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What pulley do i have and why so much boost.

C

ctspoolintsi

New member
well i was told my car has a 2.75. so i went out and measured it just in case and from what i am reading you measure from the dead center of the pulley and x2. i am seeing 1.50 so it should be a 3.0 pulley. if im wrong on the measuring please tell me. but if it is a 3.0 why am i seeing 17psi ? mods below

- Gen V Supercharger 17psi, Thrasher-Performance Modular Interchangeable Pulley System
- 75mm North Star Throttle Body, 85mm LS6 Mass Air Conversion
- 4 inch Air Intake
- 42.5 lb Injectors
- Alcohol Systems Methanol Injection System
- DHP Computer Tuned for Supporting Mods
- Scanmaster II
- Pacesetter 1-3/4 Race Headers with 3 inch Downpipe, Dual 2.5 Tailpipes w/ Flowmaster 40 series Mufflers
- ZZP Performance Full Stack Stage 2 Liquid to Air Intercooler with Stage 2 Heat Exchanger and Cooling Fan
- ZZP Performance 1.9 Modded Rockers
- ZZP Performance Under-drive Water Pump Pulley
- ZZP Performance Alternator Amp Booster
- New ZZP 10.3 Wires & MSD Coil Packs
 


IIRC, the Gen V is a more efficient blower, so a 3.0 on a Gen V will net more boost than a 3.0 on a Gen III. As long as you are scanning and have no knock then you're good to go I would think.
 
17 psi of boost seems way to high. measure with a ruler or tape measure across the hole diameter, should be more accurate then approximating the center. 3.0 pulley should not be 17psi, maybe 13 or 14psi peak before a shift. I'm not sure you gen get a Gen 5 to 17psi.

How are you measuring the boost pressure, the scanmaster or a mechanical gauge?

P.S. MSD coils are none to fail, they don't offer any added performance and are less reliable than stock. But they are RED!
 
sseilmnop said:
17 psi of boost seems way to high. measure with a ruler or tape measure across the hole diameter, should be more accurate then approximating the center. 3.0 pulley should not be 17psi, maybe 13 or 14psi peak before a shift. I'm not sure you gen get a Gen 5 to 17psi.

How are you measuring the boost pressure, the scanmaster or a mechanical gauge?

P.S. MSD coils are known to fail, they don't offer any added performance and are less reliable than stock. But they are RED!
Click to expand...

Fixed.. None to fail could be interpreted very differently
 
Im not an expert but i was just wondering if the pulley maybe is a 2.75... maybe the measurment is where the pulley rides. and the lipon the side of the pulley is prbly about .125 so thats where the extra .25 comes from... idk just a thought
 


sounds to me like something is wonky with the tune.
too much boost and not enough timing? idk, im a noob.
 


Your prolly seeing so much boost because your not flowing the air as much as you should be through the motor. 3.0 on genV = 2.8 on genIII. IIRC you need a cam and full size IC to run that small of a pulley with an agressive tune. You are prolly running very rich and low timing to keep your KR down. My guess would be to pulley up and get re-tuned and you will run faster.
 
thomas mcnulty said:
What proof do we have that msd coils suck? Just curious. Did uncle jeb run one with little success?
Click to expand...

I've heard on many forums they're known to crack, in fact I can remember several cases of defect returns at work (Advance) on MSD coils because they did indeed crack and/or just stop working after very short mileage.

In regards to GM vehicles, I believe they have less output than stock coil packs... this article is from ZZP on useless mods...

Aftermarket coil packs
The stock ignition on a Grand Prix is very good. It is so good that we run stock coil packs on all of our cars at ZZP. Failure rate of stock coil packs is low and the spark output is extremely high. We have A/B dyno tested aftermarket coil packs and seen no difference in HP. We have seen many aftermarket units fail and when customers have a problem it’s very hard to diagnose with extra unneeded mods on the car.


The ignition control module sits under the coil packs. It sends a limited current to the coils for a predetermined pulse (dwell). You cannot change the wires or the coils to get ‘more spark’ because the ignition control module will not send more power to the coils. You would have to change the ignition control module for a significant increase. The MSD coils and/or the MSD wires are a downgrade in your ignition system in regards to the 3800. The best you can do is run a wire with slightly less resistance or more insulation. These are very small improvements but the only meaningful ones.
 
well i re gaped the plugs to .35 and i have 0 knock the entire pull. talked to the actual builder of the car today (guy before one i got it from) he helped alot. its a 2.76 pulley smallest he said they had. and he ran a 12.3 in the 1.4th with that . so now i got no knock im going to take it to dyno and track and see whats truly going on
 


For 17 psi?

Op, have you confirmed the map reading is 14.6? Typically the pcm has some issues when going past 14.6 psi boost.
 
Without a cam that could be possible he's seeing boost pressures that high. On my Gen 3 with an xp cam and IC I would see 13-14 psi on a 2.8 pulley. But without a cam and a with a gen 5 and a slightly smaller puelley I can see his boost getting that high, especially if hes shifting higher.

One question: Do you still have a cat?
 
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