I am going to replace the cam,lifters & timing set, I would like to freshin up the "882" heads with new guides/manley streetflow valves & springs, I am currently running 8.5-1 comp. and would like to increase the C.R. for a XE262 cam which needs at least 9-1 C.R. so before asking a mach. shop does anyone know how much to mill off the heads to achive this C.R.? Some pepole say to change the int. man. also but I belive G.M.'s engineers new what they were doing so I will try the stock one out.

 

I had .040 " shaved off my 624 heads when I did my rebuild last fall. Believe it resulted in C/R increase of approx. .4, from 8.2 to 8.6, since I had OEM steel shim head gasket and used felpro composition .039" for re-assembly, which resulted in about a net reduction of .022", assuming factory steel shim gasket is .017 compressed.(I'm not real sure about this #) I did install an Edelbrock Performer Intake during the rebuild, and performed a test fitting before using using sealant to make sure I had enough space between intake and lifter valley after milling the heads, (since I understand sometimes milling heads will require milling intake as well to get proper fit), but my clearance was OK.

Perhaps you should price out a set of World Products SR Torker heads, or a similar after market head before spending the $ to rebuild the 882s, I've read where the 882s and 624s are NOT recommended for performance applications, and that they both are thin wall castings, which are prone to cracking, and they run hotter than other heads due to two holes for the exhaust crossover. I did have my 624 heads hot tanked and checked for cracks before the milling, and they were OK. I only spent $50 for the hot tank/milling, and lapped the valves myself and I installed new springs and positive valve stem seals, and used new locks, but did no other head work as the valves/seats/valve guides were OK, and I didn't want to spend a lot of money. (Originally started out to be just a cam and intake change, which turned into a lot more due to the 'while I'm at it' syndrom)

 

(Originally started out to be just a cam and intake change, which turned into a lot more due to the 'while I'm at it' syndrom)

I can relate!!!



:rolleyes:

 

How do you know what kind of compression ratio is required for a cam? Why does a cam require a certain compression ratio?
I have a stock long-block GM Goodwrench 350 (LM-1) and want to put an XE262 cam and AFR 190CC heads in, but I don't want to open up the bottom end of the motor. The GW350 is supposed to be good for 8.5:1 compression stock.
I want this motor to run right/nice, but I don't want to dump more than $2000 into it, either.
-Steve

 

Pacin, in answer to your question, the more lift/duration of the cam, the greater the loss in compression ratio in low RPM range, due to valve overlap on compression stroke of a 4 stroke engine. Cam manufacturers therefore always will state, or will suggest a minimum compression ratio for each of their camshafts. Too much cam will result in a huge loss in low rpm torque and performance and can result in very poor idle and streetability characteristics, enough that your engine may not produce enough vacuum to operate power brake booster, and other engine vacuum operated systems, like headlights, heater control valve, etc.

Ganey, who frequents the forum is one of the resident cam experts, and offers great advice for those who are cam shopping. Rear gears, and transmission (auto or manual) also figure into "proper" cam selection equation.

 

I for one, would never shave any more off a head ,then was needed to to make it perfectly flat. Milling too much can cause problems with intake manifold runners and bolt holes not lining up properly. Lifter preload is not a problem on small chevy engines due to the adjustable valve train. I would suggest mill them till they're flat and no more. I also believe the XE262 will do just fine in your 8.5 to 1 motor.

 

Also, Iam in an emission state, cat. converter, air pump, so on so on :mad

 

I was told by a repetable engine builder that w/8.5-1 a cam int. w/ 214 adver. dur. @ .050 lift was acceptable over 218 adver. dur. (XE262) effecting acceleration from 1000-1500 rmp (making the engine hesitate or lag).

 

Stingraynick75:

Don't judge cams by their 'advertised' duration, it's not a good, constant measuring stick when evaluating one manufacturers camshaft against anothers. Have been told to look at duration @ .050 as a much better means to compare camshaft lobe duration of one cam to another.

Believe with your setup, something like Comp Cams 260H, or their newer fast ramp XE256 would work good, assuming you have an automatic transmission, and stock rear gears.