jak

The structural support was designed primarily for the air bag sensors. NOT CRASH PROTECTION. The support is made of materials and properties to trigger the sensors to set off the air bags in a crash of PREDETERMINED impact.

1. If the sensors are moved to a new location the sensors will not function as designed.

2. If the sensors are mounted to a material more rigid than the structural support it will take a greater impact to trigger the sensors or the air bags will not deploy at all.

3. If the sensors are mounted to a material less rigid than the structural support then the sensors will trigger the airbags over every pot hole.

My brother in law works for Ford in Detroit as a design engineer for the air bag systems. The support most likely is for the airbag system and nothing more.

Jeff

PoWeRtRiP

^good info thx^

jng1226

What a fantastic thread! This really should be a sticky for this section, as almost every question is answered here regarding the SC vs. TT debate.

More importantly, this critical issue of potential reduced safety seems to also be qualified in this thread. People should really know what they're getting into with any aftermarket modification that can affect OEM safety systems (i.e. airbags)

Is there any warning in the Greddy TT install manual about this risk?

If I were them, I would be shaking in my boots from the potential liability issues with this.

alpine

It sounds like you have the "facts" on this entire incident, where did you get your info? Or where is it available?

I know the modiciation is to accomodate the IC, I just don't see why it can't be done properly without losing airbags.

There is a greddy TT kit for the g35, so I don't know if that is the problem.

alpine

At this time there is no factual information on this safety issue, I will see if I can get some/any from Greddy.

Also this is a good thread, there are dozens on this board and more on others, this has been a better one IMO due to us sticking to the point vs flaming one or the other.

I've been enjoying this thread very much, when I first initiated it I got the 3rd degree about how this information is everywhere and this thread is NOT necessary.

Glad to see others are continuing to find it usefull as well.

alpine

bump.

PoWeRtRiP

the greddy kit for the g was just released? it was not available back in jan when this happened. i read an article on it that was posted here a while back and heard about it in a few threads. if you search you may find some info

alpine

gotchya.

thanks

ct roadster

This is a great thread, but there have been several misconceptions posted. In no particular order:

1) The boost from a turbocharger (exhaust gas supercharger) is not "free"; turbos do not use otherwise "wasted" power. Driving a turbo very definitely takes power away from the crank; in fact, the turbine shaft can carry significant horsepower. When properly sized/applied, a belt driven supercharger and a turbo will be operating at similar efficiency, and thus will consume similar base horsepower. This power "loss" is more than made up for by the engine's ability to pump more air, so in effect both turbos and superchargers are best understood as if they made a small engine seem larger. But the most important bit is that driving a turbo is not "free".

2) A Roots SC (Stillen) is fundamentally different than a centrifigal SC (Vortec): the Roots makes pretty much the same boost over the whole rev range (but is able to deliver more volume at the higher end), while the centri has boost that increases with RPM. The Roots blower is a *very* simple machine: two rotors (non contact, no contact with the housing, either) and a gear sync'ing them, plus a pulley. A centri unit has a pulley, a step-up gearbox (typ 15+:1 ratio!), and the turbine unit.

3) A Roots blower has zero lag because of the insensitivity of boost to RPM; turbo lag depends on the size (weight/blade config) of the turbine(s), and the length of the plumbing/intercooler.

Anyone who thinks turbo lag is a non-issue should take a 911 turbo to the track! The issue is always just when to get on the power coming out of a corner: too early any you spin, too late and you waste time waiting for the turbo to spool. What complicates the situation compared to NA is that the power is not there as you step on the pedal: the lag means you need to plan ahead.....

Our Z's have a wonderful close-ratio box so they are perhaps more able to keep a turbo system spun up, and we have a high-CR bigish displacement powerplant, and we have a nice 53/47 weight distribution, but it is still going to be a bigger challenge to drive a turbo Z really well on the track. NA and Roots has a big advantage in this, particularly if you are not really willing to find out just where the limit is.

