Ok fellas. I am currently putting the SC14 charger onto a stock N/A engine. I will be keeping the throttle body in the stock position and want to run a wastegate in between the charger outlet and the plenum inlet (AS STOCKY SUGGESTED) What i need to know is, the charger will probably run at no more than 6psi, what spring will i need in the wastegate? ie: If it is a 8psi spring, once that amount of pressure builds up within the piping, the gate will open? Thanks for any info/opinions fellas.

Why would you run a wastegate with a supercharger? I may be wrong but this makes no sense at all to me. Change the pulley ratios to control boost.

If you correctly read the statement...I said I needed a wastegate to vent excess pressure between the charger and the throttle body, not to control boost...

it vents the pressure at idle (by pass valve)

Yeah thats what im talking about....I want to know what spring rate I should use in the wastegate if I am running, say 6psi boost...Any help appreciated

Quote: If it is a 8psi spring, once that amount of pressure builds up within the piping, the gate will open? Yes. I am fairly sure if the charger is setup for 6psi the pressure will climb until 8 then release. Edit: whoops I cant read. No idea what spring you need. Some original photos have not been recovered yet.

no that's not quite right. if you have a 10psi rated spring, the wastegate (under normal conditions) will begin to open when there is 10psi UNDER the diaphragm. the area of the diaphragm inside the gate is much larger than the area of the poppet valve itself, and if you recall from year 11 physics: pressure = force x area so 10 psi under the diaphragm will force the spring open, but 10psi under the poppet valve will not even come close to forcing it open. this makes sense because at full boost most street engines have 1.5-2 times the exhaust back pressure relative to boost (inlet) pressure. as boost pressure is used to control the wastegate, the poppet valve must need to "resist" these large back pressures. hence the diaphragm is much larger than the poppet valve in terms of surface area. if you get 6psi out of the blower, you'll be lucky. the only reason to change the gate spring (or alter it) is if your throttle response is still too violent for your liking. a 10psi spring might see full upstream boost (valve closed) at even 1/4 throttle, which is not good for highway cruising, where you want to stay in vacuum. i set mine up to have full boost at 3/4 throttle and above, which gives a nice mix of drivability and response. you can putt around all day without seeing boost, but put your foot down and it's all there straight away. i had a standard 7psi spring in a garrett 32mm gate, and i pulled it apart, cut 1/3 of the spring off and stretched it with some pliers and a vice until it was back to original length. this alters the spring rate a bit and basically makes it weaker. you can stuff around with the springs as much as you want, drive it and if you don't like it, take the spring out, cut it and stretch it again till you get it just right. edit: alternatively, a 3-4psi replacement spring from the wastegate company would do the trick just fine.

Stocky is spot on, I have also run the same system as his, and it works extremely well. The answer to your question is at what throttle opening do you want the bypass to begin closing so you see boost ? You want to be able to drive around most of the time and keep up with the traffic without the blower working. That will save a lot of fuel and keep the blower running cool. A good all around figure to start off with might be about a 4psi spring, (that is about eight inches of mercury manifold vacuum). That pressure has absolutely nothing to do with boost pressure, it is the pressure drop across the throttle body when it is only open just a small amount. When you floor it, the pressure across the throttle body drops to just about zero, no matter what boost is there. The wastegate diaphragm only sees the pressure difference across the throttle, because there are two hoses, one going to each side of the wastegate diaphragm. Before you fit the wastegate to the engine connect it up to the throttle body with two long hoses, and sit in on the passenger seat or the floor, where you can watch what it does. As soon as you start the engine, vacuum will pull the wastegate fully open. As you drive, there should be enough manifold vacuum to hold it fully open at light throttle. Give it a bit more throttle and it will progressively begin to close. Stomp on the throttle and it will snap shut tight. It is fascinating to see how quickly and progressively it follows even the smallest movement of your right foot. (It is just like watching a vacuum gauge needle). You experiment with the spring to get the opening characteristics you want. It can come in slow, or fast, and you can set the throttle opening point where it comes in. It is an interesting thing to play around with. When a suitable spring is finally sorted out, it will give a wonderfully smooth and progressive build up of boost over the final part of throttle travel. But you can still drive around without seeing any boost at all if you want to. I had mine set so boost came in smoothly above about 3/4 throttle opening but you can have it come in earlier than that if you want.

