problems with breaking up right after 10lbs

[oomuskablindoo]

Hey, here's a little background information. I've got a 95 gsr which i was running at 8lbs via an 8lb pulley. Everything ran fine. However, I recently swapped blocks to a golden eagle built b16 bottom end and with this swap I used an endyn (yea .... endyn) stepper pulley to up the boost. Well, in doing this, it upped the boost to 12 lbs. I realize that 12 is pushing the jrsc to its limits ... but i'm not worried about that at the time being. All i want is for the car to run right with no problems. Here's my problem - before upping the boost, the car ran completely fine throughout the RPM range ... except for a minor breakup at 4500, which it would pass up and run fine at 4550+ rpm. Now, the car runs fine at any RPM, still the minor breakup at 4500 but its a lot less noticeable. If I run partial throttle throughout the RPM band (enough not to pass 10lbs) the car runs like it should. If I give it full throttle and its not at 10lbs it runs like it should. As soon as it reaches 10.1lbs, it breaks up fairly badly, no matter what RPM range. My EGT readings are the same as the were before, no change in that. The air/fuel guage sometimes does run very lean, but sometimes runs just a bit past stoich in the rich side. As far as fuel/engine management, I'm using the JR FMU, MSD 6 AL, MSD BTM, NGK 7 plugs, venom 255 injectors (i need bigger, i i know) I'm running 94 octane with ignition timing of 8 BTDC. I've tried running the btm anywhere between 0 and 1/2 a degree retard per lb of boost. I found the best setting was about 1/3 degree retard. I thought it could be the map sensor sensing boost, but that shouldn't happen till 11.5 or so lbs I think. And 10lbs should definately be okay. Anyone got any ideas? Once again, I know i shouldn't run the jrsc at 12lbs, and i'm not planning on it really - just want to get it running okay for the time being. Anyone got a hot setup for me?

[Jaker]

If your car is running anywhere leaner than 12.5:1 at full throttle, you're going to see internal engine parts outside the engine really soon. With so little boost retard, and what sounds like a really lean setup, I'm not surprised you're not running very well.

Richen that puppy up lots.

[oomuskablindoo]

i'm taking the stepper pulley off and i'm just gonna run 8lbs again ... its not worth the risk of ripping the charger up. I'm not really all that worried about this setup being fast anyway - i'm gonna take the blower off and go turbo soon. Anyway - you really think the retard isn't much. Jackson says 10 btdc with no retard is fine at 93 octane gas at 6lbs. With 94, 8 btdc with about 1/3 per lb at 10lbs of boost should be fine in theory

[oomuskablindoo]

i'm gonna just drop the stpper pulley like i said before ... i appreciate the help though. I didn't realize the displacement would matter at all ... but i'm between 1.7 and 1.8 liters with the block - its bored to 84 mm. How does displacement increase/decrease ffect boost?

[JRCivic]

I think more information will be helpful before we may be able to help... how about trying to describe the symptom better.
First, the Endyn pulley didn't just make 4 psi more boost than you had before... it only made 2 psi... and reducing your displacement from 1.8L to 1.6L made the other 2 psi. If you remove the stepper pulley, you will probably be making around 10 psi.
The retard on your MSD BTM doesn't sound bad... you might try to bring the retard up to 3/4 degree per pound of boost and see if there are any changes in the symptom. The more advance you can run safely, the more power you will make. So, experiment with the retard knob a bit.
Your A/F gauge readings sound a bit scary... if under WOT you are not seeing the far right hand yellow PLUS the next two or three green LED's light up... you are WAY LEAN. So, if you are seeing all yellow... and the occasional red LED... stop boosting until you find the reason for your fuel delivery inadequacies.
Concerning your MAP sensor... I see no reason for this to be the problem since you have not indicated that it is seeing boost... you didn't mention in your list of mods either a JR MAP mod or the use of an engine management system (like Hondata) in which you would need to allow the stock MAP sensor to "see" boost. Also, if you in fact do overboost the MAP sensor's voltage limits, the ECU will initiate a Check-Engine light indicating a MAP sensor failure. Since you didn't mention throwing a code, I suspect this is NOT the problem.
Lastly, what about spark plug gap ??? At 12 psi, I would suggest a fairly tight gap to avoid blowing the spark out and mis-firing... say .035".

[blownLS]

Think of it this way;

At 10psi your blower is attempting to stuff 3.0 liters of air into 1.8 liters of space. So if you do not change your blower speed, but decrease the space for that 3.0 liters of air to be stuffed into, what will happen to the pressure?

It should increase at the same rate of change as the displacement change.

It is a lot easier to understand when you start thinking in measurements of Bars instead of PSI. For every 1 bar increase you are doubling the air volume of your engine.