Doug,

I see on the link you posted the hardened shaft for $295 extra.
How does changing over to 4.10s affect the broken rears we've seen in the 2005s? Does this increase the odds? Is the hardened shaft you offer to help prevent this ? or am I mixing stuff up here?

thanks!

 

Well some of that was in the housings that were being used in 05, but the gears and shafts that we use are stronger than stock, so I would have to say that the odds are much less with stronger parts in general.

 

just to be clear, are you saying that the $1195 4.10 package should have added strength over the stock 2005 rears? even without the $295 shaft option? Is the hardened shaft recommended mainly for higher horsepower cars?

 

The gear price is $1,395, with an additional $295 for the hardened shaft installed,(while you wait if necessary) as listed on our web site that I linked to earlier.
We use cryo treated gears, so they are stronger than a stock gear. They actually look like they were chromed, to bad you wont see them unless you are here for the install.
We recommend the shaft for anyone who races the car, regardless of power level. It is cheap insurance for a part that is known to fail, and no additional labor while the rear is being built If it breaks later, the rear has to be removed again, which is more than the cost of the shaft in labor alone.

 

The internals arent what fails when a 2005 unit gives up the ghost. Getting a build up using the 2005 case is only as strong as the weak link which is the case. The case gains no strength from being rebuilt with better internals. Many members posted that the case broke and the internals were fine to be transplanted into a new housing.

The 2005 diffs were breaking with stock power on the street with stock tires. Better options exist for getting a strong diff in the back. The best one is to swap the diff case for a 2006+ unit and change the rear trans case to accept the newer diff.

 

I'll take a chance and post here to discuss for those who want to. I am not interested in gear thread wars anymore....

I will never understand why people think gears are only a launch thing. Gears work for making you faster because they get you higher engine power for any given vehicle speed. The geared car has more power at that rpm and will wind to redline faster as a result of it. At high speeds you wouldnt leave your car in 6th for a roll-on. You would downshift because the gearing helps you when you are steeper because of the power band. You select a gear that has you in the upper power band right? Gears do that at all times.

In this dyno sheet look at the rpms you would be in for 1st gear at 30mph for your roll on example:

At 30mph in 1st the stock geared car is at 3150 rpm (Z51) making just over 200HP; Lets say its 210. The Z51 with 4.10's in 1st is at 3800rpm's and making 280rwhp. Thats a 70rwhp difference and its why some people say thats about what they feel. There is a basis in fact here and its not just the butt-o-meter. When the 4.10 car shifts it wont fall as far in rpm as when the stock geared car shifts and again after all shifts, the 4.10 geared car winds all gears faster because it always lands at a higher rpm and thus a higher HP. At 120mph at 3000 rpm the stock geared car is at 210hp and the 4.10 geared car is at 3600rpm for the same 100mph and thus producing about 265rwhp. This dyno sheet is for a header car with a FAST manifold. Stock heads and stock cam. I realize I may not be exact in all speeds and rpms but the issue here is gear keep you higher in rpm at all times over a stock geared car. Thats why they make you faster. Another aspect is less inertia due to less forward resistence but I am not even including that. Try pushing a car thats in 2nd gear as opposed to first to see whats needed to get you going.

Now to really see the serious issue FI cars have with gears look at the dyno sheet for a FI car and compare rpm's vs HP. The boost comes on so steeply that the differences for a geared car vs non -geared will be staggering.

It can be a 150hp difference if you over-do the boost for your chosen tire. Now look at the power levels that the gear change makes for you: At 3100rpms its 210hp and at 20% more rpm from 20% more gear it would be 340rwhp @3800. When the boost comes on like that it will break the tires loose for just about any street tire. Not flooring the car would let you retain traction but then why not only have the power level for your tire. You wont get the throttle position right every time.

