To Turbo or Not To Turbo... That Is The Question.

[5isalive]

Hello all.

Please bare with us for a moment as we're not very knowledgeable with all the inner workings of an MX-5 as neither of us are mechanics nor tech heads. We just drive. So here goes...

We have a 2003 NB that we find is somewhat lacking when it comes to a reasonable size hill or when we need to overtake. My wife and I drive just about everywhere in it, but we find when we go away for a few days or so, we tend to end up with a boot full of gear, like clothes, cameras and a laptop etc.

We had initally wondered if a turbo would be a good idea, but it seems it's a very expensive option to make it become a reality, and we're both on a reasonablly tight budget. So I guess our question is... How do we give the old girl a little bit more pull in the midrange, without costing us an arm and a leg?

We've heard that a set of extractors may give her around 5hp. We were also told that a chip would give us a bit more power? Would any of these options be viable as apposed to turboing etc., or would we be just wasting our time?

We don't need a "beast" or anything like that, and we don't want to sacrifice the reliability of our MX-5. We just want a little more grunt when required.

Any suggestions would be much appreciated, and please, if you could deliver your replies in layman terms, that would be a great help.

Thanks in advance of any replies and for passing on your valuble knowledge in these matters.

Cheers, Wayne & Cath.

[TrackAttack]

The answer is... Diff ratio. You'll have a 3.6 if its stock. Your options are 3.9, 4.1 or 4.3... Personally I would pick the 4.3 simply because its an awesome pair with the 6 speed and SVT engine, but any of the 3 will improve acceleration.

Downside is the rpm when on the highway, but I feel its not an issue.

[Odd]

I have a NA8....but this should work on your NB

I've added a set of extractors + high flow catalytic converter + advanced timing by 4 degrees
Cost less than $1000....however it does require High octane fuel....but
Very Happy with outcome ....ATM

ps....Just did some research...perhaps advancing the timing is not feasible in your car

[Trackphotos]

....Just did some research...perhaps advancing the timing is not feasible in your car

Correct. NB timing can't be changed without an aftermarket ecu.

As trackattack said, diff ratio is the quickest way to get some extra torque to your wheels. The cost is higher rpm at all wheel speeds, so highway cruising will be a bit buzzier. Nobody seems to mind it though. I felt the difference going from 4.1 to 4.3, so a change from 3.6 to 4. 3 would be a significant one. You can find a 4.3 diff ready to install for probably $1100ish, $1250 if you go the easy way and buy from a store rather than private sale. It's not a big job to install for a workshop, so if you're not up to doing it h swap yourself, probably add another couple hundred on for installation, and new seals just to head off any leaks while the diff is out of the car.

Naturally aspirated is always going to be an expensive route, and will not less power overall. Not to say that it's the 'wrong' way to go, just a different path if your priority is not absolute power output. Since your situation seems to be more aimed at ease of use where acceleration is needed, I wouldn't think the cost and potential reliability hit would be worth it.

[toppertee]

The answer is......NC much better option. Motor is a gem.

The car is tons better than a nb

[davekmoore]

Add location to your info. Then we'll know how far you are from NitroDann.

[hks_kansei]

Diff ratio will help, but at the expense of increasing the RPM at any given speed. Think of it as 6th gear becoming like 5th and a half.
If you can live with that it's the easiest option, also quite cost effective

a secondhand replacement diff would be maybe $500 (plus maybe 2 hours max to fit it), just the ring and pinion (the parts that denote the ratio) would be substantially cheaper but at the expense of more labour (rather than a direct swap it involves the diff being disassembled)

If you want to know the RPM change at any speed (presumably 100kph) I can do the calculations and post them here.



Any bolton parts will make minimal gains at best, extractors, intake, etc you're only really looking at a few horses.
"chipping" the ECU is often a lot more expensive than it's worth. the cost can often end up almost as much as a standalone ECU, which is frankly much better in most ways.

Also, lots of chips in Aust are from Powerchip, which is run (or at least used to be) by Wayne Bezanko who is a complete and utter knob end.




If you aren't really interested in doing modifications, it might even be worth considering selling your current MX5 and looking at an SE (factory turbocharged) or even an NC (larger engine)

Unfortunately MX5s are hard to get any useful power gains from without spending time and money on having the ECU done first.

[davekmoore]

Diff ratio will help, but at the expense of increasing the RPM at any given speed. Think of it as 6th gear becoming like 5th and a half.
If you aren't really interested in doing modifications, it might even be worth considering selling your current MX5 and looking at an SE (factory turbocharged) or even an NC (larger engine)
Unfortunately MX5s are hard to get any useful power gains from without spending time and money on having the ECU done first.

If you really like your existing car adding an aftermarket ECU and a small turbo plus inlet and exhaust from NitroDann will give you a much nicer car to drive than an SE.
If you're not in too much of a hurry I might know where you'd find a 2.5" stainless exhaust, an SE exhaust manifold and downpipe, an IHI turbo and an SE ECU. You'd still need bigger injectors and maybe other stuff.

[rascal]

Please bare with us for a moment as we're not very knowledgeable with all the inner workings of an MX-5 as neither of us are mechanics nor tech heads. We just drive. So here goes...

We had initally wondered if a turbo would be a good idea, but it seems it's a very expensive option to make it become a reality, and we're both on a reasonably tight budget.

The above suggests that you wont be doing any of the work yourself, and therefore a drive-in/drive-out turbo conversion is probably outside your reasonably tight budget.
Also not knowing your location, getting it registered with the turbo may also make it cost prohibitive, again given you will be relying on others to perform the necessary steps.

