If you port the intake and you increase the cfm and using formulas can workout you have not effected the speed.
Does it mean you should port the exhaust port with the same level of CFM increase you gained on the intake.
Does that not make sense? What goes in the same must come out the same.
On my kwacker 80 all I did was open up the intake take the restrictions out the exhaust so it flowed nice and free and ring ding ding did it fly...
I suppose the theory is the same for 4 strokes as too big on the exhaust side can ruin the back pulse...
Intake ports tend to be bigger than exhaust ports, there are many factors to this, but over time the ration of inlet to exhaust has not changed that
much.
There is usually capacity available in the exhaust ports to take up the extra flow.... to a point.
Most porting will work well just adding bigger inlet valves and widening the port under the seats and doing 3 angle seats.
For forced induction engines it is often more beneficial to enlarge the exhaust ports and leave the inlets alone.
Discus
The other aspect is pressure.
On the inlet (unless forced induction) you only have atmospheric pressure pushing the air in to the vacuum created by the piston moving down, so
approx 14psi at best.
Exhaust side you have the piston pushing the gasses out with greater pressure. So the exhaust ports are going to have much less effect.
Look at what the top head people do. I believe virtually all the work is done to the inlet side.
Picture attached.
1) Looking into the intake does it not make sense to increase the width so it aligns with the valve seat edge.
Then the air flows in at STRAIGHT LINE.
We are talking 2.5mm on each side. This would align it.
2) Knife edge the dividing wall.
*Having trouble uploading pic
[Edited on 29/6/17 by bikecarbfred]
[Edited on 29/6/17 by bikecarbfred]
[Edited on 29/6/17 by bikecarbfred]
Volume of a circle?
Volume of a rectangle?
I suggest the single rectangle has a bigger volume than the 2 circles therefore no benefit
Knife will help
3 angle valve seats will help
Matching manifold port to head face ports will help
There are more useful things to do before carving lumps out of the head with little idea of what the results will be
"Matching manifold port to head face ports will help "
Shall I do it on the exhaust side too.
Personally I wouldn't port match either, I would have the face of the inlet port on the head slightly larger than the manifold face thus not
needing to align the manifold, on the exhaust side you need a mismatch, at the bottom of the port is best as it stops the exhaust pulse wave running
up the short side radius.
Generally cylinder heads are really good now a days, just smooth the casting lumps and bumps off and get a decent 3 angle valve job done by some one
who knows the engine well, so uses the correct angles, get the valves back cut to make the most out of the valve job.
Shooter
@ snapper
Area for both valve opening combined: 1366mm
Area for rectangle section: 1115mm
This is area cross section: not volume
[Edited on 29/6/17 by bikecarbfred]
Also there is potential to do the below if any improvement can be made.
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quote:
Originally posted by Shooter63
Personally I wouldn't port match either, I would have the face of the inlet port on the head slightly larger than the manifold face thus not needing to align the manifold, on the exhaust side you need a mismatch, at the bottom of the port is best as it stops the exhaust pulse wave running up the short side radius.
Generally cylinder heads are really good now a days, just smooth the casting lumps and bumps off and get a decent 3 angle valve job done by some one who knows the engine well, so uses the correct angles, get the valves back cut to make the most out of the valve job.
Shooter
) then ports where most certainly
matched & the manifold/head dowelled. I think most important for the exhaust ports is to grind/polish out any significant casting lumps &
bumps or general surface irregularity as providing gases can flow freely is generally more important than the size of hole they are going down -
tho' I certainly doubt you'd lose power by opening the ports up a little
If you can't dowel the manifold to get a perfect overlap, you want to ensure the downstream diam is slightly larger so no step-in occurs.
On exhausts it's potentially beneficial to have step-outs (again, downstream larger) so that it provides some anti-reversion properties, but
I'm not convinced as to the efficacy of it.
In both cases, you want to match flow in and out, out has the pressure behind it but also has increased velocity (so higher losses) and intake has
lower velocity but increased density due to colder mix and fuel load.
If you widen ports more than the runners you'll slow the gas as it enters the valve area, which is generally not considered a good idea.
I think any single item may give some results, but you'll likely see best results from an "all together" approach.
Port sizes relate to the valve sizes so unless the ports are known to be too small, (not usually the case on modern engines), then there's little
if any real value in increasing the port sizes unless you go up on valve sizes. If you increase valve sizes then you'll need higher lift cams to
make best use of the bigger valves and then higher compression ratio to make the best use of all of the above, all of a sudden you have a big bill for
what is still going to be a modest increase in power.
Clean and tidy up inside the ports as any sharp corners casting flash etc a light skim to give top limit on CR and radius the inlet port entry as
shooter63 suggests (no real point in all that dowling and matching the port to manifolds like in the old days - it's just a lot of work for very
little gain)
HTH
quote:
Originally posted by chillis
Port sizes relate to the valve sizes so unless the ports are known to be too small, (not usually the case on modern engines), then there's little if any real value in increasing the port sizes unless you go up on valve sizes. If you increase valve sizes then you'll need higher lift cams to make best use of the bigger valves and then higher compression ratio to make the best use of all of the above, all of a sudden you have a big bill for what is still going to be a modest increase in power.
Clean and tidy up inside the ports as any sharp corners casting flash etc a light skim to give top limit on CR and radius the inlet port entry as shooter63 suggests (no real point in all that dowling and matching the port to manifolds like in the old days - it's just a lot of work for very little gain)
HTH
Divide cfm by area will give you speed.
So if the most critical point where speed must be measured is right at the valve seats.
1) So if you know the cross sectional area of the valve size, you can work out the speed by dividing CFM (flow rate) by the area of the valve seat
hole.
2) Or do you measure the cross sectional area of the first point air enters the head which is the intake port?
Lets be honest, there's little point in all of this on a modern engine. The gains are so small for the cost it's farcical. With an aftermarket ECU you'll get the best tune for the hardware you have with easy stuff fixed. After that, the £perHP is vast unless you bolt on forced induction.
Your right. To be honest it's about the knowledge to gain. I like diy and to learn how things work. Mess up , then try again and find out what
was done wrong and put right.
The project's I enjoy. I have thought about just using the money and buy a new car but the thought of that did not excite me.
I love science too much.
Edit: im using aftermarket ecu. using megajolt
[Edited on 2/7/17 by bikecarbfred]
quote:
Originally posted by coyoteboy
Lets be honest, there's little point in all of this on a modern engine. The gains are so small for the cost it's farcical. With an aftermarket ECU you'll get the best tune for the hardware you have with easy stuff fixed. After that, the £perHP is vast unless you bolt on forced induction.
quote:
Originally posted by bikecarbfred
Your right. To be honest it's about the knowledge to gain. I like diy and to learn how things work. Mess up , then try again and find out what was done wrong and put right.
The project's I enjoy. I have thought about just using the money and buy a new car but the thought of that did not excite me.
I love science too much.
Edit: im using aftermarket ecu. using megajolt
[Edited on 2/7/17 by bikecarbfred]
quote:
So am i reading this correct to take a blacktop zetec from say 125 you need to add a aftermarket ecu plus a set of aftermarket fuel injection plus the fuel pump and swirl pot system then with a good map you can get around the 175. The cost of this has got to be around £2000 so 50 hp for a little over 2k.
Then you can get a well ported head off the shelf put a pair of nice cams in it for say £1200 and get it up to say 215 ish
Strange so many people go down this road . Oh and have you seen the cost of force induction kits be it turbo or superchargers