@abg7 that’s a fairly good summary of my suggestions, although I want to emphasize that nothing I say here is the end-all-be-all. I’m still learning just like anyone else, and what I’ve suggested here is based on my experience building competitive everyday cars.
For valve train type, it’s important to note that DOHC is not always the best choice; the power and efficiency is good but it’s also very expensive. All of the valve train types have their purpose. While I generally avoid OHV/MOHV in modern years since they don’t offer VVL, there’s nothing inherently wrong with using them, and they certainly have their uses when trying to build an engine that is easy to produce or very lightweight. (In real life, OHV is a staple even in modern, high-performance muscle cars, so it makes total sense to use them for a muscle car challenge!)
If you want to send me your cars, I would be happy to do a review for them. Seeing as how you were the only one I didn’t get to review, it would be nice to round this out so I can say I reviewed every car. I for one am interested in seeing the lineup with by far the best efficiency!
@koolkei One thing to keep in mind is that for most of these markets, comfort is valued far more than sportiness. A lot of people tend to ignore engine noise, but it plays a very important role in comfort. Adding noise is easy, but reducing noise is a lot trickier. That’s why I think it’s important to choose quiet engine options, when they aren’t too expensive.
For the mufflers, double baffled is the better choice as long as you don’t choke the exhaust. They really are a lot cheaper and quieter. I’ve found that choking the exhaust doesn’t help efficiency that much, and tends to hurt drivability as well. There are better ways to achieve efficiency.
Keeping the intended market in mind, it makes a lot of sense to trade some power/efficiency for comfort. My retuned engine only gets about 0.3 mpg less fuel economy in the cars, and the reduced noise offsets the loss in smoothness from +0 in bottom end. So it’s almost 20 PU cheaper with next to no loss.
This is also part of the reason for the really bad interiors. Your cars are over budget, and a good interior puts them further over budget. So rather than just leaving the basic interior, you should consider where else you can lower costs so you have money for a good interior.
@rk38 glad to hear that I helped! The next update is arriving in the coming weeks, and I’m going to need some time to get familiar with the new balance tweaks. We’ll see about stage 2 after that. I’m thinking it will be in a different era, and maybe I’ll throw in some additional judging criteria to keep things interesting 
)
