68 440 HP cam

Mackman · Nov 13, 2020

I have a 67 R/T with a 68 440 HP motor. Stock AVS carb, cast iron manifolds. 727 trans. 3.23 rear ratio. I believe the motor is stock. I'm thinking of changing the cam to perk it up a bit, and am considering the Edelbrock Performer Plus 270/280 degree, .420"/.442" lift cam. I would like some opinions. Thanks

forphorty · Nov 13, 2020

That is smaller than the stock hp cam.

Don Frelier · Nov 13, 2020

The larger Summit cam is a good one.
My brother has one he took out a year ago, he had very high cylinder pressures with a 10.5 - 1 build. Too high.
They idle smooth and have real good mid range power.
https://www.summitracing.com/parts/sum-k6401
Pretty sure we ran into you down at Panorama this summer, you were unhappy with your tailpipe arrangement.

oldbee · Nov 13, 2020

Here are the specs on the '68's. 383-Bee's& roadrunners also had the 440 power pack cam.

turbine68rt · Nov 13, 2020

Mackman said:
I have a 67 R/T with a 68 440 HP motor. Stock AVS carb, cast iron manifolds. 727 trans. 3.23 rear ratio. I believe the motor is stock. I'm thinking of changing the cam to perk it up a bit, and am considering the Edelbrock Performer Plus 270/280 degree, .420"/.442" lift cam. I would like some opinions. Thanks

I'm running this in mine. Same setup as yours. Very happy with it so far.
https://www.summitracing.com/parts/cca-21-305-4

BSB67 · Nov 13, 2020

Mackman said:
...I believe the motor is stock...

Compression ratio is an important piece of information. If the motor has the stock pistons and compression ratio, it would unlikely run on pump gas without detonation.

If you think the motor is a little soft in its current form, it could be because of low compression ratio.

What is the cylinder cranking pressure?

Mackman · Nov 15, 2020

Cranking pressure is all over the board, from one cylinder low of 100, to one cylinder a high of 130 psi. Five cylinders in the 110-115 psi range.

BSB67 · Nov 15, 2020

Mackman said:
Cranking pressure is all over the board, from one cylinder low of 100, to one cylinder a high of 130 psi. Five cylinders in the 110-115 psi range.

The low cylinder pressure puts things in perspective. Someone has been inside that motor. Do you know any specifics about the cam in there now? Don't get you hopes up too high on the improvement a cam alone will make. But if cam is what you want to do, here are a couple suggestions:

https://www.lunatipower.com/voodoo-hydraulic-flat-tappet-chrysler-361-440-256-262.html

https://www.summitracing.com/parts/sum-k6400

But that's just an amature's opinion. Call a professional and have a discussion on what you have, and what you're looking for.

beanhead · Nov 15, 2020

That's a lot of variance in cranking psi for lower numbers.
Just for shitz-n'-giggles run a top-end cleaner through it (Sea-foam, or even water) beacuse it's quick and easy. Buildup on the valves/pistons etc may be the cause. If cleaning produces zero change, a rebuild is likely in your future...

Curiousyellow71 · Nov 15, 2020

The summit cams and the edelbrock cam will not help build build compression probably will run similiar to how it runs now and not worth switching unless you have a bad lobe on your hp cam(if its a original hp cam?).
I would look at a jones 256 or the lunati Bsb67 mentioned. Comps xe cams of a similiar size would do ok with low compression. If you had headers and more convertor you could go much bigger.

In 68 compression was over rated but to be that low the rings are really, really sad or its had low compression pistons installed or both.

Don Frelier · Nov 15, 2020

Did you try putting a tablespoon of oil in a couple low ones? If your numbers jump appreciably then your in for a new short block. If not then you might benefit from a new set of heads.

Challenger340 · Nov 17, 2020

Mackman said:
Cranking pressure is all over the board, from one cylinder low of 100, to one cylinder a high of 130 psi. Five cylinders in the 110-115 psi range.

How are you testing ?
Remove all 8 spark plugs
Disable the ignition
Wire the throttle plates wide open
Retest each cylinder..... 4 needle bumps only....record the 4th and final bump, however, watch for the first needle bump to be 75% of the 4th and final bump .

Any info on the current Camshaft would be beneficial moving forward, nonetheless, sounds like to may have the notoriously low compression rebuilder Pistons in there ?

68 440 HP cam

Mackman

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forphorty

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Don Frelier

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oldbee

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turbine68rt

Turbine Bronze Member

BSB67

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Mackman

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BSB67

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beanhead

May I Land My Kinky Machine

Curiousyellow71

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Don Frelier

FBBO Gold Member

Challenger340

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