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.

BKbroiler

In my opinion, you might get your desired output with the new cam and heads (and a bigger carb), but I can't believe the dyno numbers from the original setup. 442 HP with a very mild cam and small heads seems a little inflated. I have a 383 with a slightly hotter cam and Vortec heads and based on 1/4 mile speed and car weight, I'm making about 350 HP.

biscuitville

Sully,
I too was a little skeptical of the numbers you showed. For what it is worth, I cranked a fascimile of your data through Desktop Dyno and the output is shown below. The caveats are that I had to make some assumptions and I am running the low-cost version of DD which doesn't allow for all of the desired inputs. This was done with the choices of a medium acceleration cam, small-tube headers/mufflers, and a high-flow dual-plane. I used the valve timing events for a 218/218 hydraulic flat cam from COMP but my version of DD doesn't allow me to input the style of cam.
Perhaps someone who has an upgraded version of DD can give you a better estimate.
AL

RPM HP TQ
2500 180 379
3000 213 374
3500 264 396
4000 316 415
4500 359 419
5000 391 411
5500 414 395
6000 420 368
6500 414 335

Sullyman

BKbroiler, Biscuitville,

Thanks for the responses. Yeah the first cam/combo seemed to small for the optimistic Hp/Tq dyno number I was provided (given the cam specs alone, and then the choice of heads). In fact your DD result was probably more acurate throughout the 4,000 rpm range, a little high on the 2500 through 3,000 range, but accurate over all. The new head/cam combo should be a lot more promising and closer, if not a bit higher, than what I was originally hoping for (450hp/450tq). I will definitely have to be more interactive with a builder as to what parts are being used to build the motor the next time I consider a build. A huge learning curve for me after the fact. Thanks for the responses.

OzzyTom

Dyno numbers supplied by any engine builder will usually be optimistic.
The big numbers sell engines, so an honest dyno result can cost a lot of sales.

That cam does seem a bit mild for the quoted results though.

Having said that, engine dyno tests do not take into consideration all the losses resulting from running an alternator, power steering, mechanical fan, and full exhaust. All these items consume real world power. Some engine dyno runs are done with an electric water pump too, to minimise losses.
Then there's the driveline losses too. Auto trans is worse than manual trans, so a fair wack of power is just converted to heat energy rather than driving the rear wheels. Uni-joints also have losses, and with the IRS setup we have in Vettes, there's a few horses lost there too.


Before you do any further mods, it pays to get your car on a chassis dyno to establish what you are actually getting at the rear wheels now.
My "475hp" crate engine managed 340 real horses at the rear wheels, so either there's 30% losses in my setup (which is a tad high with manual trans) or I have a tuning issue, or the real flywheel power output is more likely to be about 425hp.

But numbers can be deceiving.
Real world, butt cheek quivering, adrenaline rushing acceleration is what we are after.
I have found my Nirvana with road cars occurs if I have at least 200 real rwhp / ton

Your selection of components seem to be on the right track for what you want. Reasonable daily driver with some real get up and go.
Just for comparison, my cam timing is 242/240 @50 with 0.594" lift and 112 LSA.
With the 3.36 diff gears I originally had, it was NOT good around town.
Replaced the diff with 3.73 gears and the character has changed immensely. Car is a pleasure to drive now. I can crawl around and short shift and use the available torque from about 1200 rpm, pulling without issue... or drop the clutch with a few rpm, and fill the street with smoke through 1st and 2nd and get a nice "chirp" going into 3rd. The motor pulls exceptionally hard from 3000 to 6000, and the Tremec gearing fits very well, with each change at near redline dropping straight into the peak torque point.

Your choice of the 230/230 cam timing is good for a strong street motor. It should provide better manners than mine around town.
The AFR heads are certainly the way to go too.

