Octane vs. Altitude (blending for hp)

[dcstep]

In several other threads I've talked about the problems of tuning my '09 M3 coupe at the altitude around Denver, generally 5100 to 5400 ft above sea level, so long as you stay out of the Rockies which are only about ten-miles away.

The graphs below all show my car with the Dinan throttle bodies installed, a Dinan chip and a Macht Schnell high performance air filter. The only difference is the fuel octane, which I vary by mixing 91 and 100-octane unleaded gasoline. The 91 is Shell and the 100 is Sunoco.

The dyno is a Dynojet showing SAE adjusted results, as follows:

• Maroon Run is 100% 91-octane, yielding 340.17 hp
• Green Run is 30/70 blend of 100/91-octane, yielding 345.74 hp
• Red Run is 50/50 blend of 100/91-octane, yielding 338.65
• Blue Run is back-to-back with the Red run, only using 5th gear instead of 4th to see if 5th was more efficient, which it was, recording 344.47 hp, around 6 hp better.

Clearly, the 30/70 blend is the way to go, which yields roughly 94-octane. The 50-50 blend is around 96-octane.

YMMV giantly depending on your altitude. 100-octane at sea level yields a 30-ish increase in hp. It's not so easy at altitude because our effective cylinder compression drops due to lower air density and the slower to ignite and burn nature of higher octane fuel just screws up the timing once the engine has reached its maximum advance, at least that's the prevailing theory around here.

So, to summarize, I gain roughly 6 hp by blending 100/91-octane 30/70. From that point, I lose 7 hp by upping the blend to 50/50 and a gain 6 hp due to the efficiency of 5th gear vs. 4th.

I've got a line on a custom ECU tune that may allow me to improve these numbers, a little, but that'll have to wait for a future report.

Dave

[J08M3]

Did you give your ECU a chance to adjust to each octane change before the dyno? I think it takes about a full tank of gas of a certain octane to do that (so I've been told on here). In which case how could you do this in one day? If it's more than one day between runs you could easily see +/- 5 hp just by the weather that day.

[dcstep]

Originally Posted by J08M3

Did you give your ECU a chance to adjust to each octane change before the dyno? I think it takes about a full tank of gas of a certain octane to do that (so I've been told on here). In which case how could you do this in one day? If it's more than one day between runs you could easily see +/- 5 hp just by the weather that day.

SAE is trying to adjust for the weather. It was about 10-degrees hotter in the dyno bay today, which isn't a lot, but might have accounted for 1 or 2 hp.

I do at least 50-miles on the newly topped off tank before the dyno runs. I include plenty of full throttle, mixed with light throttle. I had more miles on this 50-50 blend than on the 30-70 blend, so the ECU should have been fully adjusted to it.

Also so of importance, we keep running with only short cool downs (allowing the fans to all get off high speed) until the hp and torque peaks (usually 4 or 5 runs). The engine likes to get a little heat into it before it gives its max.

About running in 5th gear, I've got a 4.10 final drive and the speed governor off and the redline raised to 8600 rpm. I noticed that fifth was right at 155 mph when we hit the 8600 rpm redline. A stock 3.85 FD if going to be dangerouly close to being speed limited right at 8400 rpm. You should hit peak hp before the governor kicks in, but you might not get a "full pull", in case you value that. I think it'd be worth getting a more accurate run if 100 or so rpm were not used. Just a thought. On a Dynojet, 5th will give you a higher result than 4th.

Dave

[dcstep]

Originally Posted by PencilGeek

Did you try the dyno in different gears?

Just 4th and 5th. 5th gave about 6 hp higher reading. No one knows which is more accurate. Now that I've got a benchmark in 5th I'll use that going forward. It's the Blue graph.

BTW, my shop will hopefully be able to a custom dyno-tune before the summer's out. Some tuners from Phoenix were there with an 800+hp GT2. They got some bootleg software out of Germany and my tuner is trying to work a deal to bring it to Colorado. Looking at my AFR curves, all the tuners were guessing that there's 15 or so hp in just AFR and no telling what if we work with the VANOs and fuel mixes. We'll see, I hope.

Dave

[rbk1115]

Thanks for the graphs Dave! It is interesting to see that fuel really makes a difference.

[mvagusta]

try 104 octane it'll blow your dyno..

[Lemans_Blue_M]

Originally Posted by mvagusta

try 104 octane it'll blow your dyno..

[mvagusta]

Why is that funny???

[dcstep]

Originally Posted by mvagusta

try 104 octane it'll blow your dyno..

I suspect you're trying to be funny, but I failed to mention in this thread that 105-octane lost over 10-hp.

Dave

[mvagusta]

You are wrong. Maybe altitude is the problem? I notice a big diffrence. I ran it with a camaro SS 2009. Before it was closer. Now I put 6 cars on him by the quarter mle. It was no mistake. A 10 mph role. Over and over again.

