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post #1 of 17 (permalink) Old Jul 20th, 15, 08:52 AM Thread Starter
Engine Choices

After buying my 69 Z that was just rebuilt ( apparently by an idiot ) I found out that all I really have is a good standard bore 350 block and a new cam. I am thinking about building a 383 but looking at all of the choices I'm confused. Forged, cast, flat top, domed, Eagle, Scat I'm not sure where to start. The one thing I know is that I'm working with the original 69 DZ 302 heads the block is the same casting as a 69 DZ casting and I want a good street performance engine. Any help would be appreciated.

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post #2 of 17 (permalink) Old Jul 20th, 15, 09:33 AM
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Re: Engine Choices

If crank and rods are good the use some forged Pistons to get about 10:1 add a roller cam and ditch the dinosaur heads and install a good aluminum head.

No reason imo to do a stroker

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post #3 of 17 (permalink) Old Jul 20th, 15, 10:04 AM
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Re: Engine Choices

How and what you build will depend upon two factors. What you want from the build, or more exactly how you expect to drive the car, and the second thing is your limiting budget.

As to a SBC motor, as with a BBC motor bigger is better. A 421 or a 406 is as powerful if not more so than a 396 or a 427. This is because of the SBC's head that has the potential to make more power per cube than the BBC head. However your old school 2.02" steel flat bottomed intake valves and pent roof (wedge) combustion chamber will cost you a serious horsepower penalty compared to swirl polished tuliped stainless steel valves and a heart shaped fast burn combustion chamber. The intake port size on your 302 heads were only 190 cc in volume, which is plenty for a 302 but as displacement increases think to follow the engineers lead from Chevy and increase the port volume accordingly with a 396-427 using a 230 cc intake port.

The difference in the materials will not affect the power level that the engine makes, only in whether there will be any parts that are reusable if and when it dies. A cast engine is just about junk once a piston shatters, or the crank breaks. But as far as the risks of a cast crank failing; it is miniscule, as they are just as strong as a forged one. A forged crank will bend instead of breaking, and as such it can be straightened in a press after reusing the same part, and a forged crank is more likely to be internally balanced. That explains the difference in price (the desirability of the part).

It is a mater of opinion as to which is better Eagle vs. Scat. I have built hundreds of engines using both (they weren't mine they were built for customers who had their own opinion's and budget's). I have found SCAT to be the better of the two in terms of finished product "as received", but since both go to the machine shop to be reworked there was no difference between them when installed. In my own personal builds I used forged internals from Callies, Lunati and Isky as vendors for parts (except for Chevy using Crane for cams and valve train parts they agreed with my choice of vendors).

If you want a high reving motor (who doesn't) then you want to keep the stroke on the short side. This doesn't eliminate a big bore it just requires more money for an aftermarket block. Keep in mind Pro Stock 500 cube big blocks out rev a 283 but they are built entirely out of big bore short stroke parts that are machined from billets or custom cast. You can build a 350 out of a 400 SBC aftermarket block and a custom 4043 327 crank and forged pistons that will rev like a 327 but make more power than a 350 ever could with aftermarket heads and a solid roller cam. How fast do you want to go?

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post #4 of 17 (permalink) Old Jul 20th, 15, 11:12 AM Thread Starter
Re: Engine Choices

Thanks John and Dave. My original crank is a stock forged GM that is ground .020 under, the mains are fine but the rods are bad and need to go at least another .010 maybe .020 more. Apparently the joker couldn't figure out that you shouldn't run .010 bearings with a .020 under crank. My fear with the crank is the .040 under kind of scares me. The rods are pinkish in color and I was told that they are good rods but I haven't checked them to see if they have stretched from the bad rebuild. I'm not after an all out race engine I just want a decent performer and reliability. I also want to resemble a stock engine as close as possible and use my air induction hood, I also have the original intake.

I guess I'm not stuck on the 383 thing I just want something with parts that work together and I thought a stroker kit would give me that without a lot of hassle. If I can get enough advise on here maybe I could use most of the parts that I have.

