For a street motor with occasional strip runs, is there any hope of making this combo run decent on 91 octane? I don't mind dialing back the timing a bit when it's on the street.

10.5:1 Static Compression
Lunati 00083 cam
Qjet
Flowtech headers 1.75" primaries
Dual exhaust
3.73 rear
Automatic (TH350)
??? Converter (I've toyed with the idea of using a switch-pitch TH400 I have lying around)

I've also considered trying E85 now that it's becoming more available around here. Just not sure 10.5:1 is taking full advantage of the corn juice.

 

You left out the most important aspect of running 10.5:1 compression on 93 octane, what type of head are you using? If it's an aluminum head you're just fine...I run 10.63:1 with Edelbrocks on 93 octane in Houston. If it's iron head, you're in the "Danga Zone" as Archer would say

 

D'oh! That's what happens why I try to post while the kids are still up. Too many distractions.

It's a 425 rotating assembly, +.060"
Here's the kicker - Stock CA heads with stainless valves.

The calculator I used shows DCR is 7.85:1. If the cam were installed 4 degrees retarded it shows as 7.56.

Yeah, I know it's really pushing it. But I have been told that with the right cam you can get the cylinder pressure low enough to get away with 10.5:1 static. Just curious if this one would let me get away with it.

 

The original question said "91" octane. That will definitely cause some problem. To avoid pinging, the timing would have to be so far retarded that the engine will run like some sick 4-banger.

 

Yeah, that's kind of what I was afraid of. Just hoping someone with direct experience could comment on just how bad it is.

There's only one place anywhere close that has higher than 91 at the pump. That one place has 100, but it's across town and pretty far out of my way. I plan on driving the car enough that I'm worried I'd get caught needing fuel when I'm too far away.

 

I'd be mixing some racing fuel, for longevity - that's too close!!

 

"It appears that most gas engines make the best power with a DCR between 7.5 and 8.5 on 91 or better octane."

http://www.empirenet.com/pkelley2/DynamicCR.html

 

Mine is at 10.25 and runs best on 93 or Ultra 94. I tried 91 and the pinging was pretty bad.

 

How much timing advance do you run?

 

I'll have to check on that. When it comes to timing and tuning I am clueless. The guy who worked on the engine for me set it up.

 

How do you know that you have 10.25 compression?

 

Just based on what the engine builder told me. I have a spec sheet at home I can post later.

 

My true 10:1 461 with G heads rattles with the timing at 36, it likes 34*. I doubt if your combo is going to like 91 octane.

 

Install a methane tank

 

You mean methanol?

 

Thanks for the constructive input, guys.

Does anybody know where the sweet spot is for compression if you run E85? I have read that if you tune specifically for E85 you get better power and economy than running E85 in a flex fuel setup. But I haven't found much documented that is specific to an Olds V8, and it seems like different engine designs would behave differently.

 

With E85 you could run over 11.5:1 with iron heads easily.

 

I've heard that. So is the deal to run as much CR as you can get away with and not ping? Or is there a point of diminishing returns?

 

Most of those folks that run hi compression with E85 are not really interested in fuel economy. You need to get with some of the performance guys. You will definately need to modify your carb and fuel system.

 

You also need to consider your location. Find out how close or far the nearest E85 retailer is...I know a guy that drives his '72 Nova around w/ 3 - 5 gal gas cans in the trunk because the E85 stations are few and far between here in Houston.

If you're driving 40 miles to fill up w/ E85 then you're more than likely going to be using a DD to get gas and do driveway fill ups of your Cutlass.

 

oldcutlass - I'm not worried about economy exactly. My point with that comment was more that if you optimize the engine for E85 your range per tank won't be much different from gasoline, everything else being equal. I have a pretty good handle on the mods required to the fuel system

ah64pilot - Availability is my biggest concern. However, several Valero stations in the area have added E85 and it's about $0.40 less per gallon than gasoline. It's going on a road trip where things get iffy.

 

I would convert mine but there is NO E85 in my town!

With all else being equal I think you will find a minimum of 10% less in fuel economy.

