line pressure readings

B18B1LS1

B18B1LS1

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Aug 22, 2006
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Just went on a test drive, came up with 90 psi at idle, 100 psi steady cruising, 120 psi converter locked cruising, and 210 psi WOT with the converter locked or unlocked. But I did notice something interesting. I have my 4gsk setup super tight, it is VERY touchy, I can make 60 psi of boost at less than half throttle. Well, that means I'm making pretty decent power but the tv cable has barely moved yet, which is giving me pretty low line pressure down there, around 120 psi. Thats seems like an issue? Can I get more aggressive with the line psi somehow? I think I need it to come in way faster?
 
120 psi is allot, mine is at 155 WOT and it lasted 70k before the billet input shaft broke, there was nothing more than fuzz in the mag plug.......for the non-believers, yes that is the same set of clutches.

Jim
 
Well dang it Jim, I need positive answers! Haha just kidding! Thanks for the info. I did some reading and people have made levers to get a faster throw on the arm, sounds like what I was thinking about doing. I might try to raise the "base" pressure up a little and see if that helps.
 
Just tried wiring the tv lever about 3/4 open, that got me to 110 psi idle pressure. But of the 5-6 times I did some short WOT blips, only once did the pressure pass the 120 psi I have while just cruising. I assume it should snap up to full pressure at WOT right? Do rpms affect line pressure at all?
 
I made a arm that ramps up faster and wont limit the full throttle operation of the pump.
 
My base pressure is 100 psi! Brad makes the wheel turn while guys like me are carving it square.....lol, love ya brother......he has a sharp mind!

Jim
 
Bponci said:
I made a arm that ramps up faster and wont limit the full throttle operation of the pump.
Click to expand...

I did some searching on here and found your pictures. I may try and whip something like that up. The extra 20 psi seemed to help, it just threw my part throttle shift points way off. And the fact I don't see the pressure rise every time I go WOT worries me too.
 
when we had probs with the ats 48re they said we should have around 75 psi in gear and shift around 150 psi... but it was all aftermarket. but i can see you conundrum. definately sounds like a good idea to mod the linkage
 
I agree. It seems all my shifts happen at 120 psi or lower, unless I am 100% WOT. Doesn't seem to be a linear middle ground anywhere.
 
You can get aggressive with the arm ratio but you will have to go with lighter shift springs to maintain part throttle shifts for daily driving.
 
That sounds good to me. Should the line pressure go up gradually with the throttle position? My base pressure is around 90 and my WOT is around 210. Shouldn't half throttle be somewhere in the middle or does it not work like that? How much base pressure is too much for a weekend cruiser?
 
It won't work that way due to the spring rate or spring stages of the tv valve. The key is to have a rapid ramp up of pressure so the pressure is there before the power is applied so the clutches will hold properly. You can have too much pressure (max pressure) and flaten the belville spring (behind input shaft hub) or even crack the case.
 
So if I can get my shiftpoints where I need them I could cruise around at say 150 psi and not hurt anything? And keep my same WOT psi at 210.
 
The best pressures i have found is 110 psi@ idle and a quick ramp up to 210 psi@wot. Put your truck in gear measure your reading in drive sitting still with your foot on the brake. Then stroke the throttle down to 1/2 and read your pressure. Then do the same for wot readings. You dont have to build a ton of boost, do this test quickly. Let me now......Brad
 
Doing it like that I know I had 90 psi at idle and 140 psi at wot. ill have to check half throttle when I get home.
 
Okay did some more test driving. In 1st and 2nd gear I'm only seeing 120 psi max at WOT. I can't see 210 unless I'm in 3rd or 4th. I have the tv lever set within 1/16th or less of full travel.
 
would this affect it downshifting too? I usually barely have to push the throttle to go, but if I come to a rolling stop and don't actually stop, then start to go, it won't shift down into 1, and its real hard to get it going. I have to manually put it in 1, or hammer it and flood the street with smoke until it downshifts.
 
Lance said:
would this affect it downshifting too? I usually barely have to push the throttle to go, but if I come to a rolling stop and don't actually stop, then start to go, it won't shift down into 1, and its real hard to get it going. I have to manually put it in 1, or hammer it and flood the street with smoke until it downshifts.
Click to expand...

Id like to know this also.
Since I have done my manual to auto conversion, my trans does the same thing. Come to a stop sign and if I dont come to a complete stop, it stays in 2nd.
Probably has something to do with the TV/kickdown cable.
 
I may be totally wrong in this but I remember from my drag racing days ( many, many years ago ) that we never ran more than 160 - 170 psi line pressure...
The internals would disintegrate at higher pressures.....
 
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