[78w72]

Originally Posted by Shockwave78

Thanks, ill give the crimped nuts a shot

Just be sure you do the adjustment right based on what the lifters instructions say, crimped nuts are only good for 2-3 times adjusting, 1 time is ideal. Can buy them at most local auto parts stores, just say you need rocker nuts for a 1978 350 chevy.

Heres a link to show how it can be done on smaller cams... for bigger cams its best to do when the cam is on the base circle for each valve.

https://www.pontiacstreetperformance...p/rockers.html

[Gach]

Originally Posted by Shockwave78

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

Lets say that cam was ground on a 108, you installed it dot to dot. per instructions. But never degree it, now for some reason (gear set ) being off, you check it ( degree it in ). And it comes in at 114 thats severely retarded. So now its not filling the cylinders hence the low compression reading. No matter what aftermarket cam it is, you just can’t take for granted that its actually on a 108. Also it may not be the case, the cam is off, but it could be timing gear set itself, thats why the offer timing gear sets with 9 key ways. Hoping now you understand why ever cam should be degree and checked to make sure. This would now eliminate the cause of that being the power lost. Then you could move on to valve adjustment valve train being problem. I mean you did a could job on checking all the obvious things.

[steve25]

To judge how the timing chain install went I always make a cranking compression test before the timing cover goes on.

[Stan Weiss]

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.

What is your CR and what do you see for cranking compression?

Stan

[steve25]

Stan, the op said he was only able to test out 4 of the cylinders for now, but found between 145 and 150.psi.

[johnta1]

If you don't have an adjustable rocker nut, I can about guarantee your problem is the valves need to be loosened. They are too tight and the valves are not closing fully.

Do you have stock rocker studs now?

[Stan Weiss]

Originally Posted by steve25

Stan, the op said he was only able to test out 4 of the cylinders for now, but found between 145 and 150.psi.

Steve,
That question is for the person running the XE268.

Stan

[Gach]

Moving onto valve adjustment, usually once valve is close ( with hyd lifters) you take up the slack, by turning push rod until there’s no slack, then go 1/4 or 1/2 turn what ever they recommend. It’s been a while since I’ve done hydraulic lifters so thats my vague memory. Its kind of hard to mess that up, only thing that could is if, even though you thought valve was completely closed, may not have been. So that would hold valve open, partially. Could happen on either intake or exhaust, so thats why I take the time to go though them again, just to check.

The other thing, with hyd lifters what I used to do, was put the lifter in a can of oil and pump it up. Because i’ve found that some times, if the lifter wasn’t pump up, now your adjusting it, taking up the push rod slack up, but it’s actually already depressing the plunger. Now you fire it off the lifter pumps up. But the valve isn’t completely closeing. But anyway definitely going with the studs and adjustable nuts is a plus, just assures a more solid adjustment

[Stan Weiss]

4.12" bore, 3.75" stroke, 6.625" rod, 8.0:1 CR, 270 intake duration 109 ICL (26/64), should at sea level should produce about 148 psi cranking compression.

Stan

[Jay S]

The pumping compression sounds about right to me for that combo. (Stan’s numbers on the next post look good. )

It is going to run good with 150 lbs of compression, I kind of doubt you have the cam install wrong.

The lifters could be too tight and cause power loss.

I rather doubt the cam is the problem, unless the cam went flat on break in on a couple cylinders that have not been check yet.

Does it have a tach? If it does where are you shifting at? How bad does it run? Can’t get out of it’s own way sounds like it has a massive issue somewhere.

Is it W72 car with 3.23 or 3.42s? Dual 2.25” exhaust and log manifolds, qjet and stock intake?

Been parked awhile? Bad gas? Fuel sock on the tank partially plugged from being parked?

To hot of spark plugs? Often a bigger cam drops the heat range at least 1, sometimes 2.

Does it have full timing? Stock dizzy? Chinese junk? What all got changed? 18* sounds like to much advance. If it takes that much timing to run good it could be a issue in the distributer.

[Gach]

Originally Posted by Stan Weiss

Steve,
That question is for the person running the XE268.

