mx5cartalk.com

So, the engine in my NB8A is getting a bit tired.

Still runs fine, but has a fair bit of blowby, and the oil seems to start stinking of fuel after a while.
Yeah, probably rings. (havt dug the Comp tester out to confirm, but pretty sure as is)


Anyway, in future i'd like to put in some moderately lumpy cams (still comfortable enough for road use) and obviously an ECU to run it properly.

Which means that I have the following options:

1: Rebuild NB8A engine to standard specs
2: Secondhand NB8A engine (build my current engine into something better later on)
3: Rebuild NB8A engine to standard, with NB8B pistons (higher CR)
4: Secondhand NB8B block, and use my NB8A head


So, the big question is.

Does the factory NB8A ECU have enough scope to happily (and safely) run the higher compression NB8B bottom end (or an equvalent CR)
(noting that the car has a few existing mods that likely make little difference, being NA8 extractors (EGR deleted) and a coldside short CAI)


Thanks all.

(btw, the budget will in no way allow for an ECU to happen at the same time as a new engine, so that's not even an option)

Talk to STM.

Yes.

I ran big cams, worked head, decked block, zorst and intake with stock ecu. Secret was an adjustable FPR, so the stock injectors flowed more than the ECU knew. I ran it this way for several years, can't remember how many before the Haltech went in.

...or keep the Adaptronic you've currently got for sale.

If you end up buying a NB8B engine for the bottom end I'd be interested in the head!

My nA6 ecu had no noticable isses coping with compression & cams
My cams were not hugely agressive but perhaps on the more agressive side for those that come off the shelf.

If anything. Compression helped idle. So shave to your hearts content without getting to the stage of interference.

I found the caR runing super rich in most cases. I used a lot of petrol.

An aftermarket ECU will make it run more powerfull. Mine lost a certain amount of urgeny after changing from aftremarket to OEM.

But it ran fine.

It really depends how agressive you go with cams. The problem will be where the O2 sensor is not active. Eg. idle or above 85% WOT. In places Where it does not compensate for AFR....or if its that agressive your injectors cant keep up.
On patchy the AFR was like 10:1 in the high rpm ranges... which was safe but essentially drowning it.
On E85 injectors coulnt keep up at lots of ranges at the fueling was all wrong.
I had 272 @ advertised duration. I dont recall what it was at 0.050"

But really id say i was at the upper side of what the ECU can cope with


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On my Bp4W conversion ive only dríven it around the front yard. I currently have the standard cams fitted for blue slipping.

But i have other issues at hand. But its running a Megasquirt.

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Back in mid 2000s Mason on here successfully ran Toda cams & cam gears in his NB8A with an Emanage piggyback - a few of his posts about the cams are still available: http://mx5cartalk.com/forum/search.php? ... 5&sr=posts

Should probably clarify.

The Cams are a future plan, and wont happen on the stock ECU.

Was more that I figured if i'm potentially changing the bottom end anyway, i'd prefer a bit more compression ready for future ECU and cams.
But not if it wont run on the current stock setup.

You can adjust OVERALL fueling with an AFPR, and OVERALL timing with an adjustable crank trigger wheel, HOWEVER..

If you change the characteristics significantly with (for example) camshafts which reduce low rpm cylinder filling and increase high rpm cylinder filling you will still have the same fueling and timing 'curve' of the stock ecu, with only the ability to add or remove timing and fuel uniformly across the rpm range. So keep that in mind.

For example,
Adding a huge cam which needs less fuel and more timing at the low rpm and more fuel and less timing up the top will leave a compromise at the low rpm band if you use the above methods to uniformly adjust fueling and timing in order to take advantage of your top end heavy camshafts, amd vice versa.

Dann

NitroDann wrote:Adding a huge cam which needs less fuel and more timing at the low rpm and more fuel and less timing up the top will leave a compromise at the low rpm band if you use the above methods to uniformly adjust fueling and timing in order to take advantage of your top end heavy camshafts, amd vice versa.

Dann

I understand all that, hence why i'll not be putting anything other than stock cams in until I've sorted an ECU out.

I'm more asking about the bottom end, ie: higher CR bottom end (likely just a cheap NB8B block) with an untouched factory NB8A head/cams/etc bolted to the top of it.



Mainly since the current bottom end isnt too healthy, but the budget doesnt cover an engine AND ecu at the moment. (and there's no point spending money on a new ECU if it's going to be bolted to a block with stuffed rings)

But I figured if I can get away with some more compression on the stock ECU, that saves me having/wanting to do it again later on when/if I do change the ECU and have the head worked.

Without changing the ECU, I don't think some of your options will work.

I'd either buy a second hand engine "IF" you know the history of the engine.
-or-
Rebuild what you got. Sounds like just your oil rings. My old Astina engine was the same. Ran perfect, just drank a lot of oil.

Yeah, in the meantime i'm just doing the usual.
Run thicker oil until it basically becomes a 2 stroke.

haha

By the time I replaced the Astina engine at 260,000km old, it was drinking 1L of oil per 1000km of travel. Or 75L of fuel. So 1:75 oil mix was going into the chambers.