HarleyTechTalk

  Evening  Gents  ,  I am doing the final  cc/measure    "as built "  for my 124   race project   . My target is  12 :1   compression  . Looks like Im` right there   (using a few different calculators )    My Dynamic compression will be   9.88 :1   calculated .  I have 93 octane pump gas available. I have 105 race gas available  and   can dilute  if necessary.  This is new territory for me . My last build was a 107 @ 10.7  compression and I had no problems tuning that . I have A DTT ignition that I  have been using ,and   it will go on the new build .   I`m going to break in using a G carb ,  ...any guidance will be appreciated  on the fuel issue  thanks   ........bladerunner

With those base numbers you could run 93 pump,  if you have a bit of ping issue that adjusting timing is costing you too  much power, slight mix of race fuel to pump gas. Don't forget,.. the ability of fuel to resist detonation is a function of more than just octane. One station to the next on pump gas is a "random guess at best"  Straight 105 would get you there as well, and you may or may not  find some more power with more  ign advance as well.. Your engine is not what most would call a race gas engine.  Plenty of guys running that dynamic comp ratio on pump fuel.

Just trying to use a DCR is only the start, much more to it than that. Testing it at the track will tell you the rest of the story.

More pressure = more power but also puts you closer to detonation. The closer you stand to the brink the better your setup has to be.

Minimum squish is essential. Spark curve must be custom tailored. Air fuel ratio must be smack on and even on the rich side. Air inlet temperature . Piston speed rate of change near TDC can make or break a borderline detonator. Atmospheric pressure changes will effect an engines octane tolerance.  And that is not even getting into the cam you choose , or how it works with the rest of the set up..

If this is a "race" engine you better be at the limits of race gas or you are wasting your time. because I know when I hit the track I was at the very limits of what the class would allow. Just my thoughts on racing.

Quote from: bladerunner on December 22, 2011, 03:52:47 PM
  Evening  Gents  ,  I am doing the final  cc/measure    "as built "  for my 124   race project   . My target is  12 :1   compression  . Looks like Im` right there   (using a few different calculators )    My Dynamic compression will be   9.88 :1   calculated .  I have 93 octane pump gas available. I have 105 race gas available  and   can dilute  if necessary.  This is new territory for me . My last build was a 107 @ 10.7  compression and I had no problems tuning that . I have A DTT ignition that I  have been using ,and   it will go on the new build .   I`m going to break in using a G carb ,  ...any guidance will be appreciated  on the fuel issue  thanks   ........bladerunner

Let me guess..........S&S .640?
You'll be in good shape tuned correctly, and if using this as a street/strip bike, then I'll do more than assume your gearing will be enhanced to use the entire gearbox in your 1320 ft. rides, so shooting from the hip................3.44 gear ratio??
It'll never load the engine hard enough to be concerned.
When going to the track, a D with 2/3, T/Jets will be your man.
Scott

 Right now a 3.597 final drive   ...  and yep 640 cam . I am a novice at drag racing . This is just for fun  ..sometimes bracket, sometimes  ,  heads up . I broke into the high tens last summer and I have been  smitten    ...   just a small fish  in a small pond   thanks for the help

Run it.
Scott

QuoteOffline bladerunner

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Re: Do I need race Gas ?
« Reply #4 on: Today at 05:44:04 PM »

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Right now a 3.597 final drive   ...  and yep 640 cam . I am a novice at drag racing . This is just for fun  ..sometimes bracket, sometimes  ,  heads up . I broke into the high tens last summer and I have been  smitten    ...   just a small fish  in a small pond   thanks for the help
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Erie , pennsylvania

Noticed the "Erie  PA" Do they still have the Presque Isle (PITA) track there? I used to race there in the late 50s early 60s I remember the shut down area was up hill !!

Just a heads up. When pumping gas from a single hose pump using three different octane ratings selections, be aware. If the previous gas pumped thru that hose was not the 93 octane, you are pumping by some estimates close to a gal of the lower octane gas before getting the correct 93 octane. This can make a significant difference in a motorcycle.

QuoteJust a heads up. When pumping gas from a single hose pump using three different octane ratings selections, be aware. If the previous gas pumped thru that hose was not the 93 octane, you are pumping by some estimates close to a gal of the lower octane gas before getting the correct 93 octane. This can make a significant difference in a motorcycle.

I don't know if it's as much as a gal. but it is true that you pump whatever grade is in the line before you get to the higher octane you selected. Whenever you can find the stations that have pumps with a separate hose for each grade; or let your buddy pump his first than use the same pump !!!

