Owen Posted January 27, 2005 Share Posted January 27, 2005 Hey guys, Does a turboed engine with an automatic tranny need a blow off valve? My thinking is that there will be no lifting off the gas with the auto, so there will be no reverse flow of air back to the compressor. I guess it couldn't hurt for those sudden braking manuevers etc. when I have to let off the gas... Thanks, Owen Quote Link to comment Share on other sites More sharing options...
lifegrddude Posted January 27, 2005 Share Posted January 27, 2005 I'm running one on my a/t ZX. A blow off will help even under light boosting loads as the compressor surge will make it feel as though you've let off the gas when you haven't. (i.e. during the middle of the corner when you have to reduce throttle pressure it will make the car unstable when it surges) If you're drag racing, you would want one anyways since at the end of the strip you have to let off and that pressure would have to be relieved some way. Just my opinion though. =) John 82ZXT Quote Link to comment Share on other sites More sharing options...
Guest Magnum Rockwilder Posted January 27, 2005 Share Posted January 27, 2005 I suppose if you go WOT and never let off it'll be fine. Quote Link to comment Share on other sites More sharing options...
mtcookson Posted January 27, 2005 Share Posted January 27, 2005 this is a very common confusion and i don't know why... you still lift the throttle on a car with an auto tranny... if you didn't you would never stop going. lol if you boost and lift the throttle you'll still have compressor surge without one. the absolute only difference between the auto tranny car and the manual tranny car is that you lift inbetween shifts. on both cars you always lift the throttle to slow down. on some manual cars with a sequential tranny you don't lift between shifts so it would be exactly like having an auto tranny. Quote Link to comment Share on other sites More sharing options...
Owen Posted January 28, 2005 Author Share Posted January 28, 2005 this is a very common confusion and i don't know why... you still lift the throttle on a car with an auto tranny... if you didn't you would never stop going. lol Right, which is why I mentioned braking. Aside from repeated hard braking like on a course, I think a street car may not need one, tho having one wouldn't hurt. The other difference between auto and manual is that not only are you lifting between shifts, you're most likely accelerating hard too. So with an auto, accelerating hard and not lifting, any excess boost is handled by the wastegate, so again, a BOV may not be necessary. I have a line on an turbo engine and auto tranny, but I like manuals and I WANT the BOV sound! Owen Quote Link to comment Share on other sites More sharing options...
mtcookson Posted January 28, 2005 Share Posted January 28, 2005 technically a blow off valve is always necessary to keep from ruining your turbo. if you don't have one and lift the throttle on any vehicle there with be pressurized air trying to find any way out that it can. when the butterfly slams shut the boost no longer has anywhere to go into the manifold so it quickly goes whichever way it can.... which is back through the turbo. this can cause your turbo to slow down, stop, or even worse spin backwards with enough boost. this is called compressor surge and is very, very harsh on your turbo. Quote Link to comment Share on other sites More sharing options...
tyson Posted January 28, 2005 Share Posted January 28, 2005 When I got my intercooler on my 280ZXT, and was still at stock boost I could hear the compressor surge every damn time I let off...Not even from full boost, just putsing around it would surge. Its an annoying sound, and it can be an expensive sound as well since it will wear down your turbo. If you arent running very high boost, just get a cheap DSM BOV. I got my BOV and flange for $35, and had it installed for $50. Quote Link to comment Share on other sites More sharing options...
mtcookson Posted January 28, 2005 Share Posted January 28, 2005 yeah, the hose on my bov came off once and every time i let off that throttle there was some major compressor surge (at only 7 psi). it actually sounded pretty cool but that turbo didn't last long at all. i pulled it off at one point and come to find out the blades on the compressor and turbine were ripped clean off at some point. (i only had compressor surge 2 or 3 times!!) i'm still blown away that i didn't score the cylinder walls of my engine from those damn compressor blades flying through there. i believe another common happening with compressor surge is ruining the shaft that the wheels are bolted onto. on some turbos that have larger shafts (like the holset turbos on the dodge ram cummins diesel engines) and those hold up a bit better to the compressor surge (especially considering most of those trucks don't have a blow off valve). there is still a chance of wheel damage. (the holset hold up pretty well to it due to some crazy designs... like for instance the newer holsets have cast titanium compressor wheels... they developed a new way to cast titanium and have good results and such from it). Quote Link to comment Share on other sites More sharing options...
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