Dane

I've thought about this quite a bit myself. Just by looking at the inside of an SU...I think the airflow is too turbulent...improvements in laminar flow might be just as good as simply getting a bigger SU. For example, even when the air piston is at full lift, it still protrudes into the bore, so that air passing through the top of the bore smacks into the air piston and has to make a sharp turn to go around it. Grinding down the edges of the air piston so that it makes a smooth transition with the roof of the bore when at full lift would probably help, just so long as the portion of the air piston that goes directly over the bridge still makes full contact to maintain decent vacuum. The bridge itself could probably be improved. It forms a fairly steep angle with the floor of the bore. If metal could be added in front of and behind the bore, then smoothed out to reduce the angle formed between the bridge and the floor of the bore, it might smooth out the flow even more. You could also grind down the throttle shafts to reduce the obstruction it causes as well as making a smoother transition between the throttle shaft and butterfly valve. Then theres air horn design and the availability of different air filters. A high flowing CAI wouldn't hurt...but would need to be fabricated somehow.

Well...since the increased "average" rocker ratio doesn't just increase the peak valve lift...but raises the entire lift curve...you get more valve lift throughout the entire rotation of the cam. It makes me wonder what kind of increase in engine breathing ability this correlates to? This is purely speculation on my part, but I imagine it would almost be like running a stage higher cam profile altogether.

Thanks for the replies guys. The more I thought about...the more I realized how time consuming it would be to do this kind of thing anyways...not to mention the potential problems with wheel balance. I think I'll just look around for something cheap and light...those 6 spoke ZX wheels sound nice.

Would it be practical to use another method to restore timing chain tension after a head shave aside from shimming the cam towers? In the How to Modify book, on page 81, there's a picture of a timing chain tensioner with bolt holes that have been slotted. That would pick up a little slack. Then there is this: http://www.thezstore.com/page/TZS/PROD/PRC16/10-5452 http://www.thezstore.com/page/TZS/PROD/PRC16/10-5470 The twin idler gear kit is pretty expensive...but if you used that or the adjustable tensioner it could probably make up the tension lost from reduced distance between the cam and crank. Cam timing could be corrected with an adjustable cam gear...or if it isn't shifted too much, you could choose between the three timing settings on the stock cam gear. The benefit to this is that you could do the P79/P90 head shave without shimming the cam towers, using N42/N47 valves, and shimming the valve springs. Is there any chance this would work or am I way off base?

heavy85, Awesome...you're speaking my language. Yes...I understand that the pump isn't positive displacement...it would probably be appropriate to model it with a map as a function of pressure and flow (kind of like a turbo compressor map). I know what you mean by Power = Pressure * Flow, with the pressure actually being the pressure difference between the outlet and inlets of the pump. We're on the same page so far. Here's an equation for fluid flow through a pipe that I referenced from a college physics textbook: Poiseuille's Law: Change in Volume/Change in Time = (pi/(8*Viscosity))*(Change in Pressure/Change in Length)*(Radius^4) Plugging that into the "Power = Pressure * Flow" equation: Power = (Change in Pressure)*(Change in Volume/Change in Time) Power = (pi/(8*Viscosity))*(Change in Pressure^2/Change in Length)*(Radius^4) But with that in mind...I don't see how you can come to the conclusion that reducing the pressure difference doesn't reduce the power required. I mean...plug in a smaller number for "Change in Pressure" on the right side of the equation, and you get a smaller number for "Power" on the left side of the equation. As far as the electric pumps burning up with too light of a load...would I be correct to assume that these types of pumps are designed to work against a load? Can we be sure that this applies to an L6 water pump as well? The only way I can think of that reducing pressure would effect the operation of the water pump is that if it took the impeller out of its operating efficiency range (kind of like a turbo compressor out of its efficiency range)...so that the impeller generated more heat and moved less water. I just can't see how reducing the flow restriction through the cooling system...therefore reducing the pressure difference for that flow...wouldn't decrease the power required to force that water through the system.

How about underdrive water pump pulleys? I swear I've seen a photo of an L4 engine with a larger than stock water pump pulley. Any kind of parts interchangability with other cars or anything aftermarket? (I know that some aftermarket crank dampers have a smaller pulley diameter...I'm thinking specifically about the water pump pulley.)

If I'm not mistaken, the 280Z electronic distributor still used mechanical and vacuum advance...so to do any sort of tuning of the ignition timing curve would require adjustments in centrifugal weights, spring rates, etc. If you kept that distributor that is. If you could somehow use this Unichip to delay the spark response from the transistor unit...you could advance the distributor mechanically and then retard timing with the unichip to get the correct timing curve. Of course, if it didn't retard timing you would be too advanced. Please take what I just said with a grain of salt...as I've just been thinking about that while reading your post.

