Octane vs. ethanol
 

Short version: 91 octane non-ethanol or 93 octane 10-15% ethanol?

Wondering which fuel would be more forgiving on a 9.7:1 467, basically a Jim Hand build. 95cc 6x heads, 250cfm. Flat tops, all forged, RAIV cam, Rhodes lifters. 3750 lb T/A, manual, 3.70 rear, 28" tire.

91 non-ethanol has more energy than 93 ethanol blend.

Tune the engine for93 octane 10-15% ethanol fuel and i t will ping with 91 non-ethanol fuel.

Tune the engine for 91 octane non-ethanol fuel and it will be ping-free with 93 octane 10-15% ethanol, but may use a little more fuel.

I ran my old 455 with any octane I wanted and it never grumbled once. It was 9.97 to 1 compression, 6X-4 heads with 91cc chambers, zero decked and Crower RAIV camshaft. I never ran any quicker at the track with 92-93 octane but that's what I typically ran in it. Got stuck once using 89 octane and raced it all weekend at Norwalk at the Tri-Power-Nat's on it and it ran fine.

My last 455 was 11.3 to 1 compression with KRE aluminum heads and Dave's Old Faithful cam on a 112LSA with the ICL at 109.5 degrees. It ran fine on 92-93 octane and really didn't care if you ran 87-89 in it but it would "run-on" after shut-down on 87 octane if it was fully heat soaked and really hot/humid.

Keep in mind when you read what I've done that I have the tune "spot-on" and it's not adding any timing at high RPM's or going lean, etc..........

Street on 87 Octane, no ping and yea will heatsoak too (sometimes) when really really hot.
Strip on 89 Octane (12.2s) and no ping (top signature)
Shot too low with 9.0:1, nicely over-cammed with 112 LSA, with ILC advanced 2-4*
Pretty sure no reversion, which is a big deal for low compression.

428 (4" stroke): take 5* off 0.050" Duration (top sig)
400s (3.75" stroke) take 10* off 0.050" duration (top Sig)

High compression, do same for bottom sig durations.

i would run the higher octane and be sure to tune for the ethanol blend, which will need a richer tune than the 91.

The best we have here is 91 and it's 10% ethanol. The only real gas here without ethanol is 87 octane so that's not much of an option for me.

I tune for the ethanol content (so slightly rich) so the cars are safe whether I find real gas or not, plus it compensates for the occasional crappy tank of gas you might get. Better to be on the richer side of things and forget about it.


for a 9.7:1 455 build with iron heads and the RAIV camshaft, as long as the build is solid and things done properly, should run just fine on 91 octane. I'm running an iron headed 11:1 compression engine on 91 and have been daily driving that for the last 6 years, but many things have to be paid close attention to. It's really dynamic compression at play, and a RAIV camshaft in a 455 does a pretty decent job controlling that. I just wouldn't go too crazy with lean AFR's searching for gas mileage.

I think CA is messing with the E in our gas.About every 3 weeks I take a 750 mile trip to the Sierras.My 2017 Yukon for the last 3 years has been dead on 21 MPG like clock work.My last trip was 22.2 and the one before was 19.1.My car is a Flexfuel car so the computer is set to run any E level.I always run 87.Makes me think that some of the gas is getting a higher load of E than 10%?Tom

Just for giggles, and I'm sure someone here may know the answer.

There are formulas available to plug numbers in and figure your dynamic compression, which is useful for figuring octane requirements.

Off the top of my head, a 9.7:1 455 with the RAIV camshaft will probably have a dynamic compression of somewhere in the mid 7's which is easily safe on pump gas (camshaft install position plays a roll) If it started to get up in the lower 9's for dynamic it starts to become a problem.

Cranking compression can be another clue.

Yep, I suspected that years ago and tried a few of those cheap test kits you could get on ebay. I found that the 10% ethanol pumps were sometimes actually as high as 17% at times..

Which is why I tune things on the rich side anymore because you just never know what you're getting from one tank to the next.

I haven't done the test in years but I'd bet money it still fluctuates.

Yep, Tom when the price of gas hit $5.00+ a gallon here in Ca. I saw on the local news the manufacturers were going to increase the ethanol to help slow the rise in fuel price
I think they just need to increase production and stop making up for the lost revenue from COVID. But that's JMHO

Always best to test; every engine is different.

