I did a couple of quick searches and didn't find any answers, so.....

I have heard of people running wastegates on a Centri. and just pulleying it to max impeller RPM and using a boost controller to control it. I have seen a couple of cars in the past that were set up like this, but don't know how well it works. I was wondering if anyone here has experience with this? I am Joe P. from www.joembc.com, so a setup where I could use one of my MBC's would be ideal. If not, I'll just go the restrictor route. Thanks.
Joe

 

Both are stupid ideas if you ask me.

 

Well i wouldnt want to have my blower spinning that fast and making that much heat if Im not evan going to use all the boost its making.It just seems harder on things.Im no supercharger guru though

 

Stupid? I thought not making real boost until 6000 rpm's sounds stupid . The corvette guys are having very good luck making nice peak power along with very good "under the curve" power (something the centri's are weak in) by using restrictors. Even procharger recommended using a restrictor. Guys are running over 4-5mph faster with the same peak boost just by increasing the blower RPM and using a restrictor to get more mid range.

Hmm, maybe I'll just take my 650 WHP blower and headers only LS2 car and leave it as is since I have stupid ideas .

Joe

 

That was one of my concerns, but many people are doing the restrictor with good luck. From what I have read, even running a restrictor will technically increase the heat too, but people keep making more and more power by doing so. Maybe it is because most of us run alky and it is negating any increase temps? Or maybe just that the increase in mid range power makes up for the light loss due to the heat?
Joe

 

Not me. Engines are less prone to detonate at high rpms. If you make boost anywhere, it would be safest up top.

Remove the restrictor and power "under the curve" WILL go up. I promise. Removing the restrictor will increase peak power and not reduce power anywhere. This is fact.

Imagine how much faster they would go without the restrictor!

Adding a restriction to a high performance combination is one of the most asinine and backwards things I've ever heard of. It is a thermodynamic CRIME and absolutely will not perform as well as if you remove the restriction. If you want to boost low-end and rob top-end, then install a milder cam with a sooner IVC and later EVO. At least this way, you'll gain some fuel mileage in the process. Or maybe you can swap your LSx intake for TPI! (Yes, I DO realize that's impossible) That'll boost low-end alot and you can even spin the blower faster to get some top-end back! Or maybe you can just put the stock mufflers back on. Get my point?

Mike

 

I agree with this- that's why I am getting away with 23* timing and 12 psi on a damn near 11:1 LS2 .

Not from the charts/mph I have seen from people doing this. You are not using a restrictor to limit max power- you are using it to limit peak boost. Yes, that will affect top end power also, but if you can only safely run 10 psi (and whatever CFM that would be on the P1), then there is no need to flow more than that through the blower. Pulleying the blower up so it spins faster sooner will give you more "punch" while the the restrictor will limit the top end to the same CFM/PSI it was at while running 10 psi without the restrictor.

I understand what you are saying, but you are talking like the restrictor is limiting power- in this case, the "peak" power and PSI are limited by the motor and we are not exceeding that, just bringing it in sooner. Or am I missing something else here ?.

Again, this is assuming you are restricting an application that is already optimum- in that case, yes a restrictor will kill you, but we are keeping max CFM the same and just running more boost sooner, which would help- as I said, I have seen people gain 4-5 mph from just upping the RPM, adding a restrictor and keeping the same max psi. It seems your argument is assuming that you can just up the airflow/psi and gain all around, but I am talking about a setup where it is already maxed up top.

I am up for learning something new all the time, so if I am wrong, let me know. I just know I have seen it done and have heard of great results from it. Thanks!
Joe
PS- If not, hell then I'll do a cam swap, I was just happy on my stocker making the power I am making, I just want more down low- my car doesn't really pull hard until ~4.5k

 

Okay, let me explain it another way.

Baseline:
10 psi boost in the intake, no restrictor. Supercharger is producing 11 psi boost at its outlet and requiring 70 hp to spin.

With restrictor:
10 psi boost in the intake, with restrictor, spinning supercharger faster. Supercharger is producing 14 psi boost at its outlet and now requires 90 hp to spin.

Get my drift?

 

We're working on a wastegate on a blower car. Strictly for traction control, bleeding off low end boost in the first second or two of the run.. We still need to max out the blower on the big end, but it's too much for the radials to handle on the launch or even first 100' or so.. It's far from "stupid", it's just a different approach to getting down the track..

 

That sounds intresting Brady but what if you spin before you get into significant boost? I've got a problem with that part. Ofcourse, if I had a custom rear end this may not matter?

 

Using it for traction control is entirely different from the stated goals in the initial post.

 

Exactly, and that does work to a degree for super high output applications that need to dump a few hundred horsepower briefly. You just bleed of the reference to the bypass valve and let it unseat.

Dumping boost you've already made and paid for in a street application isn't smart.

Your parasitic losses will be way over just the drop in charge density. Removing the load from the outlet of the compressor will greatly increase the drive load and you still have the penalty of the higher boost IAT.

 

Pretty much sums it up.

