fenix99

iTrader: (1)

ok guys, the kit is a Vortech V-9 G trim w/ Aftercooler and the 3.125" pulley on the supercharger....i ran the boost gauge lines off the brake boost/vacuum...and after installing and checking everything we made a few runs and only saw 5, 5.5, and 6psi MAX no more no less..

now the guys at vortech told me it could be that we're not taking the car to redline, but we were shifting at about 5800 to be safe on the first few runs, and also the guy told us if we had changed the intake manifold on the car etc.. yes more volume of air but why the drop in boost? is what i dont get...he tried explaining but i wasnt getting the picture maybe u guys can help

Car Mods are as follows (so nobody asks later lol)
2000 Trans Am WS6, 19000miles
Vortech V9 Gtrim w/ aftercooler (3.125" pulley)
SLP Lt's-Ypipe,no cats, Borla catback
FAST 78mm Manifold/Throttle Body
Granatelli MAF (80mm?)
38lbs injectors and the SuperChips tune that came with the kit,
STOCK EVERYTHING ELSE

-What do you think it could be because alotta $$$ was paid for this kit assuming it would boost 8-9psi and its pegging the boost gauge at 5.5-6psi the MOST, so im here like where are my 8-9LBS???

thanks in advance any opinions are greatly appreciated

ABeasst

iTrader: (5)

boost is a measure of restriction so with the ability to move more air boost will drop. however I would not have thought your mods would reduce it that much.

fenix99

iTrader: (1)

thats whats messing with my head boost is a measure of restriction lol i do get what ur tryin to say with that but at the same time for some reason its sounds retarded to me...i duno thats exactly what One of the guys told me at Vortech but then again c'mon im losing THREE FULL psi... thanks for the response tho'

mahhddgtp

There must be a leak somewhere, you won't drop 3psi from those mods. What cam do you have?

fenix99

iTrader: (1)

stock motor, stock heads/cam stock everything except for FAST manifold/TB

GTOLarry

I have an S-trim kit on my O4 GTO.

Well the part about redline could be part of it. I know mine jumps up about 1.5 psi in the very last part of the rpm range. I only hit 9psi at 6200 rpm.

Do you have a catch can on your motor? If so did you add a check valve to prevent it blowing back into crankcase and essentially creating a boost leak.

Bypass valve may not be sealing well.

Check all of your piping, clamps etc.

If you have mods that are an improvement over stock intake... manifold, cam, throttle body etc it may reduce boost, but increase airflow. You are not interested in boost really. You are interested in how much air is flowing through. More air allows for more fuel which can make more power.

Best way to tell what is really going on is to put it on the dyno and see if you are getting the power you expect.

DeltaT

iTrader: (5)

Since the boost of a centrifugal is proportional to its rpm, you need to spin it up to get the last 2-3 pounds. Stopping at 5800 I am not surprised at all with those numbers.

Try 6200 as your next stop, as long as AFRs are reasonable - I would target 11.6-11.8 as an early target. I bet you hit 8+ there.

Jim

fenix99

iTrader: (1)

k cool thats more like the answer i wanted to hear. Noo i dont have catch can on it

What i also thought was the blow off valve setup...i think its losing some boost because of that. The blow-off is tapped into the aftercooler and then the air that is expelled to the atmosphere is routed with a rubber hose back into where the filter is(before it is processed by the blower).

My question is would bypassing the blowoff valve (disconnecting and blocking off the 'tee' from the brake/vaccum line) give me the boost levels i think i should have; ok taking into consideration the manifold/TB etc. takes away some boost so i know its not going to give me exactly 8-9psi like Vortech advertises but i should be around 7-8psi, not 5.5psi, the car still has a stock motor basically i would expect a pressure drop like that with heads etc.

thanks for the info though i get a better understanding of everything now...BaDaSS gto by the way, very clean

fenix99

iTrader: (1)

gotcha yea thats another thing Vortech told me, we're just gonna raise the rev limiter up alittle so we dont hit it by mistake, and try out alil over 6000 to see what happens i swore he redlined it at one point but i guess i saw 5800 cuz the pasengers view is alil different...the driver on the other hand did see 6psi on one run top of 3rd gear i believe. so we'll see

keep 'em comin, ill be checkin out all these suggestions in the next couple days

mahhddgtp

Larry, your GTO is

Inspector12

iTrader: (29)

Well you will see a small drop due to the intake and the headers. I am not sure about why you would be loosing 3 PSI. Those bypass valves are known to leak and go be frequently might try a new one it is a fairly inexpensive thing to replace. If it were me I would start by changing the pulley start with a 2.75" after you find out if the bypass valve is good or not. Boost is a mesurment of resistance in the intake track. One car will show 8lbs and another with heads and cam might show 6lbs with the same pullies etc...But do you think the car with more boost is moving more air of course not the one with the H/C is just doing it more efficently and making more power by doing so.

300bhp/ton

If you're having a hard time getting your head around pressure and air flow think of it like this.

On your push bike you can inflate the tyres to 30psi, yet a big ol' truck tyre can also be inflated to 30psi.

Do they have the same amount of air in them? - No.

The truck tyre is much bigger and requires much more air to generate the same pressure.

The same is true on a FI engine, by changing parts that affect the dynamic compression ratio such as intake manifolds, exhaust, headers, heads, cam, etc.

You are making less resistance in the same way as the truck tyre was a bigger space. So to generate the same amount of pressure in a larger or less restrictive space you need more air.

So if you had a setup producing 8psi and you replaced the exhaust, headers and intake the restriction would be less so the psi level would drop, although the actual amount of air would be the same. If you wanted to retain the same psi you would have to spin the blower faster (different pulley) so there would be an increase in air flow. However 8psi with the additional mods would be producing more power than 8psi without the mods.

This may be part of your problem. Also just check and double check for any leaks.

The rpm issue as mentioned is another key factor, the faster the engine spins the faster the blower spins. And the faster the blower spins means increased air flow and psi.

When you ordered you kit did you tell Vortech that you already had induction and exhaust mods on the car?

I have no idea what size pulley is standard on those kits, but if you are using the pulley designed for use with stock intake and headers then it's most likely that that is the issue.

Inspector12

iTrader: (29)

3.12 is stock size pulley that comes with the kit.

GTOLarry

You definately don't want to block your blowoff valve or you will have a boost leak pretty quick. When you decelerate and throttle plate closes the boost has no where to go, if you are in gear the blower is still pumping air, so the valve blows off excess pressure. Without that relief the blower would just keep pumping and your boost would keep on going up and up since there was no way to realease it. The release would probably come in the form of something like a hose coming popping off or rupturing.

Thanks for the compliment on the GTO, I am trying to get it to 600rwhp on 91octane plus Alky.

Bikeboy1

iTrader: (8)

I was only seeing 6lbs of boost with my set up because of the bolts on. The intake and full exhaust with no cats makes everything more efficient. I had no leaks and no belt slip. Check my sig for numbers and mods at 6lbs.

fenix99

iTrader: (1)

well im 99% sure we tied everything down correctly and connected everything properly so i doubt there is a leak but i will check it when i get a chance, also bikeboy im happy to see what kinda numbers ur putting down with basically the same bolts ons...at first it just felt like the car was underpowered at 2000-3000, i was expecting it to be insane fast but its just "very fast"...im happy with it and yes i know ill have to rev it up to see somewhat more boost...

thanks again every1 for clearing some stuff up for me, imma wait n take it to the dyno with the superchips tune it has right now and see how i like the numbers and air/fuel, then ill go from there and find someone to tune it further