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post #5 of 17 (permalink) Old Jul 20th, 15, 12:20 PM
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Re: Engine Choices

Depending upon your current bore size a thirty over 383 rotating assembly from SCAT would fill your bill. You finish hone the block's cylinder bores to fit the pistons, not to try an stuff a piston into an existing hole. I would add a new Mellings oil pump and stuff it all into a cleaned fully machined block.

Cheapest solution would be to buy a running late model 1996-2004 Vortec 5700 out of a pick-up truck. Convert it to a carburetor using your intake and distributor then bolt on center bolt to perimeter bolt valve cover adapters after painting everything orange. Be sure the running motor retains the one piece rear main seal flex plate that should adapt to your tranny if you have a TH350. If you have a manual you will need a new fly wheel as the bolt hole pattern changed when they went from a two piece rear main seal to the one piece.

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post #6 of 17 (permalink) Old Jul 20th, 15, 02:49 PM Thread Starter
Re: Engine Choices

Thanks Dave. My block is a standard bore 4 bolt and I guess my first questions are about the block and crank. I've heard that you have to UT the block to check for minimum wall. How thick does it have to be after its bored? Im figuring on .030 over. And for the crank. If I have to go .040 under can I trust it? I'm not on a budget but I don't want to throw away money for no reason.

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post #7 of 17 (permalink) Old Jul 20th, 15, 03:18 PM
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Re: Engine Choices

I don't like using a crank turned under that much (never favored the use of Honda rod bearings on a Chevy crank for that reason). The strength of a cylindrical shape is on the exterior. This is why you can hog out the center to lighten the crank's reciprocating weight without affecting the overall strength, but the bigger the outside diameter the stronger the part will be.

You can bore a standard block thirty over with out any worry. Before I go sixty or more over bore on a block I ultra sound check the bores for any core shift. Additionally over boring a stock block too much, even with cores where they belong, causes the motor to run hotter than a thicker cylinder wall; as the heat of combustion travels through the cylinder walls at a faster rate when they are thinner.

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post #8 of 17 (permalink) Old Jul 20th, 15, 04:42 PM
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Re: Engine Choices

Jeff, You could purchase a Scat rotating assembly like this : http://www.summitracing.com/parts/sc...make/chevrolet Checkout a bare set of these Pro-Filer heads. http://www.profilerperformance.com/r.../sbc-23-degree Once you have the rotating assembly you can take the block to your machinist to be cleaned, bored & honed with a torque plate. Replace cam bearings and check lifter bores. Then have him zero deck the block so you can purchase a .039 or .041 thick head gasket so your Quench will be which ever gasket is used. Once machine work is done have have him balance your rotating assembly. As for the bare heads for $950 then have your machinist install the valves and springs to match the camshaft you choose. I recommend the 195 cc intake ports, 70 cc as cast chambers, straight plug, 2.02/1.600 valve job size for the street. These will give you 10.148 c.r. The 72 cc chambers would give you 9.939 c.r. This would be an awesome engine with plenty of power.
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post #9 of 17 (permalink) Old Jul 20th, 15, 08:27 PM Thread Starter
Re: Engine Choices

http://www.summitracing.com/oh/parts...75bi/overview/

This is the kit that I was looking at before I started this thread. I know my old pistons are domed and I like the light weight rotating assembly because of the quicker rev. and less stress. Is there anything I can do to the stock heads to make them better? I really want to keep the outside looking as stock as possible. Also if the assembly is balanced why have it re balanced before assembly, and what is up with two different rod lengths of 5.700" and 6.000"? Sorry if some of these questions sound stupid but I've never done a stroker engine before and I like to do as much of the work myself as possible.

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post #10 of 17 (permalink) Old Jul 21st, 15, 01:10 AM
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Re: Engine Choices

Quote:
Originally Posted by HUGGER Z View Post
http://www.summitracing.com/oh/parts...75bi/overview/

This is the kit that I was looking at before I started this thread. I know my old pistons are domed and I like the light weight rotating assembly because of the quicker rev. and less stress. Is there anything I can do to the stock heads to make them better? I really want to keep the outside looking as stock as possible. Also if the assembly is balanced why have it re balanced before assembly, and what is up with two different rod lengths of 5.700" and 6.000"? Sorry if some of these questions sound stupid but I've never done a stroker engine before and I like to do as much of the work myself as possible.
Lets go through this a question at a time:

