Talk to me about port timings

[Deleted]

So I measured the port timings on mr DR130 kit. I did this by eye using a timing wheel.

Out of the box they are: 

Transfer: 119
Exhaust: 163
BD: 22

Squish = 2.0 mm

If I simulate a 1mm packer under the barrel these change to:

Transfer: 125
Exhaust: 170
BD 22.5

I could use a 0.8mm packer too, which would bring these numbers down a bit i guess? Maybe to 124 / 168

If I use a packer I will have to mill the top of the barrel down to set the squish. What squish am I aiming for - something around the 1.5mm mark?

I'm going to be using a Sip Road exhaust to start with.  So what will be the effect and difference between of the tow different set ups? My limited understanding is that raising the port timings sends peak power further up the rev range but also allows the engine to rev higher (i appreciate it is a lot more complex than this, but I just want a simple understanding to start with).

Many thanks
Olly

[tzsteve]

transferes of 125 and exhaust of up 175 are ok with those cheap heavy pistons but it`s better to go for width and area of exhaust port rather than just going higher also try to avoid going for too square an exhaust port as that could increase ring ware.

blending is also a big help. keep the squish down to about 1mm if you are doing any tuning work and try to get a head with a very central combustion chamber rather then the ones where the combustion chamber is of to one side. a propper skim and profile on the head is a massive help ( see davet`s thread on fetling the TS1 ) the best way of raising the transferes is by barrel shortening ( 1-2mm off the top and then use a packer )

inlet timing of about 180-185 is about right for a road scoot with a standard crank and cheap piston. if you start looking at real pipes and a carb over 22mm you should consider an ets crank as they are stronger this would also allow for a little more inlet timing due to the strength of the crank.

the more you do to the barrel and inlet the more you will need to invest for reliability.

and yes tuning does produce more power at the top end of the rev range but if you keep it simple you may be suprised at the results. i did a dr130 kit for scooterfreak about 25-30 years ago so ask him how it went.
i think he mudered a dog with it and spent ages picking dog out of his forks

[Deleted]

Thanks Steve,

Are you saying I should take my dremmel to the barrel to enlarge the exhaust port rather than raising the barrel - or should I do both?

I already have an ETS crank - how do I measure the inlet timing?

The exhaust is a sip banana - when you say real exhaust I guess to mean a true expansion pipe?

Should I get my squish down to 1mm whatever I do? Can I just take 1mm off the top of the barrel?

Thanks

Olly

[henri]

rather than just skimming 1mm off top , raise it with a packer til pistons just proud of exhaust port base at btdc ,that will give you more transfer n exhaust duration .then re-measure ya squish an take off whats needed to get a squish equaling 2% of ya stroke ,bout 1.2mm .that an a general cleanin-up an matching whats i did with my dr130 .an i was pleasantly surprised at the result .
an inlet timings done by degree wheel an staring down the inlet whilst turning crank , mine was a stock large taper crank,a ets should give you near 200degs out the box if memorys workin today .H

[tzsteve]

as H says packer and lathe the barrel top using a mandrel (that helps keep the bore 90 deg to the gasket face this is needed when you get a rebore )

get the dremel into the exhaust port raise it and widen it 65% of bore radius the edges, do not make the port too square just copy and enlarge what you have, then blend away.

re checking the inlet timing; check old posts there are loads showing showing to do it, max out the pad as a starter but leave about a mm all round for sealing the inlet against the crank.

a proper skim and profile on the head will not break the bank and is a good investment as a close squich band will help stop detonation

[Deleted]

Thanks Both.

Was planning on raising and skimming the top of the barrel. Do you know any who can do this to the barrel. If I raise it by .8mm and I currently have 2mm squish I need to lathe 1.6mm off the top of the barrel to get 1.2mm squish.

Re the exhaust port and the dremel, I might have a go at this.

I'll check the inlet timing using your method Henri. Im not going to open up the sealing pad at this stage as the cases are together...

Steve, when you say a proper skim and profile on the head - is this really necessary? And if it is necessary why does one need to do it if the squish is set correctly using the above method?

Thanks
Olly

[henri]

theres more to squish than just a measured gap , theres the width of the squish ring an the angle of the roof aswell ,matching it to the dome of the piston . its a bit in depth for a dr kit really ,an from my measurements on mine not necessary unless your plans to have the fastest dr ever.
i didnt do any porting ,but as tz points out theres room for improvement on the exhaust port. raising the roof an increasing the blowdown might be a idea,but 1st get it packed/skimmed an measure again your port timings .H

[Deleted]

Jun 19, 2016 8:21:42 GMT henri said:

theres more to squish than just a measured gap , theres the width of the squish ring an the angle of the roof aswell ,matching it to the dome of the piston . its a bit in depth for a dr kit really ,an from my measurements on mine not necessary unless your plans to have the fastest dr ever.
i didnt do any porting ,but as tz points out theres room for improvement on the exhaust port. raising the roof an increasing the blowdown might be a idea,but 1st get it packed/skimmed an measure again your port timings .H

Ok brilliant - sounds like a plan.


One more question on inlet timing. Measured my ETS crank with timing wheel and the duration of the cutout in the crank passing the inlet is 126 degrees, just a SiP reports on its website.  I guess this is good enough for now (I don't want to cut the crank or enlarge the sealing pad just yet)?

[henri]

yep, sorry earlier when i said "200 degrees out the box " i must of been having a brain-fart .with cutting an enlarging a ets can get you upto/near 200, with just enlarging the inlet to the max ,depending on inlet being large or small size ,150 to 170 degrees of inlet duration is achievable .the sort of duration needed for a fast/road tune .an its not just the duration that counts ,opening an closing degrees should be noted ,so any enlarging is done in the direction needed for the tune you want .H

[Deleted]

Ok thanks Henri - so next question. Is there any point faffing about with raising the port timings, enlarging the exhaust port, reducing the squish if I stick to stock ETS inlet timing?

[henri]

i think if i was you i'd raise the barrel to lengthen port timings an adjust the squish to start with .an match barrel to casings aswell, that will give you your 50mph easily . a stock ets isnt that bad a inlet timing to start with an will be fine for a fettled dr . later as the need for speed grows ,a bigger exhaust port with engine breathing out better would need inlet work to breathe in better aswell. H

[Deleted]

***UPDATE***

.8mm packer on. 1.3mm milled off the DR head. I measure a 1.5mm squish now. PKXL2 clutch installed.

Just cleaning my 19.19 carb and have ordered some new jets, and should be ready to fire this bad boy up really soon.

Excited..

Olly