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Old 04-16-2008, 07:12 PM
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GM aluminum head specs

I just got a set of GM heads for my 1998 350 dish piston stock engine.Can someone tell me what they came on and what compression ratio I would have with them and what cc chamber they are?The part number is 10088113 and 6257.They are angle plug.

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Old 04-16-2008, 08:20 PM
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They are 58cc angle plug,Raised ''D'' port Exhaust,1.94''/1.5 values. year 88 up 350.


http://www.mortec.com/castnum.htm
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Old 04-16-2008, 08:35 PM
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Thanks a lot. But I would still like to know about what compression ratio they would give me.
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Old 04-16-2008, 09:32 PM
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Quote:
Originally Posted by speedydeedy
Thanks a lot. But I would still like to know about what compression ratio they would give me.
What's your current compression and combustion chamber cc?
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Old 04-16-2008, 09:54 PM
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Quote:
Originally Posted by speedydeedy
I just got a set of GM heads for my 1998 350 dish piston stock engine.Can someone tell me what they came on and what compression ratio I would have with them and what cc chamber they are?The part number is 10088113 and 6257.They are angle plug.
Whoa up partner, what 98 engine? If this came factory installed in a pick up it's a Vortec. If it came in a passenger vehicle of some sort it could be something from an average Gen I to an LT4 or even an LS1, so you gotta find out for sure where you're starting from as 113 heads won't work at all with some of this, or require extensive and expensive additional parts to work with others.

Bogie
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Old 04-17-2008, 10:55 AM
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I don't know my current compression ratio. This engine comes out of a bread truck and is not an LT1. I don't have the stock heads as the reason it was removed was it was run hot and cracked the heads. I think it had vortec heads but not sure. It has a factory roller cam. If all I have is a gen II short block that I know is not an LT1, why wouldn't these heads fit?I have a lot of experiance on gen I but none on gen II.
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Old 04-17-2008, 11:06 AM
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about 9.2 with a typical .040" gasket
about 9.8 with a .015" steel shim head gasket
assuming the heads are actually 58cc
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Old 04-17-2008, 11:50 AM
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Thanks fbird88. The factory specs say 58cc but who knows how close they build them. I think that should be a good streetable ratio.
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Old 04-17-2008, 12:16 PM
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Quote:
Originally Posted by speedydeedy
I don't know my current compression ratio. This engine comes out of a bread truck and is not an LT1. I don't have the stock heads as the reason it was removed was it was run hot and cracked the heads. I think it had vortec heads but not sure. It has a factory roller cam. If all I have is a gen II short block that I know is not an LT1, why wouldn't these heads fit?I have a lot of experiance on gen I but none on gen II.
If it came out of a truck it's by far an L31 Vortec. Look at the passenger side of the block for large numbers cast into it that say 880 or on the back pad drivers side will have the complete casting number which will be 10243880 for a Vortec.

You need to pull the bottom end apart, Vortecs that have been cooked enough to crack the heads often, also, spin a rod bearing or two, so you can't assume the bottom end is OK. Stick a higher pressure oil pump on it or if in good condition, replace the bypass spring in the existing pump with what is often referred to as the old 302 spring. In the quest for high gas mileage figures the factory reduced oil pressure to reduce power used to drive the pump and used "Energy Saving' oils, the problem this creates is that in the lower RPM ranges its easy to put enough instantaneous load on the crank either by sudden acceleration or by lugging, that the oil film fails and bearings are fried and or spun. A delivery truck would have seen a lot of that kind of service.

The heads you're proposing to use are the old L98, OK in their day still used on the ZZ crate engines to good effect, they are the predecessor of the Vortec and 1990s LT1 & 4 combustion chamber, just not quite as good and don't feature the outstanding ports of the latter heads, but plenty good enough for everyday use.

The heads are advertised as having 58 cc chambers against the original 64 cc Vortecs. However, there's not much, if any change, in compression as with aluminum heads you must use a thicker multi-layed head gasket which provides enough additional volume to pretty much even out the chamber size differences.

