mx-5 donor 1.8 or 1.6??
 

Hello all newbie here.

Looking to use a mazda as a donor but can't decide if the 1.6 engine has a good weight saving over the 1.8 which only has a 15bhp advantage. Obiously it will have more torque through out the rev range but.....

Any ideas anyone? Anyone know the weight advantage?

Personally speaking I went for the 1.6 vspec as you just don't need the torque IMHO but I am sure others will have differing opinions.

Matt

Yeah I think your right seems there's really not much between these engines 10lbft and 10bhp isn't going to make much difference? Is there a weight advantage though? I suppose the reciprical rotational weight will make a difference (lighterflywheel and crank etc). What's the vspec sorry?

V-spec stands for v-special. Basically the same car but with uprated suspension and LSD. The interior is also different (tan leather with high back seats) and they generally came in BRG but a few were sold in a high gloss black.

I found this engine comparison:

1.6 or 1.8?
I probably get asked about this more than any other aspect of an MX5 purchase. Lets look at the facts: when new, the 1.6 was good for 114bhp while the 1.8 produced 130bhp, an increase of 15% and had around 10% more torque produced lower down the rev range. However the 1.8 is a little heavier (50-70kg depending on exact model) so performance is not so different – an extra couple of mph on top speed and a couple of tenths of a second quicker to 60mph. Remember all these figures apply to nice shiny new cars: time and useage will have played a big part in how they drive now. In reality, a 1.8 has a little more low down power and seems to cope with motorway cruising a little more easily than a 1.6 but I reckon most people wouldn’t notice the difference. The 1.6 is a sweeter revving engine and a few well chosen modifications will significantly boost bhp and driving fun. In fact the 1.6 cars are the default choice for enthusiasts wishing to undertake serious tuning – fitting either super or turbochargers for example.
The real world answer is forget the engine and just concentrate on finding the nicest car you can. The exception to this is the late model UK 1.6 introduced in 1995: this was detuned to around 88bhp and is noticeably slower than the early 1.6 cars.

my mx5 i used for the exocet is a 1.8 it had a fair bit more poke than the 1600's i test drove

Good bit of info that! LSD! 50kg! I'm sold thank you so much. Do you have plans for your chassis? how does your design vary from what Saturn are putting together?

My build has taken a little longer to do as I started mine last March so I have had to start from scratch. Generally they will be very similar. My rears are adjustable and the shock mounts low, also my diff sits much lower (25mm by eye) but apart from that I can't see a massive difference in the designs although I think comparing the geometry would show some differences.

I will be starting production of the wishbones in conjunction with some local companies soon as well as part built chassis kits and donor packages but I will be concentrating exclusively on the MX5 as it is what I know and love.

I recently acquired the most exciting bit for my build, a shiney new turbo! A little bit outside my comfort zone but the beauty of living in Cornwall is that there are plenty of retired enthusiasts with a lifetime of knowledge and time to help :)

I will go with that, Cornwall is a cracking place to live...:cool:
I like that beach near St Keverne called a "car park"!! you could actually just keep going and drive straight into the sea...:eek:

That'll be Porthallow and/or Porthoustock then. Apparently it is a regular spectator event watching the poor fools who have got too close waiting to see if the tractor driver is going to reach them before the incoming tide!

(oops thread hijack - sorry :o )

Matt

I see, once I have my donor and commited myself as it were I will need to get some steel, can't decide if I want to go precut or cut the steel as I need it. Can't see myself making the wishbones though. Yep a turbo is on my my future list but may just have a play with a bit of NOS just for fun and the quarter mile. What other mechanical parts do you need other than the mazda donor? Do you still need to use an escort rack?

It is perfectly feasable to cut the steel for the chassis yourself, the old adage "measure twice cut once" was written by someone building a Locost.

Personally I used an Escort rack as it fits the front frame perfectly avoiding issues with bump-steer, the Mazda unit is too wide so needs a section cut out of the actual cylinder which is just too big a risk IMHO.

I was originally going to use the MX5 pedal box but am having second thoughts due to the available space so will most likely go with the book offering.

The other main things I can think of are that you can't get off the donor are the shocks.

M

Ahh thanks Airhead, think I'll buy enough steel to make the bottom frame and see how I get on. If I fail I'll buy precut stuff, money, or the lack of it is my main motivation!:)

I've had a 1.8 for a couple of years now, and just bought a 1.6 for my donor.
There's not a lot in it, but the 1.8 does feel a tad quicker.
Either should be a whole lot of fun in the roadster though :D
If you do go 1.6 I'd avoid the early shortnose crank engine (up to about 1991).
The 1.8 diffs might be heavier, but they're also a lot tougher. The 1.6 diffs are a bit weak and break if abused - particularly if turbo'd.
You can retrofit the 1.8 diff onto the 1.6, but they go for silly money, and you have to change the driveshafts and propshaft whilst you're at it.

Thanks for your input. What's the issue with the shortnose type is it the crank pulley damaging the keyway as I have an good easy fix for that sort of thing I've done in the past. Good info about the diff does this still apply to a 1.6 v-spec lsd?