 

You might want to look in to water/methanol injection. Snow performance makes a good kit. This will be the route I go on my build.

 

I have 11:98:1 in the 507,with iron heads,and I run straight 93 in it.If I know I'm going to the track,I'll mix it with some hot stuff,for insurance,but otherwise just 93.I think the quench,or the quality of the burn has an important factor as well,along with camshaft,and the other points stated already.Other engines would have rattled with even less compression.

 

Wow Brian, you're running a smidge under 12:1 with 93? If you don't mind my asking, how radical is your cam? And how tight is your quench? I'm looking at .039"-.049" depending on how much comes off the block when it's resurfaced.

 

My cam is 257/265 @ .050,.668"/.668" lift. My piston are flat tops,with valve reliefs,and sit .045" in the hole.My heads are 70cc,and my head gaskets are .038".I had the total timing at 36 @ 3,000rpm,but decreased it to 34 or 35,and picked up 6hp on the dyno.
The only time I could get this to rattle with 93,was when I had my friend in the car,who is 6'4",250+lbs.

 

Thanks for sharing. What's really interesting is your quench distance is about .083", which I've heard a lot of people say is way too much to help with detonation - but obviously it works for you.

That cam is way bigger than anything I intend to run. Do you think that accounts a lot for the detonation resistance? What's the advertised duration? I'm curious how the dynamic compression ratio compares with some of the cams I'm looking at. I also may not be running as low a rear axle ratio as you - mine is 3.73:1.

 

K1 kerosene...better known as jet fuel.
Don't over do the mixture...just use as an additive.

 

While the correct mix of Jet A (which IS NOT K1 kerosene) and gas will effectively increase the octane rating, the Jet A has a higher flash point and will not burn completely in your engine. You will soot up your engine and gum up your carburetor. This is really bad advice and I urge you not to try it.

Jet A and Kerosene have similar distillation processes and are similar fuels, but they are not made from each other or identical in any way. Diesel engines can get away with using Jet A, but they require an oil additive to add lubrication to the fuel for valves and injectors. Jet engines likewise can use diesel fuel but will gradually lose performance because of the lubrication in diesel. Jet engines do not require fuel lubrication because they do not have valves or other "friction" parts in the intake system. They are oiled internally by a multi-sump oiling system.

CW2 Steve - 152H AH64D Longbow Pilot / 15B Aircraft Power-plant mechanic

 

In the home brew octane booster recipe that is often cited, they use mineral spirits, diesel or kerosene as a "cleaning agent" component, but toluene or xylene is the octane boosting component. I have no idea if kerosene really acts as a detergent in that application, but that's what they claim its purpose is in the recipe. They also use a small amount of ATF for upper cylinder lube, which I find dubious especially in such a small amount.

I've read anecdotes that using high percentages of toluene as a booster accelerates upper cylinder wear since it is a rather "dry" aromatic hyrdocarbon. I suppose adding upper cylinder lube like the methanol guys use could mitigate that to some degree. But by the time you do all that, might as well just go get some race gas.

 

My rear axle is also 3:73.
You also have to realize that as you go up in cubes,it takes more cam.What might be radical in a 455 will mellow-out in something like the 507.As far as the advertised duration,I don't pay too much attention to that.I focus on the numbers at .050.
You can also look into things like piston speed,and how long it sits at the top.

 

I've yet to see any harsh affects of running some K1 as an additive.
I've studied the MSDS and realize they are not 100% the same,but close enough.
When using it in my cycle,I can instantly feel the power difference.

 

Two important things here about Kerosene:
1) It's flashpoint is significantly higher than gasoline, a minimum of 140 degrees. In order to vaporize kerosene or diesel you need heat. This is why diesels have such high compression. It heats things up far more than any gasoline engine does or needs to be in order to operate.

2) It's octane rating is drastically lower than gasoline and will not give you increased power. Nasty455 you are not feeling any power in your cycle from pure kerosene. Unless you have a diesel bike Preignition is the only outcome from that mixture in a gasoline engine.

Here's a good article on it.

