Agreed. This is a very simple build at the end of the day. We do this on pretty much a daily basis. Hell, I just finished up (3) 555 CI engines with 4L Whipples. 2 of them were part of a pair and a single. All were on pump gas with an hydraulic roller. All of them ran less than 9 psi of boost and all made over 1100 hp at 6000 rpm. The pair made 1125 and 1132 hp.
Eddie

To answer your question to make 1200 HP I use an M5 the MB1250CSCefi package we offer is a 540 CI based engine and makes 1288 hp @5600 RPM and 1300 Ft lbs @5600 RPM
this is on REC 91 marine fuel at 10 PSI boost. There's been lots said about Procharger engines not making good torque numbers on the bottom compared to other blower set ups this package
makes over 1000 ft lbs everywhere above 1800 RPM and the torque never falls off , the torque and HP will climb all the way to 6000 RPM . I've used smaller units and feel this is the best
for the power you're looking for. We also build roots, whipple, turbo engines as well depending the application . Best of luck Laz Mesa

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https://www.procharger.com/how-much-...-add-my-engine
Prochargers website explains boost vs hp .

we know theoretically, adding 14.7 psi of boost to a typical pump gas engine, will double its naturally aspirated output, minus any losses from parasitic, etc.

To make 1260hp, with 10psi, textbook says the engine would need to make 750hp naturally aspirated. Again, minus parasitic losses.

procharger states, to gain 100% power increase with a 9.5:1 compression, intercooled pump gas engine, it typically takes 17psi of boost to do so. Im assuming the extra 2 psi of boost is needed to make up for parasitic losses.

a friend built a m4 procharged 522ci. It made around 1200 or 1250 on the dyno with 17psi. If what procharger says is true, that engine should have made approx 600hp in NA form. Which, is prob really close, for a 522ci with edelbrock heads, decent hyd roller, etc.

dart has a neat airflow(boost) vs hp calculator as well

It is hard to know which way to go whipple or procharger.I have not heard of whipple doubling the horsepower even with 17 psi.My 602 with all the good stuff and "Young" heads should be 900 hp, so if this procharger math is right with 17 psi I could have 1800 hp engines! I would only use about 7-9 psi so maybe we could say 1400 hp? 1400 x 2 I like it
the main thing for me is if the make a procharger mount bracket to mount the prochager going the other way not up to the right but to the left

I just asked a friend of mine who is one of the top tuners @ ProCharger and he said right side only

+++

The bolts that hold the compressor to the bracket use socket head bolts that are counter-bored into the mounting plate, so you can't flip it around.

So then maybe I have to use whipple.The biggest one I saw is a 8.3 whipple with two rotors inside and there is another one that has 2 rotors outside and I think 4 rotors inside.Does anyone here know about that model.I think it cost about 14,000 usd.double head or pulley whipple.Is that one bigger than the 8.3 ?

Whipple Big Block Chevy Tall Deck EFI, Standard Intercooler Kit, 16 Rib (2) 200ci, V-Belt, Polished Finish - Hardin Marine

That's called a quadrotor. It's simply 2 superchargers on 1 intake. You don't need a quadrotor to make 1200. As I mentioned previously, a single 4L will get you there. If you want room to grow, then go with a 4.5L. The 4L with a MOAC intercooler is right around 10K. The 4.5L is a little bit more, but not that much. I've used the 4L to make 1200 on a 598 with a moderate hydraulic roller cam and moderate heads. Nothing fancy.

Here is what a 4L quadrotor can do at just under 17 psi of boost. This one is 582 ci, killer heads, 55MM solid roller, on race gas.