Exhaust question? Open pipes & burnt valves??

[Thunder1]

I hate to appear stupid but what the heck! Would someone explain why running open pipes without baffles burns up valves?? The answer might be very obvious to you but it's not to me. I've seen so many rat rods that appear to run open zoomie style headers or just plain straight pipes out the side without any problems but a friend of mine argues that it's a sure way to burn up your exhaust valves.

Aside from the noise dampening quality of baffles, What's the theory behind it? Does it have to do with a lack of back pressure on the valves, heads, or pistons??

I'd appreciate some educated opinions.

Thanks guys!

T1

 

[Tripper]

I hate to appear stupid but what the heck! Would someone explain why running open pipes without baffles burns up valves?? The answer might be very obvious to you but it's not to me. I've seen so many rat rods that appear to run open zoomie style headers or just plain straight pipes out the side without any problems but a friend of mine argues that it's a sure way to burn up your exhaust valves.

Aside from the noise dampening quality of baffles, What's the theory behind it? Does it have to do with a lack of back pressure on the valves, heads, or pistons??

Thunder,
My car has zoomers & I haven't had any problems. I drove it for a year B4 I installed cheap JC Whitney motorcycle baffles to cut the noise down ever so slightly to avoid any problems with the boys in blue.

BoB

 

[moronthethrottle]

IIRC

The patchy answer that I can vaguely remember hearing years ago was that after a motor is heated up and then shut down having only manifolds or short pipes allows the cooler air to make its way up to the valves too quickly and can cause them to warp....I believe this is also part of the reason why we see the little balls inserted into (upward pointed) zoomies after they've been run.

Relate that info to a weld cooling down too quickly causing your sheet metal to warp...same principle....I think.

 

[Sniper]

I would chalk it up more to 'Wives tales and urban myth' than any real fact. There have been a lot of times short stacks are used with no problem. Check out some of the WWII aircraft with Alliston or Rolls V12 engines to name a couple. No problems encountered due to 'bent or warped valves'. Ran old beater stock cars with no manifolds at all, never had a problem. The guy that still recites this "FACT" is the guy that uses the "My brother inlaws second cousins father had it happen". Yeah...ok. Been a licenced mechanic for a lot of years, haven't seen it happen yet. The bent ones I've seen are from 'Kissin a piston' and I don't think the pistons were 'cold' at the time. Sniper

 

[Thunder1]

I would chalk it up more to 'Wives tales and urban myth' than any real fact. There have been a lot of times short stacks are used with no problem. Check out some of the WWII aircraft with Alliston or Rolls V12 engines to name a couple. No problems encountered due to 'bent or warped valves'. Ran old beater stock cars with no manifolds at all, never had a problem. The guy that still recites this "FACT" is the guy that uses the "My brother inlaws second cousins father had it happen". Yeah...ok. Been a licenced mechanic for a lot of years, haven't seen it happen yet. The bent ones I've seen are from 'Kissin a piston' and I don't think the pistons were 'cold' at the time. Sniper

Thanks guys! Thats what I told my buddy - about the WWII Rolls/Merlin V12 & Allison engines. They run short stacks straight off the manifold. If a 2000 hp engine can handle it without any damage I doubt there's much than can happen to an automotive engine. Although, Moronthethrottle's explanation does make sense regarding the potential for warpage. Either way, I'm opting to use a set of pipes shorter than most. Thats what brought this up in the first place.

Thank again,

T1

 

[livingdeadguy]

the only thing i have heard is if the pipes are short the valves can cool too quickly and warp, i ran 8 pipes coming off my old motor with each one being about 2 feet and it didnt do anything to it, just very loud.

 

[Sam_Fear]

Only other thing I can think of is the idea of it messing with the back pressure/scavaging. If a fool removes the restrictions and doesn't re-adjust the timing, you get less resistance, the motor turns easier, and will fire later.

I've seen where CAT systems get cut off and cause serious timing differences, but would removing baffles from pipes retard the timing that much?

 

[rustybeercan]

Cooler

This might be a problem in the colder areas of the country where you turn off a hot motor & the cold air could possibly warp the valves but in the warmer states I doubt this would be a problem and valves are probably made out of better steel than they used to be too.

Beercan

 

[ANNAMEL]

My rule of thumb is all pipes equal length to keep equal temp and backpreasure.
atleast 24" with a bend somewhere to prevent cool air from being sucked into a hot cylinder and expanding . Dont thinks its any different than having an exhaust lead and hearing it pop when you back out of the gas. Cold air expanding.

 

[Gearhead10]

My uncle used to run short zoomies on a mod and always inserted rubber balls into the ends of the pipes to keep the cooler air from warpin the valves. I'd think if the pipes were 18" or longer the chance of that happening would be alot less.

 

[BigIrish]

Crap, now I'm paranoid about my exhaust plan! I was planning on just 8 straight pipes, 15" long, with baffles probably. They will be at a down angle.

Think I'll have a problem with that? Not sure how baffles would make a difference. Also, not really sure how the angle would affect - as MoronTT pointed out about seeing balls in upward pointed pipes.

I'm hoping that with the pipes pointed down, it will keep some heat in. Also, my engine is an '84 (unleaded heads) so I know they have hardened valve seats - - but don't know if that means the valves are also hardened, less prone to warping??

Was going to start building them this weekend....

 

[livingdeadguy]

i spoke with a drag racing club up here and i asked them about it, I had my pipes going up and they said the heat could leave too suddenly and hurt it, but if they were down the heat would rise and the valves could cool as usual. They used a certain material for there vlalves though i cant remember off the top of my head. I had mine with 8 pipes about 2 feet long each on my car for about a year and I had baffels and never had a problem with the motor.

 

[BigIrish]

OK great, that makes sense to me. I can see how hot air would rise out of upward pipes and cool air would sneak in behind. I may lengthen them to 18" though and I'll be sure to tilt them down a bit. Thanks!

 

[cmcdanl]

i used to have an 81 datsun 280zx that we put an LT1 from a corvette in. I ran straight headers on it for a while cause i had cutouts. I ended up throwing a rod. I dont know if that was caused from running open headers or not.. Just thought i'd throw that out there.

 

[livingdeadguy]

i used to have an 81 datsun 280zx that we put an LT1 from a corvette in. I ran straight headers on it for a while cause i had cutouts. I ended up throwing a rod. I dont know if that was caused from running open headers or not.. Just thought i'd throw that out there.

I have actually heard of that happening from that type of exhaust setup, i know the exhaust needs some sort of back pressure. I found myself using harley davidson mufflers

 

[Lightning]

Just the length of the exhaust pipe can cause back pressure - and they must have some back pressure to help with exhaust scavenging[exhaust pulse] as far as puting balls in upward pointing pipes - it's just to keep forgein objects out, just as they do with velocity stacks - if they were put in while the pipes were still hot, to help them cool off slower - they would melt. I've run straight pipes on my H.D.'s for yrs. with no problems at all, but I would color them with a type of grease paint - run them till the got real warm,and where the paint stopped melting that's where I would cut them off at - kind of like tuned exhaust for each cylinder.But on mutiple cylinders, you would end up with different lengths for each cylinder,because each cylinder will be just a little different.So run the pipes at a certain length - say 24" and cut off where the average hot spot is or grease paint stops melting.Think about this - all your dragsters with straight pipes run hotter than any regular cars do - types of fuel,high compression,some type of forced induction,higher fuel pressure.