pluto

Hey Howard, when you come down to Texas for Texas mile, let me know, maybe you can take a test drive on my track car at the track. You can use my dyno anytime if you need some fine tuning down here.

StavFC

Looks great. Do you not think 600bhp, even at the wheels, for 200 in the standing mile is a bit optimistic?
Ive times countless cars in my job, many over 200mph, but although 600bhp is enough for 200+, it generally takes about 1.25miles with that sort of power on your average weight/grip/aero car.

Also the wastegate direction being exactly the opposite to optimal once open- Do you think this is no issue, in respect that the flow out of it is so little it wont hurt performance? Just you see the big efforts works race teams put in to a smooth flow from exhaust port to wastegate makes me wonder.

Brekyrself

iTrader: (30)

Can you elaborate.

Howard Coleman

iTrader: (6)

"Do you not think 600bhp, even at the wheels, for 200 in the standing mile is a bit optimistic?"

a 550 rwhp LS7 FD ran 196 w the front end looking to take off last october. the V8 has torque from the moment you drop the hammer so i figure 600 rotary and get the nose down will do it... but actually i don't have a clue.

i will tell you this: the coefficient of drag and frontal area of the FD is in another world compared to the ZO6. if you took the 550 LS7 that was in the FD and ran it in the ZO6 you would be down 15 mph due to frontal area and drag. aero is everything at 200.

....................................FD............ .......................ZO6

frontal area..................19.26 sq ft......................22.3

drag coefficient...............29...................... ..............34

aero drag.................... 5.585............................. 7.582

advantage FD 26.3% less drag

drag goes up w the cube of the speed. the FD should be a top end monster.

"i will also be running a brand new design Pettit intercooler."

i will see it for the first time when i open the box. supposedly the end tanks were done on a flow bench. makes sense to me... i will post a pic when it arrives in the next few days.

thewird

iTrader: (8)

Wastegate is used to reduce boost and has nothing to do with performance except for the fact at having stable and controllable boost. At high boost pressures, you need less and less of your wastegate as you bring the boost up.

thewird

SirCygnus

iTrader: (1)

hm... where are you getting those numbers? from wikipedia...

http://en.wikipedia.org/wiki/Automob...ag_coefficient

Cd
0.33 Mazda RX-7 FC3C 1987
0.31 Mazda RX-8 2004
0.31 Mazda RX-7 FC3S 1986
0.31 Mazda RX-7 FD R1(R2) 1993
0.31 Chevrolet C6 Corvette Z06 2005–present
0.29 Mazda RX-7 FC3S Aero Package 1986
0.29 Mazda RX-7 FD 1993
0.29 Chevrolet Corvette 2005
0.29 Chevrolet Corvette C5 Z06 2002
0.286 Chevrolet Corvette C6 2006

Trots*88TII-AE*

iTrader: (11)

In the rotary world, I'm going to have to disagree. Because our turbos are not matched perfectly to our motors, we need the wastegate. I agree, the harder you run your turbo, the less you worry about wastegate flow. But for 99.99% of our applications, exhaust flow is always traveling through our wastegates, except during spool-up. How much flow is dependent; but as an example would you purposely design an intake manifold to flow very un-optimally through the primary ports just because they don't see the majority of flow? If wastegated (word?) exhaust flow had nothing to do with performance, then people would not need to be concerned with exhaust re-entry angles, etc.

In my opinion, a reduced lifespan of my wastegate is less of a concern than an efficiently functioning wastegate. Diaphragms are cheap...

Howard Coleman

iTrader: (6)

"where are you getting those numbers?"

"Aero tuning reduces total lift and balances the front and rear lift coefficients while increasing the base Vette's 0.28 drag coefficient to 0.34."

(http://www.motortrend.com/features/1...#ixzz0pJsyVADu)

while the number comes from Motor Trend i don't think they have a wind tunnel. the article was the introduction to the 2006 ZO6 and featured lots of neat X ray pics etc. my wild guess is that the data came from Chevrolet. they do have a windtunnel. Wiki probably does not.

clearly the ZO6 trades alot of drag for downforce which works on road course especially when you have alot of torque.

similarly the R1 trades some drag for downforce .31 for .29.

if you check results at the Tex Mile you will see alot of high hp ZO6s struggling to reach 190.

obviously if you wanted to run the number you'd leave the ZO6 at home and bring the standard slippery Corvette. you would still be pushing 15.7% more frontal area.

hc

thewird

iTrader: (8)

I was merely suggesting that the the wastegate not having exhaust priority has no performance loss and therefore no performance benifit from having an efficiently designed wastegate routing. As long boost is stable in both setups the backpressure would be the same for the engine and make the same power.

