Oil Pressure drop under boost.. this is strange! help!
08-10-2006, 12:06 AM
#1
Launching!
Thread Starter
iTrader: (3)
Join Date: Feb 2002
Location: Wilmington, NC
Posts: 281
Likes: 0
Received 0 Likes
on
0 Posts
Oil Pressure drop under boost.. this is strange! help! hey guys.. on my way home from the local wednesday night gathering, I have about 20 miles of great testing road. so i always usually give a 3-4 run out on the way home for kicks. well tonight i noticed that when the car goes into boost, my oil pressure drops to about 20 from betwwen 50-60 psi. I just happened to catch the needle going back up as soon as I let out of it. so i tried it again.. and sure enough.. under boost I drop pressure into the 15-20 psi range.. this is not a very warm feeling and was wondering what it may be... engine was too hot to mess with tonight when I got home and its pretty late.. so gonna check the level in the morningto see where everything is.. I was under the impression that pressure would rise with rpm not drop.. never noticed this on any of the other vettes and was curious to see if any of you experience this as well? under normal driving it NEVER goes under 40 and usually hovers between 50-60 under cruise.. any takers?
Chris
Chris
08-10-2006, 08:55 AM
#6
Teching In
Join Date: Jan 2005
Posts: 8
Likes: 0
Received 0 Likes
on
0 Posts
my car is not supercharged, but i can tell you that i noticed a drop in oil pressure at upper RPM's on my small block when i was running a 10w-30 weight oil and had my oil pan filled to capacity. when i switched to a 10w-40 and left it one quart low, it was perfectly fine. i believe that i was experiencing oil aeration. maybe you should try using one quart of oil less than full. but then again, we have different applications, so take this with a grain of salt.
Trending Topics
08-10-2006, 11:56 AM
#8
Launching!
Thread Starter
iTrader: (3)
Join Date: Feb 2002
Location: Wilmington, NC
Posts: 281
Likes: 0
Received 0 Likes
on
0 Posts
ok.. typed out a long post and it wouldn't let me submit it..
so heres a break down..
no windage tray
10w-30
melling m55HV pump with 3/4" pick up tube
stock pick up
stock pan
could I be pumping the oil toi the top of the engine and running dry on the bottom with some crank case pressure, it may be hard for oil to return to the poan through the lifter valley holes?
Chris
so heres a break down..
no windage tray
10w-30
melling m55HV pump with 3/4" pick up tube
stock pick up
stock pan
could I be pumping the oil toi the top of the engine and running dry on the bottom with some crank case pressure, it may be hard for oil to return to the poan through the lifter valley holes?
Chris
08-10-2006, 02:34 PM
#9
Senior Member
iTrader: (24)
Join Date: Nov 2001
Location: Tampa, FL
Posts: 6,034
Likes: 0
Received 0 Likes
on
0 Posts
I have to run 1 quart over full (7 quarts) to avoid this. My n/a setup did the same thing. When I went above 6500 rpms, the pressure would drop like a rock. Added the extra quart and it quit. It may be the pump cavitating... or it could be some bearings going bad. I have a ported and shimmed LS6 pump and main studs.
08-10-2006, 02:39 PM
#10
Launching!
Thread Starter
iTrader: (3)
Join Date: Feb 2002
Location: Wilmington, NC
Posts: 281
Likes: 0
Received 0 Likes
on
0 Posts
I have been doing some researech on it, and I think you are correct.. I think I need to drop the pan and swap the HV pump for a blue printed std pump and probably run some extra oil in the pan. I am not convinced the bearing clearances are bad simly because I would think with less pressure at lower rpm, it would be pushing past the rod and crank more then at higher rpm..with more supply from the pump. I am also thinking of yanking the motor anyways to put a new cam in and port the block in the lifter valley for better return and to work the trickflow heads which seem to have the same return issues as the AFR's not enough room to get the oil back to the pan.. I am noticing pushing oil out the valve covers at the seal on the cylinder head.. this tells me I am pooling the oil in the top of the engine.
guess its time for some more modding.
Chris
guess its time for some more modding.
Chris
08-10-2006, 03:03 PM
#12
Launching!
