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Discussion Starter · #1 ·
This is related to the MAP sensor. When running a much hotter cam, and having a considerably lower vacuum, the MAP sensor will see this new reading, but things will be off kilter, thus, there will be some issues. I'm mainly thinking of the overdrive engagement on an '89 Dak setup. I was looking at those vacuum amplifiers used on the RC's, and was wondering if you could run one of these in-line between the vacuum source and the MAP sensor, and fool the sensor into "seeing" a higher vacuum reading which would change with engine rpm (if so, about how much higher would it read?), and thus, have the SMEC think things are hunky-dorey, and engage/disengage the OD as intended. If one wouldn't be enough, how about two in series? I have no experience with the "vacuum amps" as they were called, and am not really sure how they work, well basically, but no clue on specs for the device. If not possible, where would the problem(s) be?
 

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I don't have the answer for this...buuuuut...here's some places to check and something to try?

http://www.speedtweaks.ca/tipsandtricks.php#lobesep
Search this board for "MAP" http://www.dodgedakotas.com

Poor idle with big cam (112 degrees or less on Lobe Separation)

If you install a larger cam that has a Lobe Separation of less than 112 degrees, you will notice a very poor idle (sometimes dies at the light) and running too rich at idle as well. This is caused by the MAP signal being too low due to the cam. The MAP vacuum at idle (with a stock cam) is 12-13" at the MAP port on the throttle body. With a larger cam, that has a 108-110 degree Lobe Separation, the vacuum at the MAP port is 6-8". This is too low and will cause poor idle qualities.

Plug the MAP port on the throttle body and relocate the MAP line to manifold vacuum (should be about 12-13" at idle). This will simulate the factory signal and your idle quality will be back to normal. There is no adverse affect on the cruise or WOT performance with this modification.

Recommendation: Select a Cam with 112-114 degrees Lobe Separation. They are MAP friendly.
 
G

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Discussion Starter · #3 ·
Thanks C. I'm kinda doin' a hybrid experiment. Ditched the TBI, and am figuring how to run the AFB in place with just enough feedback to the computer to handle the tranny as mentioned. The cam I got was a bit of an accident. I thought I'd won a Magnum RT cam, but when it arrived, it was a bit bigger! Just a little.....right. Actually, it's very close to the CompCams Xtreme Energy 268 (including 110 degree lobe sep.), but has more lift. Didn't exactly hurt my feelings. The little Dak was kinda spunky stock (well, 0-30mph anyway), but this time around, I want it to scream rip-snortin' nasty (in a streetable way for a 360). Anyway, I've been going over it for a while, and I just would rather have something more than a toggle switch for the overdrive, but if the tricks don't work, I'll use the toggle. I have a vacuum amp, and I'm curious if it'd work, but it's good to know the manifold relocation offers that much of a boost.
 
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