924Board.org

[endwrench]

Has anyone had a chance to look at any high compression pistons designed for the 924NA? Did any have any quench area? Quench would be an area of the piston that actualy reaches the top of the bore like most engines instead of stopping .185" from the top. I just towed my car (i.e. basketcase) home last nite and was a bit flabbergasted to find this out. Overall I am pretty impressed with the engineering I see on this car and have found it to be in pretty good shape overall so have become rather excited about getting up and running.

I am leaning heavily towards a custom set of Ross pistons with plenty of quench designed in to the top. What do you think max compression should be with premium pump gas? I have a milion questions but will try to post one at a time for now!

Todd Fanton

P.S. None of the pictures I have seen do these cars any justice. They have great lines!

[Joes924]

Theres a couple guys whove gone 11-1

[Richard]

If you want a street car I wouldn't go more than 9.5:1 Compression is highly over rated and sometimes I think it is an ego thing. High compression puts high stress on head gaskets, rod bearings etc. Volumetric efficiency is more important. Make the engine breath as best you can afford and keep the compression reasonable (9.5 is already very high) and all will fall into place. Get a stage one cam. If you want a race car, anything goes.

[Cbass]

For a naturally aspirated street car, 11:1 is about the limit. I have seen engines with 14:1 compression, and they are streetable. They just need really good gas. Of course, if you have your own means of producing pure ethanol....

[endwrench]

In theory, having the combustion chamber in the piston top intead of the head is the best design for air flow but I am not sure when it comes to detenation problems. I feel if I could design a piston top with a fair amount of quench area and still leave the area around the valves unshrouded I could alleviate some of my detenation worries. I figure with this mod along with polished combustion chambers, bigger cam and the inherint qualities of an aluminum head, I should be able to boost compression to 10 or 11:1 or so. If I could go to a longer rod I am sure I could easily get away with 11:1.

Richard, I agree with your contention high compression is not the do all magic bullet but for this anemic little motor every bit will count!

Cbass, I do make my own beer and have plans for a still but I think I will stick with pump gas for now! I noticed in some earlier posts you mentioned you had an 11:1 motor you were planning to sell. Did you yet? Could you tell me if the pistons in this motor had any quench built into them? Appreciate your help.

Todd

[wdb]

info on alternative fuels, biodiesel ,methanol, stills, etc. forgot the link
http://journeytoforever.org/biofuel.html

[ This Message was edited by: wdb on 2002-05-24 13:23 ]

[Cbass]

The motor isn't mine, but it will be soon.

I haven't cracked it open, but the motor has supposedly has 11:1 compression, and has the compression test numbers to corroborate that story

As for ethanol fuel, it is surpising easy to manufacture ethanol. You just need to brew up your choice of wort, then build a still. I wouldn't know anything about stills though, they are illegal and what not

My advice is to go for a reflux design, it has a large column on top of the boiler, packed with any number of mediums to remove the water. End result is as high as 96% ethanol, or as I like to call it, moonshine.

As for biodiesel, I do believe it is made from grain and straw, using fermentation and bacterial processes to convert it into a fuel with similar properties to diesel. It makes more power and burns much cleaner though. In fact, there is a racing team somewhere in Europe that runs a TDI Beetle running on biodiesel.

[Richard]

My experience is that with pump gas, too high a CR will just make you need to retard the timing to prevent detonation, therby loosing most of the gains the high CR was suppose to give you. I am new to 924 engines and not yet sure of how detontation proof the dished piston is. The thing to remember is that the flame front has to travel through the charge faster than the shock wave. I've been twin plugging BMW's twins for years and this really allows high compression ratios. I'd get some hard facts on how resistent this design really is. Of course you could always use water injection... Also remember higher CR means a higher heat load. My project goal is to squeeze 135-140 hp out of this "little anemic engine" and keep driveability and reliabity very high. I'm staring out at 115hp though. It's all a balanacing act.

[endwrench]

Cbass, that is an interesting little factoid about biodiesel. Never heard of it. Another reason IC motors will never be completly replaced by fuelcell technology. From what I understand, owning and operating a still is not illegal for the production of your own fuel.

