tobb14

Does anyone know how a centrifugal supercharger to start boosting earlier. I have a C6 Grand Sport and it seems like my car doesn't really start boosting until I'm really high in the RPM's 4500-6000rpms. Even under hard acceleration my car only made about 2lbs of boost and this was a 60 to 140 mph pull. The boost was building but at that speed I'm pulling out of the gas. I thought it was my boost gauge was not working but the MAP sensor was reading 17.4psi which equates to about 2.7lbs of boost. I have the 3.8 wheel on the supercharger and wondering if i change it out to the 3.4 wheel, it will start boosting earlier. If anyone has any suggestions please provide your thoughts.

JetstreamGS

How much peak boost do you make? What supporting mods? I run a 3.6 and it doesn't feel soft down low at all. A 3.4 would spin it faster and create more boost throughout the rev range.

tobb14

I only have long tube headers 1 7/8, high flow cats, and methanol. My peak boost so far is only 3 lbs maybe. I feel like I have to run it to 200 mph to get 6lb pull. When you switched to the 3.6 did you have to replace the belts

JetstreamGS

Something doesn't sound right if you're only seeing 3lbs. Have you had it on a dyno? What power does it make? Yes you need a different belt.

Mike's LS3

Stock LS3 with SI V3 A&A 3.8" with oem NPP:

Make sure you are commanding 100% throttle in the logs when you are reading Kpa or psi.

What MAP sensor do you have? I am running ZR1 MAP sensor.

Looking back at some 2nd gear W0T logs:

[RPM / Boost

4100 / 3.2 psi
5300 / 7.2 psi
5900 / 9.0 psi
6200 / 10.0 psi

Since this log, I have swapped my complete exhaust with Z06 exhaust, I probably lost about a 1/2 psi due to less restriction.

However, my Hp and torque went up throughout the entire rpm range.

Look at your Kpa or boost graph, it should be a smooth increase as rpm increases. If you have dips, you might have belt slippage. Check your tensioner, my (not the latest) tensioner is tightened to about 65-70% of range as A&A recommended for that tensioner.

tobb14

I haven't taken it to the dyno yet. In the past it laid down 593 rwhp and that was with stock exhaust with a tune done by tick performance. The second time it was dyno in el paso it made 623rwhp. After the long tube headers, high flow cats and methanol it hasn't seen a dyno. I just tuned the MAF and VE tables and plan on taking it to be dynoed when i get paid to see where i truly stand. MTF

tobb14

hey,

Thanks for the advice on the throttle. It looks like i was only at 83%. As of now i'm running the stock 2 bar map sensor. I looked at my MAP kpa in HP tuners and it flat lines after 120 kpa, meaning it doesn't read anything above that. I'm assuming that I may have to upgrade to the ZR1 map sensor and re-tune the car. HP tuners also shows that the car is making 635hp i'm assuming that that's engine hp not rwhp. I know that boost is being delivered just don't know how much.

1966427

How much power and torque did you gain from ls7 exhaust?

Unreal

Belt slip or boost leak. You have issues. Fix them first.

HP reading in HP tuners is so far off it is a joke. Ignore it. Get a map sensor that reads, otherwise tuning your VE is pointless at this point.

DanC8

I believe the stock MAP sensor is only 1 bar so you can't read boost with HP tuner. If you want to check your boost, hook up a mechanical boost gauge to the vacuum line.

Mike's LS3

After having the emissions recall (added 2 cats at mid pipe, 4 total) my car was not happy. Swapped complete LS7 exhaust (2 cats) and with a tune picked up 28 Hp/23 torque on the same dyno with the same tuner, 595/516 Hp/torq. on 91 octane, no meth.

Mike's LS3

The stock MAP sensor is 1 bar, I recommend the OP to install a ZR1 3 bar MAP sensor and adjust the tune.

tobb14

I changed my MAP sensor to a ZR1 and the car wouldn't crank because my OS system doesn't have a 3 bar option in HP tuners. I changed the linear settings to stock ZR1 readings but again with out being able to tell the car it's a 3bar not a 2 the car won't start with this sensor.

Unreal

All you need to do is set the linear and offset and it should be just like before.

Nothing to do with not cranking.

Mike's LS3

Make sure the linear and offset values were written in the new tune with correct values. Car should start up as normal.

ZR1 MAP settings:

MAP Linear: 312.50
MAP Offset: -11.25

Daddy Freeman

Wastegate/BOV stuck open?