Perhaps your speedometer is out of whack somewhat as a result of the wheels and tires. I suspect it reads faster than you are actually going, but not significantly.-

 

the reason why he gets lower rpms with same speed after the mods is because he's got an auto.

 

... ... ...

 

an auto does not have direct power to the wheels. That is why if you floor it there is no direct relationship between mph and rpm. Just like if you break torque...you can rev your engine to 2000 rpm but still read 0 mph.

 

It's all mechanically related, so breathing mods wont change a thing, only different gear ratios or tire sizes will.

And you're referring to stall speed when talking brake torquing....not 'direct relationship '

I agree that an MT is mechanical and an AT is more clutch packs, tranny fluid But still has direct relation (RPM/SPEED)

 

I Dont Know

 

why is it then that depending on elevation, at 2k rpm I can going anywhere from 45mph to 60mph when in the last gear? or if you quickly push down the gas there will be a jump in rpm but not in speed?

edit...after i saw edit of nmexmax.

I see what your saying about a relationship between rpm/speed but I do not believe it is a direct relationship as in a set multiple between the two. I could see why after the mods an auto can go the same speed a lower rpms, not sure how big difference is but there could be a difference since with the mods at lower rpms you have higher horsepower and torque which could negate the huge powerloss in the auto drivetrain and acheive the same speed at a slightly lower rpm.

 

Oh god......

 

Once again ... ... ...

 

My intake lets me reach 114 mph in first gear.

 

in a manual transmissoned car, the speed displayed on the speedo is directly related to the rpms on the tach, theres no question about it, ever hit a patch of ice in second gear and spun the speedo up to 65mph when your really only doing 15, its because they are directly connected

 

yeah in a manual transmission car...not an auto. In an auto hitting an ice patch would just make the rpm gauge go crazy...not the speedometer.

 

Not true. There's a big *** hill going up to my house, and in the rain if I floor it and break traction (auto), I've been able to get the speedo to go up to around ~45 MPH before, when my actual speed on the ground is 15 or 20.

****, I'll make a video of it if you want.

Or, just do this - pour some sort of lubricant under the front wheels (water, oil, etc), pull the ebrake, and floor it. The speedo will rise even though you're sitting still.

 

. . . . .

 

ok here's what headers do for you:

your rpm will still be the same, however you will notice the engine revs slightly freer (but still keeps the same rpms as before) your speedometer will show you how much faster the car is,
i.e. to go from 60-80 takes much faster with headers than without, because you're making more power
but you still keep the same RPMs as before, just picks up speed faster because there's less restrictions.

before you rip into your tranny get a 00vi, trust me on this one.

 

lol at this thread. part of it is legit and part of it is pure craziness.

 

My headers gave me 2800 RPMS ...

 

you know what...i reread my last post and just realized it didnt make sense...

my train of thought is that in an auto the speedometer looks at wheel rpm not engine rpm. This is why with an auto if you tap on the gas quickly...the rpms shoot up but not the speed. for example if im going 2k rpm and hit the gas it will shoot up to 2.5k which is an engine speed that is 25% faster. This should translate to 25% faster speed but if you look at the speedometer, the speed did not jump by 25%. This shows that there is no direct connection between speed of car and rpm of engine.

 

Those fractions do not take into account gear ratio, transmission . . . .

Are you serious man?

 

30,000 rpms?

 

This is in the 4th gear for an auto. If you are in the same gear, 25% higher rpm will equal 25% higher mph if you have direct power to the wheels ie a manual transmission car. If you have an auto its not direct so the road speed lags the engine speed.

 

So what are you saying? That the wheel and tire rotates at the same speed in 4th gear as the engine? It doesn't, it's not a 1:1 ratio dude.

 

not at same speed but there is a ratio. THis means that if you go 60mph at 3k rpm then at 6k rpm your gonna go 120mph. THis is true in a manual transmission but in an auto I can be going 50mph at 2k rpm and at 2.5k rpm in the same gear depending on a variety of factors.

If I put cruise control once I reach 50mph Im at about 1.8k rpm...
but If Im at 50mph and I press the gas half way somewhat quickly but not enough to cause a downshift, I shoot up to about 2.5k rpm but only at like 55mph.

so here are two instances of different speeds at different rpm
50/1.8 = 27.8
55/2.5 = 22

At this point I can keep my rpm at 2.5k but the speed will gradually increase and at some speed it will stop increasing...this shows a definite lag between engine speed and wheel speed. This happens in an auto since autos dont have direct power to the wheel. This shows that the engine rpm does not matter much but the power at that rpm does. By putting mods, the engine is able to put out more power at lower rpm.

