Thread: SBC 350 build

Tweet

As Dave suggested and I agree with him,have someone that knows what they are doing,do a leakdown test first.Then let us know what the results are.One other question is how is the engine doing in terms of oil pressure??.

First off, thanks for the replies. Tech, you really seem to know your stuff but I'm not really interested in building a 383 or anything near 470hp 490 ft/lb torque. That's more power than I need and I'm not looking to beat my dad in a race... yet. I see the general consensus is to get a leak down test done on the motor so I will have that done. I don't know if the previous owner played around with the gearing so I'll pull the cover off the rear end and check the rear gears and then go from there. I'm not sure what it's like for oil pressure and I won't be able to do a leak down test or check compression until spring time because it's in the back of a barn blocked in by another 20 cars. I also have another option. It has vortec heads on it right now. Do you think I could make solid ponies and torque with those heads and new cam, intake, carb?

A leakdown is going to give you a good assessment of where you are with the engine at that point.Don't let mileage on the engine allow you to think about anything or assume you need to do any replacements.As for a oil pressure check,consider doing a oil change and oil filter change to a Wix oil filter then do a cold oil pressure and hot oil pressure check at idle and at cruise speeds.

Originally Posted by Louey

A leak down will, providing the valves aren't leaking.

170,000 km on the motor = 105,633.103 miles.Rings are way cheaper to do now, than later.At that mileage, I would advise seriously thinking about checking the cylinder wall condition. And also the main and rod bearings. You will have the heads off anyway right ?
Looks like a real nice pickup though.

Hey Louey-it would give ya a idea of the condition of the rings too.I agree a mod is only as good as the weakest link.But there again has been many top haft mods done successfully on engines that where qualified as being in decent shape.I just ask myself how many rods on this site have 105,000 miles on them or more since built??.I would guess thousands of them.Again the oil pressure check could give him somewhat of the condition of the rod and main bearings.

What has been said makes plenty of sense to me. Since I'm going to have the motor mostly tore down, I might as well go a little further and check over the bottom end. It sure can't hurt to take a look at the bottom end. I will be popping new rings in for sure to improve over stock and I will take a look and the cam, main and rod bearings. Again, all the input is greatly appreciated. Thanks for the compliment on the truck, Louey. I think it's gonna be real sharp when I'm done with it and plenty of fun.

Originally Posted by Bowtiepickups

First off, thanks for the replies. Tech, you really seem to know your stuff but I'm not really interested in building a 383 or anything near 470hp 490 ft/lb torque. That's more power than I need and I'm not looking to beat my dad in a race... yet. I see the general consensus is to get a leak down test done on the motor so I will have that done. I don't know if the previous owner played around with the gearing so I'll pull the cover off the rear end and check the rear gears and then go from there. I'm not sure what it's like for oil pressure and I won't be able to do a leak down test or check compression until spring time because it's in the back of a barn blocked in by another 20 cars. I also have another option. It has vortec heads on it right now. Do you think I could make solid ponies and torque with those heads and new cam, intake, carb?

What you got was my signature approach, to come galloping in like Caligula, lopping off heads and taking no prisoners. I guess that's because I have always built stuff by the old hot rodder's axiom...."If some is good, more is better and too much is just right." I may not always be right, but I will always be opinionated.

There are lots of copy-cat, so-called "Vortec" heads out there in the aftermarket, but the only ones that are worth fooling with, other than the RHS heads I linked in my first post, in my opinion, are the genuine Chevrolet production RPO L31 heads off a 5700 Vortec motor that was in the '96-'99 Chevy trucks and vans. Same motor that I suggested using the block out of to build a 383. These heads can be found under casting numbers 12558062 (induction hardened valve seats) and 10239906 (separate pressed-in exhaust seats in some, but not all of these heads). Some people will tell you that there is a "good" head (induction hardened seats) and a "bad" head (pressed-in exhaust seats). Builders who have flowed both heads will tell you that the heads flow the same after you clean up some sharp edges at the seat and blend them in.

