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Old 06-02-2011, 08:12 PM
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882 or 993? which is better

OK, I bought a block today just for the heck of it. It is a 39700010 so a good block, but it came with 882 heads on it. I am lookin for some 993 heads because my machine shop guy says thats the route I wanna go. I want to run 350-375 hp on pump gas and keep C/R at 9.5. Do I just keep the heads and forget about the 993's. I bought the motor for 100 bucks so I couldn't resist. If I wanted to sell the whole motor what's it worth? The motor isn't stuck by the way. I plan on building up a motor to move a 66 impala, so closer to 375 the better!!!

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Old 06-02-2011, 09:06 PM
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Would you be interested in a list of parts that would make 356 hp and 422 ft/lbs of torque with the 882 heads?
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Old 06-03-2011, 03:33 PM
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I guess not.
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Old 06-03-2011, 04:41 PM
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As far as the heads are concerned, neither. They are wheezy smoggers. They make nice doorstops or wheel chocks
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Old 06-03-2011, 09:10 PM
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Originally Posted by techinspector1
I guess not.
Heck w/him- I'D like to hear it, if you don't mind...
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Old 06-03-2011, 11:36 PM
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Quote:
Originally Posted by cobalt327
Heck w/him- I'D like to hear it, if you don't mind...
Sure Mark, glad to oblige....
This build is for the fellow who is absolutely cash-strapped and needs a motor for a heavy car or truck using the stock converter and stock rear gear and needs to run it on cat-pea pump gas. It assumes that the fellow has a standard bore 350 block that needs cut to +0.030" and a set of 882 heads. If the heads are stock 76cc, the static compression ratio is 9.0:1
Summit hyper pistons....
http://www.summitracing.com/parts/SUM-17350-30/
Stock crank, rods, pushrods, retainers, stamped rockers.
Crane 113502 Zcam flat tappet hydraulic cam kit (includes lifters)....
http://www.summitracing.com/parts/CRN-113502/
Installed 3 degrees retarded. Timing events @-3 (-7, 33, 43, -5)
Crane 99848-16 valve springs. Stock diameter, install at 1.700" with fresh seals.....
http://www.summitracing.com/parts/CRN-99848-16/
RPM intake...
http://www.summitracing.com/parts/EDL-7101/
650 Edelbrock AVS rebuilt...
http://www.summitracing.com/parts/EDL-1805/
1 5/8" long tube headers

RPM HP TQ
1500 104 365
2000 149 391
2500 187 392
3000 234 409
3500 281 422
4000 319 419
4500 347 405
5000 356 374
5500 314 299
Peak volumetric efficiency 86.5% @4000
Peak BMEP 179.1 @3500

Last edited by techinspector1; 06-03-2011 at 11:42 PM.
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Old 06-04-2011, 12:03 AM
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Thanks. That's bound to come in handy for someone. Especially when they see a detailed run-down of what parts are needed.
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Old 06-04-2011, 01:06 AM
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Dynosim 4.2
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Old 06-04-2011, 07:29 AM
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Quote:
Originally Posted by techinspector1
Dynosim 4.2
IIRC, don't you use a "correction factor" of some sort? I seem to recall that you reduced the advertised head flow of aftermarket heads a certain percentage to try to bring the published figures in line w/the real world. Do you also use something like that in the case of OEM heads?

AFA "garbage" goes, I see a LOT of numbers- AND engine combo's- on this board bandied about that I consider BS, so at least you're in good company.

Regardless of the actual output, I DO believe the 'recipe' presented above very likely represents an optimized combo for those type heads. So even if the numbers can be argued as being high- the combo itself is valid IMO.

