[UPDATED: 8/3/09]

Introduction
C3 Tech seems to be the hotspot for GEN I engine builds. I spend a fair bit of time offering guidance in the forum, but I thought I’d take a moment out and address the stuff that underlies all the specifics about a particular build – how to get successfully through the process. Picking parts is fun, but there is foundation work that will ultimately have a much greater impact on your success than the parts chosen.

The goal is to have a successful build that’s on budget, on power targets, and successfully back in the car within a reasonable timeframe. The intent of this guide is to help the builder avoid the most common pitfalls :

• Unrealistic budget that does not allow you to complete the build.
• Machine shop that’s not prepared to work with a home rebuilder, is a race-only shop, or is just a lousy shop period.
• Poor design that’s not well-matched to your drivetrain or usage – or worse, building an engine of mismatched components that you’ll “fix later when I have the money” that never really runs right.
• Builder lacking the expertise, tools, discipline or patience to complete the build.

In closing this introduction, I’ll note that there’s probably no surer way in any online forum to get flamed to death than to post this kind of guidance I’m not a professional builder, but I have been successfully building GEN I’s for a long time and I believe all this to be good guidance. It’s all IMHO, of course! I’ll be completing this over the next couple of days, and I’ll make ongoing adjustments where appropriate based on feedback and suggestions!

Step 1: Budget
What? Talk about money first? NO! I want to talk about cams, and heads and pistons and stuff! Well, more engine builds fail from unrealistic budgets than from any other single cause. The worst part of this is if you’re rebuilding your existing engine, then you’re dead in the water – the engine’s out and maybe in pieces and you’re going nowhere until the build is done. Everyone wants 500 HP…but ultimately your budget will determine what you can realistically achieve. A $2,500 build back in the car is way better than a $10,000 build that's sitting on the engine stand waiting for $7,500 in parts or machine work

As a very general guide for a GEN I SBC, consider the following budget numbers for initial planning:

• < 1 HP/CID: $2,000. This is a “performance overhaul” where mostly stock-quality parts are used – but the configuration is optimized for performance. Basic machining operations.
• ~1 HP/CID: $3,500. This is as above, but with better heads and a bigger cam.
• 1.2 HP/CID: $5,500. This is better quality components throughout, forged pistons, etc.
• 1.4 HP/CID: $7,500+. All forged, all top-quality components, excellent street heads, roller cam, full machining.

Anything beyond 1.4 HP/CID you’re best to buy a crate or have the engine designed and assembled by a reputable shop. That’s a generalization, but overall these types of high-power builds require very careful planning, mock-up and assembly that’s beyond the home rebuilder. The price is in the "if you have to ask you can't afford it" range.

Step 2: Machine Shop
The success of your build will ultimately hinge on how well you can partner with the machine shop. A good shop is hard to find, but one that doesn’t fit your needs will be a disaster. There are “job shops” that specialize in quick turnaround of stock rebuilds, racing shops that build high power, highly complex engines and everything in-between. What you need is a shop that is willing to work with a home rebuilder – offer advice, listen to you, keep you from making any huge mistakes and help you get what you want. Not all of them are, and the quickest way to tell is to stop in and talk to them. Don’t call – go there. Tell them your budget, timeline and that you’ll be doing the design and final assembly…but also that you’ll listen to their guidance and adjust where required. If they’re really not willing to talk to you for 10 minutes…they’re probably not the right shop. Take a look at the shop – is it clean? Organized? Busy? How much work do they do in-house vs. farming out? Do they do high-performance work? Bottom line is that you should get a good “vibe” from the shop.

I want to reiterate the word “partner”. The machinists are professionals – they know what they’re doing and they know what works. Don’t go out and buy a bunch of mismatched parts and expect them to make it work, and don’t go counter to their guidance and then blame them when something goes wrong. If they give you guidance you don’t understand, ask them why. At the same time, if you're going counter to their guidance, tell them why so that they can help you understand the risks.

You also need to be 100% clear that as you’re doing the design and final assembly you have full and sole responsibility for the outcome of the build. Let’s say the shop was supposed to cut the crank by .010, and cut it by .030 instead. Catch it before assembly, their problem. Catch it after (in pieces) – your problem. You may get another crank, but they’re not going to replace your engine.

Bottom line: You must have a quality local machine shop willing to work with you to succeed - period.

Step 3: Preliminary Design
The intent of preliminary design is to find the balance between the power you want and the power you can afford.

