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Author Topic: Rd 350 porting  (Read 453 times)

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Offline yellowandfast

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Re: Rd 350 porting
« Reply #15 on: January 12, 2018, 09:00:50 AM »
TR3 was a nice race motor for the time but the powerband doesn't start to around 8500 or 9000 and goes to 10.5 or so.  That's not a lot of use on the street. If you have the tools to work on transfer ports, go ahead and port the barrels to whatever numbers you like, but there's a balance between transfer time area and exhaust time area that make a huge difference to how the motor will work.

A stock exhaust can be widened quite a bit and different tuners have different ideas as to shape and width of the port.  Search on line for articles by Scott Clough and Dale Alexander to see what they did on race motors and dial it back a bit from there. Or send your barrels and heads to Chuck Supertune and have him do his magic.

So jut by looking at the map aND reviewing what others have done how does just raising the exhaust port up to 27mm and dropping the intake to 93 mm, effect the charracteristics of the motor?
 One fellow did just that and sand left the transfers alone and claimed the power was seemingly increased over the whole rpm range - any truth to that?

 What if I did go to 26mm exhaust height and a 94mm intake floor and left everything else alone? Besides correcting the squish?
Oil is your friend......

Manitowoc, WI

Offline teazer

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Re: Rd 350 porting
« Reply #16 on: January 12, 2018, 09:49:29 AM »
Short answer is that it would increase revs and maybe power but ports and pipes have to match and to gain power across the range without losing at the bottom half favors wider ports all round.

Intake on an RD is controlled by reeds, so you can more or less do what you want there. If you raise the roof of intakes, make sure that the rings stay above the new floor or else they will break.

As a really crude rue of thumb, a good place that many people use as a starting point is EO at 90 degrees ATDC and 30 degrees of blowdown. It's not a bad place to start, but width is everything. There used to be a little rhyme about that, but this is a family show....

Stock RD350 transfers are pretty bad IMHO. Especially auxiliaries and boost port. 

Offline yellowandfast

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Re: Rd 350 porting
« Reply #17 on: January 12, 2018, 10:11:52 AM »
So the tr3 has a 26mm exhaust and 40 mm high transfers,

The rd has an exhaust of 29.5 and 44mm high transfers with a blie down of 35* as I have found, so what's the bd of the tr3 and how do you find that? Other than using a degree wheel?

« Last Edit: January 12, 2018, 10:25:09 AM by yellowandfast »
Oil is your friend......

Manitowoc, WI

Offline teazer

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Re: Rd 350 porting
« Reply #18 on: January 12, 2018, 03:44:55 PM »
Stock RD as measured by Ed E is 29.5 exhaust Opens (EO) (88.3ATDC) and transfers open at 43.5mm (121.6ATDC) B/D = 33.3 degrees

TZ350C from Ed's port maps is EO 26mm (81ATDC) and TO 41.5mm (116.1ATDC) B/D = 35.1 degrees

What that suggests is that raising the exhaust on an RD without raising the transfers, would reduce B/D timing but what we can't see with those simple numbers is Time-area of the ports.

It also shows that the RD is already in a pretty good state of tune for a bike of the time. 

For ideas, you could check out the port map of a Cheetah Cub which has EO of 27.18mm (83.4*) and TO of 42.16 (117.8*) = BD of 34.4, and lots of ports.

Offline SUPERTUNE1

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Re: Rd 350 porting
« Reply #19 on: January 12, 2018, 09:56:46 PM »
So jut by looking at the map aND reviewing what others have done how does just raising the exhaust port up to 27mm and dropping the intake to 93 mm, effect the charracteristics of the motor?
 One fellow did just that and sand left the transfers alone and claimed the power was seemingly increased over the whole rpm range - any truth to that?

 What if I did go to 26mm exhaust height and a 94mm intake floor and left everything else alone? Besides correcting the squish?
Not good unless on race gas...IMO
Pump gas and or Pump gas w/ethanol will need more transfer timing (slightly less blowdown)
You have to understand the makeup of todays pump gas fuels...not just ethanol content.
Its full of solvents!! Today's gas is for fuel injection and not too friendly for a aggressively run RD imo without careful setup.
I even have had tuning issues using the wrong 2 stroke injector oils...

Chuck
Racegas + Lots of oil = HORSEPOWER
2 time Daytona AHRMA Formula-500 winner '06
'78 RD400E
TEAM SCREAM RACING
RD machine work, boring, porting, cranks and engine building.
New email: cqsupertune@tampabay.rr.com