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Sorry -- but I have to say that statement is just a bunch of hoohaw...:unibrow: You'll guarantee that a motor won't be AS susceptible to detonation on the dyno with higher octane fuel... and especially the use of this for finding (experimenting with) the max timing settings etc without running into trouble. This is an extremely smart decision on the dyno operators part. The actual power difference between 91 octane and say 100 octane is so negligible it's hardly worth discussion. And it's been proven that the tuning set up for 91 octane and 118 octane can be exactly the same - same jet sizes - same timing. Having said that.... If I tuned on a dyno with 100 or 110 then I'd probably pull out 2* of total timing for the street -- AFTER I found the max I could run - just because pump gas is so "variable" these days. Octane rating is defined as the resistance to detonation a fuel has in an internal-combustion engine. The higher the number, the more resistance it has. That is why engines with higher compression require higher-octane fuel. As a result of its resistance to detonation, it has a resistance to burn as well. This resistance to burn is a non-issue in motors tuned to the edge; the edge being just before detonation occurs. When a pump-gas engine is subjected to a higher-octane race fuel, it may result in a decrease in power from an incomplete burn. Here's the deal -- the higher the octane - the less resistant to detonation -- that also means it's less resistant to BURNING as well.... If you're going to run an engine on the ragged edge - then best to run on higher octane and not hurt the motor - particularly if you have maximum timing etc so max power. But todays OXYGENATED fuels actually burn really well because they carry what? Extra oxygen! In a N/A engine that's a plus! Stick 100 or 110 in an engine tuned for best power on 91 and you might see a LOSS of power... not an add. Funny -- and OPPOSITE of what one would think huh! |
We'll just have to agree to disagree. A leaded racing fuel and an unleaded street fuel will effect tuning. Sure you can run both on the same tune up but how do you find the sweet spot on your intended fuel by using a band aid on the dyno? Alot can be learned from exhaust temperature, air/fuel ratio, and ultimately loss and gains in power making changes.
I do agree that using the higher octane fuel doesn't mean more power unless pump gas is insufficient. It's probably a safer bet to break in an engine for the less experienced. I specifically remember Pettis shutting mine down and leaning out the carb to reduce exhaust temperature at start up. At the end of the day, we found max power on 91 octane with safe exhaust temps, safe air/fuel, and 34 degrees of timing. That was my intended application. Seemed to work out alright. :D I'm no expert but I know enough to disagree with you.:rofl: |
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I think you'll need some more research before you can really make that statement. I don't think you really paid attention to what I was saying. That he wouldn't necessarily make more power using 100 than he would have running 91 -- but he can tune the motor without fearing the dreaded detonation while he's fooling with timing etc. The motor was built to be run using pump gas... therefore the compression etc doesn't demand 100 octane fuel... and 100 octane fuel doesn't "make" more power - they just protect against detonation. The higher compression motors demand higher octane fuels - but that's a different situation. We're talking about a street motor with normal compression. I should add that VP makes Streetblaze that is a 100 octane unleaded OXYGENATED fuel that will make more power... so I guess we really should know what fuel he tuned on. My guess is leaded 100 octane non oxygenated for the safety factor. And it's okay if we disagree... I just like being right. :D |
By the way -- this is a great discussion because there's a lot of thinking out there by people that don't know that might learn something from it.
I know plenty of guys that think they should toss in some 100 octane because they're going "racin'".... On a hot day - pushing to the max - it might help protect their motor - but they're NOT making more power. |
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Don't we all!! Gasoline and A/F ratios are really misunderstood. Can't tell ya how many people think A/F ratio is the magic bullet... and that 38* of timing in their SBC is still the right thing to do... Despite having modern aluminum heads etc. They have to be shown on the dyno and even then my guess is the first time they get a chance - they bump the timing back up! :lol: |
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Congrats on the results Rob. :thumbsup: Especially since it's a TP headed FE. :unibrow: |
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Thanks DG, good luck with winning that $20 if your is able to run on pump.:rolleyes: See below grasshopper and follow the conservative path to engine testing. Quote:
The gas was some leaded 110 sold at the local MN race shop. The old style combustion chamber in these heads requires a lot of timing and 11 to 1 with iron heads is pushing it. The DCR looked a little higher than I'd be excited about running on 91 during tuning. Max power came with 40 deg of timing. My distributor is locked out and wired to a digital 6 MSD on the dyno. I have a 6AL II that allows you to program in your timing curve that I will run in the car. For street use I'll program a fairly lazy advance curve all in at 3k and retarded 2 deg to 6500 or maybe redline. If vp 100 is available on a track day I'll run it with the distributor locked out to the digital 6 box with no curve or I'll flash in an aggressive curve to 40. Actual road manners and on track performance isn't alwyas dialed in after a dyno session. I believe it is just getting you in the ballpark and ensuring nothing is going sour in a controlled environment. AF meters are a good indicator of possible danger but tuning to a number on those sensors isn't the way to go. Tune the motor on the dyno for power. If it is unhappy with the small changes you make the power output will start showing you are headed to trouble before you hurt something. I have an LM1 that I will use to do some final road tuning on the jetting. I personally think at my compression level the 110 hurt the hp figures some (some as in very little but no gain). + I need to give DG every chance to give you bowtie guys a win :unibrow: I don't think running it on 91 on the dyno would have led me to different jet sizes. I think one of the rags even did a dyno shootout with gas to prove that fact a few years back. I'm the rookie in the group of three of us at the dyno, one guy owns the dyno and the other guy is a long time racer, builder and NHRA record holder. Both of them have done hundreds of pulls. They liked the plan and so did I. So that is the plan we went with. :cheers: |
I'm sure your guys know very well what they are doing. My point is that it CAN effect jetting and tuning. Why leave that variable on the table? I'd certainly chassis dyno it before you start hammering on it. I had the advantage of being at similar elevation and air to my engine builder. Your air is different anyway.
Greg, you don't win.:D |
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I'm glad you "get it" ---- some guys just think they know. :rofl: |
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