Different boost readings (Is this normal??)

[Mighty1]

Now that the truck is broken in, I have been getting on it testing everything out before I go to the dyno. My pulley combo on a stock engine should produce around 13 lbs of boost with Novi2000. My engine is not stock. My heads are fully ported and intake has been cleaned up, x-metal tb, forged pistons/rods, bassani headers, no cats, true dual 3" exhaust, custom cam for blower, etc.

With the boost gauge hooked into manifold vacuum (along with brakes, and everything else that needs vacuum or boost) I am getting a max of 5lbs of boost. This doesn't seem high enough. I next get a reading at the pipe from the blower to the intercooler and this shows no vacuum and constant boost pressure of between 2-5lbs, even while just driving normal. When on the gas hard I got max boost of 10lbs. So to see if it is my intercooler causing the problem I get a reading from the pipe that goes between the intercooler and the TB and it goes to a max of 7.5lbs of boost.

My intercooler is costing me 2.5lbs of boost?? Does that sound right?? And then I am loosing another 2.5lbs once into the intake??

Is this normal or what the heck is going on???

 

[mysrt10]

I know several guys have had lower than expected boost levels with ported heads. That is normal.
Also, switching to t-bolt style clamps will help eliminate additional boost loss through your system.

 

[Mighty1]

I know several guys have had lower than expected boost levels with ported heads. That is normal.
Also, switching to t-bolt style clamps will help eliminate additional boost loss through your system.

All clamps are t-bolt. I expected the port work to make the boost lower but are the differences in the boost readings normal? Like an intercooler costs 2.5lbs of boost and then loose another 2.5lbs going into the engine? Something just doesn't seem right.

Where does everyone else hook their boost gauge up at?

 

[yellowfever#154]

Sounds to me like you have a leak somewhere, I have mine plumbed into the intake just behind the throttle body.

 

[Mighty1]

Could pressure be leaking from the IAC valve? I have a filter on this instead of being plumbed into the intake tubing. Does the IAC close under full throttle?

 

[yellowfever#154]

Try plugging it off to see. You will have to screw in your idle screw a fair ways to get the truck to idle if you plug it off.

 

[VENOMOUS1 RACING]

Could pressure be leaking from the IAC valve? I have a filter on this instead of being plumbed into the intake tubing. Does the IAC close under full throttle?

Yes an intercooler can lose a couple pounds of pressure but introduce a cooler charge therefore preventing detonation.

Yes....the IAC is closed on wot and anytime you have the pedal down, once you lift, IAC takes over idle and decel.

 

[Mighty1]

Yes an intercooler can lose a couple pounds of pressure but introduce a cooler charge therefore preventing detonation.

Yes....the IAC is closed on wot and anytime you have the pedal down, once you lift, IAC takes over idle and decel.

Thanks for that info Was getting worried about what the IAC did under full throttle.

So then the drop in pressure from the intercooler is within limits at 2.5 lbs. So I have 7.5lbs going into the intake but the reading from the boost gauge hooked into the brake booster line (along with meth and extra fuel pump, etc.) at the back of the intake is 5lbs. Would another 2.5lbs drop off from the front to the back of the intakebe normal?

 

[VENOMOUS1 RACING]

Are you conducting these readings under same conditions and under same load? Your manifold positive pressure should be the same after the intercooler as it is the the manifold unless your manifold gaskets are leaking and blowing boost out before your boost guage nipple.
No you shouldn't loose another 2.5 lbs!
Blow off valve/wastegate working right?

 

[JeffBoyette]

Boost at the rear of the manifold could very well be 1-2 pounds lower than before the tb butterflies or the fitting right below the tb. The intake plenum size is fairly small for the displacement of the engine coupled with modest intake runner size. Imagine it as a reserve tank of compressed air waiting to be sucked down. At rpm when the engine is in boost you have 10 thirsty cylinders taking gulps of air in pulses. These waves of vacuum pulses will reduce pressure at the rear of the manifold compared to in front of the tb. Also that rear fitting is right near the opening of one of the runners. This distance from the tb and proximity to the runner provides a good vacuum signal to the accessories and further strengthens the likelyhood boost pressure measurement would be lower at this location. .hope this makes sense.

 

[Mighty1]

Are you conducting these readings under same conditions and under same load? Your manifold positive pressure should be the same after the intercooler as it is the the manifold unless your manifold gaskets are leaking and blowing boost out before your boost guage nipple.
No you shouldn't loose another 2.5 lbs!
Blow off valve/wastegate working right?

Taking the readings on the same day, making a blast in the same area, using the same gauge and same line. Manifold gaskets are new but that doesn't mean they aren't leaking I suppose. Truck seems to be running fine, just not making as much boost as I was hoping.

How do you check the blow off valve? I am using the paxton one. Although when I check the boost before the intercooler (in same pipe the blow off valve is in) I'm getting 10lbs max.

 

[JeffBoyette]

Taking the readings on the same day, making a blast in the same area, using the same gauge and same line. Manifold gaskets are new but that doesn't mean they aren't leaking I suppose. Truck seems to be running fine, just not making as much boost as I was hoping.

