[Shockwave78]

I just finished rebuilding my w72 400 with a Crower 60240 cam, new lifters, valve springs, rings, and rod bearings, I didn't have any work done at a machine shop as the engine didn't need anything. After break-in, I took the car for a drive and it makes less power than with the stock cam, it can't get out of its own way! I have checked compression, firing order, spark, fuel, and timing and all seems to be as it should be. Compression was at 145-150psi for cylinders 1, 2, 3, and 4. I will be checking the other 4 cylinders after work today, as I just did a quick check on the easily accessible cylinders. Timing is set to 18 degrees btdc. I'm out of ideas as to what could be amiss. A friend of mine suggested that the issue could be the stock non-adjustable valvetrain preventing the valves from operating properly. I did a rough check on the valve lift with a valve cover off cranking the engine and measuring valve movement and came up with ~1/2", which is close to the advertised lift of .422/.446 with the stock rocker arm ratio. It doesn't look like the rockers are binding or otherwise hanging up.

Any help would be greatly appreciated!

[Stan Weiss]

Originally Posted by Shockwave78

I just finished rebuilding my w72 400 with a Crower 60240 cam, new lifters, valve springs, rings, and rod bearings, I didn't have any work done at a machine shop as the engine didn't need anything. After break-in, I took the car for a drive and it makes less power than with the stock cam, it can't get out of its own way! I have checked compression, firing order, spark, fuel, and timing and all seems to be as it should be. Compression was at 145-150psi for cylinders 1, 2, 3, and 4. I will be checking the other 4 cylinders after work today, as I just did a quick check on the easily accessible cylinders. Timing is set to 18 degrees btdc. I'm out of ideas as to what could be amiss. A friend of mine suggested that the issue could be the stock non-adjustable valvetrain preventing the valves from operating properly. I did a rough check on the valve lift with a valve cover off cranking the engine and measuring valve movement and came up with ~1/2", which is close to the advertised lift of .422/.446 with the stock rocker arm ratio. It doesn't look like the rockers are binding or otherwise hanging up.

Any help would be greatly appreciated!

Do you know what you CR is?

Did you degree the cam? If so what is the ICL?

Stan

[steve25]

140 psi is not going to cut it!

Did you degree the Cam in?

I bet it's installed retarded and not even straight up.

Once 1972 came around Pontiac never used anything bigger then the factory 067 Cam in a 400 so as to maintain good drivability, that crower Cam your running is bigger then that.

[b-man]

Make the valvetrain adjustable anytime you run an aftermarket cam. Yes sometimes you can get away with not doing that with some milder grinds but it’s always best to convert to adjustable.

You may not be able to perform a valid compression test until your valves are properly adjusted.

Recurving your distributor would be wise as well.

[Gach]

Yeah thats awful low compression, its either cam timing not degree in right, or valve adjustment bleeding off compression.

[Shockwave78]

I did not degree the cam when I installed it, I was not under the impression that it would be necessary for the engine to run well, just to make a few extra hp to squeeze out the full potential and the CR is stock at 8:1. How/why would the cam be installed retarded if it was installed according to procedure at tdc of the compression stroke on #1? What pressures would you expect for a compression test? I apologise of any of these questions are simple or things that should have been thought of before the engine went together, I was under the impression that this cam was a good choice for a stock low-compression 400 with minimal changes needed.

[Shockwave78]

Originally Posted by b-man

Make the valvetrain adjustable anytime you run an aftermarket cam. Yes sometimes you can get away with not doing that with some milder grinds but it’s always best to convert to adjustable.

You may not be able to perform a valid compression test until your valves are properly adjusted.

Recurving your distributor would be wise as well.

Would the stock valvetrain cause the valves to hang open/not close all the way?

["QUICK-SILVER"]

what kind of timing chain/gear set was used with this?

Mistakes with multi keyway types is when cam timing can be a problem.

Clay

[Shockwave78]

Originally Posted by "QUICK-SILVER"

what kind of timing chain/gear set was used with this?

Mistakes with multi keyway types is when cam timing can be a problem.

Clay

I installed an Edelbrock 7812, it does have multiple keyways. I made sure it was installed dot to dot, corresponding to no advance or retard.

