vacuum modulated or not?
03-04-2005, 10:06 PM
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vacuum modulated or not? I've done some searching, and asked a couple friends, and most seem to say vacuum modulation is the way to go for high HP....
i'll be making around 500hp, and most are telling me to go with it except the person who is building my tranny and he builds pretty nice trannies...
my only worry is, will the transmission get pressurized since i run a turbo? i dont think it should, but still lol :p
also what if my vacuum at idle isnt so great (it will have a midsize turbo cam) and everytime i put it in gear, it'll shift like hell into Drive?
this is for an LT1 btw... i much prefer computer conrolling everything but ppl are telling me to just let it do the shifting with vacuum...
what do i do?
i'll be making around 500hp, and most are telling me to go with it except the person who is building my tranny and he builds pretty nice trannies...
my only worry is, will the transmission get pressurized since i run a turbo? i dont think it should, but still lol :p
also what if my vacuum at idle isnt so great (it will have a midsize turbo cam) and everytime i put it in gear, it'll shift like hell into Drive?
this is for an LT1 btw... i much prefer computer conrolling everything but ppl are telling me to just let it do the shifting with vacuum...
what do i do?
03-04-2005, 10:15 PM
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Vacuum modulated line pressures is the way to go,no neck snapping part throttle and no problem with boost damaging the transmission with a check valve that protects the vacuum line.
03-04-2005, 10:24 PM
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well cant u set how hard u want it to shift based on RPMs through the PCM so there are no neck snapping shifts@part throttle?
i noticed cars that have low vacuum ad idle (because of a big cam or something) shift hard as hell with vacuum modulation...
i noticed cars that have low vacuum ad idle (because of a big cam or something) shift hard as hell with vacuum modulation...
03-06-2005, 03:01 AM
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The vacuum modulator will do well even in overcammed vehicles. You can have smooth shifts at light throttle openings by not adding the spacers to the 2nd gear accumulator. The vacuum modualtor will increase line pressure from about 170-180 pounds at WOT, to about 220-235 pounds in the "D" position at WOT. This will help the 3-4 clutch pack live much longer. It does not effect the shift points, just the shift feel. I setup almost all of my units this way, with very good success. If I can be of help, let me know?
Last edited by Pro Built Automatics; 03-07-2005 at 02:20 AM.
03-07-2005, 01:53 AM
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alright, going to get the tranny done tommorow, i will mention the spacer thing to the guy whos building it... he strongly reccomends against this... he says let the computer do the work
230ish pounds sounds alot
230ish pounds sounds alot
03-07-2005, 02:20 AM
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Remember you already have this pressure in manual "1", "2" at WOT. The added pressure is at WOT only in 3rd & 4th gear. manual "1" & "2" get a little more boost, but not as much as 3rd gear in the "D" position.
Last edited by Pro Built Automatics; 03-07-2005 at 02:30 AM.
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03-07-2005, 08:49 AM
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I think vacuum modulated has the potential to save your
trans, vs "letting the computer do the work". Computer
is easily fooled whilst always trying to be smart. A month or
two of it deciding it can "get away with" a little less line
pressure than makes the clutches hold, and you have a
nice new varnished-up set of clutches. Especially at part
throttle where you may be putting out substantial torque,
but the PCM is still "allowed" to be making fussy line pressure
adjustments based on its stale factory, EPA/CAFE-oriented
decision weights.
Vac mod is not going to go changing its mind on you, and
in general the things that would fault, drive it to full pressure
(like the hose coming off). You have less freedom to tailor it
(like, if you wanted Cadillac shifts at high vacuum and NHRA
shifts by 25% throttle, too bad, it's probably linear and you
have to just like it) but I reckon by the time you break your
first one, you're over the Cadillac expectation.
trans, vs "letting the computer do the work". Computer
is easily fooled whilst always trying to be smart. A month or
two of it deciding it can "get away with" a little less line
pressure than makes the clutches hold, and you have a
nice new varnished-up set of clutches. Especially at part
throttle where you may be putting out substantial torque,
but the PCM is still "allowed" to be making fussy line pressure
adjustments based on its stale factory, EPA/CAFE-oriented
decision weights.
Vac mod is not going to go changing its mind on you, and
in general the things that would fault, drive it to full pressure
(like the hose coming off). You have less freedom to tailor it
(like, if you wanted Cadillac shifts at high vacuum and NHRA
shifts by 25% throttle, too bad, it's probably linear and you
have to just like it) but I reckon by the time you break your
first one, you're over the Cadillac expectation.
