I've been seeing a lot of Nailhead posts lately and wanted to join in. After re-rebuiling my Nailhead, I got it on the dyno. Stock air cleaner, stock cam, stock exhuast (single), stock carb. After going through a THM400 (ST400) and two driveshafts, I ended up at 200 HP and 300 FT LBS of torque. I'm happy. Smiles per gallon.
Cool, I bet it feels good to get things straightened out and the car back on the road. I would've expected more power out of 401 cubic inches though,. How much of a loss can be expected measuring power at the rear wheels instead of the crankshaft?
Ch***is dyno’s show very different results than engine dyno’s typically. The guy I use says to go down the street if you want big numbers. The compe***ion’s dyno shows 50% more horsepower. All in how they apply the correction factors.
Happens a lot I see people with rear wheel HP and Torque figures that their parts spec wouldn’t produce . It’s easy to fool some people. Wouldn’t mind seeing more Nailhead dyno results.
There used to be a similar **** fight with trucks. ***mins and Cat rated their engines at flywheel H.P.. Mack were rated at H.P. at the drive wheels. The Holden Grey engine in my avatar was originally rated at 60.5 H.P. at the flywheel, much less at the drive wheels. Mine has got just shy of 100 H.P. at the wheels so probably a bit more on an engine dyno.
A modern 602 GM Create Oval Track (350 cubic inches) is rated at 350 crank HP @ 5400 R.P.M./396 lb.-ft. @ 3,800 rpm, and they are full on race engines. 200 @ the wheels I wouldn't feel too bad about 200 hp out of a street engine.
So a little searching around found some interesting information. There is no good formula for calculating what should be a standard % difference between ch***is and engine dyno, there are far too many variables at play. This is a good overall explanation of the different technologies: https://www.onallcylinders.com/2012/05/11/dyno-duel-engine-vs-ch***is-dynos-what-you-should-know/ And this one gets into more depth explanations and comparisons: https://www.motortrend.com/how-to/1106phr-comparing-ch***is-and-engine-dynos/ I think basically the best use of a ch***is dyno is for tuning a car, not for determining the max hp/torque of an engine.
I'd use one for being able to lean over the fender as some one drives the car as if he was driving on the street if it was that type of car. Give it full throttle one or twice like you were p***ing someone. Think of it I sure miss my old Plymouth van.
Did you do any tuning on the dyno? I'd expect maybe 230 -250 hp and maybe 350 ft lb torque. That's about 80%. That's what we looked for on heavy trucks. I'm running a very similar engine in my Model A. It's 0.030 over bore and I used the cam that was used in the 425 with 2 4bbl. Never dyno'ed it, but thought about it.
We did not do any tuning. They are mostly an EFI shop, and I’m not real good with carbs. It was fun hearing the car go 110 MPH. I’ve never been above 60 in it, at least in my adult life.
there can be no formula everything is different from car to car, The only ch***is dyno I used had a system where the dyno could run the wheels to give you a loss figure, generally people have a guess and dont stress it too much, ch***is dynos are for tuning (the accuracy varies from business to business)
Interesting numbers. I will see what the fresh 401 does when I drop it in my 40. I expect higher numbers with a cam and dual exhaust.
I’d also bet a different air cleaner will wake it up. Mine was using the factory snorkel, which is likely 2 inches in diameter on a good day.
^^^^ It will have an appropriate air cleaner for the 800 CFM carb, head work and 10 to 1 compression.
The numbers by themselves aren't really important most of the time, unless it's bragging rights you're looking for. If you're not happy with the numbers, try the dyno on the other side of town, even if it's the same kind of dyno the numbers won't be exactly the same. So forget about exact power numbers, it will just give you a more or less rough idea about what you've got (it won't even be the same after the weather changes), as you say the really good use is for tuning - if power increased when you changed the carb jetting or ignition advance you know you went in the right direction, keep going and run it again until you've found the max. If your engine isn't properly tuned there may be a lot of free power to find in it on the dyno. Or on the road, with a stopwatch, but that's far less accurate.
Years ago I worked at a race shop that had a ch***is dyno. My flatty powered T Bucket was the first car on it. Figured we'd break it in lightly. After some tuning it made 118hp at the wheels! 5sp, Merc, dual carbs, mystery cam. We had the best tuner in the world at the time so that prolly helped a bit.
I worked for a company that built dyno's. We had a 19 lb. dyno for testing APU's, and we built 2, 20,000 lb. units for testing LM2500 turbine engines. We had a test cell where we ran some of the smaller dyno's. We did a test for ***mins, and told them that our 13" rotor water-brake would stall their big diesels. They didn't believe us, but we made believers out of them. I remember going to a customer facility in January for a test run. The water coming into the dyno was 35 degrees Fahrenheit, The water coming out was boiling due to the turbulence from the 6 stage rotors.
I just rebuilt the carb, recurved the distributor, new points and plugs and got the ST400 working like it should on my 65 Riviera. Damn, it runs pretty strong! I am pleased witth how it moves tthis big old car. The switch pitch was a great idea. Too bad the bean counters killed it.
To me a dyno gives you basic numbers but to me where it shines is tuning. The dyno will let you know what works, what works well and what doesn't. You can do a simple intake swap and know whether it was money well spent or money spent that didn't do much if anything. Also I've seen guys who's "seat of their pants" didn't agree with dyno results either. It's a tool, it has its place and when used properly it's a good one. ..
That makes perfect sense, when you think about it. A dyno will (usually) test the engine under some very simple conditions, it can either hold it at a steady rpm or let the rpm rise gradually (depending on type of dyno). You get a test of how the engine performs under exactly those conditions, and that's great. On the other hand, you do NOT get to know how it responds to quickly going to full throttle at 4000rpm after hard braking and a tight left turn. Maybe the carbs flood under the braking or turn making it run crazy rich when you get back on the throttle, maybe the carbs have horrible throttle response but performs well as long as they're left alone at WOT, maybe the engine can handle the current ignition setting on a dyno that lets it accelerate past max torque quickly while your high gear driving makes it linger around that rpm longer, building heat, causing detonation that makes the engine destroy itself... As you say, it's a tool and properly used it's worth it's weight in gold, but it can never completely replace all aspects of testing while actually driving. Different tools for solving different problems.
That's really awesome. One thing that Centerville preaches is these cars are under carbureted. I'm guessing yours has an 800+ CFM Edelbrock AFB on it?
I don't mean to be a jerk but you are mistaken. There is no way it could put out that much HP on a CH***IS dyno, unless it was blown and running some exotic fuel. Those engines just can't pump that much air in normally aspirated form, due to the small valve sizes. Perhaps you meant to say 425 ft lbs of torque, which is how Buick promoted them. A Ch***is dyno has losses for the transmission, differential, tires, etc. Usually, you would see at least a 15-20% loss or more on a ch***is dyno.
A “good” ch***is dyno operator can doctor the inputs to give an owner just what he wants to hear……so can an engine dyno operator.
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