[Stan Weiss]

JMO the problem is the cam.

It has 270/276 seat duration and 210/221 @ 0.050" 0.422"/0.446" 112 LSA

I know some people don't like this cam, but I think it would have been much better in this engine.

Comp cams xe256 - 256/268 seat duration and 212/218 @ 0.050" 0.447"/0.455" 110 LSA

Stan

[400 Lemans]

https://forums.maxperformanceinc.com...greeing+crower Crower cams are often retarded when dot to dot without degreeing.

[Shockwave78]

Originally Posted by Stan Weiss

JMO the problem is the cam.

It has 270/276 seat duration and 210/221 @ 0.050" 0.422"/0.446" 112 LSA

I know some people don't like this cam, but I think it would have been much better in this engine.

Comp cams xe256 - 256/268 seat duration and 212/218 @ 0.050" 0.447"/0.455" 110 LSA

Stan

I will keep that in mind to mess around with later down the line, I would prefer to get the cam that is in the engine running ok, even if it isn't the best choice. Although it doesn't seem reasonable to say that just because the cam isn't the best choice means it won't make any power at all. What would the shorter seat duration on the Comp cam help with?

[b-man]

Originally Posted by Shockwave78

Would the stock valvetrain cause the valves to hang open/not close all the way?

If you’re torquing the rocker nuts down to 20 ft/lb onto the tapered stop on the stud as per factory specifications then there’s definitely the possibility that some of the valves aren’t fully closing.

I would buy a set of ARP BB Chevy rocker studs (7-16-20 UNF top threads and 7/16-14 UNC bottom) and some polylock nuts and make the valvetrain not only fully adjustable but much more stable and durable.

The 60240 is a very good cam choice for your application, just make everything else right and you’ll reap the benefits.

["QUICK-SILVER"]

Originally Posted by Shockwave78

What would the shorter seat duration on the Comp cam help with?

Intake valves close ABDC (after bottom dead center). Earlier intake valve closing lets the engine build more compression.

Clay

[PunchT37]

I installed that same cam in my buddy`s `79 PWH, W72 400 as well. Ran well BUT, I did install aftermarket rockers, studs and poly locks.

[Stan Weiss]

What is your idle speed and what vacuum are you seeing?

Stan

[Shockwave78]

Originally Posted by "QUICK-SILVER"

Intake valves close ABDC (after bottom dead center). Earlier intake valve closing lets the engine build more compression.

Clay

That makes sense, its a lot simpler than I was expecting. Is the base circle of aftermarket cams larger to allow for greater duration and lift? Im trying to think of all the reasons that the valves would stay open.

[Shockwave78]

Idle speed is set to 750 and I am seeing about 15" of mercury. With the stock cam, the vacuum was 18-19", I was expecting a drop with the new cam, but I wasn't sure how much it should be.

[78w72]

Agree with making the rockers adjustable, ideal way is to get BBC 7/16 studs... but for a smaller cam like that you can just buy some SBC crimped locking nuts and set them according to the sbc procedure in most manuals or do the individual lobe on base circle procedure. doing this will be much less cost & is a quick easy way to go to adjustable to see if the stock 20lb/ft setting is the problem. the final adjustment is based on the lifters used, some want 1/2-1 full turn after zero lash but some want 1/4 turn, follow what the lifter manufacturer says to use.

I have a comp xe268 cam in my 78 w72 that runs excellent for 13+ years using the stock rocker studs & crimped nuts, has more lift than yours at .477.

[Shockwave78]

Originally Posted by 78w72

Agree with making the rockers adjustable, ideal way is to get BBC 7/16 studs... but for a smaller cam like that you can just buy some SBC crimped locking nuts and set them according to the sbc procedure in most manuals or do the individual lobe on base circle procedure. doing this will be much less cost & is a quick easy way to go to adjustable to see if the stock 20lb/ft setting is the problem. the final adjustment is based on the lifters used, some want 1/2-1 full turn after zero lash but some want 1/4 turn, follow what the lifter manufacturer says to use.

I have a comp xe268 cam in my 78 w72 that runs excellent for 13+ years using the stock rocker studs & crimped nuts, has more lift than yours at .477.

Thanks, ill give the crimped nuts a shot