I'm also on the fence about what way to go; I'm definitely not impressed with the safety issue of the Greddy kit, but I don't like the hood mod of the Stillen either. I guess I'm secretly hoping that the DreamWorkes people get their act together soon......

-frank

Sharif@Forged

iTrader: (92)

Ct Roadster...don't take this the wrong way...but you are 100% wrong on your thesis on turbo vs. supercharger efficiency. Yes, you are correct...a turbo doesnt use totally free energy to drive the turbines. But without a doubt....and you can ask any engine builder to confirm...a turbo is significantly more efficient that an SC...all things being equal. Whereas a typical SC is about 60-70% efficient, and turbo can be 90% efficient or more. Read Ken Bells book "Maximum Boost" for a very good explaination of this. True, true....I imagine if you use a sickenly big mismatched turbo, you could end up with less effeciency that a properly match SC...but that is not reality for the TT kits avail for the Z.

Second, yes...there is lag on a 911turbo....but that is a totally different animal than the 350Z! There is virtuallly no turbo lag on the PE or Greddy TT. I have driven both.

Also, take a look at my dyno chart. Notice...I have 300plus lbs of torque at about 3000rpm. That is certainly NOT turbo lag....in N/A form...i was lucky to get 210lbs of torque. Compare these charts to a Vortech or ATI, or STillen dyno...and you'll see the difference. The TT's have much more meat under the curve...across the board.

There are many old wives tails and misconseptions about turbo vs. SC...but if you drive these cars...you'll know..they are unfounded....at least with the 350Z!

Check out the one called "6psi......blablabla"

http://www.savepic.com/pf.php?fid=635

Thanks for listening.

Sharif@Forged

iTrader: (92)

GREDDY safety issue update:

I spoke to kenji at Greddy today. Couple of things here


1) The airbag sensor does work. That is good...whew.

2) The aluminum brace will fit...even with the intercooler in place. woohoo! That is the good news. The bad news is that you need to custom fabricate some piping, and replace the left side IC end tank with a single lower unit. The upper intake pipe blocks the mounting points for the brace. That is the reason we cant install the brace...its not the thickness of the FMIC that is an issue. Greddy tried to design the kit to keep the brace in place, but the elabroate piping was too complex for a bolt-on it...and they said it would require too much welding and cutting.

But this is certainly an option for those that want to reinstall that brace. I am going to look into the costs myself...it couldnt be too terribly expensive.

Sharif@Forged

iTrader: (92)

Hey Alpine....thanks for starting this thread...it's really turned into a treasure box of good info.

SQUILL

You stole post #150!!!! LOL.. any way here is the funny thing about "LAG"

Look at the evidence... dyno charts, turbos are making more power from 2000rpms all the way to redline.

under 2000rpms both systems are barely making more power than stock N/A

There are alot of people saying turbos have this huge lag issue....lets get more specific people lets stick with turbos on a vq35de. regardless of that still alot of people are saying S/C is better on the 350Z because of the no "LAG" arguement..

I ask you if both systems hg gains are virtually non existant under 2000 rpms and then from 2000 rpms and up till redline the TT is making significantly more TQ and HP where does the "LAG" hurt you?

I ask you does the supercharger not have a period of time untill its boost is high enough to significantly increase TQ and HP would not this period of time be considered "lag"

Look at the dyno charts the turbo dynos are beautiful with big TQ down low and fairly flat throughout the powerband

Does not the HP curve have a nice gradual increase throughout the powerband?

does not a 60 ftlb TQ and 10 HP advantage @ 2500rpm over ATI/VORTEC systems yeild superior accelaration in street/track conditions?

People may have misunderstood my stance on turbos.

On the VQ35DE superchargers are good.

My stance is that on the VQ35DE turbos are better nothing more nothing less.

Throwout everything else, the ati tuning issues, the greddy safty concerns, the stillen hood modifications, price, tuning.

I am comparing simply the effects of each forced induction system on the VQ35DE properly tuned and running flawlessly on their ability to produce power and the kind of power they produce nothing more nothing less.

