View Full Version : Chevy 307ci build up questions


LT1
06-05-2009, 10:28 PM
I have a pre 73 chevy 307ci would like to know if anyone knows more info, I did some search and read few different combo's but still unclear on what will work.

what heads bolt up to 307?
what crank can fit into 307 block?
what camshaft fit into 307 block?

what I know 307 has 3.85 bore and 3.25 inch stroke. I was thinking maybe to turn it into a large journal 327 is it possible? I will most likely have to bore it out if I run 327 pistons.

Please Do Not tell me not to mess with the 307 because I already know its not worth messing with (cost Vs. power), I wanta do it anyhow. I would like to just see how far the 307 can be pushed.

ZONES89RS
06-06-2009, 12:00 PM
Everything will swap out that i can remember, 350 crank, heads and the works, but the big valve heads are too big and they will hit the bore so 1.94 i think is your limit on intake valves.

the schoob
06-06-2009, 01:50 PM
Just dug out an old small-block book and this is all it had to say about the 307... This engine was introduced in 1968. A 283 bore with a 327 crank gave 307 cubic inches. Boring one of these blocks to 4 inches gives 327 C.I. A 4 inch bore on a 307 usually leads to a failure rate of about 1 in 10 due to porosity being found in some cylinders.These odds are not as good as they sound so be sure you have reason before choosing this route. As in the case of the 350, the 307 block in notched at the bottom of the bores to give connecting rod clearance. These are sufficiently large to allow the use of 350 crank in a 307 block. YOU CAN ONLY USE THE 350 CRANK IN THE 307 BLOCK IF THE BLOCK IS BORED TO 4 INCHES AND 350 PISTONS ARE USED.The 307 took the place of the 283 and production of it ceased in 1973. What I get from this is to leave it as it is or just go get a 350. Hope this helps.

726.0chevelle
06-06-2009, 03:51 PM
a 327 is a 4.00 bore that will be a .150 over bore i didnt think they could go that much

726.0chevelle
06-06-2009, 03:52 PM
oh yea good luck with the boat anchor lol jk

speedy55
06-07-2009, 05:25 PM
sell the 307 for scrap iron and get a 350!

jimmy92rs
06-07-2009, 09:49 PM
i agree, 305, 307, just about worthless

SanitysBane
06-08-2009, 12:41 AM
Wow, way to tell the guy exactly what he said he didn't want to hear.

T/AWS6969
06-08-2009, 01:12 AM
I say go with your passion of what you wish to do, and to hell with everyone else. :D I say forge the bottom end , throw on a weiand blower or Edelbrock E-Force (Magnusun) with a nice blower cam and some decent aluminum heads and go rape all kinds of 350's :D

fast01
06-08-2009, 03:18 AM
If you're willing to spend the money, any large journal crank will fit. You could use a 283 piston by performing a .025" overbore or even an LS1 piston with an .048" overbore. Both of which are possible. There is no way you're going to open it up to the 4.00" bore of the 327. I think the LS1 piston would be interesting due to the low drag of the metric ring pack. You will have to play with rod legth, compression height and stroke to get the slugs where they need to be within the 9.025" deck height of the small block Chevy. I could figure it out for you, but it's 3am and I should really try to get to sleep. Bear in mind, there may not be an off-the-shelf combination that will work (or there may be) and custom parts may be required. That's why I started out with "If you're willing to spend the money".

I agree that you should build what you like and forget about what everyone else has to say. In fact, I believe there was a 307 entry in one of the Engine Masters Challenges a few years back that made crazy power. Of course, I'm sure it cost crazy money too!

LT1
06-08-2009, 08:11 AM
What do you think of going 0.030 inch overbore 4cc dome piston, double-hump aluminum heads 64cc, stock Chevy 400 rods (5.565 inch), mill block 0.025 and get 9.00 deck height to run 10.0:1 compression and 311ci

Would get about 350hp? and power adder later down the line.
BTW Thanks for the responses and encouragement, I really wanta go thew with this.

TT632
06-08-2009, 11:06 AM
I rember a guy running an 11 second nova back in the eighties with a 307 and a good cylinder head. If you can find decent forged pistons you can get some good flowing heads even with a 1.94 valve.

LT1
06-08-2009, 11:46 AM
I rember a guy running an 11 second nova back in the eighties with a 307 and a good cylinder head. If you can find decent forged pistons you can get some good flowing heads even with a 1.94 valve.

Will I get valve shrouding if I run 1.94 intake with double-hump heads?

fast01
06-08-2009, 05:33 PM
What do you think of going 0.030 inch overbore 4cc dome piston, double-hump aluminum heads 64cc, stock Chevy 400 rods (5.565 inch), mill block 0.025 and get 9.00 deck height to run 10.0:1 compression and 311ci

Would get about 350hp? and power adder later down the line.
BTW Thanks for the responses and encouragement, I really wanta go thew with this.

Yeah, that'll work pretty good actually. Make sure you use good hardware on the rods and maybe have them shot-peened and the beams polished. Given the short stroke, the short rods won't be a problem as they are in the 400 and 383 strokers and with a .039" head gasket (Fel Pro 1010) your quench distance will be spot on! I think 350 horse would be a realistic possibility, but with the small cubic inches watch your cam choice, because it wouldn't take too much to make it miserable to drive on the street.

TT632
06-08-2009, 06:07 PM
Will I get valve shrouding if I run 1.94 intake with double-hump heads?