Put in half a tank of the highest octane you can buy.

Find a level stretch of highway that culminates in a medium hill (up).

At the speed limit, in high gear, push down just hard enough to maintain speed without downshifting; listen for ping.

If no ping, and you wish to try less octane, mix half a tank of the next lowest octane with what is in your tank (should give you an octane that is an average of the two).

Repeat the test until you experience ping, or get to the lowest octane.

As stated there is less energy in ethanol diluted fuel that in real gasoline.

Depending on whose figures you believe, gasoline has 117,600 BTU/gal; ethanol 67,000 BTU/gas.

So E10 would be (.9 times 117600 plus (.1 times 67000).

105840 + 6700 is equal to 112540.

Obviously, the math would be different for different percentages of ethanol.

Jon

they announced a few weeks ago they are raising the ethanol to 15%, wonder if cali & other states label it accurately? gas stations around me in the midwest still label each grade & show the E0, E10 & E15, so at least we know & have a choice.

E15 is cheaper by about .05-.10/gal than E10 around here & a lot cheaper than E0... but it takes more to get the same distance, so any savings on ethanol is a complete wash on MPG.

just a gimmick to make people think they are spending less. plus ive read it takes more than a gallon of gas to produce a gallon of ethanol, if thats true the entire ethanol thing is a scam... just like electric vehicles!

Ethanol has an octane rating of 100 so anything with it will have an overall higher octane level. But, ethanol has 37% lower energy compared to gasoline because of the number of carbon atoms so you will use more ethanol than gasoline to make an equivalent power level.

The next generation of energy will be deuterium and dilithium crystals. ;)

Jon

X2. But remember cranking compression on the same engine will vary. It is less in Denver than it is at sea level.

Stan

I bought a barrel of all gas 92 for 5.50 $ before it shot up.Have 70 gallons of it for bracket 11.5-1 engine.
It was much cheaper than 87 is right now.
You can still get it in Oregon for a decent price.

The little test kits with the graduated syringe or the vile that you mix the fuel sample with water are pretty accurate. The new law just signed last week allows 0-15% ethanol for road use with a sticker on the pump. When the limit was 10%, we used to sample fuel all the time. A class project was for students to bring 9 fuel samples from 3 different gas stations. Then we would test them. This would give us a couple hundred different samples in a typical test. We would use the home test, (water method) and the electronic tester sold through Kent Moore/SPX to GM. Results were all over the place. From 0% alcohol to a high of 13.5% the last time we tested which was a year ago. With the limit now raised to 15%, I wouldn't be the least bit surprised to see 17%-18% out there. Your lawnmower won't like that stuff.

Isn't elevation figured into the equation? It should be.

I'd use a formula that includes it if that's what you're looking for. Or better yet, just figure it at sea level then you'll know it's fine everywhere.

I would expect it even a pinch higher just based off what I saw years ago, if the fudging stays the same.

Interesting Tom. My Yukon is a 2016 and performs almost exactly the same as yours. We just went to Lancaster and I noticed the mileage dropped to19+ on the way back but was in the low 20s on the way there. Might have something to do with the wind direction but who knows. Like you I always run 87 octane, usually Chevron. Hint buy gas at Vons in Bishop for about 5 cents cheaper than anything in town. Mike

Yes it is. But if you don't leave the mountain then you are leaving a lot on the table by tuning for sea level.

Stan

I can't imagine not leaving the mountain. :D

Shucks around here I can't even drive 20 miles in any direction without the elevation changing one way or the other. I keep the sea level tunes in the cars and it's been fine up here. You lose power up here regardless, about 3% for every 1000 feet gained. I can lean them out a tad and pick up a pinch, and maybe add another couple degrees of timing if I wanted up here, but I don't want to fiddle with them every time I drive down to Phoenix. Not real practical on our daily drivers.

And just how is raising the level to 15% going to help with the big main problem, that being getting every day products to stores and in the making of many of those products from petroleum?

