[Gach]

When Crower design that cam, over what ever cam it replaced 068 ? Don’t know….why do you think it made more power over a stock 068. I’m just using the specs as an example, so don’t hold me to them. Lets say 068 was on a 112 what ever. The Crower cam on a 109. What 3-4 degrees advanced plus the added more lift. Plus the opening and closing changes. Which increases cranking compression. Better cylinder filling more power.

[Shockwave78]

Originally Posted by 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.

the cam looked ok after break in, no scoring or abnormal wear

[Sirrotica]

As long as the base circle on the cam is close to the same as the OEM camshaft you could use the non adjustable OEM nuts. The lift is probably okay with OEM springs.

The way the OP description sounds like the cam timing is off. He's not going to have 15 Lbs of vacuum, or 150-175 Lbs of compression with the valves are off the seat. Just because the cam and timing chain, and gears are new doesn't mean that the keyways are all cut exactly where they should be, or there wasn't some error in the assembly. If the valves weren't seating you'd likely have a miss, or very possibly a backfire when trying to accelerate.

I have had a Comp cam ground for an oldsmobile that ran like crap because half of the cam lobes were on center where they should be, and half of the lobes were off center. Machining mistakes happen. Nothing we did would make that car run well because the cam was ground incorrectly.

The hydraulic lifters are very forgiving to adjust the valvetrain even if all the specs aren't dead on. There are a good many of domestic engines that have no provisions to have adjustable valve trains. Those engines have mild hydraulic cams installed all the time without going to an expensive conversion to make the valvetrain adjustable.

While I'm not against making a Pontiac valvetrain adjustable, I don't belive that this is the OPs problem, rather that it's a cam timing issue. I have installed more than a few mild performance cams into Pontiac engines without making the valvetrain adjustable, the lifter travel made up the difference to make sure all the valves were seating. If the new cam has a base circle close to the OEM cam, it should work satisfactorily with a non adjustable valve train.

Years ago I worked on a 66 Catalina that ate the nylon timing gear teeth, when it was replaced it inadvertantly was one tooth off. The car idled just fine, but was about as gutless as a 6 cylinder full size car. After resetting the cam timing it would fry the RR tire off. Cam timing has a huge effect on performance.

I'm curious also of what carb, and intake the engine has on it, the wrong intake, with improper gearing can make a car gutless as hell because of the runner velocity is wrong for the combination. All the parts have to be in harmony to gain performance. Transmission, gearing, intake, and carb, and exhaust system, would all be helpful to know before condemming the non adjustable valve train.

[Jay S]

Hot can add 5 to 10 lbs on a compression test. 150 was in the low end of what it should have been, but still ok. Going from 150 to 175 isn’t that unusual after a lifter adjustment, a sign it was running too tight. Sometimes the lifters bleed off and don’t recover as fast as you might expect also, more true these days when lifter bleed rates vary quite a bit. it It may not stay at 175lbs if you tested it right after adjusting the lifters. Altitude and atmosphere conditions effect the pumping compression too. Hopefully it runs better for you.

If your not running all the emission controls I think you will want to back off the timing from 18. The emission controls shut the vacuum advance off until the engine reaches a minimum temp. I think that was why they ran so much initial. If the emission equipment is all hook up yet it probably needs to be at 18 like it says.

[steve25]

Stan, I was not being a wise ass, just trying to save you some time having to dig back thru post.

Not to spend the OPs money, but I would really consider stepping up to the the full 7/16” diameter rocker studs due to your new higher cam lift.

You have screw in studs so it’s a breeze!

This will save you from potentially snapping off the top threaded portion of the stock stud.

I wish I did that twice in my lifetime right off the bat!

[Lee]

FWIW, I have a cam with .443"/.435" valve lift, stock pressed-in studs, stock rockers & nuts, stock pushrods, nuts torqued to spec, but I suspect it has Crower springs (prior owner installed the springs), in my low CR 455. It has ran fine for years now. Much more duration @ 0.050", and still has great low-end.

I suspect the timing gears are mis-installed. His cam should work fine with the stock valvetrain components.

[NeighborsComplaint]

The cam timing is retarded. A long as your pushrods are stock length, There is plenty of travel in the lifter to accommodate the bottleneck studs and locknuts even when heads are milled. The shoulder on the rocker stud prevents you from over-adjusting and collapsing the lifter. If intake valves were hung open, you’d hear it through the intake tract either as backfiring or a pfft- Pfft-pfft sound from the open intake valves allowing compression to leak past the valve guides when cranking the engine over.

