I discuss several topics relating to compression and pump gas. How OEM’s used soft ramps to prolong camshaft life and deliver manageable dynamic compression pressures even with high static compression ratios. Can your 11:1 SBC run on pump gas? There are a lot of factors, and you may be able to do so if you choose the right combination of parts.
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I used the speed pro , 306 222 at 0.50.447 lift. It would improve power in about any form of 350. I agree.
Ethanol is exactly alcohol, it is vodka, unaged grain whiskey, its the exact same stuff that is in beer, wine, bourbon, Scotch, etc. EXACTLY the same stuff.
The energy content of ethanol is NOT why you need to run more of it in an engine. The amount of Oxygen in the fuel is why you need to run more fuel. Gasoline in the real world, wastes more than 80% of its energy as heat that must be removed from the engine via the cooling system and some also goes out the exhaust. Thats why heat is such an issue with gasoline engines. That oxygen, and the cooling effect of ethanol, is why ethanol makes more power than gasoline.
Most gasoline vehicles achieve around 18% to 19% efficiency on gasoline. Yes they can do better in controlled environments, where everything is cooler and less chaotic than the real world. Make the environment perfect for the test and you can get it rather high, but that does not translate into driving around town or down the highway.
In contrast ethanol wastes only 60% of its energy as waste heat, because it burns faster, more completely because it vaporizes easily and readily in the intake tract. More of the fuel is used to power the engine rather than heat it. It does the 40% of its energy being used to power the engine in the real world, as it is vastly more forgiving… and it makes more power as well.
I have an iron headed Pontiac 455 with 13:1 static compression, it has a camshaft that builds plenty of cylinder pressure with the timing events making as much as I could get. It WILL NOT run on pump gasoline and live very long, sure it will idle around if you back the timing down enough, but that takes away a lot of power. It runs great on E85 and the HE100 I produce.
What is HE100? Hydrous ethanol, meaning it still has water in it, usually around 10% of it is water, but that just means it is a slightly lower proof. If you drink it, it will not take very much before you are forgetting how to properly relieve yourself.
Now why on earth would I build such an engine, with a small camshaft that makes incredible torque from idle to 4500 rpm, and then give it some heads that allow it to keep making plenty of torque up to 6000rpm? We are talking over 600ftlbs though that range.
I made my 4100lb 1970 GTO into a mileage mule is why, and I got 20mpg mixed city/highway from it using a Qjet I converted to E85, 700R4 trans, 3.42 gear, and it had more than enough power to run mid 11s when it would hook. 90lb GTO front bumpers make it more of a challenge, and its a driver not a race car. By contrast it had a different 455 in it that ran on 87 octane, and it ran 12.60s with a 2.93 gear and a 2004R trans, and with a Th400 in it too. However, the absolute best mileage I got from the 87 octane 455 was 19, and that was following a semi down I-40 headed east, drafting off him. Usually it got 17 or 18 highway, and around town it was 12-14 depending on how I drove it.
Now just how on earth did I get better mileage and more power running ethanol than pump gas? Its simple really…
The more compression you have in an engine, both static and dynamic, the more torque it is going to produce, because it is working the fuel harder. It packs the air fuel charge into a smaller volume before igniting it. The result is more power, with less fuel.
With an engine that makes diesel like torque, you do not need a deep gear ratio like a 4.10 to move the vehicle. You can run 2.41 to 3.55 gears behind my engine and the ET stays pretty close to the same, but getting it to hook up with the 2.41 is much more difficult. It really likes to spin the tires. Put a 4.10 behind this engine and you will lose at least half a second in ET.
So the engine moves things easier, that requires less throttle angle, which feeds less fuel and air to get the same performance, you do more with less while having the potential and ability to have a lot more power available with more throttle. Work the fuel as hard as you can without it igniting when it feels like it, and you will get the best mileage. The problem with gasoline is:
1. the waste heat
2. low octane that limits compression ratio
The waste heat compounds the octane problem. You have to run a gasoline engine cold. i.e. 160F thermostats.
Ethanol doesn't like to ignite without a spark, so it takes a lot to get it to ping/knock/detonate. It has to be very lean to do it. The hotter you run an ethanol engine, the more power its going to make in relation to the amount of fuel its using to make that power. You do not tune an ethanol engine like you do a gasoline engine. Its not quite exactly opposite, its more different.
