Dumb handling and weight distribution question about the RB25DET

[dareo]

I understand the RB25DET swap will add some pounds and shift the weight distribution percentage more forward. But in my '89 240sx i've got an amp and two 10" subs that im quite attached to. All this stereo rice adds up to about 60-70 pounds right at the rear wheels. Assuming i have this extra weight in the back and maybe even a rear battery setup how much closer to 50/50 will this get my car?

I'm worried that if i go SR20 or CA18 and have all this junk in the back i'm gonna tend to understeer. This must be avoided! I want neutral to oversteer in my handling. I want to be able to drag, drift and roadcourse this car as well as semi-daily drive it with my sweet stereo and all.

[Nameless EJ6]

I doubt it will do anything unless the weight is behind the rear wheels.

I'd suggest, if you want some oversteer, get a BIG rear sway bar.

[dareo]

Actually the subs are mounted right behind the reat strut tower bar, but the amp is in front of it. (on back of rear seat). So i guess technically that counts as behind the rear wheels and adding to the rear bias?

[modestmouse]

I get the feeling that people think weight distribution is way more sensitive than it actually is. The extra weight on the front isn't going to change the way the car feels to any extent. 100lbs or whatever the change is, is not a significant portion of the cars total weight. And when it comes down to it, we aren't driving F1 racecars. As for the stereo thing, your best bet is to get rid of the subs all together. That weight won't help no matter where you put it. Drag cars down play bump down the track!

[JonPowell]

How much of a difference do you feel in the cars performance when you put someone in the passengers seat? that screws up weight distribution alot...180lbs for a full grown man?

You guys all gotta get over it. I dont care how much of a professional driver you THINK you are, I will say before what I have said MANY MANY MANY FREAKING TIMES....

Take a crappy weight distibution car, like say a porsche....rear engine rear wheel drive WAY biased to the rear and a perfectly balanced car with the same power, total weight and tires...you drive the perfectly balanced car and throw oh say MICHAEL SCHUMACHER in the other unbalanced car.....I guarante consistently better lap times from the unbalanced car.

A good driver will adjust to whatever the car can handle. If you are the professional you think you are a little different weight bias wont hurt you for more than 10 mins before you can adjust your style to still get the most out of the car.

Besides you werent too worried when you threw all the stereo equipment into the car, were you?

[Slo_240sx]

That was Beautiful Man. Brings a tear to my eyes.

[dareo]

The car's the only place i can play loud music and not get the cops called. Besides, 50lbs of subwoofer isnt that much. The subs are irrelevant and staying in my car.

Oh and a passenger sits in between the front and rear wheels so the weight added is somewhat evenly distributed. Nonetheless i can feel the difference between a passenger and no passenger.

Question remains, what engine will give the best handling with extra weight in the back? RB25DET or SR/CA?

[krayton]

sr/ca

[JonPowell]

The car's the only place i can play loud music and not get the cops called. Besides, 50lbs of subwoofer isnt that much. The subs are irrelevant and staying in my car.

Sound laws are still in effect while you are inside a car.

Oh and a passenger sits in between the front and rear wheels so the weight added is somewhat evenly distributed. Nonetheless i can feel the difference between a passenger and no passenger.

What about left to right weight balance? if you have more weight on the drivers side than the passengers side the car will turn differently in a hard right turn than a hard left turn. and since the driver and exhaust are on the same side it makes things even worse.

Question remains, what engine will give the best handling with extra weight in the back? RB25DET or SR/CA?

Just get the SR/CA. You have already ruled the RB out because of the "weight bias" arguement and are just looking for us to confirm you misguided decision.

LEARN TO DRIVE AND IT WON'T MATTER!

[Imissmyturbo]

I will say that my car feels front heavy and doesn't want to corner. But I have stock suspension with close to 200K miles on it. I am sure a good set of shocks/springs/bushing and sway bar will restore alot of the handeling lost in my 240.

[BoostFab]

Just get the SR/CA. You have already ruled the RB out because of the "weight bias" arguement and are just looking for us to confirm you misguided decision.

