I'm trying to figure out the combustion chamber volume of a 1969, 300 hp 350. The factory info says the combustion chamber volume is 4.83 cubic inches. I found a conversion chart on the web that says that works out to 79 cc's.

Does that sound right? Sounds like it is too large to me. (Yes, I did do a search).

Thanks.

Edit: Okey dokey, I must have goofed. I found some replacement heads available through GM and the combustion chamber volume is 64 cc's. That sounds better (I've never even heard of a sbc with 79 cc combustion chamber. 76 cc's, yes, but not 79).

64 cc, double-hump type chambered heads!!

Motor should be an old L-48, 295hp or 300hp/350 is all...

pdq67

Aren't the double-hump heads the big valve fuel injection heads? I've got the small valve (1.94") heads.

Originally posted by Parrydise7:
Aren't the double-hump heads the big valve fuel injection heads? I've got the small valve (1.94") heads. Same basic head, different valve size ;)

Plan on running a dished piston if you try to use these heads. It will ping itself to death if you don't.

Tom

Whether you have the 3927186 or 3947041 castings, (both were used), the CC's are 63.305.
My book shows the 186 head on the Corvette to be the only one with 2.02/1.60 valves and the CC's are the same.
The 041 head, if used on the Corvette and having the 2.02/1.60 valves shows the CC's to be 63.995, so essentially 64 CC's.
The 041 heads are NOT double hump heads. They have a triangle shape on the end.
The 186 heads have the same shape on the end as the double hump heads of years before, but considerably shorter.

Hope this helps.

What Tom said above is exactly right.

Nate

Regardless of what all the books say these heads normally run between 64 & 66cc's uncut & GM never came that close in any casting in the real world to give a spec to three decimals :D
They will work just fine on a flattop 350 at about 9.5 to 10.0 depending on where the piston is.
A stock 350 at .025 in the hole will be about 9.6 & it will be about 10.1 with a zero deck & .039 gasket assuming 64cc's
A good uncut combo is the .018 gasket which is a 10.0 engine with reasonably good quench & with a 270 degree cam is not normally detonation prone ;)

Thanks for the great info!

So I can add the big valves to those heads.

Can I also install an L-79 cam (from the 327/350hp engine) without any trouble when I do the head work?

BTW, I have to run racing gas so it won't ping. I guess that isn't too surprising because it has a 10.25 to 1 cr.

Thanks, again.

Hi--
I also have an L-48 350, but it's in my 70 Nova SS. It's a matching number car, I think this is a great small block motor. I can run premium gas and it runs just fine, even with the 10.25 to 1 CR. My car has the 186 heads with 1.94 valves also. I have heard you can add the 2.02 valves and even bring it up to LT-1 specs. I don't know.

Nice to see someone mention an L-48........

ktownkid

I said, "double-hump type chambers"!!

And right about them being right at 66 cc's when factory cut for big valves and not medium valves..

They won't flow any better cut for big valves unless you plunge cut the intakes to unshroud the chamber walls around the intake valves like stock!!

pdq67

Originally posted by pdq67:
I said, "double-hump type chambers"!!

They won't flow any better cut for big valves unless you plunge cut the intakes to unshroud the chamber walls around the intake valves like stock!!

pdq67 If I take those heads (I checked, I've got a triangle, which I assume means they are 041's), to a shop to be machined for the bigger valves, they will know how to do that plunge cut, right?

And yes, ktownkid, the L-48 is a great engine (although I wouldn't mind making it a little bit better, L-79 to be exact). So good, in fact, that GM made them until 1999. I may have some carbon build-up which requires the use of racing gas.

I said, "double-hump type chambers"!!

Although I know what you meant, You are partly right. There are 4 different "double hump type" head castings. The 461, 462, 291 and 186 and they have different sized chambers. They range from 62-64 CC, (roughly).
Of course it doesn't matter what a book says. The heads should always be CC'd to know for sure.

You can enlarge the valves to the 2.02/1.60, but the heads won't flow much better unless you open up the ports.
To make it more simple to understand, you can put a huge valve in a head, but unless you increase port volumne to enable more flow, it won't help much.

If you do put in the larger valves, then the chambers should be fly cut to unshroud the valve.

If you run a cam with more than .450 lift, then you need to install screw in studs. Although, I would recommend screw in studs in any performance application. I've seen press in studs pull out in stock engines with less than .400 lift.

Mike says you can run a flat top piston. I partially disagree. It depends on what part of the country you live in and the gasoline that is available. Out here in CA we wouldn't think of it. 10-1 is too high in a non computer controlled vehicle. It depends on the cam too.

This could go on forever......a lot of variables.
Aluminum heads vs cast iron heads, etc etc.

Nate

Thanks for the great information!

oops graemlins/clonk.gif

Originally posted by SS3964N8:
I said, "double-hump type chambers"!!

Although I know what you meant, You are partly right. There are 4 different "double hump type" head castings. The 461, 462, 291 and 186 and they have different sized chambers. They range from 62-64 CC, (roughly).
Of course it doesn't matter what a book says. The heads should always be CC'd to know for sure.

You can enlarge the valves to the 2.02/1.60, but the heads won't flow much better unless you open up the ports.
To make it more simple to understand, you can put a huge valve in a head, but unless you increase port volumne to enable more flow, it won't help much.

If you do put in the larger valves, then the chambers should be fly cut to unshroud the valve.

If you run a cam with more than .450 lift, then you need to install screw in studs. Although, I would recommend screw in studs in any performance application. I've seen press in studs pull out in stock engines with less than .400 lift.

