I have a 73 400 YX motor with 7k3 heads and a 4 speed manual trans. Looking to up the power a bit and have seen a lot on 6x4 heads, even found a set of them locally that are rebuilt. Any input on if this would improve my overall power output.
I am also looking at adding power disc brakes to the front and would love to hear what people think if they have them or not. My car currently has non power drums on all corners.
And the final thing I am considering is to change my rear end gears. I have been driving the car often since I just got it and plan to continue to do so, it has a stock 10 bolt rear end and does ~3000 rpms cruising at 70 on the highway which makes me think I currently have a 3.42 rear set. I do not plan to drag race this car just a cool cruiser so any input is appreciated
3000 rpm at 70 is about what my 373 does.... I have 6x heads on my 400 but I has the whole thing done so I'm not real sure on just adding them to a motor.... I went with right stuff disc brake conversion... no complaints at all... everything fit.. and was pretty straight forward..
Really just depends on how much more power you need. Stroking the motor, with 455 length crank, hydraulic roller cam and a set of aluminum heads would wake it up. A doug nash type 5 or 6 speed would give you low end and hi way go power.
The 6X heads will have no performance advantage over the 7K3 heads. To increase performance on the 400, substantially, you'd need more compression and a cam change. If you keep the 7K3 heads, a 262 Voodoo cam, will increase cyl pressure & performance some.
I checked Wallace racing and the 7k3's are comparable to the 6x-4's with the bigger exhaust valves and ~95cc chambers see: Wallace Head List Not sure what your budget is, but I'd suggest considering a set of aluminum heads, they come in 72 & 87cc's
I installed 6x-4 heads some time ago on my 400 YT engine and it runs well, but I gave up compression/power. The original heads were 10.75 compression #62 heads, [72cc] and they pinged big time unless I ran race fuel.
I had the similar problem when I bought my car...had a replaced later model engine.... bottom end is good...I just bought (fairly "unknown" heads) ...5 C heads w larger valves , much cheaper then 6 X...had them CC checked `d and milled down to 90-92 CC...got good power and could still run on regular gas....