don't get your panties creaming yet.. its for the bone stock 99 outside my house its getting a VSLD tranny in two weeks yes it is currently a 5spd

 

BTW, where and how much did you find a VLSD ??

 

found it off www.car-part.com .. its in texas.. and its costing $1083

 

I guess we should say that the VI gives the VQ a more "German" feel.

 

Looking at this plot, it seems to me that you would have a faster car if you just stayed in the midrange- that is shifted at 5500 RPM and rode the higher (red) curve... Am I missing something? Is there a benefit to staying in lower gears (e.g. 3rd gear up to 7000 RPM) vs absolutely staying in the torque-ey-est part of the RPM range? It does feel like the car pulls harder in 3rd up to 6000 even though the dyno says I get more power by shifting into 4th gear and dropping down to 4000 RPM. Maybe theres something beneficial to lower gearing and higher RPMs??? Something tells me theres a piece to this that I havent learned about...

 

You brought this year old thread back why exactly?





Eric

 

Because of the question that occurred to me as I was reading this old thread...

Looking at this plot, it seems to me that you would have a faster car if you just stayed in the midrange- that is shifted at 5500 RPM and rode the higher (red) curve... Is there a benefit to staying in lower gears (e.g. 3rd gear up to 7000 RPM) vs absolutely staying in the torque-ey-est part of the RPM range? It does feel like the car pulls harder in 3rd up to 6000 even though the dyno says I get more power by shifting into 4th gear and dropping down to 4000 RPM. Maybe theres something beneficial to lower gearing and higher RPMs??? Something tells me theres a piece to this that I havent learned about...

 

Of course there's a benefit to staying in the lower gears. The gear ratios are lower (or higher depending upon if you are talking numerically or size-wise). Think about First gear compared to 5th gear. Your engine has the same HP and Torque whether you are in first gear or 5th gear, but you accelerate (that is, your velocity changes at a greater rate) in 1st gear than it does in 5th gear because of the torque multiplication through the transmission.

 

The whole point of moving an engine's volumetric efficiency higher in the RPM range is to take advantage of it's gearing. Just look at the S2000 with "only" 153 lb/ft of TQ. It's gearing is excellent and takes full advantage of it's top end. The gearing is what makes it fast, because it doesn't pull HARD per se, it's engine can just do ALOT of work over time...

A VQ with MEVI, mod for mod, will not pull as hard period as an USIM because it's peak twisting force is reduced. But because the MEVI'd VQ can pull for longer in the RPM range and will do more work over time in a given gear it will be faster in all out racing...

You would have to be making MUCH MORE TORQUE than a MEVI'd engine to be able to get away with short shifting at 5500 RPM...MUCH more torque...Which goes beyond the realm of N/A mods...

 

Yup, it's because of gearing as Neal stated. Here's a quick example.

Take a stock 4th gen at 80 mph in 3rd gear. At this point you're at about 5500 rpm and well into the downward slope of the torque curve. Shifting to 4th at this point would put you back in the meatier part of the torque curve, but since it's a higher gear ratio your overall torque at the wheels is still less and it's not quite time to shift yet.

80mph/3rd: 5500rpm, 151 wtq x 1.272 (3rd) x 3.82 (final) = 733.7 wtq
80mph/4th: 4100rpm, 168 wtq x 0.954 (4th) x 3.82 (final) = 612.2 wtq

Even though you have more crank torque in 4th at that point, you still have more overall wheel torque in 3rd due to gearing, so it's not time to shift yet. As it turns out, the optimal 3-4 shift point on a stock 4g is about 90 mph and roughly 6100 rpm.


The MEVI hold the torque curve a lot flatter ala Honda VTEC style, so the torque curve never drops enough to require shifting to the next gear before redline. Optimal shift points on the MEVI are just before the rev-limiter kicks in.

 

[QUOTE=Spaniard]Looking at this plot, it seems to me that you would have a faster car if you just stayed in the midrange- that is shifted at 5500 RPM and rode the higher (red) curve... [QUOTE]

Yes, that is why it's mandatory to have the extended redline of the JWT ECU when you have the MEVI. The extra 500-700rpms allows you to stay in the correct portion of the powerband. With the JWT ECU, you also get back ALL the HP/TQ you lost with the MEVI. When I shift at 7000rpms I land into 2nd at ~4800rpms and 3rd at 5000rpms. It's a blast.


Dave

 

[QUOTE=Dave B][QUOTE=Spaniard]Looking at this plot, it seems to me that you would have a faster car if you just stayed in the midrange- that is shifted at 5500 RPM and rode the higher (red) curve... I ordered my JWT ECU last week. Looking forward to getting the most out of my MEVI.

 

Wow I feel dumb- that was, of course, the missing piece. Thanks to everyone who explained it and especially SteVTEC who really made the light bulb go off with that perfect example. Im somewhat less of a noob now

 

Well if you have an auto you know when first gear chnaged at redline it comes back to 4000 rpms in secodn gear that is almost right back into MEVI range and second gear it is even higher. I think this would benifit autos alot.

 

dam, this is very depressing. Well, now i definitely have to get an ECU. I felt weaker but i always thought my driving got worst or something. But its not as bad as everyone says it is. i've had VI for likst 2 months but for past week car feels weaker...not sure if VI just settled, bad ecu's, knock finally dieing on me...

all i hope is that with increase low end power from jWT ecu (not rev limit), i stay as strong as stock manifold if not a little stronger, then i also have potential to be WAY faster as i increase rpm

 

So will someone answer me this. I've always had this question in my head, but no one has ever addressed it very clearly:

Will a MEVI w/ a JWT ECU (including raised rev limiter) allow you to have the same numbers as stock PLUS added power? It just seems to me that I've heard back and forth that even with an upgraded ECU there's still loss of power somewhere in the powerband...is this true?