How do you check the blow off valve? I am using the paxton one. Although when I check the boost before the intercooler (in same pipe the blow off valve is in) I'm getting 10lbs max.

The intercooler causes a very slight restriction and by cooling the compressed air it condenses it reducing pressure. There will be a pressure differential before and after the intercooler because of this and on a centrifugal supercharger or turbo there is a difference between the supercharger and the tb, and the pressure in the intake itself. The blow off valve helps to vent those pressures when the tb valves are closed and to regulate the amount of pressure before the tb. At high boost levels or higher volume supercharger, larger or multiple blowoff valves are used to allow more pressure release. Your combo is tested and true so I don't think that is your problem. I also don't think you have a leak.

Too often its easy to get caught up in boost numbers. If you are making proper power with said pulley at safe temps and ratios without detonation.... Your boost pressure gauge should be used as a reference for anomolies. Remember that the map sensor is by the tb for a reason. I would discount any reading from the rear of the intake for reasons stated earlier.

 

[Mighty1]

Boost at the rear of the manifold could very well be 1-2 pounds lower than before the tb butterflies or the fitting right below the tb. The intake plenum size is fairly small for the displacement of the engine coupled with modest intake runner size. Imagine it as a reserve tank of compressed air waiting to be sucked down. At rpm when the engine is in boost you have 10 thirsty cylinders taking gulps of air in pulses. These waves of vacuum pulses will reduce pressure at the rear of the manifold compared to in front of the tb. Also that rear fitting is right near the opening of one of the runners. This distance from the tb and proximity to the runner provides a good vacuum signal to the accessories and further strengthens the likelyhood boost pressure measurement would be lower at this location. .hope this makes sense.

Yes it does make sense. So maybe nothing is physically wrong with my setup. I'm now wondering if I should move my permanent boost reading along with my meth and 2nd fuel pump activation lines to the front of the intake? Maybe I should try to take a reading there first and see what it's at?

 

[SANTEEN]

Are you conducting these readings under same conditions and under same load? Your manifold positive pressure should be the same after the intercooler as it is the the manifold unless your manifold gaskets are leaking and blowing boost out before your boost guage nipple.
No you shouldn't loose another 2.5 lbs!
Blow off valve/wastegate working right?

Scotty may have something there. I may be wrong, but I thought the Paxton BOV was set at 7lbs. They're adjustable. DO you hear the BOV releasing pressure while you're on it?

 

[NSDQ]

Have you dyno'd your truck to see what your hp is so that you can compare it with other Paxton SRT-10's? I've been out of the FI game for a while, but it sounds to me like your sensor is not placed in the right spot. I wish I could remember where mine was placed (on a different vehicle, not my 10).

 

[Mighty1]

Have you dyno'd your truck to see what your hp is so that you can compare it with other Paxton SRT-10's? I've been out of the FI game for a while, but it sounds to me like your sensor is not placed in the right spot. I wish I could remember where mine was placed (on a different vehicle, not my 10).

Haven't dyno'd yet as I just finished breaking in the engine and started testing everything to make sure all was good. Don't want to get on the dyno and have something stupid break or cause a problem and not be able to finish tuning.

As an example, my 2nd fuel pump just starting blowing a fuse so now I have to track that down. I've seen some slight belt dust on the bracket for the blower so I am gonna send the pulley out to be coated. I want everything perfect when I finally get to the dyno so I can get this thing done once and for all. (I hope lol)

 

[NSDQ]

No shame in getting things buttoned up before you go WOT on the dyno. The dyno can be your best friend or your worst nightmare. Hopefully the issue is that with your heads you're creating more flow and creating the same power but with less boost.

 

[505'sFastestViper.]

if you went crazy on your heads you miht not ever see 13 psi from that lil blower

 

[Mighty1]

if you went crazy on your heads you miht not ever see 13 psi from that lil blower

I know and I am spinning it at it's max already. I could maybe drop down to a 2.75 blower pulley from 2.85. That would give me about 2000 more impeller rpm but it would also be over the 55k that paxton says is the max and more chance of belt slipping.

 

[Mighty1]

The intercooler causes a very slight restriction and by cooling the compressed air it condenses it reducing pressure. There will be a pressure differential before and after the intercooler because of this and on a centrifugal supercharger or turbo there is a difference between the supercharger and the tb, and the pressure in the intake itself. The blow off valve helps to vent those pressures when the tb valves are closed and to regulate the amount of pressure before the tb. At high boost levels or higher volume supercharger, larger or multiple blowoff valves are used to allow more pressure release. Your combo is tested and true so I don't think that is your problem. I also don't think you have a leak.

Too often its easy to get caught up in boost numbers. If you are making proper power with said pulley at safe temps and ratios without detonation.... Your boost pressure gauge should be used as a reference for anomolies. Remember that the map sensor is by the tb for a reason. I would discount any reading from the rear of the intake for reasons stated earlier.

That is a very good point. Makes me think I should move my boost gauge line closer to the TB.