 

Thanks guys, I see where you are coming from and in theory it makes perfect sense, but I have seen so many cars pick up noticeable gains at the track in practice, that's the only reason I'm "arguing" your logic- it has proven to work well in many street cars. Maybe I'll just sit by a bit longer to see who else it works well for and go from there. I have heard East Coast Superchargers has had very good luck doing this. Oh well, thanks for the input!
Joe

 

kwiksilverz,
You're changing your tune. You originally asked about using a "wastegate" to control boost with a centrifugal. You just can't do that with a street system. Some Outlaw guys dump airflow in low gear with a PWM MSD solinoid controller via the bypass valve. Its not exact like a turbo system where you're varying the actual speed of the compressor. It wastes a great deal of power, which is the idea for those guys.

You seem to be wanting to limit the top end boost while bumping up the bottom end. Why do you want to do this? Pulley up and short shift. As Mike mentioned to you before the low end is where detonation will rear its head first.

If this is just for street driving then fine, look at restricting the inlet. If you're in some kind of competition then do some math first.

Data log rpm for a WOT run through the gears. Look and see how long you're really in low gear and under the boost curve. Not long I assure you. (positive displacement guys don't seem to get this when comparing to a centrifugal) When you shift see where your rpm drops to on each change. I'd bet you're well in the power at those points. Figure the real area under the curve and see if limiting the breathing capacity of the blower will really help you when you're running all out. There is always a tradeoff. Restricting the inlet will partially cavitate the blower in the upper rpm ranges. This causes the air to heat up more for airflow delivered. Your IAT will increase and air density will drop. This means that the 10 psi you got at 4800 is denser that the 10 psi you'll see at 6200 as an example. When you shift and rpm drops some of this temperature rise will carry along with it. What you gain in low end you will pay for as the rpm increases.

 

Thanks- trust me, I know the "positive displacement" guys don't quite understand this- hell, my old sig used to read "plenty of under the curve power with *** kicking top end" referring to the Maggie vs. procharger debate! I am the first to argue that in a drag race situation- you are never in the RPM's they claim to have the advantage in.

My problem is I am used to spool and constant boost of a turbo and after hearing that people are having similar results with restrictors and such on centris, it was appealing to me.

The thing that kills my car (05 GTO LS2, 12 psi@6800) is that it goes through first and second very quickly and hits boost hard and fast- BUT 3rd and 4th, it drops out of the "higher" boost range and takes quite a while to recoupe. I was thinking of swapping the stock 3.46 gears for 3.91's to keep it in the higher RPM's and in it's "sweet spot". However, I like the top end the car has with the 3.46's- not to mention that gears for the GTO are in the $550 range and the rear still sucks *****- plus I like having the torque to gear it tall and make the thing pull, but since it doesn't hit boost like a turbo and have the torque, it just doesn't work like that. I guess I was trying for the best of both worlds. I'm not trying to get the thing to hit my 12 psi at 4000 RPM's or anything- that would do the motor in. Like I said, the fact that it makes boost so high is the reason I am able to run 12 psi with 23* on an 11.1 motor (10.8 to be exact) and put 650/540 to the wheels on a stock motor with headers, P1, alky and boost a pump without nuking it!

I am just trying to find a way to get it to come on a bit sooner and yet maintain my 6800 rpm shift point, I don't want to short shift- unless you are saying the same power can be made in a smaller range and it would be beneficial to make my 650 at say 6000 instead of 6800 with more boost down low for more midrange punch for example? If that is the case and it would work, I wouldn't mind dropping the rev limiter and dropping hte pulley a bit more to maintain my 12 psi.

I was thinking of doing something like the gate or restrictor to accomplish this as I have been hearing a lot about people having very good luck with the restrictors and have heard of a few guys runninga wastegate- on the IC pipe with a boost controller- there is a Vette locally who does this and says it works great. I understand it takes more power to spin the blower faster, but it isn't the same amount of parasitic loss as if the full load were on the blower at that RPM, so I'd think the gains would outweigh the loss. I never really liked the idea of a restrictor, but it seems to be the most popular method of accomplishing what I am trying to do.

Just figured since the guys here seem to be more hardcore than the "dyno queens" you encounter on some other boards, if there was a method that worked- you guys would know . Thanks again for the taking the time to reply.
Joe

 

If you want more TQ in the low end and midrange use a FM7 cam. At 7.5-8psi i used to make 400rwtq at 3k RPM and 500rwtq at 4200 RPM. At 11-13psi its making 500rwtq at 3500 RPM and 600rwtq at 4500 RPM (Conservative Mustang Dyno). Peak HP is at 5800RPM and stays flat until 6600RPM. All this is done on a stock LS1 engine.

 

The parasitic loss be something like this:

10 psi and 70 lb/min: 50 hp
14 psi and 70 lb/min (10 psi restrictor setup and pulley up): 70 hp
14 psi and 80 lb/min (pulley up only): 80 hp

Note: These numbers meant to demonstrate trends based on compressor laws and are not actual calculated values.

 

Gotcha. I was thinking the gains would overcome the loss, maybe that's why people calim it works so well. I dunno. Thanks again!
Joe

 

Im all with you on this.

This dude is all about calculations and theories. If his calculator says it wont work by god it wont work..LMMFAO

Ive done the same setup you are fixing to work with. Its tricky at first but watch the tune down low and you will pick it up real quick. You are exactly right. It will get you down the track on a small tire or radial car.