Mike,its cheaper at the Indian station just north of Independence!Also last trip the Speedy gas in Bishop was cheaper unless you had Vons points for a discount.E85 down here is 3.99 and 87 is 6.05.Tom

You guys are nerds and I love it. I'm just curious which fuel would get into detonation or pre-ignition first. I'm about to fire up a new 467, going to try it with the Sniper running timing control as I don't have a suitable carb handy.

I'm sure the efi unit can handle the fueling for break-in, but not keen on taking chances with the built in all-or-nothing timing setup that brings all the advance in at once. I'm comfortable setting up a 2d timing table in the Holley software. Any input on a good starting place?

It's a fresh Len Williams 467 (4.25" stroke), zero-decked, Melling SPC-8, 1.65:1 rockers, RA manifolds with the larger collectors, RPM intake. I've seen people recommend wildly different timing specs for similar mills. I'm more concerned with a safe first 1000 miles than maximum power for now.

I'm getting stupidly excited, haven't driven this bird in 3 years, it had a stock 220hp 400 when things went south for it. Dropped compression on 2 cyl, then the next week the neighbor's house burned down and toasted the paint job. I'll post about the whole build once she's running. The only moving parts that remain stock are the steering column and wipers.

Nice build. What heads and CR? I am 470cid, 4.25" stroke, .040" overbore. Running the SPC-8 cam, 1.65 lifters on the rare #64 HO heads 87cc. Puts my CR like 10.6:1. Been thinking of Sniper. But funds are stupid tight right now and I can't seem to finish this rebuild form the crappy Comp cam going flat a few years ago.

Oh and with the XE274 cam, I used to have to have 16* initial. I think I was 32 total,, all in by 2800. With approx 12* vac advance on manifold vacuum

I recently revived this one from the distant past:
http://www.projectpontiac.com/ppsite...tio-calculator

The rest of the site is a decades-old irrelevant mess, but the dynamic compression ratio calculator is still valid and useful. It's remarkable to see how a different cam results in completely different actual compression ratio, which is what really matters when it comes to octane. This is why some people can get away with running 91 octane with 10:1 static compression and iron heads, while others will be pinging with 9.25:1 under the same circumstances.

Yep, that's how I'm able to run 11:1 with iron heads and 91 octane ;)

It would be nice too know what elevation range you expect to drive the car in.

If you want to be safe it isn’t a bad idea to start out around 28-30 degrees total on the timing to get a good feel of the fuel it likes. I don’t tune stuff much different jumping back and forth to and from ethanol blends, for me that small blend falls with an acceptable range for how the engine is tuned.

I have a friend running a similar mid 9s SCR 455 (467) combo in a 4x4 pickup. It gets driven 8-10K miles a year, it is pushing 40k now..He has more intake port flow than 250, but the exh side of the heads is almost stock, running Rhoads Vmax’s (set to .010”) and a 60919 Crower, which builds more compression than a SPC-8. Not a lot more, seems to be about .25 of a point. It ran the first 20K mile with the timing backed off to 30 and run 87 octane with ethanol. I gave him a hard time about it and he uses 91 now and more timing. It has a much tougher life than most peoples muscle car, pulls 17K trailers out on county rock roads. It has a hard life, secondaries get kicked in pretty frequently…shifts at 5500, sometimes 6. If he hasn’t killed that yet, don’t be too worried, they are pretty tough :)

So my static is 10.6, Dynamic via calculator is 6.3. What is that telling me?

Well, a stock W72 400 (6X-4 heads, 8.2:1 static compression ratio, very pump gas friendly, 38 to 40 degrees total advance stock) has a dynamic compression ratio of 6.42:1. That means that at low RPM, your engine actually compresses the mixture less than a stock W72 does. But depending on your LSA, your volumetric efficiency might increase a lot more as RPMs go up, so cylinder filing is probably higher in that range. Honestly though, if you're running aluminum heads, you're probably fine with 87 octane. If cast iron, you'd likely want 91 or 93 just to ensure you don't ping at WOT. That's a pretty low dynamic compression ratio.

I live 350ft above sea level, hoping to have no issues anywhere east of the Rocky Mtns. If I do head out west with the car, it should be easy to reprogram the Sniper to compensate. I can usually get 93 non-ethanol at a local gas station, but sometimes they get a truck of 91. At least they re-label the pump when that happens, pretty much everyone in Memphis with a cool car fuels up there.

