i have a 350 chev 71. i have put a hyd.488 lift 292 adv dur.what i want to know is by putting in hi lift cam will this lower cranking comp. i did a comp. test and it seems to be lower. thanks phil  

Yep, that's what happens as duration is extended. The increased exhaust/intake overlap causes some charge pressure to escape out the exhaust. At the other end of the intake cycle the late closing intake results in some charge being pumped back into the intake at lower RPMs where there is insufficient charge velocity to overcome the rising piston's pumping action. These two things combine to substantially reduce the amount of trapped charge at lower engine speeds. The usual fix is to increase compression to make what charge is trapped at low speed work harder.

Bogie

Advance the cam @ 4 degress.  

i took off the 76cc stoch heads and put on a set of 64cc camel heads i was trying to raise the compression with the stock dished pistons.i have not checked the comp. since i replaced the 70 z-28 cam which had a flat lobe.i was expecting to see a much higher comp. but instead it was about 100 where before it was about 150 before i started changing parts. i didnt no whether this was normal or no with the cam change. thanks phil  

When you switch heads you take a chance that the rings will give out. Your bottom end might be in need of a rebuild. Are you getting alot of blow by?  

no blowby phil  

i have put a hyd.488 lift 292 adv dur.since i replaced the 70 z-28 cam which had a flat lobe.i was expecting to see a much higher comp.

How does the car run? Did you do a compression check with the old cam in?

Are your Cam Spec's;

292/292 Adv, 234/234 @ .050, .488"/.488" lift, 114 lobe centers?

Was your 71 Z/28 Cam a Mech Cam? Was it this one;

The Cam you put in is a very good cam, I have used one similar but with 109 lobe centers in a flat top 350 with 64 cc heads. What did you install it at, is it straight up or maybe a tooth off on the chain. What comp is your 350? Now the 8.5:1 post '75 350 L-82's had a hyd cam;

IMO-The cam you have fits in between both of these factory cams and should work well, I believe something else is wrong.

the cam i had before was the3972182 z-28 cam. i have the dished pistons short block when i checked the comp. before which has been a few months and the stock 76cc heads the comp was 150. i put this cam 488lift 292 dur. and the 64cc camel heads.i  think the comp ratio would be about 9.5 with this combination. i also install timing marks right thinks phil. it could be other problems  

also install timing marks right thinks phil. it could be other problems

Have you drove the car since the cam change and how does the car drive?

Sometimes when you install the dots on the cam gears, it looks right, but when you turn the motor over one full revolution, it can be one tooth off. Best thing is to check it by degreeing the cam to see if it is with in spec's. If it is one tooth off, the numbers will be way off. Comp Cam and Isky have info on how to degree a cam and Comp has a video on this subject. It is more common than not to have this happen, I watch a guy with a dragster go from 8.90 to 13's and did not know what happen until he degree it and found his mistake. Good luck

the car seems to run strong. there was not a running problem. i was just curios about the comp. i thought  it would be a lot more than it is. i mean cranking comp.i dont have a leak down detector.the heads i put on 202 rebuilt camel heads.do you think i should advance the timing 4 degrees i would have to buy a timing set to do this. thanks proge

the car seems to run strong. there was not a running problem. i was just curios about the comp. i thought  it would be a lot more than it is. i mean cranking comp.i dont have a leak down detector.the heads i put on 202 rebuilt camel heads.

The car should be lazy and not run as good if there is that much static preasure lost. Maybe the guage is wrong, did you use the same guage, have the carb open to WOT and have all the spark plugs out with a well charged battery and turn it over at least 3-5 times when performing the test on each cylinder? Was it done on cold engine or warmed up engine? Was it the same temp as the last time you tested? If you have access to a leak down tester than use it, it will inform you better, over a comp test, of what shape the motor is in. If it runs good, it does not sound as if there is anything wrong.

do you think i should advance the timing 4 degrees i would have to buy a timing set to do this

Advancing the cam will give you better throttle responce and better bottom end power. Mr Gasket as well as other sell cam bushings to do this for @ $10-$15, and you drill your timing chain top gear instead of replacing it. You should degree it and check piston to valve clearence also when you advance or retard a cam. If the car runs good, why bother?