Quote:
Originally Posted by chevy350_Camd
Would Camel Hump Heads 62 cc 2.02 beat vortecs ?
These heads came off a 327 there cn is 3782461
If these r good how much hp per head and wat would be the compression ratio
Im trying to find out if these would be good heads for a 350 buildup
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The answer would be no, the L31 Vortecs will produce about 30 to 40 more horsepower and torque pounds out of the box. Lot of people give credence to the better porting of the Vortec which it has, the shape is different and the intake is raise about .1 inch which does a lot to improve flow into the bowl you can't duplicate this in any camel hump without getting wet. But the big advantage is in the chamber shape which while subtly different compared to camels is extremely significant in power production. This just can't be duplicated in older heads. The improved port position and shape combined with the elements of the combustion chamber shapes completely obsolete older heads regardless of valve diameter. Plus, the camels do not have hardened valve seats which are not compatible with today’s un-leaded fuels, the seat and valves will pound in pretty fast especially if the engine is used hard. As well as the camels don’t have the holes to mount modern accessories; depending upon accessory mount selection they can limit the engine to the short water pump which has a greater amount of difference in coolant delivery to the block’s left to right sides than does the better balanced flow of the tall pump. The short pump always runs the driver’s side of the engine hotter than the passenger side.
However, the L31 head does require a lot of modification when running an aggressive cam. It is lift limited by the valve guides which need to be trimmed for valve lifts beyond .45 inch. This is no big deal but is an added expense. The OEM valve springs were made to operate with the truck cam so they are not strong enough for a performance cam let alone a competition cam. The raised intake port requires caution when enlarging the spring pocket so the pocket doesn't break into the port nor weaken that area to where although not penetrating the port will result in a fatigue failure that cracks into the port at a later date. So large diameter springs are risking the casting. The answer here is to use Beehive springs, the big reason for old fashion high pressure springs was to control the harmonic response of the spring itself that resulted in valve float. The modern approach is to use a variable spaced wire wind that combines with reducing the wind diameter at the top as well as often using an ovate shaped wire rather than round wire. If you will, it’s modern rocket science versus old time brute force to get to the needed performance. Hardly anybody in professional racing uses two and three individual springs anymore and haven’t for many years. The L31 Vortec is also designed for self aligning rockers so it does not have cast in push rod guides. When using standard un-guided rockers it becomes necessary to modify the rocker stud bosses to accept screw in studs and guide plates, something usually done for a performance modification anyway. The older heads also use a larger sparkplug which is a real pain with headers. These heads also raised the rocker cover rail so oil leaks out of the heads are a thing of the past. The L31's do not have an exhaust crossover, therefore, has no means of heating the intake manifold if that is desired and if used on the street where EGR is required, this must be externally plumbed from the exhaust manifold/header tube. All of this adds enough cost to the basic L31 to make looking at other ready to race GMPP Vortec or Fastburn heads, or shopping the aftermarket if the engine is going to be much different from OEM production use. There are many great aftermarket heads out there that are comparable. One needs to be careful with used aftermarket heads as the L31 Vortec totally changed combustion chamber design which was quickly incorporated into the aftermarket in the last part of the 1990's. So earlier designs though less expensive are also less powerful. Look at pictures of the L31 Vortec combustion chamber very carefully, you want to duplicate this or come very close in any aftermarket head. The major features you're looking for are the dual quench (something the camels also have) but the L31’s include a relief between the intake and the sparkplug which is actually there to remix the separated fuel and air streams as they enter the combustion chamber, the spark is plug moved as inboard to the center of the cylinder as possible and positioned by or at least aimed at the exhaust valve, a shallow combustion chamber depth with the plug being close to the roof, and beak that projects between the intake and exhaust valves.
Now under the head you want tight clearance between the piston and head where the squish/quench chamber is formed. For a street engine; this needs to be .040 to .060 inch the lesser amount being the better for combustion. Compression is very cam timing dependant, these new heads like a fairly short cam with a fast lift rate using high lifts compared to the old muscle car cams that have a lot of total duration with not a lot of lift where much of the duration is used in long ramps. In the end the Dynamic Compression Ratio (DCR) which is driven by the closing point of the intake valve will drive the Static (measured by volumes) Compression Ratio (SCR). The Vortec chamber will tolerate more compression ratio against fuel octane than will the old camel hump which is a big advantage when today's pump fuels are pretty much limited to less than 95 octanes. This advantage will easily allow the L31 Vortec type head in cast iron run at 9.5 static against a mild cam where the camel hump will not tolerate that combination. If you go to an aluminum head you can push that static another point higher and will want to do so as the added thermal efficiency of high compression is needed to overcome the faster heat transfer rate of aluminum over cast iron in order to gain the power potential in aluminum heads. The piston choice will need to dial in the compression ratio while maintaining proper squish/quench. Depending on chamber volume and whether the block is zero decked or not the piston crown will vary from a flat top to a D or even stepped dish. The OEM piston and simple OEM style replacements use a circular dish. This has the effect of increasing the clearance between piston and the squish/quench deck of the head which reduces this function. This makes the engine much more detonation and preignition prone. Think of squish/quench as mechanical octane, its effects are of pushing the mixture to the sparkplug side of the chamber which speeds the burn rate at the start of ignition this is squish; then as the flame front progresses across the chamber becoming hotter and increasing pressure as it goes, the same close association of piston to head now sinks out the excess heat which delays the point where the mixture will explode ahead of the flame front causing detonation this is the quench function. These things can make the fuel behave as if it has 5 or more higher octanes than its pump rating.
All of these design features come together to support the high power outputs and efficiencies of modern engines. The L98, L31, LT1 and LT4 were all huge improvements on the basic Gen I and related LT versions of the Gen II SBC but they could only point the way to the need for an entirely new GEN III the LS series to really allow complete integration of these new ideas that were add-ons to the GEN I and II engines. If you've been up against a stock GEN III motor you already know that these engines will have the hottest of the camel hump engines for breakfast. It is in the Rocket Science so the more of this you can cram into an old GEN I the better it gets so the L31 head and its many clones are a huge step in that direction.
Bogie
01-09-2008, 06:03 PM
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