So trying to figure this out, just had the car on the dyno, and the new engine combination is off by 200 hp, at 14 psi from the old combination, and should've made more than the old combination. 383 sbc, twin vs racing 66/67 billet wheel, .84 t4 flange, air to air intercooler, Holley 4500 super sniper (efi throttle body), brodix Dragonslayer heads, 9.2:1 compression, basically the same short block and cam from the old combination. Things that the old combination had: brodix track one heads, cx racing 61 mm/.84 t3 exhaust housings, fitech 1200 pa(and also a qft blow thru 750, power output was within 20 hp between the pair). Power output with the old combination was 820 rwhp, at 15 psi. Power output with new combination, 620 hp, at 14 psi. New combination didn't see full boost until 5800 rpm, old combination was all in by 3500 rpm. Timing on both was set on the dyno starting at 26°, and final timing was 31° on both, using power output and the annealing mark on the ground strap, and using 112 octane. Old combination would gain 40 hp for every 2° put back in it, new combination didn't really see any gains (very minimal) from adding timing, but mark moved on the ground strap with addition of timing. Both engines ran 11.5 on wideband (Holley on one bank, Dyno on other bank, both within.1). Pulled all the plugs, everything is firing, all look normal, no evidence of misfiring. Ignition system is the same, msd pro billet, msd 6 digital programmable (the holley is running the timing, and the msd box has everything zeroed out), new pickup in the distributor, rotor phased, new cap and rotor and wires installed, new coil installed. So far I've also checked spring pressure on the new heads, air tested the system for leaks, verified cam timing, checked compression (160 psi cranking, same as old engine) no blowby out the valve covers, no oil burning, etc. So what gives with this? Sorry for the long post. Btw the cleaner plug is from#8, we kept changing it as we were reading timing from this cylinder. #ad
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That's really odd, you have put in a larger compressor so air mass should be greater, you have done really thorough diagnostics it seems like something should have reared its head. Do you have an intercooler on the combo, if so what size is it? Did you happen to measure IAT or compressor discharge temps before and after? What is your hot side piping size and downpipe size, any muffler or cats?

 

Need to home-in on what has changed. Your post has a lot of information beyond that. At a glance it looks like you have changed cyl heads, turbos, fuel management? Has the exhaust changed? Have you checked backpressure? (After turbine should be less than 5 psi.) Turbine restriction is probably OK (slower spool) Any chance the cam timing got moved? (retarded)

 

I pulled the front of the engine apart, and verified cam timing with the degree wheel and dial indicator, it's spot on. Leakdown tested the engine, 10-15%. Car has 3" downpipes, open at the bottom, same as the old setup.

 

It has the same air/air intercooler as before, 2- 2.5" inlets, 1 3" outlet. It appears that the tbi iat is 118° on the dyno, and I think it was 80° outside air temp. Has 2 3" downpipes, that have electric cutouts at the bottom. I air tested the whole system by pulling the rockers and capping the turbo air inlets, and found air leaks At the throttle shafts, I've included a link to the video, but I don't think it's enough to create the problem, Holley is exchanging the throttle body. I even just checking valve spring pressure, 220 lbs on the seat, which is fine. A tuner pointed out that it could be loosing velocity thru the heads? Both heads are a 225 cc runner though, difference is the new set has what's called"as cast cnc porting", and flow 50 cfm more. Btw the video is with 10 psi shop air.

 

Leak down is getting up there at 15%... are the heads new, or fresh? All leaks on leak down going into crankcase? I assumed you verified ign timing going into, and in boost?

 

Any chance the fire ring got left out of one of your gates? That would account for the late spool at least.

 

Verified ignition timing, basically set the holley to 15° static, then set the distributor to 15° with a timing light. I then put it in normal timing mode, brought it up to 3k rpm, display showed 32°, and verified that with a timing light. Engine has maybe 2 hours on it, so the leakdown will probably go down, just honed and reringed it. Heads are brand new and done by weingarten, with my cam card

 

I just had them out to change springs, and verified the rings are in. I even ran the engine, and verified nothing was coming out of the dumps.

