When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Nothing against John's exh. header desing, just another idea of solving flow energy losses on tight bends.
Also, there is nothing new with this, this has been known fact in fluid dynamics.
The flow losses caused by increasing and reducing the CSA of flowing canal is minimal compared to losses generated by turbulence and flow separation.
For me this approach looks better than increasing the CSA at middle of bending like what has done with later style intake plenum pipes #5 & #8.
The air velocity has more time to slow down before turn.
Nothing against John's exh. header desing, just another idea of solving flow energy losses on tight bends. Also, there is nothing new with this, this has been known fact in fluid dynamics.
The flow losses caused by increasing and reducing the CSA of flowing canal is minimal compared to losses generated by turbulence and flow separation. For me this approach looks better than increasing the CSA at middle of bending like what has done with later style intake plenum pipes #5 & #8.
The air velocity has more time to slow down before turn.
The exhaust side of John's system will be pretty much in it's final form between the heads and the cats after those manifolds are cast. In our 700 axle hp runs with hand fabricated manifolds, we recorded essentially ambient static pressure in the down pipes. It was something like 0.5 psi if I recall correctly. The exhaust side flows really well as it is now and the fabrication time will go down with the Inconel castings. The pulse separation is addresses with pipe merge angles, which is the best one can do in the space there is down there.
Solutions are still being worked on the compressor side. Like the exhaust side, that needs to be upgraded to the higher power goal levels.
The exhaust manifolds will likely be cast from iron, like almost all factory turbo exhaust manifolds. Inconel looks unlikely at this point. Ceramic coating is still in the cards, as are the heat shields on the top side -- no changes there. The new, cast exhaust manifold will flow well, especially in the right direction, because of the merge angles are favorable. The pulse interference problem should be somewhat mitigated by the favorable angles.
On the intercooler front, there's also some progress:
The compressor to intercooler pipe will get almost 60% more area, dropping the velocity and pressure drop by a factor of about 1/1.6. Running that pipe in the wheel well uncorks this flow restriction. More importantly, however, it'll give us the carte blanche on the suction side to fit in the mother of all pipes...
The intercooler will have almost 70% more core volume compared to the old design. The published intercooler "hp ratings" are simply proportional to the core volume, so this means we'll have about 70% more capacity in terms of power production.
The intercooler core dimensions will be, by coincidence or not, very similar to the 944 Turbo and 968 Turbo S intercooler, except we'll have one on each side. We're looking at 6"x5" core cross-sectional area with 20" tube length for the twin turbo, while 944 Turbo and 968 Turbo S have 5.5" x 5.5" core cross-sectional area with something like 18" tube length (don't know the exact length, the whole cooler with tanks seems to be about 24"). People are making over 500 rwhp thru that 944/968 cooler core with a two-valve head, so we should be fine.
Like with the 944/968 intercooler, the core actually flows pretty well, but the entry end tank is critical to the pressure drop. Most people hot rodding 944/968 cars keep the stock core but changes entry end tank. I am confident we'll have a better flowing end tank than any of the 944/968 modified stock intercoolers, for two simple reasons: Our entry angle is more advantageous and our inlet pipe is larger. So we'll have the air making a less abrupt turn at lower velocity -- we win! ;-)
Kewl. What will the bottleneck be in terms of producing power?
Other than scope creep, procrastination, and various day jobs? ;-)
The real answer is I don't know.
As John says on the video, everything is a compromise and some trade offs need to be made. With these intercoolers, we've made one choice now. We've accepted a little bit of core pressure loss for better cooling efficiency. The better cooling efficiency means that we'll be able to make more knock-limited power holding everything else constant.
Everything else is not constant, however. In particular, the better cooling efficiency comes at the cost of having to run the compressor somewhat harder to overcome the pressure loss. Running the compressor harder will require running a higher exhaust back pressure. Higher exhaust back pressure will make the intake port to exhaust port pressure differentials less advantageous, which will rule out very high overlap cams and reduce the efficiency of the combustion chamber evacuation.
Choosing to trade off pressure loss and cooling efficiency in this particular way would probably not make sense if we were running race gas in a race car, but it makes a lot sense running pump gas in a street car. A nice street car will not have crazy camshaft overlap anyway, so not being able to run race-car like camshafts doesn't cost us anything. The exhaust back pressure is quite reasonable with the large turbines that we have, so the exhaust back pressure (or rather the pressure differential and ratio between exhaust and intake ports) will still be lower than for most street cars. On pump gas the charge temperature is a first order determinant of power because of the knock limit, so we're getting some significant benefits in return.
Also, this new arrangement allows for a near-zero loss compressor suction side. That's huge for the efficiency.
