will i have to change the trans to put a bigger engine will a 4.8l v8 in i dont really want anoter v6 in it doesnt hold enough power and couldnt i make a harness myself wouldnt it be cheaper?
It is probably "possible" to re-configure the mounts, axles, drivetrain, suspension and so forth in order to accommodate an engine other than the one the car was designed for. You would have to add to that workload though, the need to integrate the engine computer that runs the substitute engine into your car’s electrical system, not to mention the transmission control module. You would obviously have to completely change out the exhaust system as well. Depending on the state you live in there might be some emissions, registration, and inspection ramifications.
Typically, custom built vehicles have to be inspected by the Highway Patrol before they can be registered. Finally, you will have trouble insuring the vehicle because it essentially would not correspond at all to the VIN number that you have to supply to your agent to purchase insurance. They probably will refuse to insure it as a passenger vehicle because it simply is not the vehicle that the factory sold as the VIN you would be declaring. Were they a loss, they would refuse to pay because the VIN does not "match" the insured vehicle.
With regard to the transmission, you are absolutely right. Transmissions are rated for the maximum horsepower that they can handle before they basically fall apart. Assuming the transmission for the v-6 even fit the proposed engine, the v-6 transmission might not be rated for the horsepower that that v-8 engine could develop. You could definitely, with enough advance planning and engineering knowledge, make the proposed swap, but as far as the result being practical as a street legal passenger car, that is doubtful. Also, the cost will be substantial, exceeding by orders of magnitude the cost to rebuild your existing engine or buy a crate engine.
You are way better off carefully rebuilding what you have and learning from that experience and moving onward and upward from there. If you need assistance with the engine removal and replacement, this is something that YourMechanic could help you with in terms of getting you in touch with local experts who have already gone down this road before and have the experience to do it right. Best wishes with this...you are a very enterprising, ambitious person with good questions!
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