im swapping my 350 heads for ported 305 heads next weekend and i would like to get it done in a weekend. i should be able to do that shouldnt i? in what pattern do i tighten the head and intake manifold bolts and what should i torque them down to? and for a head gasket i get a felpro .040 over gasket right? i have done alot of searching and alot of posts said to get that. if i pull the heads off and i dont have dish top pistons should i still do the head swap? im not sure the history of the engine. i was told it had been rebuilt but im not sure if it has those pistons or not. and last question, how do i know if i have a collapsed lifter? thanks alot for any info

 

You tighten the head bolts from the center out in a circular pattern. Torque the head bolts in 3 stages to 65 ft/lbs. Tighten the intake manifold bolts to 25ft/lbs.
The manifold bolts will need to be retightened after a few heat/cold cycles. (A few days)

You canuse either head gasket. The .015" felpro shim gasket will result in more compression.

DID you install larger valves in the 305 heads?
This will increase the chamber size from what you would expect.

Because of this and the fact that on most rebuilds the piston (wether dished or flat top) typically don;t come all the way to the top at TDC the compression is not near as high as you think. They are typically .025" to .045" in the hole.
305 heads with a shim gasket on a 350 rarely results in excessive compression because if this.
If you want to end up with a true 10:1 cr you'll likely need the thin shim gasket to get there.
You can measure the piston height @TDC once you get the head off.

use this to see what your compression ratio will be.compression calc page

You'll have to cc your heads to see what the chamber size is. (likely may not be 58cc's)

 

i didnt change the valves. from what i saw bigger valves just helped top end and i dont really rev it out much so since the 305 heads were recently done i am keepin them all stock except i gakset matched them and ported them a little and put a 3 angle valve grind on the valves. its a daily driver and i dont want to have to buy the really expensive gas or anything so what head gasket would you recommend? thanks alot f-bird for all the info!

 

I recommend you get the one that gives you the compression ratio your looking for, taking into account the grade of fuel you're willing to buy.

Once you get the old heads off you can make that decision.

 

on the compression calculator, do you happen to know what Piston Dome Volume in CC's use "-" for Dished Pistons is? its 18 i think but it sais make it "18" and when i do it comes up as N/A. bore is 4 inches and stroke is 3 right? and head gasket bore is 4? and whats it mean by input unit type?

 

Unit type is Inches.

the bore is 4" or 4.03" if its a .030" over rebuild.
the stroke of a 350 is 3.48"
the gasket bore is 4.166 for a .039" gasket
and 4.10" for a .015" shim gasket
the dish volume of a typical 350dished piston is 11-13cc's
The dish volume ( valve relief) of a flat top piston typically is 5cc's
the piston deck clearance is typicaly .025" to .045" below the deck at TDC
on a stock block that has not been "decked"

you won't know which pistons you have or their deck height in your motor untill you remove the old heads .
But... now you can play with the numbers.

 

i have been messing with the numbers and stuff and i cant seem to get anything under 10.5. i deffinately dont want that high of compression because i still want ot be able ot use 87 or atleast 89 octane gas. i have searched alot and found alot of people that get around 9.5 but i dont understand how. im not going to put in bigger valves so is that relaly gunna hurt me alot? thakns alot

 

cc your heads they are probabily more than 58cc's.

You also have the choice of using a corvette .051" thick gasket.

The stock valve size will limit the flow improvement
you're looking for with porting. i like the 1.94x1.50/1.60 valve combination on these heads.

 

i e-mailed summit racing to see what the thickest gasket they had was and what kind they woudl reccomend and this is what i got.


The 58 cc chamber on these heads will raise the compression beyond what
is suitable for 87 or 89 octane regardless of the gasket used.

Brad

what do u think?

 

I think you should find out what pistons are in the motor and the deck height and cc the heads yourself and see where you're at. and go from there.
Until you do that you're just guessing.