Detuned 1.6....Tune up?

[5_low]

I've read a lot about mk1s in the european (including Uk obv) market having been detuned to 90 bhp after 1995. I have a 96, and while it feels rapid, I cant help but wonder if its a detuned one.

In theory it should be, unless someone has already tuned it up (Im the 6th owner).

At the moment im running mostly stock, other than the cat back exhaust which is stainless. Eventually i'll get it on the dyno and find out how many horses it has.

Does anybody know what characteristics a detuned Uk 1.6 would have, and if it's possible to tune it up to the 115-120 bhp that pre 95 cars have without spending a fortune??

Thanks

[IllNotSick]

Check your ignition timing and see what you come up with? A lot of the time oem's will use ignition timing to de-tune.

[Racinggreen]

the differences between the 115hp and the 90hp versions are:

-different cams, the 90hp has more torque in the midrange, but looses on top.
building the 115hp cams into your engine will give you ~105HP

-lower compression, the 115hp has 9.5:1, the 90hp has 9:1. You could fit the 115hp pistons oder even higher compression pistons to gain the rest of the hp. Or you shave your head by 0.5mm, this will give you also 0.5 points of compression.

-longer rearend, the 115hp has a 4.3, the 90hp a 4.1 rearend. with the shorter rearend, the car becomes more agile.

Ask the User El Krischano, he has done the full programm on his 90hp (pistons, hot cams, headwork,irtbs, sixspeed and 4.3 rearend) ... think he's about 120-130 rwhp now

Charakteristics:
The 90hp: a good feeling in the midrange, but not so cool in the high rpm
the 115hp: the higher the rpm, the higher the fun

[5_low]

Thanks...both useful references, i'll be looking into those soon I think.

Will changing the cams cause any trouble with my valves/ecu or anything like that?

And how easy is a piston change?

Cheers

[KeasbeyNights]

Originally Posted by 5_low

And how easy is a piston change?

You'll have to tear down the motor, take rods and pistons to someone to have the new pistons installed on rods, then rebuild the motor.

[lebowski]

I wonder if the difference in cams is timing only, and lift and duration are similar or even the same. If so, an easier and cheaper fix for the cams would be to install adjustable cam sprockets and tune to the earlier specs.

[Greg G]

Another difference is that the injectors fire sequentially. And the ECU pinouts are slightly different, so the usual 'plug &play' ECU options don't work without wiring changes.

[5_low]

Thanks guy's this is all great input......

after a bit of digging around i've found somewhere to get used camshafts from for £40 each.

Are used cams ok as long as I know what year and model mx5 theyre from and the lobes are within service limits?

Is this the kind of tune up I would have to do all at once or could I change out parts, remap ecu etc gradually?

[drifter2be]

Originally Posted by Racinggreen

-lower compression, the 115hp has 9.5:1, the 90hp has 9:1. You could fit the 115hp pistons oder even higher compression pistons to gain the rest of the hp. Or you shave your head by 0.5mm, this will give you also 0.5 points of compression.

Are you f@cking retarded? Did you really just suggest someone shave half a millimeter off their cylinder head? Please do the world a damned favor and never touch anything under the hood for the rest of your life.

Yes, you can achieve higher compression by milling the cylinder head. But there is a lot of math that goes into that. You need to figure out your cylinder cc's and cylinder head cc's. Then figure out how much volume you will lose in the cylinder head off of milling it down a few thousandths of an inch. (not millimeters, only an idiot would take off more than .010" from a cylinder head) I must say i was fairly amused at the fact that you think taking off .5mm from the head would at .5 to the compression ratio.

Next time take a little bit of time to understand what you are talking about before giving out bad advice and making yourself look uneducated.

[Racinggreen]

Originally Posted by drifter2be

Are you f@cking retarded? Did you really just suggest someone shave half a millimeter off their cylinder head? Please do the world a damned favor and never touch anything under the hood for the rest of your life.

Yes, you can achieve higher compression by milling the cylinder head. But there is a lot of math that goes into that. You need to figure out your cylinder cc's and cylinder head cc's. Then figure out how much volume you will lose in the cylinder head off of milling it down a few thousandths of an inch. (not millimeters, only an idiot would take off more than .010" from a cylinder head) I must say i was fairly amused at the fact that you think taking off .5mm from the head would at .5 to the compression ratio.

Next time take a little bit of time to understand what you are talking about before giving out bad advice and making yourself look uneducated.

Oh Boy...

Well the MAX you can take off a miata head are 0.7mm, thats what El Krischano (a pal of mine and also User here, did). I chosed to go a little lower to be able to take off the head one more time somewhere in the future and to be able to grind it even one more time.

0,5mm are by the way 0,019 inch, just in case that you're too dumb to work with the metric system.

The workshop manual says max is 0,008inch, but thats a quite conservative number, reasons are maybe the available crappy fuel in the US or the reason that if you go beyond that number, you'll likely have no longer a noninterference engine. but as I chosed hot cams with higher lift, this won't be the case anyway.

And if you don't believe me, maybe you should take a look at www.solomiata.com, section cheap hp, point 6: And what numbers do we see there for the 1.6l? right, 0,02 inch...

We did the math on our German board, each 0,1mm (sorry: each 0,004 inch) will give you roughly .1 in compression
And to prove that again: from solomiata.com:
"shaving the head .010" will increase the compression ratio about a 1/4 point"

You do the math...

and to quote you:

Next time take a little bit of time to understand what you are talking about before giving out bad advice and making yourself look uneducated.

[rizk]

Seeing as you're in the UK just sell it and get a 1.8.
Getting those few horsies back will cost you a lot more.
Also you are asking in the completely wrong place really, Americans have never even seen a detuned 1.6 get on mx5nutz

[5_low]

Lol selling and getting a 1.8 isn't an option for me, not only because I love my 5, but also for insurance....im 21, and my insurance would be obscene!

Obviously, if id known about the detuning, I would have bought an older one, so my mission now is to get it as close to the stock setup for the earlier 1.6 as possible, if not a little better.