That's a very aggressive goal for a 3800. AFAIK that goal has been reached but only by boosting the engine with a turbo. ZZ Performance is the preeminent source for engines of this type but forum member Jcircs (Jerry) also had a killer 3800 engine built If you really want to hit 400HP be prepared to spend a considerable amount of money.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
400+ whp isn't unreasonable and really doesn't even require that many mods. I've seen guys run numbers like that all day with a 3" pulley, larger injectors/pump, methanol injection, intercooler, cai, and 1.9 rockers easy.
I myself just got into tuning, so not much help in that department. I just got into rebuilding the engines so feel free to ask any questions you have. I have two rebuilt engines still on the road, one of them (in my daily driver) is at over 7000 miles since the rebuild with no issues, the other in a friend's car with 4000.
I think 3800s get a bad wrap for rebuilding not because they are any different than any other engine, but because people cut corners and are surprised when they get burned. Now, I realize that you can cut corners on say a 350 chevy rebuild and it run ok, but try that on these and they'll surely live up to that "500 mile or less engine". The real secret is to partner up with a machine shop you trust.
A few big things people make mistakes on though: believe it or not, these engine's warp slightly when the heads are bolted on, so you 100% have to have a special plate to simulate these loads when the engine is being overbored. I also didn't make a mistake by saying "when" these engines get rebored. I've taken measurements from over a dozen 3800 cores and any over 80,000 miles or so have "eggshaped" cylinder chambers and require bored out to a larger size to correct the wear so the piston rings can seal properly. Which also means you need new pistons and rings gaped properly. Which also means you need to re-balance your crankshaft assembly. Which speaking of balance, requires you need to have a main line hone for these engines to run properly after a rebuild. The connecting rod caps also stretch into an "oval" requiring the caps to be planed to bring back to tolerance, which the crank needs to be checked and polished, and after spending all this money on the low end, you might as well have the valve seats re-cut and springs replaced, and magnaflux the block and heads, and grind valves. The 100% most important part is to replace ALL tty bolts. The head bolts, main bolts, connecting rod bolts, flywheel bolts, torque converter bolts, balancer bolt, camshaft bolt, crank bolt, rocker bolts, cam thrust plate bolts are ALL torque to yield and need replaced. You need the block and heads resurfaced. You NEED every spec checked and rechecked on every bearing and every dimmension. Every bearing replaced, cam checked. Everything assembled correctly with engine lube and inspected and kept clean.
As an example, I pieced together my engine rebuild kit myself and did most of the measurements and all of the assembly by myself and still spent $1500 at a local shop just to rebuild it stock. A performance engine build even if you do your own blueprinting and port work, you're still looking at minimum $2000 and up. There engines are not cheap or easy to rebuild and they are not forgiving of errors.
I would say for your goals, it'd be more worth your money to pick up a more aggressive cam, smaller pulley, n* tb with ls maf sensor, #60 injectors, upgraded fuel pump, methanol kit, and a good tuner.
I have to admit though, for my 3800 I'm going stupid and running forged connecting rods and ceramic coated forged pistons, I'm debating on splurging on aluminum heads, hand porting, hv3 L26 upper intake, n* with ls maf, #80 injectors, dual timing chain, balance shaft delete, and 75mm turbo with 6L75 transmission so I can't say too much! Feel free to ask any questions I didn't answer!
I am looking for someone that is still building and tuning 3800 motors. I tried to reach out to dark horizon with no luck. I am looking for help to get close to 400whp or more from a 3800 motor.
Check out SCHWA Motorsports. He has done many 3800 SC swaps. Specialized in forced induction of any kind. He did my 3900 swap which is scheduled to add boost before the 35th anniversary show. Ephkay is his name here on the forum.
current plan 1.6 roller rockers intense racing stage 2 cam ls6 valve springs. l67 block Camaro intake and throttle body intercooled. turbo???? injectors??? removed ac Removed balancer Double roller chain with machined front cover.
Get a Borg Warner EFR 8374 or EFR 7670. The 8374 is a perfect match but if you can go to the next smaller 7670 or larger 9174 size. Get a small turbo cam such as ZZP ST1. Dont get a large Turbo cam it's more trouble than it's worth for a DD street car.
I am building another turbo car with Gen V m90 UIM and a block off plate. I am using the M90 so I can use the plate style IC as space is limited. I am also using the BW EFR 7670 as or is a street car. If you go too big on Turbo/Cam car will be a Dyno Queen/ Race Car because too much power to use on the street. You will just spin out and never get and traction.