Sequential twin turbos are two turbos setup so all of the exhaust gases can pass through just one of the turbos then when a certain objective is reached (4500RPMs on the 93+ RX-7s) an actuator opens a valve to divert the gases into bother turbos. In the case of the 93+ RX-7s there is also a prespooling actuator that flows air into the secondary turbo as the RPM's increase so the secondary turbo is already spinning before the actuator opens up. The 93+ RX-7s turbos are both of equal size. The VR4 and 300ZX do not use sequential turbos, they use parallel twin turbos, one for each side of the engine. The 93+ Supra does utilize sequential turbos, I am not certain however I believe they are both the same size. The sequential turbos on the 3 rotor Eunos Cosmo uses a slightly larger secondary turbo than the primary.

Most people do not understand how exactly turbos are affected by the exhaust. A few things a lot of people think but are not true: two small turbos equalling the flow of one large turbo will nto necessarily spool faster, one small turbo and one large turbo will not decrease turbo lag, it will increase it as the exhaust gases are further diverted into two turbos in effect creating a larger single turbo. Boost does not stack. Twin turbos running at 10PSI does not create two 10 PSI's or double the pessure on the engine.

Why run two turbos in parallel? Theoretically two turbos equaling the flow of one large turbo will spool up faster because of reduced weight, however this usually is not the case in real world use. Twin turbos are usually used to make more HP than one turbo, because of space constraints with a V engine (having to run exhaust pipes under the engine to combine flow to the other side to flow into the one turbo), or to increase boost response. In this setup you are basically splitting the flow of the engine 1/2 into each turbo, therefore it will not spool up way faster. One a 3.0L engine you are putting basically 1.5L displacement into each turbo.

Why run two turbos sequentially? Because you use one small turbo spun by all the exhaust gases then at higher RPM a second turbo comes on, how does this add more power? Well it is able to increase the airflow without increasing the heat so efficiency is increased thus forcing more air into the engine at the same pressure levels (because cooler air is more dense) this is why 10psi with two turbos is more HP than 10psi on one turbo even though its still only 10psi at the engine. Downsides? It requires very complex plumbing and controls to do a sequential system. An aftermarket sequential system would very complex and expensive because it would be a one off. This creates more problems and more heat as well as more money.

 

You are very smart. I thought the idea behind these cars was to utilize two different sized turbos, one small and one big that come on at different times. I guess not, thanks for the technical write-up, I'll try to burn that into my head. This is a very informative thread, keep posting more fun turbo information!!

 

sh'yea jeff, triumph, really... :P

Chucky, torque is a stupid number to include in the estimation of the performance capability of an engine because of what people are inclined to think it implies (and thus the inane descriptions of how a car performs which drive me up the wall, by automotive journalists who can't tell the difference between their *** and a hole in the ground).

torque, as a measurement of force per revolution, is of course an important aspect in measuring the power of a motor and is indicative of a motor's point of highest efficiency. but, what's often associated with that number is 'how hard it pulls off the line' or some garbage, that magically torque pulls the car in the low end and horsepower keeps you going at the top end.
really, it's all just horsepower, the more you have at one speed of the engine the more the engine is going to pull you forward: it doesn't really care how you go about getting that power, whether you have a 110lb/ft 700hp wondermotor in a race car, or an 800lb/ft 320hp stump pulling truck motor. it's true that a high torque number at a low rpm is indicative of a motor which makes a lot of power at a low speed, but the power does the pulling. in an ideal world it doesn't matter how much torque you have as gearing totally negates the torque number the engine makes, and just takes the power number, devides or multiplies it out by multiplying or deviding the speed it's applied to the wheels, and presto your new real torque number where rubber meets road. so small zingy motors need to be zinged and slipped more, while chunky, manly V8's just need a drop and stomp, but equal amounts of power are equal, no matter how much torque is used to make it.

only thing that matters is the shape of the power band. BVBM is the only one that understands me *i cry*

 

http://www.yawpower.com/tqvshp.html

 

Chucky? I didn't realize you and I were that familiar yet, Wakeech. Anyway....

I completely understand the concepts of horsepower and torque and the distinction between the two. And, as I had suspected, you affirmed for me what I thought to be the real argument here; torque values are useful for people who know how to read dyno charts properly and design a drivetrain combo that best suits a given objective. Horsepower numbers have another use for the well-informed but are usually thrown around indiscriminately by idiots who have no clue what the important aspectsof engine operation are. As you stated, it is the shape of the power band that really matters but, since the math is a fixed equation, what is the variable used to determine the shape of the power band?

