ECU: CR from 8:1 to 10:1

[jass]

I am building my old engine with main idea to have it oil-leakage-tight, and some bonuses as 10:1 pistons (8:1 on early 1.8 now), exintake mod (cheers again, Andrew!) and if all runs well some R1 42mm ITBs with MS in a month time.

Have bee in playing with the idea for a while to try-start the engine with the stock ECU to minimise the chance of mistakes with more variables (MS2 in this case).
Here my thoughts - MX5 runs way too rich, leaning the mixture should not cause problems.
I have Bipes ACU, that varies the timing depending on revs, load, temperature. Starting with conservative timing, I think I should be able to control the timing to get it running.

Not planing to trackrace it like this, but am curious how it will start.

Am I missing something essential in this equation?

[Andrew]

Hi Vlad, I don't really understand the question. Is it that the car won't start now you've built the engine? Or haven't you tried yet? I have no experience of the Bipes box to alter the timing, but I have heard of them.

[Lazza]

I think he's just asking if it would be safe to try running the engine like that with the stock ecu. I don't see a problem with it myself. The stock ecu will run from the sensors (engine temp, MAF, TPS, O2) below 4k rpm so should be able to control the fuelling ok as long as the Bipes doesn't mess with the timing too much. I'd keep it well below 4k though.

[jass]

Hi Andrew, Lazza, indeed, my thoughts are if it is safe to start it with the stock ECU.

That Bipes box is a plug in controller that lets you to vary the timing of the stock ECU, considering some ECU inputs.

[Lazza]

If it's just to test that it's running smoothly then I'd run it with the stock ecu only. You won't need the Bipes with an MS2 anyway so you aren't testing anything having that in the system.

[jass]

Sure, bipes does not make sense with ms. What do you think could theoretically go wrong with the higher revs, Lazza?

Just got a call, engine is ready and waiting, I will drop the car the weekend for the swap and will see what will happen. The guys in the garage do rally cars for living, dont expect to be left without support in this, but trying to scan the options in advance.

[Lazza]

There probably wouldn't be a problem with the higher revs, it's just that above 4k rpm the ecu will run from internal maps and ignore sensor inputs so if it's going to run too rich/lean or do something stupid with the timing it'll be then.

[jass]

I had the impression the early 1.8s had CR 8:1 (dont know where I found it), but started rechecking that info and can find only informations for 8.8:1. If the second is the case, the increase is not that huge and possibly there should not be issues.

I can attach wideband to check for the fuel mixture (although doubt as well that will cause problems) and will carefully increase the timing to stock with the new engine.

Might be interesting to share that my NA is starting with 22 degrees of timing advance that goes to 10 at full load above 4400 revs. No problems and the car feels with more torque at low revs. That makes me think there are huge reserves in the stock ECU and there is even chance it might start running with no problems at the end.

[Lazza]

I'm sure it would be fine. I'm just offering the "safe" advice ;)

p.s. timing can be advanced again at higher revs...

[jass]

Cheers, Lazza:).
I am looking forward, when the theory will meet reality and will share impressions here again.

[Mazda Mender]

We will be waiting buddy to post up your findings.
M-m

[jass]

Good news I hope...
My 1.8 engine (number 1) was started today 10:1 CR pistons and head and block skimmed 0.8mm. It has been running smooth with the stock ECU and driving, looking forward to testing it tomorrow. Fingers crossed!

We made so far some measures (not dyno, but 0-100, 1/4 mile etc.) with the old stock engine, that will be compared to the new build one, then compared to the new with exintake mod, later with megasquirt ecu and later with ITBs.

[Mazda Mender]

Good news I hope...
My 1.8 engine (number 1) was started today 10:1 CR pistons and head and block skimmed 0.8mm. It has been running smooth with the stock ECU and driving, looking forward to testing it tomorrow. Fingers crossed!

We made so far some measures (not dyno, but 0-100, 1/4 mile etc.) with the old stock engine, that will be compared to the new build one, then compared to the new with exintake mod, later with megasquirt ecu and later with ITBs.

M-m

[jass]

Or vids:).

I am tempted to see/drive it tonight!

[BenF]

Your 8.8:1 sounds about right as static comp although in reality it'll be somewhere 8.5:1 ish in dynamic compression, less on an aged engine. Mazda did this to help with varying fuel grades around the world (i.e. utter rubbish in the US ) obviously you're almost done now but FWIW the stock ECU and 10:1 static will be no problem. FYI I'm going to app. 11:1 dynamic CR (12ish static) but that's with DTA, not least because the stock ECU would be too slow to manage the system safely.

Did you do leakdown tests?

As above