ENGINE BUILDING/ PERFORMANCE RAMBLINGS ( continued from page 1 )
One way to improve performance is to reduce reciprocating weight, primarily the pistons. This contributes to the longevity of a high winder. Pistons can be lightened with a little judicious removal of material under the head and around the pin boss. Again, the particular application must be taken into account because any removal of material can weaken the part for continued use. This step should only be done on forged pistons as cast pistons aren't structurally strong enough ( most have a steel strut inside the pin boss area to help keep hold them rigid where the piston is measured for size ). Drag/ pull motors are the best candidates, while circle track and any other extended hard use must be a little heavier because of the repeated stress. Drag motors can have a head thickness down to about .120 and survive. Street motors generally don't need it because of the typical rpm's they operate. Also, detonation can take it's toll. Lightening pistons on an inline will not upset the balance of anything because of the way inlines are balanced.
Rings are a definite factor in performance. Ring tension should be kept to a minimum for performance use. Ring choice is also critical. For drag/ pull use, a two ring setup ( top and oil ring )with an .043 or pressure backed top ring and gas ported piston is about the ultimate. In limited class racing where you have to run three rings, you can back cut the second ring to relieve tension. This is done by putting the ring in a fixture on a lathe and removing material from the i.d. ( this relieves the radial tension making the ring little more than a spacer along for the ride ). Also, on this setup a pressure backed ( dykes ) top ring is used with a spacer in the top groove ( stock NHRA rules state you must run a stock piston, so you are stuck with the stock ring configuration, but not limited to the use of stock rings ). For street use a 1/16 or 5/64 top and second ring should be used, preferably Moly. Chrome should be avoided since they seem to be nothing but trouble. Given the choice, I would go with a plain iron ring over chrome. Oil rings should be the 3 piece style ( Sealed Power/ Speed Pro SS50U style ) in 1/8" for performance or 3/16" for street. Again, ring tension can be reduced in a performance application by removing the plastic ends on the expander that keep the ends from overlapping and squeezing ( gently ) the expanded segments of the oil ring until an end gap of about .150 is achieved. When the lower end is assembled with the low tension rings ( minus the valvetrain ) you can get the whole works to turn with about 15 pounds of torque or less ( less torque to turn means more torque to the back wheels ), meaning you can turn it with just and end wrench and no breakover bar. Try that with a stock set of rings! For street use, gapless rings are not generally recommended, because a little blowby actually helps in oil control. The biggest problem using the .043 or the pressure backed ring is the finish required when honing. VERY few machinists possess the talent to properly finish the cylinders for the best performance. It requires a Sunnen CK-10 and a LOT of know-how. The cylinder walls look almost burnished, but when you get them in the light there is a very fine hone pattern. And for a final tip on rings and cylinder finish, do not use motor oil on the rings when assembling. Use Type F tranny fluid on the rings and cylinder walls. In fact use Type F for a final cleaning of the cylinder walls. Think they're clean when you get done using soap and water or solvent? Try some Type F on a paper towel and clean the cylinders with it. It's quite an eye opener! Using tranny fluid generally prevents any ring break in problems. They usually seal instantly. One last bit of advice on pistons and rings is don't run the clearance to tight. The clearance is built into the piston but running an extra .001 cleanance ( .031 vs .030 for example ) makes quite a bit of difference in how free they run especially when brand new.
