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Trouble Making Chevy BigBlock L78

Hey all, I’m new to the game, although Ive spent a while now designing a few engines/cars. Im trying to replicate the Chevy Big Block L78 (396 cubic inch, 6,484 cc) engine in the Chevelle and other late 60’s model muscle cars.

this engine had a peak output of 375hp and 415lbft of torque, 11.0:1 compression, with a single 4 barrel carb, revved to 6,000 rpm and got around 9-11mpg. It had an aluminum head and light weight forged pistons, conrods and crank. It was a pretty advanced engine for the time.

I can’t get real close to these values in game, and I’m wondering if anyone was able to get any closer than I have gotten?

Ive gotten around 355hp and 370lbft of torque, but the torque curve is way too late, the engine won’t rev near 6,000rpm, and i have to use double carbs plus oversized exhaust to get there. On top of that I only get about 6mpg.

I can post maybe a pic or two of the engine stats, but I’m curious if im just not optimizing it well, or if its just a limitation in the game?

From my own personal experience, OHV engines are not modeled as accurately as they should be overall.

1 Like

Massive number of slider abuse (quality) on the cylinder head/cam tab.


I think that may get me there on peak hp, but the torque will still be way low and 2500rpm late and it will get like 5mpg. Like abg7 stated, there must be something off with the pushrod engines, or there is just some adjustability missing when it comes to valve size, engine knock and carb tuning.

OHVs are fine, its just that companies like Chevy have had a lot of time to invest in OHVs. In the campaign, it will be the same if you stick to using OHV for a long time. In sandbox however, the only solution is to put the quality up.

Most important thing - SAE Gross vs SAE Net

I’m 99,9% sure that the figures you’ve provided for the real engine are SAE Gross, while the game deals in more or less SAE Net. That means about 20-33% lower power and torque, based on some real engines rated in both norms that I checked. So if you get 355 hp and 503 Nm you’ve already exceeded the real engine by a good margin, and that would explain lower MPG. Revs are probably the matter of two things - sheer experience in OHV that American manufacturers have and partially already had by then, and simplified head design in the game, where the valves are as big as they can with given bore.

Yes I had to write it that f…ing big because that’s a crucial factor that many people tend to ignore all the time.

That’s a very good point. So what is typical losses for Net vs Gross, 10-15%? This still doesn’t explain the torque curve differences though, and I’m betting that is limitation of valves in the game, as well as some other factors.

In 1971 the rating did change to SAE Net, so you don’t have to guess:


Your engine should be a little higher than 285hp, as the 454 rated at 365 gross hp was rated at 285 net hp.


Oh, and a minimum +7 on valves, as the Devs have said American manufacturers would likely be close to +12 on them for the 1960s engines.

Last note: The game simulates hydraulic lifters (IE oil fills them for regular use). Some of the engines like ford’s HiPo 289 and possibly your L78 used solid lifters which had more rpms but had to be adjusted frequently.


20-33% as I wrote. Much closer to 20% usually but I’ve seen some engine that lost third of it’s power in the new norm. And the torque curve difference is probably matter of the cam profile of your engine being higher than it should (it definitely is, as you get more power than the engine you’re trying to replicate).

+what @findRED19 wrote.