Buy a ZR1

 

I'll add a few things to consider....Although subjective, a stock '84 with 205 HP at the crank can be fun to drive....so replacing it with 350-400 CHP would be a blast to drive! That's LT4/ZR1 territory and is enough power to get you in trouble and out of shape while driving! You have to consider the platform, horsepower #'s in a C4 application are amplified/more effective (better power to weight ratio) compared to say a much heavier Chevelle or Monte Carlo...Trying to say, even if you want those HP #'s to be rear-wheel...350HP would be a rocket ship! Which brings me to the components, the D36 rear-end will be a weak link even with an automatic transmission. And speaking of the '84 700r4, they're just about the least desirable 700r4 to have...the input shaft is 27 splines (not the larger 30 spline that the '85+ 700r4's received). Not only is it weaker, but there's almost zero aftermarket support for 27 spline torque converters (not many options!!!!) and at the HP levels you're talking about and even though the stock '84 700r4 came with a slightly higher stall from the factory, you're going to want/need a higher stall converter! You could convert your 27 spline input shaft to a 30 with a few other parts, but unfortunately your transmission has been rebuilt already, but it could still be done. I believe it's possible to have/get a 27 spline torqueconverter "made", but it'll be very costly. There were many other internal upgrades made throughout the years to the 700r4, sourcing a late '80's to early '90s (before they became electronic) 700r4 makes for the best candidate (unless you'd have the ability to control an electric one) to start a rebuild. I'd be very curious to know what they did to the internals of your stock '84 700r4 to claim 500 RWHP capability and how much that cost you!? As stated above, if you factor in everything....gears, tire size, stall speed, final gear ratios 1st thru overdrive, cam profile, weight, fuel delivery, etc...I believe you'll find that 500 RWHP just isn't necessary to have the overall performance you'd likely be very happy with!!! I'd guess that 95%+ of people out there are not experienced/capable enough drivers to control a 500 RWHP C4 with no ABS or Traction Control Nannies on the streets....that is a lot of raw power!!! If everything isn't done properly, it'll be finicky, erratic, unreliable, failure prone and unpredictable....yes it can and has been done...but I believe you'll never be able to come close to using it all on the street...you'll spend more time lifting off of the gas pedal than standing on it!!! Good luck with whatever you decide to do👍

 

I like the L92 idea. You're a cam, intake and throttle body away from 550 crank HP. With LS swaps all the little stuff adds up fast but I think it could be done for about 5k if you stick with the stock rotating assembly. You'd be able to run a much smaller cam that would be a much more docile and easier to tune. You can find clapped out gen 3 Escalades for 2 to 3 thousand and harvest the L92, maybe less now with gas prices as they are. Then you'd have an engine all the sensors, PCM and wiring harness. It takes a few hours to simplify the harness and convert it to stand-alone but it's very doable. And you should be able to blow out Esclade parts and recoupe at least 500$ quickly. Maybe more if the condition is good.
Check this out. https://www.motortrend.com/how-to/ge...imple-cam-swap

If you want run an SBC to get close you'll need at least a 406 with a solid roller cam in the 240's and all the supporting mods, easily 12k to build that. For example It's takes expensive parts (crank trigger and billet dist) to get a SBC to make reliable power above 6000 RPM. You get as much as 10% misfires at high RPM with a distributor. I converted a SBC with a healthy cam and a StealthRam from HEI to DIS and it went from nosing over at 5500 RPM to pulling to 7000, it was a shocking differance. You have to keep in mind the HEI is driven off the back of a long camshaft and at RPM the dist see all sorts of harmonics that can casue spark scatter.

I'd choose the L92, it will have more bang for the buck and you get all the advantages of a modern PCM like a crank trigger, sequential injection and coil near plug precise ignition timing. AND you'll loose 100 Lbs on the nose and that weight savings equates to at least 10 HP.

 

I did have it converted to the 30 spline when I had the work done. It has a shift kit, hardened sun shell, and just general high quality parts and clutch packs. I can't remember exactly, but it got a 2700 or 2800 stall converter put on it too. I would consider going higher if needed. Honestly, it's the first automatic I've really messed with, which is why it went to a shop. As for the braking aspect, I ordered 85 spindles and plan on getting C5 rims and hardware because I know stock isn't great. I've experienced that first hand. I'll state it again though, I am mainly looking for just ballpark area and if it is possible. I mean, I'd take power addition cause right now there isn't much of a reason to drive it over my other 2 cars. One's faster, and the other rides better. Lol