Thinking about sequential options
 

I have always wanted to redo the sequential system. You know, the idea of eliminating the lag/spool effect of a single turbo is a good one. Anyone who has driven a well-tuned sequential FD knows how nice it is to be able to have linear power that seems to get stronger as the rpm rise. Its a thing of beauty and I have never driven a single turbo car that approached this.

Mazda tried to eliminate the rubber band effect by running 2 different size turbos and spooling the second up to be ready to come on line smoothly. However, its a fairly simple mechanical vacuum-based system. Porsche is doing it by using variable vanes in the turbo. Both systems exhibit the effect of "coming on the cam" when the shift or transition occurs, but they do it very well. But is this the best way to do it? Could it be better? I think so.

I would propose that a system that goes from one turbo (or supercharger) to two (or supercharger and turbo) could be built that could be designed to operate in a variety of ways from linear power to increasing power or whatever curve you wanted.

I would convert the vacuum mechanical system to an electro-mechanical system controlled by one of the aftermarket engine management systems, like Haltech or Motec or Pectel, that offer a lot broader input and out put controls. This would monitor conditions such as TPS, MAP, boost and RPM and certain programmed conditions would control the coming on or going off line of the secondary turbo. It would also control the pre-spool on the second turbo through a variable butterfly style valve connected with the second turbo. This type of system offers several benefits.

Transitions could be made much less abrupt and could occur at different times and under different conditions. You could set the secondary to come on as soon as it was sufficiently spooled up and overlap the two longer in terms of rpm. You could prevent the second turbo from coming on in a corner at all, if you wanted, by reading the side loading in a corner via a sensor. As long as the outside of the car was loaded at least "so much" (defined), the secondary turbo wouldn't come on or would be on but not as pre-spooled, so as to be ready for full throttle on exit, which would over-ride the rule. You could control the primary well, especially if it were a supercharger/turbo hybrid, during cornering, and still have the full thrust available on the straights.

Anyway, I thought I'd stick this out there and see what people think or may have done with this.

Gordon

I have thought about running 2 GT28 turbos sequentially some how on my FD, but it seems like you have actually put more into investigating this idea.

For now, I'll stick with the BNR SIII's but that's only because that is currently the best sequential upgrade for our cars on the market.

I'd love to see a upgrade for our damn turbo manifolds

I really like the idea of almost limitless customization that this system would provide. I think you would have to come up with a whole new management system though. This project could be very costly, but could prove useful to anyone from race teams on down.

Great post Gordon!! I am about 6 years behind you. I am running my old technology T78 on my track car(SSM) and hate driving it on the street because of the lag. On the track it really isn't an issue unless it is a smaller track. I'll eventually upgrade, but I'm happy with it for now and I got a really good deal on the turbo kit/intercooler. I get in my red FD, which is still sequential, and having instant boost makes the car so much more fun to drive on the street, but I just don't have the power that I want/need.

Gordon, what Mazda are you referring to that runs sequential with a two different size turbo's? Is that what the race teams run? I'd love to check it out if you have a link.

My younger brother is a Mechanical Engineer for Cummins and does alot of turbo R & D. He focused alot on forced induction(primarily turbochargers) when he was in college. He tells me about all the new turbo technology and it goes right over my head. He is a turbocharger Einstein... on a completely different level than I am. Unfortunately he doesn't have the patience to break it down in barney terms for me. The turbo technology(with the right controls like you mentioned) is out there right now to be able to facilitate what you/me/we want, I just don't think we know about it yet. I bet Charlies7 can chime in and tell us what all is available out there.

For now and cheeper, port and do some reshaping to the stock turbos to improve flow .Port the wastgate and install a bigger door with a faster reacting electric boost controler will help .

you should check my signature and a good book for you and any one else that honestly believes that the "lag" and power curve associated with most single turbo setups is normal ought to look it up.

its called "maximum boost" by corky bell

Probably the most in depth book you will ever read on the subject and after doing so will probably change your mind about what you refer to as being a character flaw of turbo set ups.

Corky Bell's book is good. It's available for download online for free. If I can find the link I'll edit this post and post it.

BTW, I don't think Gordon's FD has a turbo/turbo's ;)

I'd like to read that book if you can find the link Brent.

http://rapidshare.com/files/72011802/Maximum_boost.pdf
http://www.sufi.cc/Maximum_boost.pdf

There's a couple of them

Gordon,

Well, I guess I shoudl chime in.. Before I begin, I'm no expert in turbos... disclaimer:)

I did a little research about Porsche 911 VTG system... And when i was reading it, this was one of my concerns.. I had to search a bit because I didn't know where I read it..

.

Well, we know rotary engines are hotter than norm, so, not sure how this turbo system will last... It might but not sure..

Now regarding sequential system..

I think manifold design is crucial! If you look at your 3rd gen manifold, you'll see where some of the faults lies. Some lack of sequential problem could be the cracks on your stock manifold. I kind of wished Mazda would of made it out of cast stainless steel and like Garfinkle said, bigger door and such.

Next issues I see it the controlling of seq. system. Most are driven by vac. and solenoids. Another solution might be variable electric motors to move the actuators instead (Maybe??) Controlling turbo and wastegate thru fast acting variable motor might give better control over turbos.. Again, I'm no engineer so this is purely pulling it out of my ass.

Next, turbo technology. Back in the days, we all thought bigger is better. I never when with large single because I prefer less lag vs. more:) I wasn't about POWER!! but just something to drive and enjoy. Now, these mid size ball bearing spool as well as stockers. I think combination of couple of small ball bearing turbos, good manifold for sequential set up might do the trick...

Again, I'm just an enthusiasts and just an idea..

Phil,

I need to give you a drive in my car. Lag isn't that bad, Muahahaha

This Mazda is known as the 1993-1995 RX-7, FD3S, 13B REW or 3rd gen. You might have seen one before......maybe in your garage :rofl:

-J

Correct me if I'm wrong, but the turbo's on an FD are identical in size(Hitachi HT12 with a 9 blade turbine and a 10 blade compressor). One is not smaller than the other. That's where my question stemmed from. :D

Gordon has a set of 20b sequential turbos sitting on his workbench.. that's what he is referring to when he said that they are different sized. Both cosmo sequential setups had smaller primary turbos.

Thank you. That's what I was wanting to know :) I'm assuming it's basically set up the same as it is on an FD's sequential system, only a smaller primary?