I would like to change the headers on my modified(first pic) to short tube headers as seen in the second pic. I can make them but there seems to be a certain hesitation by some as to the use of this style of headers. I have been told that a short tube will quickly burn exhaut valves, is this true or an urban legend? I am not after any power gains(don't want a big loss though), but more for the look and sound they provide.
Can't say for certain, but that's what I've always been told. A buddy of mine said his uncle fired up a Buick V8 on a stand once with no exhaust at all and it didn't last long. Food for thought.
Yvan, you will NOT have any problems with exhaust valves if you take the time to re-jet ! ( any time you change the scavange effect, NO scavange with Zoomies, short or long) You will need to jet up .... If you race on real cold nights (or days ) will need to cover or plug the tubes when you shut the engine down ..It is a small chance , after a hard run that a hot valve will shock cool..( open valve, off the seat....) Just look at drag cars and boats that run zoomies...they use caps or balls to plug the exhaust after a run.... Dave
Urban legend. Well for the most part. If they are short enough and it is cold enough you run the chance of warping a valve when you shut it off. A lot of guys stuff a rag in the ends of them or a cap on them when they shut down. You will loose a little zot on the bottom end with zoomies and your power band will be narrower. That's the nature of the beast. So my question is this, I thought racing was all about going faster? But you say that you aren't worried about loosing power you just want to look better. I don't understand.
Ran Zoomie headers on several Dragsters and warped exhaust valves weren't a problem. I have no experience with modifieds but there has to be a reason that most run the long tube headers even thought they are harder to make and probably more expensive. I suspect the low end torque needed to exit corners on short tracks is part of it.
Beside much like every alcohol and nitro race engine on the planet having short headers...think about this... The Merlin engine in...a**** others, the P-51 Mustang fighter, had header tubes about 6" (maybe 7") long. They didn't have any problems. Just don't go squrting cold water in the header after a hard run on the freeway...! Mike
unless it is supercharged you are going backwards by putting zoomies on it - no scavenge, reversion etc. As for warping exhaust valves, whose old wife told you that?
100% spot on correct. I learned from changing the exhaust from stock to straight drag pipes on Harleys that the mixture would go waaay lean unless the carb was jetted up. It would cause more problems than just exhaust valves, detonation caused by the lean mixture can wreck havoc on your pistons, intake valves, cylinder head and so on. I've never run this type of exhaust on a car engine so I don't know if it applies, but running straight pipes on a bike it was always a good idea to add just a little bit of back pressure, it made them a lot easier to tune up. An old biker showed me how to make a simple adjustable vane baffle by welding a washer to a bolt. But again, not sure if a car engine setup would need anything like that. Good luck
all things being equal, (no mufflers) headers with the correct length primary tubes and collector, correct diameter primary tubes and collector for the amount of power being made will run LEANER than the zoomies because of effective cylinder scavenging. Essentially more burnt air and fuel gets cleaned out of the cylinder, therefore you can get more air in there so you need more fuel to keep the stoichiometric ratio optimal.
Yes it's about going faster for sure, but I am part of a vintage club that is less concerned about speed than putting on a good show for the fans. Plus the fact that my car has a 300 pound wieght advantag compaired to the next lightest car, Ic an stand to loose a few ponies. Also the fact that they are easy to swap I can have both sets on hand and chose the one that better fits the track. Thanks for all the replies so far. Keep em comming.
The operative word here is "cold". Seen it happen in really cold weather like up north. Roundy round and dragsters usually don't see cold weather, neither type of racing is a winter sport. When mustangs landed in cold like icey cold conditions the little short exhaust pipes were capped to keep the cold air off the hot valves. But you're the expert. Getting back ot it I have never seen an engine burn a valve because of zoomies.
The burning valve gig would be from select cylinders going lean from such a short clean exit. As far as warped valves, what '****** said. As far as sounding kool, yes. How to get it "all", make em long enough to serve the purpose. Maybe something like 24" would work? My .02. I love zoomies.
2 feet is a little more doable. There actually is a formula to use for tunning lenght and power band but I no longer have that notebook. Should be able to find it on the net, uh not the notebook. yvan lacroix, I understand the zoomies for showmanship thing and thanks for answering my question. I'm not much of a showman as can be seen by what I normally drive, so that part of the equation never enters my mind. But it is an important part of our hobby.
I don't know about that.I rode British bikes for 35 years,mostly Triumph 650's with 34 inch TT pipes.I rode them hard,rode them in cold weather,like 25 degrees, and never had any valve problems at all.And Triumphs have very little margin for error when modified unlike a large water cooled V-8. That's my story from actual experience,if you burn a valve don't come looking for me
There is a difference between 34 inch pipes and little short zoomies. There is a lot of hot between the end 34" small dia pipe and the valve. Way more than a short large bore pipe. I built an ice racer for a guy back in the '70s; a BSA 500 TT and he invited me up to the races. There was a guy running a Renault Daulphine that was pitted near us. He was running little short stub pipes and I noticed that the other fellas were capping there pipes when they shut down. So I asked him and he said that they thought that the cold would warp their valves, but it was an old wives tale. Long story short he made the quarter finals, but the next day when he lit it off it just wasn't up to par. He made his heat but he was done. We swapped addresses because I liked him and thought I might make it up there again. About a month later I get a letter from him. Warped valves kept him out of the running. I dunno you tell me.
There have been enough discussions about short zoomie headers and warped exhaut valves on here that you could write a few books. Want to waste a few hours/days of your precious time..............do a search. Bottom line, you stand a better chance of winning Top Fuel with a Briggs and Stratton than warping exhaust valves with short exhaust. Time would be better spent thinking about what your going to do on Nov. 2 about getting Washington back on track before it's too late. SERIOUSLY!!! Frank
Lack of power and sounding like ***. That's what you're after. And I'm sure someone is going to bring up top fuel or something else. Apples and oranges. I'd rather have a healthy engine at a lower volume than open headers and loss of power. And I have yet to hear one with these that sounds good.
Every time this comes up, I am reminded of the question somebody once asked of those that say it will warp the valves. "Please show me one of those damaged valves. Anybody?".
zoomies are tuned for one rpm depending on dia. and length where as headers with a collectors have a broader torque and hp band which is also effected by tube size and length also collector size
Great info so far, so lets push a little deeper into the subject. After a visit to the garage last night I can fit tubes of 22-30 inches. The engine is a 602 crate 350SBC with a 500CFM holley 2bbl. Revs during the race are from 4-6000 RPM. With that info whats the best starting point for tube diameter and length?
Go a long as you can with them and you might not lose a ton of power. Diameter of primary tubes should be determined by engine output (hp). RPM and displacement play a part as well. How much power do you make at peak?
i was always told that if it barks out the exhaust real bad on deceleration then you have a possibility of warping valves
We did some dyno test last week with a 602 crate with a two brl 1 5/8" x 32" with a 3" collector had a longer torque band than the stepped 1 5/8" to 1 3/4" x 32" with a 3 1/2" collector and the hp didn't drop that was only with a 500cfm holley a change to a 4brl was different. all this mean is run small long pipes
This is the most sensible answer so far. Car racers (non-supercharged) don't put collectors and long headers on their cars if a little stump pointing down out of the engine bay would suffice.
The Jalopy Journal
