Does anyone know what the CFM flow numbers are at .500 for the stock 081 castings (305 not 350) ?

thx,
RP.

 

I'd guess in the 170-180cfm range, maybe less.

 

Thats a tough question.

Checked 4 years of magazine articles and all of the casting books I have. Only information I can find is that they are stock 305 heads 87 to 95 years vary by books I found them listed in. Some say only 87 to 92 etc.

Sorry for the lack of info, but I take it these heads are on your current engine and if the factory hp rating is 230 or so the flow numbers must be fairly good and the heads would probably respond well to reducing the restriction at the pushrod, gasket matching and bowl porting. I bet there is another 30 to 60 horsepower in them depending on the amount of porting and size of valve you use in them.

Ric

 

THX for looking I appreciate the effort. I came up dry too.

I have been measuring what it will cost to work over the factory heads vs. S/R Torquers vs expensive aluminum pieces. Whatever I do/buy has to be compatible with a 350 or 400 (future upgrade).

My 305 makes 230hp factory I am dyno'd at 260hp/335lbs torque as of last August. The dyno shop (Forrest & Forrest Racing) say they can get another 25% flow out of my factory heads for about $400-500 worth of port and bowl work. I would get the valves done at another engine shop where I can get some pretty decent discounts on basic head work -- 3 angle grind, decreased radius valves, 1.94 and 1.6, etc.

I am hoping the sum total of the head work + a cam (210/218 4.80/.480) + headers + misc tuning mods will see me another 50hp I am hoping for 1hp per cube out of the 305. Hey if I can pull that off who needs a 350 eh ?

The catch is without knowing what the stock flow numbers are for the 305 heads I don't know if another 25% increase in flow will be meaningful when compared to some S/R Torquers or aluminum heads ? Rudy Held seems to think it is not hard to get 200-210cfm out of my heads for about $500 worth of grinding and given the valve upgrades. The S/R Torquers are about $1375 with tax I can get my factory heads done for about $800. Gets down to dollars and CFM.

thx,
RP.

 

Porting Heads is not that big of a deal to do yourself.

All you need is a decent air supply a $35 dollar die grinder a few carbide burs and a couple of mounted points.

The major thing to consider when porting is maintaining a constant number of square inches throughout the length of the intake port. The major restriction in a set of heads is almost always at the point where the pushrods pass beside the port once you open this up as much as you can then all you need to do is make sure the rest of the runner has at least the same amount of square inches. Bowl porting does not follow this same theory however. When you open up the area below the valves you are doing this so that there is a charge of fuel misture waiting behind the valve for the instant the valve opens. Therefore the square inches of the cross sections below the valves is usually larger when bowl porting. Similarly when you match the ports at the gasket face you are merely trying to make the transision from the intake to the head smooth to reduce turbulence. This area will also end up being larger than the rest of the port.

The exhaust port is a little different. ideally you want to match the port to you header or exhaust manifold. The critical thing to get flow out of the exhaust port is to create a radiused venture directly below the valve to excelerate the exhaust gas as it is exiting the head.

Enough jabbering. My point is save the money and do it yourself. Get the shop to open up the heads for the new valves and if they have the cutters rough in the bowls for you. Then port them yourself and have them finish the valve job. Should save you enough to buy slicks or a compressor to do the job with if you don't have one.

ATB
Ric

 

You know you have a good point. I could buy the tools and f*ck up atleast two sets of heads, replace them (used) and still be ahead of what the shop wants -- no less than $700 CDN to do the grind/port/polish work for me.

No time like the present to learn eh ?

thx,
RP.

 

I have done a few sets myself and about the only way you can screw up is if the casting has a bad core shift and you grind through the wall (This will happen if the shop does it and there is bad core shift also.) or you hit the seats with your grinder that is why I recomend not finishing the vavle job until the porting is done although I have done it both ways.

The first set of heads I did were 462s. When I finished the intake runners were 196cc. I put the heads on a 355 with flat top pistons a 2 barrel holley and a hydralic Cam with 284 duration 490 lift. Engine made 359 horsepower on the engine dyno at Kelly's engines. Just a bit better than 1 hp per qube. It is possible and there is no black magic involved. Just make the intake runners the same size all the way through and you are 90 percent there.

Ric