Transfer porting: good, bad, ugly?

[edisto]

I know a lot of guys have had a lot of success working the transfer ports. It seems there would be disadvantages in terms of velocity, and perhaps bulk flow, as well as the risk of screwing up the scavenging pattern.

It seems that transfer work is part and parcel of the port jobs now, but I was wondering if anyone had separated the transfer work from the intake/exhaust/squish work to see the effects, i.e., run a ported saw with and without transfer work.

I'm not saying it's good or bad, I'm just wondering if anyone has been able to parse out the gains from transfer work from the overall gains of the port job.

 

[Jacob J.]

I've run both- an otherwise stock cylinder with moderately and heavily worked transfers, and a cylinder with moderately or heavily worked exhaust/intake and no work to the transfers.

When you give the intake and exhaust new timing numbers and additional volume, you're still leaving a lot on the table by not working the transfers. In most cylinders, the transfers get the least amount of R&D and the least amount tweaking. A builder who knows what they're doing can actually greatly improve the scavenging by properly shaping the transfers, especially the upper outlet.

 

[pioneerguy600]

I've run both- an otherwise stock cylinder with moderately and heavily worked transfers, and a cylinder with moderately or heavily worked exhaust/intake and no work to the transfers.

When you give the intake and exhaust new timing numbers and additional volume, you're still leaving a lot on the table by not working the transfers. In most cylinders, the transfers get the least amount of R&D and the least amount tweaking. A builder who knows what they're doing can actually greatly improve the scavenging by properly shaping the transfers, especially the upper outlet.

Yup +1

 

[Trx250r180]

ive thought this before too ,on the dirt bike engines it used to help lengthening them out a little , i see on some of the saws they lower them a lot ,what does this do ?

 

[albert]

I think it depends of the saw model, some benefit more than others. I didn't touch the uppers on my ms260 and it's pulls well.

 

[edisto]

I've run both- an otherwise stock cylinder with moderately and heavily worked transfers, and a cylinder with moderately or heavily worked exhaust/intake and no work to the transfers.

When you give the intake and exhaust new timing numbers and additional volume, you're still leaving a lot on the table by not working the transfers. In most cylinders, the transfers get the least amount of R&D and the least amount tweaking. A builder who knows what they're doing can actually greatly improve the scavenging by properly shaping the transfers, especially the upper outlet.

It makes sense that you'd want to "keep pace" with increases in time area. If you are right about the R&D on the transfers (I'd be more certain if I saw Beaker), then I'd worry less about velocity drops interfering with scavenging. I'd also worry less if it were practical to tune the exhaust.

Seems like a flow bench would be necessary to improve scavenging if one hasn't done it numerous times though...

 

[50blues]

Most of the woods port jobs i have seen, are more of a shaping of the transfers. If you enlarge the transfers to much it could slow down the speed of the air which would hurt the engine performance.

If you remove the restrictions and shape the ports for the best air flow it helps. I'm sure some saws could benifit from a larger transfer, but I haven't done enough to be able to tell you one way or another.