I would like to ask that the next time you address me you do so with the same level of respect I have shown you now or in the past, whether we have agreed on an issue or not. Derogatory tones aren't worn well by people who have otherwise good information to impart on this forum. Thanks.

Charles

 

That's the point. I don't see why there's a need to write so much about it. It's ultimately about force at any given speed (of course force is torque at any given speed at the wheel divided by the wheel radius). In addition acceleration is also inversely proportional to any rotational masses (wheel, flywheel etc.) and friction forces (air friction, wheel friction, transmission friction etc.).
After all force (pressure divided by the piston/rotor area) is what moves the pistons or rotors in the first place and force is what moves the car at the end.

 

Torque is what is important to me because it is what affects HP. When I am tuning a car I am looking at how the modifications will affect the torque in all RPMS. Considering most of our cars are street driven that we modify power across the whole RPM range is important to us. The reason torque is generalized into "off the line" power is because higher torque at low RPM will = more HP at that RPM. I want power across the whole RPM. The first thing I look at is will this modification increase or decrease my torque from 1500-3500RPM where I spend most of my time driving? If it doesn't really affect anything down there, but increases the torque above 3500RPM then I will feel faster acceleration when I am using all my RPMs but won't really feel a difference in my daily driving.

Most of the time when modifying small displacement naturally aspirated engines, from the factory restrictions decrease the torque as the RPMs increase after a certain point, by replacing these with better flowing components we can increase the torque after the peak, without showing a torque gain but if we can hold the torque out longer into the higher RPM's we will see a HP increase.

Now would you rather have an engine that makes 300 torque from 2000RPM to 9000RPM peaking at 515HP or one that makes 600lb ft of torque from 2000RPM to 4500RPM still peaking at 515HP?

Paul Yaws site is very informative however his comparison is a little skewed for our situations. I dont think many of us are increasing the performance of a turbo diesel or an F1 car that revs 18000RPMs, however the same information still holds true. However most of us do not want to make our cars faster by removing Mass or changing the gear ratios, thus lowering the cars top speed to make it accelerate faster so that leaves us with increasing the torque to increase HP.

 

Now girls, play nice. ("girls" does not include you Kari because if you really are a girl.....I love you) Since I also asked Wakeesh for his reasoning on this I might chime in. Since reading said explaination I concur, mostly. Then so does Charles. Might I restate this in non tech phrase.

But first you should know that I'm so fond of torque that my dogs name is Torque.

We have no problem with the term torque, it is the USE of it. More importantly the MISUSE of it. This is continued by the automotive press and educates the newbee incorectly. "This baby makes torque" how many times have we heard that? They all make torque if they run.

This isn't any different then my personal bitch about "volumetric efficency", It's MASS FLOW you idiots. But that has been spoken so many times that it is embedded permenently, forever and ever. The same goes for torque. Just be happy we have someone to joke about.

I liked that Yaw site alot. Does he also "Pitch"?

So that's it we don't have to beat anyone up about it anymore, finished.

 

Yes Kari is a girl, she wants an Axial flow supercharger for her 99 Miata race car so if you want to meet her let me know. I know where she lives :D

 

Wonder how many people are going to get this :D

 

Back to the turbocharger. What are approximately the highest pressure ratios that you can reach with a centrifugal compressor (turbo) (still reaching an adiabatic efficiency of over 70%)?
What's the adiabatic efficiency of a simple piston, assuming it would be run as a supercharger?

 

Ice, Only pilots and sailors. Well some race car builders too.
I just happen to have a compressor that would work on a Miata. Just no kit.

On the cent comp Pr, I don't know. Holding that 70% is the hard spec to meet.
The piston if it's Otto cycle, about 37%.

 

If I had a dog its name would be Turbo, so you know where my knowledge lies Torque would be my choice for my cat though.

I don't expect a kit for a car you probably don't even have. I have done the centrifugal, done the Eaton MP62, now planning on doing the 1.2L whipple. I can get an intake manifold for that (of course I wan't cold side mount). Right now the car has headers and a catback. I am planning on putting in an ECU, most likely a TEC3 as well as a clutch and flywheel, then I would be pretty much set to get a supercharger on there whether it be yours or a whipple. Since I would already have the fuel system and ECU taken care of all that would be left is the mounting of the supercharger and belts. Removing the intake manifold on the 99+ Miatas is a chore though.

