Ok, here's my problem... my engine is on a stand right now and is completely disassembled. It's an '81 350 with stock (dished ) pistons and stock replacement heads. My first question is this: can someone help me to learn a bit about these heads. I've checked on all of the links that I could find using the search function on the site and have found nothing more profound than "350 heads"... the part number on the heads is 14079261 and I believe that they MIGHT be what are called L21 heads. (?) It also stamped with "D236". They are cast iron.

The other thing that I need to know is this: the most that I will be able to do for quite a while is port match these (most likely crappy) stock heads, so I need to know if it is a good idea to replace my current cam (XE262 from my 305) with the 268 or if I should wait and do it later when my heads are more appropriate. Something tells me that for the next little while I would be better off with the 262, however... Sometimes bigger is actually better

Thanks

 

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From http://www.mortec.com/castnum.htm all I see on your castings is that they were specified for 350 engines in 1975. None of the usual info on chamber size and whatnot is posted.

Sorry, usually there's more info available.

 

According to a few other sources, that cast number is from a 1986-only 350, not specified as passenger car or truck.

http://www.cehighperformance.com/c_t...lock_codes.htm

http://albany.isoa.net/~mharrisj/sbcheads.html

http://wanman.ca/cylhd.htm

http://www.kendrick-auto.com/chevrol..._number_re.htm

http://www.jimsperformance.com/headchart.html

http://www.stingray.nu/temp/heads.htm

http://www.onlineperformanceparts.co...les/chead1.htm

http://www.sallee-chevrolet.com/Worl...ent_Heads.html

All of these identified the casting as a 1986 part used on '86-87 350 SBC engines. As such, they might be fairly decent if they are not swirl-port designs, but should still be massaged to accept bigger valves and get treated to larger ports. If you can only match the ports, at least it's an improvement.

As for the cam selection, if you're keeping the smaller valves and runners, a little extra lift and duration might actually help, since velocities should remain high with the smaller runners you might actually get a little more charging/scavenging by holding the valves open longer. With larrger valve faces, it would be easy to go with too much cam.

 

The were cast April 23, 1986.

 

If you can match the ports, you can probably open up the bowls. It could be argued that bowl work is more effective than port matching for flow improvement.

Standard Abrasives (http://www.sa-motorsports.com/diyport.htm) recommends opening the throat to 85% of the valve diameter. That little step there is the majority of the improvement in porting work.

 

Most likely, they are in fact crappy heads. If they're the "swirl port" TBI heads, then they're some of the worst 350 heads ever, as far as flow (and therefore high RPM operation) is concerned. But they'll make good torque at low RPMs, below 3500 or so, and then nose over at 4000 or 4200, no matter what else you do to them. They are not worth spending much time effort or money on, and require a cam to match their low-RPM tendencies.

If I pick only one thing to do with a die grinder to a set of heads before I installed them, I would do a bowl blend long before a gasket match. That looks pretty but accomplishes nothing if there are giant steps and mountain peaks and stuff right at the smallest cross-section part of the port.

Especially if they turn out to have the "swirl port" ramps, I would keep the cam small, to avoid the usuall mismatch of a cam that kills low end and heads that kill high end so you end up with neither.

 

14079261 is listed in the msa-1 number guide as 82-88 350 truck 1.72 intake 1.5 exhaust valves and 76cc chambers.

You CR is too low for the XE268 cam. Like RB says it will kill your low end.

 

That sounds about right given the measurements I took last night. Thanks to all of you guys for the help, I think I'll stick with the smaller cam until I score myself some AFR's (yeah right, probably vortec's, world's or edelbrock's, I'm undecided) and get the rest of the engine ready to facilitate some better flow. A new carb and intake sound just right - one for Christmas, one for ... new years!

How many of you guys think that it would actually be worth it to jack up the valve size a bit? If it's not really going to make that big of a difference, I'm not going to bother - money doesn't grow on trees, after all.

Thanks again.

 

Given some further searches on this board and the utter crappiness of my stock heads, I'm wondering if people can give their opinions as to whether or not I am better off with my STOCK (unported) 416's off of my old 305...? They should bring me to about 9.5:1 compression ratio and have bigger valves... I don't have time or even the money (although it's not much, I'm a pathetic working student) to port and polish them right now. Whaddya' tink?

 

If i had to choose between the two the 416's would be my pick.

The other heads are more more suited for a dump truck.

If you cant do a little bowl porting on them at least have them reconditioned and a good muti-angle valve job done.

Good luck!

 

I talked to my dad tonight and he graciously agreed to fork out the minimal dough to pick up some materials with which to try grinding on these 416's a little bit. I might be able to afford the valve job... we'll see, but I figure that, aside from destroying the heads, I can't make them much worse than what I've already got! Power + LOW low budget = frustration. Hopefully when it's all said and done, I might be able to throw this motor back together with my new exhaust and headers and get somewhere close to 300 flywheel horsepower... Thanks for all of your help guys! Hopefully some day I'll get a digital camera and I can share my ride with you - I'm certainly eager to do so! (Even though it's not that impressive )