Stan

He said what compression was in his first post, think thats what Steve is trying to tell you..LOL

[Shockwave78]

Just checked the rocker nuts, and when they are torqued down per the manual, I can watch the valve open. I backed the nuts off to adjust them like you normally would with an adjustable valvetrain, did a compression test and it returned 175 psi, a bit more than I was expecting, given the whole engine is stock except the cam. Regardless I am definitely switching the nuts out today! I had to swap the valley pan after break in and had a chance to check the cam and there were no wiped lobes or abnormal wear, thank god. I have also been using the car as a daily for the past year or so, which narrows down other potential problems it might have, but this is a really good starting point (hopefully the only problem)!

Thanks for all the input and ill report back with updates after the new rocker nuts.

[Shockwave78]

Originally Posted by Jay S

The pumping compression sounds about right to me for that combo. (Stan’s numbers on the next post look good. )

It is going to run good with 150 lbs of compression, I kind of doubt you have the cam install wrong.

The lifters could be too tight and cause power loss.

I rather doubt the cam is the problem, unless the cam went flat on break in on a couple cylinders that have not been check yet.

Does it have a tach? If it does where are you shifting at? How bad does it run? Can’t get out of it’s own way sounds like it has a massive issue somewhere.

Is it W72 car with 3.23 or 3.42s? Dual 2.25” exhaust and log manifolds, qjet and stock intake?

Been parked awhile? Bad gas? Fuel sock on the tank partially plugged from being parked?

To hot of spark plugs? Often a bigger cam drops the heat range at least 1, sometimes 2.

Does it have full timing? Stock dizzy? Chinese junk? What all got changed? 18* sounds like to much advance. If it takes that much timing to run good it could be a issue in the distributer.

It has the stock distributor uncurved as of yet, I set the timing to 18 deg as a starting point per the emissions sticker on the core support.

[Gach]

Originally Posted by Shockwave78

Just checked the rocker nuts, and when they are torqued down per the manual, I can watch the valve open. I backed the nuts off to adjust them like you normally would with an adjustable valvetrain, did a compression test and it returned 175 psi, a bit more than I was expecting, given the whole engine is stock except the cam. Regardless I am definitely switching the nuts out today! I had to swap the valley pan after break in and had a chance to check the cam and there were no wiped lobes or abnormal wear, thank god. I have also been using the car as a daily for the past year or so, which narrows down other potential problems it might have, but this is a really good starting point (hopefully the only problem)!

Thanks for all the input and ill report back with updates after the new rocker nuts.

Bingo ! Yeah I knew 150 compression was really low ! good glad you found the issue

[Gach]

PS: 175 will be fine..no worries

[Gach]

Originally Posted by Stan Weiss

4.12" bore, 3.75" stroke, 6.625" rod, 8.0:1 CR, 270 intake duration 109 ICL (26/64), should at sea level should produce about 148 psi cranking compression.

Stan

Is that one of you Calculator programs simulators, maybe should adjust it, because he really ended up with 175 compression…. oops.

[Stan Weiss]

Originally Posted by Shockwave78

Just checked the rocker nuts, and when they are torqued down per the manual, I can watch the valve open. I backed the nuts off to adjust them like you normally would with an adjustable valvetrain, did a compression test and it returned 175 psi, a bit more than I was expecting, given the whole engine is stock except the cam. Regardless I am definitely switching the nuts out today! I had to swap the valley pan after break in and had a chance to check the cam and there were no wiped lobes or abnormal wear, thank god. I have also been using the car as a daily for the past year or so, which narrows down other potential problems it might have, but this is a really good starting point (hopefully the only problem)!

Thanks for all the input and ill report back with updates after the new rocker nuts.

175 psi sounds very high for that cam and 8.0:1 CR. Was this test hot or cold?

Stan

[Gach]

Originally Posted by Stan Weiss

175 psi sounds very high for that cam and 8.0:1 CR. Was this test hot or cold?

Stan

Why ?

[Shockwave78]

Originally Posted by Stan Weiss

175 psi sounds very high for that cam and 8.0:1 CR. Was this test hot or cold?

Stan

I did the test cold, I don't know how it could be higher than 8:1 because I didn't have any machining done, and I am using the stock pistons, crank and heads

[PunchT37]

Well, at least you found your problem. Stock Pontiac cams have 390 ish to 400 lift on a non adjustable system. So, when you put a cam with more lift, especially with the same length pushrods, you`re pressing on that cam too hard. Hope you didn`t round it off.