 1.75" primary into 3" collector

Static compression is 9.83:1 and I forget what dynamic is but it's probably around 8.5:1 or a hair more. It burns 93 octane and is on the edge for towing on pump gas but performs very well. I'd be inclined to go with forged pistons if I were to build it again, for peace of mind.

I originally had a Lunati 61602 in it (262/268) and that cam really surprised me. It was a little weak down low but was an on/off switch at 3000 RPM throwing you back in the seat and pulling like a raped ape through 6500 or so. Tons of fun to drive but it was a bit of a pain towing as I had to wind out every gear so it would still be making torque after the shift. The Comp 34-235-4 is very nice to tow with, tons of torque at all RPM but definitely less HP than the Lunati and runs out of steam around 5500.

Don't go too big on the cam or you'll be changing it later. Most important things to do are port the heads, at least the exhaust side, and raise the compression. Factory EFI heads are even worse than the carb smog heads and you won't be able to touch serious towing power levels with the factory EFI setup. Aftermarket EFI can perform well but unless you have an unlimited budget and like complex electronics don't bother, put your money into things that make power.

 

How does this carb act with this setup towing? I would think you need to baby the throttle a little bit with the double pumper. Nailing the throttle at low rpms towing brings on a problem till the engine caught up in rpms doesn't it?

 

Acts like it has a bunch of torque I suppose? Towing getting rolling from a stop there is no problem going to wide open from just off idle once the clutch is released, just lots of torque though in first or second it comes on pretty violently if you nail it. Higher gears lower RPM (maybe 1200+) nailing it wide open and it gets up and goes. Torque curve feels pretty flat from 1200-4000. If you mean nailing it wide open from 900 RPM/4th gear/25 MPH/towing, then I'm not sure because under those conditions I downshift to accelerate as I don't want to lug the engine or cause detonation. Same condition no trailer I just kind of barely touch the throttle throttle and it accelerates pretty quick. Please clarify as I'm not really understanding the scenario you're asking about. Maybe the answer is pick the right gear and it just goes, proportionally quickly to how far you stab the throttle open?

Of course there's no reason to beat on the truck when quickly rolling to wide open vs stomping it is much easier on the ZF5 and driving properly in general is likely quicker. I've had countless ujoint failures in this truck, several ZF5 failures. Motor mounts were a regular failure item too. Now with 1350 joints, solid drivers side motor mount, and not shock load the ZF5 excessively I haven't had any failures in a while.

 

Sounds like you keep the revs up when you nail it. With a vacuum secondary carb you could nail it at 900 rpms and go on, it would not open the secondaries till the engine built some rpms.

The carb works and adds fuel by airflow through the engine. The accelerator pump is a mechanical means of adding fuel when you stomp it, since you are opening the carb wide open and there is little airflow. On a vacuum secondary carb when you stomp it, only the two front barrels will open and it has one accel pump that squirts fuel into these two barrels. It's easy to overcome just two barrels being stomped open and the carb will respond quickly with the air flowing through only the two front barrels at the beginning.

When you stomp your double pumper open, all 4 barrels fly open. You have two accelerator pumps, the standard one in the front and the added one in the rear. It throws the fuel in there to try to cover up the bog that happens when all 4 butterflies open at once. It then has to build airflow through all 4 barrels.

It sounds like you keep the revs up during towing, and with downshifting you can overcome this to a degree. But you definitely have to allow for it's short comings. In other words with your truck if you "drive it like you stole it" it probably runs pretty good. That could explain why you had so many driveline failures in the beginning.

It sounds like I am knocking your truck, I am not. I am just trying to educate other people who may read this thread and go out and buy a double pumper carb.

 

I don't consider cruising around town at 900 RPM keeping the revs up. Driving around unloaded I typically shift by 2000 RPM. Towing I'd say closer to 2500-2800 RPM, again not exactly high RPM. Sure I could shift lower but it has nothing to do with the carb, rather it's to avoid lugging and stay in the power band. Unloaded I don't worry about being at 700 RPM after a shift because it just goes. When towing I want it to be at least 1200 RPM after my shifts as that's where torque comes on strong. I drove this truck no differently when I had a 600 CFM vac secondary 4160 on it, but it did make less power with that carb and required a lot more throttle opening to accelerate.

Driving my diesel (IDI) truck I would say I keep the revs up whether towing or not. The diesel lacks torque and the pedal is pretty much an on/off switch. Mash it to the floor, take a nap, have a snack, eventually you'll get up to speed. It sees over 3000 RPM every time I drive it because that's what's required to still be slower than all the econoboxes on the road. Not enough torque to be concerned with breaking anything. It reminds me of when a had a 302 and a 351w in one of these trucks, just very slow and underpowered for towing.

I still don't understand what you're getting at. Downshifting to accelerate with a weight of 12,000+ lbs when at 900 RPM in a high gear is making up for carb shortcomings? Care to explain your thoughts behind that? 900 RPM is basically idle speed, it's about not lugging the engine. 600VS or 750DP makes no difference in that type of condition.

It sounds like maybe you are advocating lugging engines by mashing wide open in high gears at near idle RPM, and expecting a VS or DP to make a difference. Your rod bearings won't care what carb sits on top, only that they're being abused. Driving properly is more important. I don't understand why all the concern about mashing the thottle wide open, that's something I rarely have a reason to do as there's more than enough power well before wide open.

 

I will leave it as is. I stated my opinion on double pumper carbs, you stated yours in your setup and how well it works for you. People can take this and do some more research and figure out what is best for them, maybe they will pick a double pumper carb for their truck when they are modifying/upgrading their engines.

 

I appreciate all of your thoughts and knowledge on yhis I am looking things over and getting ready to start ordering parts so I am ready to start my rebuild this next winter as I need my truck this summer to pull my trailer around I do agree on a lot of what you guys have said and hadn't really thought of it from those perspectives I will keep updating and asking about stuff as I get ready to order parts.

 

ok here are some of my ideas what do you guys think,knock the smog bumps off the heads,run a high energy hydraulic flat tappet 268H camshaft,429 double roller timing chain,weind stealth intake manifold,headers,high energy hydraulic lifters,and a smaller carb maybe a 650 or 670

 

In my opinion you have a good plan there. The cam is a tad big for my taste but it will be good for what you want to do, your idle might be a little lopy but that may be right up your alley. Make sure the timing set is all steel and the headers are long tube and a good 2 1/2" dual exhaust. I promise the first time you get to use the power you will be amazed at the difference, you'll just grin and do it again.....