TemjinX2

most cars won't hit there max limits usually because on paper the assumption is your driving on a perfectly flat road with perfectly inflated tires in the correct psi, no air resistance and you have enough hp to reach the limits of that last gear.

We all know we don't live in a perfect world like that, so your real life numbers will be slightly off there the theoretical paper limits.

I think mechanically its going to be fine, you should be more worried about the software side.

cpbeasley

3.46 pupmkin on its way.
As stated, 05 c230 w/ 20k miles before it met its demise, as the donor.

Tem-
Karo has provided some prelimiary screenshots of the ECU fix in developer mode. Waiting on johnand to provide further info since Karo is now blocked out of his star access.

doshoru

This was driving me crazy, so I had to register to explain.

Tachometers and speedometers lag behind the actual speed of the engine/wheels. Not as much as they used to, but still. You can accurately calculate speed per gear at a given rpm given the known gear ratios and tire diameter. I haven't bothered looking it up on this forum, but practically every forum worth it's salt is going to have a table for you to look up those values in stock form.

Also, I will have to agree with e1000, in the case of the c350, that a shorter gear ratio is probably not the best idea on this car. Shorter gears CAN help, but only situationally. In an old-*** fox-body mustang with economy gears that can top near 80mph in 2nd, yes, shorter gears will help you. But there's a tradeoff, and we're not talking fuel economy.

The transmission is a torque multiplier, and gears are a balancing act. A fine, fine balancing act. Changing the final drive has two effects:
1) You will rev through any given gear more quickly
2) When you shift, the revs will be higher in the next gear
These two effects are the same for ANY car...so you need to ask yourself, is this what I want for MY car?

Let's talk more about the first effect: This is GREAT if your car either has a peaky powerband, or is VERY long from the factory (read: old muscle cars that can hit 80mph in 2nd gear). You want to get into your powerband as quickly as possible.

If you take two cars of the same make, and give one gears, the one with gears will out-accelerate the one without until he has to shift. The nature of the gears means that he WILL have to shift prior to the non-geared car. When the geared car shifts, he is now at a disadvantage, torque-multiplication-wise. E.g. 2nd gear times FD (geared car) is not going to be putting down as much torque to the wheels as the non-geared car, which is still in 1st gear (1st gear times FD). The non-geared car WILL begin to close the gap at this point.

The million dollar question is.....can the non-geared car catch up to the geared car before HE has to shift into 2nd, losing his advantage????

If your stock gear ratios are absolutely terrible (think, 80's mustang with a 2nd gear than can get near 80mph), the answer would be yes. You're in a c350, with a 2nd gear that is closer to 60mph...your gears are already very short from the factory. Maybe not the final drive, but the overall gear ratio is SHORT. My guess is, any acceleration advantage you gain up until you have to shift is lost when you shift, and the other guy is still in 1st. Not only that, but you lost time while shifting, b/c you're human, and shift slowly. This is all assuming you have traction!!!!!!!!

Another, very important point -- the geared car is going to feel faster. This is because you will get that immediate shove back in your seat at every shift, as your effective torque at the wheels will be greater at the start. The problem is, your gears will top out more quickly, and the non-geared car is going to make ground here....From a standing 1/4, you may be slightly quicker. From a roll race, it will 100% depend on what speed you start the race from!!!

Let's take effect #2 -- in a geared car, when you shift, your RPMs in the next gear up will end up higher than in a non-geared car. In a peaky car like a honda with a narrow power range, this may be advantegeous. In a muscle car, or a car with a small turbo (VW GTI?) where power dies off noticeably after X RPM, this could be BAD (unless you short-shift), because your shift could land you outside of the powerband. I am not versed enough on the c350 to know what the powerband looks like, but would venture to guess that this is probably not really a factor on this particular car.

Cliff's Notes: Shorter gears are a tradeoff -- you gain an acceleration advantage in one gear, but lose it in the next due to having to shift early and losing torque multiplication. They tend to benefit cars that either have very long stock gears, or a very narrow powerband, neither of which is a trait of the C350.

TemjinX2

eh give it a shot and if it doesn't work out. Then switch it back. I think people should try more out of the box mods instead of everyone doing the same cookie cutter mods.

e1000

There's a reason why the cookie-cutter mods are cookie-cutter.

I'm also all for people here pushing the envelope and exploring new options, who isn't? The problem is when someone goes into it blindly, with little to no research.

doshoru

Here's an example of what I was talking about:

http://www.youtube.com/watch?v=e32gozeyXLo

The 07-08 350z's had their redline increased to 7500 rpms. 2nd gear tops out at 70mph, and 3rd at 110mph. This is LONG compared to the C350.

Common sense would say that shorter gears would benefit the Z...but the video says otherwise. From a roll, you can see that both cars are almost identical on the overlay. The STOCK car actually pulls ahead by 1-2mph near the end of the video.

