.................

POLICY AND TECH

**TOUGH STUFF**
**One of the toughest things I have found about developing specific
combinations to street or race is that some people want to argue about
whether they work or not. Sometimes those people are semi-famous. Sometimes
they are not. Generally speaking they have never actually built anything
themselves although they talk like they have. They usually shelled
out the gold and hired it done using the general philosophy that if it
costs more it must be better. Forgetting that everything that ever was,
was, at one time, developed by somebody. To be honest the high dollar approach
works. Given enough money and enough time success will eventually come.
It is possible, however, by using the science that is available, to develop
a very successful specific combination. Sometimes the results are amazing.
How do you argue with someone who condems a set-up you actually have running
that they have never built or seen. The answer is you don't. The results
speak for themselves and whether they choose to believe them or not has
no bearing whatever on whether the results are true. Everything you see
on this site I have actually done. If it is not a finished and tested deal
I will tell you so (as in the 380 project for instance.) Otherwise you
can "take it to the bank." ***Don Dulmage*
**If you don't have mega bucks to spend then
science is the only viable alternative.**
**The two most important words in the English
language are "IF" and "THEN"**
** TECH LIST** Scroll down until
you find your favourite

*Dons Formula for Approximate Horsepower***valve lift divided by 500, times cu inch displacement, equals horsepower**
**
or**
**valve lift/500 X cu. in.= HP**

**ie 520/500 X 440 = 457HP**

**That means that a 440 of reasonable set-up with a valve lift of .520"
would in an average set-up make 457 HP. Not too far off of the mark for
planning purposes. Sure it is possible to get more, but this is certainly
realistic and useable, not to mention, quick. I use this a lot for street
set-ups and it seems to me to be very practical. It is my own formula.**

*Dons Law***We use this to quickly calculate required carb sizes. It is approximate
but is so close to the actual results of the real formula that I use it
almost exclusively. It is my own formula as well.**

**To find what size carb an engine will require at 7000 RPM double
the cubic inches**
**
or**
**cu in X 2 = CFM @ 7000 RPM**

**ie 350 X 2= 700 CFM**

**Since carb sizes come in 50 or 100 cfm steps it is a workable and
quick formula. More detail and a comparison with the real formula is covered
in the book(Old Reliable)**

**Feel free to use and quote the above formulas but remember they are
mine.**

*Tuned length of an intake runner.***Runner length is not an exact science because of the variables involved
but a rule of thumb formula I often find handy for sorting out manifolds
is from Philip H Smith (Tuning For Speed) It states that:**
**the intake runner should be approximately equal to 90 divided by
the RPM in thousands**
**
or**
**90/rpm in thousands = length in inches**

**ie for 6000RPM 90/6 = 15 inches**

**ie for 7000RPM 90/7 = 12.85 inches.**

**The measurment is taken from the intake valve to the plenum
area. If your current 440 Mopar manifold seems too short now for your RPM
range you're beginning to get the picture.**

*Gearing and Tire Size vrs RPM and MPH*

**MPH= Rpm divided by gear ratio = Axle RPM**
**Tire height in inches X 3.14 = distance traveled each tire revolution
in inches(circumference)**
**To convert that to feet divide by 12
(1 foot = 12 inches)**
** Axle RPM X the Tire circumference in feet = feet travelled
per minute**
**Feet travelled per minute X 60 = feet travelled per hour**
**Feet travelled per hour divided by 5280 = MPH (1 mile = 5280
feet)**

**ie 6000 RPM with 4.10 gears on a 26 in tall tire is**

**6000/4.10=1463.4 Axle RPM**
**26 X 3.14=81.64 inches tire circumference**
**81.64/12=6.803 feet tire circumference**
**1463.4 X 6.803= 9955.5 Feet per minute**
**9955.5 fpm X 60 = 597330 Feet per hour**
**597330/5280 = 113 MPH**

**This is the most basic way to figure it out. I used it in trade school
when teaching because it helps understand exactly what we are figuring
out and why. Besides it works well. To find yours substitue your figures
for RPM, Gear ratio and Tire Height.**