Last edited by cobalt327; 06-04-2011 at 07:40 AM.
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Old 03-23-2015, 01:08 PM
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Quote:
Originally Posted by techinspector1 View Post
Sure Mark, glad to oblige....
This build is for the fellow who is absolutely cash-strapped and needs a motor for a heavy car or truck using the stock converter and stock rear gear and needs to run it on cat-pea pump gas. It assumes that the fellow has a standard bore 350 block that needs cut to +0.030" and a set of 882 heads. If the heads are stock 76cc, the static compression ratio is 9.0:1
Summit hyper pistons....
http://www.summitracing.com/parts/SUM-17350-30/
Stock crank, rods, pushrods, retainers, stamped rockers.
Crane 113502 Zcam flat tappet hydraulic cam kit (includes lifters)....
http://www.summitracing.com/parts/CRN-113502/
Installed 3 degrees retarded. Timing events @-3 (-7, 33, 43, -5)
Crane 99848-16 valve springs. Stock diameter, install at 1.700" with fresh seals.....
http://www.summitracing.com/parts/CRN-99848-16/
RPM intake...
http://www.summitracing.com/parts/EDL-7101/
650 Edelbrock AVS rebuilt...
http://www.summitracing.com/parts/EDL-1805/
1 5/8" long tube headers

RPM HP TQ
1500 104 365
2000 149 391
2500 187 392
3000 234 409
3500 281 422
4000 319 419
4500 347 405
5000 356 374
5500 314 299
Peak volumetric efficiency 86.5% @4000
Peak BMEP 179.1 @3500
Sorry to revive a dead thread BUT this is some very helpful info, IMO. True budget build. May give this a shot or use as a baseline when I pull the confused 350 out of my formula.
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Old 03-23-2015, 05:17 PM
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Quote:
Originally Posted by plumberponch View Post
OK, I bought a block today just for the heck of it. It is a 39700010 so a good block, but it came with 882 heads on it. I am lookin for some 993 heads because my machine shop guy says thats the route I wanna go. I want to run 350-375 hp on pump gas and keep C/R at 9.5. Do I just keep the heads and forget about the 993's. I bought the motor for 100 bucks so I couldn't resist. If I wanted to sell the whole motor what's it worth? The motor isn't stuck by the way. I plan on building up a motor to move a 66 impala, so closer to 375 the better!!!
I'd forget about 882 or 993 heads both are open chamber low compression heads with poor spark plug placement, read that slow burning and high fuel consumption for the power they give. They are intended to meet 1970s early 80s low emissions by emasculating the combustion process. To squeeze 375 horses out of them will require a lot of camshaft and gasoline.

Compression and cam run together you have to understand that relationship to pick the heads and pistons that complement the cam or conversely. But that's another conversation we'll get to.

Heads, specifically combustion chambers, underwent a belated revolution starting in 1996 with the L31 Vortec castings 10239906 or 12558062. Get on the web and shop for modern heads to see the pictures. These feature what is called a heart shaped chamber and they realign the intake ports. Simply bolting them to some old rust bucket is good for 30-50 horsepower depending on cam and compression. These heads use a 64 cc chamber which is 10 cc smaller than the 882 or 993 head. It moves the spark plug from outer Mongolia of the 882/993 into the valve position which centers it as much as is possible. This reduces the burn time from sweeping across 4 inches of bore to centering out 2 inches in all directions. Since 1996 all modern head chambers at GM (Vortec), Ford (GT40) and Chrysler (Magnum) and the aftermarket have followed this basic design. The root of these is in the work of Sir Harry Ricardo in England and Charles Fayette Taylor in the US of A.

Now the cam needs to control the compression, wanting 9.25 or whatever is not derived from your heart's desire but is the result of a backwards running equation that takes into effect the crankshaft stroke lost to the point of where the intake valve seats in crankshaft degrees. This is the Dynamic Compression Ratio (DCR) you want it between 8 and 9 to 1 depending on the combustion chamber shape and the material the head is made from. Old chamber cast iron more like 8 or even a little less, modern L31 type chamber in iron will take 8.5. Aluminum with modern chambers will go 8.5 to 9.0. Getting to this number is a backwards calculation of how much Static Compression Ratio (SCR) is needed to feed into the equations to get an effective DCR. Bunches of calculators are on line, so you don't have to enroll in the local JC majoring in Calculus to do this.

