just thought i'd ask you guys b/c i've noticed many of you run open header at the drag strip. a guy i know said that due to back pressure or lack thereof, running an open header can cause bent valves. fact or fiction?

 

Neither.........

Crap, actually.

Running an open header can cause SOME vehicles under some conditions, to run overly lean, thus burning valves.

However, the ITR runs fairly rich as is. Doubt if the valves would burn unless other mods are involved.

John

 

My friend who races Ducatis once mentioned that a lot of motorcycle guys will put something over their tailpipe (he uses a cut tennis ball) to prevent 'cold' outside air from reaching the exhaust valves after a race (motorcycle exhausts are relatively short). The exhaust valves will, of course, be very hot after a race and 'cold' outside air has been known to slightly bend valves on occasion.

Personally, I have never seen this happen. But, that doesn't mean that it couldn't happen. I have no reason to doubt my friend. He is a very reliable source of information with plenty of experience.

Any motorcycle guys have any input on this?

-kenji

 

I've never looked at it like that. I would think that it is a good idea to not let cold air into the valves either.

 

yeah but we have a pretty long header. i doubt cold air will go all the way up.

 

...don't think so. Actually, an open header is shorter than a complete racebike exhaust. So, cold air can get in there easier but, I don't think it might happend unless you put a blower at the end of it. After a race, the head and the exhaust is so hot that any air that comes in would get warm by the time it reaches the valves if it does.

 

then keep the car running

 

Please tell me how long you have to keep the car running to the point where the air coming out of the header is the same temperature as the air outside of the header.

 

no i mean't that if the car is running, it will be pushing hot air out. since it's pushing hot air out, cold air cant seep in. which i said it in a joking manner

 

approximately 3hrs after the car ran out of gas.

 

Keep in mind that motorcycle engines have much lighter (read: thinner) valves to allow for reliable operation in the high rpm ranges they see.

 

Quite good advice from your friend. I do not do such a thing, but some of the guys I race with on the weekends do par-take in said procedure. Quite funny, actually.

 

Wouldn't it be pretty hard for cool dense air to displace the hot air that is present inside the header? I mean the hot air wants to rise. When the car is sitting still I see it is highly unlikely that cold air could get to the valves. IF it got to them it would no longer be cool because of the distance it traveled through the hot environment inside the header would have warmed it.

I would think the only way to get cold air to the hot valves would be if there was some sort of vacum sucking the cold air back through the header toward the valves.

On a race motorcycle I could see there being a problem. The headers are angled up, and the hot exhaust gases would escape out of the pipe allowing the cold air to sink down toward the valves.

 

Maybe Ducatis are made like chit so ya have to protect them?