All the best in what you decide to do, but like I said above.... get a rear wheel dyno report now so you can establish what real gains you get with any further mods.
If you can get to a track and pull some 1/4 mile times (and trap speeds), it would also give you the baseline info you need to establish the gains with further mods.

cheers

Sullyman

OzzyTom,

Brought the car to a dyno chassis before the current changes. While on the chassis dyno it threw the driveshaft (wasn't there for the runs and it was not video recorded - I was out of town for work when it was done). They did not capture the dyno data, expect for on the partial run where it threw the driveshaft. The driveshaft retaining straps were sheared off at the rear differential yoke, indicating a sudden stoppage issue. Cracked the aluminum case and aluminum tailshaft housing on the brand new TKO600 transmission, took out the brand new driveshaft and left into question what it might have done to the rear end. Had to have the rear end checkout (did not cause the sudden stoppage). Had the rearend totally rebuilt because I did not know what the sudden stoppage might have done to it. Had to have the transmission recased. Had to have a new driveshaft made. Had to put in a new clutch setup. The throwout bearing was broke (suspect it was the throw out bearing that cause the sudden stoppage but cannot say for 100% certain it was) and the clutch and pressure plate which had about 100 miles on them, looked like they had 80,000 to 90,000 miles on them. So short story long, Chassis Dyno business said it wasn't their fault. The Transmission, clutch/throwout bearing/driveshaft supplier said it wasn't their fault. So my Chassis Dyno experience cost me about $2,500.00 in replacement parts/labor costs, and a whole lot of my own hours disassembling, fixing and re-assembling the car. Won't be trying another run at a Chassis Dyno. Once bitten, twice shy they say.

Have two new GM trucks (one personal, one for work) rated at 402 hp /423 tq (of course newer GM LS based series engines), much heavier than my car and they both pull harder under acceleration than my supposedly 442 hp/448 tq 383 in a much lighter car. Some could say that is comparing apples to oranges, but I have also owned a 04 Z06 Corvette, 2001 SS Camaro, 1999 Camaro, 1977 Corvette, 81 Trans Am as well as other muscle cars. So I have an idea about how a car should feel under acceleraton with that type of horsepower and it just doesn't pull as hard as it should for those numbers 442hp/448tq. Car is a complete ground up resto and all aspects of performance were addressed (i.e. suspension/chassis, engine/transmission, brakes, steering, larger modern tires/wheels, etc). Feel that the first head/cam combo fell short of the 422hp/448tw engine dyno numbers I was provided by the builder. Feel new head/cam/EFI combo will easily surpass those numbers . Want to make sure the car is done right (It has been quite a nightmare of a build, what could go wrong has gone wrong it seems, but to far into it (my time & money) to just give up).

Thanks for taking the time to respond.
Sully

DRIVESHAFT

Your proposed new combo should easily make the power your looking for.
I bet that you could meet your goal with only a cam change to your current combo.

OzzyTom

That's a terrible experience.
I can understand your reluctance to use a dyno....

Good luck with your future mods.

gkull

The first thing I would say is that they are NOT reputable

They didn't know what they are doing! Cam and piston choices show that they don't even understand how to build a stroker motor.

Hyper pistons are feet per second limited. The reason I know is because i had some smear 20 years ago in a 355 ci. So i called Keith Black techs and they confirmed that they are low er rpm non hot rod pistons made for production rebuilts with some better properties than cast pistons. So a stroker motor would be even worse because the feet per second of piston speed would be achived at a lower rpm. look up some articles on piston feet per second.

My first 383 build I used a 232/238 112 LSA crane solid roller with 1.6 RR's I also had bigger heads than you and I found it to be kind of mild. Smaller heads like yours would require more duration to get the same amount of cylinder filling. I went with about 4 more degrees on each and about .640 lift and it was a wonderful machine with my TKO 600 and 4.11 rear gears


ICL and LSA have nothing to do with each other. Most often the numbers might be the same but they are different references. ICL (intake center line) is the spot where the cam is matched dot to dot with the crank when the #1 piston is at Top Dead Center (TDC). LSA (Lobe Separation Angle) is just that, the number of degrees the peak of the intake lobe is from the peak of the exhaust lobe, it has nothing to do with the advance of the cam.

Roller cams create higher vacuum than flat lifter cams of the same duration. Advancing a cam will cause more intake reversion/choppier idle/less vacuum. I personally run or should say even ground 4 degrees retarded compared to the equivolent Comp Cam.