![]() 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. Huge at the top, like they are made for 48 IDFs, and have a huge taper.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. Has anyone tried "sleeving down" IDF manifolds to the throttle bore size (or smaller) to improve vacuum signature/velocity? They are like. (Where is Shad when you need him.Oh yeah, College. You would want a ~.7 L plenum on either side, assuming a multi stage plenum setup uses the same math. The ones I'm thinking of use 3l plenums, 2 where the std Weber setups air cleaners would be, and a central plenum/air cleaner You would want ~10" valve seat to first plenum (third reflection) for a ~6000 RPM peak. ![]() Looks like those funky turbo hat style intake setups I've seen used on German Lookers might actually be worth a few HP, and fatten the powerband. The stock throttle body would then appear a little large. The plenum is possibly also a little small, needs to be ~1.3-1.5L for a 3000 ish power peak, with an ~18" long ~1.5" dia ram pipe, 17" manifold pipes (to valve seat) (Methinks it should be at beginning of the ram pipe, so the tuning would still be in effect at part throttle, and the ram pipe could be the right diameter) ![]() Looks like a 2.0 FI intake is just about right (or could be made so) for a stock engines powerband, save for the intake ram pipe feeding the plenum via the thottle body.Īnd does it matter which end of the ram pipe the throttle body goes on? Really helps me visualize what's going on.
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