Aluminum,over the counter Pontiac 23' head,62cc,angle plug, cc intake port Over the counter Pontiac 15' head 55cc, angle plug, raised runner aluminum, "roll over" head Bowtie, aluminum, 55cc, angle plug raised runner, cc intake port Aluminum, 58cc, angle plug, raised "D" port exhaust, 1. Over the counter, Pontiac 15' head aluminum,cc ports, 61cc chambers, "roll over" head Bowtie, 45cc, angle plug, "low" port, cc intake port, aluminum, 18' race head NOTE: This casting has been used in many different versions of this aluminum 18' and 15' Bowtie race head.
Different chamber volumes, port volumes, port locations, valve sizes, etc. Check this casting carefully to determine which features it may have. I crate motor Bowtie, aluminum, 45cc chambers, 1st version, symmetrical ports, cc intake ports, splayed valves Bowtie, aluminum, 45cc chambers, 2nd version, symmetrical ports, cc intake ports, splayed valves II, L99, 4.
III, LS1, aluminum, 68cc II LT4, aluminum, reverse flow cooling, cc port, LS1 "GTZ", aluminum, 38cc, 2. Bowtie "SB2. II, "L99", cast iron II, "LT1", aluminum Vortec, truck Ideally you want the intake directly above the cylinder but this is not possible due to valves and spark plugs and cam assemblies. Many manufacturers take the intake through a 90 degree bend into the cylinder.
The straighter you can make the intake path the better it will be. Additionally the intake side of the head will benefit if you can create a Spiral flow into the cylinder as this gives much better fuel atomization. Careful work around the valve can help with this further. TorqueCars members have done a satisfactory DIY job on their heads but a specialist really has so much more to offer.
Really, as far as a DIY approach goes, do little more with the ports and manifolds than a smoothing up and polishing the intake manifold has the job of assisting with vaporizing the fuel and benefits from a pitted rough surface so please do not polish the intake manifold downstream of the fuel injectors marked f in fig1!
Polishing should not happen after the injector as the port can be reshaped but there must be a slightly rough finish to help the fuel mix better with the incoming air.
Air flows in a similar way to water, the faster the air moves the more gloopy and sticky it behaves. If you have ever hit the surface of water at speed you will realise that it is not soft and liquid! The aim in the head is to get as much air and fuel mixed as effectively as possible into the combustion chamber. The most important area within the engine, as far as air flow is concerned, is the valve seats and bigger power gains can be has here especially for engines with slightly higher lift valves with some careful blending below the valve seat insert to remove the steps and grooves.
Concentrate on a clean flow into the engine rather than just widening the inlet and exhaust ports. Bigger is not always better. Beware, not all engines benefit from the inlet ports being opened up to the size of the gasket. NASP engines rely on the vacuum created by the engine to suck in air, and widening the inlet port will actually slow up the flow of air, sacrificing low end power but it will generally allow more mixture to be introduced at high RPM.
The port sizes should be setup for the optimum desired characteristics of each engine. In a turbo or supercharged engine bigger is usually better as the air is being forced into the engine but the entire inlet and exhaust channel should match the dimensions of your new port sizes.
Putting the gasket over the ports will show how much can be taken off for a good airflow match but you will rarely want to go as wide as the gasket. Use some nail varnish to mark the area then remove the gasket and start cutting away with a grinding wheel in slow, long deliberate arc movements.
The angles on the valve seats is also of concern to the engine tuner. Generally speaking, the thinner the seat, the more unreliable the engine will be so we are back to the eternal compromise of power vs reliability. A progressive 3 or 5 angle step will greatly help the air intake around the valves. Because each engine type is different with some producing more heat than others, various cylinder configurations from an inline 4 to a W8 and a wide variety of 24v 20v 16v and 8v it is almost impossible to give a one for all guide to porting.
For best results we always recommend leaving head work to professionals who are able to measure the airflow through the head and help create the perfect head setup for you. Each type of engine is better suited to a specific valve seat shape just as your driver requirements will create a different range of properties that the head machinist has to work to.
Fitting larger valves will generally improve the airflow through the head of the engine into the combustion chambers and will help the engine cope with a much higher state of tune. Adding longer valve stems will also release a little more power too in many engines although you really need to avoid the possibility of a valve hitting the piston and you still need the valve to fully close!
Caution — if you mess up the airflow you can end up ruining the engine. It is possible to cause an imbalance of airflow to each cylinder and it is equally possible to ruin the bottom end power. It was used with the cam gear that had the small hole in the center with 16 splines in it.
It was connected to the distributor with a short drive shaft that was splined on both ends. GM had some problems with the early distributor due to both carbon tracking and moisture, so a new sealed distributor with a vacuum port was introduced on the iron-headed s and s in and used on all LT1s in The new distributor was located with a pilot shaft and driven by a pin, so both the cam and the gear were changed. The cam had a large, deep hole in the center for the pilot shaft and a longer dowel pin to drive the distributor.
The pilot shaft for the distributor extends through the hole in the cam gear and seats in the hole in the cam; the distributor is driven by the long dowel pin that sticks up through the cam gear. Look for a and possibly a The original cover had three holes, one for the crank, a small hole 0. The second front cover still had the small hole for the water pump shaft, but it had a much larger hole 2. The second cover was modified again in to accommodate the crank position sensor that was located in the lower corner of the cover on the passenger side.
This same cover was used for the few engines that were installed in , too. HEADS There were two heads used on the , one aluminum and one cast iron, along with one cast iron head for the That was impressive in , but the iron LT1 head that came out in was even better. All LT1 heads used small combustion chambers to get the higher compression ratios with flat top pistons; the s had a They were or castings.
The chambers are smaller, so these heads cannot be interchanged with any of the LT1 heads. Chart 2 on page 35 shows how they all fit together year by year, but there are a few more things every rebuilder should know in order to avoid some possible problems.
The original head gaskets on the LT1 were wider and had holes that held the pushrods in place for assembly, but the replacement gaskets look a lot like the ones used on a regular Make certain not to mix them up. Use the correct key for the year of the engine. When the crank position sensor was added in for OBD II, the cutback area on the key was shortened so it stuck out far enough about 0.
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