My car has the V-1 Old school kit, headers, free exhaust, bosh 3 injectors and some stiffening items.Currently just finished an EBL Conversion to get rid of the MAF. Previous to this, I had had my MAF go down and was only able to keep the car running by unplugging the MAF. So, as you can imagine I was not driving around with much throttle. Now that I am working on getting the EBL dialed in, I have noticed my boost does not respond as quick as I think it should. When I go to half throttle or so, I don't seem to get that snap to 0psig and start to build a few pounds like my Corvette does (96 LT4 with Procharger kit - 6-speed)

It feels as though the boost comes on very slow. Initially I thought it was either belt slip or the bypass valve was not functioning correctly.

So, I have tightened the belt to a 1/4" of play. It was about the only refrence for tightness I could find.

I removed the bypass valve and bench tested it with vacuum to open and closes pretty quickly when vacuum is removed.

I checked my vacuum lines, the one to the bypass valve is on the same run as my A-pillar gage. With the line removed from the bypass valve, the A-pillar gage shows very little vacuum. If I cap the line it goes right to 20inHG. So, looks like the lines are all sealed and functioning.

Is my mind playing tricks on me or do I have an issue?

 

Might not build boost under half throttle. Keep tuning and go deeper throttle to see when it starts

 

Unfortunately, we are getting rain here today. Last night I was keeping it in 2nd/3rd to help get some VE coverage. Everything is looking pretty good. Did a short WOT hit to about 3500RPM and fueling looked good.

 

I've had a bunch of vortech's and not one of them built boost under part throttle. My T-trim will build boost after 3k or so only when WOT or damn near WOT.

I wonder what the science is behind this? I know on turbo diesels they make boost at part throttle, but diesels don't actually have a throttle. Perhaps with the throtle blades partially open there is a pressure differential before and after the throttle blade and what pressure escapes past the blades is less than the engine requires? Kinda more of a reason to add a second map sensor in the compressor housing.


-- Joe

 

I just dont think they have the impeller speed to build boost there. And there really isnt any reason to if you are trying to keep impeller speed at or below its limits at peak rpm. Boost at wot is what you want. And again maybe a less efficient engine can see boost at half throttle. A good flowing engine might consume that airflow

a turbo is much more prone to sizing on the small side to get high shaft speed at part throttles. Then again there are setups like my new bbc that doesnt make boost til wot above 4000 rpm and need nearer 5300 to get desired target boost. Its all in how you size it and where you want power

 

i would assume your bypass valve is open at idle. full throttle results in zero manifold vacuum which would close the bypass valve, in turn allowing boost. the supercharger is dependant on engine rpm for spool, but turbos can sized to spool quicker or have variable vanes to spool them right off idle if needed.

 

It may be possible with the headers, removed cat, 1.6 rockers, 3.42 rear gear and tuning the thing is doing better than the 6PSI blower pulley can keep up with at low RPM. I will just have to keep an eye on it as I get the tune worked in.

 

It's absolutely 100% open at idle, although it closes fairly easily with a little throttle. My new BOV is absurdly loud so there is never a question of when it's open or closed lol.

As Orr suggested, my impeller speed is probably around 15-20k tops before 3,000 RPM so it makes sense that it's not flowing much air.

-- Joe

 

I can build boost rolling into the gas at less than half throttle. I am looking at an old log and at 3200 rpm, I see 122kpa and tps% is 50%, and at 2900 rpm the boost is 113kpa and tps% is 40%. Buy one of those boost leak testers that has a guage on it and pressure test your intake track. I had about 20 different leaks from everywhere you can imagine. I had to put hose clamps on all vacuum lines, tighten the crap out of all intake clamps and buy better clamps. I even had a leak at my intake gaskets which lead to me taking off the intake multiple times. I finally sealed the intake gaskets with hylomar on all surfaces, head, intake, both sides of gasket, throttle body, etc. I also had a major boost leak at my throttle body on the side where the TPS sensor sits. I measured the OD of that shaft that runs through the TB and found some rubber thin washers and o-rings to seal up both sides of the throttle body. Before sealing the TB, you could hear air blowing out of each side of the TB while doing the boost leak test.

Forced induction is a big pain in the *** if you ask me. Got to have all your T's crossed and I's dotted if you want to make any decent power.