DIY portmapping HOW?

[Vintageman]

I have rod lengths for T305 and is allegedly same as T20, T250 T350, GT250, GT380. I think 110mm . I'll check when home and update if wrong


The port map for Yam... you still don't know port timing degrees for you need deck height, piston dimensions and rod length as you know

No its casting flaws on intake bridge. No casting is perfectly smooth and varies jug to jug. And Since no Al divider they were made skinny too. I think any less than 1mm or 1.5mm?? thick would break. Seen some early T500 jugs on eBay with broken intake casting. Guys that bore this area need to feed depth slowly. In fact I would offset bore a little towards Ex if you get too thin last possible bore

Yes I put DGs on my GT250/T3xx So easy to do if you use RD400, DG for RD350 work too just need to move rear bracket... search my posts, or give a chance to find them. They work well no funny areas. It boosts power too, but not as much as when put on RD/YR5, but Yam is tuned hotter than T/GT my guess.

I am not sure what you are trying to make. But, I sure would like to know how R5 and RD350 port timing compare to T350. if milder I would go R5... too much Ex timing, is nice, but you can never drive easy why I am puting t350 in place of GT250A. That's why we need more than one bike! Same with RD400 versus GT550 curious port timing

I am going to pull my T350 jugs off and lower that intake 1mm (window area too small we learned vs 32 mm carb). I never had any problems with stock head and note T350 claims 6.8: 1 compression which is higher than RD. What I really should do is rubber mount engine. If my Ex is 32mm like your that's good for me. And if 33mm may just leave it alone too (we'll see).

[tz375]

And that 6.8 could be based on a lower exhaust port height compared to an RD.....

[dyrberg123]

And that 6.8 could be based on a lower exhaust port height compared to an RD.....

Must be. I have both here in std trim, and the RD is comming more on when it hits the power, where the T350 is more flat, with loads of bottom.

[Vintageman]

Take off 2mm from intake of T350 and try again. I did this when comparing t20 intake, but numbers we show in this post imply intake is holding the engine back and should be fixed.

Let's pretend timing with Suz 54 mm stroke engines is similar timing to Yam 54mm engine and thus we can compare port heights directly.

The R5 is 32 Ex. My R5 will still out rev the T305 even with 2mm off skirt, but t305 is 33.3mm Ex. And, I should have opened intake windows vs skirt. The R5 lugs up inclines while in the low 3xxx rpm. T305 does too.
R5 is 65.25mm bore and T305 is 1mm OS for 61mm

The RD350 is 29.5 mm ( I do not have) but, would feel more like my later GT250A (29.5mm) peaky, exciting, but has nothing below 4000 rpm. Reed valve on RD may help low end and extra 100cc won't hurt.

Have 77 RD400 not sure port timing versus RD350 (funny, Yam bikes popular, but no one seams to have published this...oops I an am hypocrite for I can now do this for t305 per Suz numbers). RD400 will, but does not like to lug in 3xxx RPM range. I mean % wise much less of its power here than r5 and rather be over 4000 rpm.

Are you sure the T350 has 32mm Ex. How many did you check?

For some reason the 72 T350 had less advertised HP than earlier models. Same carbs, muffler, and air box I can see? Mine is a 1972 and thought is was like T305 on Ex. Height. I am going to have to check again.

If my T350 is 33mm I will surely make it 32mm. If 32mm I may leave alone. for 1mm less than my t305 and I will lower intake window 1mm which I did not do on t305. I have an acceleration video of t305 before 2mm. I will take another now and compare.

So what are you wanting for a Ex height? if you want around 29.5mm. I agree you need that H1 head or RD400 head to get back some compression via low cc head ala squish band.

[dyrberg123]

Yes i am sure of the 32mm, this meassured from flush cylinder top to ex roof, late cylinder with auxilary exhaust ports.

What i am aiming for is a street riadable fast road tune, still with some broadness intact. I know that some of the low end will be sacrifised, but that i can live with.

The 2 mm you want to take off the intake, is that done by removing material from bottom on window right??

And should the intakes also be widened?

BTW i have a tuning article for GT250 somewhere if you are interested?

[Vintageman]

The 2mm I did take off the T305 was skirt only.

If you look at a T305 jug and T350 very similar. The T305 has larger volume transfer passages (same port window dimensions) and piston skirt cut out to match.