I'm not obviously saying that having an efficiently designed wastegate routing doesn't have its perks. With priority to the wastegate, your able to keep the wastegate closed longer before opening (with an ebc) which will help with spool-up. You may also be able to get away with a smaller gate which would save cost and possibly some minor weight savings.

So I don't believe it will make more power but can improve those other things I mentioned.

Howard or anyone, thoughts?

thewird

BLUE TII

iTrader: (9)

A good flow path through the wastegate DOES have a performance benifit of more power though.

With the tortured flow path through the wastegate the motor has to push harder to force the exhaust out so your exhaust manifold pressure increases.

The exhaust backpressure not only lowers power through exhaust contamination in the intake charge during overlap but also pressure cooks the engine and the added thermal load decreases performance and reliability.

Here is a set up designed around lowering exhaust backpressure through careful wastegate placement.



and some words about it by the creator.

Well to compare with other setups you would have to be factoring in back pressure..if we wanted to raise the back press we could, and did see a 1000 rpm change in spool..but what we were working on, was achieving a one to one ratio. boost vs. back pressure. and that is what we have now, 19 psi of boost and 19-20 psi of back press. the entire system works much better, runs cooler, makes more HP, with less strain on the engine and gets better fuel economy. for us and how jack drives it works just fine. we routinely out run 650 hp vipers and maintain cooler egt's, oil temps and cooling temps then even them, and they are NA....
Twins Turbo....

BLUE TII

iTrader: (9)

Here is one of Howard's old boost pressure vs exhaust backpressure graphs- 16psi boost and 25psi backpressure.

If you overlay this graph with the dyno graph you will really see what happens with the turbo rotary and wastegate flow.

A performance turbo rotary will hit peak boost at 3,500-4,500rpm and the wastegate opens. Exhaust backpressure drops as an additional flow path is opened.

Now, between 3,500-4,500rpm and a rotary's peak power at 6,000-7,000rpm the power and exhaust flow doubles to quadruples and as the wastegate flow ability is overcome the exhaust manifold pressure again increases.

The better the wastegate flow path the less dramatic this rise in exhaust manifold pressure.

To lower exhaust manifold pressure one can either put such a large turbo on that peak boost and hp point are very close to same or really work on wastegate flow and retain a somewhat responsive turbo.

On a piston engine with a performance turbo peak boost and peak power occur much closer to the same rpm and hp point so the wastegate does flow very little and poor wastegate flow has a lesser impact, but still this issue has been identified and addressed in many performance applications.

Howard Coleman

iTrader: (6)

"Here is a set up designed around lowering exhaust backpressure through careful wastegate placement."

first off i think the majority of turbo manifolds were engineered with the number one priority being packaging.

not saying it isn't a factor but the driver for manifolds should be performance. i also think that there is a significant difference in manifold efficacy based on specific design.

there are more factors in play than you might think, and they all eventually net out on the dyno given proper instrumentation which of course includes digitally logging exhaust back pressure and EGTs among other things.

when above manifold pics were posted i spent a fair amount of time looking at them. i only see one good feature which is the entry angle on the WG.

number one on my list of priorities is short primary runners. heat/pressure, the drivers that make everything happen, decrease progressively w length. i want my turbine wheel as close to the exhaust port as possible. i want no bends or as few as possible. bends bad. i see 4 bends and alot of tubing on the primaries. i see 2 bends in the WG exhaust along w the fact it is tapped into the blend so it loses the divided pulse. (mine does keep them separate until the WG opens however the WG is open much of the time.)

the manifold is beautifully crafted and probably works very well and my hat is off to the creator/s.

as the title to the thread states... "separating fiction from reality." it will be interesting to see if the angle on my WG effects performance. i would point out that the WG circuit must be viewed in it's totality... my wastgate exhaust is dead straight (2.5 inches tube diameter and very short) into the DP. it enters at a nice blend angle. i also run a 60 MM WG.

there are always tradeoffs in manifolding given our engine bay constraints. i envy the full on tube frame cars as they can really really have it all as far as manifolds.

howard

thewird

iTrader: (8)

But wouldn't higher exhaust backpressure caused by inefficient wastegate flow increase turbo boost since the flow would instead go through the turbine? Assuming two setups are able to achieve stable boost that doesn't overboost, I would assume exhaust backpressures would be identical. Maybe the inefficient gate might have to open more to compensate but once both are achieving the same stable boost, I would think the exhaust backpressure would be identical, would it not?