The SCR is a result of the swept volume plus all the volumes above the piston when it’s at TDC divided by all those volumes above the piston at TDC. This then drives on the deck clearance volume, the head gasket volume, the combustion chamber volume, and any volume of the piston this can be a positive adder if a dish or other divot in the piston or a negative adder if a dome. The DCR is always a stroke loss equation so it will always be lower than the SCR. The wilder the cam the greater amount of stroke is used up before the intake valve seats, thus the greater amount of inducted volume is blown back into the induction system, thus the more SCR compression is required to compensate in order to restore the power curve below the torque peak RPM. This is where the static compression ratio comes from. You also need to know the rod length for these equations, which unless your using an aftermarket rod for a 350 it will be 5.7 inches.

Piston crown design is also a big player. The flat top piston is the most efficient, it offers no obstruction the flame path as does a domed piston, it also offers the least amount of heat transferring surface to the cooling system and it permits the closest closing of the piston to the squish/quench step of the head opposite the spark plug. The round dish piston that GM loves to use is the worst possible design in regard to squish and quench. We like to close a flat piston surface to the head's step with as much surface area as possible. A round dish removes a major amount of this area thus reducing this vital function to the effectiveness of extracting power from the fuel being burnt and the suppression of late burn detonation or the initiation of preignition. To those ends you want the keep the squish/quench clearance not less than .035 inch for mechanical clearance reasons and not much more than .040 inch for functional reasons figure by .050 it’s just gone. The effect goes away when this distance becomes greater, so a round dish piston has too much of its surface too far away. So the measures of piston crown to deck and the head gasket become quite critical. Often to keep the compression ratio in a range that unleaded fuel will tolerate even when the squish/quench is maximized it becomes necessary to provide some dish in the piston. The way to accomplish this is with a D dish piston where the dish volume to adjust the compression is under the valve pocket while a totally flat portion is under all of the head's step.

To understand the importance of squish/quench let me prattle on some more.

Squish and quench are two functions of the tight closing clearance on the far side of the chamber that are separated in time. Squish comes first as the piston closes on TDC but spark has not yet happened, the tight closure blasts the mixture from the far side of the chamber into the valve pocket before the spark plug. This is one last super stir of the fuel globules and air which is blasted in front of the spark plug making it much easier to set on fire. It is also the major amount of mixture so it burns quickly reducing the need for huge amounts of spark advance which fosters detonation. The reduction in timing advance and of burn time lowers the time exposure to increasing pressure and temperature which if uncontrolled will force the end burn to explode before the flame front gets to it. Quench is also occurring once the burn has started by pulling heat out of the end products so it becomes less likely to initiate an independent burn before the flame front gets there. The collision between flame fronts is what melts or blasts holes into the piston and the detonation or preignition flame front is much more violent than the spark induced burn.

Modern thinking on cam design is to use less ramp and faster lift rates to higher lifts than the old muscle car cams. This preserves more useful stroke on the compression side such that super high compression ratios that today’s fuels cannot withstand become unnecessary at the same time the super low compression ratios of the early smog era are also unnecessary because the formation of NOx emissions is reduced a result of the shorter burn time and elimination of excessive spark timing advance. A win-win; today’s engine designs starting with these heart shaped chambers of the mid 1990s provide much more power with greater fuel economy and lower emissions than anything that preceded.

So go head shopping and stop thinking about obsolete designs before 1996.

Bogie

Last edited by oldbogie; 03-23-2015 at 05:24 PM.
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Old 03-24-2015, 08:36 AM
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Nice explanation. I can build an engine but do not regard myself as an engine guy, things like that I just never think of... Great common-sense stuff to read.
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Old 03-24-2015, 10:46 AM
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...and, one quick question: What do you think of the immediately-pre-good-era SBC "LT1" Camaro aluminum heads? Did they almost have it yet, or no?
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Old 03-25-2015, 01:21 AM
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. (this is an old thread, but still pertinent to many here)

. The early 1990's SBC EFI LT1 is a reverse cooling engine and the heads won't just bolt onto an earlier Gen. 1 SBC... to start with, the oil returns and coolant pathways are swapped in position...