These L31 heads flow better than any other PRODUCTION cast iron head that Chevrolet ever cast up, but they have several weak points as well. It takes some work and some money to get them to the point where you can bolt them onto a motor and get close to the same results as you can from the heads I linked, which come out of the box ready to bolt on.

First, they are thin-walled castings. If you are pirating a set of used heads from somewhere, the first thing you want to do is clean them up and have them magnafluxed for cracks. You might want to make a deal with the guy you're getting them from that you can exchange them for another set or get your money back if they fail magnaflux.

Secondly, the rockers are "rail" type rockers that have an area on either side of the rocker that shrouds down around the tip of the valve to keep the rocker centered on the valve stem tip. These rockers will work ok for short and moderate lift cams and the aftermarket has come up with "roller rail" rockers. Use caution and buy only narrow body rollers so they will clear the inside of the L31 center-bolt valve covers.

Thirdly, the heads have pressed-in rocker studs that might tolerate up to around 250-260 lbs of pressure across the nose of the cam, but any more than that will begin to pull them out of the heads. You can pin the studs into the heads with a low-buck Mr. Gasket kit to prevent pull-out.
http://www.summitracing.com/parts/MRG-806G/

Fourth, the valve guide boss is extremely large on the O.D. because Chevrolet used only a single spring on these heads. There is no room to install a 1.250" spring with damper because the damper I.D. will not clear the boss O.D. And if you're going to use more cam, you're going to need more spring. So, you must cut the O.D. of the boss if you plan to use a 1.250" spring, or cut the seats in the heads for a larger diameter spring to clear the boss. The other main problem is that the bottom of the retainer will crush the valve guide seal at valve lifts exceeding 0.430". I know there are those fellows who will tell you that you can run 0.500" lift with the stock arrangement, but Chevrolet says 0.430" limit. You have to leave a safety margin to account for valve float and that is usually around 0.060" minimum.

Crane Cams makes a spring and retainer that will clear the seal and the O.D. of the boss, drop right in on the seats in the heads and will allow more lift, but they are pricey.
http://www.summitracing.com/parts/CRN-10309-1/

Some fellows have done a "Ghetto Grind" on the bottoms of the retainers to gain some clearance between the retainer and the seal. I have heard of cutting 0.080" off, but have never done it, so have no experience with what works and what does not work. If I were going to do this, I would mount all the retainers on the table of a surface grinder and take off the material that way, instead of trying to do it with a hand grinder.

So, there's the skinny on L31 heads. By the time you get through doing machine work and buying new parts, you could have bought a set of RHS thick-wall casting heads complete and ready to bolt on for less money.

Haha. That sounds like a solid way of thinking. I read little article and the boys at Hot Rod magazine used vortec heads and used a set of COMP Cam's beehive springs and ran .490 lift. (they say they are good for .560) If i understand correctly, I can put on the beehive springs and retainers and be good for a .560 lift cam. I was thinking I would do this since the heads are already on the motor it would be a decent way to make power and save some serious scratch. Of course, I would check the casting numbers on the heads before I did it.
Link to the article:
http://www.hotrod.com/techarticles/e...ild/index.html
Check page 2
Link to springs:
http://www.summitracing.com/parts/CCA-26915-16/
Link to retainers:
http://www.summitracing.com/parts/CCA-787-16/

Originally Posted by Bowtiepickups

Haha. That sounds like a solid way of thinking. I read little article and the boys at Hot Rod magazine used vortec heads and used a set of COMP Cam's beehive springs and ran .490 lift. (they say they are good for .560) If i understand correctly, I can put on the beehive springs and retainers and be good for a .560 lift cam. I was thinking I would do this since the heads are already on the motor it would be a decent way to make power and save some serious scratch. Of course, I would check the casting numbers on the heads before I did it.
Link to the article:
http://www.hotrod.com/techarticles/e...ild/index.html
Check page 2
Link to springs:
http://www.summitracing.com/parts/CCA-26915-16/
Link to retainers:
http://www.summitracing.com/parts/CCA-787-16/

That could be a plan. Parallel springs such as the Cranes I linked really need a spiral-wound damper spring to cancel harmonics in my opinion, whereas beehive springs do not, so my choice in what you have presented here would be the Comp springs.