*Head Flow Requirments***(Smokeys)**
**To find what the actual requirements for head flow in an engine
are Smokey Yunicks formula for 8000 RPM . If I only want to turn 6000 rpm
then I multiply the results of his formula by 6000/8000 to get the required
number. This allows me to alway use the same factors in the formula and
avoid mistakes. If your a wiz at math this may seem simplistic to you .
So be it, it works!**

**the formula uses the volume of one cylinder in cubic inches times
5.5 to arrive at the required air flow for 8000 RPM**

**For instance**
**A 340 would need 340/8 = 42.5 X 5.5 = 233 CFM at 8000 rpm**
**At 7000 rpm it would need 7000/8000 X 233 = 204 CFM**

**A 440 would need 440/8 = 55 X 5.5 = 302 CFM at 8000 RPM**
**since 8000 is too high for any 440 I could afford lets try 6500
RPM**
**6500/8000 X 302 = 245 CFM which is right about where a good 452
head would flow with stock valves.**

**These figures may seem slightly low but they certainly give us at
least a place to start when calculating air flow. They are probably with
in 10% or less though and very attainable. I use them as a guideline regularily
and find them handy.**

*Engine Displacement***How many cubic inches is it now?**
**To find out multiply the bore times the bore times .7854 times the
stroke times the number of cylinders. Why .7854? Because a circle is 78.54%
of a square of the same dimensions in area. 78.54% expressed as a decimal
is .7854.**
**We use this instead of pi because we found that it completely
eliminates the confusion between the area and volume formulas and the circumference
formula. It is also very easy to remember as the 7854 are in the left corner
of your calculator pad.(across two**

**If the bore is 4.1" and the stroke is 4" with 8 cylinders then the
displacement is**
**4.1" X 4.1" X .7854 X 4" X 8 = 422.48 cu in**

**Sometimes it works better for some of us to do it in steps like**
**4.1 X 4.1= 16.81**
**16.81 X .7854 = 13.02574 (It would be OK to use 13.02)**
**13.02574 X 4 = 52.810296 (or 52.81)**
**52.810296 X 8 = 422.48236 or 422.48 cu in**

*Dons Rule for 8 cylinders on a 4 inch Bore***A 4 inch bore is a special case and allows for a terrific shortcut
I discovered by accident many years ago. It is "Stroke times 100 plus 2
= Cu Inches"**
**ie for a 350 Chev stroke is 3.48 and bore is 4 inches**
**3.48 X 100 = 348**
**348 + 2 = 350 cu in**
** or**
**3.48 X 100 + 2 = 350 cu in**
**This is my own formula as well.**

*HEAD FLOW VRS HORSEPOWER***There is a relationship between head flow and horsepower. We use
the rule of thumb of 2.2 cfm per horsepower. It gives us a reference point
at the very least and seems to be a fairly practical formula for commonly
available setups.**

*MAX HP per CU IN***It is generally accepted that the max hp per cubic inch on gasoline
in an unblown engine is about 2.2 hp per cu in.**

*PISTON SPEED in FEET PER MINUTE***What is a safe engine speed ? How much rpm is too much? When does
it become damaging to the engine?**
**Generally speaking anything under 3000 feet per minute piston speed
(or more correctly piston travel) will not harm an engine. In a high
performance application 3500 FPM can be used since the burst at that speed
will be short in duration. For racing most engines are outside of this
envelope and are hurting themselves from the minute the RPM climbs above
safe piston speed. Good parts changed regularily is the only solution to
that problem. This piece is about how to plan to keep the engine below
where it is hurting itself.**
**IE If a 440 with a 3.75" stroke is turning 4000RPM the piston speed
is--**
**Stroke X 2 X 4000 divided by 12 = FPM**
**
or**
**3.75" X 2 X 4000/12 = 2500 feet per minute which is very safe however
if it turned 8000 RPM that would be---**
**3.75 X 2 X 8000/12 = 5000 feet per minute which would require "the
broom" if anything but mega buck parts were used.**
**This can give you a pretty good idea of what a reasonably safe engine
speed is and what it is not.**