We have this interesting thing called latent heat of vaporization, where as a liquid evaporates it cools the air around it. Ethanol is VERY good at doing this, gasoline, not so much. You have to run gasoline cold to get it to be happy, cold and lean. Ethanol you run it rich and hot to make it happy. Most people run ethanol too lean and too cold, then they get all sorts of other problems, like having a milkshake in the oil pan. It doesn't get hot enough to boil condensation out of the oil, particularly with a thermostat under 180F. I run my ethanol engines between 195F and 220F. Then they make less power than they could be because they are still thinking like gasoline.
You want the intake manifold hot running ethanol, because its going to cool the intake charge more as it evaporates. Check out superchargers, you can see a 100F drop in temps under a roots blower between ethanol and gasoline.
Why did I do this with a Pontiac? Well, partly because I love these engines, and partly because of the design, which is why I love these engines. They have long intake runners, that are just a bit too small for the cubes under them, but they can still fill the cylinders. Why and how? Well its a velocity thing, the air is moving very fast through a Pontiac port at every RPM, its kinda sluggish in the chevy with the larger and shorter runners. I am talking the distance from the throttle blades to the bottom of the cylinder at BDC.
Its a longer distance in a Pontiac. The bbc has large ports designed for higher RPM and not for torque production, its a different way of thinking with a Pontiac. More diesel like… but when you take those long runners and make them flow two or three times as much air, it contiunes to produce ludicrous torque at lower RPM, but carries it farther in the RPM range, and it makes more torque everywhere.
So I made a 455 do better what it was designed to do. Most of the power increase from ethanol is between 1500rpm and 3500rpm, with smaller gains through the rest of the curve, usually around 10hp to 15hp. With a 1900 stall my engines stay right in that sweet spot where ethanol makes more power, and they are already making plenty of torque. They just make more.
That vaporization thing? Yeah.. you can use that too. Like Smokey Yunick's hot vapor Fiero, but no need to get the air fuel charge to 450F with multiple chambers and whatnot. Ethanol vaporizes at 173F at sea level, intake powers are more of a vacuum, not completely, but close to it, so ethanol is very happy to evaporate. If you heat the fuel before it gets in the relative vacuum of the intake port, it vaporizes instantly, cooling the air charge making it more dense and dramatically increasing the surface area of the fuel over atomization, thus making more power and using less fuel to do it.
Lastly.. the corrosion thing, that is from additives put in the fuel, same with the chalky white substance and the yellow or green gel. Thats all additives. Ethanol is simply vodka, there is nothing left at the bottom of vodka bottles, or whiskey for that matter, no matter how long they sit… like 12 years for scotch, or hundreds of years for wines. However wine does have some solids still in it, because its not distilled like whiskey, vodka, bourbon, etc.
I converted my first Qjet to E85 back in 2007. I am the first to do it and nearly all the information you will find online about it, or in books, comes directly from yours truly. In the last 16 years, and the previous 20 years that I was driving around with 10% pump gas in my vehicles, I have never had a corrosion problem due to ethanol. Lots of problems with pump gas, including rusted fuel tanks, rubber hoses that get brittle and rupture, fuel pumps dying, and of course that black crud in the engine and varnish in the tank. I get none of that with ethanol I make. The farther south I get E85 the more additives they put in it, and the more problems I have seen with the fuel.
Its not from the ethanol. Its from all the other stuff.
If you want the power that you can get from a high compression engine, just switch to E85/E98 and enjoy the power it makes. You can drive race car compression ratios on the street with it. Low compression will almost always result in lower mileage on ethanol, because its not working the fuel hard enough. Gasoline gets the edge under 12:1 static.
If you run an ethanol engine too lean, you will use more fuel and you will also get less power from it. With boost you can raise the static compression of the engine above that of pump gas, which will pick up mileage, power, and make turbos spin up faster to some extent. With forced induction you will probably get worse mileage on ethanol, because when you add more fuel, you are also adding more oxygen and adding more air requires more fuel and it quickly becomes similar to the Rocket Equation.
