SBC Primer

[Shadowrider]

I do 2 break in periods for flat tappet cams usually 20-30 minutes each. I use Joe Gibbs break-in oil also.
Then use another good oil for runing ..not much Zinc in oils on the shelf today and they are always changing the formulas.
VR racing is still good Gibbs has their hot rod oil and a really good LS oil.

Keep open valve spring pressures under 300 and you will be good. 345 open on race stuff for flat tappets being max.
Well for me and the cam and lifters I run.. You can go more with special cams.

I found the old school lobes like the comp magnum and high energy do not require a lot of spring pressures.. especially if you keep the valves light and stock 1.5 ratios for rockers.
You can run 80 closed seat pressure and 280 open and still run a lot of RPM.

You can thank the EPA for that. The ZDDP degrades catalytic converters over time to where they can't meet the .govs mandated warranty requirements. And if you run that much spring you better have an old school oil or you can kiss that cam and lifter set goodbye no matter how you break them in. I run Amsoil but in one of these engines I'd have to use their Z Rod oil which is specifically for old school engines. It has the ZDDP needed.

FWIW, the science in the new oils is getting pretty ridiculous. Look up low speed pre-ignition or LSPI. It only applies to the new direct injected and turbo'd engines. The fix is in the engine oil (additives) and they are very hard on them. The manufacturers are going down to 0W15 pretty soon and 0W10 after that. There are already 0W10 racing oils out there. Like I said it's getting kinda nuts...

 

[swampratt]

I hear ya on the EPA but I put a lot of blame on the big 3 also ..always looking for ways to reduce friction and improve MPG.
They must meet MPG guidelines set out by the EPA.. or is it some other entity that sets guidelines.

Anyway those thin ring packs and short skirt pistons do not control oil consumption near as well as the old school 5/64 rings and long skirt pistons.
Yea tighter clearances in piston to wall because if you rock that short skirt piston too much you will crack it.
Possibly break the ears off..seen it many times.

Yep tight clearances require thinner oil.. but a downfall to thinner oil many times is cling ability.
You are basically starting it a little drier but it picks up and circulates quicker.

Do this you must then do that.
Yep LSPI has been an issue for some time..very interesting on what was discovered with high speed video.
https://www.motor.com/magazine-summary/resolving-low-speed-pre-ignition/

When i port heads My chambers were always smoothed and any sharp edges in combustion space was removed.
My runners were roughed up as much as I could make them all the way to the carb pad.

I wanted the air and fuel to tumble and get as atomized as possible before it got into the combustion chamber.
I always tried to keep oil consumption as low as possible also.
You know my 400,000 miles on my 1969 350 uses less oil than the 1995 Geo i sold.
Ya think they screwed the pooch somewhere.

There are oils that burn off much easier than others something to pay attention to is the Noack rating.
https://en.wikipedia.org/wiki/Noack_volatility_test

But that can be misleading like all numbers sometimes can.
There are some oils that have low Noack and perform like oils with high Noack readings. burn off just as easy.

I feel it is left to us guinea pigs to test for our self sometimes.

Smooth chambers are possibly not best way to go anymore.. there has been some very neat finishes that worked very well.
dimples in chamber and in runners keeps air turbulent.
https://speedtalk.com/forum/viewtopic.php?t=34837&sid=8d8ff29c6b29fbdfbc72facd654de78b

You may need to log in to see the posts and pics.
Good sight for sure though.
Not as good as it was 10+ years ago but still worthy.

 

[Dave70968]

I build the old school reliable 350's for myself all the time.. and my buddies seem to like them also.
It is getting a little harder to come up with good cores to build off of.
There is a lot of power to be had in cylinder head work.
Get this book for cylinder head .
https://www.amazon.com/Chevrolet-Small-Block-Cylinder-Motorbooks-Workshop/dp/0879385472

There are books on blocks also.
But a lot of that is old school and the old school parts that worked very well then are not the same quality they once were.
Pistons I used were USA made Sealed power 345NP that piston today is not the same at all.

Stay away from the Hypereutectic pistons unless you build a low 9.5 compression or less deal.
I always shoot for a minimum compression of 10.3 and my 57 chevy 4 door has 10.87 actual compression and a cam that closes the intake valve very early.

Cylinder wall prep is a huge player in longevity . If you finish hone the walls coarse like 240 grit or even 400 grit you will have early wear.. basically the cylinder wall will slick up with the rings and if you finish coarse at 240 grit the final after rings are bedded in will be much smoother..think about where all that coarse surface grit went.

The filter does not filter 100% so do not expect it to catch the debris.
The cam lobes are basically oiled by splash oiling.. one reason during cam break-in you need to keep the RPM above 2000 and prefer 2500-3000 during breakin.. speaking flat tappet cam.
Roller cam is different.

