No disrespect, but have you driven an lt1 car with a supercharger or turbo? You dont have to be anywhere near WOT (or even half throttle) to see boost in either (especially one with a decent stall).

 

It would most certainly fall off up top. You'd be spinning the impeller higher, heating the air more, providing less oxygen in the inake, the longer you maintained the same psi through the rpm band. That's not how a turbo works - it bypasses some of the exhaust gasses so the impeller doesnt spin higher to maintain the peak psi. So, generally a turbo is not bypassing air that's already compressed by the impeller, like your suggesting.

 

I know how a turbo works.... and how it limits boost. I really dont understand what your argument is.

What I meant was it would hold better then a roots, but similar to a turbo.... not that it wouldnt fall off at all but it would work better then a roots, IMHO. Youd gain the same, or similar, low end boost and hold that same boost to the top with less fall off.

Whether you are venting via wastegate on the exhaust side with a turbo or venting via wastegate on the charge pipe to the intake.... why would one be worse off then the other if the motor receives the same psi considering both were ICed and similar IATs?

 

I've been thinking of this same Idea to for awhile now to, I wasn't to happy with my boost lvl with the D1SC at lower rpm's. My TPI equipped car is probably only good to about 5200-5300 rpms before the power drops off but the HP peak is at some ware around 4500-4700, and at that lvl I only make 6psi but the blower will easily make 12psi at 6000 rpm's. So the only way to fix that is install a smaller pulley on, but now I'am making about 16-17psi at 6000 rpm's

Here's some numbers of what my D1SC will do so you guys can get a better idea what it will take to make more boost at lower rpm's and how much you'll need to bleed off.

4" pulley
RPM=PSI
2500=1.9
3000=2.8
3500=3.8
4000=5.0
4500=6.3
5000=8.0
5500=10.6
6000=12.0

3.4" pulley
RPM=PSI
2500=2.8
3000=4.1
3500=5.8
4000=7.7
4500=9.6
5000=12.2
5500=14.8
6000=16.1 belt starts to slip a bit at this rpm

 

My whole point is that you would not see similar IAT's or air density at the same psi. You wouldnt even see similar IAT at different rpms in your own motor at the same PSI. You can't get around the fact that your spinning the impeller higher, and creating more heat, as the rpms go up, no matter if you bleed the boost off or not.

 

Speedmiser, I have not driven a boosted LT1 so I'm not sure how they feel or how responsive they are, but in my car I am dissapointed with the drivablity of the car and I want to avoid any more mods that are drag racing oriented, it has the hot cam kit in it and it seems to have killed most of the off idle tourqe and responsiveness of the car. I know most everyone else considers the hotcam to be a baby cam but I am wishing I had left the stock cam in it. The car is a little faster in the 1/4 mile but the car is less comfotable in every other scenario. A high stall tourqe converter does not sound appealing either, I have driven several cars with these and for anything other than all out racing it makes the car feel sluggish and lazy. I have another car that is strictly for 1/4 mile and when its at the drag strip it's great, but it completely sucks for anything else.

 

Heres another thought on IATs... you could use this device on the charge pipe after the SC but before the IC. This way the IC would only have to flow the actual boost going into the motor vs flowing boost youd need to bleed off. I was always picturing it up top by the TB...... before the IC makes more sense for IATs.

 

breakmyfootoff - If you picked the right stall for that cam, it would be far from lazy or sluggish. Off idle response and drivability would improve - not just ET's.

You can definitley overstall a cam, or pick a cam/converter combo that's to much for street driving, but the right combo is not going to make you're motor sluggish or lazy - afterall it's a torque multiplier. Your car would love a 2500-3200 stall...

 

So if you guys were dead-set on doing this no matter what problems it causes, why did you pose the question?

 

You need this:

http://web.camaross.com/forums/showthread.php?t=322317

 

Just throwing it out there to get opinions or to see if anyone had any input on how to make it work.

No thanks on the roots. Id personally rather go with a ATI.

 

The roots don't fall off on top. The reason they have such good response is they compress the air in the intake, not in the housing, and they move a fixed amount for each rotation. They do heat the air a little more, depending on over drive. My 671 on a BBC had instant reponse underdriven 9%, and would spin to 7000 rpm. Made 8-9 psi at that setting.

If you have drivability and throttle response problems, then you need to do some tuning. Adding a quicker advance will make the car feel much more peppy at lower rpms. Just have to be careful about octane requirements.

The turbo wastegate vents exhaust pressure, and keeps the impeller spinning at a constant RPM, that is why you get good low end if everything is sized right. A centrifugal, by design, has to spin more rpm to create more boost, so if you overspin it to pump up the low end, you will add heat. And more belt drag. Venting the air to limit the boost level will still be sending that overheated air into the intake. A friend with an S-trim pullied to make 13 psi sees IAT's over 200 deg. as soon as he gets on the throttle. Granted, an aftercooler would help, but since you are constantly overspinning the thing, you get that heat all the time, instead of only when you jump on it. Not to mention reducing the life of your s/c.

If the s/c and combo is not doing what you want, you may need to look at other options. A little 50 shot will pep it up off idle.