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Author Topic:   octane/compression requirement
FlyinBrian
Dirt Roller

Total posts: 22
posted February 15, 2005 03:21 PM  
I am running an IMCA type stock car with a .060 over 350 with KB hypereutectic pistons, Dart 64cc/180cc Iron Eagles,and a 350 cfm two barrel. The static compression is 12.2:1. The cam is timed at 1* advanced, at 100* intake centerline. I need to know your experiences and opinions if I can run Phillips 66 100 LL aviation fuel safely with this much compression. I ran it last year with a 10.2:1 flat top engine with the same cam and 461 double humps and it ran fine. Please don't gaff me for not running racing fuel. I will run racing fuel if I need to, but with racing fuel at 5 or 6 dollars a gallon I'm just trying to save a buck where I can. Thanks!

dirty58
Dirt Maniac

Total posts: 115
posted February 15, 2005 03:28 PM  
with that much compression i would run real fule a burnt piston cost more than fule

rico 08
Dirt Forum Champ
Total posts: 1139
posted February 15, 2005 05:22 PM  
At 12.2:1 your way over what avgas will handle..

Istock66
unregistered Total posts: 1139
posted February 15, 2005 07:14 PM           send a private message to rico 08   Edit/Delete Message   Reply w/QuoteBBBBBB
this is one of those ?s that goes around and around on here.

avgas is junk. its has the same rating as supreme unleaded.

you should run 100 octane fuel though at a minimum. 102 to 105 would be plenty safe.

iowa_dirt_track_girl
Dirt Freak

Total posts: 461
posted February 15, 2005 08:15 PM  
Av gas has lead in it to help cool your valves its made to sustain high rpms
With lead you can run higher Compression with out the fear of predetination. Cause the lead helps cool hot spots in the combustion chamber which causes your predetionation
The highest i have ever seen anybody run AV gas is 12to1

Raz_900
Dirt Forum Champ
Total posts: 635
posted February 15, 2005 09:00 PM  
Avgas is also blended with additives to atomize several thousand feet in the air under would could be sub zero temps. Unless you're racing in the Artic or flying your race car, I'd run 'ground fuel'.

Instead of running straight 110 race fuel, try and find 115 and mix it with 92 or 93 pump fuel. Mixing 2/3rds 115 and 1/3 pump premium will get you around 107 or 108 octane. That should be fine for 12.2. And mixed in 3rds like that should come out to about $4/gal give or take.

J3
Dirt Maniac

Total posts: 188
posted February 16, 2005 05:34 AM  
Ok, let me ask this question. My comp is 10.5:1 on one car and 11:1 on my other. What min octane can I run? Is 92 pump gas good enough? or should I run 110 octane racing fuel? Also, I can mix 110 and 92 50/50 to get 101 octane. (this will help on cost). So, what is best, what should I run and why? Thanks for all the help guys.


29
Dirt Roller

Total posts: 21
posted February 16, 2005 06:35 AM  
I mixed fuel 50/50 to get a little more than 100 octane at 10.5 to 1. Some people say you can run premium gas at 10.5 to 1 if it's tuned right. One thing you need to remember is the higher the octane, the lower the ignition capabilities it will have. If your motor can't ignite it efficiently, you will loose power.

juliaferrell
Dirt Freak

Total posts: 370
posted February 16, 2005 07:01 AM  
go to kb pistons website and use their dynamic compression calculator. If you have dynamic compression of 8:1 or higher then you need 107-112...... The calculator asks for your intake closing point *make sure you add 15 degrees to this** length of rods ect... Then you will know what you need. I've seen 12:1 engines that will run on regular pump gas.

Ego Racing
Dirt Forum Champ
Total posts: 724
posted February 16, 2005 07:51 AM  
quote:
Originally posted by 29:
I mixed fuel 50/50 to get a little more than 100 octane at 10.5 to 1. Some people say you can run premium gas at 10.5 to 1 if it's tuned right. One thing you need to remember is the higher the octane, the lower the ignition capabilities it will have. If your motor can't ignite it efficiently, you will loose power.

This is 100% Correct. We have run 13:1 with aluminum heads and run it on 93 octane pump gas. It was a small chamber and flat top piston motor. I would not reccomend this to anyone but we ran the motor for about 1000 laps in 75-90 degree temps and had no problems. We tested ALOT before going that low though. I was helping an offshore bower boat team and they used 112 octane fuei. In a race they had a round trip run, On the first leg they averaged 87mph. Once they got to the refuel/turn around the driver with the fuel had not shown up with the truck and was in traffic. They fueled up with 93 octane from the pump at the marina and figured they would just take it easy, watch the temp and listen to see if it knocks. They averaged 90mph on the trip back and ran it into a headwind. Later testing on a calm lake showed almost 10mph increase on 93octane over the 112.

