T305 Ex port raised 2mm to 30.5mm not good

[D&D CHASSIS]

It is a good idea to degree wheel your port timing, you want your blowdown in the correct range for what you want out of the motor. And I wouldn't put a lot of comparatives with the RD, as it is a totally different motor with stroke and all. So it really doesn't cross over to the Suki......

Thank you John! I`ve thought the same thing......

[Vintageman]

Thanks everyone

I do have a degree wheel. However, dyberg123 did the timing for me on this one. viewtopic.php?f=2&t=9856" onclick="window.open(this.href);return false;

He went to 29.5mm EX (have not heard anything about it yet) and wider too. I wanted +31mm ish and ended up 30.5mm as noted

I have had a chance to run it harder and the bike does like to run 6500 RPM -> +8500 RPM
The Ex change does does take away torque below 6500 rpm versus before, but ingition timing corrected, it still runs here with no strange behavior. It is more sensitive to timing.

The bike now has a personnality similar to my GT250A engine. You really can not relax drive which I call cruising -4000 to +5500 rpm.
It does run here but, you can tell its not as happy down here. It's happy place is > 6500 rpm and up.

The bike is exciting to drive and need to be careful to be safe when riding it happy on an unclosed course.

It defenitly has more power than before for once accelling through 7000 rpm the clutch slips where it did not before

Does Barnett offer stiffer springs for these engines?

The RD 350 and R5 has the same stroke and rod length as t250/t350/t305/gt250/gt380?. The R5 has 32mm (published who knows what it really is)Ex height and piston ported and RD350 29.5mm and reeds as I am sure we know. My R5 has great low end and revs just as high as this modded T305. I think the extra boost transfer have a lot to due with Yam and Kaw performance. Maybe a good mod to Suz it to have those finger ports added beyond my abiilty, but would hire someone to create extra boost ports. Who can do this?

I want to increase the Gt550 Ex timing but, not as much as I did with T305.. I think up to 2mm should achieve that goal?


Thanks

[Vintageman]

Just put Iridiums in it. moved to 23 degrees, drove it about 80 more miles. Nice day 75F low humidity . engine seams to be seating in nicely runs smooth low rpm, idles well smooth 1200 rpm, OK mid and pulls very hard over 6500. Doesn't ping or make any harsh top noise.

It is fast! very fun.

Thanks everyone again. I am sure i could tweek it better. It is a decent little mod if you want some more pep.


Now onto the GT550.

[ja-moo]

I want to increase the Gt550 Ex timing but, not as much as I did with T305.. I think up to 2mm should achieve that goal?

I would go to 32-33 degrees of blowdown, whatever that is, is where I would raise the EX port to.

[tz375]

I wouldn't go that far on a mild street motor. 28 degrees should be more than enough I would have thought - for a 9,000 peak and 26 is fine for 8 grand peak.

[ja-moo]

I have always considered 32-33 mild, but then I'm a Kawasaki guy......

26 to 28 is pretty darn mild for sure......

[Vintageman]

What do you work out for Ex height for milder mod GT550?

I want to shift peak 750 RPM to 1000 Max.

Is 2mm too much?

Thanks

[ja-moo]

That's what the degree wheel is for, you need to degree the ports.

[tz375]

For John's 30-32 degrees, that works out to raising the exhaust port by about 3.5 to 4.5mm with stock transfers.

But Dragonfly75 seems to suggest that for a peak at say 7500 transfer duration should be 122-124 degrees or a port opening time of 117-118 degrees which is approximately 2mm taller than stock making the exhaust 5.5 to 6.5mm taller than stock to stay within
those two parameters.

But with such small transfers, arguably, it needs even taller transfers that that to flow enough- and so the beat goes on.

[ja-moo]

I think we have our wires crossed TZ. 32-33 of blowdown, not transfer opening...... if the stock blowdown is 126, that would be 6 or 7 degrees up on the exhaust. Or opening at 94 ATDC to have 32 degrees of blowdown........

[Suzukidave]

OK .. yall stop talking in Latin or is it Greek !

[ja-moo]

If you are going to be talking porting, you gots to know blowdown! It is just the number of degrees between the EX and the transfers open. The more/longer blowdown gives more of a high rpm oriented powerband. 32 degrees is on the mild side, 35 is getting pretty hot, so it doesn't take a lot. 23 degrees is really in the super mild enduro range.

[tz375]

Yes, but......

It comes down to which variable will be fixed first - transfer time or exhaust time and work from there.

Example:
Stock GT550 T.O. is at 124 degrees ATDC. Exhaust would have to open at 94 degrees ATDC to yield 30 degrees of blowdown. Yes?
But stock EO is 101 degrees on a GT550 IIRC. That's a change of 3.6mm compared to a stock GT550 exhaust.

Or working off a transfer opening point of 118 degrees that Draganfly recommends, that puts EO time at 88 degrees ATDC as the EO target to get 30 degrees of BD. That would require transfers to be raised by 2.4mm compared to stock and the exhaust by 6.8mm or so to achieve those two targets.

Keeping in mind that the greatest piston movement per degree of rotation happens around mid stroke or 90 degrees ATDC, which is where we are playing. That's why the changes are so huge in MM to achieve Draganfly's target AND 30 degrees of blowdown.

Better to aim for a milder EO time with less B/D at lower revs because there's insufficient transfer time-area to support high rpms and with that 62mm stroke, it's probably safer to keep MPS below 3,500 with those old pot pistons and thick rings.

That's how I was looking at it, but wouldn't be the first time I got something back to front.

[Vintageman]

I most likely won't touch transfer due to skill and special tools to port them. I may use degree wheel to verify what I have is what we think.

My goal is simply to shift power up 750 rpm for maybe 10% hp gain only.

So Was curious what 1.5mm or 2mm off exhaust would show in your simulation where transfer are stock. It will give more BD which this engine seams to be short on.

Also what about adding 1.5mm 2mm of intake. believe that was real mellow too stock.

Can run those numbers and see if they are any good for a little gain in peak and HP but still good easy rider?

Thanks

Mike

[tz375]

MOTA suggests that your combination plus JEMCo pipes should be a nice upgrade without much of a drop low down and a nice increase over the peak stretching it to 7500. Exactly what you were looking for.

GT550 ports are so mild. That' s why teh numbers in my last post look so huge to get to a more sporting port time set up.