What's the issue with the 305 CID in the Emission controlled C3's? When I try to find info on doing mods, all I get is: "the only thing a 305 is good for is parts for a 350".

Is that true and are all GM 305's just parts for 350's?

Why is it that a Chevy 302 is the “shisnick son” and a 5.0 liter in any other make is a desirable engine, with the exception of GM?

 

I'm a bit confused. GM 305 and 302 are two totally different engines. 305 isnt bad by nature, but all the parts (heads/cam etc) that it uses are the same as a 350. And since the external dimentions are the same, why not trade up. To the best of my knowlage, (vetrans help me out here) the 302 was never offered in a Vette. Camaro motor if I recall. (1969?) To sum up, nothing wrong with a 305, just too easy to trade up to a 350 is all.


-Bob

 

There are a few guys that can give you tips for making big power with the 302, 305, and 307. I think they were capable of more with higher RPMs but I don't know, I have never built one. I used a few for parts for a 350, and I usually want more cubes than that.

 

California 305's from 1980 have emissions tune and use nothing but base engine grade components. They are smaller than the other 49 states 350's so they burn less gas and spit out less polution. Not great for performance, they get you there and back.

302's were built for SCCA racing in "stock" classes where Ford's Mustang was competing under a 5.0 liter engine size limitation. That was the only reason to build the 302. It was a Camaro Z/28 only engine. The '67-'69 GM 302 had the best parts Chevrolet ever put in a special high performance small block. High compression forged pistons with spirolocks, special babbit plated pin bore full floating wrist pin connecting rods, forged steel crankshaft, solid lifter cam from the 327 cube/375 HP engine, high rise aluminum intake, Holley 4 Barrel carb, High RPM deep groove pulleys, 8" balancer, etc. This engine was desinged to beat up Mustangs and help sell Camaros. The 1980 305 has none of the above.

The SCCA rules were changed for the 1970 race season so the need for GM to produce "street" versions of the "race" engines were no longer required. SCCA allowed de-stroking a showroom floor engine to fit within the 5.0 liter limit for the class that the Mustangs and Camaros could compete in. GM then stopped building racing 302's and started selling Camaros with 350 engines which were much more "streetable" as purchased. These are a much better car to live with on a daily basis. Beginning in '71, the HP went down every year and the emissions got tighter so some of the HP components went away within the next few year models.

-Mark.

 

I'm interested in this as well... I would like to know what I too can do to my '80 with the 305 to get a bit more power.

 

Easiest and cheepest places to start are the same as for the 350s of the same vintage. Get a high flow cat and optimize your timing. After that, heads are a good place to go next.

 

302 is a big bore/short stroke engine, loves to rev.
305 is small bore/long stroke, supposed to be more efficient than a 350. They can be made to make power, you'll need to follow similar rules to a 350 - it's all about the combo. Use heads that are suited to the small bore, cam suited to the stroke, etc. Big heads on a 305 will make more of a dog than an over-headed 350. If it's a numbers matching engine, I'd shelf it and build a 383 out of a late model hydraulic roller block with some vortec heads. That's a relatively inexpensive combo that'll push your eyeballs toward the back of your skull!

 

SCCA rules required a stock production engine with a 5 liter (305 cu in) limit. Other than a slight over bore the bore and stroke had to be remain stock. Dodge started racing Darts with 273's and Mustangs raced 289's. In 67 Chevy created the 302 Z28, Ford answered by bumping the 289 to a 302, AMC moved up to a 304. As the saying goes, there's no substitute for cubic inches.

If I remember right what Chevrolet did to produce the Z28 302 was the same thing hot rodders and racers had done for years. They crossed a 283 with a 327. Rodders called it a 301, Chevy a 302, I think the actual size is in fractions between 301 & 302, so either works. L88plus is right about the "big bore small stroke loves to rev", that's why rodders/racers loved this combo as the 301, they revved all day long and produced tons of power.

The small bore long stroke of the 305 just dosn't rev as well and doesn't quite respond to mods as well. With the popularity of early 80's, 305 camaros, a lot of 305's have been built up with good results though.

The old 307 just never seemed to be happy with mods. It was designed to be a nice, relatively economical 2bbl V8 and it served that purpose well,

 

My Step Dad told me that the 307 was replaced because there were issues with oiling to the center cam bearings and there were lots of resulting problems.

