I have a completely rebuilt 360 that i am currently running with open headers. I have been told that running engines with open headers is very bad for the valvetrain. Is this true? and how concerned should i be about this cause i definately do not want to have to rebuild my heads again.

 

Well I have a different opinion than most i say there is nothing wrong with it. Ive heard you can suck a valve but thats prety much impossible just by running open headers...they would be sucking valves all day long at the track if that was the case. I ran open headers on my 68 360 for 3 months after it sat in a field for 10 years and now about 7 years later its still runnin.

 

It is fine. With shorty headers I would be sorta worried. Valve damage from too little exhaust comes from cold air hitting the exhaust valve. This is much more prevalent in engines that have cams with big overlap. Basically the exhaust valve is still open for a small portion of the intake stroke. You get very little reversion of airflow back through the exhaust port with a small cam.

Stock open manifolds should cause problems but I can't guarantee it.

 

So, you're driving around town... isn't it really loud? Won't the cops hassle you? I couldn't imagine driving around where I live with open headers. It's loud enough with the delta flow 40's.

I fired my truck up once when I first put on the headers (before I reconnected the exhaust with flex pipe). Sounded awesome, but I'm sure my neighbors didn't like it.

I once knew a dude that swore by putting rags in the header collector after shutting his 289 down. Said something about not wanting cold air making it's way back up to the heads. I don't really know what to make of it...

Sam

 

1969FordF250
I can't remember for sure but, I think the shortest exh pipe off the head is 18'' or it's 24'' think about drag boat pipes and so on any less may do some cold air damage to the exh Valve. OK here's what happens with running with open headers. If your in to racing at a strip, And open your headers you need to retune or rejet to richer jets so your engine is not running to lean, running
with open headers. Why! because now you have almost zero back pressure and this makes the engine run leaner. If your running to lean all kinds of bad thinks can happen when you have your engine really pumped up. Back many yrs ago it was all about reading your spark plugs.. Just adding headers makes it run leaner.. hope this help in some way.. my 2 cents
orich

 

Hmmm.. I have never thought too much about the effects of backpressure on mixture. I would think that since your cylinders scavenge better when there is less backpressure you would be getting rid of more dead air and consuming more of the same air/fuel mixture. It would make sense to me that open headers would make the engine either richer or almost unchanged. I don't seem to notice a difference. There may be more to it than I am seeing.

 

Rat, there must be more to it. Otherwise, why are we given a choice of jet size for our carburetors? I'd think that once a carb was dialed in to your desired mixture, you could plop it on pretty much any engine and it would deliver the same fuel to air ratio at the same airflow. Carb's are designed such that they will deliver the same air / fuel ratio over a wide variation of airflows, correct? So how would opening up the headers make it run lean? Wouldn't it just suck more of the air / fuel mix from the carb?

 

Opening the headers cant possibly have any effect on airfuel mixture.....it just physically impossible, its on the wrong end of the process to do anything.If getting spent gasses out helps to lean out the new incoming fuel mix then adding headers and bigger pipes would make that (in theory) happen by increasing the flow....but by running them open or with full exaust wouldnt change anything still. I think were looking too deep into an entirely simple process.As long as exaust is flowing nothing is coming back up that pipe. I had a t-bucket dunebuggy for years and it ran true headers strait off the block and never had problems.

 

Power can be found with the right header setup. Not just the headers, but the entire header, collector, and crossover exhaust setup is important for engine performance. Depending on the torque range, header configuration can be an additional ticket to higher output. For most Saturday-night applications, good performance is seen with the crossover pipes located 11-13 inches in back of the collectors. As any part of the engine setup is changed, thought should be given to a change in header setup. For example, a change in a carburetor, camshaft, or other changes may call for a change in the exhaust system. Consulting with a reliable engine builder of exhaust-system combinations is a strong recommendation. If your out for the max power on Saturday night