[dcstep]

Originally Posted by mvagusta

You are wrong. Maybe altitude is the problem? I notice a big diffrence. I ran it with a camaro SS 2009. Before it was closer. Now I put 6 cars on him by the quarter mle. It was no mistake. A 10 mph role. Over and over again.

Impressive evidence, BUT not as good as dyno runs. Show us. A rolling start has way too many variables, as does any drag race.

I really, honestly do want to see your dyno runs. How'd it do with 100-octane? You might have gain another 5-hp with lower octane than 104.

Dave

[mvagusta]

I'm going to look around here in Michigan for someone to dyno. I'm going to try 115 and 104 and 93. If there is a 30 plus increase (pc). Can you imagine. I have the pulley, rpi,airfilter, plus I'm in the works for hfc encore system. With the stock number of 414hp plus the 30 octane and 8 or 9 pulley and rpi 10 and the encore for 25 to 30 and the filter 5 or 6. 500 hp? hahaha. I'd be nice to add everything like this. But we'll see a dyno..

[dcstep]

Originally Posted by mvagusta

I'm going to look around here in Michigan for someone to dyno. I'm going to try 115 and 104 and 93. If there is a 30 plus increase (pc). Can you imagine. I have the pulley, rpi,airfilter, plus I'm in the works for hfc encore system. With the stock number of 414hp plus the 30 octane and 8 or 9 pulley and rpi 10 and the encore for 25 to 30 and the filter 5 or 6. 500 hp? hahaha. I'd be nice to add everything like this. But we'll see a dyno..

Great stuff.

If you use a Dynojet your stock baseline probably would have been between 330 and 340-hp. I think you're other mods will be worth 20-30 hp and 100-octane gas will be worth another 30+ hp. Ideally you'll be able to do runs at 93, 104 and 115-octane. (you don't have 100?). I feel pretty certain that you'll lose with 115 such that it'll be less than at 93. At 104-octane I think you'll beat your 93-octane baseline, but I'm suspecting that 100-octane might give you even more hp.

Believe me, I know that dyno runs are not free, but it's really useful info. If you show that 115 is less than 104, then you might want to mix 93 and 104 to try to approximate 100 in order to find the max hp sweet spot.

Anyway, thanks for your interest. Even if the project takes a few months, it'll produce really useful data. I'd do it myself, but my high altitude results aren't relevent at sea level.

Dave

[mvagusta]

sounds good. I'll give it a shot. thanks for the heads up.

[Lemans_Blue_M]

Wait a minute here...you mixed 115 octane LEADED race gas with 93 octane UNLEADED premium?

[mvagusta]

I don't know. It was 115 octane. I figured it was unleaded. Why would you say leaded?

[Lemans_Blue_M]

Originally Posted by mvagusta

I don't know. It was 115 octane. I figured it was unleaded. Why would you say leaded?

Earlier you posted that it was 115 octane "blue turbo". Is that the correct BRAND name for the race fuel you used?

http://www.m3post.com/forums/showpos...02&postcount=4

[mvagusta]

Yes blue turbo. But thay make it in unleaded and leaded. I was looking at there website. Why if it's leaded what can it do to my engine? I mixed it 5 gallons of 115 octane turbo blue and 6 gallons of 93 unleaded..

[Lemans_Blue_M]

Originally Posted by mvagusta

Yes blue turbo. But thay make it in unleaded and leaded. I was looking at there website. Why if it's leaded what can it do to my engine? I mixed it 5 gallons of 115 octane turbo blue and 6 gallons of 93 unleaded..

You mean this website?

http://www.turboblue.com/typical.asp

Tell me which one is 115 octane and UNLEADED?

[Lemans_Blue_M]

Originally Posted by mvagusta

Yes blue turbo. But thay make it in unleaded and leaded. I was looking at there website. Why if it's leaded what can it do to my engine? I mixed it 5 gallons of 115 octane turbo blue and 6 gallons of 93 unleaded..

You mean beside completely destroying your cats and o2 sensors?

[mvagusta]

If it was a leaded 115 5 gallons and unleaded mix. Ths one time can't possible cause it to foul that fast the o2 and the cat's?

[Lemans_Blue_M]

Originally Posted by mvagusta

If it was a leaded 115 5 gallons and unleaded mix. Ths one time can't possible cause it to foul that fast the o2 and the cat's?

Can't know that for sure now, but I wouldn't do that again if I were you.

You have to pay attention when you are using any type of race fuel.

Since you didn't use straight 115 octane leaded gas in your car, you are probably safe.

But if a 'SES' light pops up in the next few days...that's probably not a good sign.

FYI: Use the 100 or 104 octane UNLEADED Blue Turbo stuff if anything.

Stay away from off-road LEADED race gas.

If not, it's going to cost you a large sum of money to repair the damage it causes.