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NC wayne
01-21-2007 17:34:22
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Re: OT- injectors for 8v71 in reply to JoeBob/IN, 01-21-2007 05:26:24
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I've been working on Detroits on and off for about ten years now and I don't claim to be any kind of expert, there are simply too many different combinations to even try to remember them all. I simply go by the book to set them up so there are no problems. If a customer wants to "soup one up" after I'm gone so be it, I don't want the liability of paying for a rebuild when it blows up on them. One thing right off, if you change the injectors change them as a full set or 8. Doing otherwise will create an unbalanced load within the engine and almost certain damage to it. One thing before I go any further though,I don't understand why your thinking the injectors are the blame for the one bank not firing when cold. Then injectors are cam operated so they should inject fuel wether their cold or not. In fact if it were an injector issue they would more than likely inject less as internal clearances expanded allowing fuel to bypass around the plunger as they heated up. Sounds to me more like low compression on those cylinders more than anything else. Personally I'd have the compression checked and see what you get and if it checks out OK then have it properly tuned up before doing anything else..... That said I did a search of my Field Service Data Book to see what could be done "by the book" with a naturally aspirated 8V71. For those that say a Detroit isn't "naturally aspirated" but blown, I know this, but they consider non-turboed engine as naturally aspirated since the blower is an intergral part of all of the two stroke engines. Anyway, here's what I found for you. First the book doesn't list any 8v71 engines under the automotive section, just the V92 series. All the otner 71 series automotive rated engines were inlines. The only place I found 8V71's was in the industrial and marine sections. There is one page of them listed in the industrial section that are non turbo versions, and the highest HP shown is 305 @ 2100RPM , and that's with a 7N65 injector with the timing set at 1.484. Step back to a C65, N65, or 7E65(@ 2000 RPM vs 2100), all with the same timing and the HP's are to 304, 284, and 283 respectively. Now the final HP rating is also gonna change in regards to the accessories attached to the engine. The book shows it like this, "three" engines, two with N65 injectors, timed at 1.484 and the third at 1.460. The two with the 1.484 timing are rated at 272 and 294 HP, the third is rated 304HP. The book annotates these three engines saying they are "the same engine" with different accessories attached. None of these, engines, in any rating, have anything showing the blower being either over or under driven in relation to standard as one post suggested. Like I said this info is straight out of the book. Not to say there's no such thing but I personally have never heard of or read in any of the manuals we've got about a "B" setting on the injectors. The injector type determines the amount of fuel injected per stroke and the timing does just that, it times the injection of that set amount of fuel in relation to the stroke of the piston. On every two stroke engine I've set up, be they inline or V, you always set the injector rack at full stroke in relation to the governor. I other words if you floor board the throttle the rack pushes all the injectors to a full fuel position and they do just that, give full fuel output, til the governor takes over and pulls the rack back when the needed fuel amount is reached in relation to the upper RPM limit set in the governor mechanism. Now there are throttle delay issues involved with the automotive style engines that are designed mainly to cut down on smoke/reduce emmisions when accelerating but that has no effect on the engines final HP output. That limit is gonna be based on the size of the injector and how much fuel it can provide the engine to burn in relation to the amount of air it can pull in to burn, all at a given RPM. Like I said in the beginning I'm no expert, but I don't see how your gonna make 350HP out of your engine as one post suggested. I'm not saying it can't be done without a turbo, but it's a long way from 305 to 350 as HP goes. Now of you had a turboed (8V71T) engine you could bump the HP to 413@2100 RPM using a N90 injector set at 1.460 and a TV8101 or with a turboed and aftercooled (8V71TA) engine you could bump it on up to 520@2300 using a M95 set at 1.484 injector and a TV8513 turbo..... ..Again I'm no expert when it comes to Detroits but the info I've provided is straight out of the Mfgs data book so you can use it and feel safe that you won't damage your engine. Good luck.
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