Dyno test result

[srisant]

Just had my 230sl dyno today. The result is very disappointed because I have overhauled my engine with new rebuild injection pump, non resistant  spark plugs with electronic ignition. Fuel/air mixed ratio is good from lambda reading close to 1. However from dyno my car only have 100hp and a bit less when fan operated. Any one have idea what else to look at to regain the power? From my reasearch 230sl should have 150hp net and should be around 120+ on rear wheels.

[srisant]

Any thought to help me gat back HP?

[stickandrudderman]

Is that at the crank or the wheels?

[Benz Dr.]

What year is your car? It might have low compression pistons in it - nothing you can do about that..... except change them.

[Cees Klumper]

And, for what it is worth, I read somewhere that dynos are notoriously inaccurate. I imagine you know the reputation of the place you had your car tested at, but thought I would mention it. Does the car feel peppy or sluggish when you drive it? Otherwise I would take it back to the shop that rebuilt the engine. Check the compression also, if that is normal (ie at the high end of the range since the engine was rebuilt) then it should be possible to get it to like-new specifications.

[srisant]

Wheels

[MichaelB.]

I ran a dyno facility years ago. I could (within reason) get the dyno report to read most anyway I wanted it to. There are setting in the machine & little extras that can be done that will effect the outcome either direction.

1st off in general some dynos will report higher numbers than others. For example Mustang (a manufacture) dynos report lower readings than the DynoJet dyno. There are still others that report even lower. So keep that in mind. Secondly as you seem to know already the wheel output is less than crankshaft output because of parasitic losses. We would normally find that most cars had a 12% drivetrain loss on most dynos. Automatics had sometimes as much as 18% loss. Trucks even more! So your 100 wheel HP reading could easily extrapolate to closer to 130 crank power pretty quickly.

Wheels & tires (and tire pressure) can do a lot, pump up the pressure & you will make more power. Cool the engine, thin out the oil, adjust the graph & altitude readings in the dyno program. All of those can make a difference.

Remember ~ a dyno is a great tool of tuning. You make changes & can use the same dyno to see what effect the changes made. When the dyno is used just to get a base power reading period / that is not used for its best intended purpose.

[srisant]

Spoke to the mechanic who do race car. He said that it might be camshaft that was not properly adjusted. Engine can run well with slightly camshaft out of tune but power can be significantly off. I will have him re tune the engine and dyno again to see if there any improvement.

[Cees Klumper]

Just to note that the camshaft on our cars can't be adjusted. Only the valve clearances but those you want to make sure are exactly right. Perhaps your mechanic is talking about using a woodruff key to adjust the cam timing, but on a rebuilt engine with new timing chain this should not be necessary, in fact would probably be a bad idea.

[stickandrudderman]

Cam timing can be a tooth out. The engine will still run but HCs will be really high.