Louis

iTrader: (7)

What happens with a turbo car on a shift?

If you have a boost spike, your boost controller isnt working properly.

And really, a SC car doesnt boost instantly, especially a centri car, which we are talking about. Not enough to blow it up.

white01ss

iTrader: (37)

Nothing happens "instantly". Once you stab the throttle it still takes time for the pressure to build up behind the throttle blade. Remember, behind the throttle body it is still a vacuum. Any properly sized wastegate, bypass valve, or blow off valve is going to react in plenty of time to expel extra pressure.

Think of how supercharger bypass valve (BPV) works. When you are full throttle and let off the gas, like each time you shift a manual, the throttle blade shuts and now there is a pressure build up between the s/c and the throttle body. That pressure is released by the BPV very quickly and is trigged by manifold vacuum.

In the configuration we are talking about where we are pullied, for example, to 18 psi max, but want to limit it to 12 psi using a cockpit controlled wastegate. The motivation is that we want to achieve that 12 psi much earlier in the RPM range, let's say 4300 rpm instead the normal situation where you would pully for 12 psi, but only hit it close to redline. In this scenario, you're driving along at 4300 ready to stab the throttle. The manifold is under vacuum and the bypass valve is working like mad letting the 18 psi of potential boost out. Once you stab the throttle, many things are happening simultaneously. The manifold begins to fill up with pressure, the BPV starts to loose it's vacuum reference and begins to close. Once the BPV is fully closed, the manifold fills to 12 psi then the wastegate opens to release anything over 12 psi. You might see +/- 1 psi, but it would stay very close to the trigger point and this variance is easily accounted for in a 2/3-bar SD tune. Hope this helps.

Mr.Big

very well typed

ysb02

Just for example if 20psi was your max boost and 15psi your wastegate limited boost the SD/MAF setup would compensate for not seeing 20psi and lean out with 15psi?

I thought you had to tune it for both levels then switch maps back/forth as needed.

chriswtx

iTrader: (5)

no switching of maps back and forth needed for different psi levels in a SD tune...

Old _School

iTrader: (1)

2/3 bar SD does that for you, that is why you tune for max boost and everything in between...

Very well typed post white01ss

ysb02

Sounds great. Where did you tune it at?

chriswtx

iTrader: (5)

Corey Henderson of Henderson Performance in New Braunfels.. tuned both my Corvettes..

white01ss

iTrader: (37)

Thanks for the comments...

Check out this thread where JoBy compares restrictor plates vs wastegates to control boost.

http://forums.corvetteforum.com/c4-f...st-levels.html

What about putting a standard voltage controlled throttle body into the SC inlet path? It could be controlled manually with a simple voltage controller ****. Best of both worlds, cockpit control and max supercharger efficiency.

sciff5

iTrader: (1)

That thread got technical but from what I gather the general concensus was that the restrictor plate is a better alternative than the wastegate solution.

white01ss

iTrader: (37)

I thought so to, but after I read it to the end the restrictor plate may cause boost to fall off after peak boost is reached. Certainly, sounds like it is easier on the supercharger than the wastegate. Maybe someone can post a dyno run with a restrictor plate to see what happens to the boost. That's the missing link here. From the fast fords magazine article the wastgate solution looks like it works very well and maintains a flat boost curve more like a turbo.

Louis

iTrader: (7)

Right, but at a large cost. If you are looking to make a quick change, add 80-100 rwtq in the midrange, but cap boost at the top end, FOR CHEAP, the restrictor plate is the way to go.

Mr.Big

agreed... several 9 second centris out there with plates... I know someones gotta be working on a neat solution for this...

sciff5

iTrader: (1)

Your saying the wastegate and boost controller would be large cost?

I'm a pretty cheap guy but even if the wastegate solution worked as well as I hear the restrictor plate works and I dont have to change pullies I think I'de still spend the money.

I just wish there was more real world results. I meen I know in that ford magazine article they claimed some great results.. but I never trust mags.

chriswtx

iTrader: (5)

I've ran the restrictor plate, but I like being able to switch boost on the fly..
here are my real world results..

Low boost at 13-14psi was the 693(blue lines) and high boost was the 832(red lines) at 17-18psi...3.25" pulley and 8" overdrive balancer, Paxton Novi 2000, Still having some belt slip above 6000rpm, I need a shorter belt..

motor details:346ci, Eagle LS1 6.125" rods, Diamond -8.6 dish pistons, stock crank, new LS6 block, ARP head bolts, custom ground Comp Cam 226/232 116LSA, Texas speed CNC LS6 stage 2.5 heads 2.04intake 1.575 exhaust valves hand finished by me, right at 9.6:1 compression, single nozzle meth inj...

Louis

iTrader: (7)

Yep, a restrictor plate costs 40-80$, a gate setup would cost 450(larger gate, like a tial 44, Tial 60, or TurboSmart 50) boost controller ( 600) and fabrication to put it on, plus a new pully. All in all, by the time its all said and done, expect to spend 1400-1800 give or take.

chriswtx

iTrader: (5)

I spent, controller $295, pulley $110, gate 50-60mm $100-250 depending on how well you shop around(you don't need a high dollar one since its never going to see high temps like they do on the exhaust), fabrication FREE did it myself... Got right at $500 in my setup... $395 if you count the fact I was going to buy the pulley anyway..

sciff5

iTrader: (1)

Yeah thats what I was thinking. I'm a DIY type guy, only because as said before I'm cheap.

Chris I know you posted that graph before but I was looking for more of a before and after wastegate graph that we could overlay and actually see the differences.

I will try and search for a similar setup to yours without the wastegate to try and get a basis of comparison.

Mr.Big

my graph is not near the same peak numbers, but hope this helps... throttle was eased on at 3700rpm...

sciff5

iTrader: (1)

That graph would be perfect if you had started it a little sooner but it hints at the actual area under the curve gains.

Comparing your dyno to chris's wastegate controlled 13 psi run his car is up on yours in tq and hp from the start of your graph 4k to about 5500. I would assume that the gains under 4k would be even greater even though your peak numbers are obviously a good deal higher.

This looks promising