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Chevy 307 Build

19K views 48 replies 11 participants last post by  77racing 
#1 ·
I'm currently building a chevy 307, I dont need to hear anymore "Why a 307?" or "Better off with a 350". It's set in stone, the 307 is what I got. Heres the route I'm going- Bored .060 over-400 rods shot peened and polished-KB 3.935 Hypereutectic 4cc dome pistons-Block .025 milled off-.039 Felpro head gaskets-ported and polished 416 heads with 1.84/1.5 valves-ported and polished weiand 7504 intake topped with a Holley 700 carb. I'm debating on cam choice. I've almost convinced my self a Comp XR264HR-10 is the perfect match. I also can't decide if I'm going to have it balanced and blueprinted.Any thoughts and opinions appreciated.
 
#2 ·
I understand using what you've got on hand but 400 rods? are you putting in a 400 crank as well? If you're porting the heads might as well open them up to 1.94 valves. If you will be mixing up parts in the rotating assy you will need to balance it. Do a mock up assemblely before you mill the block.
 
#3 ·
Sounds like if you cut the block .025 you'll be at zero deck with pistons. The 416, 305 heads have 56-58 cc chambers, (flowing about 175 cfm), I figure your parts list will give you 11.40 scr, high for pump gas.

I understand those heads are prone to crack, have them checked out. Keep in mind your quench as well.
 
#5 ·
Sounds like if you cut the block .025 you'll be at zero deck with pistons. The 416, 305 heads have 56-58 cc chambers, (flowing about 175 cfm), I figure your parts list will give you 11.40 scr, high for pump gas.

I understand those heads are prone to crack, have them checked out. Keep in mind your quench as well.[/QUOTE


So do you think it would be best not to mill the block? The heads have just been gone through they're ready to go except for porting and polishing. If i dont mill the block, how thick of a head gasket shoud I use to have good quench?
 
#4 ·
The rods were already shot peened and polished, and I got them at a really good price with ARP studs and nuts. 307 crank, shaved .010 and .010. The heads have just been completely remanufactured, so they're done except for polishing. I've read on a few different sites that this combination should work great. I still cant decide on a cam though, If possible I'd prefer not to have to use a stall converter
 
#8 ·
You do understand the 400 rods are shorter than any other small block? Unless you're trying to build a short rod stroker with a stock piston they are worth $190 per ton (scrap) to you. When you mill parts before a trial fitment or specialized measurement you're very likely to get an unfortunant surprise. If it came from Detroit it fits on the outside. If it came from a hotrod catalog it fits in the shipping box. And that's all you can count on before you mock it up. If you heads are already done either used them as is or plan on another valve job. You will end up bumping a valve seat if you port them. Sounds like you'll either need to find a 307 piston with a big dish or different heads anyway. Also don't order you pistons until you get the bores measure. Boring it .060 over when .020 or .030 will clean it up is just wasting a chance at another rebuild and your machinist might want to charge you more. It will offer little if performance gain.
 
#10 ·
Yeah I know they're short, but If there's no clearance issue they're staying. I plan on having someone professionally port them, if they bump em they buy em lol. Thats what it took to clean it the cylinders up, it had been sitting in a barn for a long time. Actually its not quite .060 yet, after I get the pistons, the cylinders can be honed to fit the pistons. What about my cam choice?
 
#12 ·
as others have said..
the 400 cid rods are shorter than the other small block rods you need the 5.7" rods..
the other is yes to balance blueprint, not needed but if they are decking the block they'll need to do some of it anyways..
if they line hone the mains remember you'll need a shorter timing set..
if the heads have the valve job already done. leave them be..it's to late..
save your time and money and start saving for a set of vortec heads (299 each complete)
with your rods your pistons going to be so far down the bore, decking the block would do zero..
I know you want to use what you got, but you need to go over this build again..


your rods are 5.565" way to short
 
#15 ·
The 5.565 rods are fine to use in a 307 with the 3.250 inch stroke.
This gives it a rod ratio of 1.7:1 which is good for a street engine.

If you went with Vortec heads, had the block decked .012 and used a GM 4 inch bore .028 compressed thickness head gasket you would land right at 9.5:1 compression ratio which is ideal for the street on pump gas.
It would also put the quench distance at around .041 which is also ideal.
Run a dual plane Vortec intake and a Quadrajet on top, with small tube headers and a summit hydraulic flat tappet cam with .214 Duration @.050
and .440 lift, tune it up with the best pieces you can afford.
What you'll have is a strong running street 307 with outstanding throttle response and good fuel economy to boot.
 