Ive done this before , i nix it in a drum 20 lrt to 10 of ave gas gave ne a great motor , plenty HP , but out of limits when on travel had to have a  bottle of that improver  to add to the gas , it was a pain other wise it would ping it ass off , we have great fuel in Austrailia , but still have this ,with a 19 lrt tank doesnt get you far and back to home base,may be you will take it out on timming  but on the road it has to be adjustable to do so ,been there done that, good luck cheers Barny

  Golfman  the track is still run`n     http://luckydragcity.com/     I can play all day Saturday for $15    ,(test and tune ) . They generally only run the 1/8  on Sunday ,      cars too fast for 1/4 and available shutdown area .  Definitely a "country track "   but It works for me  . I`ll get dialed in there and  then head for Thompson's in  Ohio   .   This bike  is street legal       sort off   , But will never see a full tank ride   so mixing / buying fuel won`t be an issue . I allways   take a 5 gallon can and put some 93 in the truck 1st and then fill the can....thanks...bladerunner

bob,find a VP dealer & get either 110 or C12 in 5 gallon cans,i wouldnt trust it out of the ground

  Yea Kirby   , we have two circle car tracks  close by  , I found a local  racer / garage that will sell me 5 gallon cans of fuel  .  New Question ....is it better to start with   higer octane   and work back to the Ping  ?  That was my plan..........

110 or C12 will be fine,some of the higher stuff has a slower burn rate,dont use it unless you have to (you wont have to)

Quote from: prodrag1320 on December 23, 2011, 05:24:29 AM
110 or C12 will be fine,some of the higher stuff has a slower burn rate,dont use it unless you have to (you wont have to)

Yup-
C12 worked for me when I had my 12:1 124"er. Had a 55 gallon drum delivered to my house by my VP guy every few months and pumped it myself.
With the new technology in fuel however, now I would go with VP U4.4 (and I use it when I take my streetbike out to play)-
U4.4 is almost a direct, pour-in replacement for pump gas, with horsepower gains up to 6% over pump. You will prob. need to go up 2 main jets and 2 inter jets at most  There is no residue build-up, and it will be more resistant to heat. U4.4 is set up for engines with 10:1 to 13.5:1 compression, and with its Motor Octane of 103 and oxygenation, it has excellent detonation protection.   

I used C-12 but this was 20 years ago, when if I remember correctly, VP had the C-12 for high comp n/a motors, the C-14 for the high rev (PSM and road racing, mainly), and the C-16 for the blown motors. The new formulas are pretty trick but there are so many of them.

FWIW We have a NASCAR dirt track here in town and the local VP vendor sells VP 110 cheaper than the VP 105

because he buys it in bulk for the modified series cars which are required to run it.

You can take your own fuel can to be filled as you will be charged extra for the blue can with a VP label on it.

QuoteGolfman  the track is still run`n     http://luckydragcity.com/     I can play all day Saturday for $15    ,(test and tune ) . They generally only run the 1/8  on Sunday ,      cars too fast for 1/4 and available shutdown area .  Definitely a "country track "   but It works for me  . I`ll get dialed in there and  then head for Thompson's in  Ohio   .

Glad to hear it is still open. I raced my 409 there in '62 and my A/FX Chevy Z-11 in '63 before selling it to someone who was involved in Quaker City Dragway. I had also raced at Thompson back in those "Ohio Gasser" days.

Quote from: Golfman on December 22, 2011, 10:56:46 PM

Quote... pumping gas from a single hose pump... If the previous gas pumped ... was not the 93 octane, you are pumping by some estimates close to a gal of the lower octane gas before getting the correct 93 octane.

I don't know if it's as much as a gal. but it is true that you pump whatever grade is in the line before you get to the higher octane you selected.

If it was 15' (probably not) of 3/4" I.D. plumbing (probably not) it would contain 0.344 gallons.

Here are a couple charts mapping 15' of plumbing, one each at 3/4" I.D. and the other at 5/8" I.D., using 87 and 93 octane values:

[attachment removed after 60 days by system]

Quote from: Sixspeed on December 22, 2011, 10:41:31 PM


Just a heads up. When pumping gas from a single hose pump using three different octane ratings selections, be aware. If the previous gas pumped thru that hose was not the 93 octane, you are pumping by some estimates close to a gal of the lower octane gas before getting the correct 93 octane. This can make a significant difference in a motorcycle.

I don't know where you heard up to a gallon. The numbers I come up with, and what I have heard, are closer to a quart. The hose itself holds less than a quart. No big deal unless you are just topping off the tank with less than a gallon.
If you average the numbers out one quart of 87, plus 3 quarts of 93 come out to about 91 octane for a total of one gallon. Two gallons with one quart of 87 comes out to just over 92 octane. Three gallons and up it becomes insignificant. The age and quality of the fuel has more affect than the advertised octane.

No matter what fuel you end up with.........pull 2* of timing from it,(after dyno tuning) after you make a pull at the track, then take look at your time slip.............
Scott