Conference oass::racers

I assume that your engine starts life in the mid 100hp range. Thirty
hp. is a very large number in that case.


I'm no expert on getting more power from an engine but I'd start with 
a full rebuild. New bearings, rings, guides, re-seat valves. While 
it's apart, you'll want to do the other internal things.

    Balancing;
    Blue-printing;
    port matching (not more than 1" inside the head);
    Electronic ignition

In that order.

You aren't allowed to lighten the flywheel but there must be a weight 
that it can go down to after being refaced. The same holds true for 
the crankshaft. You have to take off weight to balance it. There are 
also maximum numbers on head refacing or compression. In IT, those
numbers are all very small, but I think if you want that kind of
increase you have to do everything possible. 

Good luck

    Without a machine shop a lot of the work is going to be impossible,
    However a rebuild is probably a good place to start. But be for you
    embark on this task there is a book you might want to read. I don't
    remember the full name or the author but it is call something like
    "performace tuning 4 stroke engines". I never made much use out of it ,
    for that matter if it is redily availble in the US. However it does
    have a wealth of technical information about a large number of engines,
    US and european build engines as well as motor cycle. It covers every
    aspect that I can think of with regard to engine tuning, that also
    includes exhaust tuning.  I'll have a look on the book shelf for the
    right name and author and post it here.
    
    
    Good luck 
    
    
    Garry 

    Thanks for the replies.  Maybe you can clarify a couple of points:
    
    1) When rebuilding, especially wrt bearings and connecting rods, etc.,
       are there any issues around tolerances I need to be aware of, beyond
       simply specifying auto Mfr specs?
    
    2) Do I need clearances to be on the low side of the specified range?
       high side?  Does it matter?  Can clearances be different between
       cylinders?
    
    3) What aspects of rebuilding are MOST critical for high-end power?
       Torque?  Max engine speed?  Powerband width?  Reliability?
       
    4) What could I hope to gain from installing electronic ignition?
    
    
    Thanks again for your info.
    
    
    Mike

    The book was called 'Performance tuning practice and theory, 4 Stroke',
    its by a guy called Graham Bell and its published by Haynes/Foulis.
    
    Garry

What are you starting with?  You haven't mentioned carbs.  One way to get more
power is to get more fuel (properly mixed with air) into the cylinder.  What do
you mean by no cam change?  Stock?  Blueprinted?  I had a 2002 that I put a
"half race" cam, .020" over 10.5:1 Mahle pistons, tii distributor, a single 
40 DCOE Weber, and headers/exhaust.  The single Weber was a compromise between
absolute power and economy.  (This was a street car.)  I estimated that the 
power went from about 100 (1970 stock) to about 130.  That was close to tii
horsepower.  If you are going to get in there and replace all those parts, why
not go all the way?

Jeff

Re: .-1
From what I remember of the IT rules, you can't -
touch the cam
touch the carb
touch the pistons

You can put headers on it and he's probably already done that.

The electronic ignition should get you a strong and more reliable spark. 
Since you still have to use a distributor, you can't get the 
advantage of a crank fired ignition. With that you can map the advance 
better and insure that you don't get cross-fire which can happen at 
high rpm in a distributor.

I'm not sure what to use for clearances. Double check this but I think 
they should be a little on the loose side. This will compensate for the 
expansion which will take place because the temperatures are higher in 
a race car.

Glenn

>    3) What aspects of rebuilding are MOST critical for high-end power?
>       Torque?  Max engine speed?  Powerband width?  Reliability?

I believe horsepower is directly proportional to RPM, within the limits
of the equipment, so if you can raise your redline from 6000 to 7000 (and
do whatever you can to make it pull to that RPM), your horsepower should
be increased by 17%, assuming a linear HP curve.  A lot of assumptions,
I realize, but that's why all the "big boys" (F1, Indy, NASCAR) have their
mills buzzing up into 5-digit RPMs.

The importance of a wide powerband and maximum engine torque are going to
depend a lot on the type of driving you do.  I'd think for road racing
high rev power, even at the expense of low and some midrange, would be fine,
unless you couldn't bring yourself to wind it out all the time.

Reliability is greatly influenced by car prep, but the more power you pull
from your engine, the more it will be stressed, and the more often parts
will fail.  You will have to decide what tradeoff is best for you.

Carl

.7>  A lot of assumptions, I realize, but that's why all the "big boys" (F1, 
.7>  Indy, NASCAR) have their mills buzzing up into 5-digit RPMs.
    
    Minor nit, NASCAR doesn't get 5-digit RPMs.  They only get seven or
    eight thousand out of those pushrod V-8s...
    
