Now I know for real, that what the acceleration sensor in my butt sensed is about right. I had my 455 Buick on the Dyno and max horsepower peaked at 215 PS which is somewhat equal to HP. If I take the 360 gross hp and deduct 20% I end up with about 290 net hp, so I am 75 ponys short. I do know only a little about the engine, as I did not built it on my own. The previous owner stated, that the heads do have the big valves and that the cam is Stage 1 also. It has a performer IM and a 69 Quadrajet, which I did rebuild and modified per the advice from Ken. The exhaust manifolds are stock and the pipes are 2.5" Ignition is converted, but no race stuff Timing is set according to the Larry-bible to 44° incl. mech and vac How would you go about in order to get the horses back? Any easy checks or fixes which you could recommend?
You deducted 20% to convert from the gross to the net standard? Did you then deduct another 20% off the 290 hp to account for drive train loses to the wheels?
I have even less power at the wheels. The 215 number is already calculated back considering the drivetrain losses.
Chassis dynos can be off. Run it in a quarter mile. The mph along with the weight will enable you to calculate the horsepower. Camshaft degreed when installed?
The compression is probably pretty low,..and if the heads were converted to the 2.125/1.75 valves and done incorrectly they only hurt performance
I had a ported set of small valves converted to big, heads ran pretty darn good for what they were, after getting them back, car ran 1/2 a second slower. Ends up the shop that knew what there doing took a bowl hog and ran it through and opened stuff up, valves fit, but the totally destroyed the short turn and made the heads paper weight
If the carburetor, and ignition timing is right, then the engine combination of parts isn't producing what you want. Without knowing what the true static compression is, what cam you are running, and how the heads actually flow, it's hard to say. Checking to see that you actually have full throttle when the gas pedal is matted is a good idea. Beyond that, you'll need to pull it apart and see what you actually have. What the PO told you might or might not be true.
Thanks for all your replies, I guess I was mostly looking for some comfort from you guys Throttle opens completely. Dragstrips are not common here, so I need to carry out the acceleration test with an external GPS receiver and an app on my smartphone. Not sure how precise that will be. I will do another run on a different dyno, but my hope is limited that this will bring back the power. I guess I will do the walk and check things out one after the other. Will start with a compression test and take a peak into the cylinders thru the hole for the ignition plug to try to get an impression about the size of the valves
44 total timing , or 44 total with vacuum advance? If not with vacuum advance it sounds high for those heads and there chamber shape and the piston speed of a 455 motor. What's the motors hot cranking compression at?
44 is total, including mechanical and vacuum. Did the 1/4 mile couple of times. Best result was 16,79 seconds and 86mph. Thats about 152kW = 207 HP, so the dyno result is not that far off. I scheduled another dyno run for Thursday next week. What is typical gas milage? I get about 8 miles per gallon.
That is pitiful for a 455. Something is very wrong. Without knowing actual static compression and cam, it's hard to say. Gas mileage should be 11 or 12 MPG depending on rear gear.
Never mind the size of the valves. It doesn’t matter for your build. What is your total timing at with the vacuum advance hose removed and plugged? What rpm is it “all in” at?
Correct at WOT there is no additional timing from vacuum advance......there should be 0 vacuum under full throttle.......so if you vacuum is giving say 20 degrees advance your motor at wide open would be only 24.........that would ge an issue
If the Carb jetting is in the ball park then that terrible gas milage points to a cylinder pressure issue which can then point to the Cam being in wrong if it's not just plain too big for your static compression to begin with.
The car is a Stage 1 tribute. I installed a TH200-4R this year, along with a 3.23 posi 8.5. The timing is set so, that I see the 44° at about 3000 1/min, when the mechanical is already maxed out. Thats how I understood the recommendation from Larry in the timing thread. Maybe I misunderstood something? Don't have a compression tester, so I will order one. Will do a crank-test and a hot test. Will post the results here. There is probable no easy way to tell about the calmshaft, right? What I probably will do, is to measure the circumference of the balancer, using a stripe of paper or tape, puting a 360° scale on it and tape it on the balancer. When turning the crank, I will watch the valves opening and closing and note the respective °-numbers. Does that sound like a plan to you guys?
