I've owned my stock 427/390 for over 20 yrs and trust me... these things were not dogs unless something was messed up. Could be your quadrajet. Fantastic carb if it's set up right. But they're not as simple as a Holley. Make sure it was rebuilt by someone who understands qjets. Then I'd check something simple... make sure the cam is in proper rotational alignment to the crank. Amazingly, ours was off by one sprocket tooth. Dumb things do happen.
I'm assuming you've talked to the shop who charged you $9k for the work. If not, do it. You are not making an appropriate amount of power, bottom line. Something's wrong. A reputable shop will not be any happier with the results than you are.
Yup, we all know about parasitic losses. But come on... 40%? No. Not unless your brake discs were glowing orange after the dyno run.
So... take heart. The L36 is a sweet engine. Mine's nearing completion of a rebuild right now. Will be installed probably this week. Up until a few years ago the car really pulled hard, across a wide rev band. It was a blast. Looking fwd to having that back. I plan to get it on a dyno after a few hundred miles. But, that'll be a while yet.
Good luck-

 

What type of chassis dyno was it on, do you know? In general, DynoJet brand usually reads fairly highly, where as brands like Dyno Dynamics and Mustang for the most part read lower. They can always be tweaked but from what I've seen, that's the consensus. It's hard to tell from your printout though... Maybe Dyno Dynamics?

 

Sounds like dyno tuning will identify just how much you can get out of that set up. Or you could just drop a procharger in and see what you get...

 

I'm say pure stock LT1 and L-36

You can warm up anything. but that is not an apples to apples comparison. I had a 12.38 355 in my 79 Vette. It was fun. At the all Vette drags in Sacramento I was always in the second fastest run group. I was way out in front of the lower powered big blocks and the majority of under 360 ci small blocks. They are not the animals that the solid lifter big blocks were.

 

Pro Charged 78.....432 rwhp....435 rwtq....was there and took this vid...

 

How many of these small shop dyno gizmos actually calibrate their equipment? You might ask the shop where you got yours tested that question. The first thing I would check is to see if the carb is really opening up all the way when you push the accelerator pedal to the floor [being able to open it fully with your hand on the linkage doesn't mean a thing]. You would be surprised how much of a problem this really is. If that is not your problem, it's in the carb and/or distributor....or in a faulty build of the engine.

 

I appreciate all the input. I'll check the carb tonight, for sure.

I appreciate that all dynoes are different and are typically just good for comparison when changes are made. but I wanted to make sure that I didn't have unrealistic expectations.

The engine was rebuilt up in New England by the previous owner. I only have the invoice for the engine work and all the parts.

 

Have you driven this thing yet? What happens when you hammer the gas? Does it drive like a POS or does it want to break the tires loose all the time - should be easy w/ a 4 speed regardless I guess.

You should be sideways six ways from Sunday with that set up and a 4-Speed... right?

 

Set the timing at 38 degrees of total advance, richen up the carb so you are at or near 12.8-13.0 and then see what you get. Timing is a big thing on big blocks, take the air filter off for the dyno run so that you can verify that the secondaries are opening all the way. Put some 94 sunoco in it or mix that with 25% 110, YOU DO NOT WANT IT TO DETONATE ON THE DYNO. It should be close to or over 300 hp and tourque close to 375. Timing and carburation are the answer to big dyno numbers. I have gained 25 hp in jetting the carb. Do not be so concerned with the numbers, make changes and see what you gain, always go back to the same dyno.

 

Don't forget that HP numbers from 69 were not the same as we see them today. See this quote from Wikipedia:

"SAE gross horsepower
Prior to the 1972 model year American automakers rated their engines in terms of SAE gross horsepower (defined under SAE standards J245 and J1995). Gross hp was measured using a blueprinted test engine running on a stand without accessories, air cleaner, mufflers, or emissions control devices and sometimes fitted with long tube "test headers" in lieu of the OEM exhaust manifolds. The atmospheric correction standard (e.g. barometric pressure, humidity and temperature) that was utilized in obtaining the Gross ratings was more idealistic than that which is used under the SAE net rating system. The resulting Gross power (and torque) figures therefore reflected a maximum, theoretical value and not the power of an installed engine in a street car. Gross horsepower figures were also subject to considerable adjustment by the manufacturer's advertising and marketing staff under the direction of product managers. The power ratings of mass-market engines were often exaggerated beyond their actual Gross output, while those of the highest-performance muscle car engines often tended to be closer in actual output to their advertised, Gross ratings. It should be noted that no pre-1972 "muscle car" engine in its unaltered, production line stock form and in its as "as installed" (SAE net) condition has ever yielded documented, qualified third party validated power figures that equal or exceed its original Gross rating. Claims that such engines were "under-rated" are therefore highly dubious. It is therefore more accurate to say that the ratings of the highest performance engines from that period tended to be less exaggerated than those of more typical passenger cars, but still exaggerated relative to what could be obtained in the SAE net configuration. For example, the ultra-rare and exotic 1969 427 ZL1 Chevy (rated @ 430 Gross HP) is frequently cited as one of the most "under-rated" high performance engines from that period, yet it could only produce 376 SAE NET HP. [5] It should be noted that today's various "Stock" drag racing events (e.g. "Pure Stock Drags" and the "Certified Stock" sub-grouping) allow the engines to be fully blueprinted per NHRA technical bulletins, which yields ideal tolerances and can increase actual compression ratio by more than 2 full points. These series also permit various other performance-enhancing alterations (e.g. over-bores, wide-flank cams, forged internals, stiffer valve springs, adjustable push-rods and poly-locks for optimal valve train geometry, modern exhaust systems with mandrel bent, 2.5 inches (64 mm) pipes and low restriction mufflers, fully locked differentials, etc.). Therefore, the results achieved in those events often don't reflect the performance potential (or engine output) of the car in its original, unaltered and production-line stock form."

