Going to Aluminum heads

[nivvy]

My current compression is about 10.1 - with 906 heads 88cc they were milled .007...I have .013 deck height....what compression will I be at with a set of edelbrock 84cc heads...or how much do i have milled to get to 11.1 because of aluminum heads...thx


8 Pack

[firefighter3931]

My current compression is about 10.1 - with 906 heads 88cc they were milled .007...I have .013 deck height....what compression will I be at with a set of edelbrock 84cc heads...or how much do i have milled to get to 11.1 because of aluminum heads...thx


8 Pack

What is the valve relief or dish volume of the piston ? The compressed gasket thickness will also influence the static compression ratio. How much piston to valve clearance do you have with the current cam and iron head combo ?

Ron

[Chryco Psycho]

you will need to reduce the chamber size by another 6 cc to get to 11:1 , I would shoot for 10.8 :1 just to be sure you can use pump gas
before milling make SURE you have adequate valve to piston clearance as Ron said

[firefighter3931]

The Key to running a pump gas combo at higher static compression ratios is Quench. With a .009 piston to deck clearance you should be looking at a .030 compressed thickness head gasket. The chamber volume can be adjusted by milling the heads. We need to know the valve relief volume to properly calculate the static compression ratio for this combo. Neil's suggestion on measuring piston to valve clearance is very important and we're on the same wavelength here. The e-head chambers are shallower than an oem iron head so this will decrease piston to valve clearance somewhat. I like to use .080 intake and .100 exhaust P/V as a safe margin for street driven combos.

Ron

Edit: Made a small mistake....your deckheight measurement is .013 and not .009 so you can run a .027 Cometic head gasket and still achieve .040 Quench. The Cometic gaskets are very nice allthough a little on the pricy side.

[nivvy]

Motor specs
440 block bored .55 over
.013 deck height
1973 block
Piston to Valve Clearance
exhaust------------  .186
intake--------------   .130


so have the alumiunum heads milled to 76 cc's.

8 Pack

[firefighter3931]

8-Pack,

The E-head chambers are .080 shallower than an oem iron head. This means that you automaticly lose .080 P/V clearance. You'll be fine on the exhaust side but you're a little tight on the intake side, unfortuanately. How was the P/V clearance measured....the clay method or with a dial indicator and checking spring ?

Ron

[firefighter3931]

Edelbrock will be releasing a new Victor head sometime soon....might be worth waiting. Spoke with the Edelbrock rep at Columbus and he said it should be ready for the SEMA show in Vegas this fall. Longer valves, smaller chambers (75cc) and offset intake rockers which means the pushrod has been relocated for bigger port volumes. The chamber is supposedly going to be a dual quench (heart shaped) pattern for improved combustion.

Ron

[nivvy]

dial indicator...

8 Pack

[firefighter3931]

dial indicator...

8 Pack

Ok, next question : was the P/V clearance checked at multiple points before/after tdc ? If you're positive that your intake valve P/V clearance is correct then you'll need to make some changes. Options would include : Cam change or rocker arm change (if running 1.6's) or flycutting the pistons (if possible) for more P/V clearance. Basicly you need to create more P/V clearance if you intend to run the closed chamber e-heads with your current combo.

Ron