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Topic Review (Newest First)
12-06-2004 08:31 PM
Stickman "the p51 also used water injection did it not to supress detonation and increase milage?"

To supress detonation, yes..to increase range, no. The water injection system was of limited quantity, for very limited use. The Merlin engine used in the P51 (this engine was also used in the Spitfire, and an early version in the Hurricane) was rated to sustain 67 inches boost for up to 5 minutes, using water injection. At this power setting, the engine delivered about 2000 horsepower@22,000'. Of course many pilots talk of using this boost level for 10 minutes or more, but I think half of it may be just that...talk. Most pilots wouldn't deliberatly take such a chance, especially deep in enemy airspace. I'm sure it happened, just not routinely.

Anyway, to answer your question, yes, and no

By the way, the P51 had a wonderful range from the time it was built. It had a large fuel capacity to start with, and the Merlin engine, when leaned out and set for cruise flight, was very economical. Unfortunately, it wasn't in squadron strength until very late in the war. Until then, it was up to the Spitfires and P47's (both with a positively dismal range, though the Jug got much longer legs later on) to escort bombers. Until the P38 began operations in the European theatre, the escort fighters were forced to turn back shortly after landfall on the continent. When the P38 showed up, it was the only fighter in Europe (or the world, for that matter) capable of escorting bombers from where the other fighters turned back, to the target, or nearly so, giving German fighters quite a surprise initially. For a short period in Europe, before the P51B went into operations, and the P47 was equipped with drop tanks and larger internal fuel cells and got a better range (Spitfires never got legs worth mentioning), the P38 was the only saviour of many Allied bomber pilots. Before that, German fighters simply loitered just out of range of Allied escort fighters and beat the **** out of the bombers at will. Do a search for "Black Thursday" and you'll see what can happen to bombers without fighter escort.

You can probably guess I'm quite a fan of the P38, and Lockheed, the company who built her
12-06-2004 05:23 PM
1BAD80 This has been discussed before and all the info is in the Knowledge Base along with the flame throwers sites.

The concept that maximum power is obtained by zero pressure in the exhaust is only partially true. There should be absolutely no back-pressure from the collector rearward, but the diameter of the system beginning with the exhaust valve is a compromise.
The highest efficiency for the system requires a minimum speed for good exhaust gas velocity to insure that gas does not "back up" into the chamber during overlap at low engine speeds,
and that the "suction" (negative pressure pulse) effect of a resonant (tuned length) and/or collector (overlapping exhaust pulses) system is optimized.
To predict what primary size will be best for a specific motor, you must know where you want the engine to develop peak torque.
If the existing torque peak is at bit lower RPM than you prefer (typical in under-cammed or stock motors), it can be "bumped" a bit by increasing the primary diameter. If the torque peak is too high (motor is "peaky", with no range and poor recovery from gear changes), the peak can be adjusted down by using a smaller pipe. A change of 1/8" in the primary diameter will raise or lower the peak torque RPM by 500 or so.
This factor slightly overlaps the effect of primary pipe length, but the pipe length generally will not change the peak torque or the RPM at which it occurs.
A length change has the effect of improving the torque on only 1 side of the peak by "borrowing" it from the other side. A shorter pipe improves the torque after the peak (reduces it at lower RPM), preventing the curve from flattening out so quickly as speed increases. A longer pipe extends the torque curve backwards to improve the engine's flexibility, at the expense of after-peak torque.
Another instance where a slightly larger pipe may help is where the departure angle of the pipe from the flange is very sharp (typically downward). The added cross-sectional area immediately after the flange apparently helps reduce the restrictive effect of a small radius after the port.
This partially explains why some header models or brands work better than others with similar dimensions.
If the primary pipe inside diameter is more than 1/8" larger than the actual port opening in the head, the header flange bolt pattern can be slotted slightly to raise the centerline of the primary pipe above the center of the port, until the bottom of the pipe just matches. This puts the pipe's effective center closer to the most active area of gas flow, and the mis-alignment at the roof allows the highest-pressure gas an easier path away from the port; also adds some degree of anti reversion.
If controlling reversion is more important than maximum port flow (e.g. primary diameter is very large), the mis-match should be at the bottom of the port where gas flow is slowest, and therefore most likely to reverse-flow at low engine speed.
12-06-2004 05:03 PM
Siggy_Freud It shouldn't matter what kind of muffler you use with flamethrowers because the whole system should take place after the mufflers anyways. You definitely dont want flames going through your mufflers lol.

