So, what is it that makes an engine accelerate?

[steelcomp]

Gearhead:Look at the parts for a 500" Pro Stock. Now, everyone is not going to tell you what they are using, but just observe the parts that are being sold by Pro Stockers in the back of National Dragster, etc. Now with statements by several major engine builders saying "we don't care about the rod ratio". Well, let's look at their engine… Now these are just out of the air figures for thought… Let's say the deck is short… 9.200 range and the stroke is in the range of 3.625… and with the thin rings and the ring package high in the piston.. lets' say a compression height around 1.265… well, we could just hook up the parts with around a 6.125 rod. This would give us about a 1.69 rod ratioIn 1998, Larry Widmer wrote a response to a question asking for a description of a Pro Stock engine build, which I have read, and it's very detaialed. One thing I noticed was that he chose a particular rod ratio to start, and let everything work from there.
Larry Widmer:This is where the package height starts affecting everything we do. Since I attempt to run a rod length to stroke ratio of 1.75 - 1, calculating the rod length combined with the compression height(distance from pin C/L to deck), and (.5 x stroke) will yield our block deck height once we settle on the stroke. The combination using 4.6" bore, and 3.75" stroke, with a 6.5" rod, and a piston with a 1.265" compression height will yield a deck height of 9.635"and the rod length to stroke ratio will be 1.73 -1 which is "good". Since you were good enough to give your input, I thought I'd offer another view on geometry, and the importance of rod ratio. So much so that he was willing to allow his package be designed around it. Maybe thigs have changed since then, but that's a littel different than "the rod's just a device that connects the crank with the piston" theory. Larry's pretty sharp.

[MikeF]

In a N.A. application, focus should be on getting the maximum charge into the combustion chamber/cylinder 1st. With only suction (and resulting waves) being the only motivator for the action to happen, it is difficult to pull the mix into the cylinder. You would want the pull to be as great as possible. How do we keep that moving forward to fill it best?! :boxed:
Pushing the now lighter gasses out is taken care of by that moving wall called a piston. It's got to go somewhere.
I was looking for some 3 valve heads that I've seen in the past (2 in,1 ex), but I did not locate ones for a bbc. There are however some on the barrygrant site for some sbc ones.(they do not show the rocker side of the head) Also Jim Feuling had some heads he designed awhile ago w/small figure 8 style chambers but that website is now gone too. I know I've got pics somewhere.

[UBFJ #454]

Let's keep this Thread going ... How about some discussion of N/A motor header design and how you can gain Hp there ... stepped header design, primary tube lengths, etc..

[cstraub]

Bear,
When it come to combustion I am not that well versed except for some basic knowledge and a few tricks so I really don't feel I am qualified. Steelcomp may want to e-mail Larry Widmer and see if he would come on and "type" some. If not a link to his site on combustion may be a good deal.
After that we can tackle the stuff above the deck surface. I would invite any of the machinest on here to share tolerances and stuff like that they feel help contribute to an engines performance.

[HOSS]

I usually through a bunch of gas at em and they just seem to work good.
I really love what one guy told me about having 235 in the hole and being at 9.5:1. If he is then half the charge is going out the exhaust. Must be shootin flames.

[cstraub]

I am going to try and get French Grimes to post something on combustion here. In the mean time lets move on to heads: Who wants to start? Does Velocity or Volume win races?

[Squirtin Thunder]

I am going to try and get French Grimes to post something on combustion here. In the mean time lets move on to heads: Who wants to start? Does Velocity or Volume win races?
Wouldn't it be the velocity of the volume witch does the work ???

[cstraub]

Wouldn't it be the velocity of the volume witch does the work ???
Yup.

[Infomaniac]

I'm curious about that single power stroke that is doing the real work. How much of that stroke is actually utilized?
I read somewhere years ago in my quest for info that once the crank reaches 90 degrees ATC of the power stroke, all the torque has been delivered by the crank so you might as well open the exhaust valve.
Thoughts?

[steelcomp]

What do you think would happen if you opened the ex valve 90* ATDC??