I'm pretty familiar with Toyota's "A" heads and the port opening into the head versus the valves diameter is significantly different between this "F" head and the "better performing", aka smallport, "G" head. What my goal here was to maximize volume while minimizing velocity loss. What we are after is the correct mixture between volume and velocity - maximizing cylinder filling. In this case the losses are small, and only encompass the lowest lift points, while the gains in the remainder of the lift points is substantial. What would one do to improve the very low lift flow of that port - or is that just part of the compromise? Does it even matter?ĭoes it matter - it can. What to be wary of - Port flow(volume) that doesn't seem to taper off as lifts go up. This is because the valve size hasn't changed - but the port has - the port is more efficient. In that case there is little or no improvement, until lifts go up. If you look back the June 21st 2016 post above. But you can kind of get that - bigger holes, flow more. is O/S valves do improve filling at most lift points over stock valves. The immediate above example doesn't make it easier because it is like comparing apples, to oranges - as the client's engine is already prepared for the larger valve head. it depends, but what you are looking for is change. This is typically accomplished by reducing, or eliminating eddy points - irregular flow patterns, as well as "fixing" mass produced castings to be more equal. Ideally you increase volume, without hurting velocity. Too big of a hole - volume is good, but velocity falls. Too small a hole - the velocity is high, but volume is restricted. in an N/A car overall cylinder filling is almost entirely created by the downward motion of the pistons. The goal: more cylinder filling - the more you fill a cylinder with air/fuel, the bigger the power output. an entire section of a library could be filled with this. What is different is the time frame.Īh a lesson in reading flow. The cam opens the valve the same amount 1000 rpm as it does at 7000. Remember engine speed(rpm) has nothing to do with how much lift the cam produces. Yes - improved low lift filling works over the entire rpm range. You can get a whole kit at WalMart for around $20 that will give you most of the mandrels, stones and cutter bits you need, then from there its just buying extra rolls and throwaway stuff.With the extra flow at low lift will that help the whole rpm range? Aka please give us a lesson in how to read flow numbers. There are different kinds of mandrels, some for sanding rolls, some for cutting disks, for polishing rolls, sanding disks, different mandrels for different things. 700 in less than an hour with the bits and rolls I have, then spend a couple more hours working the choke side, adding epoxy and smoothen everything out and have a nice S/A carb done and ready to go in just a few hours.have actually done it on race day before heading to the track and came home with the win I can take a stock predator carb from stock bore to. I use the dremel for everything from porting/polishing heads to boring carbs, works really well. I've used the same high speed cutter bits for 3 years now, they don't seem to wear out at all. I got mine at the local Ace hardware store, they have alot of dremel stuff to choose from, WalMart does also. The high speed cutter bits I mentioned are perfect for removing alot of material quick. Price out everything you need for the job, if you're only going to do a single head it might just be cheaper to buy one, a lot of members on here can set you up with a good head for a decent price. Best advice I can give then is don't try to enlarge the port at all, just try to round off all the sharp edges and roll the short side into the valve seat. Without a flow bench it's hard to verify if what you're doing is actually helping or hurting. If you don't have seat cutters then don't go near the valve seat, if you nick the seat then the valves are not gonna seal. All the right tools will cost a good chunk of change. You're also going to want a set of quality carbide burs in various shapes and sizes, and then some sanding rolls and mandrels in various sizes and grits. Im assuming harbor freight has a larger one, but I have no idea the quality and if it can stand up to the abuse. You're gonna want a more heavy duty one and one with a variable speed control. The $9 one won't cut it, it will just stall out.
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