What would be the advantages to pistons with really high compresion (11:1) for the 300 i have a 92 EFI. and what would they do for me found some really cheap there jahns cast pistons (what does this mean) it lso says they use .912 wrist pins so can these be installed on my stock rods? and what other mods would i have to make in order to use these.




Thanks

 

With greater compression you get greater punch from the same spark - meaning you get more power, but at a cost. Everything will run hotter, take a greater beating, and you'll have a greater tendancy for preignition. That said, you won't get any great performance running pump gas - even 92 won't get you far. You may have emissions problems, and your computer probably won't be fond of it. The smaller pin size is for the early 300 rods. If you bought them you'd need new rods - your's take a larger pin - you maybe able to bush them. Even that said - don't trust a compression claim without running the numbers given the CC's of your head and pistons, along with any kind of o/s bore.
Ebay can be a great place to buy parts, but don't get caught up in all the hoopla. If your not sure about a purchase, your better of saving your money to pay retail price when your ready for it.
BTW, welcome to FTE.

 

11:1's Wow. If your state has emissions checks, you can kiss the prospect of passing those goodbye. Oxides of nitrogen would skyrocket due to the increased combustion temps. Do expect that the engine may be harder to start in addition to what's already been said. You might also have to replace starters as frequently as changing oil as well. I'll second the comment on fuel. To get the thing to run without destroying itself on fuel that's available to you at your local petrol stop might be hard. Of course, you could retard the timing, but you may have to retard it so much that you'll not have much benefit vs. what you've got now.

What's happenin'? The force you get to push the piston down is directly related to horsepower, right? It is. Ok, that said, what happens in the combustion chamber is that the pressure inside the cylinder AFTER the explosion is a direct function of what it was BEFORE the explosion (precipitated hopefully by the spark and not a hot spot or whatever). So, the deal is that if you bump up the pressure before the spark (compression ratio), you'll get not just a 1-for-1 increase in cyl. pressure after the spark, but instead, something quite a bit more than that. Voila! More horsepower. The trick is to keep the charge from exploding (technically, it's not an explosion, but it's controlled flame propagation, but I'll not split hairs) before it's supposed to and to keep the flame starting where it's supposed to. If you get a hot spot in the combustion "vessel", upon compression, the flame may start before the spark occurs or at the same time and now you've got two flame fronts and it's bad news on the metal where they meet. Lots more to the story, but you get the idea.

Bottom line is that IMHO, this is certainly not a change I'd get tangled up in and doubly so for anything resembling a daily driver.

 

A local gas station has either 97 or 102 (i can't exactly remember) pump gas for the dirt bike/quad/snowmobile and dragsters. would this make a differance it's not to much more expensive because they use thanol to bost the octane

 

They use what?? I don't think you mean ethanol because I don't believe ethanol will boost octane. Whatever they use, I'm sure you'll see a difference in the pump price...especially these days.

 

YAh ethanol is what i ment. maybe im wrong. but would that make a differance in performance?

 

they sell CAM2 racing gas at 110 octane at the local mobil.

I put that crap in my 2000 YZ-80 once. Holy crap. Thing was insane. I had to take off in second cuz first would wind out almost instantly.

 

what is normal compression for this engine stock (92)

 

8.7:1 for the EFI years (87-96/7), 8.4 for the carb years (65-86) and 8.0:1 for the HD's.


-=Whittey=-

 

I don't know what compression was in '92, but the other comment that I wanted to make is that if the engine is not detonating under load with a given octane fuel, putting in fuel with an octane rating of however many points higher will make no difference in how it runs. Again, that's all other things being equal. To be sure, you could bump up performance by taking advantage of the octane rating by (in the old days) bumping up the ignition timing so it was + another degree or three BTDC as compared to before you adjusted it. It's a bit harder to get 'round the computer to do that now, but that's essentially what a performance chip does (ok, I'm simplifying, but you get the drift). All this thing called "octane" measures is RESISTANCE to burning. The higher the octance, the harder it is to make burn and a higher octane buys you the protection of NOT having the explosion occur before you wanted it to (ex: from a hot spot) and having the explosion more controlled (i.e. you get a single flame front (good) and not multiple flame fronts (bad)). Bottom line is that higher octane will get you the flame propagation qualities you want IF you're not getting them with the current fuel. If you already are (not pinging excessively, zero detonation), there's no reason to put more $$ in the oil company's coffers than you already are.

 

i agree 100% with what the octane does. You're right when you say, if all else was equal, then the higher octane would make no difference on a good running engine.

I think, i'm pretty sure, that the higher octane level gasses often have some more additives in it. I would think that maybe stations put something in there that gives a little more boom boom so that people buy it more often for performance needs.

works great on dirtbikes tho!

oh and i think the compression on the YZ-80 was 8.11:1

I have no idea about the ignition timing. Different octane gasolines did make a profound difference on performance though. I think that the little super-tweaked out engines respond really well to the octane for some reason. But comparing an 80cc single cylinder dirtbike engine to the 300 is like a kia vs. mac truck.

 

You're a 2stroke mixing it with oil. I'm not sure exactly what the burnable qualities of said oil are, but that's more than enough to change it drastically (even if you run light on the oil).


-=Whittey=-

 

wait, i had to put oil in there?

that's a good point... now you got me thinking...