massive compression

[Bobby17772]

I was talking to my friend the other day and I brought up having huge compression 15:1 and even higher and he didn't think it was possible. Well I was looking around and I actualy found some, but what my question is, what kind of head do you have to use with these kinds of pistons, reguardless of model (D, B, H, F, K)? because by the dome on these pistons it doesn't look like a stock head could take it, but thats just me.

if one of you guys knows that would be awesome

thanks

 

[Briansol]

massive pistons require massive machine work of the head/combustion chamber/valves/cams/rod length, etc etc.

then, it needs serious fuel to not detonate.

 

[78civic]

It all depends on the shape of the combustion chamber..
The crown of the piston has to reflect it and be able to clear the valves and channel for the sparkplug if it's got an extended tip.
And the crown of the piston needs to be the appropriate thickness and composition for the compression also because the extra heat generated won't melt it through.

I would think that one would have to run alcohol of some sort because the gas wouldn't have enough flame travel to burn efficiently around the crown and quench area for a given time of ignition, or crank rotation.

We've all seen the pistons of the pro drag racers that are huge also. That's why the spark plug was moved to the top center for more clearance in the chamber (Hemispherical head-HEMI)

I've even seen some pistons from BMW I think that had channels milled in the tops to keep the turbulence up so they could run more compression, and not have the flame detonate all at once. Because you really want the crank pin to be passing TDC and the explosion to force the piston down rather than killing the compression for the previously fired cylinder.
(think of peddling a bike. You get more power if you push down right after you peak at 12:00 rather than 11:00 (as looked at from the side rotating) And the added pull up from the other foot on the other side (power-adder) is more work for you, but gives better performance.

You can come up with all sorts of 'theoretical' hypothisys(?) but making it work efficiently is what your after. In addition, they are just a HARD
working engine. EVERY stroke has to go thru that particular compression..

I wonder what type of compression you can use for Natural gas..?
It's a 'closed' intake system but don't know how fast it burns compared to gasoline.

That's why I was asking in a thread awhile back about filling in the combustion chamber to raise the compression. Then you wouldn't have to worry about a heavier than stock piston spinning faster than the other stock internals could handle..

Sorry for the rant, Just bored..

E

 

[Bobby17772]

damn that was actually pretty informative. I have no reason to go that high it was more or less something that we were talking about and he didn't believe it to be possible or they didn't make pistons for that kind of compression. but thank you both!

 

[K2e2vin]

<-My current build puts my compression at around 13.5:1 CR, and it will run off 93-octane or E85(if ever readily available in our area).

BTW, Bisi E. was running regular gasoline with over 15:1 compression for a while in both the D15 and F22A. The D15 was at 270hp and the F22A was at ~430hp before switching to methanol.

 

[Bobby17772]

yeah I was reading that the drag crx has a f22a with 17:1 compression

 

[K2e2vin]

Well, it's now a drag Insight...and it's getting faster too!

I forgot to mention, the figure for my motor is actually on slightly dished pistons(really, it's practically flat-tops). As stated before, it's all about combustion chamber shape. Optimal quench pads(ie: pads that do not shroud the valves) and small bores help deter detonation.

 

[B16RacerN2NR]

I\because by the dome on these pistons it doesn't look like a stock head could take it, but thats just me

Dome size isn't the only thing that effects compression. Boring and going with over sized pistons raises compression as well. It doesn't sound like it does because most people think more area = less compression when infact boring and oversized pistons allows for the bigger/ wider pistons to push more air into the same sized combustion chamber.

 

[pooksy64]

Dome size isn't the only thing that effects compression. Boring and going with over sized pistons raises compression as well. It doesn't sound like it does because most people think more area = less compression when infact boring and oversized pistons allows for the bigger/ wider pistons to push more air into the same sized combustion chamber.

*couldnt be more right
K24 block in some models come with domed pistons.high compression is possible..remember higher compression more likly to detonate &/or preignition. chamber temperatures getting to hot.higher octane fuel ex : C16 race fuel can handle a good A/F ratio with out running to lean or detonation.