I'm curious.. stock pipes and high exhaust port?

[rd400canuck]

Hi again,

I'm just wondering if anyone would know what would the powerband be like if you have cylinders like the one's I found with stock pipes and intake? Stock is 35mm and these butchered jugs were at 28mm.

[SUPERTUNE]

You might just barely get away with 31 mm, but 28 is way too high for anything!

Here's what I found out pushing my brain on these RD's...
These pic's were the Yellow Screamer on the TRACTOR setup...I had cut off the stinger tubes on my Spec 2 F1's and went bigger so I could run a lot of compression ratio for the street on pump *93. Using TDR 1 piece reed petals on ported stock cages and TM34's and my old school handmade Dyna ignition.







Now to today I'm at 31 mm on the Yellow Screamer with a lot of mods and with a bunch more porting to make them work.
My cylinders that are on my Yellow Screamer now were some old customer cylinders (we replaced like 10 years ago) that were very old school ported back when all you did back then was to raise the crap out of the exhaust port, cut the intake skirt on the piston and port out the windows.

Then mill the heads for a lot of compression.

This makes the blow down very long, but way back in the day we had *96-*98 leaded gas we could buy at the pump...no way can you do this with today's engines that have to run on *91-*93 octane ethanol pump fuels unless you dump out a lot of compression ratio.

So when I found them again upstairs that I always considered them over ported almost even for a roadrace bike, (maybe a drag bike ok)
My brain went nuts again and I decided to see if I could make them work to see how far can you port a set of cylinders for a streetbike. 
So bored them 65.50mm, used wiseco banshee pistons with .0033 piston clearance, ported the reed cages for V-Force Banshee VF4 reeds, (lots of epoxy work) and ported the crap out of them to make all of the other ports match up to these high exhaust ports to control the blowdown from being too high, used my higher than normal todays pump gas milled heads on them (I called my last experimental cylinders tractor porting).

The engine ran really good but powerband was really up there and was a little low on torque in the midrange for a streetbike, I basically said to myself yeah I'll never go this high for normal porting builds. This was using some custom high end S.S. pipes.
This was done in time for the Deals gap meet in May '17





Dynoed it at Barber in Oct of that setup...



Then my brain this year wouldn't leave me alone this year!  
I decided to put the tractor modded Spec 2's pipes back on and add 2 teeth to the rear from a 40T to a 42T.

And WOW the bike woke up from the dead!
I'm very happy I learned that when you had lost hope at making power you find it!   

Barber Dyno run with this setup...look at the flat curve and made 1 more hp and the torque all the way up to 37 FT-LBS...unheard of in RD engines....

Chuck

[rd400canuck]

Great post, Supertune!

I'm always amazed how much these motor's capabilities are changed by exhaust and intake.

When I got my new bike home a few weeks ago I let it warm up to take it up the street. I knew right away something was up when one side got way hotter than the other. So up the street I went and it felt like a moped. In my head I thought "why did I even bother?" I took the carbs apart and found missing main jet washer on one side and blocked pilot jet as well. I figured I'd clean all the jets and have another go to see what the bike was like but I took the head off to take a peak and when I saw those exhaust ports I gave up on that idea.

I assumed if stock intake and exhausts are tuned for a decent low and mid there is no way this bike will run well with ports that high but I wanted to ask just in case it's something that people actually do.

[teazer]

28mm is about where a Cheetah barrel sits for a 58mm stroke crank

28mm on a 350 or 250 54mm stroke crank is only 85 degrees ATDC and would be a little peaky but might work.

28mm on an RD400 62mm crank with 115mm rod works out to a 77 degrees ATDC port timing which is a couple of degrees more time than a TZ350, so it's a bit extreme and is unlikely to work well on the street with stock pipes.  With decent pipes and appropriate transfers it could work but would still be peaky.

If there were the only barrels you could find, it would be possible to machine the cylinder base and add a 2-4mm thick head gasket to compensate for the amount off the bottom but that would make sealing the heads more difficult.

[rd400canuck]

Luckily I found these babies from a guy in Texas. 100% unaltered aside from being freshly bored to 1mm over. It did cost me a very pretty penny to buy and get them here but I feel it was worth the expense so I could build a proper running headache free bike. Plus I want the most bottom end / mid I can get and I figure stock everything is the way to get it.

[teazer]

Nice one. Make sure the ports are chamfered to stop the rings snatching. 4 stroke shops don't always get that right.

[rd400canuck]

Good point!  Thank you.