I have a set of 882 casting Heads. I don't want to use the heads themselves because they'll kill my compression. The valves in the heads are 1.94 intake and 1.50 exhuast. Can i have the 305 heads ported to fit those valves, and will they work on a 305 with out hitting the cylinder wall? also how much Horsepower gain will i get out of port and polished 305 heads with 1.94 and 1.5 valves?

You want to reuse crappy old stock valves?

off the 350 head. The valves only have like 12,000 miles on them.

Yes, but it isn't "porting" but cutting the valve seats for the larger valves that makes it work.

And, even 2.02"/1.60" valves won't hit the cylinder walls - another myth.

Since the 305 heads already have 1.5" exhaust valves, no gain there. Porting and larger intake valves won't make that much difference of their own, but will make the heads more capable of supporting other upgrades like headers, cam, and aftermarket intake.

Hopefully you aren't talking about LO3 heads.

O wow this is disappointing. Yeah cutting makes more sense haha, i always thought that was refered to as porting.

I heard that port polish and larger valves would make a good amount of power gain. However I also heard that 2.02 valves would hit the walls on a 305.

Is it worth getting the intake valves enlarged? The valves are free and good condition. I plan on doing long tubes full exhaust, intake manifold, and carb tuning. Thats about it.

There 86 LG4 heads.

No point in wasting 2.02 on a 305. some of the tuned port 305 motors came with heads that were equipted with 1.94 intake valves and high compression, I have one sitting in a junk iroc-z.
The work you want to have done will cost about $600 in labor alone. I used to do this work for people. My advice to you is find a set of 64cc chamber heads already equipted with 1.94 intake valves. we used to called thes 305 high output heads.
I have a set with the screw in studs and guide plates for sale for $400. They are the lowback style head

I was planning to do the port and polish myself. My friend may give me his 1983 LG4 heads for free. I read elsewhere that LG4 305 heads were good to turn into performance heads for 305s. Also somewhere i found a company that did valves jobs for like 100 bucks a head. And I only plan on doing the intake valves. I was only considering doing this stuff because i could get it done cheap. Free heads and free valves. Along with the springs on the 350 heads.

Is a port and polished LG4 head with 1.94 int. valves really not that much better than stock?

Does anyone have 305 head spec info such as valve sizes and flow ratings or something?

Not from the factory. If a 305 head had 1.94" intake valves, somebody put them in after it left the factory.
They would be better called "305 low output heads". The 64cc chambers of the 350 heads would lower the compression of a 305. Since the port sizes are identical between 305 & 350 3rd gen f-body heads (not counting TBI heads), 305 58cc chamber heads with 1.94" intake valves will perform better on a 305 than 350 64cc chamber heads.
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Not if that's all you do. Like I already said, P & P lets the heads support other changes more effectively.

is your friend.

Josh: the stock 416 305 heads flow less than 200cfm in a 130 ex.

The last set I finished fully porting with 1.94" valves flowed 232@28" and 189ex. If you were to epoxy up the goofy void under the rocker stud in the intake port add an additional 6 to 8cfm.
You nailed the secret to doing this affordably. Do the port work yourself. Drill and roll pin the rocker arm studs. Then take them in for a new valve job for the larger valves and maybe get the valve guide bosses shortened for teflon seals and a higher valve lift camshaft capability. (cut the guides .200" shorter)
Have the machinist touch up the stem/guide clearance if nessessary (knurl).
Installing the larger valves will increase the chamber size a little bit (61-62cc)
chamber wall sweep.
So if you need 58cc or less finished chambers, have the heads milled accordingly.
The physical max flat mill limit one these heads is the intake valve seat edge and spark plug boss.
I have max flat milled to 52cc chambers on previous versions of these heads before. Don't remember exactly how much we cut to get that. We just kept milling till I said stop.
The increased airflow you get from fully porting these heads with larger valves will add 10 to 20hp to a stock 305. It will add 50-60hp to a well built 305 with the right other supporting parts (exhaust system, induction, camshaft, compression)
over a stock head on the same motor.
The last set I did cost me $460 total for all the machining and new quality parts (valves, springs, seals and shims). I did all the porting and the rocker stud pinning and final cleaning, spring height shimming etc.

