OK, my dad says that we wil not be able to bowl blend, gasket match, and open up the valves to 2.19/1.88 on the 396 stock heads because he says it would cost to much. Can anybody tell me about how much HP we would lose if we dont do this work.

Heck, do it yourself I did that and its not hard, even if its not so good it still helps performance. I just ordered a kit from the snap on guy 36.99 for 600 dollars worth of work. Very rarely do you mess it up unless you go really big or do somehting bad.

Motor,

I used a Du-Mor 30,000rpm die grinder with cheap hardware stones to do my last set!!

Just look where the bigger valves would fit on the inside of the 45 degree edge of the underside of each valve in relation to the existing seats.

Then just grind till the valves will fit after a good pro- valve job is done. And then take everything over to the valve-man and let him finish the install!!

Actually all you are doing is opening up the throat square so that the valve will sit on top and the valve-guy just cuts or grinds the seats to finish it....

It is shade-tree as all get-out but does work quite well when you are bucks down!!! Been there, done that.. pdq67

Thanks guys, but do you think we will be ok doing ourselves? I have no experience doing that kind of work, and my dad has very little, if we mess the heads up, we are screwed. Also, do you have an estimate on horsepower loss? I am just curious.

FWIW: At a local swap meet recently, I met a guy from up around Ft. Worth Texas who does nothing but chevy head work. He is reworking a friends TPI heads. He's enlarging the valves (and replacing them), bowl blending, porting, machining the spring lands, installing threaded studs, and milling the head for $400. That's a pretty good deal for him considering he is having trouble finding a good set of TPI-able heads. The aftermarket approaches $2000. That's probably more than you wanted to spend, and BB heads are probably more.

-dnult

If you have a steady hand do the blending part after the shop opens the seats for the larger valves. that's how I did mine - no nicks or scratches at all on the seats and IMO its a lot easier to do once you see it all afterwards. You can use a little duct tape to protect the spots you don't want to grind if you are nervous.

So budget is a limitation for you. You don’t want to spend 600+ dollars on a porting job. A cost effective alternative is doing it yourself. You could buy a kit out of Summit Auto racing for 39.99. Although I can’t tell you how much hp you will gain I will tell you that you can still do it yourself and its usually better than leaving it alone unless you really mess it up. Very rarely do you mess it up unless you go really big or do something bad.

If you decide to go this route use an 80 grit on the intake ports and lay a gasket over so you can see where the intake will lie. Also You can do the same procedure for your intake manifold but only go two inches in on the port job. On the exhaust ports of the cylinder heads grind out all the imperfections and then use a cross buff well lubricated by WD40 to smooth out the ports to a satin finish. This helps flow and really gives a boost if you use nitrous. I like to use a 120 grit around the short turn radius in your heads. Smoothes out air flow and increases hp. Only bowl blending only smooth out the imperfections in the bowl. I am always careful not to harm the seats. When I am finished I clean her out with glass cleaner (works the best) put the valves and springs back in and there you go.

I have yet to do this myself, but have been reading a lot about it so I don't mess up my heads. Check this site out...

http://www.sa-motorsports.com/diyguide.shtm

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400 in the works

I read that article and reread it. It was very helpful to me. But I was wondering when it referred to the valve throat and how it was just above the valve seat. Is that above as in, back into the bowl area, or above as in past the valve seat going into the combustion chamber. Im gonna try this out, I was A little confused about smoothing the whole bowl area, I have only heard of the Short side radius. It seems so simple. So when your deshrouding the valves do you just expand the combustion chamber size in an arch motion where the valve isnt 3/16 away and do you expand the area leading into the combustion chamber in a full circle or just an arch as well. How much lee way is there between water passages and pushrod holes and all? Is it really easy to screw up?
Thanks

There is a book called "how to modify cylinder heads"(or something like that). It shows pictures and has details on head porting and "tricks" to do to your heads. I can dig the book out of my pile and get the name and author if anyone is interested in it.

To answer your original Question, A mild pocket port job with a 3-angle valve job and backcut valves is normally good for about 25 or so HP on a stock/mild BBC. Add a big cam, compression,intake, headers,bigger valves, etc and gains be as good as 40 to 75hp and even higher depending on your combination. The fist set you do is a bitch, but once you've done a couple of sets you can knock out a pair in 2 to 4 hours grind time.

Buy, borrow, or cumshaw a set of used up heads and practice first. Get the feel of the tool and its actions. If you fall asleep too long in one spot, you'll be into the water jacket.

A joking question about porting heads, DIY asking a professional porter,
"How big do you make the ports?"
"Have you hit the water jacket?"
"No."
"Then its not big enough."

Just be careful, practice, practice, just like your band teacher told you.

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Everett "OBJECTS IN THE MIRROR APPEAR QUICKLY UPON RAPID DECELERATION"

Well I learned on a set of mustang 302 hedas. In case your were wondering that book was written by David Vizard who knows a lot. A guy I go to school with did a basic polish on his heads and then flow testede the one against the ther. It flowed 100 cfm more or so he says against stock.

On a mild street port job, the goal is to blend and conture the bowls, short side radius, and seat transition area. Hogging large amounts of metal out to make the ports bigger usually hurt flow more than it helps if you dont know how to shape the ports. A small port that flows 300cfm will make more HP than a large port that flows 300cfm. If you think you need huge ports, buy some aftermarket heads.

I think it's a game of smaller/less cc you get more lower end torque. Getting up there in breathability the low end torque disapates and you end up thriving on higher revs where your torque and HP will increase. Addicting stuff. Trying to answer the how much HP increase is hard. Rollers, forged crank and other stuff would allow getting higher revs without blowing things up... hopefully. There are shaping tricks as mentioned. Heart shaped for swirling the air and other stuff. What's feeding the cylinders determines allot of the porting increased hp also. I'd say oem style maybe 50 hp with a plane jane port job and carb tricks. Get a hard explosion shield to wrap things up if you are planning to see that hp increase even with a forged crank. If you'ld end up getting sucked into staying on it in a gear because of still good acceleration past red line.....I always wonder why some guys are in wheel chairs. Play safe.