12 mpg on a 400 with 375 hp
anyways, if I could just get 8 mpg I'd be 
400 help
Thread Starter
|
New User
Joined: Aug 2004
Posts: 5
Likes: 0
400 help
I am a new member to the site, and let me tell you I am glad that I found it! I own a 79 F-150 4wd with a 400, d44 front, ford 9" read, c-6 tranny, and np-205 transfer. I have about 6 inches of lift and 35 x 12.50 tires. I have been looking at motor options lately and this site has opened my eyes to the possibilities of my 400. I use my truck for hauling, some towing, and mild off road use. What I would really like is something that is reliable, with about 12+ mpg, somewhere in the area of 325+hp and 375 fp (I think). This is my first Ford (never owned a chevy!) and I love it. I figure if anyone could help with a recipe for success it would be you guys. Should I build my motor over, transplant, or leave it how it is with a performer intake, 1406 carb, and K&N filter. Please help.
Thanks so much
Tim
Thanks so much
Tim
Junior User
Joined: Jul 2004
Posts: 99
Likes: 0
From: Central Illinois
I've got a 400 in my 72 Ranchero GT. It get's about 10-11mpg. Rear axle ratio is 3.00.posi. One thing that I believe will help is to bump the compression up on these motors. Mine has about 100,000 + miles and effeciency is not too good. Also to note, my brother has a 408 stroker in a 69 Mustang. He's getting 18-22mpg with it. (3.25 rear ratio) w/overdrive. You could attain those numbers of yours but there's lots of variables and unfortunately the truck has all the aerodynamics of a brick!Good Luck
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
Your best chance to get 12 MPG and 325 HP is to use a flattop piston (9.0:1, +0.030), a cam with a small amount of overlap (Comp Cams 255DEH), Ported heads with 2.15" intake valve, 1.65" exhaust valve, dual plane intake, Edelbrock 1406 carb and headers.
Dyno 2000 says this combo will produce 457 ft-lbs torque@2000 RPM and 334 HP@ 4500 RPM. The cam should be fairly efficient since it has only 40 degrees overlap.
You could use the new zero deck clearance piston with about 8cc dish and 3cc valve relief (9.5:1), but you will need 93 Octane fuel.
If you use a hydraulic roller cam with the same timing and 0.550 lift, you can do better yet.
You need to improve the Volumetric Efficiency, without overlap and increase Compression without detonation.
Dyno 2000 says this combo will produce 457 ft-lbs torque@2000 RPM and 334 HP@ 4500 RPM. The cam should be fairly efficient since it has only 40 degrees overlap.
You could use the new zero deck clearance piston with about 8cc dish and 3cc valve relief (9.5:1), but you will need 93 Octane fuel.
If you use a hydraulic roller cam with the same timing and 0.550 lift, you can do better yet.
You need to improve the Volumetric Efficiency, without overlap and increase Compression without detonation.
Trending Topics
Junior User
Joined: Jul 2004
Posts: 99
Likes: 0
From: Central Illinois
While were on detonation...any ideas why my 77 400 runs on when running on regular but doesn't when running on premium.( other than it's particular and high maintenance...sounds like an old girlfriend...she used to run on too:-p)
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
Top 6 Best Deals Available on New Fords & Lincolns Right Now
Brett Foote
This Hennessey Takes the Expedition Tremor's Off-Roading Capability to the Next Level
Verdad Gallardo
Top 10 Fords at 2026 Carlisle Ford Nationals
Joe Kucinski
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
Your cylinders are getting hot spots from detonation with regular. You probably have some carbon buildup. High test doesn't run as hot or detonate as easily, so you are not getting those hot spots. It is just a matter of time, but it may be a long time, before it will run on with high test as well.
Senior User
Joined: Oct 2003
Posts: 347
Likes: 0
From: in a house
Danlee, why the the larger 2.15" (these cleavland or custom)intake valves while keeping the same size exhaust valves?
will the porting job overcome the stock lack of exhaust flow to accomodate?
also, whats the DD #'s of the stock valve vs bigger one? 457ft-lbs is impressinve but that could be a task out of my price range.
will the porting job overcome the stock lack of exhaust flow to accomodate?
also, whats the DD #'s of the stock valve vs bigger one? 457ft-lbs is impressinve but that could be a task out of my price range.
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
It has been shown by test that a 2.15" intake and a 1.65" exhaust valve are the best combination for flow on these motors. The Cleveland Intake valve is 2.19" and the Exhaust valve is 1.71". The stock valve sizes on a 351M/400 is 2.04" intake and 1.65" exhaust.
The porting job will improve the flow enough to improve the VE, without a long duration cam with lots of overlap.
If you stick to the stock valve sizes, the horsepower drops to 326@4500 RPM and the torque stays at 457 ft-lbs @2000 RPM, but it drops off a little faster at higher RPMs.
To build this with stock valve sizes, will be cheap enough. It only requires flattop pistons, a cam, and porting over a stock rebuild. Also a 4V carb, intake manifold, and headers.
Porting can be a D-I-Y project, with a little study.
The porting job will improve the flow enough to improve the VE, without a long duration cam with lots of overlap.
If you stick to the stock valve sizes, the horsepower drops to 326@4500 RPM and the torque stays at 457 ft-lbs @2000 RPM, but it drops off a little faster at higher RPMs.
To build this with stock valve sizes, will be cheap enough. It only requires flattop pistons, a cam, and porting over a stock rebuild. Also a 4V carb, intake manifold, and headers.
Porting can be a D-I-Y project, with a little study.
Senior User
Joined: Oct 2003
Posts: 347
Likes: 0
From: in a house
thanks. I think I'll stick with the stock valves. not as much difference as I thought.
regrinding a valve down .040" is one thing but to cut a new valve seat out by almost an 1/8" is out of my comfort zone. one more task added to the need to learn list.
regrinding a valve down .040" is one thing but to cut a new valve seat out by almost an 1/8" is out of my comfort zone. one more task added to the need to learn list.