Tom-Guy

Inertia very much has not been overcome. Look at a super peaky Honduh dyno sheet sometime... the slope of the horsepower as it comes up is a change in turbo shaft speed aka overcoming inertia. Look at a compressor map sometime if you don't believe me - at a fixed pressure ratio (wastegate settiing) the point of flow moves to the right as power comes up. On most Garrett maps you'll see each island is also labelled with a shaft speed... you cross over a bunch of those points as the point of flow moves to the right on the compressor map = change in shaft speed. Turbos operate dynamically; there is no getting away from inertia.

liveforphysics Luke was the major proponent of the big-merge-collector-fed-wastegate-tiny-turbine-stuck-off-to-the-side manifold design, and a lot of people in the industry sat up and listened to him because the kid was a boy genius with a BA in ICE at 19. Little known fact of the matter is that Luke changed his mind about the theory after actually building one and monitoring pressures, bsfc, and power output. Last I heard from him he was drillling holes into compressor covers and building custom intake tracts that were supposed to accomplish whale ***** like intake ergonomics for boosted rides, and he didn't care about manifolds so long as they didn't crack.


That's false. Look at the average ---- retentive NA build vs the average turbo build that has less in the whole car than the NA build does in the suspension.

Locally, Old Man Blossfield is making 248 whp at 12 psi off a D16Z6/Disco-P in a full weight 93 Si, and running 7.70's in the 1/8th with low 1.7x 60's. Travis Grimm was making 258 whp off his 85X92mm aka 2.1 liter stroker aka $9000 longblock, laid into a gutted 93 DX, and turning 7.40-7.50's with low 1.7x 60' and some high 1.6x's. There's a 500 lb difference between the vehicles, but Old Man Blossfield runs within a quarter second of the NA hatch, and with a higher trap speed to boot. If weights were equal the NA car might sit beside him until most the way towards the 330', maybe.

There's a whole lot to be said for driver talent, too. Most turbo car owners are hooligans, and drive like it. :P

Racintweek

you man w/ the turbo z6 is running so quick because of proper (almost proper) turbo sizing, which is really the root of the problem in the peaky dyno honda world. like i said, with a proper WG placement you could run a smaller turbine which means fater spool and not falling out of boost between gears.

if you run a gigantic compressor you only make 600hp for 500rpm because it took your whole rev range to get the turbo efficient.

Tom-Guy

I agree with that totally, but you don't need fancy wastegate placement to get it. Look at this internally gated GT2871R dyno chart, low power is 7 psi wastegate and high power is 12 psi... what a difference in power 5 psi makes, gobs and gobs of midrange:



And the laggy drag turbos make 600 whp for a bit longer than 500 rpms... but it does have to be revved to 9200 and the driver can't lift off the gas or the car hiccoughs and falls on it's face for a split instant. Mostly due to it being an 81mm bore instead of an 84/85mm bore which would spool a lot quicker:

Racintweek

its not just wastegate placement, its turbo size as well. when you can relieve exhaust manifold pressure super efficiently it lets you run a smaller turbine, which we all know creates mid-range power, with out choking the engine. it can be on a log, squarefold etc, mani design doesnt matter like you said.

its all part of a system, not just one part makes the whole build.

Tom-Guy

Disagree. There may or may not be a small trend along those lines, but for practical purposes it's worthless.

Using what you have pegged as an unideal wastegate placement, the 630 whp car above is running 0.39 bsfc... for a turbo car. Best I've heard of on a turbo Honduh is 0.38 bsfc. There is obviously nothing wrong with the system's efficiency with regard to wastegate placement and turbine sizing.

Racintweek

for a 630hp drag car it doesnt matter where the wastegate is because peak power is whats important. when you are trying to maintain a flat torque curve from say 3000-7500 you need a turbo that spools well and a wastegate that can decrease manifold pressure to let the engine breathe up top.


even though your intake pressure stays the same through the RPMs exhaust mani pressure continues to rise which tries makes the turbine spin faster, unless you have a wastegate to relieve mani pressure. if you keep the exhaust manifold pressure relativly constant boost will remain constant because the force turning the turbine stays the same.

Tom-Guy

The car above has a flat torque curve... As flat as the boost curve, anyway. On 19 psi wastegate its flat as a strap, everything higher just tapers but the torque curve looks just like it all the same. You can thank Brian Crower for that.

Racintweek

the sohc graph looks nice but on the 600hp car you could use a smaller turbine to bring boost in sooner and a larger/better placed WG to relieve excess manifold pressure once it hits full boost so that the top end remains the same. yeah it is a full drag car but most 300+hp honda dynos look similar, and since most car are driven on the street who wouldnt want mid range to go along with top end power??

Tom-Guy

Using the manifold design you espouse, a smaller turbine would create a larger average manifold pressure as the pressure-enthalpy conversion across the turbine would be less efficient.

Wastegate positioning does not take priority over turbine positioning. Even Corky Bell got that much right. Run both off a merge collector with nothing more divergent than a 35 degree divider, OMG YOU ARE SUPERIOR TO A LOG MANIFOLD.

Walter

yep. it's logical, if ur are runing with big turbo on low boost you willl need to throw out to exhaust more air then ull need a big wasgate..