Mk1a / MK1b engine differences

[James_Ward]

Well it's a day of contrasts. Firstly my 3 year restoration oddessy is over and (bar a few little stripes and rubbing strips to reglue) the car is complete! And it flew through its MOT as well!

Check my garage for updated pics.

However the noise in the engine that I thought was a cambelt too tight now looks to be something terminal in the head that coupled with the chewed up woodruff key on the crank really points me to the direction of a new motor

My question is - is the later MK1b motor a straight swap into the MK1a or do I need to get a MK1a lump to make it work properly?

Also, does anyone have a MK1a enigne for sale in the SW?

[HarveySS]

There are a few differences between the engine but nothing that will stop you fitting a Mk1b engine to your mk1a. Diff were Mk1b had a stronger block, had bigger conrods, and bigger crankshaft-rods connection (brain fade cant remember name now). ECU was supposedly diff mapping but they will work fine on a Mk1b so yeah chuck in a mk1b by all means

[The TVIS Kid]

I've got a mk1a with a later mk1 b engine in and have never had any troubles with the car . I'm not too sure if i have a later 1b ECU as the swap was done prior to my ownership but it the tvis seems to open around the same time as my old mk1b which would make me think they did swap the ECU too as it should open alittle earlier on 1a's. Also i don't seem to have an idle up control like my old mk1. The revs are also just under 1K rpm whether you put your foot on the brake or turn the lights on etc. I don't know if this has anything to do with the swap.

[Jim-SR]

get hold of a complete engine with everything attached to it (loom, ECU, manifolds, etc) and replace the whole lot, and then you can at least be sure it will work as intended. the ECU's are definitely different (appearance, and part numbers too iirc) and there are a few small variations, but as a standard engine it makes no odds either way really

[firstmk1]

Given the option I'd to fit a mk1b block and head but refit your existing manifold and (all) sensors/ECU/loom.

The loom has a different connector type on the later model.

The clutch is larger in the mk1b but you could fit the mk1a flywheel if need be.

If you try to fit a mk1b loom to your mk1a just be aware that it passes through the firewall on the other side of the car.

(I'm currently running a mk1a engine in my mk1b)

[System-G]

I fitted a 1b engine to my 1a. I wanted the higher flowing injectors in the 1b and I wanted them delivering fuel more agressively using the 1a ECU So just chopped the connectors off the 1a loom and soldered the 1b connectors in place.

We also retained the original inlet manifold as there are some differences in air control sensors and obviously the wiring loom. In fact we landed up using most of the original bolt-on ancillaries as the donor engine's items were in worse condition.

I have been running this engine/setup for nearly two years now. It mostly gets used on track and spends most of it at 7.5k rpm with no major issues.

There is more info on the differences at the top of the page (sticky section)
http://www.imoc.co.uk/forums/viewtopic.php?t=45035

My swap story: http://www.imoc.co.uk/forums/viewtopic.php?t=11218
Forgive terminology in the story, I was very green to this mechanicing at the time Much has been learned since

[SuperRedMR2]

you have to be weary of different sensor on the chassis when swapping engines. Although I found this when swapping from an A to a B

[James_Ward]

Given the option I'd to fit a mk1b block and head but refit your existing manifold and (all) sensors/ECU/loom.

That was my plan, just to replace the basic engine but refit all the ancilliary parts from the duff mk1a motor.

Has anyone done this?

Cheers for the replies guys!

[ligertigon]

yes, I have done it. mk1b engine mated to mk1a ancillaries including gearbox. Works fine

[System-G]

Has anyone done this?

Ansered above

I fitted a 1b engine to my 1a. I wanted the higher flowing injectors in the 1b and I wanted them delivering fuel more agressively using the 1a ECU So just chopped the connectors off the 1a loom and soldered the 1b connectors in place.

We also retained the original inlet manifold as there are some differences in air control sensors and obviously the wiring loom. In fact we landed up using most of the original bolt-on ancillaries as the donor engine's items were in worse condition.

I have been running this engine/setup for nearly two years now. It mostly gets used on track and spends most of it at 7.5k rpm with no major issues.

There is more info on the differences at the top of the page (sticky section)
http://www.imoc.co.uk/forums/viewtopic.php?t=45035

My swap story: http://www.imoc.co.uk/forums/viewtopic.php?t=11218
Forgive terminology in the story, I was very green to this mechanicing at the time Much has been learned since

[crazylegs]

gearbox will be fine with either engine. i`d go for the mk1a loom inlet and injectors. no snipping wires ,everything fits in place. the injectors flow plenty of fuel to cope with any fuel demands the engine needs so no worries there. if you are going to all this trouble in my book its worth a new clutch at the same time. remember the mk1b has a bigger clutch.the standard aftermarket clutch from you local motor factor is fine.
why not bung a lightweight flywheel in whilst you are at it ?
dont forget to do the cambelt. it will cost you £15-20 and only take 10 mins. so much easier with the engine out. then you need not worry for another 60k miles.

