open headers?

650ed wrote: so the open pipes and the possible burned valves are not a concern (the valves don't burn in a quarter mile). Ed

...Exactly, Ed. They usually EXPLODE first! :laugh:

Yikes!

steell wrote:

Hollywoodmx wrote:

steell wrote:
Might hole a piston running it so lean though.

Yup, it's called un-metered air in the fuel injection world.

Basically the exhaust pipe is going to take in air through "reversion" (like a vacuum), since that air isn't flowing through a carb or air flow meter no extra gas is accounted for so you facilitate a lean condition. Same thing can happen on with a cracked carb boot on the intake manifold side of a carb or a vacuum leak.

Are you saying that cold air is going to travel up a 20" long pipe, plus a couple more inches of port, and hit the valve while the motor is running?

Even 20" is conservative "rule of thumb" my friend, for scavenging and not warping valves. That is where there is a big temp gradient at that, so that shutting off the motor is like dropping the valves in cold water. The reasons most motors have problems with really short exhaust is the lean issue you mentioned. If the fuel is riched on up, then even then you can get away with a pretty short pipe.

Scavenging is not a big a deal in EVERY case as made in most hot-rod circles. Why would scavenging be so important if you are running, say, a single? LOL Or most twins for that matter?

I ran an open collector in my Z1 for about two seasons, no problems. Just jetted accordingly- at the time, I had it lucky, I had a friend with an exhaust "sniffer" for tunning, so I just changed the jets and tuned carbs until the correct A/F ratio was as close as I could get. I lived in Alaska then, and it was hard to get a tune really good- air density could change thousands of feet in a day, due to dry air and moist air trends and cool and hot air changes in the summer. So just had to be as close as possible LOL

know what love straight pipes! TURBOS lol boost it and you will be great lol

when jetting dont forget to increase your pilot jets too.