Best power on E85 is around 7.5:1 AFR. Best mileage, depending on bore size and other parameters is between 8.5 and 9.5 AFR. E85 and E100 will run quite well as lean as 11:1, but it makes a lot less power doing it. Ethanol will run at gasoline AFRs but will chug and buck, surging at times like steady cruise.
DO NOT GO LEAN WITH BOOST WITH ANY FUEL… because pistons do not like holes in them.
Thank you for your wisdom….I've watch David Vizard and many others…I want to switch to BBC after a life time of being a 327 fan. I appreciate the fact that you guys are willing to share your knowledge…my next project is a 1968 El Camino with 4 speed 373 gears and red line of 6,000 RPM. This is a street car that i want to be strong as i can get with a 454 bored to 60 over or maybe a 496 stroker with iron heads….any advise would be greatly appreciated. Keep up the good work.
I have seen guys post on facebook claiming to run 14:1 on pump gas.
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Static vs dynamic compression
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Just as dynamic compression, set by the camshaft events greatly influences cranking cyl pressure, a running engine has variables that determining the octane requirements. A high compression race engine with over 14:1 calculated compression ratio with a relatively short duration cam could reliably run on 87 octane gas no problem, if the torque load was kept minimal. This would require a throttle opening to maintain relatively high intake vacuum. In this case, the engine can't develop high combustion pressures/temps associated with detonation. There's a ton of other factors at play, combustion chamber temp and efficiency, total ign. timing requirements, accuracy of maintaining proper fuel distribution and ratio evenly across all engine loads and cyl to cyl, etc…
Short answer, in an old school carbureted muscle car era engine, I would agree with your assessment on taking a close look at cranking compression pressure as a good overall indicator of detonation resistance. Unless someone was willing to spend a ton of money to modernize all the development shortcomings due to age of these old engines, and taking the owners dedication and ability to monitor for signs of detonation, I'd say anything over 10:1 would really be pushing it when combined with a typical hot-rod street camshaft.
Pump vs race fuel at higher CR has a lot to do with timing as well correct so if a sbc at 12/1 is sat at 35* timing is 93 octane possible ? Idk possibly mix 110/93? What about 100LL airplane fuel ?
I have a stock FE 428 that I would like to run in my 72 F250 camper special. The book says they came with 10.5 to 1 compression pistons. The info everyone is giving me is I need custom piston 9to 1 max. I would like to get a cam to use the engine the way it is. Is that possible or custom pistons? C6 2500 stall 373 gears. Might go with 411 gears if that helps. Its a fresh rebuild just trying to get a cam selected without the custom pistons.
Answer to your final question, while I'm only guessing, I'd say low speed and load maybe, depending on many variables. But as RPM increases the addition cylinder filling would send cylinder pressures way beyond what 87 could resist. I built an 11.6 to 1 408 small block with cranking pressure of 217. It's a tight quench motor with aluminum heads. While it runs very well on the primaries, 93 octane (tunnel ram) it does rattle @ W.O.T unless I use race gas. I think it's because of the same reasons stated above. Backing timing low does not help. My W.O.T AFR is fat as well @11 to 1 so i don't think it's a lean induced rattle. Although I can not rule out poor cylinder to cylinder AFR. Love the tech by the way. I'm always looking to learn more, thanks.
Enlightening. Thanks for posting this.
Makes sense I love learning new things about engines and the why and how. Thanks for the info.
Hello, doing a 350 Chevy with 9.9 compression but a very short camshaft. Howard's flat tappet. 255/261adv duration. And 201/207@50 with 114 centers. It's installed at 109 degrees when I degreed it. What would I expect for cranking compression 200psi, maybe a tad more? And also I plan on running premium pump gas 91 octane in this engine, is it going work with 91 octane and still put a little timing in it? It's got 416 305 heads on it with 60cc chambers, .015 steel shim gaskets with 12.3 cc dish pistons with about .040/.042 quench. Going run a stock Quadrajet carb, holley street dominator dual plane intake and factory ram horn iron manifolds. Wanting a low rpm high torque engine and fuel mileage and not concerned about high rpm hp. What are your thoughts? I can't find anything on how high of cranking psi I can go on 91 pump gas.
