I would appreciate any design insights that the Nissan engineers would have in mind when developing the throttle body mechanism on the VG30DE. The butterfly valves on this motor do not open to a full 45 degrees at wide open throttle bacause of a stop placed in the throttle linkage. The valves remain ~10% closed when the throttle cam is held fully back. Is there a venturi effect that positivley affects performance and/or do Berneulli's (sp?) laws come into play? Thanks.

I don't think there is any type of venturi effect with the throttle plate. Venturi would indicate that the inside diameter gets smaller at some point and widens up again inside the intake manifold, thus speeding up air.

If it was a Bornoulli effect, then one side of the thottle plate would have to have a larger distance than the other (like a very mild dome shaped plate). I don't *think* that the plate is shaped like this, but I don't know for certain. Can you tell? It would be interesting if it was!

Other than that I can't think of any reason they would design it like that. When you mention 100% throttle, do you mean the pedal to the floor? Or do you mean the throttle valve pressed all the way back (under the hood). If you mean the pedal pressed, then you may be able to adjust the throttle cable so that it does open the throttle plate up completely.

EZcheese15 wrote:I don't think there is any type of venturi effect with the throttle plate. Venturi would indicate that the inside diameter gets smaller at some point and widens up again inside the intake manifold, thus speeding up air.

If it was a Bornoulli effect, then one side of the thottle plate would have to have a larger distance than the other (like a very mild dome shaped plate). I don't *think* that the plate is shaped like this, but I don't know for certain. Can you tell? It would be interesting if it was!

Other than that I can't think of any reason they would design it like that. When you mention 100% throttle, do you mean the pedal to the floor? Or do you mean the throttle valve pressed all the way back (under the hood). If you mean the pedal pressed, then you may be able to adjust the throttle cable so that it does open the throttle plate up completely.

Holding the throttle cam under the hood in its full back (WOT) postion leaves the butterflies short of a full 45 degrees. The butterflies are flat as far as I can tell. This added turbluence has got to affect air ingestion. This is the design. Why? Everything about these cars make sense except this oddity.

Do you mean 90 degrees from the wall or 180 [parallel with air flow center line]. 45?

Checking it at the engine does tell you much, someone must floor the trottle inside to make sure the positioning is correct [carpet bent rods misadjusted cables etc]......while you look!Getting the TPS at 0.4-0.45 idle vs WOT>4.00 is critical.

Q45tech wrote:Do you mean 90 degrees from the wall or 180 [parallel with air flow center line]. 45?

Checking it at the engine does tell you much, someone must floor the trottle inside to make sure the positioning is correct [carpet bent rods misadjusted cables etc]......while you look!Getting the TPS at 0.4-0.45 idle vs WOT>4.00 is critical.

My mention of 45 degrees was incorrect. The butterflies do not open a full 90 degrees at the throttle body. This is observed at the engine with the intakes removed and the throttle cam held in the fully open position. There is a stopper that prevents the cam from rotating any farther back. Additionally, using a board to prop the gas pedal fully depressed yields that same result: the butterflies are ~10% from a 90 degree rotation i.e., not parallel to the horizontal (<180 degrees).

This maybe a design feature to insure that the throttle plate goes fully closed when the throttle is released. Under full throttle with air blasting past the plate at high speed, it gives the plate an effect of a wing and may prevent the throttle from returning or returning quikely. Where as a slight angel of the plate may prevent the throttle from hanging or sticking open. The leading edge at a say 10 degree angel may assist the throttle in closing.

drjohn wrote:This maybe a design feature to insure that the throttle plate goes fully closed when the throttle is released. Under full throttle with air blasting past the plate at high speed, it gives the plate an effect of a wing and may prevent the throttle from returning or returning quikely. Where as a slight angel of the plate may prevent the throttle from hanging or sticking open. The leading edge at a say 10 degree angel may assist the throttle in closing.

This is the best hypothesis I've heard yet. However, the butterfly valve has no airfoil characteristics. The valve is a flat disc with a raised section running straight through it that contains the axle upon which the valve rotates e.g., ---o--- (here depicted in the "hypothetical" parallel position and, of course, the axle is proportionally smaller than this crude example.). Additionally, there is a hefty spring on the throttles so the valves will tip towards the closed position if parallel to the air stream and would then continue to close normally. Do the butterflies on the Q45 rotate to the maximum open 90 degree position?