Some things to remember: H/C cars have power curves that dotn look anything like the above stock car dyno sheet. The power leves can be made to pull all the way to a 7k redline. The 4.10's will land you in higher rpms under 5k every time and the 3.42 geared H/C car will be 20% lower in rpm and usually more than 20% less power for each shift. On my car the 4.10's land me at 50HP more than I would be at for each shift than if I had 3.42's. No header gives you 50HP. We didnt even get into the TQ multiplication gains here....

Fast cars are a series of mods that work together in tandem to produce a net result that addresses all of the aspects of the application the car is used for.

The geared car will wind all gears faster and roll-ons arent any different.

The header car will not be out in front ever. As an illustration an A4 auto gains a full second in the 1/4 going from 2.73's to 3.73's on an otherwise stock car.

I hope this different view point helps some people see things they didnt see before. In the end we mod the way we want to mod to make ourselves happy about our car's performance. There isnt a right or wrong mod or gear but sometimes people choose based upon the wrong criteria. Its valid to choose less gear for trap speeds or gas mileage but be sure you know there are trade-offs for any choice you make. Its all about going to sleep that first night after you get a mod and you're happy with all the ways things changed on your car....rpm's on the hiway too.

 

One thing I noticed about gear selection. Is that everyone on the bolt-on Fast C-6 list with sticks seems to choose 3.90's or 3.73's over 4.10's.
Also when two cars are side by side headers vs gears. With a rolling start the lower gears lose some value as the headers car will start maybe in second vs the gears maybe needs 3rd to be in the right power band. Header car wins the race at some point down the road. Thats for sure! As the power level goes up the need for the really low gear goes down. Enough power difference higher gears will pull faster and cover more ground. Out running the lower gear. Much like a Z0-6 is going to smoke a c-6 that has gears only.Something to be said for that aspect. So gear selection is really key with your final plans.

Motive gear has a chart suggesting different ratio's for different power levels
each ratio had a power cutoff level when you cross that level the next ratio higher was recommended

 

Rock'n Blue 08 has it correct!!! Thank you!

If gears is the same as adding HP, why don't trap speeds increase? MPH is the true indicator of HP.

I'm willing to bet that a geared only car will not pull a Header only car from 35/40-130 mph. You will notice, most cars with gears will stay nearly the same trap speed in the 1\4. These claims that gears are like adding 40-70 HP are a little misleading! Add 40-70 Hp to a C6 and it will trap 120-125... Most geared cars will drop a coupe tenths -.3 or so, but the mph remains static or close to static. With headers, you will drop .3 and the mph will increase by 3 or so... Gears make you quicker not faster!!!! Two totally different things... The Header car also gains a 30lb weight advantage.....

My dad and I had identical setups on our 05 z51 SX's. Heads\Cheater Cam\Fast - Exact same boltons... Out of the hole he was faster. My car was faster from a roll....

 

I gained 2mph from my 4.10 gears compared to the stock 3.42's.

 

That is possible, but I've also seen 05s with 3.23s trap higher than the same car with 3.42s....

Track conditions play a role as well, but I would say the norm is very little mph is gained by swapping gears. Headers are good for 3mph all day with tuning...

thesubfloor just went from 3.15s to 3.42s in his A6 and didn't gain anything....

 

The transmission ratios and and mph that the driver shifts at are the primary determinent of what the rpm will be at the completion of a shift. There is a bit of vehicle acceleration occuring during the the shift so by the time the shift is over, the mph is higher than the mph at the start of the shift. I don't see gears adding that much to make a measurable change in the post shift rpm.

Geared cars do trap higher. Gears multiply torque being applied to the rear wheels. More torque equals faster acceleration. Geared properly, you'll put down more average torque accross the 1/4 mile than leaving your gears stock. For an M6 with stock size tires, that means 4.10s unless you trap too high.

I 've looked at a lot of data in the LS1 f-body world and I've never seen anyone trap lower from adding gears unless it added a shift and they missed it. This applied to M6 and A4 cars, although stalled A4s typically gained less than stock stall cars for a given percentage change in gearing.

 

3.23s to 3.42s is a very small change and I doubt that there are enough that have made those change to reach a statistically valid conclusion. Look at those who went from 3.23 to 3.73s. All gained mph.