I think there's a couple of failure modes - the keyway getting damaged, and the threads in the end of crankshaft failing. The usual fix is an engine swap!

I'm pretty sure the 1.6 LSDs were all viscous, and the 1.8 LSDs were torsen.

In terms of bhp difference between the 1.6 and 1.8 this is what I have found during my research (hopefully correct)

UK Cars Only
Mk1 1.6 - 89 to 94 = 114bhp.
Mk1 1.6 - 95 to 98 = 88bhp.
Mk2 1.6 - 98 on = 108bhp.

Imports
Japan never used the 88bhp engine so all imported Mk1 1.6 are 114bhp.

I thought the 88bhp engine was from 1996 on or at least sept 1995. I've just bought a may-95 car!! :mad: I do hope you're wrong!

From Wiki

The new 1.8 L (110 cu in) engine produced 98 kW (131 bhp), which was then increased to 99 kW (133 bhp) for the 1996 model year. The base weight increased to 990 kg (2,200 lb). Performance was improved slightly, the additional power being partly offset by the extra weight. In some markets such as Europe, the 1.6 L (98 cu in) engine continued to be available as a lower-cost option, but was detuned to 66 kW (89 bhp). This lower-powered model did not receive all the additional chassis bracing of the new 1.8 L (110 cu in). Japanese and US cars were fitted with an optional Torsen LSD, which was far more durable than the previous viscous differential.

Just found this.......

Taken from the Mazda Workshop manual (12/94)

Engine
The purpose of the modification is to increase the low speed torque by changing the valve timing and compression ratio.
The following parts have been modified

The configuration of the camshafts have been modified
Valve timing
IVO 5* BTDC
IVC 40* ABDC
EVO 55* BBDC
EVC 5* ATDC

The configuration of the pistons have been modified
Compression Ratio - 9.0:1

Fuel & Emission Control System
According to the readoptaion of the B6 engine model, the following changes have been made.

Injection method has been changed from the two-group injection to the sequential injection.
IAC load correction has been added according to the addition of the rear window defroster signal input to the ECM.
IGF signal input to the ECM has been discontinued.
Signal names have been changed as follows. NE = SGT & G = SGC
Diagnostic trouble codes No. 01 have been discontinued.
Vehicle speed sensor input have been added.
In the exhaust system, the front pipe and the parts after it are the same as that of the BP engine model.
The heated oxygen sensor has been adopted and its instulation position has been changed.
The fuel tank capacity has been enlarged and the cruising range has been increased accordingly.
Features - Excellent drivability and improved engine performance due to Squential mulitport fuel injection

Have asked seller of car to email me the VIN number

The car will not be an import. It will be a UK registered car from between 1995-1997.


VIN number will be JMZNA18C200 something, something, something, something, something, something.

(The letter C tells you it's a low power 1600, B for high power 1600, P for 1800 or 6 for NB 1600)

The table above was taken from the Technical Specifications section from Wiki so looks like there is conflicting info on the same Wiki page :confused:
http://en.wikipedia.org/wiki/Mazda_MX-5

Actually I think I've bought the 90bhp version but on inspection is a good base for my build, local, has 9:1 CR, and overall looks a straight deal. Picking it up tomorrow.:)

I wouldn't read too much into the bhp figures the Japanese quote, they have been fibbing for years on bike horsepower so wouldn't expect the car folk to be any different.:rolleyes:

Yes I've read that they marketed it as lower power for budget drivers/buyers to get cheaper insurance in the uk. They've simply altered the cam timing to move the torque lower down the rev range and added sequential injection to reduce emissions and improve performance. Not sure why they dropped the CR to 9:1 but this is only a bonus to me as I intend to turbo eventually. Engines are rumoured to not have oil squirters but the 95' on 1.6 auto's bottom end does apparently and is a straight swap. If I melt a piston I'll replace the bottom end. :) These engines certainly have a nice sound to them, bonus! :)

My wifes 1990 V-Spec has 230k (km) on the clock and is still sweet as a nut. IMHO they are lovely bomb proof little motors.

Yes my friend who works at a mazda dealer has said they are solid engines, he's never had to strip an early mx5 engine yet!:)

OK I have my donor! It's a 1995 1.6 but it has the earlier B6 engine so afaik it's the earlier 115bhp version. Managed to pop the main fuse due to a dodgy headlight motor connection. So it begins!:D

Nice one!
Welcome to the MX5 donor club :cool:

sounds great, well done finding a good donor, :cool:

Enjoy the strip down, watch those knuckles :eek: :D

all the best for your build, look forward to seeing some build progress pics:)

cheers
andy

Thanks people, I'll be relying on you guys alot for info advice and ideas. Looking forward to having a go at those drawing from SaturnSportsCars.com. :D

First question....

Do you purge the tubes to get a good weld or is that not necessary? I've got argon/co2 mix bottles.

I'll get a build thread going soonish.:)

Bit more info on the weight of a 1.6 to a 1.8.

Taken from here...

http://westfield.devocht.com/