Have always seen 'exhaust snaps' on 250 GTOs, SWBs and even an LM. Just what exactly do these things do? Where do you get them?
I have for sale: a set of four, identical copies. Very high quality incl. texts SNAP and FB Tom SNAPS do nothing, so no extra horsepower! Just for the looks.
Hietbrink in The Netherlands makes them too. http://hietbrink.com/, and then on the left all the way to the bottum.
I have no idea, just knew he made them, thought I would post it. I never looked at the price, and if I ded, I have no idea or it was good or not. I'm not into prices at all. Just knew that he made them, and posted my contribution. If you can't use it, ignore it.
It was very interesting to see the internals as well. The site quite useful, just commenting on a remarkable price. thanks to all.
I think it is a little naiive to think that Italian engineers would equip an exhaust system of a racing car with a useless piece of decoration. This is *NOT* the case. Putting a huge amount of exhaust fumes out at high revs introduces a few special problems. At high speeds a Ferrari 250 engine will put out 200 litres of exhaust fumes per second. That's about 50 litres per second per exhaust pipe. At headers the exhaust fumes are very hot and they cool significantly running through the long exhaust pipe. When they cool, the volume decreases. As the volume decreases, flow speed (=kinetic energy of the fumes) decreases too***. This effect creates "an invisible choke" at the end of the tailpipe, which must be broken. Exhaust flow can be improved in various ways; on standard cars the end is usually cut at an angle or slightly bent. This way the outside flow will improve the exhaust flow. Adding a device like snap is more efficient; with a snap you can blend fresh air into the fumes as they are exiting and also create a vacuum by adding a shroud around the pipe end. Note especially that the diameter of the tailpipe end may not increase; that would slow the fumes even further and amplify the "invisible choke" effect. So the effect of a Snap won't show on a standard dynamometer because the thing does not work at stand still; you would need to integrate a wind tunnel into your dynamometer to see what it does. Best wishes, Kare *** In the ideal world the exhaust pipe would be a cone getting smaller and smaller in diameter towards the rear... It is interesting that when people design exhaust systems from the top of their head (for motorcycles mainly) they tend to do exactly the opposite...
kare many thanks for the detailed explanation - I had always wondered why hey were installed. As an aside, they look very much like the tips Borla makes on the end of their custom exhausts - they sell the tips as 'intercooled' and are similarly vented. (http://www.borla.com/ac.tips/?cartID=20040225145253198.76.95.47) Again, many thanks Russ Pics of 2 Borla intercooled tips and Hietbrink Snap cross section for comparison
Don't think so; the effect must be minimal compared to other issues that can be properly tackled - one being that the pipe will end sooner or later creating a great discontinuity point in gas flow... I also think the "conical exhaust" would operate ideally on a very narrow set of variables (revs, driving speed, outside temperature etc.). Some manufacturers have built resonator boxes to intake manifolds to make the ram effect appear on wider rev range. I cannot imagine anyone going much further using such theoretical approach. Best wishes, Kare
Interesting, because no Ferrari F1 race car has ever had one, neither do the P series (and also the 250 LM does not have them BTW, or should not). So the gains must be pretty minor ... and are they really enough to counter the extra weight of the 'snap'? Also regarding Italians putting unnecessary stuff on their cars ... hmmm, my Alfa Romeo GTV has way too many badges ... way over the top, so I do not believe that every little thing on a Ferrari is always 100% required, not when the art got in the way And also these 'snaps' really only appear on the road Ferraris. The only exception being the 250GTO, which is not considered a road car by many ... including Stirling Moss. Thus while it may have a function, it sure looks cool Pete
Few short remarks: I don't think front engined cars ever had properly tuned exhaust headers and some of the problems may be cleared out by applying a snap that helps the fumes the exit. On the other hand when you move engine to rear, exhaust pipes get very short; when you apply tuned exhaust headers, nothing remains to be done. No significant temperature difference (leading into fall of exhaust pressure and speed) will occur in a short pipe, so the exhaust pipe does not tend to choke anymore. If you gain one or two hp when driving at top speed, you top speed will be higher. That is a significant gain on a fast track!
I see Snap extractors are compared with Borla's decorative tips. In Borla the fumes come out the center hole, whereas in the case of the Snap they exit the perimeter. Looking at the design of the Snap it becomes pretty obvious what the designer had in mind. The idea was to extract or suck out the exhaust and thus reduce the choking effect. How is the sucking out achieved? The turbine like veins twirl the exhaust and the fresh air entering the oval side cuts and exiting the round end hole assist the exiting of the fumes. Keep in mind the Snaps only work when the car is at fast forward motion. Theoretically, with ordinary exhaust ends, the exhaust is pushed out using the exhaling force of the engine, whereas with the Snaps, a suction force at the end assists the exhaling; thus, the name Snap "extractor". The disadvantages of the Snaps are (at least with the Kamm tailed cars) fumes find their way to the cabin at speed, and the solids and liquids exiting the pipes spray on the rear bumper and the Kamm tail. john
Perhaps a bit of fluid dynamics is in order here.... First of all, air from the sides of the snap are DRAWN thru the inner flowpath by the momentum of the flow of the exhaust gases. The inner flowpath air tries to match the velocity of the exhaust gases and is SUCKED thru the side vents. Since there is no forward facing scoop, the air along the sides has the same dynamic inlet pressure as the flow at the outside of the tip, and thus the inner flowpath air is accelerated and actually COSTS you energy to accelerate it to the outer flowpath speed. This energy comes from the exhaust stream and results in higher backpressure. There is no free lunch and the inner flowpath air does not help extract exhaust from the snap. This effect is what is called an "ejector" and you can google it to see how they work. For the inner flowpath air to help extract flow from the exhaust it would have to be flowing out the inner flowpath at a higher velocity than the exhaust flow, and since that is clearly not the case, there is a pressure loss that you pay for with higher backpressure. The swirl vanes cause the exhaust gas flow to expand quickly and if there wasn't a supply of air from the inside of the tip, there would be a higher pressure loss at the tip. The net effect is to "fan out" the flow, and the effect of these tips are more to expand and dissipate noise as opposed to creating more power.
No, the "Coanda Effect" is best described as the tendency for a jet of air flowing over a curved surface to stay attached to the curved surface rather than separate. It was used in some high lift devices for aircraft to blow air over the top of a flap and enhance lif at low speeds. That isn't at all what is happening here.
Would ceramic coating the full exhaust path prevent or reduce this temperature drop along the length of the exhaust? Seems like a simple modern solution.
