Sullyman

I know this dosen't engine question doesn't pertain to my Corvette, however it is a SBC in my 1971 Camaro and I figured seeing as how it's a SBC you good folks on Corvette Forum would be able to provided the same input about the engine regardless of whether it's in a Corvette or Camaro.

I recently had a SBC 383 built by a local reputable engine builder. Builder chose all below listed components (went with his expertise). Wanted somewhere in the neighborhood of 450hp/450tq. Engine specs. are as follows:

1987 or newer hydraulic roller block.
.bored 4.040”, stroke 3.750”, rods 5.700”
Scat 9000 series crank
Speed Pro dished (12 cc) 9.7.1 hypereutectic pistons
Approximately 10.3 to 10.5 compression ratio (I don’t know specifics about deck height, head gasket thickness, so I am assuming 10.3 to 10.5 – have had no detonation issues running the motor on 87 to 91 octane)

Hydraulic roller cam
Cam specs (Manufacturer is Delta Cams, a local area cam company utilized by builder):
109 LSA
217/217 @ .50 advertised duration
.464/.464 advertised max lift

Pro Comp 190cc heads (aluminum)
64 cc combustion chambers
2.02 intake/1.60 exhaust
Straight plugs
Comp cams 981-16 single springs (1.254 OD)

Pro Comp 1.5 roller rockers

Headers: 1-¾ full length 3” collectors – 2 ½ dual exhaust, x-pipe, 40 series flowmasters

Holley 660 Avenger carb.

Edelbrock Performer Air Gap intake (dual plane)

MSD pro-billet (mechanical advance) distributor, 6A box and Blaster 2 coil. 17 degrees initial timing, 36 degrees total advance.

TKO600 5-speed manual transmission

3.42 ratio rear end

Engine was dyno’ed by builder (1-5/8 headers used by builder) and here are posted results:

Avg. cf = 1.152, fuel s.g. = .730, Barometric = 26.34, Relative Humidity = 33.4%, Inertia factor = .4000

RPM Torque (Ctorq) BHP (CBHP) - (taken at flywheel)
2000 355 135
2500 372 177
3000 388 222
3500 425 283
4000 443 337
4500 447 383
4900 448 (peak) 418
5000 447 425
5500 422 442 (peak)

First question is. Do these dyno results seem accurate or inflated? Seat of the pants driving seems a bit weak for these numbers (car is approximately 3500-3600 pounds). Car (71 Camaro) doesn’t seem to pull as hard as it should (complete suspension rebuild, new shocks, Hotchkis springs front and rear, car lowered 1-1/2 ", bushing, etc. so no hooking up problems ). Power comes in from about 3500 up to about 5400 RPM. Carb, timing, etc. have all been tuned using Wideband O2 sensor. Crisp throttle response, solid idle at 650 rpm, no low end vacuum issues (running dual diaphragm for 4 disc power brake set up), is factory a/c car, no idle issues with a/c on. Primary use for the car will be a daily driver.

Not totally happy with end horsepower/torque performance. Felt horsepower/torque was left on the table. Wanted to go to electronic fuel injection. So made some changes.

Just purchased Holley HP MPFI electronic fuel injection (single plane intake, 1000 cfm throttle body, 36 lbs injectors). Timing will be controlled through ECM. New MSD computer controlled distributor (small cap GM). Went with a Rick’s gas tank, with a in the tank fuel pump (Walbro 255lph fuel pump), so fuel starvation should not be an issue.

Researched cams specs and found that 109 LSA cam was not the best LSA selction for EFI (although was advised by Holley tech that with new HP programmable system 109 LSA was doable).

Researched better head/cam combos over the internet (on this forum, nastyz28 forum, pro-touring forum, Hotrodders forum, chevytalk forum, Chevelle forum, etc.). Talked with several cam and head manufacture technical reps. Was looking for more horsepower/torque/rpm plus decent street manners as car will be used most times as a daily driver. I decided to make changes to the motor top end. Based upon research from the above listed forums and input from the cam and head tech reps., here is what I ended up purchasing.

AFR 195 heads – 65 cc combustion chamber, 2.02/1.60 valves and AFR 8017 dual springs (which match cam maker’s spring requirements for cam specifications).

Custom grind Comp Cams 286HR (hydraulic roller), small base circle with 113 LSA (4 degrees advanced) rather than 110 LSA (was concerned about low vacuum /idle issues with 110 LSA. I’m hoping 113 LSA will provide a solid idle and decent vacuum at idle (approximately 850 RPM) for brakes and EFI).
230/230 @.50
565/565 max lift

Felt I could get a lot more low end torque (hoping for at least 70 ft/lbs) at 2,000 rpm with this head/cam combination (over original above listed head/cam combo) and more torque and hp all the way up through 6,000 rpm. I know 113 LSA will lessen peak torque and most likely peak horsepower, but should provide a broader torque curve. I am willing to give up some peak horsepower and torque for good low-end drivability.

So other questions are. What type of horsepower and torque do you think I will see (ball park figure of course) with this AFR head/286HR cam/EFI combo? I am hoping for at least 450-460 hp and 470 plus torque (at flywheel). What type of low end idle/vacuum quality? Fuel mileage?

Thanks for your responses.

yellovettedean

I built a 383 full solid roller from a very reputable builder and was told no way his dyno would show magazine type numbers. The engine I had built was almost exact copy from chevy hi performance. My numbers 464HP/6100RPM 446TQ/4100RPM 10% under magazine numbers. Another customer built AFR spec 500+HP same results 10% under their claim. I would think your numbers are inflated. My engine is very powerful. For example my brothers '99 frc vette(stock except better air intake) in street race with my 75' vette w/ 3.08 rear gear and 2.64 1st gear( under geared ) when I hit second gear it was like his car was going in reverse. For engine specs see C3 for sale " May sell 75 coupe "
Dean