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How much boost pressure can stock 83' 350 handle? E85 conversion

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Hello, does anyone know how much boost pressure i could safely give a chevrolet 350 with a 9.0:1 compression ratio without modifying the internals and how many hp would that be about?

My plan would be to convert it from gasoline to E85 (85% ethanol/15% petrol) to avoid detonation and possibly get around some of the european emissions standards before putting turbos on it.

The turbo would be something like a single or double t3 Mitsubishi TD05 16g turbo used on the volvo 2/7/900 series rated for 0.9 bar or 13 psi each

But the question is how much boost do YOU know a stock 350 can handle, i would be happy with "only" getting 400hp from a 200hp stock engine, but am i dreaming or is it possible?

Sorry for bad grammar, hope it is not too offensive :p
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I don't know how it works in Europe, but here in the USA, corn fed pumps that say "E85" have some fine print that says something like "50% to 85% Ethanol by volume." It's rarely exactly 85% Ethanol. That's why "flex fuel" cars have a sensor in the fuel system to figure out how much gasoline and how much corn mash is in the tank.

Unless I was really sure that I was getting 85% ethanol all the time, I wouldn't assume you know the exact blend.

Here's the official US Government website that explains it:


E85 (or flex fuel) is a term that refers to high-level ethanol-gasoline blends containing 51% to 83% ethanol, depending on geography and season
 

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After 6 or 7 pounds the ice gets thin on stock pistons in stock bores. Not that detonation and preignition aren’t issues the real point is power is developed by heat. Heat makes tge pressure that pushes the piston that turns the crank converting the heat of combustion into rotational force at the crankshaft.

Detonation/preignition is what you’re trying to suppress with the E85. Heat is another issue measured in BTU’s it is a function of how much mixture is passing through the engine. To that end the problem gets to be the piston gets hot and looses physical strength on one hand and expands on the other. Included in the expansion of things that get hot are the rings. Starting here stock end clearance rings not meant for dealing with transferring more heat than designed for meeting emission requirements will expand taking up the end clearance. Once gone they will bind ones pooch upward and outward the result being gouged cylinder walls and broken ring lands of the piston. Lower down on the piston is the skirt clearance with the cylinder wall, here the skirt will attempt to lock itself with the cylinder bore wall. In mild cases this will scratch and gouge the bore wall on the thrust sides. In severe cases the skirt and sometimes the bore wall are ripped apart.

The failure mode above is separate and apart from the distraction that detonation and preignition can do. But either mode of “overheating“ the piston or blasting it with explosive forces the factory piston quickly gives up. That is true of older low alloy castings and of the newer hypereutectic castings. Generally with the older pistons which run a looser bore clearance you get damaged walls and ring lands as these expand more than hypereutectic pistons. The hypereutectics run tighter clearances but are more thermally stable but splinter apart when they let go leaving the piston pin to hammer holes in the cylinder wall.

Detonation/preignition usually overheats the upper ring land and the ring. The aluminum on the quench side overheats melting away to the ring grooves failing the rings as it goes till finally burning through to the crankcase side at of under the oil ring groove. I keep one example on my desk as a pen/pencil holder. Here a forged piston is much more immune than any casting but not necessarily one hundred percent successful at it.

So without replacing pistons with forging and dressing up internal clearances and bearings 390 to 400 hp with a supercharge or nitrous is about the physical limit of sustained operation. You can go higher in bursts for a few seconds but keep in mind that pistons fail even on dyno pulls which last but a few seconds, so when trouble comes on it does so mighty fast. This is somewhat the same for naturally aspirated on these parts where about 400 hp can be had in bursts but not continuously operated there. The reason being how much heat is generated in the cylinder against how fast it can be removed either as work into the crankshaft and by the cooling system against how the material’s strength profiles change with temperature.

If I were in your shoes I’d expect an old engine will eat its insides in no time at all and that the destruction will be pretty complete rendering not much if anything salvageable.

Bogie
 

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Ethanol produces peak pressure much later than gas and the pressure rate ramp is somewhat digressive so it tends to be easier on pistons.
Ethanol doesn't detonate like gas, it's the ring land packing, not detonation, you have to watch for. Similar looking results, different process how is happens.
EGT's are also lower.
 

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Hence the need for more compression as the alcohol content of the fuel goes up. It isn’t so much that alcohol fuels allow more compression but rather demand it because they burn cooler that gasoline so to get equitable power you need to work alcohol harder. The saving grace with alcohol fuels is their naturally high detonation resistance allows the needed compression increase. Whether that garners more power against fossil fuel blends is a different question.

The down side of E85 is by law the blend can be as low as E51 which is quite a disparity but is usually found in winter blends where reducing the alcohol content makes the fuel easier to light off in cold weather. Here in the northwest, blenders generally make the change to easier to light off fuels whether booze or fossil in October and back to summer blends by the end of April. If you track your mileage you will see the change where winter blends tend to reduce mileage but this can get lost in the concepts of increased rolling resistance of tires that are stiffer with cold temperature and often must move snow or rain water out from their contact patch, wheel and driveline bearings and lubrication is stiff taking more energy to move so all of this can influence fuel consumption as well as blending changes. Again no free lunches, moving stuff around always takes energy.

Basically when you get into the thermodynamics of fuels the power coming out of the reaction goes up with the compression pressure which is itself somewhat related to compression ratio. With a blower you certainly separate compression pressure from compression ratio. University studies display that a compression ratio of 100,000 to 1 power and mileage become infinite. But our engineering and strength of materials don’t permit us to operate at that kind of pressure. Could be alien technology does, but here at home, not so much.

Bogie
 

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The lower the ethanol percentage the richer the carb gets. Cooler weather and adding fuel go together so the change isn't as dramatic as it may seem.

Alcohols can support using more compression but it's not a requirement. It works with 8:1 engines the same as 15:1 engines. AFR's and igniton lead both are similar on the testing I've witnessed.
On the SBC 383 test mule, swapping pistons from 9:1 dish to 12:1 domed, everything else stayed the same. AFR's and timing requirements changed very little. No more than changing intakes, heads, rockers, or anything other typical rodder combination. It made about the same peak torque/HP, but more mid range torque. That's inline with methonal as well. They are torque fuels. What did happen thoough at 12:1, it was less sensitive, I.E. a little wider tuning window. I'm unsure as to exactly why.
 
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