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I was looking for the torque formula. The main reason I wanted to add stroke to this build was to increase torque. An additional benefit is the improved combustion chamber gained from the custom Wisco piston and subsequent reshaping of the AMC combustion chamber. If curious, go to google and type in "calculating torque". You could spend all day reading.
How much torque are you lookin' to get?
The 401 builds torque real easy without any stroking or head modification. Increasing the head flow may even cost you on low end torque with this motor. Find the right cam grind and run 9.5:1 pistons with just a 4bbl and performer and you can get an easy 300hp/500ftlbs at 2,400rpm with stock exhaust and pump gas. If you're building for more torque then that.... I can see your interest in stroking it, but 500ftlbs is simply and relatively cheaply done.
Torque is King! 500ft/lbs and 300 hp at 2400 rpm would be fine. But I see this as a golden opportunity to get a little more. I do not intend to change the flow characteristics of the head, only the shape of the combustion chamber to bring the compression ratio down to about 9.3:1 and to improve the burn. I'm having a lot of fun doing this and along the way I hope others will follow along. I'd like to leave a parts list others can use to accomplish the same thing.
If you really want to get into the automotive math, check out the following web page. http://www.martindalecenter.com/Calc...o.html#AUTO-MT and play around with some of the calculators. There are some very in-depth calculations on valve efficiency, airflow characteristics and much more, stuff way over my head.
I found the formula to calculate horsepower. Torque is a measurable commodity, horsepower is calculated. The formula goes like this:
hp = (Torque X rpm)/5252.101.
So if your engine is turning 2400 rpm and there is a measured 500 ft/lbs of torque, the hp is calculated at (500 X 2400)/5252.101 = 228.47 hp.. You’ll have to go look and see how the 5252.101 is derived. Just for gee wiz, in the 1800’s James Watt concluded the average horse could move 550 lbs in one second or 550 X 60 = 33,000 pounds one foot in one minute. Hence horsepower is the ability to move 33,000 lbs one foot in one minute, friction aside.
J20,
If you're shooting for more then 500ftlbs then you are on the right track with stroking and you should get there pretty easily I would think. I've read (and read only) that ~4.0" stroke is possible.
BTW, on the 300hp, 500ft/lb @ 2400rpm of that 401 I had built.... those were desktop dyno specs, I gave the printout to the guy who bought my Cherokee and can't reach him to get a copy back. Pretty sure that the 300hp was not at the same 2,400rpm and that it was just a peak figure, peak torque at 2,400rpm was my goal. I really wish I had the cam specs, but doubt the machinist would still have it after five years
I am seriously considering spending some $ on a desktop dyno, seen the Dyno 2000 on EBay pretty cheap for like $20??? Does that sound right?
Also looking at the Performance Trends Engine Analyzer v3.2 and the v32plus.
There are several problems associated with a 4 inch stroke in a block with a deck height of only 9.208 inches. The rod to rod journal angles start to get large unless you are willing to sacrifice compression height, which will adversly affect the ring pack. Using a 3/16 top band and two standard dimension rings (1/8?) and an oil controil ring you need at least 1.1 inch. You could use a supported oil control ring but I believe a supported oil control ring adversly affects reliability. If you desire a race engine the rules change. If your after 100K miles of trouble free driving while building enough power to smoke the ch*vy, I think a 3.827 inch stroke (using the sbc 6 inch rod) should be the limit considering piston design and head work. If only the AMC engineers had increased the deck height to 9.5 or 9.6 inches when they decided the 390 needed grow some. If a 4 inch stroke was the goal, how would you get it? I think there are three options: 1) off-center grind the crank to accept a Honda size journal (1.8 - 1.85 inch) or some other rod with a 1.8 inch journal, 2) weld the crank up to increase the throw. I think a 1.8ish rod journal is too small for an engine developing such torque. Welding the crank to increase the throw is expecsive and 3) buy an after market crank, also very expensive. I think the biggest bang for the buck is off center grinding the crank (the cheapest of the above three) and I chose to use the sbc 6 inch rod because they are faily inexpensive. I welcome any other angles on this subject.
An integral part of this project is the camshaft. I put a lot of thought into exactly what I thought I needed. Unable to decide, I called the pros. I called Comp Cams (1-800-999-0853) and talked to Denis (sp). He asked me several questions: operating RPM (4000 or less), compression ratio (9.3:1), Vehicle type (J20 4X4 with manual 4 speed, future OD 5 speed), ring and pinion (3.73), tire size (33 X 9.50), cubic inch (425ish), other modifications (after market dual plane intake, custom pistons, small tube headers). After running the numbers through their software, Comp Cam's recommendation is the Extreme Energy 256H, XE256H. Denis said, considering the extra cubic inches, the XE256H would "feel" more like a 204 or 206 duration cam instead of the 212/218 duration stated for the 256H. He further stated, considering the application the XE256H would provide the performance increase (read that torque) I'm after without totally sacrificing fuel economy. It looks like we have winner. Have not ordered it yet, what say you?
I'm skeptical of salesman, any cam outfit is going to have "just what you need". That cam may actually work out perfect for your application, but I wouldn't buy it without running it's #s through a dyno first to see if it does to your torque curve just what you want. When I had my 401 built five years ago there weren't any box cams that would give me 500ftlbs at 2,400rpm with the mild build I was putting into it. That may have changed.
Maybe someone here has a file on that cam they can run for you with the addition of your other specs on the bore/stroke and run some comparisons. You might could do better with a custom grind. It's worth looking at in my opinion.
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