Notice that the builders used a cam ground on a 108 degree lobe separation angle and had some horribly low intake manifold vacuum because of it. Generally speaking, the motor will make more power the tighter you go with the LSA, but vacuum stinks for operating power brakes and other vacuum-operated accessories. You'll also note that they mentioned a reserve vacuum can or an electric vacuum pump. If you need additional vacuum, don't waste your money on a reserve can. Either pop for the pump or install a hydroboost system like was used on some Cadillacs, trucks and such. Works great with the wildest cam because the brakes are not dependent on vacuum to operate. I don't care what anyone else says, you need a minimum of 16 in hg to operate power brakes.

You can still make good power for street/strip and make a little more vacuum by choosing a cam ground on a 112 degree LSA and keeping the duration reasonable. You keep the duration reasonable by using a reasonable static compression ratio. Understand this: YOU CANNOT INTELLIGENTLY CHOOSE ANY CAMSHAFT FOR ANY MOTOR UNTIL YOU ABSOLUTELY, POSITIVELY KNOW THE STATIC COMPRESSION RATIO BY MEASURING COMPONENTS YOURSELF OR HAVING SOMEONE ELSE MEASURE THEM FOR YOU.
You need 5 values:
1. Cylinder volume in cc's
2. Combustion chamber volume in cc's
3. Piston deck height volume in cc's (the volume between the piston crown and the deck of the block with the piston at top dead center)
4. Piston crown volume in cc's (a true flat top piston will have about 6-7 cc's in the eyebrows that are cut into the crown for valve clearance. Otherwise, for a dished or domed piston, the mfg will usually publish the volume). Most of the stock-type 350 pistons have a recess that isn't actually called a dish, but it is a depression across the crown, with a very thin ring of material sitting up a little higher around the bore. That little thin ring of material is insufficient for generating a good squish and you should be very careful with compression ratio and cam if you use that type of piston. The very best type to use in a street/strip build in my opinion is a D-cup dished piston. These provide a generous shelf of material that comes up against the underside of the cylinder head to generate a very good squish. If you build any kind of reasonable static compression ratio into the motor without using a good squish, there is a good possibility that the motor will detonate on pump gas.
5. Head gasket volume in cc's
If you want me to go through the entire routine and teach you how to find the exact SCR, just ask.
The camshaft will normally be the last component chosen, after everything else is nailed down for the build.

If you do end up using L31 heads, don't let anyone talk you into increasing the valve sizes. Stock, they are 1.94"/1.50" and will do a fine job on a 350. Any cutting done on an already thin-wall casting is just asking for trouble.

Thanks for that post. It cleared up a few things for me. I will definitely get you to help me go through calculating everything when I have it tore apart and it's closer to re-build time. Which is greatly appreciated. I have no desire to increase the size of the valves. So would you recommend I get some new pistons instead of the stock ones? Would they have to be something with a D-Cup dish? Or would flat tops due alright too? Also, what would your input be on rockers? Would roller rockers be worth it for me? Thanks again for your input, it seems to be helping my understanding a lot.

Originally Posted by Bowtiepickups

Thanks for that post. It cleared up a few things for me. I will definitely get you to help me go through calculating everything when I have it tore apart and it's closer to re-build time. Which is greatly appreciated. I have no desire to increase the size of the valves. So would you recommend I get some new pistons instead of the stock ones? Something with a D-Cup dish? Also, what would your input be on rockers? Would roller rockers be worth it for me? Thanks again for your input, it seems to be helping my understanding a lot.