Now from a dead stop (0mph) the geared car will undoubtedly pull...this is because both cars must start in 1st gear...the stock car cannot downshift to make up for his disadvantage in 1st.

This proves, 100%, the point I (and e1000) was trying to make earlier -- in the quarter, you may score a difference -- less so in a car with already short gearing like the C350. Everywhere else (normal driving, road races, highway encounters, etc.), it depends on what speed you both start at, AND end at. If you're NOT starting from 1st, the non-geared car can ALWAYS downshift.....

FrankW

good stuff by doshoru...

W203E35

Doshoru and e1000

MW_ATL

A great post and explaination. I made the assumption when he made his readings that he spent some time at or near the rpm limit and read the speed to help give the readings time to stabilize. That may well have not been the case , but yet another valid point that would explain difference in calculated numbers and observations.

Exactly the case I used in my example. Of course there are trade-off, but on occasion - especially in that case, a car can just be horribly mis-geared from the factory. I would guess it was related to reaching for a fuel economy number for the "standard" option car. Those also had the little shift light to tell you when to shift for "economy." Mine burned out.

I think this is exactly the point of his project, he has said since the start that his goal is to make the car more fun to drive, in daily use. Of course the definition of fun can vary from individual to individual, but I gather that he is looking for the snappier feel at moderate speeds in normal urban/suburban driving instead of maximum performance over a quarter-mile from a dead stop.

I agree 100% with you on this. I especially find it irritating when people run into problems that a tiny amount of reading would have illuminated, and then complain about it. I am not sure what research he has done, but re-reading, I think the thread started with him throwing out an idea and going from there. It appears he has talked to several people beyond what he has posted here. I am sure I wouldn't be ready to tackle this project this quickly, but some people are more comfortable figuring out the answers as they go than I am.

e1000

What a great video. You should see how short the gearing already is. Funny that you use a 350Z as an example, it's similar in power and weight to a C350 (and name for that matter). Good stuff.

doshoru

Keep in mind that the stock 350Z HR's gears are much longer than a C350 -- and there was still no measurable difference from a roll. A C350 may end up even worse off with gears due to the percentage of time spent shifting instead of being on the gas.

FYI, a geared 350Z HR has about the same ratios as a stock C350.

C230 Sport Coup

Where did you pick this up?
At 164K miles it is something I think about.
Are you going to do the work yourself?
If not how much labor is required?

cpbeasley

Tem:
Exactly.

Dosh:
Thank you for your time spent in writing up an explanation for e1000000. You honestly didn't include any concept that I didn't already understand, but it's still useful information. Per your explanation, I wouldn't be doing this if I was street racing at every corner. See MW_ATL's response re: suburban/city/hwy driving.

Speaking of, MW_ATL:
Everything you wrote... basically, you nailed it. Thank god for some understanding. And you're right, I was just throwing the idea out there at first. Now I get blamed for asking question after the fact, when I started this whole thing with an idea requesting feedback. I didn't get proper technical feedback until doshuru. I didn't get encouraging feedback that understood where I was coming from until you.

230 Sport Coup:
I sought out eBay's european drivetrain salvage yards until I found the one for me. The business I chose was overall the cheapest, and even took my offer for a lower price. Shipping from California took about 4 days.
If I had ANY time to leave dental school in KC long enough to make the 3 hour drive home to my dad's lift/garage, I would do it myself. I believe theres about 8 bolts along with disconnecting the input shafts. Nothing too technical while leaving the pumpkin intact. A local corvette tuning shop is going to do it for me @ $300.

EDIT: I do have yet to watch the movie. So, we'll see how I feel after watching it.

e1000

Great thing about internet forums is, we can go take a ride into the way-back machine. All the way back to your original post!

Here it is!!!!!!!!

We now know, the answer to the two questions in the highlighted area are NO and NO.

If you weren't looking for a performance advantage, why were you questioning how much faster the car would be?

How's that crow taste?

cpbeasley

It was an ice breaker. I'll be sure to be all-inclusive in the future. I can take constructive arguements, but not your snide comments. Go away.

e1000

and if I don't? If I was a betting man, I'd say there's a good chance that after 5 years and almost 30k posts, I'm not leaving MBW.

cpbeasley

throwing the postcount queen thing at me from two different threads!?

(psst... it was a request to leave ME alone, not leave the board. you have the darndest time with context, you silly goose!)

Im finished with this thread now.

samaritrey

I wish i could put you both in time out lol remember when you would argue with siblings as a kid your parents would always say it doesn't matter who started it?



now stop it

If cpbeasley wants to ruin his car or make it better he has already set his mind to it and we will find out if it turned out for the good or bad.
As for E1000 i have never seen you get this way before usually you would give up by now and let them fup there car or whatever
lets go back to trying to help each other fix issues or whatever and be a big happy family lol i don't like bickering it upsets me

Glyn M Ruck

Absolutely correct! He might be able to burn a little rubber until first runs out though!