I ran the1972 T350 first, but later got as set of T305 jugs and piston and did fresh bore. I knew the T350 piston to cyl. gap was around ~0.004" and thought that was why some of the top end noise.

Also Crank was replaced … checked for true on lathe centers at work. Still, these engines have a lot top end noise.

I ended up adding rubber handle bar mounts from T350 replacing the stiff mounted ones on the GT250 which the engine is in. That helped a whole lot. Without, your hands got the tingles.

he T305 piston has thick rings and read that makes top end noise too. The T350 I got the later style piston with thin rings like GT550. The bore is new and verified it is to factory clearance.

T305 does not have little Ex ports just like early T350 I hear. Did you see my other reply to GT750 carbs on GT550? On the GT250 (two little ports) cyls vs GT380 (no little ports) the GT250 main Ex port lost area to accommodate the little Ex ports. Not sure what the point is here

Based on this post now I want to lower the T350 1mm intake since I already took 1.6mm off skirt.
Maybe I’ll add base gasket and shave head 0.020" is my thinking now. My 72 T350 cyls have those two little ports. If I find they Ex is 32mm I will be very happy

Widen? If the intake port not > 10% larger than carb area it is not optimal so maybe a little. I will run the factory 32mm Carbs

Some numbers

Yam R5 Intake 40mm x 24mm = 960mm^2, quess is effective area 80% due to roundish shape for 768mm^2
T305/T350 intake (36mm -3mm) * 21.5mm = ~710mm^2 quess is 90% effective since less roundish shape for 639mm^2

28mm carb = 615mm^2
32mmm carb = 802mm^2

R5 with 28mm = 768mm^2/615mm^2 ~125%
T350/305 with 32mm carb is 638m^2/802mm^2 ~80%
T350 with 28mm carb is 638mm^2/615mm^2 ~104%

So if you make t350 2mm wider and 2mm taller
(38mm -3mm)*23.5mm^2 = 822.5mm^2 . A little will sure help

I love the way my R5 runs and it pegs (D&Gs ) the factory tach (10500 rpm) so easy I have to pay attention to it.
(Although I have collected all parts for another R5 .... 6 speed, oil pump. clutch, etc. and maybe I’ll raise port in between R5 32mm and RD350 29.5mm -31mm?).

I know Yams have extra scavenging ports and T350 may never be like it (also ~3mm smaller bore), but I am sure you will find a little change does a whole lot for that engine.

I just want this T350 version to be a little different than T305. I was considering the HiggSpeed T350 pipes, but judging a book by its cover the D&G look a little more performance orientated. Just have too many D&Gs. Later I may try something else.

[tz375]

.....................
Are you sure the T350 has 32mm Ex. How many did you check?
...........

FYI,
According to my calculations 113ABDC is 293 degrees ATDC and with a 110,mm rod, that works out to 31.7mm which is pretty close to 32mm given the accuracy of measuring ports.

[Vintageman]

Tz375,

Thanks, If the 72 T350 cyl is not 32mm Ex I'll reply. Just not sure what they did in 1972 to reduce power? So far when Suz says they did reduce HP we have found possible reasons.

[tz375]

Normally the design process is to set a HP/RPM target and from that you can work out port time-areas from a few choices of width and duration and that and a few other things determines pipe dimensions. Pipe tuned lengths are set so that certain events happen at certain times.

Increasing duration (port height) means that the wave will leave earlier and arrive earlier than before and that changes the RPM at which the pipe works best.

Changing one dimension means that other aspects either work better because they are a better match or they get further out of synch.

I was able to use Bimotion to basically reverse engineer the DG pipe and it appears to make sense as to why it works well for a simple pipe design. The Wizard pipe is odd though and I haven't yet managed to make it work very well above a peak of about 7000. Then to be honest MOTA and Wizard pipes don't seem to play well together.

As to the 72 change, I have no idea and I don't have any data on what they changed in port or pipe design to comment.

BTW Ja-Moo's suggestion looks OK in MOTA.

[Vintageman]

BTW Ja-Moo's suggestion looks OK in MOTA.

Tz375

Great,

So what does the Ex height need to be for 90 ATDC Please
Also what does 2mm lower intake floor give for new Intake timing.