Forgot to add my dynamic compression comes out to about 8.4 to 1.
We run over 16 to 1 on Pump Gas with Cranking comp of 220 we also don't go near Peak TQ or load it going down the road and chance to Race gas at the tracks. There is lot of work goes into being able to do this but it can be done.
13.5 to 1 on propane or alcohol. daily driver
waiting over 2 months, I need the right brain. I'm building a 68 nova, It has 3:42 gears with m-20 trans. I have a 72 454 that is .40 over with speed pro h581cp pistons with a stock crank and rods, and it has been professionally balanced and the estimated compression is 10.5, at this time I have 049 stock heads an edelbrock air gap and a quick fuel 750 with fat stainless headers.
I have called comp, isky, erson, howards and clay smith and everyone tells me a different cam. Today I was ready to order Comp Cams 11-423-8, Grind # XR276HR-10,, Duration at 050 224 int./230 exh., Factory rocker ratio .502 int./.510 exh. the rear gear change is not a problem and might want another carb, What do you think ??
E85 – problem solved
I think You should be able to run off of 87 with this compression ratio! Here are the reason why: 1. Rod ration is a factor; the higher the better; 2. Combustion chamber design/efficiency; 3. Piston design/quench; 4. Constant cooling temp and adequate cooling system/components; 5. Good fuel quality/low ethanol content/low moisture; 6. Precision fuel metering/A F Ratio; 7. Vehicle weight; 8. Gearing and Transmission; 9. Appropriate Cam selection/Timing; 10. Properly machined and set-up Cast Iron head; 11. Correct Aluminum intake manifold! I also think a good oil and standard volume oil pump would be the right choice for a street application. 12. Properly sized exhaust system should complete the total package..
i have a 496 bbc with 950 double pumper carb it is suddenly running really lean after a WOT pull.. AFR reading high teens while idling and running rough. next day start it up and its back to normal running good in the high 12s/13s. Wondering why it would start running lean after a WOT pull i drove it for a few minutes after to see if it would clear up but it didnt not until the next day i went to drive it again. Good fuel pressure float bowls are not empty any experience with this?
I'd take ethanol blended fuel every day of the week for performance applications.
The cooling it provides is worth it.
I believe you but what is wrong with this running the higher octane instead of all this hub hub just make it easy and spend the extra dollar and the engine to run better ask the bottom line instead of having to get a camshaft that you don't want
OEMs (and those of us working on emissions reductions in hot rods) have other tools as well. The decrease in fuel mileage you mentioned can be combated with variable valve timing, EGR, and even Atkinson-Miller via valve timing. The tough part (which is what I’m working on) is variable duration as well, in order to maximize power when using race gas. There are other tools I’m also working on, but these are proprietary (my goals for my 4.6 liter Ford Mustang are 450 hp / 45 mpg on pump gas — not at the same time of course).
Static compression and duration are not an acceptable way to determine what fuel is ok to use. Cranking psi isn't much better.
Dynamic compression ratio, which factors in inlet valve closing degrees (numerous online calculators available free) , is the better way. Your compression isn't going to be the same if the only change is an inlet valve close of 68 ABDC vs 88 ABDC
Alloy heads will accept higher compression than iron heads.
Combustion chamber shape, piston crown, top ring location, spark plug heat range, cooling system efficiency (back cylinders/combustion chambers always run hotter) and a number of other details will also have an impact on flame propagation and hot spots that can lead to pre-ignition.
It's also worth understanding that low octane fuel burns faster and therefore requires less ignition timing. both of these are in fact more efficient. I'd rather run 28 deg total advance with 87 than 38 deg 93
Don't better grade fuels also allow for more ignition timing with less fuel allowing for more power? I know that's one of the factors that can play into your tuning
good info probably should also mention how cams with large overlap will effect cranking compression. Mine makes only around 90 psi cranking pressure but has a large overlap and duration. Effectively pushing combustion out intake port at low speed. The compression ratios is around 9.5:1 engine is turbo charged and makes 700 hp from 2.4 liters at 8500 rpm.
Makes sense. I’ve never looked at it like that so it’s a new concept of thinking. I’m always building drag engines with no vacuum and making all the power up top.