I would like to see an intelligent arguement as to exactly why the SC is superior to TT based on the merrits of the systems themselves as all the evidence that i see clearly shows that the TT on the 350Z is superior.

S12 driver

Can you elaborate on this point? I thought the root type s/c make full boost at redline like the centrifugal s/c? How can the root type s/c make full boost at any rpms?

Thanks.

PoWeRtRiP

keep in mind that the lag most of us refer to does not correlate to a dyno run where you are full throttle the whole way and in the right gear. we are talking about being driving then having to get boost while you are in say third gear @ 40 mph and about 3000 rpms, if you floor it it will be sluggish, if you down shift you will hit boost but regardless it will still have significant lag. while a sc in this situation would have boost always and get the jump in a race in this situation. or as someone else said planning ahead for the exit of a turn adn timing it so that the boost is there when you need it. all the dyno shows is that from a stop it will spool by 3000 rpms if you are full throttle. in real life ppl dont always just stop then rev it up launch and accelerate hard. try to apply the turbo lag to other situations. and yes there is substantial turbo lag, it hits full boost by what 3500 rpms? you know an evo hits 19 psi at 3800, it felt very laggy when i drove it.

ct roadster

OK, the lag issue: it doesn't matter how much power you are making relative to stock or some other config at some RPM; the issue is that when you go from part throttle to full throttle (or even just more throttle), with a turbo you have a delay before you get a big kick from coming on boost. In a track situation, the problem is that you corner at part throttle, then get on the gas coming out of the corner. In a NA car, or a Roots car, you just hit the power when you want it, and it's always there. In a turbo, you need to hit the power just before you need it. Even then, because the power tends to come on in a burst, it can upset the handling of the car much more than with a steady increase in power.

(Depending on a lot of things -- how skilled you are at driving, how well you know where the limit is, how your suspension is set up -- this lag can make you slower than a NA car on a track, even though you have lots of HP/torque. Happens at PCA events every time. Suspension setup and car handling to make the most of a turbo car is totally different; in an NA car, you tend to carve turns and roll on to the gas coming out of the corner, but in a turbo car, you tend to get the car through the corner and pointed more in a straight line then light it up. You can see this difference if you watch race vids very closely.)

You can't see lag on a dyno plot, so please stop looking for it there.

I agree that the 911 turbo is an extreme example; I said as much in my first post. (A big factor in the 911 is that you have near 100% weight transfer to the rear on acceleration, so if/when it breaks loose, you are gone....) But lag is a fact of life with any turbo, even a little turbo on a big high-CR motor -- lag can be reduced but will never be eliminated. (Audi, in particular, has done some really excellent things to reduce lag and keep turbos spun up during short part-throttle drops.)

About the Roots boost issue: Roots blowers are a positive displacement compressor, just like a piston engine, but they operate on a slightly different principle. Because of their positive displacement nature, the output pressure has a fixed ratio to the inlet pressure irrespective of the speed you drive the blower. Drive it faster and it can blow more air but at the same ratio. A piston engine has the same qualities. Thus, if you link the two together so that their RPMs are linked at some fixed ratio and the one feeds the other, the pressure in the intake plenum will be determined by the fixed pressure ratio the Roots blower is supplying and the relative air flow delivery of the Roots blower per rev versus the piston engine displacement per rev: this is very nearly fixed over the entire RPM range. (It's not perfectly fixed as the "Volumetric efficiency" of both the blower and the engine changes over the rev range.)

About turbo versus sc efficiency: yes, you're right GQ man, turbo's can be north of 90% efficient, and SC's peak out in the high 60's. But that's pretty close in this sort of context: a small amount of gas mileage that only really is an issue at full throttle. More importantly, look at the path taken as a turbo is applied in a car: the turbo efficiency varies quite a bit over the RPM/throttle range (note: significant cause of lag!!), where the Roots blower will stay much more constant. But even more important than efficiency is my original point: driving either a turbo or SC is *NOT* free (as had been said in this thread), and both require similar (within a ballpark) amounts of power to achieve a given boost.

