lowering the boost for a Vorthech

rkubara · 10-29-2005, 10:27 AM

I just bought a 1994 Corvette C4 with a Vortech supercharger on an LT1 with 95,000 miles on it. It is running 14 lbs of boost and I would like to lower it. I gather the only way to do this is change the pulley? Is there any other way? Does anyone know what size pulley I need or how I determine it? Where do I get these pulleys? Vortech? Are there generic brands?

lead foot 85 vet · 10-29-2005, 12:00 PM

Quote:

Originally Posted by rkubara

I just bought a 1994 Corvette C4 with a Vortech supercharger on an LT1 with 95,000 miles on it. It is running 14 lbs of boost and I would like to lower it. I gather the only way to do this is change the pulley? Is there any other way? Does anyone know what size pulley I need or how I determine it? Where do I get these pulleys? Vortech? Are there generic brands?

first you'll need to know which supercharger head unit you have . then the O.D. size of the superchargerg pulley on it now....shop on the internet for a larger O.D. pulley....they are rated by psi boost per size. some of the guys on here like greg at blowerworks for vortech products........also some of the guys here would give there left nut to get 14 psi on a lt1....very impressive

tjwong · 10-29-2005, 12:25 PM

Quote:

Originally Posted by lead foot 85 vet

first you'll need to know which supercharger head unit you have . then the O.D. size of the superchargerg pulley on it now....shop on the internet for a larger O.D. pulley....they are rated by psi boost per size. some of the guys on here like greg at blowerworks for vortech products........also some of the guys here would give there left nut to get 14 psi on a lt1....very impressive

Ya that is so true, them old systems had a hard time making what they claimed (6 PSI) let alone 14 without doing a lot of expensive modifications to there kits.

TM-Z06 · 10-29-2005, 07:36 PM

To lower boost:

1 - smaller s/c and/or crank pulley
2 - Create a restriction on the inlet side of the blower
3 - Lower your RPM limit (boost is relative to rpm)

I recommend #1

POLOVETTE 94 · 10-29-2005, 10:39 PM

I would like to know more details on your "14 pounds of boost". At what RPM are you seeing this? Is there a possibility of gauge inaccuracy here? If not, I'd say you may have come across a car with more "modifications" than you thought. Many have to make more than a pulley change to see that much actual boost.

rkubara · 10-30-2005, 01:49 AM

It actually reads 16 lbs at about 1800 RPM. The gauge reads 1 lb when the car is off. Yes there are other things done to the engine but I don't think they would impact boost? Isn't that strickly the supercharger?

The thing is too snakey, can't keep the traction control from kicking in and when it is off, can't keep the 285x30x18's gripping at any speed lower than 30 MPH.

zelement · 10-30-2005, 02:46 AM

i think you got a broken boost guage.

POLOVETTE 94 · 10-30-2005, 10:42 AM

Quote:

Originally Posted by rkubara

It actually reads 16 lbs at about 1800 RPM. The gauge reads 1 lb when the car is off. Yes there are other things done to the engine but I don't think they would impact boost? Isn't that strickly the supercharger?

The thing is too snakey, can't keep the traction control from kicking in and when it is off, can't keep the 285x30x18's gripping at any speed lower than 30 MPH.

tjwong · 10-30-2005, 12:34 PM

Quote:

Originally Posted by zelement

i think you got a broken boost guage.

I think you need to get another gauge and verify the boost that you "think" you are getting. A simple vacuum/fuel pressure gauge from any auto parts store will do the job. Just "T" it into the gauge port that your gauge is connected to now. Get enough small vacuum hose to get the gauge into the car and drive it. Get it into third gear if you got a M6 car, and at about 35 MPH mat the throttle. You won't be frying the tires in third at that speed and the gauge should show you what boost you are really getting.

Alvin · 10-30-2005, 12:50 PM

I think this guy is meaning vaccum.. I had a kid get in my car one day and said.. whoa you got 20 pounds of boost at idle? I said no.. I got 20 inches of vaccum

zelement · 10-30-2005, 05:05 PM

I hope that's not the case with him.

rkubara · 10-30-2005, 07:12 PM

It's not the case, the gauge reads "Boost PSI". But I will try to get another to check against it.

Bruce · 10-30-2005, 07:26 PM

NO way you are getting 16psi of boost. Unless the drive system is modified and your motor is built to hold that much boost and your fuel system is heavily modified. Have you ever ride in a car with a V8 with 16psi? Trust me and every one here is telling you some thing is wrong with guage or whatever. Because few people here answering your post including me are all own a supercharged ranging from Zelement 377ci supercharged to my 383LT1 and TJ 396LT4 Vortech charged.

ps. 16psi at only 1800rpm? yeah right. I am willing to bet, Even a SY trim cannot even do that.

rkubara · 10-31-2005, 02:18 AM

My idle has been stuck at 1800 RPM since I got the car last week and I have been trying to fix it at the same time I posted this note asking how to turn the boost down. I didn't think the two were related, but I just learned today that the IAC motor has failed and the valve it slightly open. I have no idea if this is affecting the boost or not but I will be putting in a new IAC and will try to get another gauge to check. However I am leaving on a two-week road trip and won't be posting the results for a while.

Considering all the comments, and I am new to superchargers, I gather something isn't right with my readings. Regardless, the car is way to wild and I still want to reduce the boost regardless what it is now.

Mo_Bandy · 10-31-2005, 03:28 AM

If you are running the stock balancer which is 7 inches... if you have a 3.125 pulley on the S/C thet would put you at the "stock" settings that Vortech was selling to give 6-8 pounds of boost on a LT1....

I also agree with the above posts, I was running a 8 rib up to 6000 rpm and was only tapping 12-13 pounds of boost.... I'd guess your boost guage is bad, the IAC will effect the vac reading...

16 pounds without intercooling or forged top and bottom end mmmm dun think so... I don't think a stock engine would handle it...

Mo

qwiketz · 10-31-2005, 10:53 PM

sounds about 10 lbs high for a box stock vortech kit. I've done almost everything (short of an 8 rib conversion) short of upgrading to a t trim and I'm getting 9lbs at the very most. With 9 lbs, I can light up the 335 p zero's anywhere under 70mph... with an auto.. it's probably a bad guage or wired backward somehow.

rkubara · 11-01-2005, 02:45 PM

OK, I'm convinced I have a bad gauge. I haven't found the exact one yet to simply replace it (matches the fuel pressure gauge) and if I buy a different one to check and compare I can't return it (no returns). I am out of town on a road trip for 2 weeks, but will post my findings once I check it with another gauge.
Thanks for everyones input.

neat · 11-01-2005, 03:00 PM

A generic vacuum gauge should be available at your local autoparts store for less than $20. It won't fit in the hole obviously, but you could tape it to the windshield for a quick run around the block.

drochau · 11-03-2005, 05:04 PM

Uh, wiring? I don't know about you guys, but I have a analog gauge for boost. I just have a small tube going to the cockpit gauge. It's always been spot on too with my vacuum tool.
This is the first time I've heard of a boost gauge going south itself. Is the tube crimped or kinked at some point?

rkubara · 11-26-2005, 08:53 PM

You all were right, bad gauge. It has about 6-7 lbs of boost with a new gauge. I was worried that it was too much for the high miles engine with the high boost the old gauge was showing. For only 6-7 lbs, sure hard to keep these tires from spinning.