EpDarks

Don't flame yet. I'll explain as simply as I can.

What if you slapped a little T25 turbo going directly into a T66 compressor, would the T25 help spool the T66 in the low end, while the T66 would take over in the high end?

Obviosly the T25 would run out of breath, but by then the T66 is boosting away.

I KNOW it's not "possible" (physically) in a Honda, but remember: This is THEORY!

Sinisterh22a

yea thats what supras have the have a smaller turbo to spool the bigger turbo

BudaKai

Sorry to chime in on this, but if they can build a twin turbo I'm sure they can do a Bi-turbo.

tegasaurus

same thing as rx-7 turbos... to an extend. They work sequentially... basically one powers the other.

only TT i can think of that doesn't operate liek this is the 300zx and 3000gt cars

accordking

Your going to have to enlighten me on this one.......

lazerus

The problem with that is you have two seperate spool times, on the rx-7 it is more prominent, but then again they are designed to be high speed touring cars...

ninesecrx

no...thats not how twin turbos work. If you run a smaller turbo into a big turbo, its just going to choke the smaller turbo. Also, a turbo spools on heat. At this time, all efficiency is lost.

EpDarks

I had always thought that a Supra had 1 small turbo pumping boost into all 6 cylanders, as well as a larger turbo going into all 6 cylanders.

So which is it?

SIXTYdashONE

And thats all she wrote, u cant expect a T66 to breath to full potential when your weakest link( the t25) is choking it up

BlueShadow

Here is how a sequential setup works on an RX7...the same thing is probably also true of the MKIV since it is also a sequential TT.

At low speed, the exhaust passage that leads to the secondary turbo is closed by a valve, thus, only the primary turbo is operating. As the engine speed and load rise and the exhaust gas volume increases, a portion of the gas is directed towards the secondary turbo via a pre-spinning control valve to prepare it for full operation. Various parameters such as engine load, throttle opening and atmospheric pressure are calculated by a computer, which then determines the optimum moment to open the switching valve, hence, allowing the secondary turbo to start providing full boost.

This turbo arrangement enables the engine to respond briskly throughout the rev range and deliver exhilarating acceleration.

ninesecrx

well even at that, it doesnt help get the bigger turbo spooled like the question states. Also, the second turbo would have lag if its not running and then a bypass valve opens for it to operate...and your still going to have a bottleneck in the line.

BlueShadow

The second turbo doesn't lag as bad as you think it would, if everything is in perfect working order there should be very little lag transition when the high turbo fully engages.

The second turbo starts to get pre-spun by partial exhaust flow from the smaller turbo at lower RPMs, once the conditions are high enough the valve fully opens and allows the second turbo to fully spool. The second turbo doesn't just fully engage, it is pre-spun first.

ninesecrx

I see...well to answer the original poster, the answer is no. With some thought involved, you might be able to make something work...kinda what you were thinking. What im wondering though is how they would switch from one to the other and how does it do this? I mean...does the smaller turbo not get exhaust once its reached its peak because it will still be a bottle neck once it ran out.

BlueShadow

Well the smaller turbo will pretty much always be turning...it's the bigger turbo that is usually in between being "off" (low RPM) being "pre-spun" right before boost transition, and being under full spool (mid to higher RPM) after boost transition.

I dont remember exactly what RPM the larger turbo starts its pre-spool (valve opens a little, SOME gasses going to secondary turbine) and when it starts fully spooling (valve is open, letting ALL exhaust gasses through secondary turbine).

The at higher RPMs when the larger turbo starts spooling, the smaller turbo is still spooling and it will do so the whole time. And yes that smaller turbo does end up being a restriction. But as far as switching back and forth between small + large turbo to just the small turbo, I'm assuming that once you let off the throttle or the RPMs go down, the valve that lets exhaust gasses pass from small turbine to large turbine partially closes to let some exhaust gasses through or it closes completely to cut off all the exhaust gas to the larger turbine.

EDIT: in short: the small turbo will always be spooling, the larger turbo only spools above 3000-4000ish RPM.




[Modified by BlueShadow, 2:38 AM 1/15/2003]

ninesecrx

yeah, must be hooked up on some sort of pressure valving or something. Pretty cool idea but it does have some flaws but with added advanges. The flaws I see is your going to get top hp because the smaller turbo backs up, more parts and cost that could go wrong...put for a guy who likes to have the power down low and top..this would work pretty cool.

texan

If you want power at all RPM, choose a different air pump. I.e. a positive displacement pump like a roots blower or Lysholm. Turbos have certain advantages and certain drawbacks, and if there were some setup that pooled all of the pros with none of the cons everyone would be using it by now. Sequential setups are questionably beneficial.. it heavily depends upon how well engineered the setup is and what type of driving you're doing. Witness the fact that all factory sequential setups are commonly replaced with single turbo systems for overall increased performance, at least when the throttle is buried.