Thx, ya Ported #64 HO heads I've always ran 91 in the past. Just wanting to be sure. I kept my timing back to 30-31 because with the headers and flowmasters, I could never hear pinging clearly. But in spring and fall I ran mid grade a few times and she seemed OK. I never pushed her on it tho so.

It's a Melling SPC-8 cam. advanced 4 deg if it helps

Mikes reply:

This might help, good info!

I have never tried an octane booster, have you? I would read the label to see if they have a product without any type of Alcohol!

https://boostane.com/?fbclid=IwAR1_6...2SHXa5vnz7e2uI

I should be able to tune for pump gas no problem. The combo I'm running has been scienced to the moon and back by people way smarter than me, and was assembled by a well-respected pro. I plan to run 93 non ethanol whenever possible. It won't need octane booster or race gas.

My question is if the good stuff is unavailable, will I be better off with 91 non-ethanol or 93 with ethanol?

I think I tripped a circuit breaker on the forum by mentioning "041 cam" and "Rhodes" in the same post. Next thing you know we'll be 18 pages in and folks will be playing winning lottery tickets using random timing advice numbers.

Mikes reply:

You won't know what your motor likes until you have tested and tuned it for some time and stay away from Alcohol in the gas at any cost, my 2 cents! Unleaded 91 is my choice! I wish I could get 91 unleaded here in south Florida.

You won't have to do much at all with the Sniper. We run 2 of them, mainly because of the mountains and elevation changes, and they handle the changes quite well.

As long as you still have compensation limits up around the 10% range it will adjust the fuel as needed. If you need more compensation than that to deal with the mountains then the base fuel table probably needs more work.

I just turn the learn percentage down because I don't want it to corrupt the learn table when I'm dealing with elevation swings.

You can even have a different tune at the ready with the compensation and learn where you want and quickly load that in before you tackle the mountain, and let the Sniper adjust to those elevations and then save that tune to use when needed. Only takes a few seconds to load one. I've done that before too and then compared notes of the differences.

This kind of stuff is one of the biggest reasons to have this EFI

My take on it is that I go for the octane rating and don't worry about the ethanol content. I've never noticed any real difference between ethanol and non ethanol gas as far as drivability. And since non ethanol fuel is about non existent where I live now, I've been using 10-15% ethanol fuel in the cars for a couple decades now with no ill affects. Now if it were higher in the 30% plus range I might be looking at other options.

If you have both easily available to you, you could switch back and forth to see for yourself.

I will chime in on that last post;
Not to argue, or anything of the sort, but to just offer an opposing first hand opinion.

my car:
- engine rebuilt in 1998 (un-needed - because I was a kid, and wanted to do it!?!)
- YZ 400 (0.040 over)
- stock heads, only light cleaning - no port work
- 744 cam installed (installed because what I thought was the stock cam seemed really mild, so I wanted to upgrade to the one step bigger pre-1970 RAIII-MT cam)
- 7041264 carb (it was the best I could find at the time)

When I first learned of the "higher octane" ethanol blended fuel around here, I gave it a try;
I was nearing empty, and put in 1/2 or maybe 3/4 of a tank (because that's all this broke kid could afford).
My car ran like absolute turd with it.
It barely kept an idle, and was just generally unhappy.

So please mark me down as someone who definately could tell the difference when running ethanol blended, vs conventional premium unleaded gas.

It ran so bad that my cousin felt bad for me, and shared some of his av gas;
I topped up the tank with his av gas, and you could quite literally hear when the av gas mixture made it to the carb;
The idle smoothed out unlike I had ever heard it run.

Since that time, I have stayed away from Ethanol blends - if possible.
(I will add that it is possible that the ethanol blending has gotten better since 1999.)

It is probably easy enough to adjust the carburetor to run a bit richer for the ethanol, but at that time, I could not do that, and couldn't afford to pay a professional to fiddle with carb settings (I actually looked into it).

I live at, and mostly drove my car at an elevation between 2966-3435ft.

I had people time and again tell me that there was no way I could run my engine on pump gas - which is a factor of why I have been following this discussion.

When I got my car in 1995 it was 0.030 over, had a tiny "A" cam (which I still have in a box by the way), the engine was topped off with a crappy smog era Chev carb, and was driven in an area with an elevation of 764ft.