[James_Ward]

gearbox will be fine with either engine. i`d go for the mk1a loom inlet and injectors. no snipping wires ,everything fits in place. the injectors flow plenty of fuel to cope with any fuel demands the engine needs so no worries there. if you are going to all this trouble in my book its worth a new clutch at the same time. remember the mk1b has a bigger clutch.the standard aftermarket clutch from you local motor factor is fine.
why not bung a lightweight flywheel in whilst you are at it ?
dont forget to do the cambelt. it will cost you £15-20 and only take 10 mins. so much easier with the engine out. then you need not worry for another 60k miles.

I've already done all this to the engine I swapped in - including a water pump which I believe I bought off've your good self! The motor was always a bit of a long shot because I got it out of a car I got given for free! Oh well at least the swap should go well because I've had a practice run

The clutch sounds like a plan, it was the only thing I didn't bother with last time - so I can use the larger MK1b clutch ok on the MK1a flywheel or do I need a 'b flywheel? and this fits ok in the 'a gearbox with the 'a starter?

To be honest Fensport are out of shiny low mileage motors so I might buy a complete car that's rusted out and then I can cherry pick the bits and try and recoup some money by selling spares.

Does a lightened flywheel make much difference? Bearing in mind there is nothing else modified on the engine (apart from the slowly reducing back pressure of the exhaust, due to corrosion ) How much am I looking at for a lightened flywheel?

Thanks for all your comments guys I really appreciate it.

[cartledge_uk]

gearbox will be fine with either engine. i`d go for the mk1a loom inlet and injectors. no snipping wires ,everything fits in place. the injectors flow plenty of fuel to cope with any fuel demands the engine needs so no worries there. if you are going to all this trouble in my book its worth a new clutch at the same time. remember the mk1b has a bigger clutch.the standard aftermarket clutch from you local motor factor is fine.
why not bung a lightweight flywheel in whilst you are at it ?
dont forget to do the cambelt. it will cost you £15-20 and only take 10 mins. so much easier with the engine out. then you need not worry for another 60k miles.

I've already done all this to the engine I swapped in - including a water pump which I believe I bought off've your good self! The motor was always a bit of a long shot because I got it out of a car I got given for free! Oh well at least the swap should go well because I've had a practice run

The clutch sounds like a plan, it was the only thing I didn't bother with last time - so I can use the larger MK1b clutch ok on the MK1a flywheel or do I need a 'b flywheel? and this fits ok in the 'a gearbox with the 'a starter?

To be honest Fensport are out of shiny low mileage motors so I might buy a complete car that's rusted out and then I can cherry pick the bits and try and recoup some money by selling spares.

Does a lightened flywheel make much difference? Bearing in mind there is nothing else modified on the engine (apart from the slowly reducing back pressure of the exhaust, due to corrosion ) How much am I looking at for a lightened flywheel?

Thanks for all your comments guys I really appreciate it.

try http://www.nipponspares.com/ for your 4age considerably cheaper than fensport

[Sparky_2day]

Lightweight fly wheel really improves responsivness of the moter, seems to rev a bit quicker and easier, however for a while after fitting i had problems with the revs dropping too low and then rise again when i came off throttle for a while afterwards, it would occasionally cut out. somthing to do with the lack of weight slowing the engine too quick or somthing. it sorted it's self out eventually tho.
it's worth doing while the engines out, the standard one is a brick... or two...

[Jimbo_Jet]

Yeah, I’ve got a MK1b engine and gearbox out of my old red MK1b in the back of my new black MK1a – and it’s running on the original MK1a ECU and I’ve noticed a BIG difference. The biggest difference is how high the engine will now rev!

When I was REALLY thrashing my MK1b I would change a 6750rpm which seemed the ultimate high point for me - maybe 7000rpm at the absolute most but I could start to feel the power trailing off at that point. I remember at the time reading a post by Lauren saying she shifted at 7250rpm, and sometimes 7500rpm – I tried this in my MK1b and it was awful, it actually held the car back above 7000rpm and it really didn’t want to rev much higher. I now realise that she was driving her red MK1a at the time. So it’s all down to the ECU!

Fast forward a year and I now have the same MK1b gearbox and MK1b engine running on a MK1a ECU and it will happily rev it’s nutz off all day long and is sings it’s way past 7000rpm with amazing ease. I too now shift a 7250rpm and sometimes 7500rpm when I’m trashing it with no problems, and I tell you what, at 7250rpm it’s still pulling, HARD! Even at 7500rpm it’s still got some go left in it. The other difference is that the TVIS now kicks in around 4300rpm where as when it was on a MK1b ECU they opened around 4800rpm.

Those who have this kind of set up – have you noticed that there isn’t quite as much torque below 2500rpm? Could be my imagination?