JasonC SBB

OK I'll buy the idea of "pressure at the back of the valves" and "flow resistance in the ports".

So this suggests that density (boost) will affect flow resistance.

However...

And this supports my original point. If 'k' is constant, the pressure drop is directly proportional to density aka MAP.

No, look again at your equation. For the *same velocity*, mass flow rate (power) increases *in proportion* to the pressure drop across the intake runners. And this is one my earlier key points. Velocity and thus *volume* flow rate remains constant for a given RPM. Increase boost, and mass flow rate increases proportionally. Your equation does NOT suggest that the pressure restriction rises "exponentially" with increasing pressure. IOW it does NOT support the idea that there is a "wall" beyond which the manifold cannot flow, at 310-320 hp.

The same "wall" with the same shape torque curve was visible at just 265 hp in Ian's car with a GT2560. (see earlier post with link to dyno curve).

I still think that the "wall" is simply multiple factors ganging up together at the same time.

JasonC SBB

Easy peasy.

fitting -> 1 foot 1/8" copper pipe -> 6 ft. vacuum hose -> 30 or 50 psi pressure gauge in cockpit -> sexy assistant with video camera on tach, boost gauge, and TIP pressure gauge

I used my EGT port which is 1/8" NPT. I bought a 1/8" NPT compression fitting at a hardware store, screwed it into my EGT port, inserted the copper pipe, and cinched it down.

Before anyone comments about hot exhaust gas - there is no flow and the 1 ft of copper pipe isolates the rubber vacuum hose from the heat.

If you're adventurous you can route it to a 3 or 4 bar MAP sensor and wire it to the AEM to datalog it.
You will find that during spoolup TIP abruptly peaks just before the wastegate opens.

MeOughtta

I can't speak from direct experience with RH mannys - only more general fluid dynamics experience/knowledge.

1) The volume difference simply isn't significant. Even if it was a 0.9 liters, that is only 2 revolutions or about 1/25th of a second difference at 3000 RPM.

2) The mass difference (more specifically, the thermal capacitance) might be significant. The bigger/heavier the manny, the more heat it can absorb when the throttle is applied. The more heat it absorbs, the less energy is delivered to the turbine wheel.

3) Aside from the the thermal mass issue, equal-length is unquestionably superior. The inefficiency of having independent cylinder pulses compete for the same (or nearly the same) space in the manifold/turbo/exhaust is difficult to overstate - it will be a big negative in terms of both effective back-pressure and turbine efficiency.

M.

Savington

iTrader: (31)

That's what I said:

My point with that post was that IMs won't make a difference when you are making 220whp with a GT2554R at 15psi, but they will make a huge difference when you try and make 330whp from a 2871R at 15psi because the mass flow rate AND velocity must increase.

Savington

iTrader: (31)

It wouldn't be significant if it were a closed chamber, but the turbine wheel is venting pressure from the manifold. In addition, we aren't just looking to fill the manifold with air, we're looking to pressurize the manifold.

lordrigamus

iTrader: (14)

I would also think the short ram, as long as it's equal length to rule out turbulence and reversion, would have an advantage over a longer ram horn due to the fact that there is less of a decrease in velocity and less cooling of the gas itself.

The longer the distance the gas has to travel will result in a greater velocity loss when it reaches the turbine wheel, correct?

The longer the gas is in the manifold, the more the manifold heat soaks, resulting in a cooler gas which is less expansive and has less stored energy. Also correct?

Volume would make a difference in those aspects, wouldn't it?

I'm not sure, the difference may be negligible. I'm curious myself. Forgive my ignorance, i aint gotz much schoolin.

JasonC SBB

You need to look at the % drop in torque from 5500 RPM to 7000 RPM.

On my GT2554 it was like 10-12%, when at 10 psi.
On Ian's GT2560 at 12 psi, it was the same.
I'll bet on your GT2871 with the stock IM at 15 psi it's the same.

On my GT2554 at 13 psi the drop increased to close to 20%.
On Ian's GT2560 at 15 psi the drop increased to 20% also.
Ditto for your setup with stock IM at 21 psi.

Do you see a pattern? The turbine is probably choking.

Note that the setups that choke out appear to max out and flatten at a given power as opposed to continuing to climb.

And of course, switching the IM out to an IM that breathes better at the top-end will unchoke the turbine, because the compressor needs less shaft power, good for another 3 psi or so. My theory will be supported if the data shows that your setup chokes at the top with another 3 psi, and if other setups that show the large torque drop at the top-end, show rocketing TIP.

Import Al

iTrader: (5)

Man there are some experienced & smart guys weighing in here.

I thought I'd contribute something, although its pretty plagiaristic. How
about a twin-scroll? Our engine bay constraints might make ram-horns
more plausible than longer full-length & top-mount manifolds though.
This also limits turbo choice to twin-scroll turbos, but the benefits are pretty amazing.

Pretty much every NHRA SFWD team ("sportsman" class) that's competitive runs one.
Competitive there means: 700+ whp, at least mid-9 second E.T.s & 160+ mph traps.

Nice twin-scroll article
http://www.full-race.com/modified-twinscroll/index.html



<--- Redneck drag racing fan.. NASCAR is

TurboTim

iTrader: (9)

Cost concerns complete ignored, I like twin scroll idea (i more like twinscroll turbine on std. manifold with one of those valves that block the one scroll for better spool) but you'd go back to bolted turbine connection...perhaps not an issue now with trackspeed's inconel hardware and gasses not in the "stream".