BlueShadow

errr....if you read a few posts up where I had the stuff italicized it does say the exhaust flow is controlled by a valve.

BlueShadow

Just a few tings about the original question...altough the T66 will be "boosting away" as the T25 runs out of breath, the T25 will still pose to be a restriction to the system. In order for the exhaust gas to be able to turn the T66's turbine it still has to pass through the T25 (that's the restriction).


[Modified by BlueShadow, 3:47 AM 1/15/2003]

Joseph Davis

Putting two turbos in series is what a turbojet is... might want to netsearch on turbojets and pulsejets. Nye Engineering used to have a nice site with a lot of DIY info, but it's currently under construction.

Good idea, impractical for an automotive engine. The heat involved would slag the engine.

BlueShadow

It's also how the stock sequential turbos are setup on a RX7 (FD) and a MKIV TT Supra. But it is also common to see owners of stock sequentials to convert the turbos to operate from sequential to non-sequential operation (using the same turbos, but with both turbos spooling together)....unless of course you are talking about a totally different setup.

BudaKai

Their site is back up. http://www.gas-turbines.com/ look here for some info on it.

What I meant by twin turbo was done so this is possible is the whole space and fitment issue DRT did it. This can be done without any valves or wastegates at all if properly sized and actual flow taken into account. I'm amazed at how many people like to make things nore complex than they really need to be. You would only need one wastegate to bypass the smaller turbo because the bigger turbo would never reach it's peak if you size it the right way.

The RX-7's set-up are convert to twin because the complexity of their particular set-up caused them a lot of problems, and troubleshooting these problems became difficult because of this complexity. It had nothing to do with it not working right. If someone actually sat down and fixed every problem that ran beautifully, but who would sit down and look at all those vacuum lines without going insane? Supra owner are after then peak power generally so they don't care if they have lag.

TurbothisLS

so u would place a wastegate with a smaller spring with the smaller turbo?
then when the wastegate dumps, it feeds to the larger turbo which has it's own wastegate?
is that how sequential turbos work?

BlueShadow

Isn't that kinda contradictory?

The RX7's vacuum setup is complex and far from perfect and because of that complexity, it is hard to diagnose a simple vacuum leak from one of the many hoses coming loose. By getting rid of all those vacuum lines (the "Rats Nest") and going with a non-sequential setup they get rid of a lot of potential vacuum problems and make the system a lot less complex.

BudaKai

Ok sorry if I didn't makes sense there, but the reason they went wth sequential is because (those of you that have driven rotaries know this) rotaries make next to nothing for power down low so they needed a "boost" if you will to help them climb the rpm band quicker. Especially since the third gen RX-7 weighed a ton compare to the previous two generations. So came the sequential set-up.

This set-up was far from perfect in the first three years of it's run, but by it's fourth year they had it down to where vacuum leaks were almost non-exsistent in the factory set-up. Reasoning to convert after from the factory would normally be for easier troubleshooting when you have a problem obviously, or to increase the power drastically with-out risking a vacuum leak with higher boost. At first most people switched it over to twin, but a few people upgraded the sequential for a lagless drive.

I can read the entire book to you if you wish. That was a brief summary of the 3rd gen. Unfortunatelly we didn't get that fourth year becaus America was going through it's muscle car revival. Mainly due to the fact all the big sports cars then were Japanese, and this is the birthplace of the sports car(supposedly).

BlueShadow

The weight difference between the 2nd Gen Turbo II and 3rd Gen FD is negligible.

EDIT: the 3rd Gens actually weight less than the 2nd Gens because of all the lightweight stuff they had in there. (IE. drilled pedals to reduce weight).

They went with a larger secondary turbo to give it a higher peak HP. The reason most production cars have smaller sized turbos is to give the driver the impression that the car is fast by improving its low end response. The RX7 does that with the smaller turbo, and the larger turbo enables the RX7 to have it's higher peak HP.

Actually as the years went on and the car got more advanced and complex the number of possible problems increased.

I own a copy of Mike Ancas' book "RX7 performance", I ordered it about a year ago when I was expecting to buy a FD and I used to read it a lot. I dont read it so much anymore because I dont think I'll be getting an RX7 anytime soon (maybe in the future) It's probably the same book you are talking about.




[Modified by BlueShadow, 8:08 PM 1/15/2003]