**305 heads on 350 block**

[1985K20]

just want to know if i can put 305 heads on a 350 block without having any bad surprises happening by doin so?? i heard it will increase my compression ratio, if so is it worth it or should i just leave the 350 heads on??

both blocks are pre 1986

 

[POWERMAD]

305 heads make wonderfull door stops.

And with the smaller chambers they will raise the compression ratio, but with the small intakes and small runners they are better door stops than anything else.

 

[sled_dog]

aka they flow like crap and won't net you power. I had a whole thing typed out but the damn forum hiccuped on me

 

[pauly383]

Tell ya what , best way to see if 305 heads works on 350 without actually bolting them on :

1. Get a straw , I like red slurpee straws .
2. Put straw in mouth .
3. Breath through straw only , not your nose .
4. Go run around your neighborhood breathing through straw .

You will not put 305 heads on after that simulation

Just playin' with ya , but ya get what they are saying now .

Real world , I knew a guy with a nice 350 bottom end . He used 305 heads and got lots of compression , and a nasty ping on pump gas . We backed off the timing and he thought it was a dog so put it back and ran good gas . Within a year he spent more on premium than a new set of heads

 

[POWERMAD]

At one shop I worked at a guy brought in a set of 305 heads that he wanted a valve job done on for his roundy round car, I just did a standard valve job and he freaked on me, he wanted a full blown valve job, after trying to reason with the guy I finaly did a full blown valve job on them. He paid the $$ and left.
Next week he came back with em and said I did a poor job that the heads are crap bla bla bla.
I took one look at em and busted out laughing, he took a die grider and had hogged out the runners so bad that the valve cover bolt holes were showing in
the tops of the runners.

 

[sled_dog]

some people don't get the idea of port shape vs. port volume

 

[POWERMAD]

The funniest part was the gasgets were smaller than the "new" port shape.

I did take pity on him and sold the guy a set of 882 heads and did a valve job on them and gasget matched the intakes for him. Most of the work I did for nothing just to get the snivling turd out of the shop.

 

[1985K20]

Thanks everyone, i guess ill just leave the 350 heads on the 350...by the way the casting number on the block is 3970010, i hear they decent blocks, but does anybody know a bit more bout them???

 

[POWERMAD]

Prolly the most common 350 blocks, they could be either 2 or 4 bolt mains.

Either one is just fine for just about any build up.

 

[sled_dog]

could be a 302 block, 327, or 350(basically all the samething), either 2 or 4 bolt, so yeah. Mortec doesn't get into nickel content and such. having a "good" block doesn't matter unless you are pushing big power. For most of our trucks it doesn't matter, same as 4 vs 2 bolt is kind of trivial in most of our trucks.

 

[dyeager535]

3970010 block is one of the most common out there, used in just about anything, and off the top of my head like 1969-1979. 2 or 4 bolt mains.

I don't think any of the blocks are better than others, but there were various differences that would have resulted in different casting #'s.

*Not trying to start anything* but before anyone steps in and starts talking about "high nickel" blocks...you'll see 3970010 blocks (and many others) with 010, 020, either, both, or none of those numbers cast into them. Supposedly 010 and 020 indicate a higher nickel content. However, this theory is supported by NOTHING but rumor passed down from person to person. There is no proof that GM ever changed the casting composition of the blocks (although they did I'm sure) and indicated it with additional cast in ID #'s. You might see it in a book or two, but again, there is no source for their information.

3970010 was probably used in just about every GM vehicle that had a 350 during the years it was produced.

 

[POWERMAD]

I do know that the 010 casting crate engine I have with 4500 miles on it had a main cap register break off when I was cleaning it with a wire wheel.

Not sure if the "hencho in mexico" had anything to do with this or not.
Could have been just a casting flaw, either way i have turned down a few mexican blocks due to that.

 

[sled_dog]

I won't touch Mexican motor parts, in any form, bearings, block, heads, whatever NO

 

[dyeager535]

You know, at one point in time I heard the hecho in mexico blocks were very good. I can't recall where I saw that, and it very well could have been a printing mistake.

I guess I'd have to see a few blocks fail the same way before I blamed the whole series/line/production point...one of my stock Vortec studs, brand new, snapped off, according to someone that knows machining, it was probably due to overheating the stud while putting threads on it. Certainly can't blame all GM studs for a failure rate of probably 1 in 1 million, just sucks to be that one.

I know blocks can be tested for metal content/composition, and I had the means to have that done awhile back, that is really the only way the block "quality" (besides casting and machining techniques used) can be accurately tested.

 

[POWERMAD]

On this block(4 bolt main) the break was an old one, that's why it just flew off with a wire wheel.
It could have also been damaged when the engine was assembled too. Who knows.

 

[Thunder]

I came back to the orginal topic of this post because no one addrest the reason why 305 heads are no good on a 350. I have heard the BS that they raise the CR so you will make more power. That is total BS.

305 heads are designed for a 305 engine. 305s have a smaller bore than a 350.

Putting 305 heads on a 350 will shroud the valves totally screwing up the flow. You will only loose power by putting them on. You would be better off porting a set of smog heads.

 

[pauly383]

I came back to the orginal topic of this post because no one addrest the reason why 305 heads are no good on a 350. I have heard the BS that they raise the CR so you will make more power. That is total BS.

305 heads are designed for a 305 engine. 305s have a smaller bore than a 350.

Putting 305 heads on a 350 will shroud the valves totally screwing up the flow. You will only loose power by putting them on. You would be better off porting a set of smog heads.

Which is exactly like breathing through a straw

 

[WantedaDodge]

At one shop I worked at

Powermad, what part of oregon are you from?

I'm in eugne.

 

[big_truxx]

Tell ya what , best way to see if 305 heads works on 350 without actually bolting them on :

1. Get a straw , I like red slurpee straws .
2. Put straw in mouth .
3. Breath through straw only , not your nose .
4. Go run around your neighborhood breathing through straw .

You will not put 305 heads on after that simulation

Just playin' with ya , but ya get what they are saying now .

Real world , I knew a guy with a nice 350 bottom end . He used 305 heads and got lots of compression , and a nasty ping on pump gas . We backed off the timing and he thought it was a dog so put it back and ran good gas . Within a year he spent more on premium than a new set of heads

 

[big_truxx]

also good heads aare affodable. summit sells the old style heads that flow better than the camel hump fuelie heads and also the vortec. both heads are $650.