Bogie
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Old 04-17-2008, 01:52 PM
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Thanks bogie you are right about the numbers and it being a truck votec. As far as the bottom end,after it ran hot it still had good oil pressure. I will take your advice and check and change the oil pump or spring.So far I have $100.00 invested in this engine and that includes a new holley street dominator intake.I love HEMI engines but this is why I build a SBC. Nobody has ever given me a HEMI with aluminum heads and intake.From what I understand other than some beefier internals and camshaft this is a ZZ4?
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Old 04-17-2008, 01:56 PM
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oldbogie,Would this combo use standard SBC push rods and what head bolts ? Also how would I ask for an old 302 spring?
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Old 04-20-2008, 08:15 AM
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Just hoping for a reply from oldbogie or anyone that knows the answer.Thanks.
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Old 04-21-2008, 12:57 PM
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Quote:
Originally Posted by speedydeedy
Just hoping for a reply from oldbogie or anyone that knows the answer.Thanks.
Here's a typical SBC high pressure spring for 65-70 psi http://store.summitracing.com/partde...0&autoview=sku . For an SBC that get's leaned on a lot I prefer using the BBC oil pump, it delivers more volume, this increases oil pressure system wide but what I'm after is better low RPM pressure. (note that the BBC pump takes a special length intermediate shaft) To get that I live with more upper range by-pass. Which again following a different drummer as everyone else will talk about lost power used to run the pump and excessive heating of the oil. I first worry about failed bearings 'cause you still have to be running when the checkered flag falls. So upping the bottom RPM pressure helps protect the bearing from high power loads being summoned before the oil pressure and flow is at a point to handle these forces. For a mild street engine, you don't need to sweat this so much as a simple by-pass spring improvement will cover your butt.

In all cases I use a steel coupling to connect the oil pump to the intermediate shaft, the factory uses a plastic coupling, plastic is great for tooth brushes, not what I want for connecting hot, force loaded shafts. See the Moroso part at http://store.summitracing.com/partde...0&autoview=sku

Aluminum heads must have an aluminum compatible gasket here is an example of a GM gasket for a 4 inch bore engine. http://store.summitracing.com/partde...6&autoview=sku This was used on the L98 and is currently used on the ZZ series crate engine. By their nature the gaskets used for aluminum heads tend to be thicker than those for cast iron, the gasket needing the ability to tolerate the greater expansion/contraction movements of aluminum and still hold a seal and not carve up the aluminum (called Brinelling) in the process. There are other choices by other gasket makers, just be sure that it says its compatible with aluminum somewhere in the description. You also want to keep the fire ring diameter as close to your engine's bore size as possible. Try not to use a 4.2 inch gasket on a 4 inch bore if you can help it.

Head gaskets used with cast iron tend to be thinner, therefore, when used with a slightly larger combustion chamber like the 64 cc Vortec, the compression ratio is about the same as a smaller chambered aluminum head such as the 58 cc heads you have because of the thicker gasket. However, a heavy duty truck engine such as you're starting from may have had a thick
gasket from the factory to knock the compression ratio down on an engine expected to work hard and hot all the time so as to avoid detonation issues.

Given this knowledge there is a temptation to mill these heads to gain more compression, but don't. The 113 doesn't care to have a thinner deck, so if milling is required to level it keep it to the minimum required to achieve a flat surface.

Compression gains need to come from piston shape. The Vortec has GMs crummy circular dish piston any way so if you can see your way to a new set of pistons, some KB "D" dish pistons can be used to gain overall compression and improve the combustion chambers effectiveness in the process.

Compression ratio is the sum of all volumes (cylinder, combustion chamber, piston to deck clearance, gasket, and piston shape) divided by the sum of the volumes without the cylinder's. A 4 inch bore with a 3.48 inch stroke is 717.2 ccs. Your combustion chamber volume is 58 ccs, the gasket at .053 thick and 4 inches in dia would be 10cc, the piston to deck clearance is typically .025 inch which would be about 5 cc. With a piston dish volume of 18cc you'd have 808 ccs total divided by 80ccs above the piston which makes a static compression ratio of 10.1 to 1. This is OK for an aluminum headed engine running street mid range to premium fuel.