 

What type of heads and what specifications? Should I have the 305 heads worked on instead? My concerns are that I have to smog the car every other year, and my '80 305 is equipped with the computer. The engine is original (H) vin code.

 

I don't remember the combustion chamber size of the LG4 but you would want to go that size or smaller. Any of the aftermarket heads should give you a boost in flow even if you don't increase the CR. I'd keep to the smaller intake runner heads like the 170 CC on RPM heads. This shouldn't be a big problem with smog.

The cam is much more of a challenge. Typical aftermarket cams have too much overlap for the primative computer to deal with. There was a smog cam called something like "envirocam" but I think they were for EFI engines.

 

the computers on the 80 are not very complicated. I bet a head and intake change would not affect it much (the computer). Whether it would give you a performance increase though i don't know, simply because I don't know if those computer controlled carbs will take advantage of it. Swapping the stock carb on for the emissions test would be simple if you swapped it over to a tuned quadrajet for the rest of the time. This way you could swap the heads and intake out and actually get a performance boost. Stick with an intake that has egr and paint your performance heads to look stock; then you wont have to switch the entire top-end over every two years .

 

The 305 small bore = small valves, valves shrouded by cylinder wall, limited head selection = poor flow, less power.

 

and from what I've heard, there may be some issues with installing "large valve" heads (1.6/2.02) on a 305.

Wow. I'm recalling the days of my youth when I could rattle off the bore/stroke & displacement of every conceivable combination of small block Chevy parts, and realising I can't do that any longer. How I long for those days when that was some of the most important info in my head!

 

As I understand it, the large valves may give up some torque, especially at the low end but give back some high end HP. A 1.94 intake valve may be better suited to this displacement than a 2.02.

 

Whadda U?? a olde tyme phardt or something???

cripes, I even forgetting my olde tyme PONCHO stuff anymore....only been 20 years since the last build up....and ten since I sold the last of them.....

But on topic again....I have heard constantly over the years that the 302 is the only 5 liter Chebby engine worth a damn, and the rest of them 305-307, etc are not worth a damn, the 327 is outta production too long as is the 283 much less anything earlier.....

problem is, the heads, blocks, and internals are so limited for any performance use, the only ones that did a damn thing was the 305 in the Camaros with the L98 injection....but even then the heads are thin cast and fragile....heard this countless times....

given the stories, methink it's a time waster....go for the 350 roller block that is from '88 up....or better yet, buy a ZZ4 and get over with it...

 

I'm at least twice as old as I was back when I was half my age!

The 305/307 suffer from small bores (3.74 & 3.875). The 305 was really a de-bored 350, and the 307 was a stroked 283. They're both the only SBC's over 300 cubes that have small bores.

 

307 is a de-bored 327. 3.25" stroke and small bores that will not accept any big valve heads. It does not have much of a following these days.

-Mark.

 

Which, oddly enough, matches the specs you'd have if you stroked a 283

 

WHAT????? You guys started a discussion of my favorite mouse motor and didn't inform me??? The 302 engine was highly underrated as far as horsepower is concerned. Factory rating was 290. Actual horsepower was closer to 375...even higher if you used the crossram package Chevy offered. The downside to building a 302 Z-28 engine nowadays is the internal parts. The block is identical to the 350 4-bolt main block (even uses the same part numbers). But finding all the forged goodies and correct length rods and special pistons is pretty hard to do. I know because I've tried.

The 302 Z-28 engine was made to live at 8000 RPM. And it did it quite well. Back in the "good ol' days" guys would take a 283 up to 301 cubic inches. But their life expectance was pretty short. Here's a video of a STOCK 1969 302 in a Z-28 hitting 8,500 RPM.

http://videos.streetfire.net/video/6...-DZ_156232.htm

When I hear this sound it gives me goosebumps. No fancy dancy Comp Cams bumpstick or roller crapola installed. This was with factory rockers, pushrods, and lifters. ALL STOCK!!!
Yeah...they drove like crap on the street unless you were running a stiff rear end gear (4.10 or HIGHER). No power steering. 4 wheel disc brakes. No power windows. No air conditioning. Very little in the way of creature comfort stuff like the Vette had. The 1967-69 Z-28 was built for racers to race. But they would flatten an SS396 and other big blocks with ease. I sure miss those days.

Dep