Sheesh, sometimes its like pulling teeth here eh? Get a lot of runaround before some advice comes up.


F-birds advice is solid.
I think porting these heads and upgrading the valves is a great upgrade. Throw in a cam and you're laughing. I think exhaust upgrades are so obvious that it should be assumed you've done them already.
These are the things that make a 140HP LG4 into a 230HP LG4. I think that's a very achievable number there.

I used 1.94" valves I scammed out of a set of 993 heads that I used as practice porting heads. 7/8 of them were reusable, one was a hair bit bent and my machinist didn't want to use it, so he sold me one for $8 to replace it. Not bad that I could save $72 or so by reusing the valves. *intake* valves are a lot more "reusable" shall we say than exhaust. I managed to reuse all of 1/16 of my exhaust valves (scamming valves from my existing 416's and the 993's).

He did mention he already planned on full exhaust, intake manifold etc. I'd include CAMSHAFT in there, that's crucial.
Carb is your choice. I wouldn't drop $450 on one if that's what you're looking at. Personally I don't think a $450 Holley (throwing that price dollar value out of the blue) will get you $450 worth of value. I think that money is better spent elsewhere.

Since you've got the 882 heads, practice porting on them. Once you feel good, grind STRAIGHT THROUGH a few places, until it punches a hole. That'll at least give you some idea as to how thick the metal is. Granted you're working with different heads, but it's still good to know.

sounds good everyone. I'm definetely doing this. I've never port and polished before and i feel kinda dumb asking so many questions that may be obvious to some others but here i go:
What is drill and roll pin the rocker arm studs?
What are valve guide bosses?
What is the stem guide clearance?
What seals need to be replaced?
What are shims?
What other things other than valves and springs need to be replaced?
haha i feel dumb. I'm gonna try and look most this up but if you guys could keep giving me input that would help thanks.


I think im going to port and polish the 882 heads shine them up and attempt to sell them for around 400 with just exhuast valves haha.

Uh, whew. Ok, grab a book and read up, some are harder to explain.
David Vizards cams and cylinder heads book is a good one. Or surf the forums here.

Look who's talkin'

A hole is drilled through the stud boss and the stud, and then a pin is placed in it to make it impossible for the stud to be pulled out.

The lumps in the head casting that get drilled for the valve guides to go through on the inside, and machined for the valve stem seals to go on the outside.

The clearance between the valve stem and the valve guide. Worn valve guides and stems will have more clearance than new ones.

The valve seals.

Spacers placed under the springs to set the installed height of the spring.

Retainers, keepers and seals.

Read before you do anything buddy. get the knowledge first before you start porting those heads yourself!! There's also tons of info and diagrahms on the web.

Yea, step 1 insert mouth in foot eh?

ok thanks. I've been look up stuff and reading and figured a lot out. I think i can find my way around a head now.

Can I use the valve seals from the 882 casting heads. They were replaced with the valves and don't have much use on them. Plus this way i know the valves will fit the seals since they are together now. Is it possible? And what about the retainers and keepers? There all in decent condition, so im not sure why i would need to replace them. Right now there only going on a 305 with a stock cam. When I do get around to caming it then i will change them.

No, and wouldn't be worth the trouble if it was. Valve stem seals are cheap.

Retainers and keepers are also cheap, and if you change the diameter of your springs you'll need new retainers to match.

yeah ok i get it. I ripped the valves out of the 350 heads the other day. Can I use the springs from the 350 head? Are the stock 882 casting springs better than stock 305 springs. And if I do use the 350 springs can i just use the other components? Like locks, retainers. And how do you take out valve seals??? They seem like pressed in there.

No, the springs will be similar between the 305 and 350 heads - both are garbage for performance use.
They are a wear item, buy new ones.
Comp 981's are about the best spring / dollar you can find. $65 I think on summit, drops right in.
Retainers and locks you can reuse if you want, they don't really "wear out". But they are cheap if you want new ones.

