Short open pipes "burning valves"...fact or fiction?

Come on guys...how many times have you fired an engine in the chassis or on the garage floor just to see if it would run with no manifolds. You aren't normal if you don't try to hot wire an engine just to see if it's junk. It may have been 30 years ago but we've all done it.

If it's true there MUST be 100s of good running engines with bad valves ruined by young bucks that never heard the stories. Where are the guys that had to replace valves, heads or engines because they didn't have the internet to warn them? Where is the evidence?

 

If it's true someone better tell all of those hydroplane racers with everything from 4 bangers, automotive v8's, and on up to v-12 aircraft engines that have 4"-8" exhaust stacks to stop it immediately. What were they thinking?

Frank

 

you silly bastard. thats not true AT ALL. and you know it .

 

We were burning exhaust valves on 6 cylinder Cummins engines at work on a regular basis (running on Natural gas). It was determined that oil was building up at long idle and then when the rpms were run back up, the oil was acting like acetylene in a cutting torch and burning the valves (it looked just like they were cut by a torch). We raised the idle rpm 30%, no more burned valves.
I think a deposit near the edge of an exhaust valve can heat up and burn/melt a valve if the rpm/ flow were increased enough, but it would have to be pretty high.

Flatman

 

We ran a roundy round race car with grass burners headers for years, no problems. Dump straight down no more than 8 ins. off the heads. High compression, Race gas only.

 

So what can cause an exhaust valve to burn?
I once had a head on an old engine with only one bad exhaust valve giving no compression on that one cyl.
Never figered that one out.

 

Carbon build up can be a cuprit. If the carbon starts holding the valve open a bit it can overheat it, as it is not seated properly with the head to help absorb heat. Had this happen in a Mazda PU. heated the valve and when the engine was shut down the valve stem struck in the guide.

 

The only reason I've burnt any valves is not enough fuel an air .....
If you have a restrictive exhaust an then pull it off without changing your mixtures , burnt valves will happen .....

 

Well said j-jock. Also, most all aircraft exhaust valves are sodium filled to help with cooling. Pretty sure the Merlin and Allison V-12's weren't sodium filled though as these are water cooled engines. Good excuse for a Mustang pic...

 

Okay, I always thought the old "myth" was just that...a myth!

(Like the one about leaving car batteries on cement...folks used to say that would kill them real quick, but I've done it lots of times without killing a single one!)

So, I made the shortie pipes I had in mind and installed them yesterday! (Taking care to use new gaskets...don't want it to be too loud ya know?!) All I need now is a new carb and I'll be rattling windows all over my block!


Thanks for confirming my hunch...looks like the bulk of ya said what I always suspected!

 

As said it doesnt burn them it can warp them with the hot valve and a rush of cold air can cause it to warp and not seat properly amonst other things.

 

Best engine pic ever posted!!!!! But get rid of that vac dizzy...haha!

Hack....you rule....

 

myth

 

"One thing with the aviation engines, like the Merlin, is that they would have a substantial amount of time to cool down while taxiing in and shutting down. The average would be something like 10 minutes or so. This would allow for the temperatures to drop considerably before the engine was shutdown. Hence there would be very little stress on the exhaust valves. While in the air, in the traffic pattern, they would be in a rich mixture setting, with plenty of fuel available for cooling."

Not on carriers...and the Merlin was used on carrier versions, Seafire or whatever.
Carrier landing process: WHAM!!! Cut switch!! Done!

 

Thanks!

Ha Ha...the stock distributor is on my "hatchet list" for sure! Haven't decided if I want to go with a full mechanical 009 or an electronic one yet...waiting to find a good carb first!

 

Why don't they fry when they are at -30 and get the first shot of 2000 degree heat in a cold Ohio start.

My guess is that any change in your intake or exhaust track should warrant a check of the plugs to make sure you aren't leaning out to motor. In my experience, that's the worst thing you can do for a lot of parts, not just the valves.

