DIY portmapping HOW?

[tz375]

5mm on a GT750 is still quite a lot.

JA has extensive experience with Kawasaki triples and races/raced an H1, so he really knows those motors. Stage 1, 11 etc are a little arbitrary but usually represent Slightly warm, Hot street, Almost race and stage 4 would be Race tune. Or something like that. In the Kawasaki world, Denco and Gast established certain "tunes" or "Stages" that they sold and I would guess that's what he was referencing.

5mm is a huge change in a 2 stroke. On a more modern two stroke we would be talking in 0.5mm increments. These old bikes are very tame, but we have to be careful that we don't take them too far. On the RZ350 Yamaha used a valve to change exhaust timing so that they had a low port at low speed and a high (race type) port at higher engine speeds. They also have small inl;ets, terrible transfer ports and chronic head shapes.

As performance rises, the head becomes more important to good performance and to stop it melting. On a TR750, they had to keep compression and revs low, to stop pistons melting from that heat. Heads are easier to modify on a 550 than a 750, and if you want to go past "stage 1" it would be a good idea to explore converting your heads to a squish design.

I think that JA uses Tom Turner's TSR software. I use Bimotion and MOTA.

[ja-moo]

I use the TSR, and real world results, like most tuners. The "stage" description is really just a way to break porting into sections, and is not consistent between tuners. I go in smaller steps than most.

[dyrberg123]

TZ375 and Ja-moo - Thanks. I understand, and i will start slowly, seing what will happen. I have several cylinders to the T350 so it is not the end of the World if i make something wrong. I have purchased a set oh KAWA heads for it with squis allready cut to 55% of the area. And a clearence on 0,045" But the dia of the outer edges is 62 and the bore on the matching cylinders are 63mm, will that have negative effect? Steelruler is only for example, i took the meassure with a caliper. Does that sound ok or way off?

[tz375]

That Diameter is probably OK, but it's not the only variable. I like to set the squish band angle at 1 degree more than the average angle across the matching area of the piston. You need to measure the angle on the pistons and have the heads machined to match. You also have to measure the combustion chamber volume. That's the volume on top of the piston to fill the head. Use that to calculate compression ratio and machine the heads to get the CR you want.

[dyrberg123]

That Diameter is probably OK, but it's not the only variable. I like to set the squish band angle at 1 degree more than the average angle across the matching area of the piston. You need to measure the angle on the pistons and have the heads machined to match. You also have to measure the combustion chamber volume. That's the volume on top of the piston to fill the head. Use that to calculate compression ratio and machine the heads to get the CR you want.

The compression should be 6:1 uncorrected 11:1 with ccv 18,5cc 2,5cc less than stock. - does that sound ok?

[ja-moo]

Not optimum, but will work. You do need to check your angles. And you can do a compression test to see where you are at.

[dyrberg123]

Not optimum, but will work. You do need to check your angles. And you can do a compression test to see where you are at.

Would you have a sort of play it safe and go from there suggestion on the porting? FX lift exhaust roof 2mm + 2mmwider each side, shave off 2mm of pistonskirt, or lower botton of intake 2mm. Match ports to block + intake rubbers etc.

[ja-moo]

That sounds like a good starting point. I prefer lowering the intake port, as that actually adds intake port area.

[dyrberg123]

That sounds like a good starting point. I prefer lowering the intake port, as that actually adds intake port area.

THX JA

Do you think i will ba able to feel this Work when rolling after Wards?
The squish band i must adjust anyway as it's not 100%, i will aim for 1mm in clearece, according to bell that should be somewhere in the middle.

[ja-moo]

2mm is definitely enough to feel.

[tz375]

That sounds like a good starting point. I prefer lowering the intake port, as that actually adds intake port area.

John, I take it that you are not advocating just taking 2mm off the intake per se but are suggesting that it is better to change the port than to cut the piston. Yes?

Daniel, you have to make your own determination on intake timing compared say to AG Bell recommendations. On the 750, Suzuki make a huge change on the M model year which hurts low end more than it helps at the top end. That will make it "feel" more powerful because less at the bottom plus slightly more at the top = a bigger change as revs rise and it's the change we feel. That would make the bike harder to ride and feel more powerful but it would actually be slower under normal street riding conditions.

The 550 may or may not respond the same way. You have to measure the exact port opening and closing events and make a decision.

Try the 2/2/2 approach and see how you like it. MOTA suggests (really quick pass) that you will lose power up to 6,000 (-4hp) and will make more above that (+4hp).

[ja-moo]

I "prefer" lowering the port, but that is usually with bigger carbs. Cutting the piston skirt works also. Just a preference. It would be a lot less work to just mod the piston. Sometimes I get in performance mode and forget that on mild engines you don't have to go all out.

[tz375]

Thanks JA. That all makes sense. I ran a couple more MOTA runs on a GT550 and they suggest that lowering the intake makes little to no difference at any revs to that motor. I have no data on the 350 twins.

I didn't fine tune all the variables, but it suggests that the motor is not "intake restricted" at reasonable levels of performance and that's consistent with runs we did on carbs for that motor.

I would need real data to get any idea where the restrictions are in any other motor. John and I can tell you what works and what doesn't on motors with which we have experience and data. On motors we haven't seen, we need accurate data to work out a plan.

[dyrberg123]

Hi, thanks for all your feedback, it really Means alot you Guys helping. Do you know anybody who can run my numbers in a program if i read them out of the engine? I want to buy porting tools now, and since i am a blacksmith with Family so not unlimited access to Cash, software will be later. I can easily roll some cones aswell.

Thanks.

[ja-moo]

Sure, either accurate degree wheel numbers, or the port heights, minus the deck height. We do need bore stroke and rod length for port height calcs.