I did not mean to suggest that the throttle plate was a wing but at high rates of airflow may act as a wing. Even with a return spring there is a point when air pressure can over ride spring pressure. This is evident in aircraft and the use of hyd. to control airsurfaces during flight. This poses a interesting question that I will ask the factory engineer on his next visit.

drjohn wrote: This poses a interesting question that I will ask the factory engineer on his next visit.

drjohn, I would be much obliged if you posed this question to the Nissan engineer. What do you do that gives you access to the Nissan Engineering staff? I once played golf with an older Japanese gentleman before I owned my J30. He was with the Nissan cold weather engineering section in Chicago. He asked me if I had ever owned a Nissan product before and I told him that I has once owned a Sentra that I liked very much. He was genuinely pleased that I liked the car. I had run into him several times as we both sneaked out for some midweek golf. The last time I played with him he shot a tremendous round. Mid 70's I think. He said that it was the greatest round of his life. It was a pleasure to golf with that guy. A real gentleman. I haven't seen him since I got the J30 and he might very well be back in Japan by now. I wish I could thank him for the great car he and his colleagues developed that I now drive.

Not fully opening a throttle plate has the same effect as a smaller diameter TB fully open......the air speeds up. My guess is the TB is too large for NA and was designed for the turbo version and just down sized by limiting opening.

While larger TB are required to limit the vacuum differential at WOT they always tend to be too large at low rpms, cruise, and sudden accelerations.

One must balance all aspects to get decent cruise mileage......the problem is what is the lowest rpm the engine can turn and still fill with enough air to generate enough power to cruise and still pull minor upgrades without downshifts...........too much reserve means you are wasting fuel.

To check this theory one would need to measure the cruise vacuum in BOTH plenums accurately. And the drop in vacuum from a snap open throttle. There are VE tables in the ecu which were derived from dyno testing showing the percentage of fill [how much air the engine can absorb at each rpm].

Generally all PHYSICAL MODS in input air flow [air filter, MAF, TB, plenum, runners, head ports, valve size, valve seat, etc] when enlarged lower the restistance to flow at PEAK RPM.....BUT this may harm low speed operation.

It is always a trade off between stalling the air flow speed [thru the valve] which will hurt the filling rate........why some newer engines have tuned length runners and variable plenum size.{some have two set of runners for different conditions}......they tweak the fill rate to the nth degree.

Since maximing torque for acceleration [0>30>60 mph] is a requirement you may find that a peak HP number is compromised since all factory engines are detuned to operate for long life and bad gas and iffy maintenance.

"to find the appropriate bore you need approximate the power you have and substitute to the following: Bore=SQRT(Power/130)*53 [mm]."X= SQRT[100/130]* 53 or~~~~~~~ 45-47mm for 2 TB on a 200HP 3.0 liter

For a 320 HP Q45 this works out to a single 83mm TBFor a 280 HP Q45 this works out to a single 77mm TB

The above seems to work as a decent approximation.

"Many people swear they feel a power increase after going to a bigger TB on an otherwise stock engine. On some applications, the increase is legitimate, and can be proven on a dyno. On other applications, the "power" felt is really just better throttle response. Throttle response is essentially the amount of time it takes the motor to react to a throttle change. On a TB too large for the motor, you will hit your maximum flow before you actually have the throttle plate open 100%. This also means that when you snap the throttle open, the velocity of the air is slowed by the large opening and the engine will hesitate. With a TB too small, you will have better fell for the throttle, but overall performance is lost. This is why it is important to know what your motor needs."http://www.theoldone.com/archive/intake ... .c...0.htm

the above speculates that less than 10" WC is a good number to shoot for in TB restriction at WOT max rpm................for the Q it is 9" W.C. when spotlessly clean.http://www.installuniversity.c...0.htm

By the way a rule of thumb is 1.2 CFM per HP required so 210 would be only 252 CFM or around 370 CFM for a tuned Q!

The CFM are at standard SAE Conditions.... 60F, 29.92" HG!