I don't know that The Subfloor's data is conclusive given the converter issues and weather differences. TM with the A6 may also have an impact. I realize for A6 cars this is fact of life that needs to be accounted for today in making decisions, but to apply his results to all gearing situations is not valid.

 

I've had different experiences with gearing.... Mostly on manual cars... When my dad added 3.90s to his 05, his mph didn't increase any with the same driver. We took his car to the track several times before and after. He did drop .2 tenths off his 60' with the gears

Let's say for argument sake that gears do add mph... Do you think a gear only car will pull a Header only from a roll... 30/35 -140?

The car would be down 30Hp and weigh 30lbs more but have a gearing advantage.. I just don't see it happining... the geared car might get a slight jump on the punch, but the header car would go screaming by...

 

/agree

I traded some PM's with The Subfloor (Christopher) and between the problems he had and limited testing runs I'd say its still too early to have a clear picture on the 3.42's vs 3.15's.

Spinmonsters discussion above was really good stuff! A good torque converter will work in much the same way, together they can work wonders.

 

The thing people appear to be forgetting is that while the geared car will pull harder than the non-geared car in any given gear (2nd vs 2nd, for example), the speed range in any given gear for a geared car is less.

This means that, for example, the geared car will pull harder in 2nd than the non-geared car but when the geared car shifts to third, at redline, the non-geared car has more mph in 2nd, where it is pulling harder.

Here is a graph to help explain the situation. This graph compares the acceleration over time between a C6 Z51 and a C6 Z51 with 4.10 gears. As you can see, after about 40mph, it's a toss-up.



By contrast, here is a graph of a C6 Z51 vs. a C6 Z51 with 4.10s and with headers. Clear difference.



I produced these graphs using a simulation program which I've used to model the C6. In general, I've found this simulation software to be very good and I've found it to model 1/4 mile times of the C6 and mods very closely.

Pat

 

Great information.

I'm not going to take sides.....since I have both and feel both are a worthwhile investment.

As Pat said,
Gears increase torque, allow the engine to reach the powerband faster, and will certainly help you launch. However, for each tranny gear, the engine is in the powerband for a shorter duration. Gears don't add any power, just give the impression of power by putting the engine in a better powerband. Your car may feel like it has 50-80hp more, but it doesn't. Most of the gains from gears are due to better launches. You'll get a little, but it's not staggering.

For SOTP feel and daily driving, gears can't be beat.

Headers on the other hand will add power, and serve as a good starting point for future mods. Not to mention the sound! Most of the gains from headers are in the high RPM bands, so you don't notice them as much daily.

For track performance, go with headers and a tune. For around town, to with gears. Even better, get both

Pat,
What program are you using to model performance. I'd be very interested.

 

I think it would be pretty tight assuming both cars can nail it at 30 mph. I've seen 3.42 - 4.10s swaps on M6 cars add 2 - 4 mph. Headers and related tune a solid 3 mph.

What would be interesting to see from the roll-on perspective is to look at some before and after time slips and see the change in mph from the 1/8 to the 1/4. Which cars gain more?

FWIW, I don't think I saved 30lbs in the swap and may not have save much at all. I was surprised at the weight of the headers, which may be due to the true long tube length of the LGs and the fact that I run cats. I didn't weigh things, so it is just a guess on my part.

 

Pat,

That was PHENOMINAL!!! Don't suppose you can run a similar simulation with an A6 car changing from stock to 3.42 can ya?

 

To be honest, I've invested a bunch of time adjusting parameters to model my LS3 powered, Z51 geared, 6 spd C6. Modeling the automatic version might take some time.

I'll spend a little time building an automatic model tonight (after work) and see what I can do. No promises.

Pat

 

Pat, Can you do compare the acceleration of the car with gears to the headers only car... I know you showed the geared car vs non geared being a toss up after 40, but I think it would be nice to see this plotted to show a direct comparison.

Car A = 4.10s only
Car B = Headers only

That is cool software BTW