i have a 73 Chevy Nova with a 250 L6, and I’ve been wondering about putting in a 305 but I’m steering away from the 350 b/c of the bad mpg’s. my first question is, where would i go about looking for an engine, by the way i live in Pittsburgh. Second, would I be able to use my stock 3 speed manual transmission with a more powerful motor, or would I have to upgrade that as well. And lastly, b/c I will most likely keep my 250 L6 for the time being, are there any relatively easy things that I can do to boost horsepower because 100 hp is pretty wimpy. ( by the way, the car is on jacks so it would be easy to do things around the engine)
Clifford performance is the source for all kinds of 250 CID 6 cylinder power equipment. You might stick with the 250, add some of their stuff, it’d be more distinctive than just another small block (easy for me to say)!
thanks for the info., but I’m a little confused, do they require that I use both their headers and intake manifolds or is that optional, but thanks so much for the site any way
I really don’t think you’re going to see a major difference in fuel economy between the 305 and the 350. If you’re going to bother doing the V8 swap, I’d definitely go for the 350 since those are such common engines and there’s such a wealth of aftermarket parts available for them. With a good tune-able carb you might be able to actually squeeze more MPG’s out of a 350 than the stock 250. And as for the transmission, you absolutely can keep the 3-speed but while you’re in there putting in a 4-speed shouldn’t be too much trouble (is the 3spd on the column?) and it will really help you get the most out of your new V8 in terms of comfortable and efficient highway cruising.
Personally, I agree with texases that keeping the ol’ straight six is the more interesting option. Even dropping in the 350, you’re not going to end up with a stupendously fast car and with a few upgrades to the 250 you should end up with a car that drives really nice. The first thing I’d do is lose the crummy 1bbl carb with a multi-stage 2bbl carb such as the Weber 34 series. A set of headers from Clifford probably wouldn’t hurt either because, if this is anything like the 250 in my '76 Chev pickup, the stock exhaust manifold is pretty restrictive.
Some of the later 250’s and 292’s had a combination manifold where the intake and exhaust manifold were the same piece, so you definitely would have to get both, but I don’t think that had happened by 1973.
But, to maximize the advantage of the headers, you really should open up the intake as well, especially if you put on an intake that’ll take a better carb.
305’s are easy enough to find (77-83 Malibu and Monte) plus many more… But they are not a performance motor either. You can have a lot more fun goosing up that 250 six. You just gotta get it breathing better with a decent intake and exhaust. 175-200hp can be had without too much trouble which will really perk up your Nova and still maintain decent mileage. Your engine has a “smog cam” which limits performance somewhat. Do some research and see the '69 and earlier engines had a spunkier cam. If you decide on an after market cam, choose very carefully to avoid destroying low speed driveability and fuel mileage.
would the following combination of products be a smart idea?
on the Clifford Performance site, it says that a 2 1/4 inch exhaust would provide a good sound, but the only problem is that the headers on the site require two exhaust pipes, theres a link to the headers below
so where would i go to find and exhaust kit that would meet my needs or should I just get a U-build kit from a place like Flowmaster?
Check your area muffler shops - many can whip up a set of duals no problem. They used to do this all the time, before cats. And I second the vote for a 350 instead of a 305, if you go for a v8. Of course, there’s always a $$ limit.
I’ve owned several Chevys with 350s and with some tweaking here and there I’ve always managed to get about 20 MPG with them on a highway cruise and that’s not too shabby. And those cars were equipped with TH350 3-speed automatics w/no overdrive.
If originality is not a requirement then what about a 350 and a conversion to a 700R4 automatic overdrive transmission?
To gain much on the 6, and keep it streetable, you’re just about going to have to have some cylinder head work (porting/valves) and a camshaft change. Even then a decent 350 will outdo it.
I’m sure they’ll give you some good power, but I’d go for a 4bbl manifold/carb. I’ve heard Webers can use a lot of gas. Call Clifford, they’ll help you choose. If you have the money, you might also want to look at their cams.
The 350 will of course outperform the six but if you want a BossaNova you have to start at the very beginning and that’s a lot of money. A 350/700R4 adds A LOT of weight and the entire front end of the car will have to be upgraded including brakes. If you want a V8 Nova, BUY a V8 Nova. It’s MUCH cheaper than building one.
Now your car has a nice light feel to it with balanced weight distribution. A V8 automatic Nova is a nose-heavy beast and not fun to drive except in a straight line.
I had a 1967 Chevy II, the low line version of what was the Nova. It had the 250 motor, and I drove it to New York from west of the Mississippi several times. It ran 70 mph, and I got around 20 mpg with it as well. I was told by smart guys the 6 cyl would be underpowered, but since I wasn’t drag racing never felt lack of power. Quality of the car was terrible, but it drove out well. And the 250 had a lot more torque at low speeds then the Dodge/Plymouth competition.
The 350 and the 305 won’t get different mileage. You won’t notice it. They are both gas guzzlers.
JMHO, but the 350 swap is easily done and I don’t understand why much of an upgrade to suspension or brakes would need to be done unless one wanted to exceed what the factory did in the first place.
A quick look at the interchange shows the 6-banger Nova and the 350 Nova all used the same shocks, same brakes, and almost identical front coil springs with the difference in the latter being due to whether it’s A/C equipped or not. ???
thanks for the info. I wasn’t really thinking about the weight that would be added. what i’m basically looking for is a some what sporty, good looking engine that can perform well and sound pretty good, so i’m pretty sure the L6 will satisfy my needs for the time being, but i’m probably going to upgrade it intake manifold, headers, exhaust, and getting a 4 bbl carb.
Sounds like a good plan. I grew up on 6s and 4s (Mustang 170, Duster 198, Scirocco, GTI). They were all fun cars, and I never thought I was trying to out-drag somebody in a v8. There’s always somebody with more HP, no matter what you do!
I gotta say, I never in my wildest dreams thought I’d ever hear anyone describe a mouse motor as a gas guzzler. 
I’ll just point out that converting a basically stock L6 to use a 4 BBL carburetor could result in overkill by having too much carb on it.
Many Quadrajets (assuming this is what you’re planning) flow 500-600 CFM and up and a 250 engine will run fine on 300 CFM.
A carburetor that is too large will actually slow the car down when it comes to around town driving. This is why some of the late 60s/early 70s Chrysler made station wagons used a single one-barrel carburetor on their 440 engines. The single barrel carb greatly enhanced the low/mid range torque to aid in moving those heavy tanks from the stop light.
so would it be a bad idea to get a 4 bbl if I’m planning on getting a new intake manifold and new headers? also, would you then recommend a 2bbl carb as suggested by GreasyJack?