And Hack... you are my hero.

 

So after reading like 90 posts about it I understand this. Anytime you drastically change exhaust you should check your plugs and adjust your fuel settings accordingly. Short pipes will not cause burned valves or bent valves. As long as your valves are still installed in the cylinder head (duh, otherwise the motor wont really run) then the head will "normalize" the cooldown ratio since the two parts cool at the same time, creating a heat pocket which would block any cold air simply by instantly heating it to ambient tempurature of the exhaust passage, preventing your valves from mysteriously bending. Also, the only things that can burn a valve are incorrect fuel ratio (too lean) and excessive crud in the local area. Does this sound like the general consensus of everyone here? It does to me. (B.T.W. I was thinking of this the other day. I want to put shorty pipes on my 59 caddy flat top) Thanks alot! If you think it, the HAMB will know! My .02 anyway....

-GothY-

 

Yer best bet would just be an 009....they're cheap and reliable, as long as good Bosch points are used. Get yerself a BIG 34mm Solex and hammer down.

That's gonna be one fire breather......I mean SPITTER!

 

Yeah I agree.... I've spent about half of the money on a
VW as i have my cars, and have gone twice as fast!! But... they also got me in more trouble than my muscle cars.... but lets not talk about the VW's or this thread will get closed


Mike

 

Pretty much, but a valve can hang open for other reasons. Improper valve lash can do the same thing. My truck's original 6 came from the original owner with a burned exhaust valve in cylinder 1.

 

Gothboy gets a gold star for thread analysis ! well done man summed it up perfectly ........

 

Back in 1963 we ran in the Hobbystock class at Toledo speedway. Headers were not allowed. So we ran nothing. Just dumped out of the ports. No headers, no manifolds, no pipes at all. we blew engines, but never from valves warping. bearings were the problem. Most of the cars in our class 50 or so, ran the same way. we had a ford, but Mopars and GM cars ran the same way.

By the way, it was a 312 Y block, king of short track racing at the time.

 

i've been running shorty drag pipes on my 66 triumph (motorcycle) for 20 years now. no baffles, just straight pipes, and everything is good.
these pipes are longer than a set of zoomies would be on a car engine tho...not sure how much difference that would make.

 

I don't have any experience with carriers, but those navy guys are pretty rough with their equipment, if they had a problem with an airplane, they just pushed over the side. Us land based pilots were much kinder to the stuff we flew. The first time I saw a Navy F-4 land, I thought he was going to drive the struts through the wings.
Even with all that in mind, the airplane on descent and in the traffic pattern to land on a carrier would be at a very low power setting, which would reduce the temperatures considerably.
Bob

 

Yeah, in piston days. I believe now on angle deck carriers jets actually go to full throttle on impact, and the cable just jerks them down! The full throttle is so jet can successfully take off via the angle deck if cable is missed or breaks! I wander if the piston Skyraiders landing on modern carriers off Vietnam also landed at full blast??

 

The valve damage does not usually come with short pipes, but with no pipes. If you notice in the pic of the RR Merlin, the 3" pipes. They're for a reason, and I seriously doubt it has to do with performance, unless that's a 45,000 RPM engine. The problem is worse on some engine / head designs than others. After running hard and getting things extra hot (especially if you are lean because you didn't re-tune it), when you come down to an idle, the reversion pulse (yes, even in a 3/4" long port there is a reversion pulse) carries ambient temp air to the extra hot valve, and causes a slight warpage. Now you have a slight exhaust valve leak that will eventually (it may take a few thousand miles or so) erode the valve (a 'burnt' valve). So not exactly a myth, as long as the version you are talking about is running NO pipes. To the average modern Joe, it can be considered a myth. Unlikely? Yes. Safe to run your vintage engine hard with no pipes at all? Only if you feel lucky, or like doing valve jobs.
Also note that modern ('74-up) valves are substantially harder on the surface, and more resistant to both warpage and erosion (AKA 'burning').