LEARN TO DRIVE AND IT WON'T MATTER!

i hate it every time someone bring this topic on. why do you give a **** for 50/50 weight distr on street-daily-driven car? just a pointless hype over weight dist nonesense

people don't realize that the stock ka24de strap on the turbo kit and the weight difference with the rb is pretty close.

ka24de.+trannny...560 lb + turbo kit...50 lb = 610 lbrb25det+transmission ....680 lb

get a freaking ca18 or stay with your stock ka if you care so much about weights.


Modified by BoostsFed at 10:22 AM 2/16/2005

[Spazz]

not to be a prick or anything but stop flogging the horse, its already dead.......

[NISMO_RB25]

I will say that my car feels front heavy and doesn't want to corner. But I have stock suspension with close to 200K miles on it. I am sure a good set of shocks/springs/bushing and sway bar will restore alot of the handeling lost in my 240.

you are right on the shocks. Mine had about 150K and every speed bump or hard corner was hitting the bump stops. The tein flex (despite being a little stiff) made up for any weight distribution "problems" and it now out corners my RX-7. Depending on what you are doing, you may want to go with something softer, but new coilovers will make a huge difference.

[accel junky]

With the stereo equip, its probably not enough to cause an SR20 to understeer.

[Porschephile]

Take a crappy weight distibution car, like say a porsche....rear engine rear wheel drive WAY biased to the rear and a perfectly balanced car with the same power, total weight and tires...you drive the perfectly balanced car and throw oh say MICHAEL SCHUMACHER in the other unbalanced car.....I guarante consistently better lap times from the unbalanced car.

A good driver will adjust to whatever the car can handle. If you are the professional you think you are a little different weight bias wont hurt you for more than 10 mins before you can adjust your style to still get the most out of the car.

My Porsche has a near perfect 50/50 weight distribution (probably 50.50/49.50 or something). Stock is ~51/49 and mine has some slight weight reduction in the front. I agree though, the driver is ~99% of it IMO.

Dareo, as far as a 100% perfect 50/50 distribution, that's going to be hard to acheive for a reasonable price and not doing anything more drastic. Though, I wouldn't get so focused on this. I will say that it does make a good difference, however it isn't everything and vehicles without a 50/50 split can still handle perfectly fine. You don't have to have a 50/50 distribution to be able to have a neutral car. Use suspension to adjust for this. You can use an adjustable sway bar in the front and/or rear to adjust for neutral/over/understeer.

As far as an RB swap affecting the balance of the car, it is going to have an affect. Although I look at it like this, modify the suspension to compensate and maybe do some weight reduction to offset some of the weight gain and you should be fine. Also, the RB is physically a taller engine than the KA I believe, so a portion of that weight will also be sitting higher in the car. Personally, I would do ab RB swap at least for the sound. I like i6's more than i4's and, IMO, an Sr/Ca/Ka will never sound as good as an Rb. Isn't that reason enough?

[Wulfgang]

Well, there's a lot of opinion in this thread and still nobody has answered his question. So here's some physics to put it all into perspective.

Assume that the RB25 swap adds 160ish lbs over an SR20 swap and that those lbs are centered at the firewall (since much of that increase is in the RB25 transmission). Also assume that the SR20 swap will put your car at a perfect 50/50 distribution.

Estimate the firewall to be about 3' in front of the CG and the rear axle to be about 5' behind CG.

Then the RB25 costs you a moment of 160 x 3 = 480 lb-ft over the SR swap. You can counterbalance it with a mass of 480 / 5 = 96 lbs right over the rear axle to get your car right back to a "perfect" 50/50 weight distribution.

But now you've gained 160+96 = 256 lbs. If your car weighed 2800 lbs and had the SR with maybe 210 hp (stock), you'd have a power/weight ratio of 210/2800 = 0.075. Going with the RB at 260 hp (stock) with the additional 96 lbs over the rear axle, you'd have a power/weight ratio of 260/3056 = 0.085. Still more than 10% faster than the SR, all else being equal.

Your car will sound better (engine and stereo) and go faster down the straights with the RB, but of course there is nothing quite like the nimbleness of a light car on a tight road course.

Of course there are lots of other variables as other people have said (like the driver). Also, my estimates of CG and lengths are surely wrong, so if you are really looking for 50/50, then you should put it on some scales.

[dareo]

Thanks Wulfgang, that is the type of answer i was looking for.