Because I wouldn't want to get a MEVI if I was going to lose any more than a couple WHP anywhere in the powerband...And I'm talking NA, not boosted at all.

 

IMO, you should never get the MEVI unless you plan to get the JWT ECU. Like many of us have already proven at the track, the MEVI alone gives you the same performance as the USIM because of the loss in mid range power (-10fwhp/fwtq from 3500-5000rpms) overcomes the gain in power from 5500-6500rpms. You gain more peak power and a ton more power after 5500rpms with the MEVI, but the extra upper rpm power isn't enough to overcome the small loss of power in the mid range. I know I just repeated myself, but a lot of people have a hard time understanding what's going here. Once you add the JWT ECU, all the mid range power that was lost is restored and then some plus your rev limiter is a extended and allows you to accelerate in the correct portion of the powerband.

If I were to do it again, I would have gotten the JWT ECU first because it improves performance without the MEVI. The MEVI by itself only improves performance after 60mph and the car is slower from 0-60mph. Once the JWT ECU is added the car is quicker at ALL portions of the race.

The MEVI/JWT ECU setup drives exactly like the USIM around town. Once the rpms swing past 5000rpms, the USIM looks silly.


Dave

 

thats exactly what i wanted to hear. Has the turn around time on them ecu's gotten better from JWT?

 

What Dave said.

 

Ahh, thank you for clearing that up Dave So the car is normal til you hit 5500 RPM's...then it's like the NA equivelant of a smaller shot of nitrous?

 

Guys don't laugh at me but when it gets warm I'm going to give my VI another go. That damn Harlan switch ****ed me off something good last year.

 

Good to hear....don't let that harlan get ya down. Go with the summit, $50 and your golden. And get that ECU back from Cheston, he obviously is not going to take is car to technosquare.....it's been 2-3 months already!

 

I already have the Summit switch and didn't have it hooked up to the ECU. I had it hooked up to the coil pack so I thought it didn't work. I'm done with Harlan though.

I've got nothing against Cheston except that he doesn't read the messages you need him to read. He pops in and jets outta here without any updates.

 

It's not a slam against Cheston, but sometimes things that are important to you are not others top priority. Can't blame him for having other things going on......You have tried to help the maxima community which get my respect, but at some point you just have to do it for yourself. Go with JWT.

 

The other thing is that Techno has put the new board in already and was waiting for their programmer to get back from Japan so I can't actually get the ECU back now because they already started working on it. I'll try to get someone down there. I don't need it yet anyway.

 

That would be like a Honda DOHC VTEC where you very little torque until 6000 rpm when suddenly it switches over and you start hauling butt. This isn't like that. Look at the torque curves. It's smooth (no "kick-in"), but just much less of a drop-off at high-revs.

 

I differ from Dave in that I would still keep my VI even if I never had the JWT ECU.

 

Uncle Sprinty now has a VI and is N/A so its ok for the masses to go out and purchase one

 

 

if you need some help pm/email/call me.. I'll help if I can.

I have removed my MEVI for a short time while I am getting stuff in order. I need that summit switch

 

I'll bother you and Jamie again.

 

So basically, all the power of the VQ, in a longer powerband? Like...so you don't have to shift as early to keep the power up?

 

Yes.

With the USIM the torque curve drops off so sharply after 5000 rpm that the optimal shift points are actually before redline after the 1-2. If you hold each gear to redline the engine is wheezing and you're losing time.

1-2: redline (6550)
2-3: 6200-6300
3-4: 6100
4-5: 5800

With the MEVI there is hardly any torque curve drop-off and hence no need to shift before redline. Actually, the "optimal" shift point for the MEVI is well beyond the stock redline. That's why it's tough to truly gain any 1/4 mile performance with the MEVI and the stock 6550 redline - it needs more revs to play with. That's where the JWT ECU and the 7200 rpm limiter comes in. It's like those two mods were made for each other.

 

Hiya SteVTEC, I was hoping you could help with a conceptual question...:

Since I am running with lower profile tires (50 aspect as opposed to 60 stock)

Would this impact my shift points - Im thinking yes; and if so, would it raise my optimal shift points? Again I am thinking yes...

Thanks mucho..

 

I just checked that in the cartest software and with a stock dyno and going from 205/60/15's to 205/55/15's the shift points would still be at the same points.

 

I have a question that's a bit off-topic here...

On the graph that Steve posted (USIM vs MEVI), what's the dip in power around 3700 RPM??

 

It's the characteristic bumpy torque curve of the 4g VQ. The intake manifold has resonance peaks and valleys every 500-600 rpm or so. 3400 rpm is the biggest peak and just after that is the biggest valley, and then it flattens out after 4000 rpm. Keven97SE had a really good explanation of this once, but I haven't seen him post in ages. Search for "resonance peak" and Keven97SE and you'll probably find it.

 

oh ok, thanks. I asked because I got my first dyno last weekend and I was wondering what the heck that was. No one else there could explain it.

 

Changing tire size has nothing to do with how the engine makes its power. It doesn't change the power curve characteristics at all. any change in tire size would not affect the optimal shift points. you could put go-kart tires on the max or put 35" super swampers on it and the shift points would remain the same. Only the speed at which you reach those shift points would change.

 

If you play with it in CarTest a bit, the optimal shifts points do shift around a bit, but you're right, it doesn't make much of a difference. The overall tire size affects the final drive ratio which can tighten up or narrow the gearing. But the gear spacing and the actual ratios against the torque curve of the engine are what pretty much set it. Thanks for clarification.