mx5cartalk.com

Hi there, I'm looking for some advice.

I'm not sure if I've come to the right place on this forum and what I'm about to ask is very broad. First I'll do a little explaining about what I'm currently running.
I have a 1990 Na6 Mx5 with a 2.25" exhaust complete with Apexi 4-1 extractors (mild steel, uncoated). It's pretty much straight through as far as I know and there is no resonator (desperately need one to eliminate horrible rasp) and I have the stock cat. I've also put on a pretty DIY pod filter system which is pretty much just bolted straight onto the flow meter facing the passenger seat. I'm currently looking for either a 180 degree pipe so I can face it toward the passenger side headlamp and hopefully draw cold air from the gap between the light cover and bonnet; Or making my own cowl intake from an accumulation of bits and pieces from Bunnings. I've noticed there has been top end gain since I've put this together, especially since I was running a cracked stock manifold before and a rusted muffler.
However I can't say I'm too impressed with the initial pickup. Off the line it's pretty average, I know as an mx5 I shouldn't be expecting to keep up with a Skyline/Sylvia or anything, but I feel a little gutless from a standstill. It's only when I get to about 4500rpm that it really starts to bark and I can feel the improvement significantly. I know the stock cat is restricting the current exhaust system so I'm looking at putting in a 200mesh steel cat and 15" resonator to free it up and smooth out the rasp.
I'm disappointed in my current throttle response so what would be an affordable solution to increase the acceleration and initial pickup off the line? Affordable is a little subjective so I'll be blunt, I don't want to spend thousands. So I guess my 'student budget' would set me at a grand cap. Oh and while I'm here I also have another problem, when I hit the throttle, there is a flat spot I've found. It's like a second delay after the pedal goes down the car responding. Tightened the cables and still has the problem, tension is as far as i'm willing to put it without upping the idle.
Would Dyno tuning potentially solve both issues here?

Oh and this is a unrelated but it's been racking my mind. Lately I've noticed a groan when turning the wheels at low speeds (ie- parking). It sounds like a typical power steering issue but I don't have power steering so I'm not sure what it could be and potential costs. I have a mechanic (my brother) but I won't be seeing him any time soon as he's interstate on a new contract.

As I stated initially, I know I haven't given you much in terms of details but I'm late for work and this is all I can think of right now. Please don't hesitate to request any other information and I'll be sure to add it in!

First simple change for a bit more grunt would be to set the timing to 14 degrees.

Have you changed plugs and leads? If not, they could be part of your flat spot problem... Faulty coil(s) could also be the problem, there are quite a few possibilities. Faulty O2 sensors can also cause a flat spot around 3000 rpm. Fuel system should also be checked - injectors, filter.

A dyno session would help diagnose exactly what the cause of the flat spot is, but the cause could be any number of things.

With regards to the power steering put some Lucas powersteering additive in,trust me works a treat,available at any decent spare parts shop
WASP

WASP wrote:With regards to the power steering put some Lucas powersteering additive in,trust me works a treat,available at any decent spare parts shop
WASP

Thanks for the advice and I'm sure it would help if I actually HAD powersteering haha. I don't have power steering at all in my na. It feels like a similar feeling to a power steering problem.

My car develped a bit of a flat spot when the short nose crank started to go... Not terrible but noticable. Could be worth having a look at.

As said bumping the timing to 14 degrees will help. My car seems most reponsive with either bp or mobil 98 octane fuel in it (they're both the same fuel in Melbourne ) and I find it also helps to occasionally run injector cleaner through it. Also putting some good synthetic oil (I use Elf 5w40) in it seemed to free the motor up a little too.

I know that the firewall intakes do improve throttle response, i'm not a fan of drilling a hole in the firewall so I just modified my air box though its not as effective. That and I find that if you squeeze the power on its delivery is better, if you just floor it at lowish revs it'll get to much fuel (they run very rich) and flat spot.

Your 4 into 1 extractors won't be helping matters either - better suited to top end power. 4 into 2 into 1 will give you better driveability down low and in the mid range.

Your 2.25inch exhaust may be a fraction too big as well. 2inch would be heaps on 1.6 in my opinion.

Then there's the pod filter sitting exposed on the hot side of the engine... You're better off picking up your cold air feed from the high pressure area just below the windscreen, but as bensale suggests, I believe that would involve cutting a bit of the tin work.

I don't know if you are running standard size wheels and tyres, but if you go back to 14's, this may help with the ability to jump away from the lights.

Another way to improve low down acceleration is to lower your diff ratio down to say 4:1.
You can buy the pinions and crown wheels from wreckers (they were used in some Mazda trucks).
It certainly won't help your fuel comsumprion, but the acceleration will definitely improve.

A good tune up by someone that knows MX-5's could also release more power for you.

Sounds to me like you want to turbo the car eventually, as this (and supercharging) are by far the best bang for your buck.

Benny wrote:Another way to improve low down acceleration is to lower your diff ratio down to say 4:1.

He should already have a 4.3 diff as it is a NA6

Atmo wrote:Your 4 into 1 extractors won't be helping matters either - better suited to top end power. 4 into 2 into 1 will give you better driveability down low and in the mid range.

Your 2.25inch exhaust may be a fraction too big as well. 2inch would be heaps on 1.6 in my opinion.

Then there's the pod filter sitting exposed on the hot side of the engine... You're better off picking up your cold air feed from the high pressure area just below the windscreen, but as bensale suggests, I believe that would involve cutting a bit of the tin work.

