It dawned on me this morning that I'm going about this all wrong. :/

The smart thing to do (if it's possible) is to look at torque graphs
with various parts assembled and pick the graph out -then- build
an engine to match the engine that made the graph.

Heard an engine runs at it's most efficient when running at the
RPM of its peak torque.

Is that true? :)

If so... I'd like the peak to be in the 2500 to 3000 range. LOL :)
With a 4 inch stroke.

Any ideas?

Alvin in AZ

 

A stock 351 makes its peak torque at 2800 rpm....

 

How good do '91 300-I6 heads breath compared to '91 351w heads?
The '91 Shop Manual shows the exhaust valve to be 1/10" bigger on the 300. :)

Alvin in AZ

 

Here are three articles all on one page...
1) Torque and Horsepower - A Primer
2) Setting the Record Straight on Torque and Power
3) Plato and Socrates Discuss Torque, Power and Acceleration
http://www.vettenet.org/torquehp.html

Re-read that after starting this thread about the 408w "truck engine". :)

I still want my 408w to have its peak torque between 2500 and 3000.
'91 Bronco + ZF is going to be turning 2500 rpm at 80mph.

High lift, short duration cam with short rods and a 4 inch stroke kinda
like a 300-I6 with two extra cylinders.

Is that too much to ask? :)

Alvin in AZ

 

Cool. :)

Sounds like the perfect spot for my build! :)

I see that information as... the factory knew what rpm the engine
was going to be generally used at and designed for that rpm.

How do you see it? :)

Alvin in AZ

 

....No thats not to much to ask , go for it , as some of the guys were trying to tell you the stock 351 heads are to small for a 351 let alone a 408 , then you want a hi lift cam , the motor needs to breath , so just build the motor for low end TQ , what are you using the truck for that you dont want it to rev .....Lew

 

Here are some graphs to demonstrate how better heads provide more power across the whole powerband. The lower trace is with the stock heads and the upper is with better heads. Simple put there is no downside to better heads on a 351 so that goes double for a stroker motor.

 

And for comparison sake here's a 408 graph I did for somebody using some TrickFlow heads and various cams. You still want to use the stock heads?

 

No! LOL :)
Thanks a lot, Conanski! :)

Alvin in AZ

 

You should be able to find some used aftermarket heads in good shape for not much more than what you would have spent refurbishing the stock heads.

 

I notice that the carburetion in those graphs is 800 CFM and 1000 CFM respectively. That's not appropriate for the low rpm Alvin specified. How about graphs with 600 or 500 CFM more in keeping with a 3000 rpm rev limit?

It's a question of matching components. Presumably a huge carburetor and aftermarket cam will work better with higher flow heads.

 

Those are all EFI graphs and that is intake CFM capacity which is appropriate for the particular engine combinations in those graphs.

 

Ahhh... I was thinking carburetor even though as I reread the post now I see it will be an EFI engine. Please disregard my last post.

 

I'll just add that for best results(broadest TQ curve) the intake airflow capacity of an EFI motor should be sized appropriately for the motor, but EFI is much more tolerant of oversizing because this doesn't directly affect fuel atomization like it does with a carb.