First, lets deal with fuel vaporization. I’ll begin with a brief discussion on the characteristics of gasoline vs. kerosene vs. diesel. All of these are petroleum distillates, which means they are refined from crude oil. As with any distillation process, the “lighter” elements are the first to evaporate. Gasoline is one of these elements. Diesel is considered a “heavier” element, which means it does not evaporate easily. Kerosene is roughly between the two. So here is a very simplified comparison.

Gasoline: 125,000BTU/gal. Flashpoint is -40F

Kerosene: 135,000BTU/gal. Flashpoint is 100-162F

Diesel: 138,000BTU/gal. Flashpoint is 126-204F

The key factor here is the flashpoint, which is the minimum temperature at which the fuel will vaporize with air to produce a combustible mixture. Note the jump from gasoline to kerosene is at least 140 degrees! Diesel’s flashpoint is as much as 240 degrees higher! The reason for this is the hydrocarbon “chain” of molecules is much longer in kerosene and diesel than in gasoline. This chain must be broken apart before the fuel will vaporize. The easiest way to accomplish this is HEAT.

Another important thing to remember is the difference between “atomization” and “vaporization”. To keep this a simple explanation, atomization is the conversion of a liquid to a fine mist, and vaporization is the conversion of liquid to a gaseous form. Why am I boring you with this? Because in order to effectively burn “middle distillates” like kero or diesel, they must be VAPORIZED. Fuel that is too cool will be atomized by a carburetor. The result is the poor, very smoky performance that some of us experimenters have seen. When the microscopic droplets of fuel are burned, only that fuel which is actually vaporized will burn. The rest either sticks to the cylinder head as carbon, or goes out the exhaust as smoke. This is great for ‘skeeter control, but it is a waste of fuel and not the best for your engine. Heat must be used to vaporize these heavier fuels.

Since the goal of running kerosene was to reduce operating expenses (years ago anyway), mechanical atomization (as in a diesel engine) is out of the question. Also, whatever method used needs to be simple and low maintenance. So for simplicity and minimizing cost, heat is the method of choice. On the tractor engines of old, this was easy since most integral intake/exhaust manifolds had a "hotspot" where the exhaust manifold heated the intake manifold immediately downstream of the carburetor. The fuel in the intake stream that was not completely vaporized would not be able to make the sharp turn into the intake manifold log and would be thrown into this very hot surface and immediately vaporize. Even automotive engines used this in the form of an exhaust crossover in V8 intake manifolds, and the same "hotspot" style was used on inline sixes. The principle is used on gasoline engines to improve efficiency and cold weather operation. In some cases, the fuel line from the kerosene tank was run in close proximity to the exhaust manifold to preheat the fuel so it would vaporize more readily in the carburetor.

The second problem with kerosene and diesel in a gasoline engine is preignition. Kerosene and diesel have a very low octane rating (somewhere around 25) and thus makes it very prone to compression ignition. This is why, of course, they run great in diesel engines. In a diesel, the fuel is not introduced until it is time to burn it, so the low octane is a non issue. When the intake air is carrying the fuel, low octane is a problem. There are two ways to resolve this. The simplest, and most common, is to use a low compression ratio so that the intake air will not be compressed enough to ignite the fuel. Any engine with a ratio of around 6.5:1 or less should be able to run kerosene without problems. This would include almost every flathead engine made, as well as a good number of antique tractor I-head engines. Another slightly more complicated option is to use an anti detonant. The best example of this would be the Rumely Oil Pull engine. It utilized a three bowl carburetor. One for starting gasoline, one for kerosene, and one for water. The water jet was located ahead of the venturi (where the main jet is located) so that water was only drawn when the engine was under load (half throttle or above). The water prevented compression ignition thus allowing higher compression ratios to give performance equal to (some will argue better than) a gasoline engine of equal size. Another advantage to the water/kero mix is it produces a much smoother (less violent) burn in the cylinder, making it much easier on the engine. Therefore, it lasts longer. For more information on the Secor-Higgins carburetor, follow this link to a fantastic article on the “Rusty Iron” webpage.

 

I'm not running pure K1,I'm using it as a fuel additive.
25 to 1 mixture with gasoline.