Any type of muffler should do simply because it shouldn't be even near the flames.
12-06-2004 05:00 PM
Dubz the p51 also used water injection did it not to supress detonation and increase milage?
12-06-2004 04:52 PM
packratwrecker If you decide to run straights, keep in kind that the bigger pipe you use, the more mellow the tone will me.
2" sounds nasty on a small block chev, a 6.2 diesel, a v-6 Explorer, or a 230 straight 6, with split manifolds.
If you are going to do flamethrowers with mufflers, I'd use glasspacks, or steelpacks. If you try it with trash cans, and make a mistake, you'll end up with mufflers that look like pregnant puppies.
I ran straights on my 49 Chev, out 4" stacks, until I couldn't stand it anymore.
I took the stacks off at the elbows, and welded in blocker plates, with glasspacks on them. Most people don't even know I have mufflers, until I tell them.
The 4" stacks above the glasspacks gives a pretty effective expasion chamber, so you get nice orange rolling fire, instead of blue jets.

FYI I am a redneck. I built my own flamethrower setup, so that it would be safe, and easy to use.
12-06-2004 02:02 PM
Stickman Quoted from "Trees" :"The old fighter planes had an entirely different set of problems to work with. The P 51 was liquid cooled where as most of the others were air cooled. The air cooled engines had cowl flaps to maintain cylinder heat temps in the "green" to prevent detonation (hot) or excessive fuel consumption (cold) These flaps were open for take off and landing and were mostly fully closed when at high altitude cruise. Opening the cowl vents too early or going full open at too high an altitude could cause rapid cooling and a bunch of warped heads, jugs etc. The P 51 radiator cooling air could be regulated also, but usually was not required. The unique way the aircraft was flown for the long range, high altitude bomber escort missions was developed by Charles Lindberg. Upon reaching cruise altitude and airspeed, they would lean the engine back until it quit, then slowly increased enrichment until it fired and then they set the throttle and mixture there. As fuel burned off, they would slowly climb, maintaing air speed and throttle/ mixture settings. Lindberg had to prove to all the old time aircraft engine mechanics that this procedure and super lean fuel mixtures did not damage the engines. His procedure increased the range of the aircraft by about 50% and were the only aircraft that could escort the bombers to Berlin and beyond."

You know, I knew that, someday, my being an extreme WWII fighter aircraft freak would come in useful (sort of).

Ok, some mis-information in the above...not intentionally incorrect, certainly, just not quite on-the-mark in some areas.

First:
Most WWII fighters were liquid cooled, rather than the other way 'round. All USN fighters flown from CV's (aircraft carriers) were air cooled, of course (the Navy refused to use liquid cooled fighters aboard ship), but most Allied USAAF, RAF, etc. were water cooled, with some notable exceptions such as the Jug (P-47), and the Hawker Typhoon (RAF ship).



Secondly, Lindberg's foray into the South Pacific and his work done with a fighter group down there did, indeed, greatly benefit the US as far as fuel economy goes, but his ideas to lean out throttle mixtures (and other things) were met with resistance because of the lean mixtures themselves, which, as we all know, can cause an engine to run hotter, and allow detonation at a far lower power loading. This was the primary concern...that the lean mixtures, even at cruise settings, would be certain death to an engine (most of his testing was done on P38's, twin-Allison engined turbo-supercharged fighters) because the turbo boost would cause detonation at those leaner settings, burning holes in pistons and cooking valves. He proved this wasn't the case by flying his ship "leaned out" while others in his flight flew theirs in the conventional manner (not sure how many sorties he flew this way..I could probably look it up, but I'm too lazy...it was more than just a few, I'm certain) and afterwards, the engine was torn down and inspected, and found to be in perfect condition. This simple adjustment doubled the range of the P38, and did much toward helping us win the war in the Pacific....With so little land, and most sorties, by necessity, lasting as much as 8 hours or more, it was a miracle for those fighter pilots who fought in that theatre.

Finally:
Cowling flaps on those ships that had them ( the P47, F4U Corsair) were generally opened only during METO power setting, or WEP, when the extra cooling ability was absolutely needed. A P47, for example, could increase turbo/supercharger boost enough to gain over a 33% horsepower increase, using water injection, and understandably it generated enormous amounts of heat. Also, the P51's cold air induction was often used, in the heat of combat when high power (boost) settings were used. I've never read (or been told...I've inverviewed a number of WWII fighter pilots) about jugs being cracked because of overcooling, though that doesn't necessarily mean it isn't true...

