blue thunder

I am curious if there is a rule of thumb for safe distances between exhaust valves and water mix, with various lobe centerlines? For example, say a cam has a CL of 114* and does not revert water when it is mixed 10" from the exhaust valves. Or, if you have a 111* CL, you need a 16" distance between the exh valve and water mix to not revert.

I made those numbers up, but would like to know what the real ones would be in approximate terms. What do you guys think? Any such knowledge out there?

BT

Truckin

The amount of valve overlap is what you are refering to. With a large camshaft and wide lobe centerlines you will have the same amount of overlap as with a small camshaft and closer lobe centerlines.
There are two different opinions about camshaft designs. Small camshafts with close centerlines make as much power as larger camshafts with wider centerlines. With a big block Chevy you can make as much power with a 224/230 camshaft on 110 as a 230/236 camshaft on 114. The overlap isn't much different between the two.
Actually, reversion has a lot to do with intake manifold design also. The amount of vacuum inside the intake manifold determines how much water will be pulled into the cylinder when both valves are open at the same time (overlap). Single plane intake manifolds have less vacuum so they will usually have a little less pull at overlap. Advancing or retarding the intake lobe centerline will also effect the amount of vacuum in the cylinder during overlap. Compression also has a lot to do with it. A low compression engine will have less vacuum and pull in less water during valve overlap.

Water injestion is also determined by the exhaust manifold design. If each cylinders exhaust port is separated well (particularly #5 and #7) there will be less water being pushed around inside the exhaust manifold (less turbulence).

Sincerely
Dennis Moore

blue thunder

Great info there. Doesn't sound like there will be a simple "rule of thumb" to follow. You just taught me several factors about reversion I did not know. When are you doing your next BBC book Truckin?

Your new name reminds me of the old show call "Movin On". I used to love that show.

Thanks for the learning!

BT

US1 Fountain

iTrader: (1)

How pathetic am I? Still have the model I built as a kid some 25-30 yrs ago, in it's own home made case too!


Big wheels a rollin, gotta keep em going, big wheels a rolling.....Movin On!

Infomaniac

Don't forget the amount of back pressure in the exhaust has a lot to do with reversion.

Tips that exit under the water line at idle will trap more water in the exhaust pipes. Harder to push it out.

A cam with less overlap can be succeptible under this situation.

BadDog

Jerry,
You think you are pathetic? I have three half drunk women in my bedroom doing something on the brass pole and I am still at the board and Excel graphing HP and Torque curves for various cams. I still have my Testors model paint at 15 cents a bottle if that tells you how long I have had them.

blue thunder

Man I used to love building those models!! Wish I had kept a couple. I was into building choppers (motorcycles).

Yeah, backpressure. I am working on that one with replacing the risers.

Baddog, that is not pathetic as long as the camera keeps rolling!

BT

Budman

Tim,

You have a brass pole in your bedroom too? I knew you had installed the flying trapeze, but the brass pole is something I didn't know about. Man, you get to have all the fun!

Funny that the same thread contains info about drunken women on brass poles AND backpressure!