You will always get some reduction it flow with the valve opening close to the cylinder. How much it will hurt you should be minimal compared to a 4" bore.

mred
06-10-2009, 01:00 PM
you could find a set of 283 heads and put on the 307 and you would be surprised.
i did this back in the ole days when i didnt have any money,old man told me to give it a try and i was impressed,especially for the cost at the time of install.
the heads were given to me,you might luck out the same.
good luck

twinturbo496
06-10-2009, 02:37 PM
You should check with a local machine shop regarding the over bore limits. The majority of chevy production small blocks are limited to .060 or less due to thin cylinder walls.

Spending money on a crankshaft with the same main bearing size and a 3.75 stroke could be a much more cost effective way to increase displacement.
If you look at competition products in WI, you can get a imported 3.75 crank for about $450. Chevy vortec heads are fine with an engine this small.

Still not a good combination because the small bore limits valve size, but if your stubborn that that doesn't really matter.

nver2nd
06-10-2009, 03:35 PM
What do you think of going 0.030 inch overbore 4cc dome piston, double-hump aluminum heads 64cc, stock Chevy 400 rods (5.565 inch), mill block 0.025 and get 9.00 deck height to run 10.0:1 compression and 311ci

Would get about 350hp? and power adder later down the line.
BTW Thanks for the responses and encouragement, I really wanta go thew with this.

that is a big waste of time... a 307 is a pointless motor to build, especially when you can lurk Craig's List for about an hour and find a number of good 350 short blocks for cheap. you will end up putting the same amount of money in a small inch motor, just to have people assume you actually built a 350 or 383.

do your self the favor and just build the 350.

trash the 307, or pawn it off over the internet on someone else.
:bang:

fast01
06-11-2009, 02:11 AM
that is a big waste of time... a 307 is a pointless motor to build, especially when you can lurk Craig's List for about an hour and find a number of good 350 short blocks for cheap. you will end up putting the same amount of money in a small inch motor, just to have people assume you actually built a 350 or 383.

do your self the favor and just build the 350.

trash the 307, or pawn it off over the internet on someone else.
:bang:

I know that's not what you wanted to hear, but is he right?.....Yes. You will spend the same money for less power than a similar 350, 383 or whatever, but again, if you're willing to spend the money it's entirely your choice.

With that, because I have entirely too much time on my hands, I've come up with an outside of the box combo just for fun, that could be realistically built using off the shelf parts. It would however, be expensive, a lot of work and just plain stupid to put the high caliber of parts that would be required onto a cast crank. Buying a forged crank would put it way over the edge. Here it is anyway.

307 block and crank bored .030" over for a 3.905" bore. (stock bore is 3.875 not 3.850 as I used above)
LS1 piston 3.905" 1.115" compression height
6.250" rods for a 1.92 rod ratio
Deck the block to 8.990" for 0 deck clearance or 9" to keep 'em .010" in the hole
The nice things about this combo are the metric ring pack of the LS1 pistons and the low rod angularity of the long rod. Both of which will reduce internal friction, although the rod ratio is approaching the practical limit of 2.00. A problem that will arise is the difference in valve angles between the traditional small block and the LS1, 23* as opposed to 15*. This will require the valve reliefs to be modified to the proper angle. Also, the deck surface will start getting a little thin which could cause gasket sealing problems. Again, I'm not suggesting this, the 311" combo you threw out there earlier would be much more practical, but I threw this together just for fun to show you that there are all kinds of possibilities out there for any engine. There's even more you could do with this, but I could go on forever and push the practicallity and cost into the stratosphere! Good luck and have fun with whatever you decide to do.

LT1
06-11-2009, 04:30 AM
Ive read all your reply's, thanks for your opinion I appreciate it.

nver2nd >> I love 350ci displacement and bigger, im still building my LT1 that's not changed. The 307 build im doing on the side. Im not disagreeing with the " lurk Craig's List" makes perfect senses. This build is about pushing a 307 or small displacement engine with a budget in mind (not spending outrageously) and keeping it streetable.

Fast01 >> I like your idea of running the LS1 piston with those rods, but will require more clearancing and machining than cost might allow but will look into it. My goals to keep it streetable but still make 350-400hp n/a with a budget in mind.


You will always get some reduction it flow with the valve opening close to the cylinder. How much it will hurt you should be minimal compared to a 4" bore.

I known I wont be going with a 4-inch bore. If its a minimal amount ill keep my options open, Im sure there's still a better choice for head/valve size than what Ive seen thus far.

you could find a set of 283 heads and put on the 307 and you would be surprised.
i did this back in the ole days when i didnt have any money,old man told me to give it a try and i was impressed,especially for the cost at the time of install.
the heads were given to me,you might luck out the same.
good luck

Thanks will look into it.

You should check with a local machine shop regarding the over bore limits. The majority of chevy production small blocks are limited to .060 or less due to thin cylinder walls.

Spending money on a crankshaft with the same main bearing size and a 3.75 stroke could be a much more cost effective way to increase displacement.
If you look at competition products in WI, you can get a imported 3.75 crank for about $450. Chevy vortec heads are fine with an engine this small.

Still not a good combination because the small bore limits valve size, but if your stubborn that that doesn't really matter.

Displacement isn't my concern, but knowing what head/valve size and cam choice got me pulling my hair out.

mred
06-11-2009, 06:37 PM
hey not a problem. if you dont have alot of money to work with then a 350 is not going to be your best bet. it takes a small amount of money to build a 350. so work with what you got or just save the money and then build you a 350
GL

LT1
06-12-2009, 11:03 AM
hey not a problem. if you dont have alot of money to work with then a 350 is not going to be your best bet. it takes a small amount of money to build a 350. so work with what you got or just save the money and then build you a 350
GL

Im building a LT1 350ci aswell. The 307 is just another build im doing on the side thats why im keeping a limit on the spending for it.