Thread Starter
iTrader: (3)
Join Date: Feb 2002
Location: Wilmington, NC
Posts: 281
Likes: 0
Received 0 Likes
on
0 Posts
was this drop noticed across the board when it went south or was pressure perfect at idle and cruise but would fall like a rock as country boy described.. mine will go from 50-60psi at cruise and when you lay into it and the revs hit close to about 5000 it starts falling quickly. by 6000 it had dropped to about 15psi which is not acceptable in a the upper rev range.. figure it should be a minimum of 60psi at 6000rpm.. and add a 10psi per thousand rpm there after. once I let out of it.. it bounces right back up to 50-60 psi immediately almost. thats what confuses me.. worn bearing should be showing low pressure EVERYWHERE not just at high rpm.
Chris
Chris
08-10-2006, 03:06 PM
#14
Launching!
Thread Starter
iTrader: (3)
Join Date: Feb 2002
Location: Wilmington, NC
Posts: 281
Likes: 0
Received 0 Likes
on
0 Posts
thats the game plan as soon as the clock strikes 5:00pm.. stopping by advance and grabbing 7 quarts of 20w-50 mobil1 and a new filter.. figure better change the oil and inspect it and fill with new just in case. going to the thicker oil as well.. think the 10w-30 is a little thin for this kind of engine.
Chris
Chris
08-10-2006, 03:08 PM
#15
Senior Member
iTrader: (24)
Join Date: Nov 2001
Location: Tampa, FL
Posts: 6,034
Likes: 0
Received 0 Likes
on
0 Posts
Is it a non stock motor? I have to run a 20w50 in mine, but thats because I set the bearing clearences a tad loose as I built the motor for a 200 shot and I didnt want to squish all the oil from the bearings and run them dry.
08-10-2006, 03:11 PM
#16
Launching!
Thread Starter
iTrader: (3)
Join Date: Feb 2002
Location: Wilmington, NC
Posts: 281
Likes: 0
Received 0 Likes
on
0 Posts
yes, non stock motor.. 355 built LT4 engine.. clevit 77 race bearings, polished crank all clearances were set up by the builder.. can't remember what they were but he said he set them up for drag type racing.. quick bursts non extended RPM.. I am guessing he made them a tad looser then stock oem clearances but not super loose for circle track style.
Chris
I may have needed to run 20w-50 anyways and not known it.. guess we will see. ho hum
Chris
I may have needed to run 20w-50 anyways and not known it.. guess we will see. ho hum
08-10-2006, 03:29 PM
#17
My GN did that too, we NEVER figured it out. Have you tried running with no boost to see if its RPM related? Mine was fine with no boost, hooked the wastegate back up, oil psi dropped. Bearings were fine, couldn't find a reason. I tried over filling, under filling, everything, nothing worked. I ended up getting a new motor because no one could figure it out.
08-10-2006, 03:37 PM
#18
Launching!
Thread Starter
iTrader: (3)
Join Date: Feb 2002
Location: Wilmington, NC
Posts: 281
Likes: 0
Received 0 Likes
on
0 Posts
TS6,
man you know how to take the wind out of a guys sails..lol I do have a question though.. did you have excessive crank case pressure? I was told that since my breathers are where everyone else puts them on the valve covers, that when the crank case pressure from blow by is working its way up and out of the motor it limits the amount of drain back through the lifter valley and cylinder heads.. I do have crank case pressure issues I have been battling and if the extra oil doesn't cure this,, i guess the motor is coing out which I really don't want to do again right now with all my other projects looming.
Chris
man you know how to take the wind out of a guys sails..lol I do have a question though.. did you have excessive crank case pressure? I was told that since my breathers are where everyone else puts them on the valve covers, that when the crank case pressure from blow by is working its way up and out of the motor it limits the amount of drain back through the lifter valley and cylinder heads.. I do have crank case pressure issues I have been battling and if the extra oil doesn't cure this,, i guess the motor is coing out which I really don't want to do again right now with all my other projects looming.
Chris
08-10-2006, 04:10 PM
#19
HV and stock oil pan do not mix. Sounds like you are pushing all the oil to the top of the engine. Typically you want to run stock volume, but higher pressure if possible.