If you do not plan on reving above say 6500rpm ever then the factory roller block would be a good bet and run a factory roller cam like the GM Hot cam.
Or a similar type.
I like rpm and so 7000+ and many times over 7500rpm is what trips my trigger ..the factory roller cam spider and factory type lifters will get in trouble.
I run flat tappet.
Here is an excellent read on roller cams.
http://garage.grumpysperformance.co...up-on-hydraulic-roller-lifter-selection.5522/

Here is a good sight to learn stuff from.
http://www.chevelles.com/forums/

So, reading the first link, in particular about small-base-circle cams. I understand their advantages (or at least I think I do). I understand the danger of the lifter falling below the dogbone. It seems like that could be fixed with a slightly taller lifter, though I can see where that could be a problem in that it would add mass to the pushrod stack (the linked lifters make for a clever solution). Aside from keeping the lifter from falling below the dogbone, are there any other advantages to a larger base circle in the cam? Other than simplicity and insensitivity to rotation, are there other advantages to non-roller (am I using "flat-tappet" correctly?) lifters? Other than (I'm guessing) cost, is there any downside to forged pistons?

 

[dennishoddy]

Go Electronics vs the coil/points/carb
Trust me on this. There is a reason you don't want to drive around with a speciality wrench to adjust your timing and a feeler gauge to adjust your points unless you're just into old school for neostalgia. You might as well put on a carb that you have to remove and replace the jets to get to colorado. You might have to stop in Colorado Springs on your way to score some buds to do that because your vehicle will be running like crap at that point.
Don't know how I know this, but it happens.

 

[swampratt]

for a mild build with a mildish cam that will still make 400+ HP in a 350 you can use stock size lifters and cam.
Larger diameter cam will take much more spring pressure.
But then there are machine costs. But there are small diameter cams that will take a lot of pressures also
You are not building a 700+ HP small block so no worries.

I have heard many say they had issues in the upper elevations.
I never had any issues at all I went up pikes peak in my 84 ford van and no issues. It was not stock.
302 +.030 for 306 inches.. decked block Keith black flat top pistons, ported and surfaced small valve 302 heads and ported ex manifolds and ported 2 barrel iron intake with spacers.. running motorcraft 2 barrel carb.
3" exhaust single outlet.

Timing curve was quick 16 initial and 35 total all in by 2000 rpm. 260H comp magnum cam flat tappet hydraulic.
maybe the old school timing curves hurt those going to higher elevations.
My van ran perfect up there.
My AFR at idle was 18:1 part throttle cruise was 15.1 :1. Full throttle AFR was 13.5.
That was down here in Oklahoma.

Maybe the ported heads and earlier closing intake valve helped.
Our 82 mustang inline 6 with 1 barrel carb was happy everywhere also.
Yes The exhaust was not stock and it also had a quick timing curve.
No vacuum advance on either of them.
But i do like a lot of initial timing and want it to come in quick. Needs to all be in by cruise RPM or MPG will suffer.

My van only had 170psi cranking pressure the 82 200" inline 6 had 200 psi cranking pressure.

You need to go leaner the higher up you go and most cars are not running on the lean side to begin with at lower elevations.
Even reading plugs you will be surprised how much jet you can add to one and still have white plugs.

I took 8 thousandths out front and rear from my buddies 750 which he thought was on the money.. this was at the track in Noble .. he came to me and said that is as fast as it would go the tune is perfect no more left in it.

That is when i said open the hood and i took the big jets out and stuck different ones in .008 smaller in primary and secondary and said go make another pass.
He went 4 tenths quicker!!
His plugs were white to begin with and were still the same after the jet change.

I jet down until i get a lean surge during slow throttle application.
I then jet up until that surge/bucking just goes away. then add .001-.002" more primary jet to be on the safe side.. this will put you in the 14.5 AFR range.
Full throttle power is then messed with shift recovery from first to second. if it noses over on the shift you are lean.
Add some rear jet.
Yes you have idle and high speed air bleeds but most of the time I do not need to even mess with that.

 

[Dave70968]

In airplanes, we do it a little differently: I have a mixture knob right next to the throttle knob, and can adjust it as I see fit (often, but not always, in conjunction with an exhaust gas temperature gauge); matter of fact, when we shut down, we typically do it by pulling the mixture to idle cut-off rather than by shutting down the spark (keeps the plugs cleaner, and our spark is entirely separate from the rest of the electrical system in most airplanes; also, we're still running magnetos). It sounds like you've solved the altitude problem in large degree, and I don't see myself going up high in the mountains anyway, but is there any way to add even a limited mixture control to an automotive carburetor?

Big black knob is throttle (at idle), red knob is mixture (at cut-off); small black knob is carburetor heat (turned off), drawing intake air from a muff around the exhaust stack to avoid (or remove) carburetor ice. Can also be a problem in cars--my dad had a situation once in a '84 Ram with the 225 slant-6 where conditions were just right for carb icing. Engine started running very rough, but cleared up after he pulled over and the residual heat cleared out the carb. He later discovered that there was an intake hose set to provide permanent carb heat (by pulling some intake air from around the exhaust manifold) that was missing.