Richard, I completly agree with your contention about reliability and heat load associated with high compression but I don't feel it is of great concern at these levels as long as detonation is kept under control. I have the close to the same goals in mind also but will be looking (praying!) for 150-160HP. I don't plan to make this a everyday driver or touring car so I will have a little for leway in the drivability department. This will just be a fun car for me that I will drive on weekends and autocross on occassion. I must admit I have never understood the therory of dual plugs. It always seemed to me if you have two seperate flame fronts colliding you would be more prone to detonation. I also understand it does not do this if properly designed. Care to expand on this therory for me?

Also, does anyone happen to have dimensions on stock connecting rods? I need length, width and pin diameter. It will be a few weeks before I get mine apart to measure this.Thanks,

Todd

[endwrench]

Wow, I really need to proof read before posting or atleast figure out how to edit! Sorry!

Todd

[Cbass]

A correction to my previous statement about biodiesel. Apparently the all natural biodiesel is defined as bacteria generated fuel, and true biodiesel is 80% fossil fuel diesel, and 20% soy oil. The soy oil results in much cleaner burning.

The fact of the matter is, alcohol is ridiculously cheap to make. There are two types of ethanol available in North America. There is potable ethanol, sold and taxed as liquor, and there is "denatured" ethanol, for fuel source, science purposes, the usual. What "denatured" means, is they either use a chemical dehydrant to remove the last 3% of the water the industrial still couldn't remove, or they add 5% methanol to make it undrinkable. This is where claims of moonshine blindness comes from BTW.

For all the trouble of building a "super still" to make pure ethanol, and setting up apparatus to brew the alcohol, you might as well just buy large quantities of alcohol from a distributor. Since commercial ethanol is produced from grain, and there is still a massive grain glut, denatured grain alcohol goes for pretty cheap. If you buy 55 gallon drums, it's as good as free. Get an octane tester, and you can make whatever grade gasoline you need, for little more than 87 octane pump gas.

[wdb]

biodiesel is made by using lye and alchohol as a catalyst to remove the esters and glyserine from the organic oil, veggie or animal esters are fatty acids that will coke up the engine (carbin buildup). you can run 100% raw vegetable oil in a diesel engine and it will run fine for awhile, till the coke buids up and causes problems. the benefits are the biodiesel burns cleaner , so the atmosphere and your engine benefit, biodiesel provides better lubrication ( has 300% increase in lubrication, so using a 20 % bio and 80 % dino improves lubrication by 30%) . it is renewable we can grow more ,less dependency on opec nations. it is now legal to build and operate a still for producing your own fuel alchohol, there are als power plants in the UK that use animal manure to generate methane to power generators .

[Richard]

Endwrench, It is really quite simple. When the combustion process starts it is just germ or kernel of flame that needs to grow and spread through the combustion chamber. This is called the flame front. Anything in the way, such as a high top piston in a hemi head, delays the propigation. At the same time a pressure wave is created that travels at the speed of sound ( or thereabouts). There is enough energy in the wave to ignite pockets of fuel if it gets there before the flame front. Twin plugging gets two flame fronts going so first there is better coverage of hidden parts of the chamber, and also the complete combustion occurs twice as fast. I guess when the two flame fronts collide, combustion is over and hopefuuly the shock wave is left in the dust. In BMW air cooled twins with very high dome pistons, you can easily run 11.1 on regular and retard the ignition because the combustion event happens so fast you don't need to fire the spark plug so early in relation to the piston's up travel. This also helps detonation.

Air cooled airplanes all have twin plugs for safety, more power, and detonation. When I do a mag check in my bird the rpms drop off whenever you select one of the two mags.

Sorry if this more than you wanted to know, but I just love this stuff.

[Cbass]

Great stuff!

On the still matter though, it is still illegal to distill alcohol in Canada without a liscense.

If anyone wants to know, I can give them detailed instructions on how to build a beautiful reflux still. Makes about 95% alcohol on the first run.

All you need is a keg, $60 worth of copper pipe and fittings, and a water heater element.

Alternatively, you can make the same design with the $60 worth of copper tubing if you have a water heater you are not using, I liket to call this design, "The Super Still".

You fill it with an electric pump, turn it on, and leave it for 6 hours. You come back to collect as much as 10 gallons of pure ethanol.

[Lizard]

why dont you have an engine that runs with high CR with 94 octane but when the engine gets up to a certain rpm it injects alcohol into the intake bit more fuel efficent for city driving but with same power