J3
Dirt Maniac

Total posts: 188
posted February 16, 2005 09:43 AM  
So, how do I tell which fuel will be better without putting it on a dyno? No dyno close and don't have the money to do that anyway. If I could run 93 and that work just as good as 100 or 110, would rather do that due to cost. Any ideas?

marshalr
Dirt Maniac

Total posts: 148
posted February 16, 2005 09:44 AM  
We need to remember that Octane Rating relates to Knock resistance not potential energy. If some is good, more is not necessarily better.
Av Gas is for aviation applications and
Diesel fuel is for diesel fuel engines; same difference; a pilot would not be able - legally - to put racing fuel in his airplane.
I buy my 110 racing fuel in 50 gallon drums, they bring it right to the door of the shop for 4.85 a gallon.

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Some People Race For A Living; I Live To Race

ratracer10
Dirt Maniac

Total posts: 141
posted February 16, 2005 11:00 AM  
Check this out. Not really an answer, but interesting.
http://www.diabolicalperformance.com/hotrodoctane.html

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- When in doubt, hit the gas.

Istock66
unregistered Total posts: 141
posted February 16, 2005 05:36 PM           send a private message to ratracer10   Edit/Delete Message   Reply w/QuoteBBBBBB
before gas prices went so high I allways mixed to get 100 octane for my 12.5 and 13-1 motors without a problem ever.

I pay 3.45 a gallon for 110 now in a drum and dont mix but I would bet I dont need 110 and am giving away some hp. but mixing is a hassle when gas is 180 a gallon and only drops the price a little.

racin78p
Dirt Freak

Total posts: 333
posted February 17, 2005 01:20 AM  
Ditto Istock66. I was getting 105 racing gas, but now 110. It was actually 20 bucks cheaper (55 gal. barrel) for the 110. Who would have thought!

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racin78p
if it ain't fun, then don't run

Deak-Jr
Dirt Forum Racer

Total posts: 81
posted February 17, 2005 07:08 AM  
Dumb question of the day: The Sunoco race fuel contains lead, correct? We're running #461s w/o hardened seats on a 400 w/stock dished pistons; ran a 355 w/flat tops before, plain jane late 80s GM van heads, started running straight Sunoco race gas halfway through the season and there was a noticeable difference in the water temp gauge.

racin78p
Dirt Freak

Total posts: 333
posted February 17, 2005 09:35 AM  
Cooler or hotter? The lead should keep it cooler, unless for some reason your jetting is off now. Do anything there?

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racin78p
if it ain't fun, then don't run

Deak-Jr
Dirt Forum Racer

Total posts: 81
posted February 17, 2005 12:42 PM  
"Cooler or hotter? The lead should keep it cooler, unless for some reason your jetting is off now. Do anything there?"

No, with the 355, the Sunoco racegas made it run 5-10 degrees cooler. We think we mis-guessed and were making more compression than we figured. But there were plenty of other inherent problems with that motor so it's hard to tell.

My question was about the lead in racegas -- I'll need some lead in the fuel with the older heads. I always assumed there was lead in the racegas. My 'dumb question of the day' was just making sure so I don't have to get lead additive (don't want to do that if I can help it).

29
Dirt Roller

Total posts: 21
posted February 17, 2005 02:20 PM  
Most race gas is leaded. They do make unleaded race gas too.

racin78p
Dirt Freak

Total posts: 333
posted February 18, 2005 02:26 AM  
It is leaded partner. If you buy race gas by the barrel (cheaper) it will say so on it. Unleaded would be marked as well. Know I know what you ment. The lead SHOULD help the engine run cooler, but with all the variables it necessarilly might not. High compression engines do develop higher heat range, but that doesn't mean the heat will sky rocket. How efficient everything is working plays a part too.

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racin78p
if it ain't fun, then don't run

Whitelightning
Dirt Freak

Total posts: 429
posted February 18, 2005 05:15 AM  
I alway try pump gas if it spark knocks I move up. My engine builder said to run no more than the engine required, if it dont spark knock let er eat LOl

dirty58
Dirt Maniac

Total posts: 115
posted February 18, 2005 04:19 PM  
octain refers to how fast a fuel burns the higher the rating the slower it burns there for it pushes the piston down father higher compression motors require higher octain tobalance all cilenders to reduce (knock) lead is for lubing the valves

    

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