I'm unfortunately bolting on a set of 58cc 305 heads (14014416...80-86...305..........1.84"/1.5" valves, 58cc chambers) on a 350 that originally came with 76cc heads (14102193... 87-up...305/350......1.94"/1.5" valves). According to Chevy, it originally was a 9.3:1 compression ratio motor. I know the flow's not gonna be great (I barely have enough money to get the motor running, now, but I need to, and I can't afford new heads), but I was wondering what the CR was gonna be.

 

Nobody has an answer? I just wanna make sure I'm not gonna have to run additives in my fuel.

 

It would depend on the pistons you are using. It sounds like you have a motor out of a trk and they were more like 8.3:1 with that head and dish pistons. To get 9.3:1 on a 350 with a 76cc head would require a piston with a dome. I dont have a spec sheet to look at so i am guessing close to 10:1 with a 58cc head on that particular short block.

Lonnie

 

Probably closer to 11:1, unfortunately.

I'm in a similar boat. I'm throwing money at a set of 58cc heads for my 305.

Well, I'm not stupid, and I'm looking to put a budget 350 in the car someday. To save money, I'm looking at putting the worked 305 heads on the 350.

With any sort of a flat top, you're going to end up with basically 11:1 compression.

I've found that to get a mid-9:1 compression ratio with 58cc heads, you need about a 18cc dish.

This is not a major dish, so I think that this will probably be the route I go to. When I step up to 68cc heads, I'll just have to buy a blower to make up for the resultant 8:1 ratio.

 

So, what kind of 64cc heads are out there that came stock on a 350 that I can get used, CHEAP! As long as the valves aren't bent, I don't care. I've got new springs and rockers and whatnot.

 

Your compression ratio will change by 1.6 to 2.0 cr
depending on what you have now (pistons, deck clearance volume) when you change from 76 cc heads to 58 cc heads on a 350.
The only way to be sure is to determine your present cr once you remove your cylinder heads. Don't worry, you can adjust your final cr by using different thickness head gaskets
and or carving a few cc's out of the 416's combustion chambers
to avoid exessive compression.

The budget/performance potential of the 416 castings are
grossly under rated by those who haven't really messed with them. Granted they're not sexy or high tech.
Granted the out of the box flow with the stock 1.84 x1.50
valves is a little shy, but once ported and upgraded to 1.94 x 1.60
they can hold their own on the street.
I just flowed a set I ported and got 238@28" in and 189 ex.
This is up from the last set 224/140 at 28" Thats a nice improvement over the 76 cc smog heads you are removing. 204/110@28" at best. Once you sweep out the chambers to accept the bigger
valves you'll be at 60/61 cc's. This kind of flow #'s is good enough for 12 sec 1/4 mi. times in a 350 powered f- body.
If you are willing to put the nessessary work into these heads, the power is there.
If you're not up on measuring/calculating compression ratio,
remove your heads and post a discription of your pistons and deck height and someone here will surely help you determine your present/new cr and how to best adjust it to suite your needs.

 

Well, to answer your question, I'd have to say that you should check eBay.
Arm yourself with a good list of head casting numbers (like the one on Mortec.com - just scroll down to chevy block and heads casting numbers), and look for partially assembled heads. Usually, stock, grungy 350 heads will go for under $100. I'd recommend getting them cleaned and magnafluxed, which will add about another $80.
Cars are an expensive hobby. Sometimes I wish that I was really into collecting bottle caps, or something.

I'd have to agree with F-BIRD'88, tho. The heads you have are aparently heads with a good potential.... Although, if you are on a budget, and can't afford the 1.94 valves for the 58 cc heads, then I'd recommend cleaning them up, and putting them on eBay. You can use the proceeds from the head sale to buy yourself a more appropriate set of heads.

 

Definitely love that idea, but I need this car up and running by September. The vehicle I'm using is the parent's soccer mom van and the kids go back to school in September. I need something with a quick turn around... Like yesterday. I'm thinking of hitting up a salvage yard and seeing what I find.

 

I don't understand exactly why you need to replace the heads. Why do you need to replace the heads?

'87-later have a slightly different bolt pattern (angle of center two on each side) than the 416's will have. Not a major obstacle, but you'll need to modify those bolt holes in the intake to get them to bolt up.

Also, the 193's should be 64cc, not 76cc. Mortec doesn't say (they don't always get it right, anyway - those heads never came on 305's, for instance).

I think your best bet (if you really need to replace the heads) would be to get serviceable 193's from the boneyard.

 

The heads that originally came on the motor have a valve stuck open. Then I have a set of heads off an LG4 with a bent valve. LOL And the set of heads that is going on the motor is from a CFI 305. They're decently clean. Don't flow great, but they're gonna get the motor running. That's the important part. I won't be depending on others for rides to work or borrowing the parent's soccer mom van. And once I get a bit more free flowing cash, I'm gonna move up in the world and get myself something nice, like some Trick Flows or the Vortechs with the intake.:rockon:

 

1st off..............that 350 truck motor you have does NOT have true flat top pistons, I can almost gaurantee you that, and in that case you dished 4 valve relief pistons, and with 58cc heads and .041 gaskets(head gaskets that come in stock rebuild set) you won't even be close to 11:1. Heck, more like 10:1 or less. I have the exact setup on my girlfriends camaro, and its nothing to worry about as far as compression goes, trust me.

Ok now 2nd............why does everybody rag on 305 heads??? I put those on the RS and DAMN, I am really impresssed, that thing eats up LT1 T/A's and modified stangs pretty easy, I'll have it at the track at the 2nd to get real 1/4 times too......I got the heads for free, didnt' even rebuild them, just ported the snot out of them with my porting kit and a black and decker 1/8inch grinder, slapped an RPM intake on and this motor rocks. Pulls extremely hard all the way up to 6,000 (extreme 274 cam). The cool thing is that so many people don't like 305 heads you could almost count on getting them for free if you wanted some. Don't knock it until you've tried it is what I always say. And if my testament still doesn't sway you, my friend that now owns a 10 second el camino originally ran STOCK 305 416 heads on his autozone rebuild 350 and it went 11.60's in a 3,000 pound car with a solid roller cam and good gearing.