SBC 307 build. amother one? - maybe

http://www.jalopyjournal.com/forum/showthread.php?t=712197&highlight=check+out+my+belly+button
If you need or want some background info on the first one look here

http://www.jalopyjournal.com/forum/showthread.php?t=706094&highlight=307
And here too.





I must say , I'm pretty happy with the first 307 (see link) , so happy I've been thinking about the next one.
I have another 307 sitting in the corner waiting on some love. But I want to do something
different, something a bit more powerful utilizing a methanol/ water injection system and much higher compression. I'd like to push the edge of pump gas with it. Make some impressive power, get great milage, and just for shits run it thru an E Test , Oh yea and out of a "crappy" 307 scourge of the sbcs.

In my quest for info & food for thought I found this little tid bit on another forum. Besides that winter and cabin fever make me think. Sometimes good sometimes not lol but thinking is cheap entertainment.

You can also use 283 pistons with 400sbc rods (283 pistons come in forged variety where all 307 aftermarket pistons come cast) to beef up the bottom end (you could go the eagle 5.565 rods). The reason for the 5.565 rod is the 283 piston and 307 piston use different compression/pin heights but share the same bore. You could even run a SCAT 5.580 rod and 307 pistons on a 350 3.480" stroke crank to achieve 333.4ci if running a .030 overbore. The SCAT rod would keep the compression distance on a milled 9.0 deck block at around stock, .025 in the hole. This is because most aftermarket 307 pistons run a shorter than stock compression distance (1.675 stock compared to 1.655 aftermarket). If you used original pistons you could get by using a 400 rod to keep things on the cheap for an NA motor (would put it .020 in the hole, using a .028 gasket would still put you in reasonable quench of .048)

Basically 283 pistons, 400 rods with 3.25 stroke 327/307 crank but I'd use thinner gasketes.

I'm not interested in spending silly money on this thing (under a grand plus the injection kit) but most of this stuff is laying around or had cheap so that should be easy. Saw some used high compression forged 283 pistons for cheap. Maybe some vortec heads out of pull-a-part ? Maybe aluminum heads to deal with the higher compression.
Just thinking right now.

 

Up for some discussion

 

Sounds like a fun build! What about the 305 H.O. heads could they flow enough with a little port work for that kind of power?

 

Shorter rods aren't usually they way things go....But if it fixes the piston problem and you got the rods,why not.

 

When I was parting up for the first 307, I researched the flow numbers and runner sizes for the 305 ho heads along with some others. I plugged that info into a computer dyno and the 305 ho heads with mild porting showed the highest AVG ( not highest peaks) thru the rpm band with 262 cam the torque curve was early, high and flat.

There were other heads that made marginally higher AVG #s than the 305 ho but at a significantly higher dollars. Just Not worth it for 2-5% 6 HP . Others had a lot higher peaks but the curves were late and peaky.

I'll redo the computer dyno numbers with much higher compression than 10.4:1 and see what happens.

 

Up for some more

 

Still reading. I'm currently building a 283, but a 307 is nothing more than a stroker 283.

I'm going for 11:1 static compression and lots of cylinder pressure chasing efficiency, yet with enough lift on the cam to make it fun. The only decent heads I can find are Trick Flows, at least they're aluminum to help dissapate heat for the added compression.

Like to see where this goes.

Devin

 

i like it and insist that you go for it (so that you can do all the R+D and i'll just copy the good results.........)

1) Would iron heads be better for hi-compression? Due to the additional heat?

 

http://www.stahlheaders.com/Lit_Rod Length.htm
An excerpt from here -


A spark ignition (SI) engine and a steam engine are very similar in principle. Both rely on pressure above the piston to produce rotary power. Pressure above the piston times the area of the bore acts to create a force that acts through the connecting rod to rotate the crankshaft. If the crankshaft is looked at as a simple lever with which to gain mechanical advantage, the greatest advantage would occur when the force was applied at right angles to the crankshaft. If this analogy is carried to the connecting rod crankshaft interface, it would suggest that the most efficient mechanical use of the cylinder pressure would occur when the crank and the connecting rod are at right angles. Changing the connecting rod length relative to the stroke changes the time in crank angle degrees necessary to reach the right angle condition.

A short connecting rod achieves this right angle condition sooner than a long rod. Therefore from a "time" perspective, a short rod would always be the choice for maximum torque. The shorter rod achieves the right angle position sooner and it does so with the piston slightly farther up in the bore. This means that the cyl pressure (or force on the piston) in the cylinder is slightly higher in the short rod engine compared to the long rod engine (relative to time).

 

That's funny !
A bit demanding though

 

Not many bench racers on this one

 

Use the 307 pistons with 400 rods and a 350 crank. More cubes makes high compression easier to achieve.

You also might want to check the casting number on the block. Some of the 307's used a 327 block bored 3 7/8 and can be taken out to 4".

 

Then why are engine builders using longer rods for more torque? It's been discussed here many times.

 

Higher rpm's you start seeing an advantage with long rods. The shorter stroke would be ok with the 400 rods. Hell I built a 406 with the short rods that ran in a street stock car for over a year with no troubles. Look at the 302 ford rods. Not sure of the length but they are very short. You can crank a 302 ford 6500 rpm all day....

 

I know right !
I didn't write it but it makes a lot of sense or an effective argument anyway. Took me a few times reading the entire thing , but a lot depends on the valves ability to take advantage of the quicker movements in corresponding degrees.

 

Longer rod require a shorter piston = win in the rotating weight battle. The difference favors longer rods since a segment of rod weighs less then the equivalent length of piston. Also, the shorter rod will cause the piston to hit the counter weight on the crank.

