Re: Cylinder Head; performance increase for FI too?
Rastaman;204860 said:
Con-rods maybe not as u not revving that high anyway unlike Type R engines.
Rod upgrades for NA and FI are for different reasons. NA engines pick up power mainly by increasing throughput via engine speed which puts a lot of tensile stress on the rods. FI engines pick up power mainly through increasing combustion pressure, so have to deal with raised compressive loads. All out FI engines that increase both engine speed as well as boost pressures, need to bear both very high tensile and compressive forces, although at TDC fire, the combustion loads offset tensile loads somewhat.
caySman;204885 said:
anyway I'd like to know too. All that I've read about cyl head porting... all those which max out the gas velocity etc. were WRT NA applications. What about FI? The turbo outweigh all the little benefits?
The short answer is that porting is one of the last things to do in a street turbocharged engine - esp any semi-decent 4V, which all modern examples I can think of, are. The labour costs, the time, the risks (especially in Singapore), and the small gain for all this, doesn't make sense. If you're all out of things to do in other areas - ones that yield big gains for equal or less money, then go for it. Even then I would try really hard for a US, Euro, Jap, package head before messing around local. They don't have comparable knowledge, equipment, process control, experience. It's easy to screw a port up when really trying for gains. If playing safe and only cleaning up casting flash and smoothing guides, then taking the head off was a waste of time. If the head for some other reason has to come off the head, then the needless risk is already cut by almost half.
The last % efficiencies are not practical to strive for in a street vehicle, opposite of racing where you must seize them (having captured the big ones) in order to be competitive.
NA engines create a depression in the cylinder, and with atmosphere (1 atm) on the other end of the port/plenum, flow is created. The upstream atmo pressure is fixed within a narrow window. You can create larger depressions downstream but around the 0.75 atm range the pumping loss starts to overcome the energy release from fuel burned (that which accompanies the air mass at that speed) and power starts to tail off and even decrease. At roughly 0.5 atm, any further depression no matter how large (even perfect vacuum) ceases to move any more mass across the intake port. This is why all NA ports are designed around similar nominal gas speeds based on cross sectional area and piston speed.
FI engines create >1 atm upstream, and even at sonic choke (speed limit) in the port, continue to move more mass through it because of increasing density. High boost engines have a slight increase in velocity at port discharge and just after intake valve opening, but they have a lot more pressure in the port which keeps the short turn loaded and separation doesn't occur as easy as with NA ports which are always in vacuum. Separation NA or FI is hardly a concern on 4V OHC engines though, so a lot more straight forward to estimate power gains on.
Good NA and FI ports are very similar. The best NA ports with boost applied to them, make the best power for a given level of boost - regardless of head type. You still need good flow per unit valve area, good flow per unit port cross sectional area. Intake to exhaust valve area ratios stay remarkably similar. Most relevant example I can recall for you guys is the Honda F20C (earlier S2000) engine. Makes power at unheard of low pressures because the head is such a good one. I'm sure the new BMW V10 and V8 are close just looking at the cutaways.
piggyboyz;204895 said:
block is still made from aluminium and having aluminium bolts.
There are no structural bolts made of aluminium. Misc. plugs and other items yes, but not bolts that do anything important. In fact I can't recall ever seeing aluminium bolts on anything automotive.
It's transfering the weak point from one item to another.....
This is true with any car, any change. And when the transferring is complete and everything has been built to take exactly what it needs to, all it means is that at the point of failure, a large number of components will be damaged, instead of just one. For this reason, often one hopefully cheap and easily replaceable component is intentionally left unbeefed to serve as a 'breaker'.
If porting, by reducing the surface area will weaken the cyclinder head, then adding boost and heat will warp it as well.
Yes first starting out with a new and unknown head, it will take at least 2 or 3 ports to find the limits by sonic checking, trial and error porting, and/or by band sawing heads to measure material thicknesses.
Warping is not guaranteed. You need considerable heat to warp a head. At typical thermal safety margins and mid range power bumps, usually heads don't warp.
phil;204897 said:
hmmm, i think you are a little off there. Porting reduces the area in the ports, not on the surface, surface grinding to gain comp does this, but i doubt it will warp in street conditions.
Porting typically increases port cross section, and reduces wall thicknesses. Welding up heads or building up epoxy walls to change profiles and in some areas reduce cross section , is not advisable in a street engine. Welding usually means having to re-heat-treat the head and resurface it because of annealing and warp ( from the weld process)
Gaining compression is usually done by surfacing block and/or heads, or welding up chambers. Surfacing is via carbides or other cutters, not grinding.
What will probably break first is the conrods. Not the block, well the block will break if the rods come out the side of it!!
I believe it depends on how the engine is built. The weakest goes first. Without prior experience with that specific engine, there's no telling if it's rings, rods, gaskets, crank, etc.
BlackStealth;204901 said:
Somemore it was a sincere question.
Why would anyone mind your sincere question?
To answer:
Doesn't weaken block, might weaken heads. Might indirectly stress block and/or heads more if thoughput is increased as a result of headwork. Might weaken block-to-head seal if either is over surfaced and lacks stiffness. This is more related to chamber work than port work though.
Rule of thumb is % gain from NA port multiplied by boost pressure = boosted gain. ie. 5% power gain from NA port, 2 atm (14.7 psig) later applied. Base NA engine originally 100hp, now is 100 X 1.05 x 2 = 210 hp. This is not firm rule because of separation sensitivity based on port shape, port air properties post compressor and IC, EMAP. The lower the boost pressures, larger the turbine, straighter the ports, and the better the support systems, the more accurate the above.