So on OBD2 cars you can read the ACTUAL GRAMS per second air flow with a scan tool and translate this back to CFM .....or the gms can be used [with the injector opening time] to calculate horsepower in real time.

well i got through this whole post and i am very proud to be a part of nico, where we can get together and really learn about interesting aspects of automotive engineering. thanks q45tech. i will research if the VG30DETT's throttle bodies open fully under WOT, that is an interesting proposal. From the outside, i know them to be identical. we will see what twinturbo.net has to say....

If you know the stock CFM flow [from something] you can then measure the drop of each of the input components and calculate how much if any each 1.0" W.C. improvement would make to the power...............obviously you can't improve things by 50% [half the stock measure vacuum/restriction........ but 10-15% [3"-5"] is possible]............why on NA engines from the TB forward only 3% power improvement is possible............there just isn't enough restriction in the first place to fix or improve upon!.

I improved the Q by a total of 5" [5/28 almost 18%] but the power only went up by 2.5 HP.

Just keep in mind that 1.0 psi [extra pressure or less restriction]yields 6.8% power increase and there are 28" WC in 1.0 psi so you -gotta find- improve 4 of them to get a 1% improvement.And this improvement only occurs at maximum rpm on a Q a restriction might be 3" at 4,000, 4.5" at 6,000 and 5.5" at 6,900 rpm.

Eswift wrote:well i got through this whole post and i am very proud to be a part of nico, where we can get together and really learn about interesting aspects of automotive engineering. thanks q45tech. i will research if the VG30DETT's throttle bodies open fully under WOT, that is an interesting proposal. From the outside, i know them to be identical. we will see what twinturbo.net has to say....

According to the afficianados on Z32.org, the VG30DETT butterflies also do not open to a full 90 degrees.

Measure the inside diameter for me we don't have a J30 handy and we'll do the flow calculations .....get me the exact angle and plate thichness.

I'll bet is is way oversized for any amount of air that could possible flow even with turbos but if those guys get more power from mods obviously it is restrictive but they usually add boost above oems.

Sometimes parts are designed for the future upgrades that the factory never does......more cost effective to create a new 3.5 engine rather than bore/stroke the old 3.0/3.3 to 3.5.....the 222 HP version in the 300zx might had only made 259 HP [bored out to 3.5] vs 287 for the new one......??????

"The Z32 has a similar restriction in rotation and the fix is to bend the tab for the WOT stop position to get the full rotation. I can't imagine why the reduced rotation was used in the design. Only dino tests will reveal."

>>care of ZUL8TR in Orlando,FL

so, it sounds like both the NA and TT 300zx had the same setup. this supports q45tech's idea that the TBs are designed to support far more airflow than even the TT requires. Also makes sense then that the stock manifolds and modified TBs are able to support well above 500HP in TTs with upgraded turbos.

The mathematics really do show the principles invloved here. It has been claimed that modification of the cam stop increases power on the na VG30DE by 9 hp. If so, that would be a considerable and unnecessary loss of power. Are they making a compromise between low end and high end tuning? Curiouser and curiouser. I wonder if all Nissan engines have butterfly set ups like this?

One interesting thing, is that on the QR25DE motor, which has throttle-by-wire, it has been reported that the accelerator pedal sensor when set to 100% produces only an 85% from the throttle position sensor.

So it seems that this is not just a VG issue, but also a QR issue, and probably even more engines have the same issue.

One team designs the engine and another 5 work on induction system......hopefully they bolt together!For a total engine typically 40-60 and another 50 part time engineers are involved for years.........you know how committees work......then there are the accountants that monitor each team, then the accounts that monitor the accountants.There are engineers who specialize in rods and they may never see the wrist pin guys except every few years at conventions.

then the injector engineers and the injector o ring engineers, and the fuel rail engineers, and the fuel regulator engineers, and the spark plug engineering liason aide [trainee engineer].

When you think about it, it is impossible for one person to know how to do the whole project and if they did 100,000 man hours is 50 years........so 100 guys can work on 2 engines per year.

Then there are all the computer scientist who run the simulations!$25,000,000 per engine in engineering development cost alone. Then multiply by 5 for support staff, prototyping, and final testing then double that for machine modifications........... after that you better sell a MILLION of the ENGINES or you are in trouble as all this adds $250 per engine!Can you imagine that the Q45 2002 engine having sold less than 10,000 world wide has a development cost of $25,000 each!