All of this considered, I think we're pretty close to the constrained optimum from the air filter to the intercooler outlet. No money left on the table there, as far as I can see.
Next down the road is the intake manifold. Opinions vary on the intake manifold. Some people like to use short-runner minimum restriction intakes on turbo cars, which won't particularly tune to any rpm. Others like to use long runner manifolds that add to the torque at low rpms both directly and indirectly, indirectly by spooling the turbine earlier due to higher natural VE at low rpms.
The benefit from long-runner intake manifold with resonance effects tuned to low rpms is indisputable at low rpms before the turbine has spooled. But what about high rpms?
Recall that this motor will be knock limited at each rpm after the turbine has spooled. Knock limit is determined mainly by three things: Intake charge temperature, the pressure of the fresh charge in the cylinder, and the residual exhaust gas left in the cylinder when the exhaust valve closes.
Suppose that a car has a restrictive, long-runner intake that leads to say 75% natural VE instead of 100% natural VE at 6000 rpm. Suppose further that the car has a very effective intercooler. Here's what we do: We just turn up the boost when the long-runner intake starts chocking at high rpms.
If one compensates for the lower VE with higher boost, two things happen. First, exhaust manifold pressure has to increase (to provide the power to drive the compressor harder). Second, the compressor outlet temperature increases. Both are bad.
However, let's not forget the intercooler that is riding to the rescue. If the intercooler is very efficient and brings the charge temperature to close to ambient, then we now have high pressure cool charge in the intake manifold. When the 75% VE engine ingests that air, the pressure has to and will drop because of the lower than 100% VE. With the pressure drop, the charge temperature will drop as well -- theoretically below ambient temperatures are possible. This will allow the engine to burn more charge mass before the knock onset holding everything else constant. We've cheated the detonation gods!
So why not make the natural VE really low to make the most power? There's a limit to the benefits of this strategy, mainly because the rising exhaust back pressure will result in more burned hot exhaust gas staying the combustion chamber, which in turn increases knock. So this is _not_ one of those cases where if little is good, more is better.
At this point, we have no idea where the optimum is. It's not clear whether we'd make more usable power with a long-runner or short-runner intake manifold. We may find out in 2016, but for now we're sticking with the stock intake manifold.
Recall that this motor will be knock limited at each rpm after the turbine has spooled. Knock limit is determined mainly by three things: Intake charge temperature, the pressure of the fresh charge in the cylinder, and the residual exhaust gas left in the cylinder when the exhaust valve closes.
You guys are still thinking of this the wrong way. You are missing a variable.
You guys are still thinking of this the wrong way. You are missing a variable.
Well, why don't you enlighten me about how I am wrong and what I am missing. I just hope it's not about your E85 fixation.
The goal is to build a street car that you can drive around with the A/C on, that doesn't overheat in hot weather, that runs on pump gas and that can be filled up at any gas station, has reasonable operating radius with a tank of gas, and that drives in a smooth and stock like way at low rpms. These requirements dictate many things, including the fuel octane number and other chemical properties of the fuel.
Just make it painfully clear to you: I _am_ aware of the existence of the E85 fuel, its chemical properties, how it impacts engine design, and its availability (or rather lack thereof). So that's not something I am missing.
These guys will sell you one, with all the E85 conversion parts: http://kalecoauto.com/ From memory, I think they sell the telescope design.
Since we've already burned some posts about E85, why don't we get right down to the torque vs. horsepower discussion... KaleCoAuto will by the way sell you an adjustable power band, too, which will allow you to independently adjust hp and torque:
Adjustable Powerband
$95.99
Wish you had a little more low end torque? Maybe you want a high revving formula1-esque screamer? KaleCoAuto's Adjustable Powerbands are the perfect solution! The power bands are made from titanium-injected rubber, with high grade 440 fasteners. Six links are included. One band is for horsepower, and the other for torque. You may use more than three links per side, but extreme caution should be taken!
Over here E85 is available at almost all gas stations making the choice to E85 without doubt. The authorities are talking of banning fossil fuel in the future.
Hurray for the environment.
Åke
Over here E85 is available at almost all gas stations making the choice to E85 without doubt. The authorities are talking of banning fossil fuel in the future. Hurray for the environment.
E85 pollutes, too, in two ways. First, making E85 is very energy intensive. Second, and this is a much greater concern of mine, E85 continues to pollute many otherwise interesting Rennlist threads...
Moving on...
Now with the intercooler design picked, we'll have to re-estimate where we will be on the compressor map and figure out if anything else needs to be adjusted and what goals are realistic. In other words, we'll have to figure out where we'll be on this map:
03-13-2015, 07:12 AM
Cobra head style exhaust pipe bend.
