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I just read over the 2-page VTEC article by SurferX and had a question concerning this picture and the details pertaining to it:

How does the dual stage intake mainfold help give the GS-R a flat torque curve? I have noticed it in my GS-R, but am concerned with the Physics behind the power curve.
I would think it would be more beneficial to have the short runners open all the time, this allowing quicker, freer flowing air? Does the longer intake runner allow the lower profile cams to reach their peak torque before the transition to the shorter runners?
What would be the benefit of getting a single stage manifold?
Sorry to bother you with this technical question...I hope it's not something simple that I'm wasting your time with.

Thanks in advance!
 

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The B18C1 a DOHC VTEC motor is designed to give you the best of both worlds....great fuel economy while still providing the fun stuff (HP). With a shorter single stage IM such as the Skunk2 & JG Edelbrock these are used for only one thing....and it aint fuel economy. This is also why the ITR has the single runner....it is designed for more power. The GS-R is a daily driver with a weekend warriors redline.
 

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Yep, lots conduit flow velocity for down low and lotsa flow capacity and flow velocity up top. Problem is, the butterflies and the extra surface area of the dual stage IM causes a lot of aerodynamic drag.
 

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Yes the thinner, longer runners speed up flow to give better torque in the midrange but do not have the flow capacity to handle high RPMs. It's no coincidence that the GS-R's IM opens up to the larger, shorter runners at about the same time a Type R with single stage IM engages VTEC.
 

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A long column of air moving at high velocity doesn't like to stop; it has high inertia. So once it has started moving, it will keep on moving and will cram more air into the cylinder.

A small diameter runner has a certain maximum volume flow rate (CFM) of air under certain circumstances. A larger diameter, but otherwise identical runner, will have a higher maximum volume flow rate (CFM) under the same circumstances, but it's velocity when flowing at the same volume flow rate as the smaller runner will be less. So as long as the smaller runner has a high enough maximum flow rate, it will actually cram more air into the cylinder due to it's increased velocity and hence inertia. This is also called inertia tuning.

There is much more to intake manifold design than this, I am just concentrating on this one small part for now. Runner length is another story.

The equation is Iv = vA = constant.
Iv is flow rate.
v is velocity.
A is area.

So all else being equal, an increase in runner area results in a decrease in velocity. The smaller runner flowing the same amount of air as the larger runner will have it's air flowing more quickly, and will ram more air into the cylinders due to it's increased inertia. But there comes a time when the smaller runner simply can't flow enough air to satisfy the engine, so the secondary runners are opened up (more area).

This is why getting a bored out TB when your stock one already can flow enough air to satisfy the engine will cost you power.

All this theory applies to the exhaust side as well, except that the inertia helps to pull out the exhaust and can even get the intake charge moving during overlap.
 

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I would be interested to feel the lobe changeover in an ITR, I know the GSR lobe changeover is much sooner @ 4400. When I had CTR cams and increased the overlap period too much I would feel a missing power bump there
the tuners explained to me that at that cam setting the ECU did not have enough inherent fuel and timing to make power and you lose it there for a few hundred RPM.

Its nice though, on the new GSR/ITR motor with higher compression I hear the secondaries opening now as much more evident, a louder wail. Still, the ITR with its native manifold has a different personality there is no doubt. Driving my friend's bone stock '01 its pretty docile considering I also have the same stock intake only with a 4" hose ran from the bottom of the box to the fenderwell. My friend John's B16A2 actually screams much louder and higher pitched megaphoned from his AEM CAI and CTR intake cam. VTEC is no doubt a beautiful thing...

In April after a valve bending incident on my CTR intake/GSR exhaust setup (making 158.5/121.4 118 @ 5250 all else stock 0,0 18) I played around and filed out my secondaries internally enlarging the port openings and knifedging the butterflies. At the time since I changed other things, I am not sure how it changed performance over stock. I added valvesprings, an ITR 01 exhaust cam, gears, hondata thermal IM gasket, etc. The most I saw out of that setup was 163/125 with 123 at 5250 on stock everything but CTR cams, 2 layer gasket with cam tuning and fresh air to the stock intake. I saw 155/115 at 0,0 and 18 timing initially and made it back with tuning. I know my oil pressure wasnt superb due to my intake cam freezing from an improper TQ spec that did not bend valves. After a while, the motor failed. I can write a book on that all the mistakes... oY!