You should check to make sure the oil holes are not partially covered by the main bearing shell. Machining practices in high production leave a little to be desired. If the holes are a little misaligned it can be corrected with a die grinder. The oil galleries can be enlarged a little in some cases. This would require a little judgement, as in some places there isn't a lot of wall thickness where the galleries are. Oil passages can be restricted in some cases to increase flow to other parts. The cam bearings are about the only place on a flathead that can be restricted as they don't have oil galleries for hydraulic lifters. This can be accomplished at home using set screws with an .060 hole drilled thru and tapping the oil galery past the main passage and installing the screws tightly. The oil pump can be blueprinted by tightening up the clearances between the pump body and the cover by a little flat sanding. Stock pressure is usually more than enough for most applications. Screaming small block Chevies get away with about 30/35 lbs @ 9000 RPM. Remember it takes power from the engine to turn the oil pump. Oil control in the pan is very beneficial in gaining power. There can be a lot of power in just an oil pan. you want as deep a sump as you can get away with. Then run the regular amount of oil in it to keep it away from the rotating parts ( windage ). DO NOT run a windage tray. This accomplishes the opposite effect. It's like moving the bottom of the pan up next to the crank. Oil lays on it acting like a brake when the crank runs through it. A screen type device may be alright but do not run the solid type tray used in the 60's and 70'. The idea back when was to keep the crank from whipping up oil from the pan into the crank. The main point in oil control is to keep it away from the rotating parts. A scraper can be fabricated and installed on the passenger side oil pan rail ( under the gasket ) to remove oil from the moving parts and keep it from being slung back up into the motor. It is made out of light gauge sheet metal and made to fit closely to the crank and rods without touching. The only drawback to this could be starving of the cam and lifters because they only rely on splash/ gravity for lubrication. A big kickout on the passenger side of the pan might also prove beneficial as the starter is on the driver side out of the way. This would allow the oil to be slung into the lower right side of the pan preventing splashback. It may sound crazy, but I have seen 15 hp in an oil pan alone compared to regular type pan with a deep sump. Oil itself can provide performance gains. Heavy weight is actually bad. It resists movement ( I don't know if you could exactly call it friction since it is oil ). Several pulls on the dyno showed gains in power without doing anything else. The engine was left to cool and the process was repeated and the same thing happened. As the oil heated up it made more power. All sorts of devices were tried from a magnetic stick on pan heater to spray on insulating foam to try to maintain heat in the pan. The oil was replaced with Mobil 1 synthetic and the result was the same power regardless of temperature change. There is also an argument of pressure vs. flow. If you set up the bearing clearance really tight the engine might have tremendous oil pressure but no flow past the rod bearings resulting in failure. The oil at the source of friction needs to be constantly replaced or it burns up ( think flow ). Conversely, one controversial subject seems to be grooving and/or cross drilling the main journals. This never really showed any benefit, and in some cases, seemed to be detrimental. Our theory was that there is a pressure buildup at the main before the oil hole to the rod journal passes over it causing a kind of pulse effect. When the main journal is grooved this is done away with and constant flow is maintained but there doesn't seem to be enough pressure to assure a good constant flow. The best scenario would be if the oil holes in the journals which must feed two rod journals ( #2 and #3 on an old inline ) were 180 degrees apart, but unfortunately, they aren't. I actually heard one guy saying the oil holes were strategically placed for optimum benefit. In reality they are in the only place they can be ( there's only so much space to drill a hole from the main journal through the counterweight to the rod journal ). Grooving the rod journals does nothing to aid oiling the bearing. If anything, it reduces the bearing contact area.
Compression and breathing are at direct odds in a flathead. The transfer slot ( the area between the valves and cylinder ) is the main problem. In the old days it was common practice to mill the head a considerable amount to gain compression. This reduces the height of the transfer slot, hindering the engines ability to breathe. So with a stock head, raising the compression is a double edged sword. It all boils down to volumetric efficiency. I would roughly guess that a typical flathead is somewhere in the 60% range, since most mild ohv motors are in the 75%-80% range. At least one of the old builders of flathead Ford v-8's is thinking a little different now. They have raised the roof of the chamber above and behind the intake valve and blended the raised portion of the roof out into the cylinder ( kind of like a relieving the block, but in reverse, and only concerning the intake ). It also has a higher roof in the area over the cylinder and requires a piston with a taller dome. They claim a 30% increase in flow. It was thought for a long time that the area behind the intake valve was a dead area, but now, with flow benches more common, they are finding out different. ( more later )
Regards,
Del
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