[Odd]

The other Ultimate option is to Supercharge instead of Turbo.....
Some say this is the better solution for MX5's

Also you can start with extractors/up graded exhaust....then add "supercharger" later if/when required/or funds allow

The extractors have to be replaced with a Turbo, but remain with a Supercharger

[Apu]

So from a 2003 NB owner to another who has gone from stock to turbo...here's what I did and what I experienced:

Intake and Exhaust
There was some improvement, minor - didn't make a "noticeable" difference apart from being able to pull up gentle slopes (eg a flyover) in 5th gear without having to drop to 4th. Of course, it sounded great and hearing the crackle and pop of the exhaust made it fun to drive.

Lightened flywheel, 4.1 final drive with LSD
LSD is irrelevant for cruising, but I had it installed at the same time as the 4.1 which made a huge difference with the lightened flywheel. It gave the car a life it didn't have. Revved up easily and was able to sprint from corner to corner. Made using the gearbox so much fun. The downside of going from a 3.63 to 4:1 is that the engine will be running about 300rpm high to get to the same speed...which makes highway cruising noisy. I would not go higher than a 4.1 (so a 4.7 would be ridiculous and you'll be rowing through the gears a lot!).

Don't forget that you'll need to change your speed sensor as well or speedo readings will be way out. I think a 3.9 would be a good compromise. In some ways, I do miss driving the car in this setup - it made it fun to rev the car, crackling exhaust and all.

Turbo
I won't go into too much detail here since you are on a budget. The short of it is, I got sick of being held up by slower cars on the track and not being able to pass on the straights. Turbos can be affordable but you don't want to "cheap-out" on the conversion. You will need a couple of retunes if you want the car to drive like standard.

If you want "just a little more power" then buy a kit from an SE owner who has upgraded. You'll still need an ECU.

Happy to elaborate more on turbo if you wish, but I am very happy with my set up now. I wouldn't recommend it if you are on a budget (of course, it also depends on the definition of "budget").

[5isalive]

Hey thanks for the replies so far guys. Your suggestions are helping us a lot with weighing up some of the alternatives. I must say the gear ratio change does sound like a much cheaper way to get our desired result.

I'm thinking that going for 3:9 or perhaps 4:1 may be a happier medium instead of going the whole hog with 4:3 as "Apu" has suggested? I'm a little concerned that 4:3 may be just a bit too low, what do you all think? I do realize there are always going to be trade offs, but I really like to cruise at around 110kph to 120kph whenever I can, with the occasional 140kph not being out of the question either at times.

So would these lower ratios have the old girl screaming her head off at those speeds? And yes, I am aware that these speeds are frowned upon by the boys in blue.

It's funny you know. I've ridden motorbikes all my life, and I've changed sprocket combinations at various times for many different applications, but I've never once considered changing the diff ratios in our car. It seems so obvious now that the seed has been planted. Now I feel like a bit of a dufus, that I hadn't thought about it sooner.

In reply to some of your comments... Regarding "Davekmoore's" question: We live in Kempsey, on the Mid North Coast of N.S.W.

Also, "hks_kansei" had suggested that we sell our and get an SE. We had discussed this, but were a little hesitant not only that our current MX-5 has only 60,000kms on it, but all the SE's we'd seen advertized so far, have well over 100,000 kms on the clock, which feels like we'd be taking a big step backwards.

In addition to that, even if we could get $12,000 for ours, it would still end up costing us roughly an extra $4,000 to $5,000+ to get ourselves into one. We just don't have that kind of money at the moment. And yes, if you could do those calculations for us, that would be a great help thanks. Perhaps 3:9 and 4:1, would be where we're likely to go.

Also, does anyone here know if they're readily available, and where the best place we could get one from would be please? My son has a mate who is a mechanic and would be able to do the work for us for a fair price.

Anyhow, thank you all for your considered and welcome responses. Please keep them coming if you will. They all go a long way in helping us to finally making a desicion as to which route we should go, but like I said earlier, I definitely think the diff ratio option might be the best way for us to go this point in time.

Cheers, Wayne & Cath.

[hks_kansei]

At 100kph my calculations come up with the following RPM in 6th gear.


3.6:1 = 2795rpm
3.9:1 = 3028rpm
4.1:1 = 3183rpm
4.7:1 = 3649rpm
4.9:1 = 3805rpm

Wheel and tyre sizing does have an effect here, but for these purposes I'm assuming a 15inch wheel with a 195/50 tyre fitted. (what my car has)
Generally though any wheel and tyre difference will be within only a few percent of my figures (unless you have some abnormally large or small wheels fitted)

[Apu]

As an indicator - on a 3.63, 100km/h is about 3200-3300rpm? 4.1 got me to about 3600rpm at about 100km/h...and it did get annoying on highway speeds when I used to drive to Goulburn - my passenger and I had to speak "very loudly"!

I would expect a 3.9 to be in between that.

At 60,000kms you are still a way off a clutch change so it may not make sense to go for a lightened flywheel yet, but that is also something I would recommend. I did go for a fairly light one, but I'd suggest getting a used flywheel and having (perhaps) a kilo taken off just to get that little more sprite off the engine.

Living in Kempsey, you'd have some great roads to cruise around!


Edit: Look at hks' calculations - they'll be a lot more correct than my memory!

[kalt]

We don't need a "beast" or anything like that, and we don't want to sacrifice the reliability of our MX-5. We just want a little more grunt when required.


Cheers, Wayne & Cath.

If you want only a little more grunt when required, go nitrous kit?

http://www.turbomx5.com/nitro1.htm