Proper carburetor jetting has an impact on engine performance. After an engine has been shut off, look inside the header tube to determine the header colo. This can reveal some things about the carburetor. Charcoal-gray headers are an indication that the carb is set up right, but powdery-white or dark-black colors may indicate the carburetor jet is set up lean or rich, respectively. This is a simple check that can lead to better engine output.
or
A rich- or lean-running engine is a source for reduction of engine performance. A simple way to read for a rich or lean fuel condition is by looking at the color inside a tailpipe. Using a light, look about a foot up into the pipe. You are looking for a color that is medium brown, which is an indication that engine fuel mixture is good. If the color is a powdery whitish gray, it's an indication of a lean fuel condition. A dark black color is an indication of a rich mixture. This quick read can be done without taking the plugs out. Removal of plugs at the track is always a potential source for introduction of power-robbing contamination. These are general guidelines for
stock to pump-up engine my2cents
orich

 

Hell Ive been running open headers for 4 years in my mudtruck and have had no problems...and I'm not to nice to the ole truck...lol. My new 390 is spinning well over 6 grand and a valve breaking due to open headers is the leaste of my concerns.
This spring I rebuilt the heads and there was absolutely nothing wrong with the valves as far as abuse from having open headers...just had a few that need a relapping and grinding on the ends.
As far as the lean condition with open headers.....never heard of it. The only thing that may be causeing a lean condition is a misadjustment at the carb and a WOT condition may make it surface due to the extra revs allowed by the headers.
By the way Sean open "manifolds" seem to work ok too...I had a 360 run for a year like that and the dr side was cracked wide open...although I wouldnt suggest it to any one thats looking for some longevity out of thier motor...this one was a freebe "run her till she blows" 360...but it never blew.

My .02
Rob

 

Sean this is true,

Running straight headers you are getting rid of more Esht...but your also pulling in more air thru the top end with less back pressure, hence your carb doesnt see it, there fore you run leaner, your getting the some amount of fuel but mixed with more air, thus being lean,so another step up or 2 in jetting.....

Russ

 

Well,I didn't have time last night to add this that reading the pipes was ez back before the nolead days. And now days it's a little harder, you have to read the plugs by color or take it to a shop. Their's many things that come in too play when it comes to running on the lean side and also where you live plus who's messed with the carb before you got it. One thing ford trucks didn't all come with the same carb main jets in 2v carbs or 4v same for the cars. But when you look at the out side you would say yep there the same.Trucks f-100 to f-250 had main jets from #52 up to #57 that I've come across and the f350 up may have even larger ones. Or take the car 302,352,& 390's engine most carbs came with main jets were #48's And all carbs look a like outside. So unless you know your jet sizes that match your p/n for your carb you don't know. High or low elevation changes air/fuel ratio mixtures. this calls for carb retuning as well as dry hot day in the desert or a cool dens air area. Maybe you bored your eng. added hotter coil, rv cam, and headers larger exh pipes put some flow master on it too. All newer upgrades from stock and your still running the same (carb & jetting) you could be running on the leanside. Now add this all up to running open headers. You could be running lean. The untolded little secret of running headers may affect you! Like one shoe don't fit every man or shoe's and jets would be the same size my 2 cents
orich

 

Dont get me wrong...I dont disagree with you...any changes made to the motors output will cause a change to the carb setup. Some so minor it goes unnoticed, depends on what was done.
I tuned my carb from the start with open headers so I didnt have any lean condition to worry about...but
on the 360 I had before was bone stock other than headers and I had no problems with a lean condition. If anything it ran rich after I put the headers on and it was explained to me that the carb was getting a strong pull due to the fact that the motor revved higher so the carb dumped fuel faster. Whatever was going on I just ran it, but the plugs were black/rich every time I checked them.
I guess if your running open headers your going to run it hard competeing someway, you should check your plugs often...I do after every muddrag I run...I like to know whats going on at all times.

 

Actually, going from a restrictive exhaust system to open headers WILL neccesitate stepping up in jet sizes. At least, for optimum tune. You don't need to to worry about valve damage from sucking in cold air from open headers. Maybe if you lived in Alaska, I suppose, but typically, its a non-issue for us. Open manifolds, that I wouldn't recomend.

 

i ran my 400hp 390 for a week with open headers, it was a little to loud for me and for the cops, its still loud with header mufflers.