.7>  The importance of a wide powerband and maximum engine torque are going to
.7>  depend a lot on the type of driving you do.  I'd think for road racing
.7>  high rev power, even at the expense of low and some midrange, would be 
.7>  fine, unless you couldn't bring yourself to wind it out all the time.
    
    Actually for road racing I don't think maximum high rev power is the
    optimal choice.  Car characteristics, especially handling and gearing,
    may modify this, but in general road racing consists of more
    acceleration than top straightaway speed.  Thus torque is important,
    not just horsepower.
    
    You've got to factor a lot of things into it, but in general you want
    to be able to accelerate up to speed out of corners as quickly as
    possible.  Thus you most want to make power (or torque) at the RPM 
    you will turn as you accelerate.  If you have a wide variety of gear
    ratios to swap (as we do in FF) you can match the track conditions
    fairly well, while if you are stuck with the set that's in the box you
    need a more flexible engine setup.  So FF goes for a narrow peak power
    band while IT might want a much broader curve...
    
    Like anything, you gotta consider the application in the design...

    
    
    Power, in the words of Keith Duckworth ( the worth of cosworth) '
    the power you get from the engine is equall to the size of the bangs,
    times the rpm'. 
    
    
     

    Thanks for all the great ideas & info, this really helps get the
    neurons cranking.  Please, keep 'em coming.
    
    More details:
    
    I run a stock 4 speed tranny & a 3.64 rear gear ratio.  Carb is a Weber
    32/36 DGV (can't remember jet sizes); have a header; breathes cool air
    from over the left headlight (high pressure area); exhaust is a 2" pipe
    exiting rear of the car, with a "Turbo Tube" muffler (reduces noise to
    about 100dB vs 108 limit.

    Here are some numbers:

    @Lime Rock Park:
                            		GEAR   RPM   
    Start of front straight:             4th   4800
    End of front straight:		 4th   5700
    Beginning of No-name straight:	 3rd   4500
    End of No-name straight:		 3rd   6100  red line = 6400
    Begin. of back straight:		 3rd   4700  top of the hill
    End of back straight:		 3rd   6200
    Exit of Westbend:			 3rd   5700
    
    
    @NHIS

    Same engine as above, but 4.10 rearend ratio

    Start of front straight:		 3rd    4800
    End of Backstraight:		 4th    5900  (off the oval)
    Exit turn 3:			 2nd    4700  (slowest turn)
    Into turn 6:			 3rd    6100
    Into turn 9:                         3rd    6000
    Exit turn 10:			 3rd    4200  (?)

    With the 4.10 ratio, I've been able to keep the engine between 4200 &
    redline everywhere without shortshifting or quick up-down shifts.  The
    only problem is grunt.


     Mike
    

    I don't race a car but I do race a motorcycle so the following applies
    from motorcycle experience.
    
      1)Higher RPM = more horsepower ; this is only true if your engine can
    breathe (i.e. fill it's cylinders) efficiently at the higher
    RPM.Normally stock cams are optimised to breathe best around the
    manufacturer's red line so as you can't change cams lots of revs won't
    buy you much. 
    
      2)Try to keep the engine easy to drive,don't play around with
    ignition timing etc to get more power if it's only in a narrow band.
    As is mentioned in a previous reply lots of time in a road race is at
    less than max revs. I find that an engine which has lots of grunt in
    the mid range is faster (for me any way) on most road circuits.
    
       3)Clearances--keep it nice and loose--less internal friction=more
    rear wheel HP. Additives like Slick 50 can help if allowed
    
       4)Make the best of what you've got,you say that you don't know your
    jet sizes,have you tried a plug chop to check your full throttle
    mixture. You can gain a lot that way.
    
        5) Is your sump properly baffled to reduce oil windage. With stock
    engines ever little helps.
    
        6) Have the crank/rods/pistons/flywheel assy been dynamically
    balanced,again this can buy a little in reduced  friction/flexure losses
     
     With the restrictions that you mention I think that 30 hp will be
    difficult to come by but lots of little things add up. The ultimate
    expression of this is a full blueprint job where all the manufacturers
    tolerances are exploited to the maximum,eg minimum combustion chamber
    volume,maximim cam lift/duration etc within the manufacturing tolerance
    stated for the component. After that about all you can do is alter cam
    timing using offset dowels,play about with the distributor advance
    curve etc but that needs a dyno,time and MONEY. 
    
                      best of luck
    
                               Dennis              

I don't think I have the quote quite right but it was something like:

Horsepower is directly proportional to cubic dollars

Glenn