[tbub1956]

I would like to build my 400 ci for street speed Thus far the advice I'e received is a performance cam, headers and performance intake. Any suggestions? Also the car has a M40 Turbo-Hydra transmission But if I'm driving in D and punch it, it doesn't downshift automatically. This is the third GP I've owned. Previous was 69 and 72. Any suggestions?t

[steve25]

The M40 down shifts when a switch is activated.
The switch is mounted under the dash and attached to the top of the gas pedal.

The switch is likely bad or one or both of the wires that go to it are broken or disconnected.

A simple ohm meter test will tell you if the switch is bad or not.

[steve25]

Your GP should have the 061 head castings if it’s early 67 motor, or the 670 head castings if it’s a late 67.

Either way that 400 was rated at 350 Hp and should move out pretty good if the motor is not too worn and is in a good state of tune.

If the timing chain has not been replaced yet then it’s way way over due and could be knocking 40 hp off the motor .

Also if the motor has not been rebuilt yet and has over 60K miles on it your just kidding yourself by installing a hotter cam and looking for more power out of a what is now a 57 year old motor.

[JB Eng Wis]

Do a nice compression test first.... that will give you good idea if 57 years were all good years....
Most likely the engine should come apart.... I would guess it needs a valve job for sure.... and the upper cam gear (Timing) MUST be replaced as stated .

[Goatracer1]

If you want the biggest bang for the buck change the rearend ratio. All the modifications you want to make will probably only raise the peak power point hurting low rpm power.

[Joe's Garage]

Other than the weight, they're not any better than the original intake.

A factory cast-iron quadrajet intake will work better and actually make more power for a street cruiser.

Any year up to 1971 will work on the 1967 heads.

[tbub1956]

Originally Posted by steve25

Your GP should have the 061 head castings if it’s early 67 motor, or the 670 head castings if it’s a late 67.

Either way that 400 was rated at 350 Hp and should move out pretty good if the motor is not too worn and is in a good state of tune.

If the timing chain has not been replaced yet then it’s way way over due and could be knocking 40 hp off the motor .

Also if the motor has not been rebuilt yet and has over 60K miles on it your just kidding yourself by installing a hotter cam and looking for more power out of a what is now a 57 year old motor.

The build sheet says 01-13

[tbub1956]

Originally Posted by tbub1956

The build sheet says 01-13

That's another problem. I purchased this from Streetside Classics in Atlanta and the paperwork says it was recently rebuilt but I'm skeptical.

[tbub1956]

Thanks for your input.