Stocky and Warpseed, thankyou so much for your input...I guess ill start of with the standard wastegate spring and chop it up until I am satisfied with throttle response. Cheers

Stocky isnt allways right. He said my 88mm pulley would do no more then 6. i am happy to say it does 0-10 and thats with his old cam, Extractors, exhaust.. and other boost droping items. You said you dont want anymore then 6PSI, The stock pulley is 135mm making it a 1.3 drive. I got an 88mm pulley and that makes it a 2 drive. the 135 gave me 2-4 PSI depending on RPM and the new one makes 10 low end and i forget top end.. about 7 i think.. I only ran it for 300m and 50m on boost.. PINNNNNNNGGNGGNGNNGGGGGGG didnt have the intercooler piped and the new fuel system... the intercooler will drop it a **** load also.. If anyone is out there reading this and is thinking about an SC14 VL.. my person op is DONT. not ****en worth it hay.. Yes they do make any VL ****en hall ass but go turbo unless you can aford a better blower and new motor internals. If i did it agian, i would go Turbo for sure.. and i am going to go turbo.. Some original photos have not been recovered yet.

Of course you have aftermarket engine management right ? And you set up the correct air fuel ratio and ignition advance too I suppose to suit all that extra low rpm boost ?? If it pings there is a reason. You think turbos can never cause detonation ? Of course only supercharges cause wrong ignition timing or mixture. If you fit a turbo there is then no need to tune anything. Maybe you should get the turbo.

WTF mate.. i know turbos ping.. i was stating that on 10 PSI i was pinging my head off.. and anything about about 6 it would... "Of course only supercharges cause wrong ignition timing or mixture. If you fit a turbo there is then no need to tune anything." errr..... timing should be about 15 stock and 20 for better response and power, same as all VLs I was saying... its a better option to go for a turbo, I love my SC and from when i first got my VL over a year ago i wanted to make it all. And i did. I am running a differant set up to every one else on here and from doing it all myself with a mate i am extreamly pleased and proud of what i have done and i am allways up for helping others in need. CRS are changing there SC kits to be the same "style" as i am running, I am running a drewthought, were the TB is befor the blower. This makes the temp get up a bit more and neil said with the waste gate its alot more driver friendly. I have thought about going that way and all that but i got to the same point as OziWPN with the springs and others things. Supercharging a VL makes problems not tackled by other VL kids so its all a one man trip, now there is getting a fue more out there it is starting to get easyer. But no one on here is running the same set ups that i have found yet.. But i dont look on here for car things much now, Its for the members section and the people here.. a good bunch of people come togeather by a common interest. I dont know as much as stocky but i know drifferant things, If anyone needs help i am allllllways willing to help. [email removed] Matt.

The wastegate bypass will unload the blower when not in boost mode. Right now you have a very large and efficient vacuum pump sucking hard against the closed throttle. The blower will run hot and noisy, and it will lower fuel economy by around 10%. At least it did on my suck through system when I tried it. Static ignition timing does not really mean much. Most ignitions run far too much ignition advance at low RPM under load when using a supercharger. Have you tried fitting a pressure retard system to the distributor ? Some factory turbo cars have this feature, and you may be able to fit the vacuum advance/pressure retard double can to the distributor. A better way is to just get an aftermarket EFI system and map the ignition properly so it can handle full load boost and still have plenty of advance for light throttle running. Get the blower working right, you already have most of it. All it needs is some tuning. If you still want even more power, particularly top end power, add a low boost turbo to what you already have. But get it tuned right first, or you will blow it up for sure.

i know just about everything about the SC14 setups on VLs now.. I know what a wastegate does.. And who cars about fuel eco.. its a supercharged VL if you wanted fuel eco leave it NA. if you have MSN, Add me. you sound allright.

wouldent a BOV do the same thing?

Nope.. There designed to open and close.. not open and stay open.. I have tryed.. "Pss pss pss pss pss pss pss pss pss" And your idles are up to shi t

what wastegate would u run on a blower

yes muffler bearings are essential for airway economy and fuel distribution! any gate with what we in the business call "hairline eleven flow efficiency" will do the job too. p.s. vl ben i had NFI what you were trying to say when you pm'd me. try some spelling lessons and punctuation next time.

As the wastegate will never see heat.. it dosnt matter what you put on.. bigger the better.

Quote: Originally Posted by [SC]Matty As the wastegate will never see heat.. it doesn't matter what you put on.. bigger the better. What you say is true.....but.... Make sure the control diaphragm is around twice the diameter of the poppet valve, or you will have hell selecting a suitable spring and getting it to work properly. Many of the larger wastegates have relatively small diagrams not much bigger than the valve, and boost pressure under the wastegate valve can force it open and create a boost leak. Fitting a stronger spring is not an option, because then it will not open/close at the required throttle position. 32mm gate with 60mm diaphragm will work fine 42mm gate with 80 mm diaphragm will work fine too a 60mm gate with a 60 mm diaphragm definitely will not work. Control diaphragms larger than 80 mm are extremely rare, so don't go too big with the valve. Just looking at pictures on e-bay you can often quickly see the relationship between the valve diameter and control diaphragm diameter. A 32mm gate is plenty big enough to bypass an SC-14. 32mm is a bloody big hole and will easily pass enough air at boost pressures.