It is going to vary among this type of dyno, so it would be hard to give a finite number. For a stock 71 engine around 300 hp is a ball park figure.
http://musclecars.howstuffworks.com/classic-muscle-cars/1971-buick-gs-455.htm GM "rated" horsepower for '71 (standard) was 315, Stage One was only 345. Keep in mind that this is GROSS horsepower, not measured at the rear wheels. 72 "net horsepower" tumbled to 250, and 270 for the S1. Net horsepower ratings supposedly reflected the "as installed" condition of the engine, but in fact were still on the high side. Rear wheel horsepower? I suppose about 225, 240, something like that. Depends on exhaust, transmission, intake air temp, etc.
That is what i was thinking ... The dyno shop used dynojet dyno and sae mode i got 271 hp and 360 tq .... was thinking it shold be more .. But i have 20" wheels on the car and the motor is in the caddy o No:
Stock engine? I think it's a miracle that you got 271. I am suspicious about the correction factors used.
He said standard mode would read more .. but he did real number it has couple things msd ignition ta212 cam holley 870 cfm carb edelbrock intake b-4b I will post the chart
SAE 1.03 and 1.04. That is a huge correction factor! In other words, they are correcting up 3-4% from what they actually measured. So take 3 percent from the corrected number and that is what the dyno actually saw.
What they are calling SAE, is actually what we call racers correction. SAE CORFAC is J1349 or 29.23 baro, and 77degf inlet air STD CORFC is J 607 or 29.92 baro, and 60degf inlet air If the dyno operator had the inlet air @ 100 degf, then you will get an increase in correction factor. When dynoing an engine you want the conditions to be as close to the Correcting baro, and inlet air temp. Most race shops won't even run a comparison dyno run if the barometer is not close to the correcting value.
Thank you for the explanation so did the car dyno 3% more than shown or less ? This is my first dyno ever sorry
Well... technically it made 3% less than What is indicated. Do you live @ sea level? What does your barometer read on a high pressure day? I live in Michigan, and we are @ sea level. So on a perfect day(rarely seen lol) when I dyno an engine my correction factor is 1.0 in other words I would multiply the indicated power by 1.
Dyno, just for the sake of argument the way you're talking then there must be a lot of shops that don't use their dynos much and turn work away if the weather conditions just aren't right. Or if you live in the Rockies or in the desert or way up north. You said it yourself there rarely is a perfect day. My understanding of the correction factor is it allows readings taken on 2 different days(or even time of day) and allows them to be comparable. It makes a level playing field even if you were to go to another dyno. (I do know however that even dynos of the same brand and model can vary their numbers let alone different brand dynos in different locations.) It does give some numbers that are fairly comparable. I could see how different conditions can cause the tune of the engine to change so that would have to be accounted for, say richer or leaner jetting, for more precise readings. I've had my car on the chassis dyno a few times after making changes and I feel that the changes in the HP/TQ numbers can at least give you an idea if you're going in the right direction and how much you've moved. For my use I'm not looking to see what happens when I make small changes such as changing port shape or even a minor jet change. I'll save that for the track days. I have swapped carbs, rocker arms, fans, carb spacers and a few other things on the same day and between days I've changed engines, cams, heads and a few other things. One piece of advice I'd give is if you're making changes to the car to see what they are worth stick with the same dyno to at least keep that part of the playing field level. Out in California you may be able to keep the weather conditions generally the same when you go but out here in PA I've been on the dyno with correction factors on both sides of 1 which could skew the numers a little. Use the numbers they give you and forget about the uncorrected numbers unless you're running some sort of Stocker class car where every last bit of tuning helps. I would say the 271 is suprisingly high for a low compression engine and the torque is very good. Are you sure it has stock compression? Off the top of my head in my early runs I got around 320 HP and that put my 4250 lb '76 Century solidly into the 12's. If you can hook it up, and depending on weight and driveline(converter/gears) you could have a car that goes well into the 13's which is nothing to sneeze about for a "modified stocker". Final piece of advice. Put out of your mind all the big HP stories you hear about or read about in the car mags. You run your race and let them run theirs. The track numbers are the final say.
Good grief, truer words were never spoken. Even under ideal conditions, the ratings advertised to the public were crap. Here's a document from the inside, some '67 Buick 430 engine test results as Buick did them. The public saw 360 hp on paper back in the day, here's what the engineers saw with few accessories, and without marketing folks to blind them: Buick 430 Dyno results Devon
I had my 71 gs 455 4 speed on the dyno about 6 years ago completly stock 80000 miles it made 221 hp on the dyno I dont remember the torq glen
I am not sure what the compression is; I have 170 in my cylinders i think it is 1971 455 block and now I have it in my 1961 cadillac
Sounds like the compression is bumped up some. Sounds pretty high for a '71. Did you buy the engine as it is now? Maybe some Speed Pro pistons are in there. Never hurts to have higher compression for extra power.
