trail rider Posted January 6, 2004 Report Share Posted January 6, 2004 does a two stroke have engine braking like a four stroke? Like when your on a four stroke and your coasting down a hill and start going to fast and you down shift to make it slow down. Quote Link to comment Share on other sites More sharing options...
fixitrod Posted January 6, 2004 Report Share Posted January 6, 2004 Sure it does. Every engine can be used as an engine brake. Just be careful how hard you use it. Even saves the brakes and clutch when used properly. Quote Link to comment Share on other sites More sharing options...
holeshotkid Posted January 6, 2004 Report Share Posted January 6, 2004 Compression braking on a two stroke is, generally speaking, nothing like a four stroke. The first time I road a raptor, I about went over the bars when I let off. I was used to the shee not having that severe of compression braking. Quote Link to comment Share on other sites More sharing options...
broke Posted January 6, 2004 Report Share Posted January 6, 2004 I have been corrected. broke Quote Link to comment Share on other sites More sharing options...
boonman Posted January 7, 2004 Report Share Posted January 7, 2004 The compression ratio has nothing to do with the "engine braking" effect. Two strokes and four stroke bikes generally have around the same compression ratio's. The braking effect comes from the engine trying to pump air against a closed throttle. Ever monitor vacuum in a gasoline powered car when you close the throttle at high RPM? It goes up. THis is the braking effect. The only exception to this rule of thumb is a diesel engine. To provide some supplemental braking, typically drivers downshift to a lower gear, allowing the engine to exert some braking force as the engine attempts to intake air against a closed throttle. Of course, this only works for gasoline engine-powered vehicles that have air throttles. Drivers with diesel engines, which have unrestricted air intake, face a different problem. Diesels provide little engine braking unless they are fitted with either an internal or an external device that uses the pumping action of the engine to do work. In either case, such devices on diesel engines are intended to create a pumping resistance that results in engine braking. Diesels need an exhaust brake to create engine braking. This is directly attributed to the unrestricted intake. On a diesel, there is no butterfly, or slide, or anything of that nature. Fuel is either directly injected, or indirectly injected. Diesels can have in excess of 20:1 compression ratio. Yet, stock, they exhibit virtualy no engine braking. A banshee, or any two stroke motor has noticeably less engine braking because it compresses about half the air that a four stroke does when compared stroke length for stroke length. This is why a four stroke gasoline powered engine feels as though it has more engine braking than a two stroke. Quote Link to comment Share on other sites More sharing options...
fixitrod Posted January 7, 2004 Report Share Posted January 7, 2004 does a two stroke have engine braking like a four stroke? Like when your on a four stroke and your coasting down a hill and start going to fast and you down shift to make it slow down. Damn boon, that's all he wanted to know. lmao That's it for jake brake 101 today. lmfao Quote Link to comment Share on other sites More sharing options...
Travis's Banshee Posted January 7, 2004 Report Share Posted January 7, 2004 Just a quick reply to Boons diesel analogy. I have been in the trucking business for 30+ years, I have a little experience in this area. Diesels do engine brake and quite well at that. Anything from my powerstroke to my 575 horse CAT. Any time the fuel source is shut off and there is a compression stroke, you will have engine braking. An exception to this may be the early Detriot Diesel 2-strokes. How do you think these trucks slow in areas that don't allow exhaust brakes. Its not all by axle braking. Not trying to slam ya boonman. My .02$ Quote Link to comment Share on other sites More sharing options...
fixitrod Posted January 7, 2004 Report Share Posted January 7, 2004 Just a quick reply to Boons diesel analogy. I have been in the trucking business for 30+ years, I have a little experience in this area. Diesels do engine brake and quite well at that. Anything from my powerstroke to my 575 horse CAT. Any time the fuel source is shut off and there is a compression stroke, you will have engine braking. An exception to this may be the early Detriot Diesel 2-strokes. How do you think these trucks slow in areas that don't allow exhaust brakes. Its not all by axle braking. Not trying to slam ya boonman. My .02$ So, what makes them brake ? Quote Link to comment Share on other sites More sharing options...
