I woulda sworn you had a red 'vert...Oh well...my mistake...I think I workto much to remember anything anyway.....

So uh back on topic here...uh boost=power, and power=nothing without control, and, uh, control=hard to come by.

 

Ok, so my series 4 motor is on an engine stand and has yet to be installed into my 510. I am gonna do all the prepping that I can while the motor is on the engine stand. Planned mods include full 3" downpipe and exhaust". K&N cone filter/cold air box., Front Mounted Intercooler, 720cc secondary injectors, haltech ecu, smog equipment removed, and ported wastegate. I am getting ready to pull the turbo and port the wastegate. My question is regarding the "twin scroll" flapper. Should I permanently remove this and port the exhaust manifold while porting the wastegate? This will not be a drag car. It will be a mostly high performance street and some track car. Emphasis will be on handling and turns. How will removing the twin scroll flapper and porting the exhaust manifold effect my power band? Will I have alot more turbo lag? Or will it not matter since I am running a wide open exhaust for the most part? I am probably looking to keep the boost around 12 psi (if this is possible with just porting the stock wastegate). Don't know exactly how much boost I will want till I try it in the car. A datsun 510 is considerably lighter than a 2nd gen rx7 so I probably wont want as much hp as someone in a 2nd gen. So should the twin scroll system stay or go?? If I didnt want to boost over 12, would I even need to remove the twin scroll? Thanks guys.

John

 

bump

 

I think twin scroll should go, S5 manifolds dont have it at all.

Port the manifold too, check out this site
http://fc3s-pro.com/ it has a how-to of wastegate porting, manifold porting, and many other very helpful things.

 

The bit you're missing is that the factory boost isn't "set" at 7.5psi, that's simply the result of all parts of the engine and turbo working together. The various airflow restrictions (exhaust, intake, ports, turbo, etc) plus the size and shape of the compressor and turbine, the wastegate spring tension, the wastegate port size, etc all contribute to the boost that ends up being produced. A simple pneumatically-controlled boost system like the S4's can't be set as such, but is "tuned" by the factory when they select the components that give them the results they want. It's not a poor design, in fact it's a perfect design, because Mazda gave exactly what they wanted. Unfortunately it makes modification harder, but that was the least of Mazda's concerns!
Any turbo will produce more boost if you free up airflow restrictions, but in the case of the S4 turbo the wastegate port is so small that boost starts to rise uncontrollably. The S5's double wastegate is much better, but I hear it eventually reaches the same problem.
If you want to really improve the wastegate, replacing the flap with a bigger one means the port can be made even bigger, further improving boost control. Another way to improve flow through the wastegate (more flow means more control) is to divide the turbine and wastegate exhaust flows into two seperate pipes that merge further downstream. The dramatic reduction in turbulance where they normally mix increases flow through both the turbine and the wastegate.
BTW, according to the FSM stock boost for the S4 is 6.56psi, the S5 is 8.25psi.

 

That's because S5's use an electronic boost control to bring boost up faster. The S4 doesn't have that, so removal of the twin-scroll system will result in slower boosting. Installing a decent boost controller would be advisable to get rid of some of this lag.

 

My 89 TII boost to a little over 7, not 8.25. Do I have a boost leak or something? Also, I noticed that it will boost up to like 8 or so, then it drops off to 7 and is steady after that..

 

You've just contradicted yourself. Those FSM figures are max boost, not boost at redline. Most stock engines won't hold max boost all the way to redline, in fact many are designed specifically not to.
You say you get a max of 8psi boost, and I doubt your boost gauge is accurate to 0.25psi, so it sounds like you're running stock boost levels and have nothing to worry about.

 

My S5 will get 5.5psi in 2nd around 3.5krpm and the wastegate is hookes straight to the compressor nipple.