66 427 425HP on a dyno

[vette]

I watched a very nice red 66 427 425HP roadster on a dyno in Danbury Ct on sun. As they say can you handle the truth. It made 240 rear wheel HP. Who knows what cam and pistons are in the motor. But that was just poor. Even a 390 HP should do better than that. And yes I have a 390HP 66 and think it is a slug. Im sure that guy went home sick.

 

[BarryK]

wow!
I would hope to do better with my '65 SB 327/365hp motor
I figure mine should be in the range of 280-300rwhp unless i'm really wrong on how much loss there is thru the drivetrain. But either way, 240rwhp from a 427/425 just seems way too low.

 

[Subfixer]

Me thinks he needs a tune-up.......

 

[IH2LOSE]

Those are some real poor numbers. But I have seen number like this a hundred times. Its real easey to leave hourse power on the table with these cars if there not in proper tune.

I dont know the specific on the car but I shurely hope this are from a poorley tuned car. My 427/425 car pulls real hard. It will burn the tires in 4 th gear. I know a car with only 280 hp cant do that.

But we should remember the hp rating system was different in the 60's then it is today

 

[DRTH VTR]

But we should remember the hp rating system was different in the 60's then it is today

400 gross horsepower is only about 320HP using the net ratings that have been in use since about 1972. Also, since HP is directly related to RPM, the higher reving engines of today can put out more HP than the lower reving engines of the past. The torque numbers might be a better comparison. They will also be about 20% lower when measured by the net standard than they would be using the gross standard. 425 HP X 20% correction for conversion to net, then another 20% for drivetrain loss still calculates to under 300 RWHP. Clearly that is just a crude estimate, but there is some truth in the calculation.

 

[IH2LOSE]

My wifes C5 with only a cat back excaust and an auto trans. Had 313 rwhp on a chassis dyno. I had the car dynoed when we first bought it as I was going to have it super charged and wanted a base line number to know where we started from

 

[Wilkinshc]

I'm just wondering how many miles on the motor, if its a low mileage car what shape are all the vacum hose & plug wires, any carbon build up if it not driven much, could be a million reason. I would expect around 300 hp rwhp if it's stock. Got to hand it to technology. Hard to tune better then a computer with the right program.

 

[Tom Bryant]

I saw a member here on the dyno a few years ago with a new 468 that registered in the high 2s at the rear wheels. Not to embarrass him further I won't mention his name. :L I rode in his car and it was a mountian of torque. We were all suprised. Could have been a dyno problem or that the truth just hurts. Could have been that he needed to go to work refining his engine setup.

GM's gross ratings were at the flywheel without any accessories being driven. Even the cooling water was pumped by an outsode source. Throw the engine in the car with a water pump, alternator, p/s pump, possibly an A/C clutch spinning on some cars and then the drivetrain losses. Now add engiine and tune up condition like rings, worn valves, timing chain, weak ignition parts, and the possibility that someone had leaned out the carb and messed with the spark curve seeking better mileage at some time and you can have some real pathetic numbers.

This just tells me that the guy has some work ahead of him.

Tom

 

[Grizzly]

I think the other issue here is the dyno itself. Have heard that they vary wildly in their readings. As a guess one would think that the portable ones would vary more than a permanent one. It's not like a gas pump that you can measure it's output into a jar.