You’d expect that since the SBC has been around so long that there would be tons of solid design references for how to put together parts to meet a certain power goal. In general, you’d be wrong There are very few references targeted at the new home rebuilder - and virtually all of them are from the Engine Wizard David Vizard. There are certainly other great books around, but for the home rebuilder working in the < 1.4 HP/CID range, David’s the best overall reference. I’d make a flat statement and say that the $100 or so you’d spend to buy his books would be the first and best “tool” investment you can make. My only gripe with his books is he dramatically overstates what can be done with factory and stock/replacement aftermarket heads by a home (vs. professional) porter.

Note that engine design is an iterative process; you’ll make many passes through the design – making changes, seeing how this affects other aspects of the design – and making more changes. This is a standard flow, but it can get frustrating. This is where many builders get stuck; they either refuse to set a budget so there are no real boundaries to drive decisions and so the choices remain unlimited, or they just give up and start buying parts. Be patient, take your time – you’ll get there.

Step One is to set the power targets you want: horsepower, torque and the RPM at which you want to hit those targets. You should know very well the RPM range that you’re going to operate in – and if not, get a friend and a notepad and go do some “spirited” driving or hit the autocross course or dragstrip. If you’re planning on gearing and transmission changes, those should be done first. A mistake here means an engine that makes great “numbers”, but is sluggish to drive.

Step Two is select cylinder heads to meet your targets. This approach will likely raise some hackles, but in the end the power capability of your engine will be determined by the heads. Where in the RPM range you make the power, and the ability of the engine to hold up to the power you make come later, but the heads are the key. Overall, we pick the heads to hit the power targets, the cam to maximize the heads and determine where in the RPM range the power peaks, and the rest of the engine to support the heads and cam.

There’s a general rule-of-thumb that will get you in the ballpark and give you your first indication if your power targets are achievable within your budget. As a rule-of-thumb, it sure ain’t perfect – but it’s a start and we’ll validate it later. The rule of thumb is that the power capabilities of the head = intake flow (in CFM) *2. There are other variables to consider later, but we can start here. If we take a look at a few popular combinations, we get a feel for how this works:

• ($450) Stock low-performance Chevy 350 heads flow around 185 CFM = 370 HP
• ($700) Stock Vortecs (and stock Chevy “camel hump” heads) flow around 210 CFM = 420 HP
• ($1,500) AFR 195 Streets flow around 260 CFM = 520 HP

This gives us an idea of what we can afford – if our target was a 550HP 383, but we know $1,500 heads aren’t in the budget…then we need to re-adjust our power targets – that simple. Note that as we refine the head choice later, the choices get more complex – springs, combustion chamber size, angle/straight plugs, runner size, I/E flow ratio – there are a lot of variable here that we haven’t decided on yet.

Step Three is initial cam selection. Let me be clear right up front – this thread ain’t gonna pick your cam for you. It will help you set some general parameters for the selection and with some smart help hone in on your final choice. The assumption is that you’ll be using an off-the-shelf cam; if you’re considering a custom cam then you don’t need this thread The purists and experienced engine builders are going to cringe a bit in this section with the over-simplifications

If at all possible, we want to use a roller cam. The benefits are just too significant to ignore. In a GEN I, this requires one of two paths; a retrofit roller cam which you should expect to invest $800+ in, or purchasing a roller-cam (86 and up) core for your build. If neither of those are an option, then we’ll be using a flat-tappet cam, likely hydraulic in this power range.

So, let’s start with lift: the rule of thumb here is that we want to open the valves to maximum flow if at all possible. This means if the flow tops out at .450, then a .650 lift cam isn’t going to buy us much. This is overly simplistic, but a good start. Next, duration…and the focus is less about the duration at this point than overlap. Overlap is the time that both intake and exhaust valves are open near TDC, and it’s responsible for that “rumpty” idle that we hear in racing and hot street engines – it provides the “lead time” for valve events at high RPM at the expense of low- and mid-range power, drivability and fuel economy. David Vizard sets some good guidelines here, recommending overlap of 30-55 degrees for warm street engines, and 50-75 for hot street engines.

There are a number of other criteria, but we’re in the ballpark.

