I know there is a lot "what cam do I use" on this site, But I have a little different question I think. I have a 400 with a Speed Pro 208 duration cam. I am a little disappointed with it. It is lazy of the line. It won't even chirp the tires "Stock it would." My question is what does the 400 like? Does it like equal intake and exhaust or more exhaust? I've heard the bigger the cam you lose bottom end. Do you actually lose it, or do you not gain as much as the upper end? I'm looking something that's not a dog of the line. It a daily driver, But I like to get in it to. My set up is a balanced assembly, 9 to 1 pistons, heads professionally worked, Edelbrock Performer intake, Holly 600 vac sec., stock ignition for now. Its in a 79 F150 shortbed with 3.50 gears and 32 inch tires. Any help would be appreciated. Sorry, guess it sort of still sounds like "what cam do I use." But it looks like you guys love this sort of thing. Thanks

 

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>My question is what does
>the 400 like?
>Does it like equal intake
>and exhaust or more
>exhaust?

carp1,

I think the 400 likes a lot more cam duration than some comparable displacement engines because of it's long-stroke design. In fact, one of the main reasons the 400 was so weak in factory configuration was that it was so badly under-cammed (not to mention the retarded cam timing and low compression).

In my experience, the 400 likes a little more exhaust duration and a little more exhaust lift as well. Factory specs for the 400 truck cam are 190/196 @ 0.050". I don't know the specs on your Speed-Pro cam, but I wouldn't recommend a cam with equal intake and exhaust duration for the 400.

>I've heard the bigger the
>cam you lose bottom end.
>Do you actually lose it,
>or do you not gain as much
>as the upper end?

Gaining more at higher rpm than at low rpm is almost always the case with a high-performance cam. Only a relatively mild "RV" type cam will improve low-end as much or more than mid-range/high-end. Unfortunately, "RV" cams really don't improve power very much at any point in the rpm range.

A moderate high-performance cam (say about 215/225 @ 0.050" in an M-block) will give you much more power at the stock torque peak (about 2.2K rpm) than an "RV" cam will. The HP cam will also increase the rpm of your torque peak up to about 4K, which gives you a much wider range of usable power. In general, a moderate HP cam in the M-block 400 should give about a 40-50% improvement over stock torque output at the stock torque peak, and 100% or more improvement over stock torque output at the new torque peak.

On the other hand, an extreme duration (say more than 240/250 @ 0.050") might actually reduce the low-end power from the stock configuration, and it would probably put your torque peak at over 5K rpm and make the engine unusable for a normal truck application.

>My set up is a balanced
>assembly, 9 to 1 pistons,
>heads professionally worked,
>Edelbrock Performer intake,
>Holly 600 vac sec., stock
>ignition for now.

Sounds like you have a solid foundation. I'd suggest for a moderate (but substantial) performance improvement, you go with a cam that gives about 215/225 duration @ 0.050" and gross lift of about 0.52-0.54".

Good luck.

BubbaF250

1980 F250 4x4 Custom, 351M/NP435/NP208/D44HD-TTB/D60-FF/3.55s 6750 GVW, Rust & White.

 

Thanks. That exactly what I was looking for. It will be a while before I do it though.

 

I posted a list awhile back of all the cams that made my "short list" for the 400 I built. Although my engine has yet to make it off the engine stand in my garage I'm pretty hopeful that the cam I chose (Crower 15241) will turn it into a fire breather. You can see the list at:

http://home.pacifier.com/~bbeyer/Cam_Comp.htm

 

the big issue with the cam is its a 400 grind, if you say opt for the 351c grind, well, ill stop there........

 

I think your setup sounds OK. Your cam (208 duration?) is is very conservative and should give you good low RPM torque. Longer duration will only improve your peak Torque and HP. Your problem may be a lean mixture.
Change the primary jets in the carb to make it richer. Better yet get a 650 Edelbrock carb, but you may still need to tune the mixture.

Dan Lee
'53 F100
400C-4V

 

I have tried the carb thing. I have made it rich and lean "went far on both scales" I had a Carter 625, same as the Edelbrock. The stock cam would out pull this one. This one does extend the rpms a little more. Sorry about being veg one the specs. It is 208 duration on in and ex, and .484 lift in and ex. Not happy with it.

Thanks for the suggestions.

