If its big horsepower your chasing the C18 would be the way to go, there's no substitute for cubic inches!!! but for over the road the C16/18s are know to have head gasket and liner fretting issues, I would think if you are chasing 2500hp you will be doing a few head gaskets anyway so it wouldn't matter.
Building a C18 up from scratch would be pretty expensive, no idea how much though, It may be worth trying to get a secondhand marine C18 if you can find one for a good price, then you'd have all cats biggest bits to start from, C18 crank, rods and pistons (lower comp for big power), big cam and injectors, just add turbos and ECM of you choice, pull off the heat exchangers and connect it to an aftercooler and radiator and go racing.
Other option might be ex-millitary, I know there are 950hp C18s speced for the millitary but not sure how easy it would be to find one, dont know how many were built.

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Speed costs money, how fast do you want to go?

Cooper doesn't have 3100 hp, his record is high 12s or something, in Malta they run 11s with about 1500 hp. Bouchard has maybe 1600 hp if you calculate from his 1/4 mile top speed, max 1800.

dont forget bouchard's truck weights 3 times more than cooper's

I didn't forget that. I have heard that they didn't let Cooper use full power for safety reasons. Also those truck vs. Saleen videos seem fake to me. Bouchards 1/4 mile record is 13.8/98mph, I used a weight of 9000 kg when calculating.

I think V8Lenny is right about the HP ratings. Most of the NTPA guys are running over 3000 HP coming out of all mechanical engines (no electronic controls allowed in NTPA). But they have the added benifit of using water injection to cool things down. From what bern009 is saying, no water injection is allowed up north. If this is the case, I don't see how Coga, Bouchard, and others can be putting 3000 HP down and still keep the pistons from melting. Also the amount of boost pressure is upwards of 150 PSI. I just don't think that 3000 HP is a real number, I feel that they are in the neighborhood of 1500-1600 HP with gobs of torque. I would love to hear someone that actually races up there (maybe DDS if he is still around) speak out about this.

bern009 if you want help figuring out what it would take to build a mountain motor, then you need to help us. Post a link to the rules (perferable in english) or just type them. Also all the HP/TQ in the world doesn't mean a thing if the rest of the vehicle isn't built to handle it. The clutch, transmission, u joints, driveshafts, and rearends all need to be just right. If a person is gonna spend the money to build a great motor you might as well spend a little more and build a truck that is capable of it and best suits what you are asking of it.

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'06 379 Pete with a MXS C-15 550 with heavy haul program, 200gph FASS, high flow mufflers, fuel and boost harnesses, shimmed fuel pump, Bully Dog downloader, Spinner II bypass filter, Schaeffer's synthetics in all boxes, and a 18 speed tranny. Leased to Schneider on their Choice program.

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so that one is fake too.....

I know cooper doesn't have that power, he advertises that power but he's been around for the last few years and he's never won anything, only makes smoke.
I am sure it' going to take a while for us to see someone get close to Coga & Couture

what's the winnings' amount during a NTPA weekend

Yes. Or the Mustang driver don't know how to drive.

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You really need to stop posting video's I don't get much done as it is I don't need any more distractions. HAHA