Step Four is the shortblock configuration. The decisions here flow pretty easily from the power levels and the usage of the engine. Let’s start with the rotating assembly – and setting some boundaries. Sometimes, it’s easier to work this backwards with some proven rules of thumb:

• If you are considering a power-adder such as NOS (150+ shot) or forced induction, an all-forged assembly is a requirement.
• If you are making more than 1.2 HP/CID or turning beyond 6000 RPM, forged is highly recommended. You may be able to get by with less; people do, and for all the talk about breaking cranks it’s actually very rare outside of hard-core racing. But the risks are higher and the cost of a forged crank is good insurance.
• Below 1.2 HP/CID and 6000 RPM, a good aftermarket cast crank is fine, along with hypereutectic pistons. Old-style cast pistons should not even be considered as the price differential is trivial. You could still use forged pistons if you plan to spray 100 or less NOS shot.
• A stock-style cast crank is good for < 1 HP/CID and 5000 RPM – and with the price of aftermarket as compared to the cost of machine work – generally not a smart investment.
• Note that all rods are forged (except for billet machined and the LT1/LT4 sintered rods) and the power capacity comes from the shape of the rod and the size/type of the bolt/screw. Note that we’re not going break any rods at 1.4 HP/CID

Now let’s take a look at the block, starting by recognizing that “old style” non-roller (pre-1986) blocks are now more than 20 years old – many more than 40 years old. If you already have a block, that’s great. If not, finding a good core these days can be a frustrating experience. I’ve pretty much stopped buying GEN I cores as they’re junk about 4 times out of 5 these days. If you have to find a core to build from, your best investment will be a post-86 roller-cam block – subject to the information below.

The flames will fly, but the stock GEN I block is generally good up to about 450 HP and 6000+ RPM with 4-bolt caps. 2 bolt caps with ARP studs are good to 400 HP and <= 5500 RPM. Note that it is generally cost-prohibitive to put 4-bolt caps on a 2-bolt block, although it is possible. With a few exceptions, the stock block will work for builds at the level this thread addresses.

At the end of preliminary design, you’ve got a pretty good idea of what the big parts are and a reality check on your budget. You are not ready to buy parts; not one, not a gasket. There are a lot of details to sort through. But you are ready to start connecting the dots between what you have in existing parts and what you need to buy.

Step 4: Assessment
Coming Soon

Step 5: Final Design
Coming Soon

Step 6: The Build
Coming Soon

Step 7: Installation
Coming Soon

 

I think you left out some things, #1 most posters here have NO IDEA of what it takes to build a properly running motor (too much cam, too large cylinder heads, "pie in the sky" HP requirements, ect.) #2 I want the shop I am using to have agood track record meaning I am expection my motor to perform well and last a long time, so, I want good machining practices, quality equipment, and reasonably current technology going into my motor (plateu honing, carbide cutter valve job, proper suface finishes on gasket surfaces, ect.) The best way to find a shop is by looking around and intrviewing your machinist, I picked up a set of Manley Sportmaster connecting rods from my machinist for $250 that were almost like new because of a rules change at the local circle track (helped me keep my build costs in check) because I am a regular customer of my machine shop. If the shop your using dosen't maintain their equipment and cycle in new lubricants into their machines (like the cylinder hone) you are going to end up with an oil burning POS of a motor. Many forum members here listen to posters here, go shopping at Summit/Jegs/Doug Herbert/wherever and by a totally WRONG combination and mistakenly belive their local machine shop will charge them more $$$ for the parts than Summit, THIS IS WRONG, my friend;s shop can BEAT SUMMIT on all prices and build you a good running combination that he will GUARANTEE the parts/performance of even when the customer SCREWS UP on the installation (cranking excessivley-wiping out cam lobes, not properly filling the cooling system, wrong fuel air mixture, ect.) Quality shops make up maybe 30% of the industry, you need to talk with a few shops before making your decisions.

 

I'll just note that I believe I've addressed several of these, and I plan to address the rest in the other sections to be completed.

 

Billla, I look forward to your forthcoming installments. Thanks for taking the time to put this together. I've built a few engines, and am always looking for "experienced insights" into the process.

I hope you'll be able to factor in some of the feedback you'll undoubtedly receive from other seasoned builders.

Robb

 

thanks for taking the time to share your experience.

 

 

Updated with the addition of Step 3: Preliminary Design.

This is taking me a while to distill out I hope suggestions/corrections will be phrased as helpful suggestions - and not flames.

 

This is good, thanks for the effort.

 

Thanks for putting the time and effort in Billa

 

As usual Bill, thanks! If you get too many flames don't be discouraged. Guys like me appreciate and need this info. as it is always practical, realistic and reasonable.

 

Thanks Billa. Having the info broken down to the shady-tree mechanic level helps me out alot.

 

Thanks for the input, I've spoken to many performance shops and every one has a different sugestion...You put some insight into the process.

I'm looking forward to the completion of the thread.