fyi, i'm posing this as a question and not trying to argue :P

thewird

Trots*88TII-AE*

iTrader: (11)

I'll agree with you there, however it would seem to me to be more beneficial to divide the bends pre and post wastegate evenly, because as it stands, the exhaust has to make a very abrupt turn into the wastegate (at least that's how it looks) I would think that a slighter angle into and a bit of an angle out of the wastegate would work better. Do you have any plans on trying different manifolds out on the dyno? It would also be nice to compare short runners vs. long runners.

The problem here is that there is more to turbo spooling than just exhaust backpressure. If that were the case, every setup would need identical backpressure for a given intake manifold pressure, but it is not the case at all. Increased backpressure can help increase spool, but in your peak power band, any positive delta pressure on the exhaust side hurts the scavenging effect on your intake during overlap. That was the theory behind the Twins Turbo manifold pictured above, it was designed for efficient wastegate routing, and decreased backpressure, and to fit in an FD, not so much for spool-up.

thewird

iTrader: (8)

But wouldn't the exhaust be flowing the same when comparing the 2 different wastegate placements as long as the engine is generating the same stable boost on the same turbo and engine?

thewird

Barry Bordes

Howard's manifold is great.
Simple, compact, and efficient.

We want flow to the turbine wheel not the wastegate.
The wastegate is just a leak to stop the turbo from building more pressure.
If you are having boost creep then work on that.

The turbine is driven not just by pressure but the explosive port pulses and heat.
The closer and straighter the better.

Here is an HKS SS which is similar but not as compact as Howard's. (pic from Pete's SP)

Barry

Howard Coleman

iTrader: (6)

"explosive port pulses"

which decrease in power exponentially with distance from the source.

Speed of light

iTrader: (8)

+1; additionally you can say:

AND [explosive port pulses] decrease in power with any increase in total runner volume or loss of heat.

I think you are on the right track Howard. Proximity, minimum volume and heat retention are the key factors IMO. I'm not so concerned about the unusual WG entry angle. Exhaust gases are not very dense and can make that turn--in fact, the impedance of the turbine housing is going to reflect some energy right into the WG. And I like where the actuator is. Looking like a well engineered factory piece.

I'll bet it works real well....

BLUE TII

iTrader: (9)

If your combustion/expansion of exhaust continues outside of the engine the most energy to drive the turbine will not always come from the shortest distance/smallest volume manifold.

If you factor exhaust tuning the shortest manifold will not always have the strongest dynamic pressure waves at the turbine wheel.

BLUE TII

iTrader: (9)

There are many trade offs depending on how you want the system to perform of course.

For good low rpm boost response you do need the small volume, high velocity manifolds with the closed wastegate path not impeding flow (90 deg off runner) for all the reasons that have been stated.

This and ease of packaging is what 99% of factory and aftermarket turbo manifolds are designed around.

If you are focusing your manifold design for operating best within the narrow rpm range used in a race and with the reliability concerns of that racing the manifold design may look very different.

black06g85

iTrader: (3)

good info here.
tagged for future projects

Prometheus

iTrader: (2)

This is awesome, I love learning.

I'm very interested in seeing what data is result of this demonstration.

Barry Bordes

Are you saying that short individual tubes would be at a disadvantage in driving a divided housing turbo?

Do you have some supporting data?

Barry

Barry Bordes

Even some of the guys going for high RPM, high power use short as practical tubes.

Eye Candy,
Barry

BLUE TII

iTrader: (9)

Are you saying that short individual tubes would be at a disadvantage in driving a divided housing turbo?

It is all compromises.

At low rpm (say 1,000-3,000rpm) where exhaust flow is small and there is no intake charge being forced into the exhaust to enhance the external combustion there is a definite advantage in spool to standard short tubes with high velocity and less heat loss.


At higher rpm (say 3,000-6,000) where exhaust flow is large and intake/fuel charge is being forced into the exhaust enhancing the external combustion a long runner manifold will allow more time/space for the exhaust to combust/expand before it hits the exhaust turbine.


Even some of the guys going for high RPM, high power use short as practical tubes.

The eyecandy is pretty, but those tubes look like the typical length of a shorty tuned header. Also, what is the overlap on those turbo cams compared to a rotary- usually much lower on a turbo piston engine.

Apples and oranges.