Mike says you can run a flat top piston. I partially disagree. It depends on what part of the country you live in and the gasoline that is available. Out here in CA we wouldn't think of it. 10-1 is too high in a non computer controlled vehicle. It depends on the cam too.

This could go on forever......a lot of variables.
Aluminum heads vs cast iron heads, etc etc.

Nate =
Nate,
While I tend to agree with most of what you said,
I happen to live in Ca (notice signature) & I have done a number of flattop 270+ cam 9.5 to 10.0 engines & with good quench I will repeat, they are not normally detonation prone if done properly ;)
The quench along with the timing curve & cam is a big deal in regards to detonation.

The combo was either a zero deck .039 gasket or .018 shim with just a cleanup cut to 9.020 & an Isky 274 Mega Hyd or the Comp 270AH-10 hyd cam along with some other solid ones.

I have seen combos with destroked 1.540 rebuilder type pistons that put the piston in the hole .040+ thou & calculated about 9.0 that people thought were 9.5+ because they didn't measure anything that were a detonating pig.
I have also seen some that seemed happy with a combo like this that shouldn't work??

As for valve size, we have used a LOT of these castings in circle track deals where they mandate a stock casting & outlaw Vortecs.
There are lift rules on some & low lift flow is everything.
A poorly installed 2.02 intake will lose as much as 15-20 CFM in some cases.
This same deal with an unshrouded chamber & attending throat work with NO GRINDING ALLOWED will improve flow at all lifts.

Also, in cc'ing probably close to 100 sets of these different small chamber (64cc type)castings over the years I cannot recall ever having one come in at less than 63cc's UNCUT with original valves but that doesn't mean there are none so I will sort of agree that there are probably some 62cc ones out there,,, I just haven't seen them in almost 40 years of doing this ;)
Most were 64-66cc's with some going larger ;)

Now, all that said, I personally think spending any money on the old casting to install screw in studs, adding hard seats, big valves etc is a complete waste of money as I can do a set of the new SR type heads that already have all this done for less money (but I don't give my time away either :D ) & you will have a better casting that will be as good or better than the best of the early heads.

Tell your neighbor Joe I said hi if you see him graemlins/beers.gif

Mike, I understand and agree with all you have said here. Good info ! I've experienced the same.

Kinda baffled, who's this Joe ?
I know a lot of Joes.
Brown ?

Nate

There's at least one more double-hump type head, but doesn't look 100 percent the same AND that is a 305HO, -601 head. Pretty darn good head if I do say so myself too!

Mine are a schosh above 160cc, intake port-wise and down around 55 cc's chamber-wise so will do great on a small motor like a 283/292, imho... 1.84"/1.50" valves with hardened seats too...

pdq67

Originally posted by SS3964N8:
Mike, I understand and agree with all you have said here. Good info ! I've experienced the same.

Kinda baffled, who's this Joe ?
I know a lot of Joes.
Brown ?

Nate =
Sorry about that, being where you are I figured it to be an automatic graemlins/clonk.gif
The Mondello's of course,,, good friends, super people

Oh yeah I gotcha. That Joe.
I haven't seen Joe in a while.
The earthquake a year ago shut down our machine shop. Joe used to come thru about 6-7 times a year. He runs the tech school, you know.
I have done some work for him on occasion.
Mainly putting in seats that he couldn't do, for whatever reason.
I drive right by Mondellos on Paso Robles street several times every day ! Sold them my 71SX w/455, then got the carcass back. :rolleyes:

Nate

Okay, guys, one more question.

The Fast Burn heads have a 62 cc chamber. Could I plant a set of Fast Burns on that engine without any modifications? (I think I'd also have to change the intake).

What would be a good cam for that? Would the HOT cam with 1.6 rockers work? (The car has an a/t)

Would the old L-79 cam work with this combo?

I posted this question on another location but got no response. Thanks, again, for all the help!

Originally posted by Parrydise7:
Okay, guys, one more question.

The Fast Burn heads have a 62 cc chamber. Could I plant a set of Fast Burns on that engine without any modifications? (I think I'd also have to change the intake).

What would be a good cam for that? Would the HOT cam with 1.6 rockers work? (The car has an a/t)

Would the old L-79 cam work with this combo?

I posted this question on another location but got no response. Thanks, again, for all the help! You betcha except for the cam as it is a roller & I would expect about a 50HP increase over the old heads with a newer cam.
Also, if you are looking at new heads a less expensive route would be the Vortec with the spring upgrade.

Also a set of AFR 180cc heads would work killer & are not that much more than the fast burns (at least not from me :D ) & take the standard style intake.

I don't keep track of all these damn L-XX blah blah numbers so you will need to indulge me but I am assuming you are referring to the old GM 221 @ .050 350HP 327 cam??
Good cam for it's day but there are a lot of better cams out there now ;)

Originally posted by Wolfplace:

I don't keep track of all these damn L-XX blah blah numbers so you will need to indulge me but I am assuming you are referring to the old GM 221 @ .050 350HP 327 cam??
Good cam for it's day but there are a lot of better cams out there now ;) [/qb]Yup, the L-79 is the old 327/350 hp engine. Since the design is about 40 years old, yes, I guess it is a bit dated, isn't it!

Thanks (again) for the great info!

Imho, the sucker still runs good in the old stock L-79 motor it came in if you can find pump gas to feed it!!

A '66 Duece Coupe 4-speed car will get right up AND go...

pdq67

You are definitely right about the pump gas. I found a station that has 103 and 110 (!) octane gas. Damn pricey though.