Duckie_uk

iTrader: (1)

Then what the **** good is it? first is next to useless as it is with the 5 speed! There must be a diff ratio that will make the first 5 gears of the 6 speed the same as the 5 speed and then have 6th as an over overdrive

JasonC SBB

That's only true in the MSM which had the extra short 4.3 rear gear.

Other 6 speeds had the 3.9.

miata2fast

iTrader: (2)

I am not exactly sure why you want to have such a tall gear. You will not enjoy your n/a if you have a really tall gear for cruising, especially If you are going with much of a camshaft. This is coming from my experience with my n/a. The performance gains from having it geared properly will pay off. If it is wrong, a Prius will outrun you.

In an n/a car, first gear is not useless. I would be willing to bet that when you get it running, you will be turning about 1000 rpm or more from stock. Get the car together first, then start driving it. Ask yourself what you plan to do with the car, then make a decision what gear and transmission you will use.

I have a five speed and love it. N/A cars do not make enough power to be concerned about breaking a five speed, which answers your question about what good is a 6 speed. They can tolerate a lot more power and torque.

Rennkafer

iTrader: (3)

The good part is twofold, 6 speeds are stronger (not a big issue with NA cars), and they're closer ratio than a 5 speed (less needed on turbo cars, great for n/a cars). Closer ratios are a good thing on a built n/a which is going to have a narrower power band, you won't find yourself wanting that 3 1/2 gear coming out of corners as often.

Savington

iTrader: (31)

Pretty sure MSMs came with 4.10, just like every 6-speed shipped in 2004/2005.

Joe Perez

iTrader: (8)

I haven't been able to find anything to contradict this. All evidence suggests that the 5 speeds got the 4.30 while the 4 and 6 speeds got the 4.10, regardless of whether there was a turbo or not.

Savington

iTrader: (31)

I thought they had a 4.30 too, but VagaXT has a 4.10 in his '04 MSM and it's the factory ratio. The 2003s might have a 4.10 in them as well, but I am probably wrong there.

Duckie_uk

iTrader: (1)

I know I'm going to have to rev the engine quite hard to make it wake up and be enjoyable but I do make some longer journeys and driving a miata for over 300 miles really starts to fatigue me (yes yes I know I should man a pair and put up with it) I thought that by using the 6 speed I could just use 6th to drop the cruising revs and allow me to use 1 - 5 as per usual. I can see now that this is not the case.

I've been doing some research mainly at Solomiata and they say:

4.1 94-97 Miata and 99+ automatic Miata
4.3 90-93 99 Miata stick
3.636 2001+ Australian 6-speed
3.909 Miata 6-speed, RX-7 automatic, 79-83 RX-7 all

This could all be bullshit but FM now run solomiata so I'd like to think they check it.

So it looks like my car has a 4.1 diff ratio, 2fast reccon this should suffice?

The gear breakdown for the 5 & 6 Speed


5 Speed 1st 3.136 2nd 1.888 3rd 1.330 4th 1.00 5th .814
6 Speed 1st 3.76 2nd 2.269 3rd 1.645 4th 1.2575th 1.00 6th .843

So yes the 6 speed will raise revs, bad for cruising but good for n/a performance and like Rennkafer says a nice close ratio box.

Is the 6 speed much different to use than a 5 speed, my box is feeling quite stiff nowadays not always wanting to slip into gear easily. I hear the 6 speed is quite slick?

Once I start driving the car I think I will have to do a comparison of revs in each gear for the 5 speed with a 4.1 and a 6 speed with a 3.9 to see if that will net me my extra gear if I still want it.

Rennkafer

iTrader: (3)

Ask and ye shall receive...

comparison of 5 and 6 spds with both having 4.1 diffs:


same but the 6 spd with a 3.9 diff:


same but 6 spd diff at 3.636:


Comparison of mph speeds stock rev limit/5 spd vs 6 spd with 8k rev limit (built n/a engine), both 4.1 diffs:


For those who'd like to run their own comparisons... I found this gear comparison calculator here (the above were just screenshots)
Fatboy Raceworks Graphical Transmission Gear Ratio Calculator

miata2fast

iTrader: (2)

Nice work Rennkafer.

I had no idea that the six speed had that low of a first gear.

Duckie_uk

iTrader: (1)

Awsome! Thanks for going the extra mile with the comparisons. So it's looking like the 6 speed with a 3.636 is going to give me a very similar setup to what I have now but with the extra gear that I wanted.

What's really confusing me now is the ratios for 1st 2nd and 3rd. Looking at the quaife gear sets for both the miata and other cars such as my buddy's westfield they have really long 1 2 & 3 why? Certainly for hillclimbs and sprints which is what the Westfield does
I would have thought low gears would be used to keep the engine where the power is. :s

I'm not really sure why I'm even considering a gearbox swap yet, I still need to save up for cams yet!! Another total ******* mystery to me

Rennkafer

iTrader: (3)

Circuit cars rarely have to start from a stop so a taller first gives you a gear you could use for slow corners... a number of the lower powered cars we run from work actually need a push to get started unless the driver really abuses the clutch.

johnmatt

iTrader: (8)

Not wanting to threadjack but since we're on the subject of gears I've been wondering if anyone has ever heard of 3.63s with a 5 speed? Seems like it would be awesome for street driving with a good responsive turbo. Maybe I'm wrong though

y8s

iTrader: (8)

you did threadjack, whether you wanted to or not.

Duckie_uk

iTrader: (1)

Theres a link to the funky trans comparison web site above. Compare dem revs home boi.

johnmatt

iTrader: (8)

I've compared it before I was more curious about real result instead of seeing something on a screen

miata2fast

iTrader: (2)

It may sound like I am kicking a dead horse, but it depends on what you will be doing with the car, and how much power it is making. My lower powered car set up for drag racing would be a total pig with a tall gear. A car with 500 horsepower, a different story.

Duckie_uk

iTrader: (1)

Ok next series of questions. I have pulled the crank now and gone over it with the micrometer. Endfloat and main bearings are perfect at just above mid limit and the surface looks good. The rod jornals have a nice surface on them but are close to bottom limit. The rod shells show the expected polishing at the top and bottom. Can I assume that this is all ok to go ahead with seeing as it's all within haynes manual tolerances?

Also my oil seals seem to have worn slight polished grooves in their "journals" front and back and the haynes manual seems to get a bit enthusiastic over this saying that the crank should be ground and a sleeve pressed on! This seems extreme, I mean it wasn't actually leaking before I tore the motor down. Any opinions? I'm going with "if it ain't broke don't fix it" for now until Im told otherwise.

Tia

etang789

Anymore picture of your porting job?

Duckie_uk

iTrader: (1)

I'll try and grab some more pics when I finish the head off. Its now getting +1mm stainless ferrea valves

Which brings me to my next question. Can someone with a workshop manual for the 99 tell me what the standard valve seat Dimensions and angles are? Damn haynes manual doesn't stipulate just says take it to a machine shop.

And no one have any info on my oil seal grooves mentioned above?