TurboTim

iTrader: (9)

I tend to agree with all of this theory until I test otherwise. These also would mean 1.25" would be smarter than 1.5" pipe.

lordrigamus

iTrader: (14)

It seemed to make a difference when I switched from a 1.625 I.D. runner to a 1.375 I.d. runner. The runners actually were made a little longer to make it more of an equal length manifold too but yet it still helped spool.

It used to lag terribly from 1 to about 6 psi, then pick up a little speed afterwards. After the tubing change it seemed to spool at the same rate from 1 to 20 psi. It seemed to be more consistent.

That's was what I can tell from the boost gauge anyway. Unfortunately I installed my 750 cc injectors, P&H driver board, raised my rev limit and smoked my clutch directly after so I didn't get a chance run a log and collect any reliable hard data.

I'm going with a heavier flywheel now also, so I think I missed my chance to collect any accurate data. As soon as i get it together, I'm going to compare it to the figures I posted in Brain's spool data thread anyway just to see how they differ but I figure the flywheel will corrupt the comparison.

JasonC SBB

The flywheel won't be significant when doing a 2nd or higher gear comparison.

Braineack

iTrader: (62)

i didnt notice difference in spool when I added a 1.8L flywheel last month. I can hit 15psi at 3200RPM or so in 4th gear.

lordrigamus

iTrader: (14)

Well then maybe a comparison would be somewhat accurate. I'll post some numbers up as soon as it's in. Got to fix my cousins stabilizer links real quick.

owengt

wow, just came back to this thread. did not know what i had started. have not read every post but some interesting posts, cheers for taking time to reply. the manilfold i posted up is for a toyota starlet gt turbo. alot of people do use extremely good manifolds i just did not look hard enough lol

MeOughtta

Of course, but these effects apply to both equal- and unequal-length manifolds so

1) Equal-length or not, the size of the turbo manifold is insignificant compared to the engine's mass flow rate. Maybe more important, it insignificant compared to the capacity of the intake/intercooler tract - so the EM's volume simply won't have a perceptible effect on spool unless you have a rear mount turbo or maybe a very short, no I/C, intake path.

2) The turbo manifold *does* represent the majority of the thermal capacitance between the exhaust valves and the turbine inlet. Doubling the mass of the manifold will double the amount of energy lost to thermal capacitance. I'm not certain, but I believe that is significant.

3) Something I didn't think to say before: If the runners are restrictive, then then the longer would increase back-pressure. The greater back-pressure would result in less power/exhaust gasses from the engine. I know it will affect ultimate power, but I couldn't even guess how much or little that might affect spool

Flame away - I do know you are 1000x the fabricator and driver that I will ever be. (That's not sarcasm -- that the truth.)

M.

JKav

iTrader: (1)

Volume has a distinct effect on spool. The larger the volume of the manifold, the more it dissipates pulse energy. OEMs go for extremely compact / low volume manifolds partly for this reason (also to minimize 'wetted' wall area for less heat loss, and cheapness).

Again for optimum boost response you want to recover as much pulse energy as you can (twin-scrolls rule for this). You want a low volume manifold with equal pressure drop (not necessarily equal length) across primaries, and those primaries should be of as generous a radius as you can reasonably package without unduly introducing more length aka unnecessary volume.

Logs suck despite being low volume because they have crappy bend radii, dramatic changes in cross section and crappy collectors, all of which kill pulse energy.

MeOughtta

And reliability and cheapness (again) and reliability (again). Are there any OEM rams head turbos at all?

We all agree that minimizing heat/velocity loss is the key power criteria in manifold design. And, generally speaking, the larger the manifold the more heat capacitance and heat/velocity loss it will suffer due to wetted area, greater heat transfer area, and greater thermal mass. Hell make it big enough and you have a pre-turbo muffler....

But that is all outside the context of the original question which concerned equal- vs-unequal length rams head manifolds. Briefly, which is more important: uniform pulse delivery or minimal runner length?. I stand by my original assertion. The volume increase from lengthening only two runners just enough to evenly space the pulses will not perceptibly effect spool, but will improve turbine efficiency.

I feel I'm in good company since Corky wrote in Maximum Boost: "a design that allows exhaust gas pulses to arrive at the turbine at regularly spaced intervals is ideal but difficult to achieve”.

M.

jasonb

i haven't seen it mentioned yet that in the original link http://www.full-race.com/Miata.html the thumbnails are actually reasonable size 640x480 pics. just right click in firefox and select view image.



this is a great thread as i'm currently trying to decide on a manifold. i'm liking this one best so far (although i'm still reading this thread to evaluate it)



uses the tial housings which seem to be more compact. i have got to figure out a strategy to use the $100 ebay manifolds. miata engine bay is definitely the asian girl of engine bays. everything is just such a tight fit.

JKav

iTrader: (1)

Neither. They're conflicting goals. Ultimately what you want is a compromise between the two. That's why I keep emphasizing equal pressure drop among primaries rather than length.

I've seen manifolds with equal length primaries in which one primary goes through a series of tortured tight radii bends just to achieve the equal length. And there goes a big chunk of the pulse energy from that cylinder. Sure, it has "uniform" pulse delivery, but the pulse is severely compromised by the time it reaches the turbine, so what was the point? The only time this would make sense if you are trying to build tuned-length primaries in order to achieve some scavenging effect in the collector for some quasi-steady application like an LSR car.

For any other turbo app, neither uniform pulse delivery nor minimal runner length should come at the expense of balanced cylinder reversion AND maximized pulse magnitude.