*Horsepower***The condensed formula for horsepower is Torque X RPM/5252 =HP**
**Because of the 5252 factor used to divide torque and rpm then
torque and horsepower are always the same at 5252RPM. I always check
Dyno charts to see if this is so. If they aren't the Dyno charts are fakes
and yes I have found a couple of them.**
**Torque is the amount of twist**
**Rpm is the number of twists**
**Horsepower is the combo of both of them**
**Bigger torque is a stronger twist**
**Bigger Horsepower is a larger of number of twists but not nessecarily
bigger twists**
**If you have sufficient number of twists per minute you can raise
HP even though torque is beginning to fall. (to a point but eventually
torque falls off so bad that HP does as well)**
**Max torque occurrs at max volumetric efficiency (or where the engine's
breathing is the most perfect)**

*Rod Lenth to Stroke Ratio***There is a ratio often cited relating to rod length ratio. Rod length
ratio is found by dividing the centre to centre length of the rod by the
stroke. For Instance: If the centre to centre length was 6" and the stroke
was 3" then the ratio would be 6/3=2to1 or just 2.**
**Ratios of around 1.85 are thought to be ideal. The longer the rod
is, the less the rod is moving the piston by draging it from the side and
the more piston movement is related to the crankshaft. A long rod motor
tends to move the piston up to and away from TDC at a measurably slower
rate and therefore requires slightly less peak flow in the cylinder head
and will have a slightly broader torque range. There is much debate over
the effects of this and how actually important it is. It appears the effects
of a long rod are significant but not the, be all/end all, of the whole
deal. If this is difficult to comprehend make yourself a cardboard model
and watch how much the piston moves away from TDC for each degree of crankshaft
rotation with both a long rod and a short rod. There is no debate though
that a long rod motor is easier on the cylinder wall and piston.**

*STROKERS, PROS AND CONS***What are the advantages of a longer stroke?**
**Are they real or just hype?**
**These questions are often asked but the answers are not always as
straight forward as we might like.**
**It is generally thought that the ideal bore stroke ratio is 90%.
That means that the stroke should be 90% of the bore. This combination
gives a reasonable amount of piston travel per degrees of rotation without
being excessive. It also allows the bore to be large enough to carry valves
of sufficient size to properly feed the engine. A Hemi, because of its
inclined valves, can cheat this a bit but in a wedge it is a severe limitation.
If the 90% rule is followed then all should be well. To properly understand
this, one should ask, "Are there any disandvantages to a short stroke?"(Looking
at the opposite problem will often clarify a point) The answer is yes.
A short stoke motor requires a high dome to obtain a high compression ratio
which comes with its own set of problems. Sometime the dome is so high
that flame travel in the cylinder suffers. The piston does not move away
from TDC as far (travels a shorter distance per degrees of rotation) so
it may be plagued with valve to piston clearance problems that will be
difficult (but surmountable) at best. It will have to operate at higher
RPM to obtain the same HP because it will be smaller in cubic inches than
say the 90% motor. RPM is expensive. Valves ,valve springs, cams, retainers
, pushrods etc etc must be of the very best (read expensive) quality to
survive this. If the engine is only making the same HP as the larger one
can at a lower RPM, then all one has accomplished is to build a difficult
,expensive, high maintainence "gernade". However, the same problem exists
at the other end of the scale. If the stroke is too long then the cylinder
heads cannot keep up with the sheer volume of air being pumped . Often
a stroker will produce the same power but at a lower RPM. Is this because
of the torque characteristics of the long stroke, as some would suggest,
or is it because the cylinder heads have reached their peak at a lower
RPM than would have happened on a stock stroke engine? In many cases the
latter is true. Also in a long stroke engine the rods are stressed as piston
speed in feet per minute increases to the danger point. Even a high dollar
engine with the very best parts will require constant replacement if pushed
to those limits. The best reason to built a stroker is because you want
one. What are the guidelines? Like we said at the start. Stroke should
be 90% of the bore and no more. This is not the total sum of the story,
by any means, but these are some of the things worth thinking about before
you part with your gold.**

**If you like this page and would like some more of this let me know
at "big-d@sympatico.ca"**
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