 

Problem is lack of dirt cheap high compression forged 307 pistons.
Piston pin is at different heights so 307 is 307 only. I'm very surprised GM didn't use 400 rods .

 

I understand what you are thinking about... The only way to find out is to build it...

 

http://www.mayfco.com/rods.htm
Pretty interest stuff here

Here is the frosting off of this guys cake

Results:
1) Longer rods have lower piston/cylinder side loads, hence less cylinder and piston wear [note1].
2) Short rods have a higher axial loading, hence potentially more bearing wear [note 2].
3) Short rods produce higher torque early, less torque later [note 3].
4) Short rods produce a higher peak torque [note 4].

note 3. I can hear it now! There are some of you out there who will throw in cam timing, valvelifts etc to make the argument that one rod or the other is better. But, that would be changing the problem by changing multiple parameters at a time. I agree that each can be tuned with cam changes, carb or EFI changes to get more performance for any given particular set of constraints.

note 4. This also surprised me a little. I had expected that the torque would be less. But I can rationalize the data by short rods having more axial force which pushes on the crank. But it does happen earlier in the power stroke. As a matter of fact all rods produced torque peaks before the 90 degree rotation point and fell off slower.

-------------------------------
I believe when he says "early or late " it referred to piston position after TDC not rpm range.
And really the rods aren't that much shorter but I thought this was pretty interesting.

 

I'm not sure how a segmemt of steel rod can weigh less then an equivalent segment of alumimum piston but,the real advantage of a longer rod is that you can make the piston skirt shorter to reduce horsepower robbing friction.

 

If you take this ^^^
And add this


http://books.google.com/books?id=OA...a=X&ei=X-0TUdW4ILT8yAGjsIGwCw&ved=0CEAQ6AEwAw

It makes for some interesting thinking especially on a high compression engine

 

327 the hard way !

I'm pretty sure that is similar to the ls series 5.3 configuration

 

Friday night bench racing

 

as it was explained to me, the advantage of longer connecting rods is the piston gets stuck close to TDC for a longer period of time, as the rod swivels under it. a shorter rod gets the piston to TDC only when the centerline of the rod is parallel to the centerline of the crank's stroke--and then instantly pulls it away, increasing volume in the cylinder and reducing the pressure that should be pushing the piston down on the power stroke.

with a longer rod, it pushes the piston to TDC and holds it for a relatively longer period, so the combustion pressure builds and builds before the crank finally "gets out of the way" of the downward stroke. turning your piston 180degrees horizontally in the bore so that the wrist pin is on the other side of the bore centerline can accomplish a similar result.

Reher and Morrison race team tested out Smokey Yunick's theory, however, and disagreed. either way, your cam will want a wider LDA, which also broadens the torque curve.

a smaller diameter bore may help resist detonation, b/c the flame front from the spark plug can travel the length of the bore before a glowing hot part of the chamber (say the edge of the exhaust valve) can cause a second flame front to travel the chamber.

increasing the stroke increases piston speed, which could act on the exhaust stroke to push the exhaust out faster, and on the intake stroke, pulling the piston down the bore faster can cause a pressure drop before the intake valve opens (due to the sudden increase in volume while the air quantity stays the same, and the molecules spread out and lose density). with air in the intake port being at atmospheric pressure, the lower pressure in the cylinder could cause intake air to rush in faster attempting to equalize pressure in the cylinder.

its believed increasing stroke but not rod length because piston speed and rod ratio creates more cylinder pressure at the time the rod has the most mechanical advantage on the crank due to angularity.

How tricky do you want to get with oil control? a 350 crank allows for an LT1 windage tray, and a V shaped lifter valley shield will keep hot oil from splashing up and warming up the intake manifold. you can pick up a few HP here and there, and it adds up...and with a little fab work, you won't need crazy money, just extra money angle milling the head's deck surface can angle the valves away from the cylinder walls and help out the breathing.

 

You have the shorter piston reduces friction part.

Now consider ...the piston is shorter when the rod is longer. The shorter piston is shorter above the pin and has a large cross section. And the rod is longer in the beam and it has a small cross section. While steel is 2.89 to 2.98 times the weight of aluminum (depending on grade and forging techniques) the piston has 15 to 35 times the cross section (depending on the manufacturer and design). The assembly is lighter. At high RPMs that load is significant. And the longer rod decelerates and accelerates the piston at a lower rate and F=ma.

 

Great stuff, thanks

 

http://books.google.com/books?id=yE...pO&dq=short+rod+valve+timing&output=html_text

Here's some more talk about using rod length as a tuning component.
Condensed :
Since the piston has shorter dwell, higher compression can be tolerated ( almost needed) Since the piston leaves quicker, and approaches quicker larger ports & runners can/should be used and not effect velocity because the piston is pushing faster on the exhaust stroke and pulling faster on the intake. Proper cam timing can be really beneficial to take advantage of this. Probably not the best for Bonneville or drag racing but great for road course racing ( read spirited street use ).

 

Theresa guy here who started fuel racing in '56. He has a massive stash of brand new and used small journal speed parts from the '60's and '70's, including forged Venolia pistons for the 307. They do have massive domes on them though so compression may be in the 12 to 14:1 range. A buddy of mine also bought a set of those 307 Venolias from him and won't be using them. I could get a hold of these guys if you are interested.

 

I think if you took the average V8 street build and swapped rod lengths ,you might be hard pressed to find any meaningful difference in power.

 

Very interested ! Perfect
Thank you