My goals are a modest 170rwtq across as much of the powerband as I can get without an intercooler. If I were to go with the whipple I would need an A/W or A/A ic to get the 200+ rwtq, then I would need to go ahead and upgrade engine internals for my ultimate goal of a stroked to 2.0 and 300rwtq to 8000RPM. With that much power gonna need to go fender flares and new suspension with wide rubbers all the way around to be competitive for the class we will be in.

I manage a car dealership in Garden Grove so Chatsworth isn't too much of a stretch to visit sometime and see what you have going on and see what challenges would need to be overcome installing one of these.

Kari is complaining that her car is way too slow even though I put on the header and catback for her Guess she got spoiled driving the van that has triple the power of her car

 

I know Paul can certainly roll with the best of em....

 

Having built both a turbo system and installed an SC system on a Miata, I can tell you that the turbo is definately better.
We can go back and forth on why and have all kinds of scientific discussions about it, but the turbo produces a better result.
There are a lot of intangibles in place, so you just need to drive both.

 

I'd like to see an axial flow on a Miata. The cool thing about that supercharger would be that the intake manifold doesn't have to be removed.

MM: If you are comparing a turbo kit to the Eaton kit for the Miata, I would have to agree.

 

Eaton, yes. Also the Lysolm twin-screw and the Whipplecharger.

Turbo experience is better than all of those. I've never driven an axial-flow vehicle, unless you count the Turbo-Zet. :D

 

I got that ranger.

 

I have also had an FMII Turbo setup on a 1.8 MX-5, I am well aware of the differences between supercharged and turbocharged miatas. This debate has raged for years over on Miata.net, turbos vs. superchargers however most experienced racers are in agreement that the turbocharger seems to be the better solution for higher speed track racing, i.e. club racing wheel to wheel on buttonwillow etc. while the supercharger is the better solution for autocrossing. Head to head comparisons running turbo vs. supercharger has convinced me to go this route as well as the success of the FM Ubercharged cars in SMII this past season.

This particular car is for Kari in Solo 2 SMII class, on these tight low speed tracks a supercharger will have the advantage as their are lots of on/off throttle situations where the lag of the turbocharger becomes painfully apparent. This is why I gave up campaigning my 93 RX-7 seriously in autocrossing and have stuck to the Miata. After having seen an Eaton MP62 car making a good amount less power than a GT28R setup M2 MX-5 run over a full second faster with the same driver on the same course, that was the nail in the coffin for me.

Also if you have seen the recent results of RJW over on Miata.net, making over 340HP with an Eaton MP62 roots supercharger on pump gas, I have no doubts I can make plenty of power for a 2200lb car with a supercharger. Considering how there are a few supercharger kits out now that push the limits of the miatas stock motor and transmission there is no reason to go for the solution you like best.

I won't ever say again a turbo is better than a supercharger or vice versa, just that they are different.

In addition the Whipple is a Lhysolm.

 

When I play tuggy with my dog he can almost pull me over. If Torque were a cat he would have to be a lion or such to make that kind of torque. Therefore Torque would be a poor name for your house cat. Now if Kari has a tiger for a pet besides being a girl, then I shall forever be quiet.

 

Torque was a poor name for a movie about motorcycles as well...

No pets in our house, yet.

Now back to our regular program...

 

Talking about high compression ratios on turbocharged engines:
Apparently the new VW 2.0 l turbocharged gasoline engine with direct injection has a compression ratio of 10,5:1.
http://www.germancarfans.com/news.cf...kswagen/1.html

 

The upcoming Mazdaspeed 6 will also have a relatively high compression ratio as well, I think 9.8:1 or something, but both engines are direct injection which helps cooling and lowers the chance of detonation with higher compression and boost levels allowing the power output to be increased.

 

Alot of research has reulted in different combustion chamber shape in piston engines that helps reduce the chances of knock. That is how compression ratios are rising yet boost is still being used. I'm not sure how we can change the combuston chamber shape in the roaty to do the same thing.

 

RG, the only thing left to shape would be the quench zone on the rotor face, itself.

Charles