Now that I have a fresh ITR block and GSR head, the power seems to be strong to the limit using that same manifold. Oil pressure light goes out on startup in an instant where it took 3 sec on the old motor
It also seems more powerful than it ever was on the previous setup. Back in April I also tapered my TB out to 70 at the opening, leaving the 60mm knifing the butterfly and opening the rear to 68, portmatching the manifold. I dont claim to be a machinist, I wanted a project so I can understand how things work
I would like to put back a stock GSR manifold and see the diffs on a dyno. I have one I should make it a project, the shops around where I live sell alot of Skunk2s so there are many P72s and stock TBs to be had.

Being that I am on stock cams now coming from CTRs, I cam stunned that the current GSR/ITR motor pulls hard up top where it in stock form was gasping for air. I guess 11:1 compression really makes a difference! Since I have this larger TB charge and internal ports, based on the previous post my intake charge velocity has no doubt reduced from increasing the flow rate of the runners. Theoretically for those cams I should be on the unlodified manifold for peak output... I am therefore stunned that my car pulls up top with the stock 230 cams at 0,0 and 16 degrees. I really need to dyno compare the two.

Ideally, staying on the GSR computer one could tune the manifold for the engine to breathe "well" everywhere. A stock ITR has less in the midrange than a stock GSR before 5500 rpm, where the ITR changes personality completely, tq comes on strong and lives happy all the way to cutoff. However looking at the graph there seems to be power "missing" from 4000-5500, the engineers made up for this with the gearing no doubt.

If I could, I would like to stay on the P72 manifold with total tuning achieving a strong bell shaped curve virtually flat 7800 peak to 9000 without losing upper end power. I would like to see a 150whp/tq 5250rpm value, a 210-220 peak with the right set of mods and tuning for the street, maintaining above 25mpg also... we will see. I also plan on going 4.785 on the FG with the Honda LSD in my GSR tranny. Hopefully this will be a fun, torquey setup that rivals entry level 6-8lb turbo cars for performance NA.

Our dyno guy here moved so doing this might be a pain however there are several guys I am hearing about so I can get in and do something like this soon.

Anyone interested can email me directly.
 

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Quote:Back in April I also tapered my TB out to 70 at the opening, leaving the 60mm knifing the butterfly and opening the rear to 68, portmatching the manifold.

So what you're saying is that you basicaly made your TB like an hour glass? I would think that would cause some problems with flow rate going from big/small/big again. Am i totaly off on this or does this make sense to anyone?
 

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MikeSarrGsr,
If you only changed the diameter of the runners with all else being equal, then the velocity would go down. If you also made changes to the engine, such as cams, that increase the flow rate along with increasing the diameter of the runners you don't necessarily lose velocity. You have changed two variables. Increasing the flow rate all else being equal, means that the velocity will have to go up. Increasing the diameter all else being equal, means the velocity will go down.
A certain runner will have a maximum flow rate under certain circumstances. You can change the maximum flow rate by changing the diameter of the runner, but the flow rate at any time is governed by the pressure differences between the ends of the runner. So putting in different cams might change increase the pressure differential across the runner and result in a higher flow rate.

I am saying that the flow rate is governed by external variables. If a 1" runner is flowing 60 CFM with a pressure differential of 6 PSI across it and you switch to a 2" runner with 6 PSI across it, the 2" runner will still flow 60 CFM; it will simply have a larger volume moving at a slower velocity. If you increase the pressure differential across both runners, the velocity and flow rate in both runners will increase. There comes a point when the smaller runner will not increase it's flow in proportion to the increased pressure differential across it. Up to this point, it has matched the flow rate of the larger runner and has done so because it's velocity is higher. So what you want is an intake runner that is only big enough to flow the maximum amount of air that the engine will ever need, because it's velocity will always be higher than an oversized runner.
 

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Justin 3,
I don't see any problems with the TB setup. Tapering the outside edge will help the air make the turn (velocity stack). Port matching the inside will also help flow by removing any obstructions. The velocity will speed up through the TB and then slow back down. The maximum flow rate is still governed by the 60mm throttle plate.
 

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Thanks for the input kelly, your remarks are no doubt thought out and helpful. Now that I have the GSR cams again, I am suprised that the motor pulls strongly with the ITR bottom end in it with this manifold and TB. The higher compression bottom end on the GSR head has made for an interesting feeling driving it. As it has been breaking in I have felt it get more responsive through the midrange. I am metering my 6K+ RPM driving while it is still in its bedding cycle. I still want to dyno the car with this TB and a stock TB on a stock P72 manifold, then change the manifold and repeat the test.

