Keith

I am of the understanding that a smaller bore chamber will allow for a better burn due to the shorter distance that the flame has to travel in a given time period. I'd imagine this why the F1 teams run V10's? That would make for a smaller bore than an eight cylinder with a given displacement, while still remaining within a piston speed limit right?

Thoughts? How does chamber design affect this?

Armageddon

iTrader: (41)

A larger chamber allows for a longer burn time if im not mistaken. When the flame finishes hatching and begins propagation it has an area to cover measured in cc's... I forget what you call the amount of time the burn lasts but it's a legit measurement to take into consideration in a max effort build. The only thing I can think of with the F1 cars is a smaller chamber with a quicker and more precise burn could help with the insane RPM these cars maintain. Actually... I think the longer the flame burns the more torque you produce also. This all relates back to valve overlap and how much power is lost pushing the spent mixture out of the chamber. I'm hitting all around what I want to say here. Maybe somebody else can fill in my blanks.

bygblok

iTrader: (4)

chamber design and piston shape both play a huge roll in flame travel(or propagation) by allowing the mixture to travel freely in the cylinder and completely fill the quench area when it's time to light off. If you have a large dome on the pistons and a head design that's not at %110 you have a very good chance that the mix will light off all on one side(or close to it) of the piston. The chamber works in conjuction with the piston design, port configuration, camshaf, etc in order to keep the mixture mixed and swirling as efficiently as possible in order to allow a complete lightoff. If it ligts on one sideor the other you will build hot-spots that will cause detonation and/or with all the loading being on one side or the other the piston will have a harder time moving in the bore because the explosion is tryin to send it sideways. This is a HUGE HP robber that many back-yard builders fail to ever see but it's there. For this very reason I have ALWAYS preferred to use a flat-top design piston with a very efficient set of heads. Add to that the hottest ignition system you can get and it MIGHT run. I like all the fire from the plugs I can get. A big compression motor can qute literally blow the spark out in a cylinder if the ignition isn't up to the job. I also like to run a big plug gap as well so the spark has the best possible chance to ignite all that junk I just threw in the hole....... oops, you asked about chamber design and I got off on another page...sorry. Yes, chamber design has a HUGE affect on flame travel since that along with camshaft selection and ignition are the brains of the motor........ wow, that was too simple, sorry!!

bigdsz

iTrader: (1)

I believe there are also maximum theoretical bore calculations available. If the bore gets too big at some point there is inefficient or incomplete flame propagation. You don't see any see any 5-6"+ high rpm gasoline engines around. Diesel bores are a totally different matter, they can be massive, but real low rpm's.

Keith

So a max effort engine would have a small chamber to direct the flame in the proper direction. And a piston to help direct it and give the desired compression ratio. Like a C5R head I take it. But then you are at a 4.215" bore, which is a pretty large bore.

What about the 3.898" bore that Gm designed for the LSx. Is that small bore size and the set of bitchin cylinder heads that they put on the cause for really good torque and power?

Old SStroker

Combustion flame travel is far from simple. Here's a fairly interesting discussion of it especially as it relates to high-output engines:

http://speedtalk.com/forum/viewtopic.php?t=3652

Keith

Some good reading there, Thanks.