I think the Thumper cams are overall designed best for Chevy engines where the piston has more acceleration off of top dead center at lower RPMs. Generally it seems like the shorter the rod to stroke ratio, the better they work. The longer the connecting rod, the worse they work, the worst engines for those thumper cams seem to be a small bore engine using long rods. Just my observation, but on a lot of those applications is appears there is not enough piston speed coming off of top dead center for the RPMs too utilize the extra overlap. The result is a bunch of the fuel and air charge gets blown out the exhaust. That 235/247 thumper is not a big cam, at least not in terms of useable RPMs. In a 400 it only has the same top end power band of a 60243 Crower (228,
[email protected] 112LSA) which to me is pretty small yet. I would guess the 60243 could pretty much match the road kill (HFT)thumper cam for toque and on that same engine beat it by 20 HP up top. If you swapped and put that thumper cam in a 400 SBC with stock length rods I think the results would totally flip. I did a 110LSA Bullet HFT 235,243 @.050” with .566” lift in a 10:1 406, had VPro lifters. That could bury a 60243 and was still very tame. The thumpers can work in Pontiacs, but they generally don’t work great. Seem like they work much better in 455s than 400s.
Road kill cars have a lot of parts in them just because it is available and in stock. Their goal is just to get the engine running and on the road, not necessarily to get the most out of it. It is still fun. I have noticed the thumper cams are almost always on stock.