Anything you can do to lighten reciprocating weight is going to reduce stress on parts and allow faster reving. A hollow forged piston is lighter than a stock cast one because they have to be reinforced with a steel skirt and pin boss strengthening clip to allow the cast part to live under the conditions it is exposed to. The forged piston is strong enough without the added steel because of how it is made. A longer than the stock length 5.7" inch rod also lightens the reciprocating weight by making the compression height (distance between the center of the pin and the top of the piston) less. Less material less weight. Additionally a 6.00" inch long rod improves the rod angle (the angle piston makes with the crank throw to put more effort into forcing the piston down than pushing against the side of the cylinder: which goes back to trigonometry and the ratio of the sine of the angle).

Yes you can rework your stock heads for a modest improvement. Read David Vizard's excellent book on the subject:

http://www.walmart.com/ip/15760642?w...935408&veh=sem

The greatest improvement if your budget would allow it would be to buy a set of AFR 195 cc heads and have the ends milled in a CNC machine to replicate the ID casting marks of a stock Chevy head and then paint it orange



As to balance how balanced does it need to be? I balance my personal engines to plus or minus two grams (bear in mind you have to have confidence in your machinists as balancing is as much art as science). SCAT or Eagle says plus or minus five grams is good enough, and the factory back when these cars were new coming out of Detroit balanced their motors to a half an ounce (14 grams plus or minus) and they survived for 100,000 miles.

So why is balance so critical? For two reasons. Longevity of parts and making power. The higher you can rev a motor the more power per unit of time it will make (RPMs stands for revolutions per minute). At higher RPMs the bearings and rod bolts are being beaten to death. add an out of balance vibration and things get worse in a hurry. For street driven cars 14 grams is good enough. Street strip I say you can get by with the 5 grams. For a class competitive drag car or road racer you want the 2 grams.


Additionally how it is balanced is also critical at higher RPM's. Internally balanced means most of the balancing weight is inside the crankcase. With an externally balanced motor they hang the extra weight on the snout and the end of the crank that can cause the crank to flex. The higher the RPM the likely you are to hit a harmonic with the crank flexing causing the crank to fail.

I am a degreed mechanical engineer and have been building motors for decades (used to any way but old age has finally caught up with me). I read on my own (not part of my engineering curriculum)everything I could find on the theory behind designing engines. To be truthful my degree is in Industrial engineering so I had to additionally study the procedures involved in making engines from raw materials (taking it from Bauxite or iron ore to a finished product). I paid for my early racing career by working in heavy industry (using the companies machine or tool and die shops after hours to work on some of my motors along side master machinists because they knew more about machine tools and their proper use than I did).

Because of this I think I know how a motor works, and had a lot of good luck in racing (there is more to racing than having the most powerful engine by the way). Hope I clarified some things for you.

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post #11 of 17 (permalink) Old Jul 21st, 15, 05:53 AM Thread Starter
Re: Engine Choices

Wow Dave, I think if I lived near you we would be spending a lot of time together. I own a large capacity machine shop specializing in hydraulics and love making anything with metal. I like the AFR head idea and I can do the milling at my shop. Any of the machine work that I can do on the block I would like to do myself but what we do and engine work are miles apart.
In the 90s I built a few 440 Chryslers and did the balancing myself just by weight matching the rods and pistons and it seemed to work but I have no clue how to balance the crank.
Do you think the stroker kit that I have listed is overkill?

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post #12 of 17 (permalink) Old Jul 21st, 15, 07:45 AM
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Re: Engine Choices

That is the kit I would use with a 4.00 bore 350 block. I would verify the block is a large journal two piece rear main seal block before I ordered any parts. The SBC went to the large journal in 1967 with the introduction of the 350. At the same time Chevy continued to produce the small journal 283 (307) and 327 up until 1968 when all small blocks went to the large journal and had bolt holes in the head for the use of a long water pump that wasn't introduced until 1969.