Precisely my thoughts. The 4 to one and 2.25 tend to maximise at the top end.

As far as the changes to the exhaust you propose .... just be aware that the positioning of the cat, hotdogs etc willaffect the flows and the back pressure.

PM me if you want to try a 180 degree 3" stainless steel mandrel bent pipe for the NA

What you need is torque for getting off the line. 14 degree bump helps, so does a 4/2/1 and a 4.3 diff and original wheels.

I can see that this is the beginning of a long journey ... make sure you document all the changes so that you have a history of what works and what don't.

Good luck

Rob

Benny wrote:I don't know if you are running standard size wheels and tyres, but if you go back to 14's, this may help with the ability to jump away from the lights.

Another way to improve low down acceleration is to lower your diff ratio down to say 4:1.
You can buy the pinions and crown wheels from wreckers (they were used in some Mazda trucks).
It certainly won't help your fuel comsumprion, but the acceleration will definitely improve.

A good tune up by someone that knows MX-5's could also release more power for you.

Sounds to me like you want to turbo the car eventually, as this (and supercharging) are by far the best bang for your buck.

Just realised i didnt hit submit, so 2 other replies have beaten me to this! Anyhow, heres my 2c worth.

Doesnt the NA6 have a 4.3 diff ratio, so going to 4.1 would actually increase the gearing?

Atmo might be on the money there - from what ive heard 4 into 1 headers may decrease low down torque. Different headers and the bumping the timing to 14 should help.

Before i had my NA6 i had a stock 200SX, and found that low down (say below 3500rpm), the MX5 equalled or bettered the Nissan for torque and drivability. Once the turbo kicks in its a different matter though...

My bad.

I thought it had a taller diff.

Still, a shorter diff ratio would get you off the line quicker.
Otherwise, use a few more revs when taking off rather than trying to take off from idle.

At the track a good launch in a stock car is a quick lift off the clutch (not a dump though) at about 4500rpm, it will spin for about 10 metres and then hook up and you can just about immediately change to second. Add 1000 rpm if you have an LSD. Off the line you will really get the jump on a lot of faster cars with practice launching and an lsd ($500 bucks to buy one) and on the street a quick 1st gear traffic light dash you will embarrass a lot of fast cars.

It should already have a 4.3

Dann

All good advice. As they said, do the basics first:
- Fresh spark plugs and leads. Borrow a known good coilpack to see if it makes a difference
- Clean air filter
- 14 deg timing bump adds a bit at the bottom end
- Get your injectors tested and cleaned. Replace the fuel filter at the same time.
- Check the cat for blockages and make sure it's reasonably matched to the rest of the system
- Mobil or Caltex 98 as the track choice in Vic, then BP Ultimate as a good cleansing day to day fuel. Sometimes our cars go like cold porridge on Vic Shell
- Don't use heavy oil. 5W30 or 0W40 work fine
- Use the lightest wheel/tyre combo you can

manga_blue wrote:All good advice. As they said, do the basics first:
- Fresh spark plugs and leads. Borrow a known good coilpack to see if it makes a difference
- Clean air filter
- 14 deg timing bump adds a bit at the bottom end
- Get your injectors tested and cleaned. Replace the fuel filter at the same time.
- Check the cat for blockages and make sure it's reasonably matched to the rest of the system
- Mobil or Caltex 98 as the track choice in Vic, then BP Ultimate as a good cleansing day to day fuel. Sometimes our cars go like cold porridge on Vic Shell
- Don't use heavy oil. 5W30 or 0W40 work fine
- Use the lightest wheel/tyre combo you can

^ This.

Matty wrote:

manga_blue wrote:All good advice. As they said, do the basics first:
- Fresh spark plugs and leads. Borrow a known good coilpack to see if it makes a difference
- Clean air filter
- 14 deg timing bump adds a bit at the bottom end
- Get your injectors tested and cleaned. Replace the fuel filter at the same time.
- Check the cat for blockages and make sure it's reasonably matched to the rest of the system
- Mobil or Caltex 98 as the track choice in Vic, then BP Ultimate as a good cleansing day to day fuel. Sometimes our cars go like cold porridge on Vic Shell
- Don't use heavy oil. 5W30 or 0W40 work fine
- Use the lightest wheel/tyre combo you can

^ This.

Hey thanks for all the advice so far guys. Should be putting new plugs and leads in on Sunday/Wednesday (depending on when I have time), air filter is currently clean but it's sucking too much hot air in it's current location so I will be making a cowl out of it when I gather the materials>
Timing will be changed later this week after it's run on the computer. Injectors will be checked and fuel filter replaced same day.
I'm not sure about the cat having blockages... That's a grey area because I have a feeling the guy actually knocked the guts out of my cat and it's just a hollow pipe now, which is half the reason I have that god awful noise.
Oi is Penrite HPR 40 (I think), with Ryco filter.
Petrol has recently changed to BP Ultimate and I'm running RS Watanabe 14x6.5 F8 wheels with 185x60,14 Yokohama C-Drive tyres.

I'll give an update later this week when the car has been run on the computer and timing changed etc...

I've been thinking about what I want out of all this long term and the performance I want end game. After talking through with my brother (my mechanic and consultant haha) I'm thinking of maybe going the turbo route and collecting parts etc. I'm in no hurry and not looking for immediate results, so when it's done it's done. This is going to be a long process so I might have to make a build thread!

Any more advice is welcomed!!!!!!!!!!