Thanks

I messed up above numbers for I used T250 width not T305 and just took my engine off shelf and T350 intake wider and higher than T305 I remembered incorreclty sorry

Ex height with piston in and flash light into Exhaust was 31.2mm (both sides)

Intake window 0.925" wide by 0.825" (paper traced one of them) or ~23.5mm x ~21.0mm

Corrected #s ->
Yam R5 Intake 40mm x 24mm = 960mm^2, quess is effective area 80% due to roundish shape for 768mm^2.
T350 intake area (23.5mm*21.0mm) *2 = 987mm^2 quess is >90% min. effective so 890mm^2.

28mm carb = 615mm^2
32mmm carb = 802mm^2

R5 with 28mm = 768mm^2/615mm^2 ~125%
T350 with 32mm carb is 890m^2/802mm^2 ~111%
T350 with 28mm carb is 890mm^2/615mm^2 ~145%

I think all is well!!! since I took .063" (~1.6mm) off skirt I am going to leave as is and try.

Should be different than my T305

I compared a T305 piston with a T350, pushed wrist pin into both. Same piston edge height and skirt height. I guess that is the one I should crack open and add a little here and there if the T305 Suz manual I have is correct.

[dyrberg123]

Normally the design process is to set a HP/RPM target and from that you can work out port time-areas from a few choices of width and duration and that and a few other things determines pipe dimensions. Pipe tuned lengths are set so that certain events happen at certain times.

Increasing duration (port height) means that the wave will leave earlier and arrive earlier than before and that changes the RPM at which the pipe works best.

Changing one dimension means that other aspects either work better because they are a better match or they get further out of synch.

I was able to use Bimotion to basically reverse engineer the DG pipe and it appears to make sense as to why it works well for a simple pipe design. The Wizard pipe is odd though and I haven't yet managed to make it work very well above a peak of about 7000. Then to be honest MOTA and Wizard pipes don't seem to play well together.

As to the 72 change, I have no idea and I don't have any data on what they changed in port or pipe design to comment.

BTW Ja-Moo's suggestion looks OK in MOTA.

Hi Guys, sorry for my delay these days in getting back, but i went for installation last sunday in Chile, bretty far away when you ive in Denmark, but now the WIFI is working

TZ - the wizzard pipes on my bike was build for target peak at 7000, so more torque than hp. They where on the bike when i got it, so your believes are spot on i guess.

Would the DG's be better, and could i find better than those aswell, maybe 2 stage ones?

Daniel

[tz375]

Peak of 7,000 on a 350 twin! What were they thinking? For sure we could design better pipes than DG, but to be honest, they are really good pipes for the money and if I have the correct dimensions, they will work very well on a T350 - stock or ported.

So far I have "tested" 3 pipes with spacer and with JA suggestion and then some other alternatives and so far I'm liking JA-Moo's suggestion as an easy way to add around 10hp. We can add another 10 with spacers and further porting and some other changes but that also raises the intake floor and we need to drop that from stock and the question is by how much.

We could drop it so far that it was coming out the bottom of the lower flange and get another 5 HP at 8,000 but we would lose 5hp at 4,000 where we can't afford top lose that much. We could probably get close to 60HP if there was enough metal to remove but you would need thin ring pistons and a different transmission. So we are not going there.

What I'm thinking is raise and widen the exhaust as per JA-Moo. That's a change from 93 degrees to 90 degrees or 1.4mm.

Widen the intake slightly but not beyond the piston skirts - that's what will probably dictate the limit to width. Stock intake duration is really short compared to say AG Bell's recommendations, so there is scope to drop that a mm or two but you will lose as much below 4000 as you will add above that, so you need to decide how far you can afford to go.

Those changes will put it it ahead of a stock RD350 in power, but it won't be quite as torquey at lower revs.

[dyrberg123]

Thanks TZ,

I know for sure it is a balance between giving and taking. Besides JA suggestions, and the intake modification, what base plate thickness have you been looking at? I know that might not be the way to go but just thinking? 2 -3 - 4mm? Also keeping some low end would be great, still a nice ride in town.

You should have a mm overlap between skirts and intake port right to get a decent seal?

Cheers

[tz375]

The biggest spacer plate I have seen on one of those motors is 6mm I didn't try anything that outrageous yet.

And yes, we need to have the piston completely cover the intake port. I have a set of GT750 barrels that were professionally ported that are 1-2mm too wide and are basically useless unless I find pistons with wider intake skirts.

[ja-moo]

It's only 1.4mm up on the EX if you are going to use my spec, and that is also to add some blow down. Spacer plates will not give that, it raises everything the same.