Thread: 305 vs 307 (whats the main difference?)

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techinspector said

"A standard bore 307 with a 350 crank will produce 329 cubic inches"

im just tryin to figure out if theres a way to make a 307 a 327 WITHOUT having paper thin walls.

i have two different people now telling me things and the way im reading this is, if i bore it .125 and put a 350 crank in then the walls will be too thin and if i dont bore it and just put the 350 crank in the cylinders will be pushed out .125 and ill have to have custom ones made for an expensive price. the reality here is im probably not goin to be gettin a 350 and i just want to know if theres anyway to up the cubic inches and get some good performance, not a 10 second car, but probably horsepower in the 350s? and not have the engine blow.

thanks, cooper

Sorry, I had not seen that Tech had cleared that up.

Tech, I know of 5 ---350s made from 307s with no heating problems. It's not ideal but it will work. To me ,the only way it would be worthwhile is if he just had to have the original motor,and in this situation I dont think we a talking about
Central Office Production Order.
Me, I'd go with a 350 to start with .I love the 400 but its harder to hook it up in a stock chassis Nova.

i completely agree with you on this one. 350s dominate. but haha see im only 15 and am tryin to get up money to buy this nova from this lady and my dad wont let me spend any more to even get a 350, if i had a 350 id definetly stroke it to a 383 and thats whta got me stared on the strokin a 307. but i dont know if its that worth it to risk blowing up the whole engine if the walls are too thin because i do want it to be a strong runnner. got nay more ideas besides bolt on hp? (thats ultimatly waht ill resort to obvioulsy haha)

Gene, screw a piece of lumber onto the floor under the accelerator on your 400 to limit the primary butterfly opening

cooper, I feel compelled to offer you a lesson of life like I used to offer my kids when they were growing up.
Lesson # 107: Economics.
If you want your car to be fast, start with the largest cubic inch motor you can find and afford.

You bought a 307 and you have a certain feeling that you should use it to go fast. You feel pride of ownership and that's fine, that's just human nature. You don't want to be made to look stupid for buying the motor and you're determined to make a world beater out of it to justify your purchase and prove to everyone that you made an intelligent choice. The problem is that you're approaching it with emotions, not logic. If you had bought a 262 SBC, you'd be wanting to hot rod it the same way and wring 350 hp out of it.

Can you make 350 hp with a 307, sure you can, but it's gonna cost way more than if you started with a 350 or 400 SB. The larger the motor you start with, the more conservative you can be with cam choice and other parts to make the motor civilized enough to make a good street motor. To underscore my point, a boneyard 262 will cost the same initially as a boneyard 350 or 400 and you'll spend less than half the money to get 350 hp out of the larger motor as you will the smaller motor.

While we're on this bigger/smaller motor subject, the absolute best bang for the buck will be with a 454 from a derelict auto or truck. They'll make 350 hp without trying, STOCK. You should be able to find a good-running 454 for under $750 and you're through. It'll bolt to any transmission that a 307 will bolt to.

haha man i tell ya id kill for a 454, but another factor comes into play here, insureance haha, and i havent bought the 307 yet, but thats one of the only novas that is ofr sale in the area that had an 8 in it for less than 3000 persay. the others are eother no motor, or too big a motor, or a on running 350. now believe you me if a 350 does opo up u can bet ill jump on that one, but if i were to get a 307, my dad doesnt want me to do a motor swap, theres a chance i could talk him out of it but theres no hope for anything 396 and above. so then i got started on the 307. my thoughts were "well its a 307, and a 327 is only 20 cubic inches bigger. so theres got to be a way to get that 20 cubes and have a lil muscle car on my hands, now that 307 stock comes with 300 ft lbs of torque at 2400@RPM ! and stock with 200 hp. now theres a 327 that can get liek 325 hp i think? im not exactly sure but i guess i could bore to somewhere below 4 inches and bolt on of course a 4 barrel, some new headers and cylinder heads, new exhaust to open it up, new intakes you know the whole story, what do you think about all of that? i definetly know that my car will be nothin specail when it comes to the quarter mile, but you know with those 307 decals on the side, it would be nice to have a lil sleeper on my hands!!

but the 307 would be a numbers matching, thats also kinda nice since a 350 is probably out of the question but since it would be numbers matching i really do not want anything to happen to it where the piston blows and cracks the block so what would you suggest tech? not boring it to 4? maybe liek .30 over and just the bolt on stuff?

Here's something to think about. What if you get the 307 Nova and the motor has already been bored 0.060" and is worn out. The next stop is 0.125" over and you risk overheating.

Let me explain overheating from an overbore. With a stock bore, the factory has designed the block with cylinder walls that are thick enough to dampen vibrations that are produced by the piston rings as they make their way up and down the cylinder walls. The rings don't slide smoothly like you may think, they make a series of very tiny little jerky movements like "skidding" on the walls. When you overbore a cylinder, you are making the walls thinner and if they get too thin, there won't be enough mass to absorb these vibrations. The vibes are transferred through the wall to the water jacket on the other side of the wall where the vibrate the water and separate the air bubbles which are present in the cooling water. These air bubbles then stick to the water jacket wall, preventing cooling water from getting to the wall of the water jacket to carry away heat into the cooling water, so the motor overheats.

Gene said he knows of several motors that are overbored and are just fine. That's all well and good and I'm glad for the fellows who are running these motors.

Which brings us to......
Lesson of Life #108
No matter which motor you end up with, the cylinder walls will be thin from the factory and further boring will end in disaster!!!

I, also, was faced with the insurance dilemma as a youngster. I got around it by purchasing a 6-cylinder car and doing an engine swap. I took the title to the insurance man and showed him that the car was a 6 and got a reasonable insurance rate. I'll bet there are quite a few very affordable Nova 6's in your area if you just look.

i doubt it has already been bored over because shes the single owner of this car and shes 92! haha but i have one more question for ya tech, isnt there an equation to figure out cubic inches where u multiply the bore and the stroek or somehting liek that?

Yep.

.7854 X bore X bore X stroke X number of cylinders

The constant, .7854, is 25% of pi

To convert cubic inches to liters, divide cubic inches by 61

thnaks a bunch, this really helps me out!

Originally posted by techinspector1
Which brings us to......
Lesson of Life #108
No matter which motor you end up with, the cylinder walls will be thin from the factory and further boring will end in disaster!!!

somtimes sometimes not teehehehehe just givin ya gruff tech no offense inteded here

Scooter, you can pick on me all you want, I like ya'.

It's just my freekin' luck though. Everything I've tried to do in this life has fought me back all the way through it. I'm not whining, I'm just sayin' that if it weren't for bad luck, I'd have no luck at all Maybe that's why most of my answers to these guys are conservative, I want to give them valid information and keep them from making silly mistakes (like pouring money into a 283)

Just teasin', one of the fastest cars I ever drove was a '57 chevy, 283 with 2-4's and a four speed. It was a close-ratio Muncie and the whine of the gears almost made me wet myself

I'm currently in the middle of a 350 swap from a 73 nova. The 307 was fun to play with. I rebuilt the 2 bbl and put some headers on it. Open headers to school, that's fun. You know pissed off the neighbors, the usual good stuff. It's my first car so I have an excuse. I agree with all these guys though. Don't waste your time on a 307 unless your going for a parts matching car. It's not worth your time or money.

By the way, from just eyeballing it, it looks like the factory gm hei distributor is going to hit the firewall. I guess this means i should buy an aftermarket distributor, or I've also seen kits to rebuild an old delco points distributor into an aftermarket one.

How about a little firewall massage with a BFH?