I just bought my 68 bird about 2 months ago. The car ran really sluggish so i finally took it to get dyno tuned. Base hp was 117hp and after carb adjusting and timing it went up to 167hp. Now my question is what the hel l i thought these 400 were pushing at least 300hp. Its a stock 400 with an edelbrock performer intake and a holley 650 heres a pic of my bird
For one the factory rated hp was gross hp in most cases. That means it was measured at the flywheel with no accessories. Add all you accessories and drive train losses and gap difference isn't so big.
Next we need to know more info about your motor. What heads? What Cam? What transmission? What gears? Has the motor ever been rebuilt?
What was changed on the dyno? Any carb re-jetting? Any changes to the timing/advance curve? Is it still sluggish after the dyno tune.
Yes, a nice looking car. Don't get too caught up in the numbers. If you get your car to perform the way you like, that's what counts. People are always asking me how much horse power my car has, I usually tell them I don't know or who cares- it goes like stink. I do know exactly what the engine puts out, but I don't know what goes to the rear wheels. The 1968 Pontiac service manual has three listed for V8 four barrel Firebird: 400 Firebird 330 at 4800 rpm; 400 HO Firebird 335 at 5000 rpm; 400 Ramair Firebird 335 at 5300 rpm.
The more important number is the torque, that is rated at 430 pounds feet at 3300 to 3600 rpm. You have over 400 lb/ft at a relatively low rpm That's what burns the tires off. On the street, better to have high torque at low rpm than high HP at higher rpm.
I wouldn't change out the intake or carb you have, they should both give you good performance, just as the stock intake and Q-jet would.
As Rohrt says, the HP output numbers are at the flywheel taken on an engine dyno. No alternator, engine fan, engine water pump, power steering etc. The difference in HP from an engine dyno to a rear wheel dyno can be from 15-30%. Don't worry, I'm sure your engine has over 300 HP at the flywheel, but like I said it's just a number. How it performs is what's important.
1968 400 Coupe, verdoro green, black vinyl top 1968 400 Convertible, verdoro green, black top 1971 Trans Am, cameo white, auto 1970 Buick Skylark Custom Convertible 350-4(driver)
First off are you sure it's a 400? Second, if you can burn rubber you probably have more hp than that. Can you post the dyno sheet? Was it a Mustang dyno? What as the torque number? The first 400 I had run was stock with a little cam and it came in at 298hp/360tq@5000ft elevation on a dynojet machine. Should be about average numbers. Best I could get out of it was 14.4 in the 1/4. You won't get as good of numbers from a Mustang as you will from a dynojet.
I wouldn't go by the numbers that dyno's spit out. Quarter mile ET and MPH are the closest to reality you will get. There are a lot of snake oil salesman out there.
Easiest way to do that is with more cubic inches. A good 455 or non "557" 400 block stroker, with 6x heads will make 400hp /500ft lbs of torque, easily.
And there are probably a few guys who can build one for you, slightly cheaper. And there are LOTS of guys who will build you one for a much higher price.
OK what are some "Budget friendly" power gain mods ?
Originally Posted By oldskool
"...i want this thing to run like a beast.."
Easiest way to do that is with more cubic inches. A good 455 or non "557" 400 block stroker, with 6x heads will make 400hp /500ft lbs of torque, easily.
And there are probably a few guys who can build one for you, slightly cheaper. And there are LOTS of guys who will build you one for a much higher price.
"Budget Friendly"? Depends on what your budget can withstand. Cam, headers, carburetor and distributor are the featured players. But remember things will always expose the weakest link. Upgrade one thing and something else will fail. At least that's been my limited experience.
Sounds like you're happy with the way it runs after the dyno tune but not happy with the numbers. If the number was 325 horses would you still want more performance?
I took my engine to Mid-Island machine shop to dyno tune after I built it. The guys there told me they don't sell horsepower, when I asked them what they meant by that, they said they calibrate their dyno to give as close to real numbers as possible. One of the flat track racers from Victoria took his engine to a shop with the exact same dyno, after running there he took the engine to Mid-Island, the output was 15% lower at Mid -island. Same engine, same dyno, different calibration. They could have calibrated theirs to get me a higher number. I wasn't there to prove I could build and get great numbers, just to break in and tune. A dyno sheet with high HP numbers may be handy when it comes time to sell, but it doesn't really mean anything, it's how the car performs that counts.
One cannot plan or start modifications for more power until you know what you have now. That engine is 47 years old, unless you've owned it since new you don't know what's inside. If you're determined to overhaul or rebuild yours to get more power, you'll have to pull it out of the car, dismantle, measure every component and all clearances. Then you know what you have and what you will need to get the power output you are looking for. A few manufacturers boast [fill in the blank] more horsepower right out of the box, for their heads, cams, carbs etc.. But a high flowing head won't do you much good if you have deep dish pistons with a huge deck height and a smog cam. But if you're happy with the way it runs now, save the money for gas and drive it.
l i thought these 400 were pushing at least 300hp. Its a stock 400 with an edelbrock performer intake and a holley 650 
power gain mods ? 