P.S.
If any of you guys want to know anything about WWII fighters, just ask...I probably know the answer, whether it's concerning combat tactics and maneuvers generally used by specific aircraft pilots, powerloading differences between aircraft, or even loadouts and ordnance capabilities for specific aircraft....or historical facts about engagements, fighters, etc. Alot of this information is extremely tough to find these days, and I'd be happy to pass it on if I know it
12-06-2004 10:02 AM
Siggy_Freud You dont have to run straight pipes to run flamethrowers.

First off before even attempting to do flamethrowers, research research research. And then go buy yourself a fire extinguisher.

A few companies make full flame kits while others just make a spark box that provides a "feed" to the coils you mount back there causing the sparkplugs to rapid fire. You then have to design a fuel or propane feed system. When my vehicle was carbed I ran a 3way filter to two fuel solenoids, one closer to the filter, and the other back closer to the fogger nozzle.

The fogger nozzles were a good two feet from the sparkplugs in the tail pipes.

Just remember to keep safety in mind as much as you can if doing this sort of project. The results can be very cool but also very hazardess. If an officer of the law sees you doing this . . . you'll be talking about the cool car you USED to have lol.'

Research on google and you'll find some good starting info.
12-06-2004 09:52 AM
Mollard So what about these "rat rods" that run a 2 foot peice of pipe of of each cylinder? If the air/fuel mixture is richened, you should be ok?

BTW, this isn't on a high preformance engine, just a stock 350.
10-11-2004 07:55 PM
trees The old fighter planes had an entirely different set of problems to work with. The P 51 was liquid cooled where as most of the others were air cooled. The air cooled engines had cowl flaps to maintain cylinder heat temps in the "green" to prevent detonation (hot) or excessive fuel consumption (cold) These flaps were open for take off and landing and were mostly fully closed when at high altitude cruise. Opening the cowl vents too early or going full open at too high an altitude could cause rapid cooling and a bunch of warped heads, jugs etc. The P 51 radiator cooling air could be regulated also, but usually was not required. The unique way the aircraft was flown for the long range, high altitude bomber escort missions was developed by Charles Lindberg. Upon reaching cruise altitude and airspeed, they would lean the engine back until it quit, then slowly increased enrichment until it fired and then they set the throttle and mixture there. As fuel burned off, they would slowly climb, maintaing air speed and throttle/ mixture settings. Lindberg had to prove to all the old time aircraft engine mechanics that this procedure and super lean fuel mixtures did not damage the engines. His procedure increased the range of the aircraft by about 50% and were the only aircraft that could escort the bombers to Berlin and beyond.

Trees
10-11-2004 07:16 PM
Old School Nut that warping the valves myth i think started in WWII with fighter planes, and their realy short headers. suposidly an airplane (like a P-51, spitfire...) could do a manuver that could introduce enough of a cold air blast to warp the valves... i dont know if this is true.
10-11-2004 04:41 PM
BstMech You will blow your motor with any kind of exhaust modification.

I had a guy tell me this one time and it's believable to an extent.

He told me that those great sounding pipes will have you revving your motor all the time to get that........great sound.
10-11-2004 03:28 PM
bowtieorbust (IMO) if i were to run an open exhaust right out the back, instead of a (2 1/4) or a (2 1/2) in. pipe, i would problebly go down to a 2'' exhaust to give some velocity to it, but i believe the straight pipe ordeal will get old quick.
10-11-2004 07:51 AM
Mollard So if the air fuel mixture is richened should be alright? I am thinking about doing this on my '83 Mazda B2000 becasue I want to run some flame thowers on it. I was thinking about running a straight pipe al the way out back and dumping it just behing the paasenger side tire.

How will I know when I get the right air/fuel mixture?
10-11-2004 06:38 AM
DoubleVision There is some truth to this, and that is, a stock engine or one modified, either way, stock exhaust changed to true duals with straight pipes, no other changes, the valves get cooked, due to the mixture being too lean, any time that back pressure is reduced, the mixture must be richened to compensate, since back pressure was reduced the engine can now pull in more air/fuel and when it`s not richened more air is added but fuel is not, hence it being too lean which results in excessive cylinder heat and the exhaust valves get burned or a piston gets hollowed.
10-11-2004 12:43 AM
Steve-0321 If you have a stock cam in a all stock engine then you will probably be in trouble............i was running straight pipes on my 351C 2V motor and there was no torque at all because of the cam i was told..........if you got the cam......then you should be ok....but its noisy as heck....i wouldnt suggest it
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