Re: vac secondaries
He probably needs a weaker spring inside the vacuum diaphragm.
He'll need to buy a spring kit.
Take the spring out and drive it without it, and see what happens. It will very likely open to early and stumble so you can try different spring tensions and find the right one.
4L I6, naturally aspirated producing 173.5rwkw.
14.410 @ 96.49mph with street radials.
What's that?..... Did I hear you say TQE power?