Chassis Dyno Chart of my 1972 Challenger

[Smallblock340]

Please have a look at attached Dyno Chart. The Chart is showing the results of last week Chassis Dyno Run of my 1972 Challenger:
- Blue = Dyno Chart from my engine (314 Hp @ 5864 rpm, 442 ft-lbs @ 3200 rpm)
- Red = Dyno Chart from Edelbrock catalog (417 Hp @ 6000 rpm, 397 ft-lbs @ 4500 rpm)

Note: results are presented in Engine Hp (left) and Nm (right). Air/fuel ratio is presented in the lower graph (values around 12.7, after changing the jets of the carb).

My drive train specs: 340 4BBL V-8 Engine (built: 26-2-72 w/forged crank), 727 Automatic Transmission, Bore 4.040, Scat connecting rods w/KB 243-040 pistons, Compression ratio 9.5:1, Edelbrock Top End Kit #2049 w/Edelbrock Heads #60179, Edelbrock Cam #7177, Hughes Engines Rocker Arms #HUG 15023, MSD 6AL Ignition, Edelbrock AVS2 650cfm Carb, Edelbrock High Flow Air Filter, Stock 1972 Exhaust manifolds.

Question 1:
What could be the reason for the huge differences between the dyno graph and the Edelbrock catalog graph? During the dyno run the tranny shifted from 2nd to 3rd gear @ 3700 rpm. This is exactly the point where TQ and Hp values are dropping. Is it an idea to redo the dyno run using slapstick 2nd gear only?

Question 2:
Engine has difficulties with running idle in P or N @ 800-1000rpm. With the idle rpm set to 1200 the engine is running fine. What could be the reason for this? Cam? Timing?

I look forward to hearing from you!

[GoodysGotaCuda]

I expect the Edelbrock chart is off of an engine dyno and not a chassis dyno, correct? If so, then you can pretty much bet on a 15-20% loss between the crank and wheels. 20% puts the Edelbrock figures at roughly 330whp.

I would expect the stock exhaust manifolds are going to be a huge restriction on an application like this, especially on the top end.
AFR looks fine, did you play with timing?




I am surprised a dyno operator gave you an end result with a shift in it, the data goes out the window for that period but after the shift is usable data.

Running in second next time will result in a little more efficiency loss and a shorter run will not have the same resolution, but the end result will be within a percent or two of what it would be in 3rd.

Depending on the wheel speed, i would try to adjust the kickdown linkage to keep it in third during the run. If you have a high axle ratio [3.23 or less] I would pay attention to the tire speed rating so that you don't run into issues when pulling in 3rd gear.

[HP2]

I went to the Edelbrock site, pulled up the 417 hp Chrysler LA power package and immediately noticed this line in their description: "This Top End Kit produced 417 HP & 397 TQ on a 390 c.i.d Ford FE with 9.5:1 compression."  So, you are already down 50 cubic inches by comparison.

I never could find a dyno chart on their site to clarify if they are using an engine or chassis dyno. I suspect it is like Goody said and their engine dyno will produce higher results than your chassis dyno. Figure in drive train losses and the above mentioned 50 cid extra they had, and your combo did pretty well.

For the idle issue, I'd look for a vacuum leak. Of course the usual areas around the intake manifold and carb, but also any nipples in the manifold, power brake hose or booster, or the vacuum lead to the hvac control head or the switch manifold.

[Scooter]

^^^
So minus 50 cubes to the FE and engine vs. Chassis dyno...

[JS29]

^^^
So minus 50 cubes to the FE and engine vs. Chassis dyno...

The nickname for an automatic transmission was a slush box!!! 

[7212Mopar]

Assume 15% driveline loss from trans and diff, the engine is making around 370 HP at the crank. This equates to around 1.09 HP per cubic inch. Typical for a warm over small block. Need more info on the engine build.

[Smallblock340]

Many thanks for the prompt replies and very useful advice!
And thank you very much for your detailed explanation of the slush box

I could not find any vacuum leaks. It looks like my original tachometer is not working properly.

The Edelbrock Dyno Chart I was referring to in my Chassis Dyno Chart was taken from:
https://www.edelbrock.com/performer-plus-camshaft-kit-for-small-block-chrysler-318-340-360-v8-7177.html

I agree with "GoodysGotaCuda" that my stock exhaust headers are a huge restriction. I will check if I can find some information about the TTI 1-5/8" Shorty and Step headers. I prefer the Step headers but the roads in my country are full with speed bumps...

[Smallblock340]

Check the link below for a video of the Dyno Run! 
https://youtu.be/MBG3SAJE_NQ