I think it would be most helpful if people stopped lumping the centri SC's with the Roots SC's; they are not at all the same. They are both belt driven, but that's about where the similarity ends.

Lag in centri SC's: the centri SC's (ATI, Vortec) only really boost in the high RPM range as seen from the dyno plots; the effect is to make the engine have a steeper torque/hp peak. (This is a consequence of the huge variance in efficiency experienced as the turbine speed is varied). But this isn't really lag; it's just having a peaky engine, like the 4-banger in the S2K. The difference is that with a peaky engine, you can keep it in the upper powerband just by keeping the rev's up, using the close-ratio 6 box. Turbo lag is different: that's a pure delay -- no matter where you are in the power band, when you ask for more power, there is a delay before all the power you asked for comes on line. A high-CR big displacement motor definitely helps, as a) there is more baseline power available, and b) there is a smaller jump to the full power, but lag is lag.

And GQ, you're right, I've never driven a turbo'ed 350Z, so maybe the lag here is so small as to be non-existant. But seeing as I have read lots of people saying that they do have some lag, I'm inclined to believe that the VQ35 follows the same rules as all the other turbo motors out there.....

-frank

Sharif@Forged

iTrader: (92)

This aluminum's brace primary purpose is NOT to trigger the airbag. It's primary purpose is to provide physical impact protection in the event of a front end accident, and also saves the radiator and engine for damage in a low speed accident.

A pothole will not trigger the airbag...regardless of where that sensor is located...this is simply not the case.

Sharif@Forged

iTrader: (92)

CT, the Roots SC's without a doubt have more TRQ and a flatter power curve than a cert. SC. BUt the TT...on the dyno...show even more TRQ at a lower RPM than the Stillen SC.

Sure...of oucrse, you dont see lag, per se, on the dyno chart. But you do feel the beefy trq curve when driving the car...no lag. The VQ motor has so much nateral trq down low, that the "lag" you are refering to is virtually non-existent in gears 2-5. 1st can be a bit laggy, becuase there isnt enough load to create full boost until about 4500rpm in that gear. With the TT, full boost/trq occurs at different points in the powerband based on the gear you are in. In 5th gear...full boost happens at 2500rpm. Those that are experienceing eccesive lag, likely have an exhuast leak at the wastgate, or the wastegate gaskets are burned out. A couple Greddy TT installers experienced this. Fixed the leaks and gaskets....LOTS more boost at lower RPM.

On the track, I suppose you have a point...that turbo may take a split second to spool up...coming off part-throttle. But if you are really racingo n the track, you arent letting your RPM fall below the threashold point where boost and peak trq are too low. If you are keepin the reves mostly in the 3500rpm plus range......you'l again....have almost no lag.

Sanderman

Gee, funny thing is I can't seem to remember the last time I drove my car without using first gear.

But look at the bright side - you only feel this every single time you take off from a standing start. Or take off from a rolling start. Or are running at a constant speed and want to immediately accelerate. Otherwise - VIRTUALLY NO LAG!

I guess the ultimate tuning mod to completly eliminate this virtually insiginficant negligible reisudal lag would be to start running stop signs and red lights.....but why would you want to do that? That little lag time simply gives you a moment to ponder and enjoy the 90% efficeincy of your turbos compared to lowly inefficient SCs and how lucky you are to have them.

joe (a guy who ran twin turbos for 200,000+ mile over 11 years, unlike some of the dyno reading turbo theoreticians around here)

G3po

iTrader: (8)

The phenomena in first gear from a standing start has more to do with the "boost threshold" as opposed to lag. The lower the boost threshold the less noticeable the delay in TQ rise from a standing low RPM start. I expect that the JWT 520BBs will offer an even less noticeable lag and provide a lower boost threhold, so I'm waiting to see the results when released.

From personal experience, (several years with a KB Twin Screw setup which offers the best possible off idle low end TQ), is still a "slight lag". The Twin Screw SC still needs about 2.5k rpm to build full boost (10psi in my case), but it's still there. So no boosting method is absolutely perfect.