I was looking at map values at wot and I was still pulling some vacuum. If I had a larger throttle body, would the value go down to zero? So the stock throttle body is creating a restriction at wot? Is it worth it to get a 85mm?
There will always be a small amount of vacuum in the manifold, no matter how big you go with the throttle body. Otherwise, the air would not be sucked into the cylinders. Of course this is completely false if you have a supercharger. LOL. A larger throttle body, all else equal, will drop your WOT vacuum reading... to a point. Then you have to look at the next restriction.
All that said, I would recommend the larger throttle body. I went with an 85 mm TB and dropped 2-3 tenths off my ETs and gained 1-2 MPH at the track. With a proper tune, you'll see even better results.
maybe these electronic map sensors are super sensitive. i have used mech vacuum guages on carb engines and at wot they are at zero. i have entered the new world of tuning off live data. i was thinking about a tb upgrade after i saw the map sensor reading while i was tuning today. did you add fuel at wot with your tb ? im also thinking about putting in a wideband to fine tune mf a\f when i install cat back.
I know what you're talking about with the zero vacuum with a gauge. I see zero as well with my gauge on my carbureted vehicle. But it depends on where you measure as well. I measure at the manifold, so it gets pretty close to zero at WOT. But physics says there must be some vacuum there. Just not quite zero, probably around 0.5 - 1 in Hg. Also, I didn't get those low numbers until I did a cam swap and reworked heads.
When I installed my 85 mm TB, at first I didn't do any retuning. Just bolted it on. I'm not sure how well the computer coped with the extra air, but it ran fine. I now have a custom dyno tune. According to the tech, it was running rich to begin with, so I'm sure I didn't have an issue before the dyno tune.
throttle body is really a single fuel injector that sit on top of the intake manifold. a carburetor is a gravity fed devise using engine intake vacuum and carburetor jets and a float reservoir to control fuel flo http://www.automd.com/answers/
throttle body is really a single fuel injector that sit on top of the intake manifold. a carburetor is a gravity fed devise using engine intake vacuum and carburetor jets and a float reservoir to control fuel flow.