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Discussion Starter · #1 · (Edited)
I have a 383 stroker, solid cam,12 to 1 comp, flat top pistons, I think 202 heads, the guy who built it ran race fuel only in it,it has just over 500 miles on build, I am wanting to drive it on the street and the race fuel is at 7.00 per gal,and at 4 miles per gal it is expensive, can I mix 94 octane? If so at what ratio is safe, I don't want to blow the motor!!!!! But I don't want a trailer queen either!!!!!! Any and ALL input is appreciated.
 

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to run E85 you need to rebuild the carb with the right pieces and SHOULD rebuild the fuel system. But yea, 12:1 will run fine on E85. The biggest problem with it is that its very corrosive on rubber- hence you need special seals and lines.
 

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e85 is a good way to cheaply run this engine, but it will lose significant power. Of course, I think you probably have power to spare :)

e85 has more effective octane rating, but a lower BTU content. If you compare the same engines; one with lower compression for pump gas, and the other with high compression for e85, they will both make very similar power. You also run the risk of reducing your 4mpg to about 2.5 mpg. It takes a lot more e85 to be balanced with air for a proper mix; about 12:1 instead of 14.7:1 with gasoline.

e85 is a good way to do it inexpensively. You'll need to completely redo the carb and fuel system, but that's probably cheaper than buying heads to lower the compression and a cam to correspond to your new compression. Converting a 12:1 SBC to run on pump gas can get pretty expensive if you do it right. e85 might be your cheapest bet, and its perfectly kosher.
 

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I disagree running e85 will pick you up 5 to 10 percent on power and tourque.While it is true it has less btu per pound it has more pounds burned per lb of air resulting in a higher btu content per pound of air.
 

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Ya know.......(and this is a long shot), You may be able to run straight 94. I mean, 12 to 1 static compression really does not mean all that much if your camshaft is nasty enough to bleed off a lot of the pressure.
Do you happen to have the specs on your cam?
 

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everyone forgets that static compression still counts as soon as they learn the word dynamic.... You cannot just blead off all of the cylinder pressure, when you nail it and get over 3500 RPM the cylinder pressure will build rather quickly and before you can hear it rattle you'll have a hole in the piston. running 12:1 on pump gas is insanely difficult to do with a traditional sbc. Simply using a large cam doesn't cut it. That trick can help you squeeze by with close to 11:1 but its a case where if some is good more is not better...
 

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You need to verify the compression ratio.

A 383 with flat tops would need 58cc heads (305 heads) with a zero deck and a standard felpro gasket (0.040") to make 12:1 cr.

If the heads are 64cc (most common) and the block has the typical -0.020 deck height then compression would be 10.7:1 cr with a standard felpro gasket. And this compression would be fine for pump gas if the cam is big enough (sounds like it is).

switching to 76cc afm heads would also be an option.

what is the ignition timing set up (initial, and total)?
what heads?
 

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Discussion Starter · #12 ·
I have a pretty radical cam in it, not posative on the lift, I don't think I have the money to try running only 94 and hope it works as, ap72 stated if the pressure doesnt bleed off and I rap it up real fast, then I have to explain to the wife I need a new motor. I think if I mix 10 gal 115, and 5 gal 94, it will give me a few more rides down the road, and cut my fuel cost a little, hopefully without doing any damage internally. But I am kinda new to a high compression stroker motors. Not sure if I like it or not. It sure is fun to drive though.
 

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strokedout said:
I have a pretty radical cam in it, not posative on the lift, I don't think I have the money to try running only 94 and hope it works as, ap72 stated if the pressure doesnt bleed off and I rap it up real fast, then I have to explain to the wife I need a new motor. I think if I mix 10 gal 115, and 5 gal 94, it will give me a few more rides down the road, and cut my fuel cost a little, hopefully without doing any damage internally. But I am kinda new to a high compression stroker motors. Not sure if I like it or not. It sure is fun to drive though.

that ratio is probably a bit conservative, but better to be conservative than to be left stranded. Check your compression ratio though- as noted it'll take either domes or small chambers to make that compression, you may have been told 12:1 and really have 11:1- which is still high but safer.
 

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Discussion Starter · #14 ·
WOW you guys are really giving me some things to think about, I wish I had paid more attention when my dad was working on cars.It all sounds overwhealming, thanks for the time and information, do any of you guys live near Cincinnati ?
 

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ap72 said:
everyone forgets that static compression still counts as soon as they learn the word dynamic.... You cannot just blead off all of the cylinder pressure, when you nail it and get over 3500 RPM the cylinder pressure will build rather quickly and before you can hear it rattle you'll have a hole in the piston. running 12:1 on pump gas is insanely difficult to do with a traditional sbc. Simply using a large cam doesn't cut it. That trick can help you squeeze by with close to 11:1 but its a case where if some is good more is not better...
Yes, but,...the 12 to1 static really means very little, considering the pressure changes almost constantly. Dynamic compression remains the same throughout the entire rpm range and does not change.

I personally have found that octane requirements are dictated by what an engine needs at low speed. At the drag strip, detonation on "lower" octane fuel only shows up upon launch. Ideally...you want to run as low of an octane as you can without detonation. Like right on the edge.

So, if he has a low dynamic, it will not change. High load, lowish rpm is where he may need more octane.

I'm not certain he has a 12 to 1 motor. I can tell you that I have a 12.2 static 496 in a relatively heavy car and can run premium "most" of the time without trouble.
 

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full mcgillicutty said:
Yes, but,...the 12 to1 static really means very little, considering the pressure changes almost constantly. Dynamic compression remains the same throughout the entire rpm range and does not change.