Tony, I have read about the LD water pump and the larger impeller...that is very interesting. I'm kind of following the school of thought of reducing the pressure drop across the cooling system required for a given flow...as opposed to increasing total water pump output. I wasn't aware that electric water pumps used variable speed control. I was under the assumption that they worked similar to electric radiator fans with a cut-off temperature when they just turn on or off. Of course that works for a cooling fan...it can have a low duty cycle since it only kicks in when airflow through the radiator isn't sufficient for cooling (like idling at a stoplight). But it wouldn't make sense for the water pump to just shut down altogether...because then you would have these up and down spikes in engine temperature as the coolant in the block goes from stationary to moving to stationary again. Whatever...I'm just thinking aloud. Anyways, what would be used to control the water pump speed...a temperature based variable resistor or something like that?

Lately I've been wondering how much the pumping efficiency of the cooling system could be improved for the sake of reducing parasitic drag. I know that many engine modifications are made to improve the pumping efficiency of the intake and exhaust system...but considering that water has such a greater density and viscosity than air, I think it would be a good area to look into. Some little things I thought of: -Knife edge the ends of all pipes where cooling hoses attach to maintain laminar flow at pipe/hose junction. -Smooth casting bumps within water pump housing and on impeller to improve laminar flow. (I know casting bumps within water jacket increase surface area and turbulence for better cooling) -Install a higher flowing thermostat or somehow modify thermostat to increase flow. -Replace any T-shaped pipe bends with smoother radiused bends. -Install a higher flowing radiator. I also had another more radical idea that I got from looking at pictures of the OS Giken DOHC head in the How to Modify book. It has sort of a coolant plenum on the exhaust side with coolant runners going over each cylinder...with the thermostat on the end of the plenum. Maybe holes could be drilled and tapped on the spark plug side of the head (in the interest of available space) for barbed fittings...which you could then run to a similar coolant plenum via short heater hoses and fab up a flange for a thermostat housing and an external bypass line. This could help cylinder to cylinder temps in the head...but I'm not sure what effects it would have on pumping efficiency. BTW...the reason I like the idea of using barbed fittings and short heater hoses to the coolant plenum is that the system could be removed and plugged if necessary, and it would allow more tolerance in alignment between the holes drilled in the head and the holes drilled in the plenum (hoses are flexible). The shortest possible hoses would be used to minimize flexing/bending in the hoses due to the weight of the plenum. Anybody ever seen any gains from improved pumping efficiency or using a head cooling set-up similar to the OS Giken head?

Yeah...it might cost me more than $100. I still need to buy the dimple dies, the scales for static balancing, and possibly the labor charges for dynamic balancing. I've been looking around for used alloy wheels (mostly on the net)...cheapest I've seen that I liked where in the high 200's/low 300's. Definitely not a bad price. It seems like a lot of the wheels out there don't offer that great of a weight reduction over my current wheels though (35 lb wheel and tire combo stock). If I were to simply lighten my current set-up...I would without a doubt reduce inertia since I would be just removing material...as opposed to a completely different wheel with a completely different weight distribution from center to rim...which might reduce inertia but might not depending on total weight and weight distriubution.

Here are some ideas I came up with just playing with it with paint: Sorry it came out small...I'll try to fix that...but you get the idea. The black areas are the stock holes that would be enlarged (most likely with a grinder), the red areas are holes that would be drilled and then flared with the dimple die, and the blue areas are holes on little flat spots between the lugnut holes. One of my concerns is that the blue and red holes don't line up consistently (9 red vs 4 blue), so there might be some thin spots between them. It might be good to eliminate the blue holes all together...especially since they don't contribute to the inertia much with their short radius. As far as wheel balance is concerned...I could take careful measurements and scribe out the boundary marks where I can't grind any further. Then I could take the static balance by placing several scales under the tires along the edge and grinding to adjust the balast until I get consistent readings between the scales for all rotational positions (scale set-up consistency would be key). Then...if any tire shop will be willing to touch this monstrosity due to liability concerns...I could have them dynamically balance it. I could also paint it...you know...put a little lipstick on that pig after the liposuction treatment. Any thoughts?

This is the inertially challenged (not to mention aesthetically challenged) abomination I have been referring to:

Ok...I understand...I'll try to get some pictures as soon as I can.

I'm talking about the stock steel rims on a '71 240Z. I'm not sure if these changed between Z's of different years.

Do you think it would be possible to lighten a stock wheel without sacrificing too much strength? The mod I had in mind would be to drill holes and then use a dimple die to flute the holes to maintain strength. Own of my concerns is that I've seen this technique used on flat pieces of sheet metal...but not on curved pieces. Maybe if the holes were kept small to minimize curvature you could still get a decent flare in the surface. The oval holes in the stock wheels aren't fluted at all and they're obviously strong enough...its just that since more material is being removed than the design originally intended...it would be good to do whatever was possible to maintain strength. This is obviously a very "budget conscious" idea...and simply buying lighter wheels would be the standard way to go. I just figured that maybe this wouldn't get tossed in the trash with all the other "bad decisions made because of budget constraints". Hence...I'm asking for opinions first. Maybe I could take two identical wheels...perform the mod to one of them...and then have the wheels "crush tested" somewhere?