I wanted to seek some advice on how to get more out of my 383 Vortec TBI. The blueprint engine Dyno'd at 434hp with 750 carb and .510 intake .520 exhaust lift 230 intake 236 exhaust duration 110 separation cam. I switched to Hot cam .525 intake and exhaust lift 218 228 duration 112 separation cam to make tuning easier. I have 50mm bored TBI with 68lb injectors at 32 psi. Its running 12.8 @ 108. I think that's maybe 360-370 hp. I was thinking of getting a MPFI intake and running 8 injectors which would allow my TBI to run dry and remove the injector hat. Would have to look into getting my EBL modded to run the injectors. Thinking I could get a lot more air flow that way though. Not sure if it would pick up much. Any thoughts would be appreciated.

 

Are you using "production" Vortec heads, or some aftermarket version? Porting? Larger valves? Different seat angles?

What intake manifold?

 

The heads are Blueprint version of Vortec. 2.02 intake, 1.60 exhaust and allow for .570 lift. Not ported . The intake is Edelbrock Performer RPM. I ported it to match the wider TBI. It's a nice unobstructed path thru the TBI, adapter plate into the intake.

 

The Hotcam is only .525" lift if you are running a 1.6 rocker arm. Do the blue print heads have guideplates or do they use self aligning rocker arms? My last two setups I have eliminated the self aligning rockers and used guideplates and hardened pushrods. I have run 1.7 scorpion roller rockers on both. I have seen that small GM Hotcam make better than 430 HP in a LT4 with stock port heads and 1.6 rockers.

 

I am running 1.6 rr with harden pushrods and guide plates so .525 lift. I have read repeatedly that HotCam SBC with my intake and heads should be 400HP. Mine was dyno'd 434HP with the somewhat larger cam but not much larger. I wonder if the TBI is causing a restriction vs the 750 carb they used to dyno it. Also my exhaust is 1 5/8 primary shorty header with 2.5" custom y to 3" out the rear of the car. Not sure if that is also causing a restriction. If I were making 400HP what do you guys think my trap MPH should be?

 

We are missing part of the equation, vehicle weight.

If you are making less than 415-420 HP with those heads and cam, you need to figure out what is going on. Stock Hecho en Mexico gm goodwrench heads that flowed 218 cfm when they were tested still allowed a L31 with a Hotcam/1.6 rocker swap to make 401 HP @ 5,600 rpm when tested.

My 4,700 lbs boat of an Infiniti M56S took 428 hp at the tires with 434 ft/lbs to run 112 mph trap speed. My 1980 Vette would trap 110-112 MPH with a cammed vortec 305 in it that probably made less than 300 hp at the tire. Difference is the Vette weighed about 3,000 lbs with me in it!

1 5/8" primary is probably not costing you too much hp at that power level, but the design of the Y-pipe could be killing you. TBI might be slightly restricting the power on the extreme top end, but honestly I bet if you looked at overall average power numbers from 1,000 rpm through 6,000 rpm the TBI if tuned correctly hangs in with a carb all the way in average numbers because of the smoother power delivery. 50mm TBI should be in the 650-700 cfm range wet. I have seen engines with the 500 cfm Holley 2bbl carb make over 400 HP.

 

Should be about 3400 lbs with me in it .

 

I would say to run 112 mph at that weight you should be putting down a solid 320 HP at the tire. If you are running a 700r4 that is about 18% loss. 320/.82 = 390 HP at the flywheel. HP/ET/MPH calculator shows 320 RWHP pushes a 3,400 lbs car to a 12.73 @ 112.5 mph.