Question about porting my own heads
Hello. I have a set of heads that I am very confident I can port myself.
The heads are casting # 333882 they are sbc heads that have been cleaned magged, etc. I am not sure what they came off of, but I am going to put them on a 4-bolt main 350 block from the '77 -'79 era.
The motor is being set up for street use with the rpm range from 0 to no more than about 5500. I was initially going to go with a 383, but decided against it.
I have read plenty up on do it yourself head porting and I know I can do this if I am careful. The specs on these particular heads are as follows;
Intake flows about 137 cfm
Exhaust flows about 95cfm
The two obvious things that come out at you are the exhaust number and the large chambers. I plan on alleviating the large chamber size by running a domed 11 to 1 piston to get the compression to about 10:1. As far as cleaning up the runners. I am going to use a few intake manifold bolts to postition an hold the intake manifold gasket in place on the head--using the gasket as a template--to scribe out excess material on the intake runners. Basically I am matching the intake runners to the gasket. I am not going to get to carried away on the intake side, however on the exhuast side I am going to spend a little more time to bump up that exhaust number of 95cfm. I plan on cleaning up the bowl area staying a 1/2 inch or so away from the seat area. The idea in using these particular heads with 1.94 intakes, 1.5 exhaust, and not heads with say 2.02 intakes and 1.6 exhaust is so the velocity of the mixture going into the chamber will be a little better. At higher rpm--above 5500--I know the 2.02's would probably be better.
Can anyone provide any additional insight, potential problems I might encounter, or there own success on doing the same job?
Yeah, I know I could have bought aftermarket heads that flow better right out of the box, however; I basically got these heads for nothing, so there you have it.
Don't waste your time messing with the pushrod pinch. Those heads need plenty of work in many other area's. Sounds like you're on the right track.
If by chance you can locate a cracked or broken head of the same # as the ones you plan to port out, have the head cut directly through the ports so you can see what the port looks like from the inside. This will let you know where your water jackets are, and help you prevent getting into a thin area where 1/16th of an inch of grinding could ruin the head. Studying these cut ups will also give you a better chance to analyze how the intake and exhaust runners are constructed, and give you a better idea of how the flow goes.
You are correct about fuel air mixture velocities, and this holds true regardless of the RPM design of the engine. The trick is to maximize the velocities and volume of flow to correspond with your desired RPM range.
Just remember that a little of grinding will help a lot but a lot of grinding isnt always gooder.
What i would do is bolt the heads on just as they are with a fresh valve job. Then after you run the engine awhile and you really know how it runs pull the heads and go with your plan. This will show you if what you did made a difference or not. You can flow bench and port heads till the cows come home and untill you can verify the changes you have made work it just a waste of time. You may actually be suprised that the engine runs better with the un-ported heads!!!!!
Just my .02 Keith
I wish I had access to all the stuff needed to check out any gains/losses on my porting, but I just did it in hopes of gaining a few hp. I don't have any way to check it out, but atleast in my mind, it runs very strong.
my porting job on my 882's
I use a screw-in stud with a 3/4" long bottom as a quick gauge to be sure Im not getting carried away on the gasket match for intake ports.
At the very least get the valves backcut, I like 25 intake and 30 exhaust but everybody has their own theory on what angle to use. Good low buck mod that will pick up a few cfm.
Staying with the smaller valves will cause less problems with cutting through induction hardening on exhaust valve seats for sure. Larger valves will flow more and with same size port volume will increase port velocity not reduce it.
Theres better stock heads that will flow more but this is what youre working with. I think it boils down to how much do you spend before you could buy better different heads.
I would get one to practice on theres no shortage of junk 350 heads.
Thanks for all the good info.
I have another question that I hope does not show my ignorance. In regards to a previous response:
" Don't waste your time messing with the pushrod pinch "
What is the pushrod pinch?
Also, thats a great idea about building a box attached to a shop vac to safely carry all the metal shavings away.
I will ask some of the junkyards in the area to see if they have any cracked #882 heads that I can have so I can cut them in half.
I agree with what everyone says so far. Practice, practice, practice. You really need to get a handle the die grinder first or you can hack up the valve seats and guide bosses QUICKLY.
I'm attempting to repair a hacked up set of 291 heads. They'll need thick walled guides pressed in to repair the damage to the guide bosses and probably won't do much more for the engine than they would've in stock form.
Too much metal removed in the bowl area created a low pressure area, see the circled area. A hump behind what remained of the guide boss further upset the flow, see the arrows. The picture on the right is of the same bowl after the port cieling was raised and the hump removed.
This pic shows how far the port ceiling had to be raised above the already raised ceiling to eliminate the low spot in the bowl.
Here's one of them ready for the machine shop for a cleaning, new guides, a valve job and resurfacing.
Take baby steps when you're removing material or you'll end up with a mess like this. It's going to cost this guy a bit over $600 for the work I'm doing plus the new guides.
The pushrod pinch is at the port entrance right next to where the pushrod passes through the head.
Welcome to the world of cast iron boogers.
Why didn't he just buy new heads?
Beats me, sentimental attachment? He bought some Dart heads, well I bought them for him and he gave me the dough. If the other head cleans up as well he'll use them and I'll get the Darts for my services. If not then I'll keep the 291s unless he want them too. It'll cost him $300 plus the machine work to get his 291s. These heads, supposedly, have the correct date code for whatever he's doing. I think he's full of it but as long as he's paying I'm grinding.
A fool and their money...
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