running straight headers??

GPzephyr wrote:

Excuse me for sounding stupid. But why would low back-pressure burn your valves?
I was always brought up on lower is better.

cold air does bad things to hot exhuast valves,used to do that when i was young and dumb before i knew back pressure was a good thing on street motor!:whistle:

GPzephyr wrote:

Excuse me for sounding stupid. But why would low back-pressure burn your valves?
I was always brought up on lower is better.

If the pipes are long enough, then it won't.
It normally happens when running either no pipes or very short ones, what happens is the valves get really hot and when you shut it off cold air gets to the valves and causes them to warp. When the valve warps it no longer seals against the seat and exhaust escapes during combustion. I have seen notches cut into a valve due to the plasma cutting effect of escaping combustion gases.

So it's not to bad with a long piece of straight pipe in there? i am already jetted for a header and Free flow muffler. i still want one for beach days, but wanna keep it quiet in the city. I really want it on the 1100, but with the efi i have no way to compensate for it.

Post edited by: tnutz, at: 2007/02/14 20:08

tnutz wrote:

So it's not to bad with a long piece of straight pipe in there? i am already jetted for a header and Free flow muffler. i still want one for beach days, but wanna keep it quiet in the city. I really want it on the 1100, but with the efi i have no way to compensate for it.<br><br>Post edited by: tnutz, at: 2007/02/14 20:08

any way to hook up a power commander or yosh box? or better yet just go mega(or micro) squirt

Have to switch to later model throttle bodies or adapt a TPS to the original ones, hard to believe but the early model throttle bodies basically had an on/off switch instead of a TPS. I didn't believe it myself when it was first posted here so I checked a set I have, and it's true.

i always though it was the super hot exhaust gases being blown through the valves too fast due to it being too free flowing, kinda like a plasma cutter, or a cutting torch.

themachine wrote:

i always though it was the super hot exhaust gases being blown through the valves too fast due to it being too free flowing, kinda like a plasma cutter, or a cutting torch.

Nope, that's the purpose of porting isn't it, to get the exhaust gases out faster?
The exhaust valve and port size/shape limit the speed of the exhaust gases, just like on the intake side.

It takes time to transfer heat, the less time the valve is exposed to exhaust flow the cooler it runs.

steell wrote:

GPzephyr wrote:

Excuse me for sounding stupid. But why would low back-pressure burn your valves?
I was always brought up on lower is better.

If the pipes are long enough, then it won't.
It normally happens when running either no pipes or very short ones, what happens is the valves get really hot and when you shut it off cold air gets to the valves and causes them to warp. When the valve warps it no longer seals against the seat and exhaust escapes during combustion. I have seen notches cut into a valve due to the plasma cutting effect of escaping combustion gases.

Yup! that makes sense. Especially regarding no or very short pipes.
So the length of a typical street system isn't likely to suffer from this, regardless of how low the backpressure is. The cold air simply isn't going to be able travel up the pipes to the valve. Disregarding the noise factor of course.:blink:

Why would you even want to think about not running pipes?

tnutz wrote:

So it's not to bad with a long piece of straight pipe in there? i am already jetted for a header and Free flow muffler. i still want one for beach days, but wanna keep it quiet in the city. I really want it on the 1100, but with the efi i have no way to compensate for it.<br><br>Post edited by: tnutz, at: 2007/02/14 20:08

Oh yes you can!...compensate with EFI that is..

The 81 had the older analog setup but you can still tune it to a degree, certainly enough to compensate for a pipe.


Adjustable Fuel Pressure Regulator will get the job done.

how so!!!! tell me now!!!:laugh:

oh... pleaseB)