What kind of valve seals are we talking about? Positive "wiping" type ones? You should be able to lift it straight up.

How much of the modifications to the 305 heads that have been recommended are you planning on doing? Getting the valve guides cut for positive stem seals is one I would recommend regardless of what else you are doing.

Stock retainers have a heavy "rotator" on the exhaust valve springs. They really don't help anything, but do lower the RPM capability of the springs. I highly suggest new valve springs, retainers, and keepers for that reason and the ones stated above.

When reassembled, the heads need to be set up properly. Each valve needs to be measured for closed spring height, which needs to be done after the valves & seats are ground. Any competent machine shop can do this, although they may just measure one intake and one exhaust and set them all up the same based on that - ask them to verify each and every valve (unless you do this step yourself). The valves will have to be shimmed for proper spring installed height.

uh huh i see... i guess this is going to be a more expensive job than i thought. I guess I'll get all new components.

I think im confused what is a valve stem guide and whats a valve seal. The hole that the valve goes through on the top of the head, near the rocker arm studs. Are they the seals or the guides? And do they need to be replaced? I mean like seriously need to be.

I don't plan on making a super performer. I'm going for about 14sec 1/4miles and around 220 -250 hp. I want to just fix the flow issues in a 305. And im getting free valves so i thought i'd put them to use.

When you say shimmed you mean shaved down on the top so the rockers are all touching at the right heights?

The valve guide is the piece of the head that the valve stem goes in. The top of it isn't machined by the factory, the piece the valve spring fits around. The guides can be replaced - a machine shop will drill/ream out the existing guide casting and install a guide insert - often a softer metal like bronze. If there is only slight wear, the inside of the guide can be knurled and reamed to restore its proper size.

The factory valve stem seal is an o-ring that fits over the stem after the retainer is installed but before the keepers. It basically keeps excess oil from running off the rocker arm and down the valve stem into the combustion chamber. They typically get hard and crack over time and lose their effectiveness. A more effective design is a seal that fits over the OD of the guide and around the valve stem itself - I call them "positive type" seals, rather than the "passive" seal the factory uses. In order to use a positive type seal, you need to machine the outside of the top of the guide so the seal has a good clean place to mount.

Spring height refers to the distance between the spring seat (the part of the head the spring sits in) and the valve spring retainer with the valve closed. That distance is typically more than the spring needs to be compressed, so a precision thickness shim is put under the spring to get that distance down to the proper dimension. Shims are typically 0.015", .030", etc., so the shop will choose a thickness that gets the installed height close to the spring manufacturer's specification. You don't want to put too much shim in, either, as this shortens spring life and could cause the spring coils to bind up - things get bent when that happens.

You don't adjust rocker height with spring shims - that's a function of other parts.

now that you have told us where you want to be power wise here you go

get some z28 springs off ebay. keep the lift of the cam under 480. get the valve seats cut for 194's- you will have to hog out the bowl if you want to see any gains

pin the studs for sure- buy a really good drill bit

grab all the retainers on the intake valves off both sets of heads and toss the exsaust rotators

do a good gasket match on the heads and intake and smooth out all the ports(buy a carbite bit and the sa port and polish kit) you dont have to take out alot of material except for the bowl area

before you do anything have the heads checked for cracks

FWIW, i just went 12.56@106.08mph with a backcut stock 1.84/1.5 valve combo in my 305 yesterday. i don't see them as necessary...

ok. There were some broken stem seals when i took the valves out. I know what your talking about. And ill pin the rocker studs, but is it really needed?

Also how much is a regular valve cut sizing job?
And how much will it cost to get the shims measured and made?

My 305 heads only have 45,000 miles on them.

Pinning isn't "necessary" until after a stud pulls out. Then, it's too late.

The measuring is part of the head assembly process. You determine the distance I described above after the valves and seats are ground, using the retainers you're going to use, subtract the proper installed height for the springs you're going to use, and use a shim (they are pre-made - you just choose the right one) of that size.

It's a standard machine shop task.

How much a machine shop will charge? Depends. Figure at least $150, could be more.