 

Also, there was no blowby coming out of the breathers with it running on the dyno, and no blowby smell driving it on the street. Btw here's the new turbo specs, my tuner is saying they are probably too big. Dyno operator just explained to me just because it reaches 14 psi by 5800 doesn't mean the power would all of a sudden just go vertical on the printout, that it's a ramp, and just doesn't climb like that? #ad

 

Sounds like one of your turbos isn't working.

 

They both spin

 

Turbos definitely are not too big. There are plenty of builds out there with about the same turbo on similar cid and head flow. There's something wrong that they're coming in so late. Check all the easy things first. Timing in boost, don't assume its correct, could be a map, or even a tune issue. Eliminate any bovs, and tape the wastegate outlets.

 

I air tested the whole system, basically pulled the rockers, capped the turbos, and pressurized the system with 10 psi shop air, only thing I found was the throttle shafts leaking on the holley, so they are going to replace it. As far as timing we kept adding 2°, and it really didn't gain. Stopped at 29° when the annealing mark was in the center of the ground strap, and the mark did move every time we added timing. Old engine gained 40 hp for every 2° we added. #ad

 

I'm running out of things to look at with this, engine is super laggy as well, driving the car out of boost it runs fine too, plenty of power, about the same as the old engine, if not even better. I even hired a remote tuner who works on Holley to tune it, and he felt it was either cam timing or turbos are too big. These also have a .96 ar, my old turbos were.63 that made 1k crankshaft hp.

 

And just did the cam timing this weekend #ad

 

There's something off. There is a 383 build on this site thats pretty similar to yours with twin p trim 70's and he needed to go to .96s to get under a 2:1 back pressure ratio. Ive seen a stockish 5.0ho spool twin 54mm p trims quicker than you are.

 

Question is where do I look next? I feel like I've exhausted all the possibilities, unless something is going on with the ignition and it's misfiring. But no evidence on the plugs of that, and nothing coming out of the exhaust. I'm getting close to just giving up on this whole deal

 

I'd start with the simple to fab/hack ideas:

Cap off WG's completely with a plate.
Cap off blow off valve with a plate.
Test the above.

Then:
Can the old turbos be retrofitted back on?


ks

 

1. Your fingers look like mine, please take better care of your body, joints, skin. Use gloves (disposable) IMO at the very least.

2. I've read most of your diagnostics and I can tell you are no stranger to this. Boost leaks will definetely screw you over so fix those leaks, and perform a full pressure test from compressor cover (pre-turbo) all the way through the engine intake manifold so ensure you are not losing air molecules.
Each air molecule that leaks creates additional exhaust gas pressure and raises EGT and throws power away.

3. Now that there are no boost leaks, examine the PCV system, pressure test the crank case (no more than 1 or 2psi max) look for something wrong with the flow there. It needs a pcv valve (check valve) on one end and the fresh air supply from a post-air filter somewhere else.... I'm pretty sure you know all that... but this is a critical step in performing a complete diagnostic.

4. You check the cam timing, ignition timing, plug strap, and so forth, good good good

5. Now you are ready for an actual diagnostic. Turn the boost all the way down to 0psi. Take the springs out of the gate if you have to or use compressor air to hold them open (on a dyno for example). See what the engine does without boost. Use a cheaper fuel if you can (93 octane). I'm not sure what the compression is or supposed to be but you may find an error there somewhere (ultra low compression or something). If not, the engine should make what you know it should make at 0psi of boost. If it does, then you add boost slowly bit by bit and keep track of where the power comes in per psi of boost. You may have a situation (with twin turbos) where one turbo is bad or not flowing properly. Or flowing 'against the grain' somehow. Kinetic energy of airflow moving through pipes should coincide with the direction of total flow, it isn't like a slow moving water flow where you can merge at any point with only slight perturbations. You may find a restriction or blockage in the intercooler plumbing for exmaple. Or a sharp corner somewhere that it should not be. You are at the stage of inspection and math, math from the engine to determine if it makes what those cubes should make, and inspection of the parts that carry the directional unit of airflow.