Tuning for specific HP target
 

'92 racecar w/ VVT transplant, ported/polished head/RB header, flattop IM, Rev built MS3 Enhanced. Stripped to 930 kgs (2050 lb). Dynoed to 162 HP/181 Nm torque on the flywheel on Rev's base map + autotuning.

Runs like a scalded cat and is great fun, but put's on in the wrong group when racing in the Youngtimer cup here in DK. We need to either increase the weight by 35 kgs or lower the max HP by 8 ponies to get on the safe side of 6.4 kgs/HP (car including driver). I'd rather tune the MS than add weight, question is what's the proper procedure for doing this?

We will use a tuner with a dyno for sure, but would like to know how best to obtain the target. Is it as simple as leaning it out a bit and reduce the timing advance when approaching the max HP range?

Thanks

You can reduce timing to limit power, but it can cause EGT's to increase. Are you still on the stock timing map or have you already tuned it for MBT?

No change to the stock timing map (Revs)

You could reduce timing and add a little fuel or put a restrictor in the intake

I would like to hear the expert opinion on this, but I think an intake restrictor is the best solution for engine durability.
If you tune with speed density I guess you can also run the same tune with and without restrictor? That would be a nice solution because you can take out the restrictor when not running the car at the specific events/competitions to fully enjoy your mods.

Most(all?) pro racing teams use restrictors to hit specific power goals.
I'm guessing that's the best way to go so that you can optimize fuel/spark and flatten the torque curve as much as possible while still keeping peak power at target.

Thanks for the feedback and suggestions.

Restricting airflow sounds right to me. As the throttle plate is already there, reducing the WOT a fraction may be all that's needed? Or am I missing something ?

Setting that up in a robust and repeatable way is going to be much harder than making a restrictor plate.

Pro teams generally use restrictors because they are mandated by rules. I have played with some really expensive restrictors (Raetech) in hopes of finding one that would produce a flat power graph, but I found that they all choked power through the midrange, instead of just flatlining power at the top end. If you truly want flat power, it has to come from the tune. Camshaft timing will be your best friend here.

Having said all of that, you will go faster if you add 35kg to the car vs. removing 8whp. You can probably put the weight low enough and place it strategically to aid in weight distribution, so it won't be as big an impact as you might think. The extra 8whp means the car will accelerate harder at speed, because you have more power to overcome wind drag.