The numbers I saw on the dyno corresponded pretty well with my 1/4 mile speed of 100MPH and were also close to what Desktop Dyno said. DD also said I could gain a quick 100HP with headers and a slight port job on the heads.

Ken

 

This is very, very close to my 69 427/390 stocker.
Interesting thing about the af ratio. My q-jet was running a little rich, and when it was leaned out to the theorically correct af ratio, my performance went down, so we put the origional rods back in.
But you have a much bigger cam, etc then I do, so, yes, something is not right.

 

One thing to check is if they changed compression ratio on the rebuild. It was very common that pepole dropped the CR on their Vettes as gasoline octane dropped and leaded gasoline was discontinued for sale at the pump. Stock CR on those cars wasn't too pump gas friendly, so people would either install heads with bigger chambers or dished pistons. Lower compression (for example from 11:1 to 8.5:1) will significantly drop power..

 

I use a G-tech and MEASURED weights to check RWHP and think your numbers are what you would expect.

The following are G-tech results:

Stock '69 350-300 gross 170 RWHP
Stock '63 327-300 gross 165 RWHP
Stock '93 350-300 net 195 RWHP
Stock '04 505-500 net 414 RWHP (Viper SRT-10)
Heavily Modded 355 320 RWHP (My '69 Corvette)
Near Stock 427 L-88 345 RWHP (Taranchala Manifold, Headers)
1991 ZR-1 350-375 net 313 RWHP
2002 270 net Trailblazer 180 RWHP

These were all run using the same technique.

The G-tech was calibrated for each run (read 1 G when held vertically).

I believe that most Dynos are set up to give people the big numbers they like to hear.

 

I dont know what q-jet you are running but a lot of them from the factory do not open all the way, you have to adjust it. I had a 427 with 9to1 pistons running a 292 comp cam with 66 bath tub heads and a predator in my 70 nova and ran 11.90 with it. guess what I am saying is low comp smaller cam 427s will run hard.

 

HP sells cars, torque wins races.

 

I hear what posters are saying about stock bb numbers, but those numbers of steves still look a little low for the build he has.
Torque is certainly strong, from down low.... but could be higher IMO.

I'd be replacing those stock manifolds and getting a decent set of free flowing headers and exhaust, and with a proper carb and timing tune, I think steve will pass 300 rwhp easily.

I've got over 300 rwhp and 350 lb-ft in a small block, so I'm sure there's more horses in Steve's big block motor looking to be released.

cheers
tom

 

-Especially on the early 1969 accelerator linkage... terrible design... my carb was opening about 50% of the way and I never knew it due to flex in the pedal lever. Eventually pieced together the later design with the solid pedal lever assembly. It's still not perfect, but 1000 times better (opens 95% of the way now).

 

Besides what everyone else mentioned...what's under those sidepipe covers. Anything stock sure isn't helping matters!


Check those piston numbers and maybe we can get an idea of compression ratio. Are heads closed chamber or did someone install opens?


JIM

 

Looking at the engine bay, you are running all mech. accessories..

Here's my guess:

Original output: 390 flywheel HP

1) mech. fans - 12+ RWHP
2) mech. water pump - 7 RWHP
3) mech fuel pump - 5 RWHP
4) stock exhaust manifolds and stock exhaust - 45 RWHP
5) drivetrain - 15% -60 HP
6) lack of tuning - 30 HP

Total power after accessories, drivetrain and lack of tuning:

231 HP

After tuning:

261 RWHP
after going to electric fans:
273 RWHP
after electric fuel pump
278 RWHP

 

Cannot find anything on the engine build sheet about the compression ratio.

For the pistons, it lists F/M L2300F30 forged, for $548.
Q-Jet jets .073
Hyd Lifters
CC Heads cut to 106.6/108.4
Camshaft Degree 106 LC
Resurface head cut for 103cc 1-.018/1-.027

Not sure what all that means, sorry for my ignorance.

Seems like I'm in a quandry. I like the mostly stock look (yes, the sidepipes are stock too, the expensive ones) but didn't realize the huge power loss by keeping it this way.

I didn't buy it to race but do enjoy the torque it has. What's a man to do? LOL