The picture for the kit shows BBC pistons, and the description states that the it can have a number of different parts in the box (two possible cranks, three possible piston tops and three vendors offering bearings and rings). I suspect that those pistons are flat tops with deep valve reliefs based upon the negative eleven dome size. This kit offers a chromemoly crank and chrome moly H-beam rods with ARP 2000 series rod bolts (ARP's BIGGEST and strongest cap screws). H-beam rods do not require as much clearancing of the block as the cap screws are recessed. You should be able to run a cam with a lift in the neighborhood of a half inch at the valves. Any higher you might have to go to a smaller base circle cam. But in either case you always measure the clearance between the rod and the cam (I use a nylon plastic tie strap of about 0.050" inch thickness to verify there is enough room as a go no go gauge).

As far as balancing at home you can buy a rod balance jig for your scale to determine weights and grind them to match the lightest weight.

http://www.summitracing.com/parts/pr...FY2RHwodGa8JVg

The crank has to be spun with bob weights. A bob weight is a steel mass bolted to the crank throw that is equal to the mass of the piston, piston pin, rings (and the oil on the rings) as well as the reciprocating mass of the rod). This is where the art of balancing enters the process. The bob weight and rod weight depends upon where you determine where the reciprocating weight begins on the rod (less than half the weight is counted and you have to choose a point based upon years of experience). The electronic balancing tool used to balance the crank can detect a difference of a tenth of a gram. But it is a judgment call to determine the actual bob weight mass.

I can accept the weight of a dime spread across the entire reciprocating mass in variance (a little over two grams) as I run four bolt blocks that have been line honed and the registers verified for a tight fit. I tell my machinist to balance to a half a gram, which informs him that I am fussy about balance. But I also know that the process will only yield a plus or minus two gram balance with the equipment that he uses. Before any one gets excited think of the variables; oil on the rod pin offset, or even over balancing an engine for higher RPM operation. Economically you just draw a line and accept that level unless you have unlimited funds that the pros do.

I also grind a knife edge on my counterweights if I buy a cheap crank which throws the weight way off from the what SCAT said it is, so It has to be rebalanced (preferably without heavy metal but that is a better choice than the flat edge of the counter weight creating excessive windage. But once again every choice you make affects something else. Reduce windage and control the oil in a wet sump pan with louvers and scrapers and you reduce the oil needed to lubricate the cam (which is splash lubricated). So I then have to spend over a grand to buy Isky Red Zone solid rollers to lubricate the cam and the tappets. Like I said how fast can you afford to go? Building a reliable high horse motor isn't cheap. Most don't even concern themselves with a the bottom end. Concentrating their entire budget on the Heads and the Cam, the two items that most profoundly effect power.

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post #13 of 17 (permalink) Old Jul 21st, 15, 07:56 AM
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Re: Engine Choices

For a street engine that will be revved around 6500 rpms, yes. That is why I suggested the cast iron crank and the Hypereutectic aluminum pistons. Unless you are building a 302 engine spinning up to 8000 rpms you don't need the light and forged pieces. But if it makes you feel better to have forged crank and pistons look at this kit http://www.summitracing.com/parts/sca-1-40610/overview/. The 383 engine is an engine that makes torque at low rpms. Sort of like a big block 454 it doesn't take high rpms to make the torque and horse power. You are also looking at spending money needlessly on AFR heads when Pro-Filers which are made In the USA are just as good. One thing to remember when using 6" rods is the piston compression height get shorter. This puts the piston pin into the oil ring groove. This means you have to use oil ring supports. It is up to the individual and what he wants. When I build my engine I want good forged parts and I want aluminum heads made in the USA but I don't want to throw money away. AFR, Brodix, Pro-Filers, Dart, ProMaxx, and Edelbrock all make good products. How much do you spend on a name? Like Dave said do you trust Scat or Eagle to balance your assembly or do you trust your machinist that is doing your work? Which one gets the specs closer to what you want/

Last edited by Cdminter55; Jul 21st, 15 at 08:12 AM.
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post #14 of 17 (permalink) Old Jul 21st, 15, 08:12 AM
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Re: Engine Choices

This is all great info however before any decision is made the OP needs to determine how he intends to use the car, his HP and Torque goals and RPM range.

Easy to build a High HP motor that runs WOT. Takes a little more thought to build a reliable, driveable and enjoyable street engine.

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post #15 of 17 (permalink) Old Jul 21st, 15, 08:55 PM
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Re: Engine Choices

Dave I always enjoy reading your posts on this, and similar, subjects

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