lower plenum work doesn't really do much. The ports for the first guy will do good on a 2871 or a 2860RS turbocharger. Flowing any of these heads wouldnt mean anything because we do not rely on natural atmosphere to dictate how our engine will breathe. The turbos create its own and force it down. You want least resistance with smooth transitions. I"ve done cylinder heads where for shits and giggles i put them on a flow bench and they did terrible on the flow bench but put out amazing numbers on the engine dyno. so again...flowing a FI cylinder head will tell you nothing on what that head is capable of.
Nice pics, makes me want to pull my heads down and do more work with them You don't leave much of a seat left either
How much have you decked the heads? By the looks you have taken a fair ammount off them. Why so much?
theres plenty of seat left. You only need a few thousandths for seat contact. Anything larger is just a waste.
But isn't the valve seat the main site of heat transfer from the valve to the cylinder head? The exhaust valves can reach tremendous temperatures, and requires adequate contact area with the relatively cool (water cooled) cylinder head to keep these temperatures in check. Of course the valve guides also assist cooling, but adding excess stress on an already stressed system. I believe cutting the valve seat so fine is a considerable trade-off between air-flow (power) and reliability. Worth considering for those of you who want a engine that will require a pull-down and constant repairs, and a somewhat-reliable streetable vehicle.
Original Nissan design = 200000Kms depending on servicing etc (exclude the crappy 30p inlet valves in that) Cut down valve seats and guides = .... well it's a gamble. I've had an engine that was fitted with exh valve guides that were to short, when it was pulled apart (for a different reason) there were signs of serious trouble starting in that area - less than 10000Ks after they were fitted. As above "worth considering" Also think about the teardrop design used for tubes etc exposed to airflow on race cars and planes etc - just curious as to why that doesn't seem to be used in porting jobs? Nissan did include that to certain degree in the original ports but in nearly all modified heads I have seen it's gone.
I think people should take into account what has to be done to take advantage of a port job like this guy (Tech@EPR) has done, and how the car drives after its done.
Valve seats seal best at minimal widths, the trade off in heat transfer is very minor. Stainless valves will take alot more heat than stocks and will not wear as fast on a narrower seat. Same story with valve guides, stainless valves and short guides are perfectly safe, I do not shorten bronze guides as they will wear quite fast. Also I will not use bronze guides in an engine that will not be pulled down and inspected periodically. They do not last as long as the standard guides.
I was under the impression bronze valve guides were meant to wear less than stock ones... at least that's what the ones on say CZP are sold as.
Stock TT exhaust valves are made from inconel, far superior to S/S in terms of heat transfer and longevity, Basic metallurgy really
The more of the seat angle you have in contact with the valve the worse off you will be. I only leave a .005 wide seat contact on all the seat angles that are ground on the valve. I don't want a .060 wide seat angle on the valve...thats bad for flow/performance and also puts more heat in the valve. If the engine is maintained properly and kept running cool..you won't have to rebuild anything no more than you would anything else. Please don't scare ppl into thinking something that isn't. False pretenses is what gets rumors and bad information around.
bronze guides maintain dexterity and cooling much better than steel. Being softer its advantagious to use rather than steel. Theres a lot of info around that just isn't correct now a days.
correct..however the newer exhaust valves being made by companies such as Manley and Ferrea are higher in grade to Inconel. Ferrea states this directly on their website.
OK. Lots of info here. From what I'm gathering from all this is that, 1. Port matching is of little benefit to a turbo car(more important for NA). 2. Only place that can really be properly port matched is the upper to lower plenum. 3. It is ok to widen the valve seat provided you use stainless steel (or harder) valves 4. Bronze guides can be cut down provided engine temperatures aren't too high? I'm gonna get stuck in tomorrow and have a go at the other ports. Obviously I cant open the valve seats myself. Ill post up some pics tomorrow night. Once I'm happy with the ports I'm gonna send the heads off to the flow tester man and get some results before and after having the valve seats opened. Fun times ahead.:zlove:
Port matching is very important in a turbo'd car. The smoothness of transition and taper and so forth is very vital in how the cylinder head produces power with the correctly matched camshaft. You widen the valve seat area meaning pull the seat contact point to the farthest point on the valve throat so that you are maximizing the full area. Bronze guides are good for any application but best suited for racing applications. Its ok to remove the guides from the port but you must realize that when you do this you leave the valve stem open to harsh temps and thus will run into premature valve issues. You have to sacrifice some things to get gains in others. Overall though you have the right idea. Take your time and let us know how you make out.
So you keep saying, but all advice I am receiving is to not touch the lower plenum to heads and not to mess with the venturi for the injector. If you are port matching these could you please explain or post pictures of what you do to the lower plenum to match it to the heads. This was the initial question in this thread. This lower plenum, will not match up to these "stock" ports Without removing this 2-3mm lip and compromising the venturi. and has no way in hell of matching up with
In this image you can either do one of two things...either port match the flange area...as thats the reason for doing so. You don't have to touch the venturi. Port matching refers to the flange area. So you can either lay the lower plenum on the head and blend the two together....or...outline each flange area with the stock gasket and match from there. Port match/gasket match.....is the same thing. Ideally you want to port match as no two gaskets are the same. You don't have to mess with the venturi if you don't want to. That is an option to you.
Today's efforts. I didn't do any port matching today but I had a good go at removing the guides and cleaning up the runners. In 5 hours I did 2 exhaust ports and 1 inlet. Interesting work in finding where to take metal off to make the transitions smooth. They arent perfect but each one I do get better. Ill pick up some telescopic gauges this week so I can make sure all the internal dimensions are accurate, The valves no longer seat properely but it shouldn't be an issue as they will be reground anyway.(when I do the porting the the propper heads) Exhausts Intake
