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110 vs 93 octane

Posted By: A727Tflite

110 vs 93 octane - 01/25/20 12:15 AM

Has anyone done any testing, on track or dyno comparing power made using 93 versus 110.

Baseline motor is a hemi, aluminum head, 11.5-1 ratio, cranking compression 180, 2 x 4 inline manifold.

So to be clear, if this engine made x power would you expect it to make more or less on 93 versus the 110 used on the dyno.

BSFC numbers climbed as the engine speed increased, EGT was less than 1100 at 6500.

It didn’t like more than 32 degrees either.

Not sure if the fuel is part of the problem, or maybe just the high speed bleeds, jetting or combination of all.
Jetting was lower than what was called for and while it helped by leaning it out it seemed way too fat for what it was running.


Posted By: INTMD8

Re: 110 vs 93 octane - 01/25/20 01:55 AM

Most of my experience is with calibrating efi cars rather than gen2 Hemi's specifically. That being said I'll throw in my .02.

On naturally aspirated combinations I start with a relatively conservative timing curve and first dial in target wot air fuel ratio.

Once that is done I'll put a few more degrees in and see if power increases (along with watching knock sensor output on the stuff I'm working with).

As long as it isn't getting knock I'll continue to add a degree at a time as long as power is increasing, noting if this is making the same result throughout the rpm range or varying at different rpm ranges.

I've at times been surprised by how much timing something wants to make max power and also, how little an engine required to make max power.

As far as octane playing into this is concerned, I've only seen higher octane add power if as I was increasing timing and seeing power gains I ran into excessive knock/knock sensor output before I reached a -peak- as far as total timing and horsepower is concerned.

I feel many say "race fuel has a slower burn rate". Truth is many factors influence burn rate but most gasolines burn rate is very similar. If anything, some race fuel is tailored to a faster burn rate as there simply isn't enough time for complete combustion at 9000+++ rpm as there is at 5000 rpm.

So, moving on, look at the energy value of the fuel, or BTU's per lb. Regular pump fuel is slightly higher BTU/lb than most race fuel so if the added octane isn't needed for your combination you will generally get slightly less output from using it.

Exception is E85 which has a much lower energy value but also a much lower stoich value which more than compensates for it. (as in you are burning much more of it)


Your engine at 11.5-1, hemi, aluminum head. I would be surprised if you were leaving much on the table with pump 93. I wouldn't expect it to like more than 32-33deg no matter what fuel.

That being said, only way to know is to test it. Run it back to back at the track or dyno. I would probably try something like 260 GT, 100 octane oxygenated if you are willing to spend the money on race fuel, rather than 110, IMO.
Posted By: Fig

Re: 110 vs 93 octane - 01/25/20 09:22 PM

Dvorak wrote this awhile ago, I thought it’s a good read. http://www.dvorakmachine.com/tech_WhatAboutFuel.shtml
Posted By: INTMD8

Re: 110 vs 93 octane - 01/26/20 12:06 AM

Have to disagree a bit. Octane is resistance to pre/ignition or auto detonation before spark due to heat, not burn speed once ignited.

Or/also ability to achieve smooth controlled combustion after spark event.

If you’re on the edge you can see this on a dyno with a stick car as it goes from a bit of a jagged curve to much smoother after introducing higher octane fuel.

Always open to other ideas so if someone can provide any links to info supporting octane vs burn rate I would like to read it smile
Posted By: RustyM

Re: 110 vs 93 octane - 01/26/20 12:50 AM

MD8: I think you will find this article both interesting and helpful.
I actually called Vp to talk about it and, can say i "think" i understand better than i did.
Yes, burn rates and vaporization matter and often the ingredients used to raise octane also reduce burn rates /hurt vaporization and thus, cures knocking etc but also makes less power in some applications.
By the same token, they can blend fuels to take high compressions but burn very fast for engines with really high rpm , which is needed because there is so little time at 10k (and up) to burn fuel.

Vp amazed me in explaining what all they can do with fuel blending.
Part of the article your likely most interested in is a few paragraphs down.

Hope this helps a little .
Tuning is a blast!

Rusty

https://dsportmag.com/the-tech/fuel-101-race-gas-octane-and-alternative-fuels-explained/
Posted By: cudaman1969

Re: 110 vs 93 octane - 01/26/20 02:10 PM

Got me thinking as to why our Hemi ran better at 37 degrees, maybe the old Sonoco 260 and first out racing gas was a slow burning fuel. RPM=slow burn=more timing. I remember after using Cam II purple it would evaporate out of the cell one week to the next, switched to blue and it never evaporated. As to the OP, I can't see using 93 and not pinging with a true 11.5 unless very little max timing, I'll find out soon since I'm putting together a iron head Hemi 485 cube with 12.5 (down .055" shorter deck height piston, long story) so I'm all ears guys.
Posted By: second 70

Re: 110 vs 93 octane - 01/26/20 04:21 PM

93 @ 11.5 to1 is no problem on an aluminum headed hemi @ 34 advance. Mine is even fine on 91 non ethanol.
Posted By: hemienvy

Re: 110 vs 93 octane - 01/26/20 04:32 PM

Second 70,
What are your cam specs?
Posted By: second 70

Re: 110 vs 93 octane - 01/26/20 04:42 PM

Originally Posted by hemienvy
Second 70,
What are your cam specs?