Drive by wire saves money [no extra TB for TCS] plus avoids all the fuel wasting accelerator pumping that some drivers do.....you would think they are playing drums.

Hook an analog meter to the TPS voltage watch how you drive better yet graph an hour of throttle [even on the highway at what you think is a fixed speed] the cruise control does a 5 times more stable job thus better mileage.Remember the old fashion mileage meters which were just vacuum gauges.

i feel sad for nissan/infiniti. truck sales have gone down despite great recent offerings. a whole new burst of ad campaigns across the board are a good attempt, yet many are just really horrible. Their M45 video available on their site is really just sad compared to the BMWfilms they aimed at ripping off. I saw a Murano ad in the new issue of Automobile and i couldnt even figure out what it was about, or who the hell it was targeted at. luckily, despite its uglyass looks, the murano will sell all the copies it plans on selling since its in the highly lucrative mid range SUVish category. I am sure we can expect to see a lot of VQs in all the nissans to make up for the flop of the new Q45 plant. unfortunately, in america, a car company needs one of two things: either cars that sell themselves or an ingenious ad campaign. Few nissans sell themsleves over here, and ad campaigns have been spotty. A few diamonds in the rough, but most are worthless, uninteresting. How do so many POS eclipses get sold annually? A horrible yet perfectly aimed ad campaign featuring trendy music. The demise of the R34 Skyline GTR signaled Nissan's fall. I have always loved nissans, but its getting hard to embrace such a failure. Low expectations for the forseeable future...although i am not foreign to this...i have the bears as well.

Since we're all talking engineering here, what are the best classes a student could take to get a solid start in an engineering field.(Note: I probably need a trig&physics refresher already as the last thing I wanted to be in HS was an engineer, and ironically now that's all I want to be)

start with some physics, then calc, diff eq, and linear algebra.

then crank it up with some theoretical and applied mechanics: statics, dynamics, mechanics of materials

if you go for mechanical engineering:

next step is analysis and design of dynamic systems, control systems, design for manufacturability, design of machinery.

now your ready for classes on finite element analysis, vehicle dynamics, and whatever your other interests are

we cant forget thermodynamics, incompressible fluid flow, heat transfer....but...yeah..that part is not my forte

miteymax86 wrote:Since we're all talking engineering here, what are the best classes a student could take to get a solid start in an engineering field.(Note: I probably need a trig&physics refresher already as the last thing I wanted to be in HS was an engineer, and ironically now that's all I want to be)

Well, here is some information on the degree I have. It might help steer you in the right direction:

http://amet.mnsu.edu/aet.htm

But in general, for an engineering degree, you will most likely need atleast through Calc II, and most likely Calc III and Differential Equations. Also, though atleast 2 semesters of physics, possibly 3.

I wouldn't spend time on a trig class if you are able to move into something higher up. Generally trig is inbetween Algebra and Calculus somewhere. If you need it for a prerequisite, then take it, otherwise take something a little higher.

It really depends on your degree you are pursuing though. There are usually 3 types of technology/engineering degrees. They are technology, engineering technology, and engineering (in order from easiest to hardest). Technology requires very little math and physics (still basic stuff though), while engineering requires pretty much all the math and physics anyone can handle. ET is right inbetween.

my curriculum required Cal I-III, Diff Equations(still having nightmares), 2 chem, 4 physics, statics, fluids, C+, and a million other specific engineering classes...but those were the foundations.

come down here to University of Louisville's Speed Scientific School. They got the engineering going on. My GF is almost done with her masters in Chemical Engineering. Civil engineering is all i got to show...to bad I don't have interest in that anymore :rolleyes

yeah mayhem, diff eq really scarred me for life. you dont ever really recover from a class like that. theres no going back. i wish i was still innocent.

Remember Calculus was a created language to solve real world problems.

Yeah, I've got the curriculum from the college I'll be attending in the fall(Grand Valley State University, D2 national champs in football, whoopee) anyway, I'm pretty much destined to fail, but I want a job that pays and doesn't suck, and engineering seems to be the right choice however, the math skills are a little lacking(taking an AP pre-calc&trig class at like 7am is not a good idea) and then physics my senior year was well, my senior year, I got way lazy and didn't crack a book

btw, thanks for the responses fellas