#18 ·
Tres, the 307 came from the factory with the same stroke as a 327 which is 3.250. The 307 was created by merging the 283 bore and the 327 stroke.
Gearheads, the idea would be to use a piston with higher compression height to compensate for it, such as the pistons out of a 283. I used to keep up with all the tricks but since I never come across any 307's I didn't care to remember. When building a performance 307 there's one problem we run into and that is the pistons. The stock compression height 307 piston from the factory is 1.675. The hyper aftermarket pistons are 1.655, so as you see they whacked .020 off the compression height. The majority of cheapy "rebuilder" pistons are made this way. That is why we use the shorter rod and a 283 piston which has a higher compression height due to it's shorter stroke.
When you look at my post count I hope you realize I didn't start turning wrenches yesterday. I say that because if I didn't know by using a shorter rod would cause all kinds of deck problems I wouldn't even bother to be on this site and I sure as hell wouldn't answer any questions based on something I know nothing about and make myself look like a fool.
 
#20 · (Edited)
HE IS USEING 400 CID RODS THAT ARE SHORTER THAN THE 307 RODS.
and the factory 307 stroke.. you can't just take the 307 5.7" rods and drop 5.565 400 rods in and it work.. the stack is to short.. how are you making up the .135 that the stack is now short..
even shorter with rebuilder 307 pistons..
do they even make 283 pistons in the bore size he wants to run?

oh and I'm a fool now too..
 
#35 ·
Hello DoubleVision,
Can you take a 350 4 bolt block and put in a 307 crank and 5.7" rods, That will basically make a 327 correct?
In doing so what pistons should be used with edelbrock heads to get max comp ratio for pump gas, flat tops?
What would the best distance be in the hole for the pistons? zero?

Kind regards
 
#37 ·
You CAN go this route, but why?

To be different you may as well just go for the Chevy 302, for power there's no reason to not go with at least a 350. A well prepped mostly stock 350 short block can take more abuse than people realize, with sbc's the limiting factor is usually cam and valvetrain, NOT stroke.
 
#38 ·
Not trying to be different, just wondered if that is the route to go to get a 327 without being able to find a 327 block, since i don't seem to be able to find one...
I'm aware of a well built 350 being able to handle abuse, that's why everyone has one...


You CAN go this route, but why?

To be different you may as well just go for the Chevy 302, for power there's no reason to not go with at least a 350. A well prepped mostly stock 350 short block can take more abuse than people realize, with sbc's the limiting factor is usually cam and valvetrain, NOT stroke.
 
#19 · (Edited)
Thanks for clearing that up. It's been 30 years since I had a 307 apart and I was thinking 3" stroke for some reason. Got rid of 307's as soon as I could. I admitt I should have looked up the numbers. Even with a stock crank he very likely have the only one in the county. They've all gone to the scrappers around here.
 
#21 ·
I hope he is talking about using 283 pistons which will work fine.

1/2 the stroke= 1.625
rod length = 5.565
283 piston CH = 1.78
______

8.97

.030 shy of a 9.00 deck height but, maybe he can find some 1.805 CH pistons
 
#22 ·
I'm using 283 pistons. Replacement 307 pistons have a compression distance of 1.655. The 283 piston I'm using has a compression distance of 1.779. Using .015 head gaskets, 60 cc heads, and milling the block .025 I'll have a 9.61:1 compression ratio and a .046 quench height. That will please me
 
#31 ·
I didn't say you were a fool gears, I was referring to myself. If I didn't know about small block pieces that could be interchanged there wouldn't have been a reason for me to reply at all as I would look like a fool doing so.
Let me try and explain this in more detail, this is another engine but the concept is still the same.
In 1994 and '95 Chevy released the L99, which was also referred to as the "baby LT1" it was a 265 cubic inch reverse flow cooled V8. It was the
LT1's baby brother.
Now, these engines came with rods that were PM, and measured 5.940 inches long. We take these rods, then find a 880 casting Vortec 350 Block, then get a 1 to 2 rear main seal adapter, then drop in a crank out of a 307
or if we get really lucky a large journal 327 crank. Next we have the block decked .010 and we use 383 Chevy pistons with a 1.425 compression height.
Slap it together and now we have a roller cammed long rod 327 engine with a rod to stroke ratio of 1.82:1.
As said, he is using the shorter 400 rod, yes, but he's also using a 283 piston.
As we know, all small block generation 1 engines used the 5.703 inch rod, except the 400. Chevy used the interchangeability to it's advantage and it was smart to keep the same rod length and just change the compression height of the piston. This kept costs down.
The 283 came with a 3.000 inch stroke crank, so the compression height on the piston is 1.800, the compression distance is measured from the center of the rod pin to the top of the piston.
The 307 as said has a 3.250 inch stroke, and it too used the same 5.703 rod.
The 307 was a merger of the 283 block and the 327 crank. All chevy did was discontinue the 283 in 1967. In 1968 they made the block into a large journal block, kept the bore size the same at 3.875, stuck the 327 crank in with it's longer stroke, then reduced the compression height of the pistons down to 1.675 and that was that. Since he's using the shorter 5.565 400 rods, he can use the higher compression height pistons of the 283 to compensate for the shorter rod. This practice is done as you can't get 307 pistons anymore that aren't "Rebuilder" pistons that have the shorter compression height and if these pistons were used with a 5.7 rod then the block would have to be decked to it's max plus use the thinnest head gasket available to give it some compression and quench action.
 