Travis's Banshee Posted January 7, 2004 Report Share Posted January 7, 2004 Any time the fuel source is shut off and there is a compression stroke, you will have engine braking. This will occur in gas or diesel engines. Valves closed with nothing to burn=engine braking. Quote Link to comment Share on other sites More sharing options...
fixitrod Posted January 7, 2004 Report Share Posted January 7, 2004 I guess I could see that with those heavy ass pistons and crank dragging it down too. But, look what I found Click here about diesel exhaust brakes Quote Link to comment Share on other sites More sharing options...
boonman Posted January 7, 2004 Report Share Posted January 7, 2004 Trav, you are mistaken. Any time the fuel source is shut off and there is a compression stroke, you will have engine braking. Not in a diesel engine. Diesel engines, by their inherent design have an unrestricted air intake. Meaning, there is no butterfly, slide, or other device to close off the air intake. The engine can suck in as much air as it wants, no matter where your foot is in the throttle. When you back off the throttle on a diesel, you are just shutting the fuel flow off. Diesels are mechanically injected. The fuel is shot into the cylinder. Not sucked out by vacuum like a carburetor on a gasoline engine. Even on fuel injected cars, there is still a butterfly on the throttle body that shuts off air flow when you close the throttle. This will occur in gas or diesel engines. Valves closed with nothing to burn=engine braking. This wil not occur in a diesel engine, because even with your foot off the go pedal, the enngine can still suck in as much air as it wants because the air flow does not get shut off... Rod, the Banks site is FULL of information on alot of different things!!!! HERE is where I quoted 2 tthings from... Also, trav, Diesels are not as effective at engine braking as compared to a gas engine when unaided. I know that diesels do provide some engine braking stock, but not what is possible on a stock gasser. Quote Link to comment Share on other sites More sharing options...
fixitrod Posted January 7, 2004 Report Share Posted January 7, 2004 This will occur in gas or diesel engines. Valves closed with nothing to burn=engine braking. This wil not occur in a diesel engine, because even with your foot off the go pedal, the enngine can still suck in as much air as it wants because the air flow does not get shut off... That's the part I was wondering travis. The air pressure in a diesel will stay pretty nuetral. In a gas motor it will get create a vacuum to slow it. If that makes since Quote Link to comment Share on other sites More sharing options...
fixitrod Posted January 7, 2004 Report Share Posted January 7, 2004 does a two stroke have engine braking like a four stroke? Like when your on a four stroke and your coasting down a hill and start going to fast and you down shift to make it slow down. So, from this we have learned two strokes do have engine braking because the air intake does get cut off allowing the air pressure inside to get all friged up. It doesn't have anything to do with compression, but air volume..... because of air pressure. We learned a little about diesels while we were at it to prove WHY we have engine braking on a two stroke. There you have it. Quote Link to comment Share on other sites More sharing options...
rebelbanshee2 Posted January 7, 2004 Report Share Posted January 7, 2004 sweet this thread was quite informative!....so then when its called "compression braking" its not really accurate? its really "vacuum braking" maybe im wrong but thats my understanding of it Quote Link to comment Share on other sites More sharing options...
Travis's Banshee Posted January 7, 2004 Report Share Posted January 7, 2004 Rod and Boon. A simple but effective test can be performed. I own a ford powerstroke diesel2002, 4x4, 4door. I also own a f-250 that had a blown powerstroke. 1997 also a 4 door 4x4. This truck now has a rebuilt 460 in it for towing. When backing out of the throttle the diesel will pull down from speed in a much shorter distance than the gas. Don't know why. Weights and wind resistant are not much of a factor. I understand what you are saying about the unlimited air supply. But with nothing to burn. Beit diesel or gas. You will still have the braking effect. I'm by no means an engineer, just a consumer. Thanks Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.