. Fine heads to use on their original block... although the later iron LT1 heads being a newer design, actually flow better and make more power then the earlier aluminum ones... and the even newer LT4 aluminum heads flow better yet...

. The 1996 - 2002 Vortec heads are like EFI LT1-LT4 heads, but designed to bolt to Gen. 1 SBC blocks...

. The budget Summit Hypereutectic pistons spec'd above would have to be checked to see if they actually have the specified compression height of 1.560... there's only one review of them, and it's bad, as well... of course, the $95/set price is great...

http://www.summitracing.com/parts/SUM-17350-30
.
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Old 03-25-2015, 08:19 AM
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Quote:
Originally Posted by kso View Post
...and, one quick question: What do you think of the immediately-pre-good-era SBC "LT1" Camaro aluminum heads? Did they almost have it yet, or no?
The 1990's LT1 and LT4 heads don't fit because the coolant holes don't line up. These engines were a unique variation on the first gen small block they became known as the second generation small block because of the unique differences but yet maintained much of the original design. The engine was revised to reverse the cooling flow such that coolant enters the head first and returns to the radiator from the block. This caused a lot of redesign of coolant passages in the block and heads. When interchanged with a Gen I there are huge coolant passage mismatches that result in large leaks into the valley. The aluminum heads can be modified to fit Gen I blocks but it is extensive and costly. The mismatched passages are welded closed the gasket surface remilled and new holes drilled. Custom coolant returns have to be fabricated as there is no provision to flow coolant out of the head into a conventional coolant return that is part of the intake, so a standalone external system has to be built. Gen I intakes don't match the bolt pattern nor the port size and height. GM makes a carbed LT1/LT4 intake that is quite expensive. This intake also allows the use of a conventional distributor. The exhaust port height is also changed by .1 inch, doesn't seem like much till you try to get headers that when bolted to the head will also clear the components of the chassis.

There are many good heads out there from GM and certainly the aftermarket that fit without the difficulties of the LT1 and 4 heads. Certainly the L31 Vortec stands out in front when you think of modern heads but there are many options including the slightly earlier heads that bridge the period of the first generation smog engines and the later (96-up) L31 head. The L98 Corvette and Camaro head aluminum casting number 14101128 uses the earlier 90 degree center bolt of the 55 through 86 engines or 10088113 which uses the later 72 degree angle of the center intake bolts. This head is also available in iron as 14096217 and 14101083 either of these were finished with the older 90 degree center intake bolt angle or the 1986 to 96 pattern with 72 degree angle bolts. These are not quite as effective as the L31 head but are a vast improvement over the smog era heads they are all 58 cc chambers in aluminum and 64 cc chambers in iron. They are widely available as rebuilt at decent prices on EBay. An aftermarket head I particularly like is the Engine Quest EQ23 a very aggressive combustion chamber connected to decent flowing ports, this is accepted by IMCA as a stock replacement head, essentially you get an improved L31 chamber with more conventional ports. In aluminum an excellent domestic head is the Pro-Filer by Ray Franks. Decent import aluminum heads can be had from ProComp, NKB, Speedmaster, Assault, and FloTec at moderate prices. Of course if your budget allows there's the wicked stuff from Dart, World, AFR and such. While their upper end heads are great, I'd shy away from stock replacement heads unless I was rules bound by a racing association. While good heads these are beefed up versions of the first gen smog era heads which because of chamber shapes fall sort of the power seen from modern heads. However, these stock replacement heads really respond to porting and the extra beef certainly eliminates the discovery of water so common when grinding on GM castings.

Bogie
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