The factory runs these engines at 200 degrees or more, this is too hot given several other factors, the edge your left to play with is pretty thin. First, thin wall cast iron is very sensitive to cracking to start with. This has been an on running issue with GM heads since the mid 1970s when they began to apply this casting technique. Given these engines are close to the edge when new, the lack of in service maintenance and hard working conditions will take these babies over the line pretty quickly when they get some miles under their belt and the cooling system starts to deteriorate. You can drop the operating temp with a 180 degree thermostat and not foul the programming in the EFI computer, this buys another 20 degrees of working space with temps. This is still a good idea even going to a carb.

The other edgy thing with these engines is lubrication, which I've touched on. Oil pressures were lowered and thinner oils employed to lower power losses from parasitic drive of the oil pump and lower viscosity losses in the bearings specifically to improve corporate average fuel consumption averages for which they have to pay a fine if they drop below a certain level. So the games the factories are playing with the Federal government's tests pose significant in service risks to the end user. This is a game you can pretty much get away with as the end user if you keep synthetic oil in the crankcase and stay on top of the condition of the cooling system and don't work the engine too hard. It's a game you'll lose if you don't do these things.

Like I said you need to still be running when the checkered flag falls is my basic criteria for street or competition engines. So I run 'em cooler with more oil pressure, and thicker oil whether synthetic or mineral. There are several ways to get there, you can add oil coolers to the transmission and engine which not only reduce their operating temps but take BTU load off the engine's cooling system giving it more working space before it exceeds the thermostat's ability to manage the situation. Oil pressure in the upper RPM ranges is usually not a problem, even the SBC can get to 50-60 psi up there. The problem is keeping sufficient oil going thru the bearings at lower RPMs with high loads. Oil not only is there to keep moving parts separated, but is there to cool them. So you really want to start pushing a lot of oil thru the engine pretty early when the engine is used for hauling a load or in competition. For a 350 moving a 2300 pound roadster this isn't much of a problem, for a 350 moving a 5000 pound pickup towing a 4000 pound trailer or a bread truck making its rounds this is a whole nether matter where none of it's very good for the motor. So I gyrate toward high volume oil pumps, these have bigger gears that move more oil with each bite, My pump of choice is the BBC for use in the SBC as you get 12 pulses per revolution instead of 7 for a smoother delivery rate and being bigger it delivers a greater quantity. Since only so much oil can get out of the bearings, the greater quantity being pumped in at lower RPMs results in more bottom end pressure to carry all that heat off the bottom of the pistons and out of the bearings. The down side is you've got to blow off the excess pressure at higher RPMs. But for a slower turning hard working engine this is a better solution than a SBC pump with a high pressure spring as this tends not to alter lower RPM pressure but will make more pressure available in the higher RPM regions.

For oil viscosity, I don't consider a multi weight below a 15W as suitable unless extremely cold weather dictates such thin oil. Again in modern stock engines where the factory recommendation is more concerned with CAFE standards, running these so called energy saving oils is stepping up to the edge of the abyss. Besides how loaded your vehicle is, certainly where you live has an effect, where the topography is mild you can get away with something closer to factory specs. Where you get into mountains, especially when combined with hot weather, the specs aren't good enough.

You can get away with a thinner synthetic oil, so if you've just gotta buy in to Energy Saving oils, when going under 15W always go synthetic. At 15W and above I make that optional, though synthetic is still the safer choice.

So you've got to spend some time thinking about all this, since you can go a bunch of different directions at this point.

Bogie
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Old 04-22-2008, 01:11 AM
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For higher pressure with a standard SBC oil pump, go down to the Chevy place and ask for part number 3848911. That's the one used in the old 302cid Z-28's and some other factory hi-po small-blocks. Costs ~$4. Be sure it's not installed in the pump if you decide to weld the pickup to the pump. The heat might ruin it.

You need to use washers under the head bolts with aluminum heads, and you might have to use bolts that are a little bit longer to allow for the thickness of the washers.

Last edited by jimfulco; 04-22-2008 at 01:32 AM.
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