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Old 05-07-2020, 08:38 PM
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14vision 14vision is offline
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Join Date: Feb 2014
Location: Royal Palm Beach, Fl
Cobra Make, Engine: Backdraft #964, Roush 427, T56
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Quote:
Originally Posted by olddog View Post
It occurred to me that the OP has never actually explained the bad manors. We have all assumed that he just doesn't like the low rpm tendency to want to buck and hop if you try to make a quick blip on the throttle or open the throttle too much at very low rpm.

An engine running too lean can hesitate, even pop up the carb and backfire. It can also cause surging. Not all engine builders take the time to tune anything other than WOT on the dyno. In fact most do not. Especially if they are a large shop that builds cookie cutter engines (100s of the exact same engine). They may tune one or two and just set all the rest the same.

Then there is the timing. The big three engineers spend hundreds of hours finding the ideal timing to make maximum break torque at every rpm and every % load combination. Then they change the commanded fuel ratio and do it all over again. All this while measuring emissions. This is how they maximize mpg, minimize emissions, and get good manors and good Hp.

Most engine builders will not even make a low rpm dyno pull. This is the danger zone where engines self destruct from detonation. They will argue that you should never operate a performance engine in that range anyway. Fair enough, but this is the proof that nobody has spent the time getting a good tune down in the low rpm range. This can be done with EFI, but there are not many tools to work with on a carb and mechanical distributor.

Does your engine have vacuum advance? If not, one less tool, and a terrible way to run a street engine. It's fine for a race only engine, because it will spend little time at low rpm.

I have digressed. My point to all this is: Take your car to a good tuner with a chassis dyno. The best dyno for this is the type that can hold a set load or a set speed and can change this on the fly. I forget the name for this. The dyno that just spins a heavy wheel is better suited for WOT pulls. You can do some tuning, but not everything. Then they have to take the car out on the street to finish up.

With the engine well tuned, it may resolve most of your issues. Then it is a matter of training the driver not to try to run the engine where it does not want to run. At some point in time you just have to realize this is not your fathers station wagon. It's a fricking race car, and you need to treat it as such.
Very valuable information and I certainly appreciate it. I am in a unique situation as I live relatively close to BDR down here in south Florida , but I bought the car from an out of state dealer for several reasons. Car is brand new, 3 month old build with now 100 miles on it. The issue I see mainly is in first gear starting out I experience surging and even if I try to just drive at 10mph steady car runs rough unless I increase rpms and get into 2nd gear. As speed and rpms increase car runs strong. I probable agree the car needs a good overall tune. Engine was installed at speed fanatix in Boynton which is bdr’s engine installation sister company. The real challenge as I have experienced in the past with my former bdr cobra is BDR lack of customer support etc. This is 2nd time I have experienced this and I thought over the last couple of years as they grew they would address this and other issues many customers have had issues with. I know there are many in the community that have had a great experience with BDR which is good, but unfortunately I haven’t been that lucky. I am obviously not as mechanically inclined as many out there and that is ok, and I am willing to pay for what is needed. I will try to locate a shop in south Florida like you mentioned that has the experience to handle high performance engines for a tune. I have learned a lot from reading many of the valuable posts. The warranty as stated probably would end up being a waste based on parts only and having to pay $135 hour for labor to deal with a warranty issue.

I certainly appreciate all the great feedback....

Thanks
Doug
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