Corner weighed my RB25 s13!!!

[Bluefire]

Alright guys I just corner weighed my car at my shop.

This is a bone stock base model 91' 240sx hatchback.

Full interior and spare except for the back seats which have been removed.RB25DET with mckinney mounts, driveshaft and downpipeKoyo radiator2 12" electric fansGreddy ManifoldGTR FMIC with mild steel pipingTrunk Mounted batteryRemoved front Bumper SupportRemoved Entire AC system and Heater Core1/2 tank of gasOpen Downpipe

Car weighed in at about 2660 lbsCross Weights were close to 50%Front to Rear was 54% - 46%

Apparently the problem is not the weight of the motor but the position of it. Basically 1/3 of the motor sits in front of the axles which is what makes a difference. The only thing to fix this weight wise is to move weight in front of the axles to behind the rear axles. Hood, Fenders, and Bumper weight is negligable. Only thing worth losing weight on is the fmic and the pop headlights. Any weight within the wheels will not affect front-rear balance.

Suspension wise, you would have to use some higher spring rates in front than normal to compensate. Hence affecting weight transfer and front to rear body roll, which in turn affects the way the car handles corners

-Bluefire

[Nameless EJ6]

Sweet, I've been waiting on someone to do this.

Do you think modifications like carbon hoods/front fenders/bigger (more heavy) rear wheels would effect it much? It'd be cool if you could get it to 50/50 or 51/49 front to back.

[Bluefire]

Well basically using the front strut tower bar as a reference point, anything in front of it is what affects the front to rear ratio. And same thing for the rear, anything behind the trunk strut tower bar will affect the ratio. So even though you may lose like 30lbs by switching to cf or glass, you really only losing like 15lbs since half of the weight is behind the front wheels. Samething with heavier wheels. It won't do anything front the front to rear weights.

You want to focus on items before the front tires(Headlights, Front Bumper, Bumper Support, Battery, Radiator, Intercooler) and behind the rear tires

-Bluefire

[Nameless EJ6]

Makes more sense.. Thanks.

[Darius]

Were you sitting in your car when you cross-weighed it?

Also, a full-tank of gas would add ~50 lbs to the rear...just a thought.

[Bluefire]

sitting in the car does not affect front-rear weights only cross weights

-Bluefire

[zauber]

does the rb20 weigh less than the rb25?i am swapping rb20det into my 91 nissan 240sx se coupe. thank you for the post because i have been thinking about for some time, and i thought it would be a larger issue with weight.

[DETurbine]

were you in the car though....when it weighed out to be 2660lbs?

[goofynick6]

does the rb20 weigh less than the rb25?i am swapping rb20det into my 91 nissan 240sx se coupe. thank you for the post because i have been thinking about for some time, and i thought it would be a larger issue with weight.

RB20's weigh less, and the transmission weighs considerably less.

[Sil240]

I thought that the block was the same but it just had the smaller transmission(RB20)

[RMiller]

Thanks for some great information. I wonder why so many people said that the 25 with transmission weighs 200+ lbs more than the KA. A base '91 hatch weighs 2650 (According to Edmunds, this may not be accurate), so the 25 really only adds maybe 60 lbs (?) considering you removed stuff from your ride. Nice! I have a ca but I have dreams of a rb26 some day.

[RMiller]

I thought that the block was the same but it just had the smaller transmission(RB20)

No, water passages are different. Remember you can't bore a 20 block to the 25's diameter.

[AmoebAssassin]

Well basically using the front strut tower bar as a reference point, anything in front of it is what affects the front to rear ratio. And same thing for the rear, anything behind the trunk strut tower bar will affect the ratio. So even though you may lose like 30lbs by switching to cf or glass, you really only losing like 15lbs since half of the weight is behind the front wheels. Samething with heavier wheels. It won't do anything front the front to rear weights.

You want to focus on items before the front tires(Headlights, Front Bumper, Bumper Support, Battery, Radiator, Intercooler) and behind the rear tires

-Bluefire

This is wrong. According to simple physics principles, any weight removed ANYWHERE forward of the car's center of mass or any weight added behind the car's center of mass will reduce the front sprung weight and increase the rear sprung weight. There is some truth in your statement though, the farther forward the weight is removed from, the more drastic the weight shift will be.

[Bluefire]

Yes I understand the true physics of weight transfer but my main point was to emphasize the weight before and after the front and rear tires. Any weight transferred between the two tires is really negligable. Even the weekend track goer would not feel a difference. And instead of having people waste there time transferring weight between the wheels, it would be better for them to concentrate their efforts on the areas that will largely make a difference

-Bluefire

[Wulfgang]

I don't want to kick a dead horse, but it's really a question of moments (weight x distance from CG). So using that, if your FMIC goes on a Slimfast diet and loses 18 lbs (assuming it's 6 feet from CG), then a 200 lb driver could get the same effect on the F/R ratio by sliding his seat back 6 inches.

And btw, you can't discount the fact that the cf hood saves 30 lbs. That means your car is 30 lbs lighter and will now have more than 1% more acceleration. (However, my OEM hood can't be over 30 lbs, so unless the cf hood weighs zero that number is inflated.)

[AmoebAssassin]

I don't want to kick a dead horse, but it's really a question of moments (weight x distance from CG). So using that, if your FMIC goes on a Slimfast diet and loses 18 lbs (assuming it's 6 feet from CG), then a 200 lb driver could get the same effect on the F/R ratio by sliding his seat back 6 inches.

And btw, you can't discount the fact that the cf hood saves 30 lbs. That means your car is 30 lbs lighter and will now have more than 1% more acceleration. (However, my OEM hood can't be over 30 lbs, so unless the cf hood weighs zero that number is inflated.)

Exactly

[goofynick6]

Stock s14 hood = 41 lbsCF S15 hood = 20 lbs

Just an FYI

[Bluefire]

Yeah I totally agree with you guys, by switching to cf you do save weight, improving acceleration. But the focus was on weight distribution. Also what sounds more reasonable, shaving that 18lbs off the front of the car or transfering 200 lbs 6 inches back. Trust me guys, i've been sitting in physics classes and applied mathematics classes for a few years now, and what i've come to realize is that all the laws and formulas don't factor in all the real world variables. The easiest way to transfer weight is to go to a point where the weight makes the biggest difference, nose and *** of the car.

-Bluefire

[lyon23]

I just weighted my s14 with an rb20 ac, ps eveything else on full interior and some junk in the trunk and it came at exactely 3000 lbs.