#34 · (Edited)
I have no idea why you seem so hell-bent on using a lot of static compression ratio in this motor. Current thinking puts the cap at 9.5:1 using iron heads and 10.5:1 using aluminum heads.
Using excessive SCR with iron heads will require that you pull all the ignition timing out of the motor to prevent it detonating itself to death and there goes all the power that you thought you were building by using a high SCR in the first place. Build it 9.5:1 with iron heads, use a cam with somewhere around 212 degrees intake duration @0.050" tappet lift, narrow lobe separation angle (108/110) for more power at the bottom, wider lobe separation angle (112/114) for more power at the top, 1 1/2" long-tube headers for good low end torque and horsepower in this small motor, 16 degrees ignition advance at the crank, 20 degrees centrifugal advance all in by 3000, stock converter and stock gears. 600 cfm vacuum-secondaries carb mounted on an Edelbrock RPM, Holley #300-36 or Weiand #8016 intake manifold.

Your combination of parts will never make a race horse, but it will make a good plow horse if you pay attention to detail.
 
#33 ·
If you plan to use flat tops it would be a better idea as it'll lower the compression ratio enough to survive on pump gas.
With the overbore added in, head gasket, stock deck height, piston crown and stroke the ratio with 58cc chambers comes in around 9.7:1 which will work well on 93 octane as long as you have a good quench action.
Depending on how far down the piston is in the bore at TDC will judge the quench action. Lets say it's .025 in the hole at tdc. Then add in the head gasket thickness of .028 and we get .053 which isn't horrible. As long as it's under .060 your okay.
However if you were to use a thicker head gasket you'll lose quench action entirely and when the ratio is in the higher 9's you'll run into detonation problems unless the timing is set real carefully. A higher compression ratio is safer with a good quench action and without it the risk of detonation becomes greater.
 
#36 ·
Yes, You can throw a 307 crank in a 350 block and it makes a 327.
With 5.7 Rods you would use 327 pistons with the 1.675 Compression height.
It would depend on the combustion chamber size of the heads. If they are
64cc's a flat top design would work nicely on pump gas. If the heads are aluminum then you can run higher compression on pump gas due to aluminums ability to dissipate heat quicker.
You can even use the 307 crank in a 1 piece rear seal block, however you'll need the 1 to 2 piece seal adapter. However if you go this route with the
307 crank, I recommend you have the crank balanced since the 327 used heavier pistons than a 307.
 
#43 ·
I've decided to sell the 400 rods and use 5.7" Eagle rods with Keith Black 307 Flat Top Pistons(283 pistons have to high of a compression height to use with the 5.7 rods and the 307's 3.25 stroke). I'll have a 10:1 CR with the 416 heads. I'm using a Weiand 7504 intake and a Holley 600 CFM. What cam should I use? I can't make up my mind
 
#46 ·
You started off saying +0.060" on the block bore. What size is it now? If it's stock at 3.875", could you back down to boring it +0.030" instead of +0.060"?
Is the block deck height stock right now at ~9.025"? You said the heads have been cut. Do you know how much?

By the way, if Crower posted an operating range of idle to 6000 on any of their cam grinds, then shame on them. An engine may operate from idle to 6000, but it will not make useable power from idle to 6000 with any one camshaft. The camshaft operating range, where it makes power, is normally 3500 to 3800 rpm's, like from idle to 4500 or 1000 to 4800 or 1500 to 5300 or 2000 to 5800 or whatever. I just wanted to make that clear so that others reading this thread will not get the wrong idea and think there is something magical about Crower cams that permits them to make power over a 5200 rpm range (idle to 6000).
 
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