[SteveO (Steveo)]

I dyno'd my car once again this year after some mild port work and installing a set of 1.6 ratio roller rockers over the winter.
This year my engine made 305 Hp at 5400 RPM, Last year she made 302 HP at 5725 RPM.
That was a lot of work for such small gain!
Could there be a different factor involved here?
I have a High Volume Mopar Performance fuel pump with the stock size fuel line coming from the tank and 5/16 (.312 Diameter) inside diameter braided line going from the pump feeding the Demon 750 double pumper.
I'm talking 360 small block here, edelbrock heads, edelbrock intake, headers, 10.5 compression.
What are your thoughts?

[Dave-R (Roppa440)]

You should have been monitoring air/fuel ratio and pressure during the dyno runs.

Are you keeping up a constant fuel pressure? 3/8th line is best on a performance engine.

You also want to be very close to 12:1 air/fuel ratio right through the rpm range of your dyno test for best power.

What porting did you do to the heads? The Edelbrock heads flow well without touching them. You should only smooth things in the bowl area and not remove any metal from the runners. Also make sure the valves are sealing well by filling (with the heads removed) the runners with old brake fluid (part used bottles of fuid are useful for something) and looking for leaks into the combustion chamber. Lap the valves until you have no leaks.

The fact that you made peak power at a lower rpm suggests to me (but I am not an expert in this) that you are going leaner now or the exhaust is more restrictive for some reason.

I am sure with a bit of tuning you will do better.

[SteveO (Steveo)]

The Air/Fuel was monitored throughout the run. It stayed fairly constant in the 13:1 range up to 5700 rpm.
Does this indicate "no fuel delivery problem"?

Do you have a 3/8 line running all the way back to the tank on your Challenger?
What is the diameter of the tube coming out of the gas tank?

The head porting I did consisted of smoothing dowm ridges left by the cutters on the intakes and on the exhaust side I reshaped the short turn radius area. I didn't touch the bowls, they looked perfect.

That's a good method for checking for leaks. With my car now ready for summer I hate to pull the heads off again.

Thanks Dave

[Dave-R (Roppa440)]

You want nearer 12:1 well past the rpm at peak power but if it was at 13:1 it is almost there so I don't think your drop in power is to do with that. Still it would not hurt checking the carb is tuned right.

You need to disable the secondaries so the engine runs on the primaries only while testing. Set your idle mixture around 14:1 or whatever it seems to like idling at without sooting the plugs at all or being too lean. Connect a vacuum gauge to the distributer vacuum port on the metering block and make sure there is no vacuum at idle. If there is you are running on the primary jets instead of the idle circuits and you need to fix this before you go any further.

If no vacuum at that port do a dyno run (or if you have a rich/lean indicator fitted go for a drive) and make sure that when you are on full or part throttle the mixture never drops below 13:1 or goes over 12:1.

Then re-connect your secondaries and do a full throttle run. Again make sure it never drops below 13:1 but this time try to get it as close to 12:1 as possible. Also try a high speed drive if you have an in-car monitor.

If you have poor fuel delivery the fuel bowls will slowly enpty and you will get a sudden lean condition at high rpm. This was happening to me last year on the strip. It had been fine on the road but when shifting from second to third on the strip it was suddenly going flat and loosing power. I noticed it also went lean on the monitor.

My problem was found to be a restriction in a fuel line bend.

I have a full run of 3/8 fuel pipe in my car. Some of my friends run half inch!. I also have a 3/8 sender in the tank. This was very hard to get at one time but they make reproductions now.

The short turn radius is the most sensitive part of the port. It needs to be RAISED more than anything. Removing metal from here can loose you power.

[Glenn Jackson (Henner)]

stevo I was just wondering if you ran the 1/4 mile with this combo and what it ran if you did? is this a stick or auto trans?

[SteveO (Steveo)]

I have not run the quarter mile yet this year with the 1.6 ratio rockers.
Last year with my 1.5 rockers, I ran 13.41
I have a 727 auto trans.
For more info on my car, see my personal site I just put up.
www.challengerboy.com

How about you Glen, have you ran your Challenger thru the 1/4 mile yet?

[Glenn Jackson (Henner)]

hopefully within the next couple of weeks I will go to test and tune at route 66 on tuesdays. hope to run low to mid 14 for starters my 340 is 40 over edelbrock cam intake and carb.