Breaking in a stroker on original tune

Hello all, I have a BMW E30 fitted with a M20B25. (6 cylinder SOHC normally NA), its been turbocharged with a gtx3076. The vehicle was dyno tuned on a haltech elite 2000 by an experienced tuner, running a wideband, 900cc injectors, FPR, knock sensor with the usual standalone required sensors for engine monitoring. It was tuned with safety in mind at the time due to a factory unopened engine and made 350rwhp.

I am in the midst of building a new stroker engine for it, taking it from 2.5 to close to 2.9. Will run a slightly larger cam and 1mm larger valves. Same intake/injectors/turbo will be used. Considering the vehicle has a wideband installed. Do you think the dyno tune it had on the 2.5 turbo setup would be safe enough to break in the engine as long as I stay off the power? Would the fueling just adjust for the AFR Target? Obviously once engine break in has been established it would be taken to be tuned correctly after.

interested in input to guide my decision, thankyou.

Those changes warrant significant retuning and I suggest having it redone so your new engine has a good start of life.

You certainly don't have to have them tune it for high load right away, but I'd get all the low load work done right away at least.

I'd say it can be done with a lot of coution and few things being put in place and controled. You definitely will need to watch your afr at low boost as it surely will go leaner and no one wants to bake the pistons. How much leaner it will go depends on weither you are in the closed loop or not. If ECU is not in the closed loop there is not going to be any fuel compensation for additional air getting to the cylinder and this is where you get in the area of your own decision and risk. If you don't have any or very little experience with turbo engines behaviour i wouldn't take chances. But if you know the limits you can complete breaking in safely. If ECU in closed loop then it's much easier as it gives you some safety margin as far as fuel mixture goes. In both cases you do not want to go to a high boost areas but progressively increase the engine load from very low to low and mid...

Not clear if you're using mass airflow or manifold pressure - I'd expect the former to give some auto-correction, but the latter to increase the error?

Yeh its Map, thankyou for the info as thats very informative. Interesting as I thought that open loop meant it had a degree of fueling adjustment dependant on 02 sensor where closed loop it stuck to a table setup by the tuner. Guess i have that back to front.

So road test out of the way then, what about just breaking the cam in whilst im doing coolant bleeding or is it pretty much dont even go there and do it all on a dyno?

Thankyou much appreciated

My personal way of doing it - all at once during first 60 miles (100 km), starting from vacuum at the beginning and finishing with up to 0.4-0.5 bar of peak boost by 60 miles mark.

Daniel,

If you're tuning it, adjust displacement, fire it up and start adjusting fueling.

If you're not tuning it, I would ask the tuner for some base adjustment and see if they can remotely or in person adjust on 1st start.

Thats a great idea, thankyou for your help 😊

You're welcome!