Chad

 

At low RPM any decent cam, valve diameter, timing or lift will produce good power, since there is plenty of time to fill the cylinder. You cannot get more into the cylinder until the intake and exhaust manifolds begin to 'tune' and produce a supercharge/scavenge effect. Long duration cams can affect the low RPM power due to overlap which reduces manfold vacuum. Other factors to consider are mixture, valve timing, and spark timing.

You checked the mixture, how about the accelerator pump. Set it on the longest stroke.

I hope that you have a zero degree timing chain.
Your initial spark advance is set at least to stock.
Your vacuum advance is connected and working.
Check your manifold vacuum, you may have a vacuum leak.
How is your idle, smooth and steady? With that cam it should be.
Did you degree out the cam when you installed it to verify that the timing is right and it is installed right?

I am using a Crane H278-2.

Degrees Duration @ .050 Int./Exh. 222/234
Degrees Advertised Duration Int./Exh. 278/290
Degree Lobe Separation 114
Open/Close @.050" Cam Lift Int./Exh. 2/40 56/(2)
Lash Hot Int./Exh. .000/.000
Gross Lift Int./Exh. .539/.534

This works good for me, but I have a high stall torque converter and I am not concerned about power at low RPM.

Another thing to consider is venturi velocity. A carb that is too large will reduce the venturi velocity and will cause a loss of power at low RPM. Also large ports or headers can produce this.
What is the size of the primary venturi's in your carb as compared to your stock carb?

Dan Lee
'53 F100
400C-4V

 

Answers to questions.

You checked the mixture, how about the accelerator pump. Set it on the longest stroke.

Check

I hope that you have a zero degree timing chain.

Check

Your initial spark advance is set at least to stock.

10 btdc

Your vacuum advance is connected and working.

Check

Check your manifold vacuum, you may have a vacuum leak.

17 inches Removed all hoses and plugged them at manifold to check and no change.

How is your idle, smooth and steady? With that cam it should be.

Not always, This is another problem I have. It dosen't idle real smooth and it has a shake at 1200-1500 rpm. Check post "The Shakes Have Me Stumped". Maybe you can think of something.

Did you degree out the cam when you installed it to verify that the timing is right and it is installed right?

I had a builder do the engine. I am not sure if he degreed it or not.


Another thing to consider is venturi velocity. A carb that is too large will reduce the venturi velocity and will cause a loss of power at low RPM. Also large ports or headers can produce this.
What is the size of the primary venturi's in your carb as compared to your stock carb?

It is a Holly 600 vac secondaries. I don't know the size of the ventri's
Stock exaust manifolds, 2 1/4 dual exaust with twin cats.

Hope this helps you to think of something. I thought I was decent with engines, but this ones got me.

Well thanks.

Chad

 

Have you checked the firing order?
How about the plug wires, do you have a dead or intermittent wire? Use a timing light on each plug wire, look for one that misses.
What color are the plugs? Are they all the same?
Have you done a compression test or better yet, a leak down test, or both?

You said that sometimes the idle smooths out. That eliminates anything mechanical and leaves air(vacuum), fuel, and spark. I'll put my $0.02 on spark.

 

I pretty much came to that conclusion too. Since I had two brand new carbs and it ran the same with them. But here's the thing, I have two trucks, this one that is rebuilt and one that is not. #2 truck has over 200,000 original miles and it ran smooth. So I have swapped the module, dist, wires, coil, and I put new plugs in it and no change. I am thinking about getting a new dist and after market ignition system. To clarify a little, the shake or miss is not an actual miss as to pull a wire or something, it's more of an ueven fire. If you put a glass of water on the truck it shakes it and you can feel it in the truck. You can watch the tach jump a little. The #2 truck was rock steady.

We did a compression check after it was built and it was well within specs. Haven't done a leak down test though. The pluggs look fine, but two had a little carbon on them.

Whats I am worried about is I have a lot of money in the engine and I don't know if this shake and ueven fire, even though its not really bad just annoying, will lead to machanical problems in the future. Will it put stess on the bearings and wear them out faster or am I worried about nothing.

Thank for the info keep it coming.

Chad

 

Put a timing light on the coil wire, shine the light on something white like paper, look for uneven firing. Also try it on all plug wires, especially those two that had the carbon. If it is spark related it will show up.