Let's find out what pistons are in the motor first. Another thing that I didn't mention about pistons, the compression height is the distance from the centerline of the wrist pin to the top of the crown. On a 350, this dimension, stock, is 1.560", so that when you add the 1.560" to the rod length of 5.703" and add to that the stroke radius of 1.740" (half the 3.480" stroke), you get a total "stack" height of 9.003". Since the block is normally ~9.025" give or take a few thousandths, you can see that with the piston at top dead center, the piston deck height (distance from the piston crown to the block deck) is 0.022" in this case. Now, when these motors were put together at the factory, they used an embossed steel shim head gasket. It has been a long time since I measured the thickness of one, but I seem to remember somewhere around 0.020"/0.022". OK, so if the piston is 0.022" down in the bore and the gasket is ~0.022" thick, you can see that there will be 0.044" of clearance between the piston crown and the underside of the cylinder head with the piston at top dead center. This is the squish dimension in this case, 0.044". Since most builders will agree that 0.035" to 0.045" is ideal on a small block, we are right there for this example.

Now, that was using a piston with a stock compression height of 1.560". There are also pistons made for a 350 with a 1.540" compression height. These are usually, but not always, cheapo cast pistons with an ultra-cheap price. They're called "Rebuilder Specials". The reason these are made is so that the rebuilder of the motor can take a 0.020" cut on the block decks to clean them up and still have the same crown to deck dimension (piston deck height) as the motor had stock. The problems begin when Henry Hotrod is looking for pistons and sees these really inexpensive pistons for sale. He has no idea about squish and how it affects his motor and is totally unaware that there is any such thing as piston deck height and squish. All he sees is the cheap price of a new set of pistons, so he springs for them. He also has no plans to deck the block. So, he ends up with the piston sitting 0.020" deeper in the bore at top dead center and has eliminated any possibility of generating a good squish. He bolts the motor together and is dismayed when it will not run on his regular grade of pump gas without pinging (detonation). Desparate to stop the detonation, he pulls all the ignition advance out of the motor and now it won't pull the hat off his head. Or maybe he just lives with the detonation and the motor finally throws in the towel with several cracked pistons.

I have seen this scenario come to life time after time after time in the years I have been on these forums.

The very best combination you can put together is a motor that uses absolutely flat-top pistons with just some shallow eyebrows for valve head clearance. Problem with this is that you have to use a cylinder head that has chamber volumes that will produce the proper static compression ratio for the fuel you plan to use. For instance, if you have L31 heads, the chambers are ~64 cc's. If you used flat-top pistons with those heads, your static compression ratio would be around 10.3:1, which would be over the line for using pump gas with iron heads. With aluminum heads and a very tight squish of 0.035" and the proper cam that would close the intake valve at the proper time, you might get away with it. But with iron heads, you'd have to run so much camshaft that the motor wouldn't be any pleasure to drive on the street and I don't think that's what you're looking for.

So, the answer is dished pistons to lower the static compression ratio so that you can use less cam and run pump gas. Using a 12cc dish with 64cc heads would result in a 9.6:1 static compression ratio. Here is an example of such a D-cup piston from Keith Black. Notice in the photo on the left side, that there is a generous flat area on the crown. This is the flat area that comes up to the underside of the cylinder head to generate squish across the chamber. When the fuel/air mixture is squished or "jetted" across the chamber, the turbulence homogenizes the mixture and eliminates any over-rich or over-lean conditions in the chamber, making a more complete burn that will result in maximum power and minimum chance of detonation. The tighter you run the squish, the less octane you can run in the motor.
http://www.kb-silvolite.com/kb_car/p...tails&P_id=155
With such a 9.6:1 combination, I might use a camshaft like this one, or something close to it...
http://www.summitracing.com/parts/CCA-12-420-8/

Now, if a fellow moved to an 18cc D-cup instead of a 12cc,
http://www.kb-silvolite.com/kb_car/p...tails&P_id=154
then the static compression ratio would be somewhere around 9.1:1 and you might use a camshaft such as this one....
http://www.summitracing.com/parts/CCA-12-410-8/

It's all about the combination. You have to choose pieces that will like each other and make max power for the combination.