Crane solid roller 112 lobe separation 14 vacuum @ 1100 idle Low rpm motor Lol!

Mike

Attached picture IMG_2122-1.jpg
Posted By: cudaman1969

Re: 110 vs 93 octane - 01/26/20 05:41 PM

I see the spring spec but not duel or triple? Mine is set up for a big roller but I’m using a cam similar to yours so I’m thinking something lighter
Posted By: second 70

Re: 110 vs 93 octane - 01/26/20 08:08 PM

Originally Posted by cudaman1969
I see the spring spec but not duel or triple? Mine is set up for a big roller but I’m using a cam similar to yours so I’m thinking something lighter


Dual https://www.summitracing.com/parts/crn-96878-16/
Posted By: Cab_Burge

Re: 110 vs 93 octane - 01/26/20 10:14 PM

I've heard the old adage, racers theory, that aluminum heads suck enough heat out of the combustion chambers to equal one full point of compression ratio lower work
My last pump gas motor that made decent power had a true 10.78 to 1 compression ratio in it, it ran real good on straight 92 octane Oregon pump swill with no ethanol alcohol in it with Indy SR heads up
Posted By: justinp61

Re: 110 vs 93 octane - 01/26/20 11:39 PM

My 434" small block made 30 more hp on pump 93 than on Crate 98 race gas. All the tuning on the dyno was done with the 98. We pumped out the fuel cell and drained the carb then put in the 93, started it and allowed it to warm up, then made the pulls on 93. I've ran it on 110 unleaded gas too, the afr's were good but it didn't run the numbers that 93 does.

It's 11.2-1 with a 263/271° @ .050", .711/.719" solid roller.
Posted By: cudaman1969

Re: 110 vs 93 octane - 01/27/20 03:55 AM

Originally Posted by second 70
Originally Posted by cudaman1969
I see the spring spec but not duel or triple? Mine is set up for a big roller but I’m using a cam similar to yours so I’m thinking something lighter


Dual https://www.summitracing.com/parts/crn-96878-16/

Thanks
Posted By: jbc426

Re: 110 vs 93 octane - 01/27/20 09:48 AM

I'm running 10.2 to 1 that cranks 200 psi on both my Magnum and stroked 493" RB motors. I'm able to run full advance on both motors burning the 91 octane ethanol additive fuel we get he in California with zero detonation. My RB is actually locked out at 35*, and it never even kicks back on start-up.

While the 101 octane street legal race gas that's available at the pump nearby smells way better when burned, it's supposed to make less power than the 91 octane pump gas. The difference is so subtle that I can't feel it in either car.
Posted By: GTX5877

Re: 110 vs 93 octane - 01/27/20 02:52 PM

As reputed engine builder and tuner, John Lingenfelter, once said

Running an engine on the edge of detonation, will always make more power!
Posted By: Cab_Burge

Re: 110 vs 93 octane - 01/28/20 01:34 AM

Originally Posted by GTX5877
As reputed engine builder and tuner, John Lingenfelter, once said

Running an engine on the edge of detonation, will always make more power!

How many real car people, not real hard core racers, can tell the difference between the edge of and in detonation ?
A hot humid day can take a N/A carbureted motor on the edge of detonation deep enough into detonation so bad that you can hear it pinging shock
Way better to be on the safe side on the street, IMO up
Posted By: an8sec70cuda

Re: 110 vs 93 octane - 01/28/20 01:31 PM

Not scientific at all, but mine slowed down almost a tenth and 1 mph when I put some 110 in the tank after running low on pump 93.
11:1 572" hemi at 34° running mid 9s at 140 mph. I didn't adjust anything for the fuel change b/c it's a dedicated pump gas motor.
Posted By: Mattax

Re: 110 vs 93 octane - 01/28/20 04:09 PM

.Choosing the correct gasoline, Motorsports Village archive

I made a graphic of some pump fuels and race fuel distillation curves.
That helped me understand the references to the heavy end characteristics discussed in that thread.

Attached picture Fuel-distillation-Race-AV-2007.png
Posted By: cudaman1969

Re: 110 vs 93 octane - 01/28/20 05:04 PM

Originally Posted by an8sec70cuda
Not scientific at all, but mine slowed down almost a tenth and 1 mph when I put some 110 in the tank after running low on pump 93.
11:1 572" hemi at 34° running mid 9s at 140 mph. I didn't adjust anything for the fuel change b/c it's a dedicated pump gas motor.

Good to know, I’ll be close to that
Posted By: 440Jim

Re: 110 vs 93 octane - 01/29/20 06:55 PM

My engine is so much different, I don't know if this helps. But since you asked.
When I dyno tested my new engine, it made within 1hp in back to back fuel tests.

The dyno shop starts all new engines with their carb and 112 octane race fuel.
After verifying A/F and trying various ignition timing settings, we put my 1150 carb on the engine (still with 112)
Then after verifying A/F was OK, we switched fuel to 93 octane pump (up to 10% ethanol).
We did manage to get 4 more horsepower with minor jet changes and putting an additional 0.5" open spacer under the 1" tapered 4-hole spacer. Most was from the spacer, not the jetting.

496 CID wedge (4.15" stroke, 4.36 bore)
factory iron heads
10.3 CR flat top pistons
268/274 at 0.050" mechanical roller cam (kinda big for CR)
race car's headers stepped 2" to 2-1/8"
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