["QUICK-SILVER"]

If you back rocker nuts off to the point of having lash instead of lifter preload... The engine will have higher cranking compression from intake valve closing earlier in the compression stroke.

Clay

[Stan Weiss]

Originally Posted by steve25

Stan, I was not being a wise ass, just trying to save you some time having to dig back thru post.

Not to spend the OPs money, but I would really consider stepping up to the the full 7/16” diameter rocker studs due to your new higher cam lift.

You have screw in studs so it’s a breeze!

This will save you from potentially snapping off the top threaded portion of the stock stud.

I wish I did that twice in my lifetime right off the bat!

Steve,
Not a problem.

Stan

[Stan Weiss]

Originally Posted by "QUICK-SILVER"

If you back rocker nuts off to the point of having lash instead of lifter preload... The engine will have higher cranking compression from intake valve closing earlier in the compression stroke.

Clay

Clay,
This is my thinking also.

It will be interesting to see what happens when he has it up and running again.

Stan

[78w72]

Originally Posted by Gach

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

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.

Stan quoted me in his post asking for CR & cranking comp...

Originally Posted by Stan Weiss

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

Stan

Didnt want to sidetrack the OPs thread, just stating that I have a lot higher lift than his cam using the stock studs & crimp adjustable nuts with no issues for many years with lots of street use & drag strip runs. 7/16 studs are ideal but for lower-mild lift cams the stock studs work ok... using some cheap priced crimped nuts will let the OP see if that helps his issue, if it does then he can change the studs or keep them as is & it will likely be fine for a very long time.

I can only estimate my CR, used wallaces calculator at the beginning of the build and havent done a cracking compression test as I havent felt the need since the engine runs so good, but might do it at some point just for curiosity. Heres some specs of the build, pretty basic parts & machine work.

1978 W72 4 speed, 400 .30 over bore, 6x-4 heads no porting, 3 angle valve job, milled ~.030. speed pro forged pistons, stock rods/crank. felpro gaskets. stock intake, original cliff built q-jet. removed EGR & bypassed emission stuff. headers, 2.5" exhaust. XE268 cam installed "straight up" by me, along with the rest of the engine parts. short block assembly done at machine shop.
car starts & runs about perfect, no detonation, no hard starting when hot, no overheating on stock radiator, runs on 87 octane just fine, runs mid to upper 13's at 103+mph taking it easy on the launch to not hurt clutch, 5000-5500 shifts, not max effort runs, just fun at a test & tune.

["QUICK-SILVER"]

Originally Posted by Shockwave78

Idle speed is set to 750 and I am seeing about 15" of mercury. .

Was the needle steady or bouncing?

Leaky intake valves would of had the needle bouncing hard.

Clay

[Shockwave78]

Originally Posted by "QUICK-SILVER"

Was the needle steady or bouncing?

Leaky intake valves would of had the needle bouncing hard.

Clay

The needle was bouncing about an inch of vacuum both ways. Something I did forget to mention was that there was a hissing sound coming from the top end with the valve covers off after cranking stopped. I suspect it was happening while cranking, but the engine turning over was too loud to hear it, but ill see if I can hear it today, I assumed this was in part due to the valves not being all the way closed.

[Scarebird]

With the valves at rest, shouldn't he be able to turn the pushrod once the lifters bleed down?

[PunchT37]

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.

If he did this on the base circle, he found his problem.

[Stan Weiss]

Just some computer simulations of a W72, 8.0:1 CR with stock manifolds. Using the 3 cams talked about.

Stan

[Shockwave78]

Installed the new rocker nuts and....... still no power. Might be a bit better but not by much. On the highway at WOT it cant get past 60. Also on the highway cruising at part throttle it missed or coughed 3 or 4 times, on the 30 minute test drive, that was the only time. The last thing I noticed is, at WOT when the top flap of the secondaries open as much as they can (which isn't much, maybe a quarter open) there is white fuel vapor being blown out of the top of the carb, enough to hit the windshield and cover it in gas droplets. I cant tell if it is out of the primaries or secondaries.

And to add insult to injury, my oil pressure gauge stopped working and is stuck at 60 psi

[PunchT37]

Hmmm. Reversion?

[Dragncar]

A tooth or two off on the distributor.

[Gach]

Question what kind of lifters you put in with that Crower cam ?