You should be around 36-39 PSI.
85 adjustable fuel regulator question
Instructor
Joined: Jan 2008
Posts: 217
Likes: 0
From: Coopersville MI
Stock fuel pressure is not that high on an 85. You will cause the car to run real rich until the computer and 'learn' and make the adjustments. When I did mine, I think i bumped my fuel pressure to 41psi, from 39 stock. Any more than that and I feel I should have it retuned as the 85 cars have 24lb injectors and 86+ have 22lbs with higher pressure.
Thread Starter
Racer
Joined: Jan 2007
Posts: 252
Likes: 5
From: bethlehem PA
Melting Slicks
Joined: Mar 2008
Posts: 2,141
Likes: 76
From: Santa Maria, CA
Read the TPiS Hints Book. They have dyno test results for a stock 85 with fuel pressure increased to 47 PSI. It is not too high. There's a section in their book dedicated to the subject.
Melting Slicks
Joined: Sep 2010
Posts: 2,422
Likes: 203
oK!!! you crank up fuel pressure... you still need to balance out with a tune to match..
it will do very little for performance!!!!! I have played with pressure all they way up to 60lb down to 38 experimenting years ago
it will do very little for performance!!!!! I have played with pressure all they way up to 60lb down to 38 experimenting years ago
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Melting Slicks
Joined: Mar 2008
Posts: 2,141
Likes: 76
From: Santa Maria, CA
I did not have to retune. I have a tuner program and I monitored BLMs after the change.
The way TPiS explains this is that the increase in pressure better atomizes the fuel. Better atomized fuel burns more completely and actually creates a leaner condition. If you look at some of FICs videos, you will see that the stock injectors shoot a stream of fuel rather than a spray. Now look at the 85 injectors. They are 24 lb and operate at a lower pressure than later years. The result is less atomization. Chevy figured it out and fixed the problem in 86 and up. I'm not saying you will see a significant change in performance. The few Hp gained is not enough to feel in the SOTP. But you will get a better burn that the 85 chip can easily compensate for.
The way TPiS explains this is that the increase in pressure better atomizes the fuel. Better atomized fuel burns more completely and actually creates a leaner condition. If you look at some of FICs videos, you will see that the stock injectors shoot a stream of fuel rather than a spray. Now look at the 85 injectors. They are 24 lb and operate at a lower pressure than later years. The result is less atomization. Chevy figured it out and fixed the problem in 86 and up. I'm not saying you will see a significant change in performance. The few Hp gained is not enough to feel in the SOTP. But you will get a better burn that the 85 chip can easily compensate for.
Safety Car
Joined: Jan 2004
Posts: 3,759
Likes: 8
Could you do any damage to the fuel system if you raise the fuel pressure up too high? I was thinking of putting in an AFPR on my 89 to try and get my BLM numbers down. So since my fuel pressure with the stock FPR disconnected is 42-43 which is where it should be. I'll have to go higher than the stock setting.
Melting Slicks
Joined: Mar 2008
Posts: 2,141
Likes: 76
From: Santa Maria, CA
Could you do any damage to the fuel system if you raise the fuel pressure up too high? I was thinking of putting in an AFPR on my 89 to try and get my BLM numbers down. So since my fuel pressure with the stock FPR disconnected is 42-43 which is where it should be. I'll have to go higher than the stock setting.
Pro
Joined: Mar 1999
Posts: 678
Likes: 0
From: Oslo, Norway
I have an 85 4+3 z-51.
I bought an adjusable fuel pessure regulator.
It is right that the 85 have 24 lbs/h injectors. They do not atomize good . For the stock engine one should not increase pressure much. One reason for that. Over I think it is 3/4 of full throttle the ECM do not read the Oxygen sensor and adjust the injectors dutys cycle only after a table and that means fixed dutycycle for a spcific position of the TPSover 3/4 throttle. With an adjusted fuel pressure this will of course be wrong especially with as high as 47 psi pressure.The engine will be rich then. The chip has to be reprogrammed then or a new chip.
My advice will be go for Gen III Bosch injectors from FIC . They atomize very good and manage very high fuel pressures so with modified engines they manage to give the engine quite a volume of fuel.
I installed those and I got better start up, better throttle response and if I am not wrong I seem to feel a better pull(this may be placebo of course, have not dynoed yet)
I bought an adjusable fuel pessure regulator.
It is right that the 85 have 24 lbs/h injectors. They do not atomize good . For the stock engine one should not increase pressure much. One reason for that. Over I think it is 3/4 of full throttle the ECM do not read the Oxygen sensor and adjust the injectors dutys cycle only after a table and that means fixed dutycycle for a spcific position of the TPSover 3/4 throttle. With an adjusted fuel pressure this will of course be wrong especially with as high as 47 psi pressure.The engine will be rich then. The chip has to be reprogrammed then or a new chip.
My advice will be go for Gen III Bosch injectors from FIC . They atomize very good and manage very high fuel pressures so with modified engines they manage to give the engine quite a volume of fuel.
I installed those and I got better start up, better throttle response and if I am not wrong I seem to feel a better pull(this may be placebo of course, have not dynoed yet)
Safety Car
Joined: Jan 2004
Posts: 3,759
Likes: 8
I have an 85 4+3 z-51.
I bought an adjusable fuel pessure regulator.
It is right that the 85 have 24 lbs/h injectors. They do not atomize good . For the stock engine one should not increase pressure much. One reason for that. Over I think it is 3/4 of full throttle the ECM do not read the Oxygen sensor and adjust the injectors dutys cycle only after a table and that means fixed dutycycle for a spcific position of the TPSover 3/4 throttle. With an adjusted fuel pressure this will of course be wrong especially with as high as 47 psi pressure.The engine will be rich then. The chip has to be reprogrammed then or a new chip.
My advice will be go for Gen III Bosch injectors from FIC . They atomize very good and manage very high fuel pressures so with modified engines they manage to give the engine quite a volume of fuel.
I installed those and I got better start up, better throttle response and if I am not wrong I seem to feel a better pull(this may be placebo of course, have not dynoed yet)
I bought an adjusable fuel pessure regulator.
It is right that the 85 have 24 lbs/h injectors. They do not atomize good . For the stock engine one should not increase pressure much. One reason for that. Over I think it is 3/4 of full throttle the ECM do not read the Oxygen sensor and adjust the injectors dutys cycle only after a table and that means fixed dutycycle for a spcific position of the TPSover 3/4 throttle. With an adjusted fuel pressure this will of course be wrong especially with as high as 47 psi pressure.The engine will be rich then. The chip has to be reprogrammed then or a new chip.
My advice will be go for Gen III Bosch injectors from FIC . They atomize very good and manage very high fuel pressures so with modified engines they manage to give the engine quite a volume of fuel.
I installed those and I got better start up, better throttle response and if I am not wrong I seem to feel a better pull(this may be placebo of course, have not dynoed yet)
Melting Slicks
Joined: Mar 2008
Posts: 2,141
Likes: 76
From: Santa Maria, CA
Just try it. I'm not surprised it runs leaner. The better Bosche spray pattern atomizes better and burns better giving a lean condition. Make sure you disconnect the battery to clear the chip memory. Then give the computer some time to relearn.
