I installed a tach from Summit and I can't get my 400 to go over 4000rpm. I have a C6, 2wd, so why wont it spin any higher? Im not real sure of my gearing. It's 77 F-150 custom.

 

In gear or in neutral? The old Ford engines had a rev-limiter called a restrictive exhaust and intake.

With some improvements you can make them better. My old 390 in stock trim would only turn 4500 RPM but when I finished my modifications it would sing along at 9000RPM with no problems. I often cruised down the highway at 8500RPM just to see the effect the noise had on the livestock and farmers. Hey, -gas was 25¢ per gallon and I had to have a little fun. BTW, I was exceeding the speed limit by a bit even in low gear. Racing new caddys and lincolns out on the highway was much more fun when I downshifted at 120MPH and left them in the "dust". Nobody in town would race.

 

I thought that the performer intake and hedman hedders would help that out. it was in gear im sure it would spin to five grand or more in nuetral but I dont feel too froggy for that lol

 

Which gear? In my truck 4000 in high gear is about 110mph. That's a lot of wind to push. The most I ever saw was 4400 rpm. I don't know how fast that was, and at the time I didn't really care if I lived another day or not. Now I have better reasons to live, so I don't do those things anymore.

Otherwise I would say that you are running out of fuel. The line from the tank is only 3/8 and it's full of bends and curves and it's pretty far from the pump. But it could be a lot of different things like timing and the size of the cam. A stock cam is optimized to produce peak HP at 3200 rpm or some ridiculous crap like that. A good 400 is going to need something in the neighborhood of 215-220 degrees of duration at .050 lift in order to make peak HP at more than 4000 rpm. The stocker only has around 190 degrees of duration at .050 lift.

If you want RPM you need to change engines. The 351 will rev much better. A good 351C with 2bbl ported heads and a 268 cam will spin 7K pretty easily, but not in high hole in a big truck, unless you've got a lot of gear. Don't try to spin the 351M that high, the rods are too long and the pistons are too heavy, they tend to part ways at around 6500-7K rpm. That is if the stock valve heads don't come off the exhaust valves first.

A good example of speed vs rpm is that of the Shelby Cobra. With the Nascar engine in it, you could top 100 MPH in 1st gear at around 8500 rpm give or take a little because the old tach's weren't always that good when you spun them that hard. In my friends Chevy truck 8500 rpm in 2nd gear ( 4 spd truck trans) is about 50-55 mph. Now if you've never heard a smallblock run past 8 grand, I'm gonna tell you it's a sweet, but scary sound in a fullsize truck.

 

Im not sure how fast the truck was going, ran out of numbers a while back lol. it has an Edelbrock Performer Plus camshaft in it though, so the stock cam is out of the question. I just wonder why the engine wont spin over four grand.

 

According to Dyno 2K, the peak Horsepower with the Edelbrock cam is 312 @ 4500 RPM. That is with a 600 CFM carb, Dual Plane Intake, 9.0:1 CR and headers.
The torque is good (448 ft-lbs@2500 RPM), but falls off rapidly at 4000 RPM.
I think that you are getting all the RPMs that you will get with a load on it.

I never did like that cam.

 

I have all of that except its stock CR. What would be a better performing cam without sacrificing driveability?

 

The dual pattern cams from either Comp of Crane. I have a 941 Crane in mine which calls for a minimum 8.7:1cr and I'm right there. Spins to 5200 easy and that's where I stop it but it's still going. Their 901 cam I thinks has a powerband to 4700 and you wouldn't need a cr increase for that.

 

Is milling the heads the simplest way to bump up CR in a 400? What about the Comp Cams 268H thats spoke of here often?

 

How much low end torque are you willing to give up? A Comp Cams 275DEH or Crane H272-2 will give you more RPM, but you will lose a little low end torque, and probably some fuel mileage as well.

The best way to increase the RPM range is to get it to breathe better. You should get some work done on the heads, or better yet some great flowing aluminum heads.

You could run 64cc alloy heads with your pistons and a 265DEH cam and pull over 5000 RPM.

Why do you want more RPM, most want low end torque?

 

I just want to be able to take advantage of the full powerband. I expect it to pull to five grand.

 

Volumetric Efficiency (VE) is the percentage of the cylinder filled in one intake cycle. High power requires high VE. To get high VE at high RPMs requires high air flow rates (CFM). There are three major components that affect the air flow rate.

The first being the carb. The larger the carb, the higher the CFM. The downside of a large carb is driveability problems at low RPMs.

Another component is the cam. The amount of lift, the rate of lift, and the time the valve is open all contribute to the ability of a cam to supply high VE at high RPM. The downside of a long duration cam is reduced Dynamic Compression ratio and reversion. This robs power at low RPM, and creates driveability problems.

The third component whch contributes to high VE, is the head flow. Both the intake and exhaust ports and valves must produce the highest flow possible from low valve lifts to the cam's maximum lift. Most ports on V8 motors are poor when it comes to head flow, because they have been designed for intake manifolds that fit under a low hood, and exhaust manifolds thst fit a tight engine bay. With careful porting a head can be made to flow good at any valve lift. There is no downside to porting a head properly, so that it flows better across the range.

Ford 335 series heads flow fairly good as is, but the exhaust ports are somewhat restricted.

I recommend that you port your heads and have them checked on a flow bench. Also call Edelbrock about their #2172 cam. Tell them that you can't get over 4K RPM. Maybe they have a better cam in 2005. If they can't help you, call Comp Cams.

Ported Aussie heads or CHI or AFD heads will make a big difference. Aussie heads will raise your Compression Ratio, so you can run a bigger cam, but they don't flow any better than your heads.

 

Excellent information. Do you have any power figures for a 400 with aftermarket heads, a decent cam and exhaust?

 

a 400 (+0.030) with a 600 CFM carb, dual plane intake, headers and replacement dished pistons, CHI-3V heads, and a 265DEH cam will give you 444 ft-lbs torque@2000 RPM, peaking at 459 ft-lbs@3500 RPM and 417 ft-lbs@5000 RPM. The peak HP is 397@ 5000 RPM.
If I go to a 275DEH cam, I get 415 ft-lbs@2000 RPM, 451 ft-lbs@4000 RPM peak, and 427 ft-lbs @5000 RPM. The peak HP is 416@5500 RPM.

If I use a Hydraulic roller version of the 275DEH cam, I get 431 ft-lbs@2000 RPM, 472 ft-lbs@4000 RPM peak, and 421 ft-lbs@5500 RPM. The peak HP is 441@5500 RPM.

If I use the XE268 cam, like Tim Meyer used, I get 396 ft-lbs@2000 RPM, 440 ft-lbs@4000 RPM, and 402 ft-lbs@5500 RPM. The peak HP is 422@5500 RPM.

I am using a flattop piston in my motor (10.3:1 CR) with CHI heads (64cc), and a 281 degree duration Hydraulic Roller cam. Mine comes in at 540 HP @6000 RPM.

The CHI heads are raised port heads, so adapter plates are required to mount a 351M/400 intake manifold. CHI supplies the adapters, but some matching is required.

I believe that the 2V AFD heads will mate to a 351M/400 intake without adapters. Those heads flow as good as CHI. I would check on the fitment issues before ordering.

Let me know if you want any other combinations.

 

Whats the difference between a hydraulic cam and a hydraulic roller cam? What makes the roller more powerful? Sorry for all the questions, im just less informed than others.