[Pvon]

Ok, so my question is if i have say 14:1 compression and am at say half throttle, would my compression be equal to an engine with 7:1 compression at full throttle?

Now I'm asking this question in relation to this idea I had. I was thinking if i could run alcohol at anything over say 75% throttle and gas under that then i could run really high compression and also possibly avoid the contamination and rust issues with alcohol.

Heres how it would work. You have 2 fuel tanks, one gas one alcohol. Your gas tank uses the stock pump and the alcohol tank uses a really good pump. The line from the alcohol pump has an adjustable fuel regulator and you set it to something like 100psi. Idk the exact psi you would use but you would want it so that you get the correct A/F ratio with gas and with alcohol using the same ecu settings. This would prolly be the hardest part.

Then the two fuel lines merge into one then go into the fuel rail. Where they merge is a gate type thing that will only let one go through, so if the gas is going through the alcohol is shut off and vica-versa. Whichever line has more pressure is the one that goes through.

Then the only thing left is you make a switch so that the alcohol pump is turned on at 75% throttle and voila ur running alcohol when the dynamic compression gets high and gas when its lower!

Let me know what you think

 

[Lude-icious!]

thats kind when VE comes in, and I really don't know alot about it...the use of alcohol though is goin to be hard, and expensive to get the motor built to handle it too...you aren't intending to drive this daily are you?? I don't think you can get the "best of both worlds" when it comes down to gasoline or alcohol, its either one or the other, or just running a little in the gas...

 

[Chiovnidca]

Ok, so my question is if i have say 14:1 compression and am at say half throttle, would my compression be equal to an engine with 7:1 compression at full throttle?

No, compression isn't going to change with with the throttle.

 

[singlecizam]

compression is compression, no matter how far the the throttle is open

 

[Pvon]

How is that, if the engine is only letting in 6psi (ie half atmospheric) and then you compress that its going to have less pressure than if it lets in 14psi. This is what dynamic compression is all about i think. You guys are thinking of static compression.

 

[HondaPACT]

No, compression isn't going to change with with the throttle.

static compression doesnt change but dynamic does, do a compression test closed throttle, and then full throttle you will see the difference, its just like boost in reverse I can have a static compression of 8:1 but if I add 10 psi to it then my dynamic is 20:1 (example) at closed throttle you might get 100psi if that out of a compression tester...but at full you can get the full 200psi, the idea that you have is doable as is anything in life, but is it really worth the time and effort? on top of having to tune for both XXOctane gasoline and Alcohol, and to switch maps at the precise time that the second stage injection would occur, I dont have any experience with alcohol motors but I would assume that it burn at a different speed and temperature then Gasoline...

 

[Pvon]

I can see how it could be work to tune it, but I dont think it would need different maps because the extra fuel required when u start using alcohol is provided by the higher pressure. However i didnt think about timing, but maybe a msd ignition box with like a nitrous timing advance function could take care of that.

 

[HondaPACT]

like I said I dont have any experience with Alcohol so Idk what it takes to run it on a engine...but if it requires a spark advance or retard then a MSD module might be a solution

 

[SOHC_Rules]

your dynamic compression can change all it wants, but the static will remain the same regardless. just cause the compression is 7:1 at 1/2 throttle (by your example) doesnt mean that there isnt a massive dome on the piston..

and i would only run alcohol at the track. it runs cooler so you can throw some more timing at it :TU:

 

[inh]

If you really want to do something like this, do it right...
Get a standalone ems, and a second fuel system.. tank, pump, rail, injectors, fpr, etc...

The standalone will allow you to use secondary injectors to run alcohol and gradually change over to 100% methanol by the time you are at WOT. This is done on turbo cars fairly often so that they only use C16 in high boost and 93 the rest of the time.

For example, the AEM EMS allows you to specify a percentage amount of how much you want the secondary injectors to be used at each load cell on the fuel map, so you can be 100% on the secondarys at WOT and 0% everywhere else, for example. You can also wire up a switch to enable/disable the secondarys, so that, say you are empty on C16, then it wont try and use them.

Someone might be going this route on thier boosted CRX when they get back from Iraq.. maybe..

 

[Pvon]

Oh thats cool, kinda sux cuz i thought i was being original lol. That way does pwn my way tho lol

 

[BigTuna]

Dont forget compression has a lot to do with cam and cam timing, compression test a vtec motor on the small lobe and the big lobe, huge difference.

Also remember that the dome of the piston is going to be the same distance from the plug no matter what the throttle position is. Alot of people forget that detonation on high compression engines has alot to do with the short spark plug to piston distance because of the elevated piston dome. When your dealing with 7000rpm and only a few degrees of timing between a great running motor and a paperwieght AND you move the piston 5-10 mm closer to the plug. Just think how fast a flame travels and 5-10 mm dome height can make a huge difference in your timing window.