1980’s BMW 745i.
The car disappears in a crowd aside from the kidney grill, and the three letter badging. Euro bumpers might give it away to a BMW enthusiast.
With out modifying much out side the turbo system, you can have a street able 450bhp+ (stock: injectors, engine management, bottom end). The getrag 265 5 speeds can handle the power, and a conversion from auto to manual is actually easy (i have done it). You can even find 3.91 LSD rear ends pretty easy and cheep, and you can change the diff in 20 minutes.
Parts are cheep, it’s a comfy ride, okay after market, and no one would see it coming.
You might consider an old Volvo 240. Looks like a kitchen appliance, plenty of room in the engine compartment, existing components much stronger than they need to be for the stock 4 cyl engine. Install diesel 240 springs on front to handle the weight of a V8. The down side is that the car is relatively heavy.
You can probably find a sleeper car already built on e-Bay. What happens is people build them and then move, and discover that they cannot pass emissions in their new home state, so they have to get rid of them.
Get an old police car. They usually have bigger engines than were available to the public. A late 70’s Volare with a 318 is fast. An ex-police Volare with a 360 is even faster. If you like the Diplomat/Gran Fury, again get an ex-police car. They had 360’s in them when the public could only get 318’s. Go back to the 70’s though, and you may be able to get a Dodge or Plymouth with a 400 or 440. Crown Vic is good, but I read where even the cops could only get the 4.6 liter since about 1992 (whenever the 4.6 replaced the 302). (I hear they do okay, though, even with the smaller engine.) In the 80’s though, I think the cops got 351’s. Some Grand Marquis from the first half of the 80’s also had 351’s in them. Chevy police cars (Caprices) got 350’s until they stopped making them in the mid-90’s.
If You want to swap engines, someone suggested putting a 302 in a Pinto or a 350 in a Chevette. Um okay… If it fits, sure, why not?
Ixnay on the adillaccay! Keep it down, you’re letting everyone in on one of the best kept secrets to budget power.
Okay folks, move it along…nothing to see here…
" A late 70’s Volare with a 318 is fast. An ex-police Volare with a 360 is even faster."
That is assuming that you can actually find one that did not disintegrate into a pile of rust particles about 20 years ago. The Tin Worms were not kind to those cars.
We had a 1964 Model 62 Cadillac with a 429 engine. It was incredibly quick. I beat everything that wanted to race. I raced an MGB-GT one night from stoplight to stoplight. I didn’t know he wanted to race until he took off. I was 3 car lengths behind, then went two ahead, backed off, went two ahead, backed off, then blew him away. At the second light, his jaw was in his lap and he asked: “what you got in that thing?..”