 

[swampratt]

Yep the heat riser tube on the 6 needed hooked up.
Some auto vehicles have coolant circulated around the carb plenum area to keep it heated under the carb.
Many factory intakes have EGR circulated under the carb.

On the enrichment or lack thereof in a carb used for low and high altitude you can thank motorcraft for the 2 stage power valve.
Holley has them also and will fit certain carbs.
http://documents.holley.com/199r7903-2rev1.pdf

I had a 2 stage in my motorcraft carbs.. only because the kit came with it.
The 2 barrel also had 50cc accelerator pumps.

The porting of the head alone will gain roughly 40HP on a 350. That is power you can use in higher elevations.

 

[skyhawk1]

Not a very good pic but I prefer the quadrant, the carb heat is to the right of mixture

 

[Dave70968]

Yep the heat riser tube on the 6 needed hooked up.
Some auto vehicles have coolant circulated around the carb plenum area to keep it heated under the carb.
Many factory intakes have EGR circulated under the carb.

On the enrichment or lack thereof in a carb used for low and high altitude you can thank motorcraft for the 2 stage power valve.
Holley has them also and will fit certain carbs.
http://documents.holley.com/199r7903-2rev1.pdf

I had a 2 stage in my motorcraft carbs.. only because the kit came with it.
The 2 barrel also had 50cc accelerator pumps.

The porting of the head alone will gain roughly 40HP on a 350. That is power you can use in higher elevations.

I'm not sure we're talking about the same thing. I was talking about needing to lean the mixture at higher elevations (or, more correctly, having to reduce the fuel going in to return it to the same mixture as the air gets thinner); your link looks to be a device to automatically enrich the mixture as demand increases (heavy acceleration).

Have I misunderstood something?

 

[swampratt]

No you are getting it ..but regular and dual stage do not flow the same amount of fuel when opening.
Basically 2 opening rates on the dual stage to keep things a bit leaner and it never enriches the circuit as much as the single stage.

The power valve circuit is needed in a carburetor application most of the time any way.. you can delete the power valve circuit but the main circuit will become overly rich because you must add a larger jet to make up for deleting a power valve circuit.
Usually .008-.010" in larger jet size.

Lets go about this differently. Simple version.
Carburetor on an engine as you know will pull air through the carb venturi and the air is vacuum this vacuum is called venturi vacuum.
This vacuum will basically pull gasoline or "fuel" through an orifice. like drinking from a straw.
The jet associated with that venturi must be calibrated to flow the correct amount of fuel to make the air fuel ratio correct.

This we know ..I will not get into other passages that help emulsify the fuel.

But if you are cruising or say pulling a hill and keeping vacuum up in the 11+ range you will be only needing the fuel from that jet.
This is called the main circuit.

After vacuum drops lower and lower from you applying more and more throttle you just can't flow enough fuel from that jet.
So the engine will go lean ..This is where the power valve circuit comes in. it adds the needed extra fuel to keep the engine in a good AFR range.

If you added a large enough jet usually 10 thousandths larger than what would give you a nice 14.7 AFR you would be overly rich during part throttle application.

The dual stage power valve flows less fuel than a regular power valve under this situation where you are not under full throttle but you are far enough into it to need a slight enrichment.

Get all the way into the throttle and it will flow extra fuel.

A Carter AFB or Quadrajet and many other carburetors use a brass metering rod that sticks into the jet.
This rod is fat in the upper portion and towards the tip it is smaller diameter.. say .075" at the fat portion and .047" at the thinner portion.. as vacuum drops you need to richen the mix and the rod will spring up due to a piston /spring assembly and the thin portion is now in the jet.. allowing it to flow more fuel. Get out of the throttle and the fat portion goes into the jet.


No dual stage available for that.
This is all really easy to see and grasp if the carb is in front up you.

Some carbs at very low RPM will not be in the main circuit but will be in the idle circuit.. giving very good MPG figures.

One carb that allows higher cruise rpm before it gets into the mains is the carter AFB/ edelbrock 750.
You can actually get a tick better MPG from it vs the 600 cfm.
Yes i said that. larger carb more MPG.
It comes back to the venturi vacuum pulling fuel from the jet. The smaller venturi passing the same volume of air will pull harder on the passage to the jet allowing the main circuit to come in much earlier.

I have many of them.
With the 600 edelbrock In park with engine running you can slowly open the throttle and before 1500rpm fuel will come out of the boosters from the main jet.
The 750 edelbrock will get closer to 2500rpm before it pulls fuel from the booster.

There are many guys running 500+ BBC engines and OD transmissions and stupid big cams like 260@ .050 and large single carbs with large venturies and pulling 15+ MPG on the highway.

Incredible.. but not so much really those large engines are barely working down low at say 1900rpm it is easy to maintain highway speeds and the whole time they are in the idle circuit.
Yep more MPG than the 350 buzzing along at 3000 rpm with small cam and small carb.

Head scratcher .