How much power do engine mods yield?

Killer6 said
A 98mph trap speed should net a 13.60 ET w/a dialed in drivetrain/chassis setup.
Assuming an as raced wt. of 3000lbs.w/driver and a full tank,that would tick off at
230hp at the wheels,use any"at the crank"guestimations at your own risk.Now,this
is theoretical,but has been proven in practice enuff to be accepted..follow;220CFM
is capable of supporting approx.440hp in a V-8 w/a fairly aggressive cam profile.
More for rollers,less for street cams,that is the "rule of thumb",and theres specific
formulas for these numbers.But we all know that isn't how it goes in the real world
and combustion chambers,plug location,thermal layout,etc.,etc.,all alter the real
output.Plugging in 220CFM still gives you a 330HP potential,and I'm sure some
have bumped up against that.Still,at 300HP for a punched /6,that would be more
like 574HP if it were a 440,so the real problem is simply uh,the engine is small!
You have no trouble convincing me about the beauty of turbos,I got hooked on
them when I worked at a CPD dealer in '86,and I own a number of them.I am
picking up another 170 for such a project,slated for a '64 GT conv.,but the coupe
is getting the orig. .060" over 225 I built yrs. ago w/some definite improvements.
And my '90 omni has a 2.5turbo voyager drivetrain waiting to go in........:D

All of your performance "assumptions" seem pretty realistic to me, and I have no argument with any of them. Your estimate of 230 rear wheel horsepower seems low until you consider that it is, in fact, rear wheel horsepower, having gone through a converter, an automatic transmission, two U-joints and a ring and pinion, and is still over one horsepower per-cubic inch, AND is naturally-aspirated, it seems pretty good, considering that pitiful cylinder head.

I use an online program called "Wallace Racing Calculators" which seems to work well for estimating power output from hypothetical engines and estimates of eighth- and quarter-mile e.t.s if you supply numbers for car weights.

I am sure it is not 100% accurate, but works well for comparing outputs of different combinations of powertrains and vehicle weights.

It has a lot of different inputs to show a variety of performance specs using any parameters you'd care to input.

The two turbo slant six cars that I have paid a LOT of attention to on this site, each have turbocharged 225 motors, and when I enter the specs of their drag strip runs along with their weights, they both calculate to numbers in the low 500-horsepower range. That's about 2.17 horsepower per cubic inch, or about 131 horsepower per liter.

In defense of that number, I would like to ask poster Brandon Weaver how he arrived at his contention that "the most powerful slant was somewhere around 370."

My argument is supported by this video: [ame="https://www.youtube.com/watch?v=7QzUfV8iTpQ"]Turbo Slant Six 10.74 @ 127 mph 7-19-10 - YouTube[/ame]

wherein a 2,800-pound '66 Valiant (2,970 pounds with driver) runs 127mph in the quarter-mile.

I don't see how that would be possible with 370 horsepower.

Tom Wolfe's similar engine makes approximately the same amout of power, pulling his 400-pound heavier '70 Dart 120 mph in the quarter.

Cameron Tilley's Australian Valiant reputedly has over 600 horsepower, do, I dunno... So far, a 500-horsepower figure has not come out of an engine-dyno test, so until it does, I guess we won't really know...

But, it's fun to compare and analyze...:burnout: