Sup all,

I have a smogger era '75 350 3970014. It's a generic one which I suspect is from a van or truck. I have 416 heads lying around off of my old blown 86 305. They've been sitting outside under a cover.

Just wanted to know if it'd be worth putting on my car. I've read around on this forum and on nastyz28, but really didn't get a direct answer as people either modified them or had modified motors.

Basically I just want to know how much I'd be looking at just to put these on and if the gains are there. What would have to be done to the heads/block? I work in a machine shop, but I'm not a machinist if that makes sense, so if it's easy maybe I can do it?

I don't know much about what's done to the engine as I bought it complete, pretty sure it's all stock specs. The PO had it in his Vette and claimed it was rebuilt 10k miles ago. He didn't drive his car much, so that 10k was a long time ago. I installed everything on the car with a friend on the street, so I don't mind the labor swapping heads.

My Goals: Not looking to put much into it, I mean I bought the engine for 400 bucks. The car is my daily. I just need it to be reliable for the next 2-3 years. Not looking for power, just figured since I have these lying around I wounldn't mind slapping them on. It's not fast at all. I know uptop it's even more slow, but that could partly be because my speedo is not working and not locking the converter. I also still have to weld the O2 bung and put the sensor on. Basically the car's a dog and if these give it a little more pep for little $, that'd be nice. Also, I'd like to run on regular.

Mods: 700r4 w/ shift kit, mid-tube headers, true 2.5" duals no xpipe with bullet mufflers, unknown LS rear gear, stock 86 converter, stock untuned 83 cc-carb, !egr, 6* timing

Of course, I'll be doing this in the summer if at all.
Thanks

 

In stock form the 416 heads will lower the compression quite a bit, which should add to the power a bit. The 416's get pretty good when they are ported/polished. That should be easy for you to do, since you work in the machine shop. You'd want to get them torn down, checked for cracks, then port/polish (plenty of instruction here, and you work at the shop, so you can get 1st hand input from a machinist), then have a valve job done, and install new Viton valve seals. You could also have cut for 1 size larger intake valve and add new intake valves. That should wake up the 350 alot over the smog heads. But with the added compression, you'd probably need to increase the octane (higher priced gas).

For the rest of us, that machine work (not the porting, just the valve job, crack check, seal install) is about $300 - for you it ought to be damn near free!

 

the 416s are 58cc heads(some vettes have the same 58cc chambers) thats the high point but the valves are 1.84 intake and 1.50 exhuasts and dont flow really great because of this,but with a little time and a bit of grinding you can improve them. your 75s is prob 78cc epa smoggers that dont flow really well either.Ive done some pretty agressive gasket matching on 416s for both 305s TPI and 350 TPI and had friends happy with the results. but you might have to run nothing but premium gas. this is just my opinion on a easy cheap way to gain a few ponies.

 

camaronewbie, Forgot to mention, it's not an engine machine shop. It's my college shop that makes parts for senior projects/research. We have lathes and mills, nothing auto specific.
So as I see it, there'd be a quite a bit of machining.
Won't the heads raise compression since they are smaller? Or do I have it backwards?

 

Sounds good. Would TPI translate the same on carb?
The premium gas running is a deal breaker.

 

no. best case with the 75 heads your probably 7:8 to 8:1 compression ratio with the 416s your 9:7 to 10:1 depending on your pistons(dish,flattop,or dome).the higher comp ratio the higher octane rating required to keep from detonation or fouling. TPI will make the system more efficient, improving throttle response over all performance through out the rpm range and mpg(you will use less gas all around) but unless you plan on gas additives (octane boosters)you will have to run premium gas

 

Yes, they will raise the compression ratio. Camaronewbie, while correct in the rest of his post, had that part backwards.

I'm running 416 heads on a 70's smogger engine in my Camaro. If you have the stock dished pistons like I do, compression ratio will be around 9.2-9.5:1. My Camaro runs fine on 87 octane with a carb. You can control the compression ratio somewhat by the thickness of the head gasket you install.

I ported my heads myself following a post by Sitting Bull. He's got a great write-up on the process with lots of pics. I didn't install larger valves due to funding shortfalls, but I plan on doing it someday if I don't install the Vortecs I found this summer.

The engine does run out of power around 5000-5500 rpms, but it pulls nice and strong up till that point. TONS of low-end power.

 

https://www.thirdgen.org/forums/tech...-pictures.html

https://www.thirdgen.org/forums/tech...6-heads-w.html

Found those two threads.

Seeing that you have a similar setup, it's reassuring that you're running 87. After what frankinmaro and camaronewbie said about nothing but premium, I was going to completely scrap the thought. I probably wouldn't do the larger valves either, as that'd be another $120 which is eh.

Let's say after popping off the heads and finding their not dished, could really thick gaskets keep me with 87? I'm pretty sure they're stock dish though.

 

If they are flat top pistons, I don't think you'll be able to get a thick enough gasket to lower the compression enough. If they are domed, you can forget about it. With dished it should be no problem. You should be able to turn the engine over to TDC on #1 and remove the spark plug and see what kind of pistons you have.

The other thing that will factor into your compression ratio is the diameter of the cylinder bores. Do you know if the PO had the engine bored when it was rebuilt? And if so, how much it was bored out?

 

Ooops! I did state "lower the compression" didn't I? I meant raise - I'm just getting senile!

 

I'll check looking through the spark plug hole if I go this route. I think I rememer the PO saying it was rebuilt with stock parts. Don't know if that means the old ones or equivalents. No idea on the bore.