If folks tuned their engines ( along with altitude, temp, usage at their location) by BTU, instead on Octane, a real feeling for whats going on inside would make tuning more accurate if you are going for details.
Octane, like Cetane, is a Flame Retardant. This " Can" , with dense fuel , make more power.
Alcohol has a higher Octane, but its a puke on BTU, much less power. So in modern fuel with Alcohol it can be misleading when compared to Suncoast 260 of the past.
Octane doesn't always mean better, or more power in the case of Ethanol.

Tuning with an air/fuel ratio meter is tuning by BTUs or energy content of the gas you are using.

thats very true. but what happens when you increase the volume of ethanol to compensate for the lower BTU? i have never had an engine set up for that but i know some people that do & most say ethanol has some benefits like cooler & cleaner burning etc. for high compression or turbo/forced induction engines the higher octane E85 is what lots of guys use. plus its cheaper than any comparable octane fuel.

as you mentioned, i have never really noticed a difference in 91 straight gas vs 93 with 10%E in 3 different pontiac engine cars, the higher HP one at the drag strip or driving any of them around town. i try to stick with straight 91 but will get the 89 or 93 ethanol if its cheaper.

Most likely it was running too lean to begin with and ethanol exaggerated that problem.

One thing you have to do with ethanol, even just 10% blend, is richen the idle circuit. More than just adjusting screws, usually requires going in and opening the idle restrictions.
Never a problem for me because I was never one to try and run a super duper lean idle on any of the cars anyway even when I was running real gas. I always shoot for best drivability in all conditions and that generally ends up with a mid 13's AFR for idle conditions. Especially anything with a decent camshaft in it, it's just going to require more idle fuel anyway.

People have to keep in mind stoich for real gas is 14.7 10% ethanol is 14. I've had cars come in here where people have leaned out the idle circuit to the extreme looking for gas mileage only to find out that doesn't work too well when you start throwing ethanol in the mix.

It's all in the tune up. None of it makes a difference if the car is setup properly. I use it at sea level and 6000 feet, daily drive them, and we drag race with it. Not just one car, but several. No issues to report.

For sure ethanol has properties that allow an engine to make more power without detonating, when tuned for it. Higher detonation resistance, and an extra cooling property that helps prevent heat buildup. On a Buick turbo V6, we can run some absolutely insane boost on E85, but it requires as much as 50% more fueling than with regular gas. That's a pretty dramatic increase. We also have the benefit of an ECU that can run different injection and ignition tables depending on what fuel is in the tank. None of that is easily achievable on a Pontiac V8.

Right now, you'll find blends with up to 15% ethanol at the pump, though 10% is most common. The biggest issue with that is the swelling it'll cause on some seals and floats if they're not ethanol-tolerant. If the carb is tuned right, it shouldn't affect idle quality enough to be noticeable.

Boost for sure works well with E85.

I had a couple friends about 15 years back that was building N/A engines using E85. Knowing that was the fuel to be used these engines were purposely built with a lot of compression. I think they were 12:1 or a little more if I remember correctly, pretty radical camshafts, carbs setup for E85 and ran strictly an E85 diet.

They ran extremely strong but the problem was E85 availability. It wasn't everywhere then and it's still not everywhere now. That really limited the distance these cars could travel and basically remained around the town where the E85 pumps were, because regular pump gas for these engines at that point wasn't an option anymore.

Yep, In the grand scheme of things 10% really isn't all that much anyway.

That's possible, and I did try to touch on it.

But as I also mentioned, back then I wouldn't have known what needed to be done to actually richen it up at all.

I don't think that the 1971 Quadrajet would have been what we might consider lean - and that carb was bone stock jetting ect.

I will say that it made for some fun "testing" with my cousin and his '71 TA;
Him: bone stock, all correct; TH400 w/3.08:1(?)
Me: as mentioned with a slight mismatch of an M22 in front of 3.55:1 gears
I had him out of the hole pretty good, but somewhere down the road, he reeled me in, probably on the merits of having taller gears.

My real take away from the ethanol blended gas (other than it being terrible for these older engines) is how shockingly smooth my car ran with 100+ octane leaded fuel - I had never heard it idle so smooth and quiet before, or since.