I think that will be an interesting post no doubt granted if my work with a file using my ideas as a basis for modifying the manifold means anything...
Like I said, I am not sure if I gained power or not since I dont really have a refrence point yet. once I find another place to dyno I can do this and it will be all good.
 

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in the "Ideas: flow capacity, flow velocity, flow quality" article here, I get into what flow quality is defined as.

The GSR 2 stage IM has 60% percent more aerodynamic drag than the Skunk2 single stage IM. More drag comes about because of the added surface area. If you take a tube and slice it lengthwise and "unroll" the tube, that rectangle is it's total surface area. We are not talking about the surface area of the opening (cross sectional area) which is another topic on it's own. This total runner rectangular area is what slows down flow. If you assume air acts like a compressible liquid, and most fluid dynamics assumes this, then added drag slows down flow velocity. It's a chain reaction after that. Sower velocity creates more turbulence. More turbulence disrupts laminar flow. The fuel droplets then coalesce or clump...and then rain out on to the walls rather than staying as a fine atomised mist. You get a less efficient burn when fuel is clumped rather than atomised.

The 2 stage IM with 8 runners open after 5750 rpm to redline which adds way more drag than the Skunk2 IM 4 runners. Despite the Skunk2 runners being shorter and having larger diameters than the GSR IM secondaries, the total area is much less. This is why you see the power gain in the upper rpms so dramatically different between the 2 despite the same BSFC.
 

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MD,
I realize there are many variables involved, I just wanted to stay with one concept for a while, and I knew you would help out.
My practical experience lags my theoretical experience in this instance.
Is the 60% figure referring to the long, short or both GS-R runners? How do the two compare as far as area under the curve? It seems to me that the GS-R manifold would make a better street manifold. I don't want to give up any of what little torque there is. At what modification level does the GS-R manifold become a hindrance? It seems to me that the Skunk 2 is a given mod.
Since the manifold is dry, I don't understand the fuel atomization emphasis.
 

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I know one thing for instance something that is done by ENDYN, they install dimples where the injectors spray to help this "fuel atomization" process. I dont know what made me rememeber that, just the way my mind works I guess. I can see where this P72 8 runner thing could be a hinderance. My friend's GSR/ITR motor has the Skunk2 and he has a Del Sol VTEC tranny on it with a happy clutch...

195/140 with 140 @ 5250
AEM 3" ITR shortram
skunk2 stage 1
skunk2 intake mani
skunk2 gears +2,+2 on cams 40 deg of overlap
skunk2 ti retainers
skunk2 cat back
DC USDM 4-1 w/ cat
GSR head and valvesprings non modified
Mugen Gasket
ITR shortblock
OBD1 Computer/mugen maps/field sfc-vtec/msd ignition
Del Sol Si VTEC tranny

that thing pulls from 4K to 9K no doubt!! I am also interested in all of this as well... I just want to make an intelligent choice and know how to overcome the pitfalls of the double hump power curve. I have seen some tuned cars with little or no loss on the ITR-type manifold. I dont consider myself a tuner by trade so if I do this, I want to know the how-tos of tuning such a setup for drivablility on the street and long term mechanical happiness. This car I give you an example because he had it built in FEB02 and it is still running strong, no problems only tuning. The only down side of this car as I see it for daily driving is that its a tad rickety for my taste. Its home is on the track!
 

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kelly on Aug/31/02 said:
MD,

I realize there are many variables involved, I just wanted to stay with one concept for a while, and I knew you would help out.

My practical experience lags my theoretical experience in this instance.

Is the 60% figure referring to the long, short or both GS-R runners? How do the two compare as far as area under the curve? It seems to me that the GS-R manifold would make a better street manifold. I don't want to give up any of what little torque there is. At what modification level does the GS-R manifold become a hindrance? It seems to me that the Skunk 2 is a given mod.


Since the manifold is dry, I don't understand the fuel atomiztion emphasis.


I'll answer the questions in reverse order:

This is Jim McFarland's comparison of the optimised volumetric efficiency curve vs. the torque curve. Notice they are similar in shape but not identical. Obviously the main way to make power is by adding more air at the correct speed and using as much fuel as needed to control the burn,... elementary. What separates the person's engine that comes in 1st and the other very good engines in the race?

