Power loss questions BBC

[Orr89rocz]

Got a 555 BBC built to be a turbo motor but currently running natural aspirated for initial tune and break in/etc

So i know the power numbers are down from what normally would be optimized but curious your thoughts on this. Power seems lower than I expected but maybe i should not be concerned?


Basics: 4.56 x 4.25. its 10:1 comp on e85. Solid roller relatively milder lobe intake 267 at .050. 183 at .200. .770’s net lift with rocker. 272 exh .730 net lift. 114 lsa in on a 111 icl
Super victor tall deck efi intake. Very mildly ported/cleaned up. Wilson 4500 cast elbow and 102mm throttle
Heads are dart 345 pro 1’s with a cnc program that flows 425 at .800. 359 at .500”. Exhaust 304 at .800 265 at .500
2 1/8 header 26-28” long except cyl 7 and 8 at 20-21”. 3.5” collector but due to chassi ground clearance it quickly tapers to 3” in 7-8” and into dual 3” pipes out back bumper
Thick ring package no vacuum pump

Th400 with tight converter for turbo
Its got mechanical water pump, alternator and power steering, belt drive fuel pump

Car only dyno’d 475 whp but i didnt really mess with air fuel to much. It was 12.5 afr on e85. 36-37 deg made best power. It only peaked at like 5900-6000.

Now i figured 750 flywheel easily which guessing 550-600 whp. Now heres my concerns/questions

1: seeing 92-93 kpa on map at wot. Thats near 2-2.25” Hg vacuum. Throttle is small but wont matter for turbo. How much could that be killing power? 10-20 hp? More? Less?

2: cam being installed somewhat late. Most cams seem to want to be 108-110 lsa in on 106-108. Would that be killing a good bit of power?

3”. Small collector size being 3.5 for only few inches going into long 3” full exhaust. I’m sure dropping this would yield some.

4: peak of 6000 rpm seems way low. Figured closer to 6300-6500. Combination of intake restriction and exhaust be pulling this down some?

So potentially i should have seen closer to 550 or so if more optimized for na in this current state?

[WeingartnerRacing]

The small throttle is still going to be an issue with boost. It doesn’t become less restrictive because more air is trying to go in. Your just going to make the turbos work harder.

[Orr89rocz]

The small throttle is still going to be an issue with boost. It doesn’t become less restrictive because more air is trying to go in. Your just going to make the turbos work harder.

They wont be working too much harder tho. I doubt the difference would be much more than 1-2 psi of boost. I’ve run 1400 hp thru a single 3” ls throttle just fine. Air density at those conditions, the cfm value isnt much different, 30 psi 130 degf roughly 683 cfm.

Street strip fun car so not setting world on fire. The cost to go 123 mm throttle and elbow is alot more

[PRH]

No answer for you, but a couple of examples.......
Procharged not turbo.

461 with basically ootb rect port RPM heads, hyd roller, headers....... dyno right at about 500hp with regular carb, no boost.
Install blow through carb, install bonnet and blower belt, 775hp.

496 with bowl blended factory iron rect port heads, solid roller(don’t remember specs...... low 260’s iirc).
No blower, 1050 carb 600hp........ with blower and intercooler, 920hp.

Both ran about 10psi.

[Orr89rocz]

Basically it seems motor makes more like 625-650 hp flywheel when i would have guessed 750. Injector duty cycle seems to agree more towards 650-700... but idk what bsfc to use. If its down a 100 due to exhaust, intake vacuum, and cam timing, i would understand