There are multiple sources of dyno pulls showing the effect of opening up the intake to the various boxes and with retuning showing measurable gains in horsepower and torque throughout the operating range. I also believe the runners and carb boots are sized small on the 750 ACE to boost the midrange velocity to cover for cylinder port designs and volumes intended for a higher specific output engine. The intake is restricted and the air box volume is small, that air box tuning does have a sizeable effect on peak horsepower. The problem being that the air boxes on the post 1988 Honda V-twins are not designed this way. I think we have had this discussion before. I include this chart for comparison, it also explains why the perky twin carb VT600C VLX makes as much power as the 750 ACE with less displacement. 400cc version of the US market Hawk GT 650. The Chain Drive 750 ACE and Spirit use the KW0 camshaft which is rather mild, the origin of it the Bros NC25 is a Japan spec. It was a problem with my 750 ACE setup with the Hawk GT cams and the less restrictive UNI Pods and I went the way of the NT650 tuners and lengthened my slide springs to keep the slides down until I had more engine vacuum.īack in the early 1970's I had a Ducati 250 Mach 1 250 that had been used as a race bike before I legalized it for street use, that thing was a bit of a nightmare and if I got stuck in traffic the velocity stack would soak my knee and then everywhere I went I'd be reeking of Sunoco 260 even worse than normal. You might be on to something with the fuel stand off, I've never run the stock setup without the air box intake runners.Īnd I figure that is why TJBC's velocity stacks were screened to keep that pressure differential between inside and outside. Then again, the crankcase vent hose could be open and you'd also feel air pulsing out of it as the pistons came down. People who used to put those little 2" tall flat chrome filters with paper elements on their VW just never could keep the stumble out of it, If I'm not mistaken, that intake roar you hear when running without an air cleaner and crank the throttle is caused by or related to the flow reversal. With the domed lid it just ran down into the oil-bath air cleaner, mixed with the oil and slowly evaporated and got burned. Incidently, their air cleaner had a built-in velocity stack maybe 6" tall and a domed lid so the fuel fog wouldn't condense on the air cleaner lid and drip back in, screwing up the mixture. Also had really long intake runners, so there was always fuel laden air in there. thing had something like a 330 degree duration on the stock cam, but it was a pretty low lift so ran relatively smooth. The old VW air cooled used to have a fuel fog standing approx 5" or so above the carb if you revved it and held it open with the air cleaner off. The airflow in the intake actually reverses multiple times per revolution depending on how many cylinders you have, cam duration etc. And I'm pretty sure the Shadow does have enough, most engines do. Depends on the cam profile and valve overlap, If the valve overlap is to where the intake starts opening enough degrees before the exhaust valve is closed, the piston will still be on the way up and can push air out of the carbs and suck it right back in.
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