The graph above shows you where. Even when you optimise volumetric efficiency to the max and the engine breathes dry air as much as it can, the power (in this case torque) lags. In the mid rpms below peak torque, torque is less than what volumetric efficiency would predict because of fuel atomization effects (flow quality) on the generation of power during the combustion process. Fuel is added in Hondas at the IM. So we are not dealing with dry air. We are dealing with wet air. If you look at the AEBS B18C motor, they follow the old domestic and motorcycle racing trick of having a 2 stage injector: 2 injectors - one before the TB at low rpms and the second on at the usual IM location activated at high rpm. So the way the manifold massages the air to affect atomization influences how much power you make and where. At the upper rpms above peak torque, the ability to evacuate the cylinder of burnt gases and mixture separation determines if your torque can match what the volumetric efficiency would predict. We deal with wet air, not dry air (in the real world, as the saying goes).



Here is Honda's famous press release dyno comparison in 1997 when they introduced the new (then) ITR (red) comparing it to the GSR (black hp/grey torque). Although it isn't a straight comparison (because of the differences in cams), you can see that they attributed the flat torque curve advantage of the GSR in the midrange to the GSR's 2 stage IM. The area is obviously smaller for the GSR here due to the smaller cam. Nevertheless you see where the ITR single stage IM shines: above 6500 rpm. No road racer or autocrosser with any driving ability ever lets his rpms drop below 6500 rpm.In a straight drag race shootout, the upper rpm difference is what gives the ITR 0.1-0.2 tenths (all else being equal).

You are correct though that you should not look at peak whp only. The total hp (or area under the hp vs rpm curve) may be greater in a car with less peak hp. How the area under the curve distributed also matters. How long the car stays at peak power will also determine an acceleration difference (you see this in single pattern vs dual pattern cams in domestics where the single pattern profile makes less peak hp but out-accelerates the dual pattern one at the track because it holds it's peak longer). Then finally there is the transient response after a shift which can also affect acceleration. So yes, the GSR IM may actually give you some advantage on the street. Erick Aguilar uses one in his world record all motor 2L B18C1 but it is heavily ported by Joe Alaniz and I suspect there are no butterfly valves in it.

Yes, the 60% extra drag figure is when all 8 runners are open after 5750 rpm. When the primaries are only open the extra drag drops to only 20-25% more drag then the Skunk2 or ITR single stage IM. Having run both IM's (even with the GSR IM butterflies removed), I can tell you that the choice of cams makes a huge difference as to whether your midrange takes a dive compared to the GSR 2 stage. BTW I have on my shelf, a Joe Alaniz ported GSR 2 stage IM for sale if anyone is interested (sensors removed).

cheers
 

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kinda at this one, dont know if anyone has asked it yet, if so take it easy on me! will the gsr or type r intake work on my 94 rs? if so, what could i expect performance wise/ problem wise. ive got my rs motor to play with and want to go all na.

thanks
 

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intake or intake manifold? this thread is about the intake manifold...the ITR IM needs modifying to make it fit on an LS. Overboost.com has an article on how to do it in their FAQ. The GSR IM needs major rework to have it fit on the LS head. As for intakes, the aftermarket intakes made for the ITR will fit on an LS IM. The GSR aftermarket intakes will not fit on an LS IM...you can't shut the hood.
 

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kelly on Sep/14/02 said:
you fully answered all my questions!
SYSTEM! SYSTEM! SYSTEM!
parts integration, engine package, analysing by systems, engine combination, the whole view (forest from the trees)....call it whatever...

the ones at the sharp end of the starting grid of a road race understand it and apply it well. The ones at the back of the grid are looking at how 1 part performs at a time in isolation of the other parts.

it really does matter as to how you look at things.

if you cannot find the answer you are looking for, it means you are asking the wrong questions (an old Japanese Aikido saying).

cheers
 

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MD,
What if the GSR 2 stage IM had another set of butterfly valves which cut off the longer runners completely and made it run on only the short ones after 5750? Would this allow it to eliminate most of the 60% drag and make better top end power while retaining low-end driveability?

Another ? How much does the Skunk2 or JG/Edelbrock IM's effect the low-end? I know before you said they effect mid-range, so is their effect on low-end even greater?When does the ITR VTEC engage? If I were to change to a Skunk2 IM, since it is single stage, I am guessing that when the VTEC engages at 4400 my exhaust will sound somewhat similar to when the second stage kicked in on the GSR IM at 5800?
 
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