I personally have found that octane requirements are dictated by what an engine needs at low speed. At the drag strip, detonation on "lower" octane fuel only shows up upon launch. Ideally...you want to run as low of an octane as you can without detonation. Like right on the edge.

So, if he has a low dynamic, it will not change. High load, lowish rpm is where he may need more octane.

I'm not certain he has a 12 to 1 motor. I can tell you that I have a 12.2 static 496 in a relatively heavy car and can run premium "most" of the time without trouble.
the compression ratio calculated as "dynamic" is just a rough indicator of cylinder pressure at a very small spot- really compared to runing cylinder pressures its pretty useless, but since its easy to find it gives a rough rule of thumb to shoot for.

I do agree that in most cases octane requirements are highest at 3,000 RPM and below- but not always. I also agree that he may not have 12:1 unless he has aftermarket heads or domed pistons. I do not see this as being a 12:1 streetable engine though. Even the LS guys have a hard time of pulling 12:1 and they have a LOT more going for them.
 

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Discussion Starter · #18 ·
HMMMMMMMM!! I am going to do some research on this motor, when I was purchasing motor I was not paying enough attention to what I was being told about it, I just knew as soon as he started it, I had to have it. And the details I did remember are not helping me at this time. It is a gloomy stormy day here so I am doing some research and getting with you guys as often as possable, sounds like I finally found a group who know their s&%#. Can't wait to hear more from you guys.
 

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Yeah, I agree.
I suppose the term "streetable" is sort of in the eye of the beholder (so to speak).
Lets take my car for example. Many (MANY) folks would not consider my combo "streetable" because of it's 4.88 ratio and 4000 stall. And I'm certainly not goofy enough to claim that I put any real miles on it in a year.

I guess what I am getting at here is that a 12 to 1 motor can be ran on premium, on the street, but, it's all about how much load your engine sees. With my low rearend gears, and somewhat high stall, my car does not see much of a load unless I do something brilliant like firewalling it against the transbrake. Pulling a move like this would not be good on premium.

I suppose that I'm really just proving AP's point...because who wants to drive around in a car that you cannot use to it's potential?

When I built this motor, it was intended to be a bracket racer only. It ended up in a stret car (long story). If I WAS going to build a street motor, it would not have 12.2 static.

However...I will tell you that I do not have to "baby" it around on premium. But, if I wanted to use it to its full potential...pump gas would hurt it.

As far as going to a local cruise, car show, a summer evening drive to the burger joint...I can run premium with no problem.

It's surprising what I can get used to in the effort to save money :D .

Your motor is not going to instantly melt down by running premium. If you hook your car onto a trailer and try a pull a big hill with it...you may have some issues. You can tell right away if running premium was a bad choice. A normal take off then a slow roll on the throttle in a higher gear will tell you. You have to use some common sense, but you will know in a second if it does not like it, you lift your foot, no harm done.

If it did not like it, ease it back home and go to plan b.
 

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A couple of random thoughts here:

The motor will detonate worst at the torque peak where volumetric efficiency and cylinder pressure are highest. Depending on the cam, this will be from 4500 on up and with the engine noise at those rpm's, you'll never hear the pinging until you hole a piston or butt the rings together and tear off the top land.

Gasoline stoichiometric is 14.7:1, max power rich is 12.5:1.
E85 stoichiometric is 9.765:1, max power rich is 6.975:1.

Copper is impervious to ethanol.

Faced with your dilemma, what would I do? I'd build a dedicated fuel system to run E85. I wouldn't use the existing fuel tank because of residual crud in the tank and lines that would be leached out and into the carb by the alcohol.

I'd mount a plastic fuel cell inside the trunk on the trunk floor
http://www.summitracing.com/parts/SUM-290102/?image=large
with a 1/2" copper supply line and a 1/2" copper return line to the front. I'd use rubber-coated Adel clamps about every 12-18" along the frame rail to prevent vibration and work-hardening of the copper. I'd mount the cell up on spacers to keep the outlet/inlet inside the trunk and face the cell with the outlet/inlet facing to the rear of the car. Two 1/2" holes in the trunk floor would allow running the lines outside the trunk floor to the frame. Be careful and don't drill into the existing steel fuel tank.
I'd mount this pump inside the trunk, securely mounted to the floor on rubber isolators to minimize pump drone inside the car. Using short pieces of neoprene hose between the lines and the pump will further reduce drone.....
http://www.malloryperformance.com/P...jID=570&minID=5703&selection=6&minselection=2
And this fuel filter between the cell and the pump....
http://www.malloryperformance.com/P...jID=220&minID=2204&selection=0&minselection=2
Then I'd use this log/regulator on the Holley to modulate fuel pressure to 5 psi....No modern 4-bbl needs more than 5 psi pressure. More pressure will not make more hp. On the contrary, it will only make tuning problems for you when the excess pressure over-rides the needle and seat and floods the motor with raw fuel. You need VOLUME, not PRESSURE. That's why we're using 1/2" lines.
http://www.malloryperformance.com/P...jID=220&minID=2206&selection=0&minselection=4
I'd convert the Holley to E85....
http://www.chevyhiperformance.com/techarticles/0808chp_holley_750_e85_conversion_kit/index.html
Mount a roll-over valve such as this on the vent line coming out of the cell and run a line from the valve to outside the car...
http://performanceparts.com/part.php?partID=56937

I'd use only brass connectors on the lines.....compression fittings, no teflon paste, tape or chemical goop....and live happily ever after.

This won't be cheap, but neither will fraggin' that high-buck motor from mis-mixing of gasoline fuels and not being able to hear detonation.
 
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