There will be a difference in rpm at a set speed but I am not sure if the difference is that big. I am expecting to get my y pipe sometime this week or next week so I will post my before y pipe rpm tomorow once I confirm my rpm at 60mph using cruise control on a fairly flat road. Once I put on my y pipe I will post up new rpm at 60mph. I beleive there will be a change but not sure how much.

 

No, there wont.

With the same auto trans. and wheel/tire combo a bone stock Maxima will be at the same RPM in 4th gear at 60mph as one with 400hp.

I can't wait for the follow up thread . . .

 

I have a RS5F50V FG41 which I've been told has a 4.1:1 (I guess hence the code) it is from a VQ20DE.. what advantage/disadvantage will there be over the standard maxima 5 speed vq30de ratios? IRC I heard I will accelerate quicker but loose top end speed? (I have MEVI with no extended rev limiter)

Anyone know?

 

Top speed is 160 mph. I went up there once and will never do it again. Your top speed will be decreased to 148 mph, which is still more than fast enough.

 

Hey was that answering my post JCLAW? So i'm right better acceleration but lower topspeed?

 

Yes, but the decrease in top speed is pretty irrelevant IMO. I went above 135 only once or twice.

 

Yeah but who needs to go to 160 mph?

In the real world, it would mean better acceleration at the expense of gas mileage.

 

Highway gas mileage. From what I've read, around town gas mileage doesn't go down much if at all because your motor is straining less to pull the car with the more aggressive gearing. 4.1:1 or 4.4:1 gears (both available) would turn even a stock 4g into a torquey little **** around town.

 

You know that's what I meant.

 

Yes

 

Can't wait then.. I was going to do the install myself.. but a local motorsport place is going to do the install for a pretty cheap price

 

There arent any kits available to change gear ratios in an auto, but that doesnt mean it cant be done. The auto has gear plates that determine the gear ratios in each gear, these gear plates are available in other auto transmissioned cars as well. By counting the teeth in the plate you can calculate a drive ratio in each gear. More teeth = higher ratio. When I had my trans rebuilt, I altered the ratios by putting in gear plates with more teeth. The stock gear ratio on an auto 4g Maxima is a 3.23:1. My new gear ratio is 3.91:1. I only lost 4 mph on the top end, but it gets there much quicker. The stock gear ratio on a 4g 5mt is 3.62:1 respectively.

 

Maybe on an auto but on a manual there are two constantly meshing gears for each set of gear. To obtain the ratio of a gear you need to divide the one on the mainshaft by the one on the striker rod. For example 4th gear in a 5 MT is 0.954. One gear has 42 teeth and its meshing gear has 44 teeth. 42 divived by 44 = 0.9545454545.

Same goes for the final drive ratio. Divide the amount of teeth on the final drive gear by the amount of teeth on the mainshaft. In a 5MT there are 65 teeth on the final drive gear and 17 teeth on the mainshaft. Thus 65 divided by 17 = 3.823529412 is the final drive ratio.

You didn't fork out the cash to have custom machined gear ratios. Gimme a break.

Wrong. It is 3.619:1.

Wrong. If you had really gone from 3.23:1 to 3.91:1 you would only be able to reach 82% of your previous top speed, which is certainly far more than a 4 mph difference. Simple math.

Wrong again. The stock 5MT final drive ratio is 3.823. I had the differencial in my hands and counted all the teeth individually on the mainshaft and final gear. As I said, 65 teeth on the final gear and 17 on the mainshaft. 65 / 17 = 3.823.


With that said, I'm gonna need a timeslip or a video of you pulling on R1's. Good day.

 

IIRC there was a chart that showed the Maxima standard gear ratios per gear and with another column showing the 4.1:1 ratio .. I hope its a good ratio as I have a feeling I'm going to have really short gears

 

This is what you get with a nitrous launch an the auto unless you have slicks


These are photos from MY car, with the auto launching on a 50shot....I did measure it, and it was over 100feet of rubber that got laid down. Following this, I lost 1st and 2nd. Now I have a 5spd. It was a good lesson

 

That's why I was hiding behind the wall ....

 

It would have been an amazing photo while it was happening, or video..but not worth the ultimate cost considering there's nothing wrong with it. From inside, it was just pooring smoke out of the wheel wells.

 

..bump bump for me ..