Author Topic: 2020 WMRRA Season: DS7 in the V750 Class  (Read 791 times)

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Offline idr5c

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2020 WMRRA Season: DS7 in the V750 Class
« on: July 24, 2020, 03:56:14 PM »
The pandemic has delayed our roadrace season a bit here in the PNW, but we are finally on the track again! 2020 has held lots of surprises, including a significant injury for me back in January that I am still recovering from. That said, I am getting serious about my next WMRRA race build so it’s time to post up some progress.

I’ve successfully campaigned  :celebrate: in the V250 and V500 classes over the past few years, but it’s time for a new challenge. Initially I thought about the V160/175 class, but those losers submitted a rule change to keep 2 strokes out (I think they were sore about that OMRRA guy with the CT-1 that spanked them), so my attention turned to the V750 class……… >:D.

750 Vintage allows disc brakes in WMRRA (and OMRRA) and is dominated by SOHC CB750’s with the occasional Seeley-Westlake, Norton, CB720 (550 bored/stroked), GT750, and so on. While a stock CB750 isn’t that concerning on the track, most of these are CR750 replicas with fully built engines so it will be a real challenge to bring the fight to the front runners on the DS7. For 2020 I’ve mothballed the SV650 so I can focus on getting the DS7 updated and dialed in.
Stephen Phillips
WMRRA #494
http://www.wmrra.com

Offline idr5c

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Re: 2020 WMRRA Season: DS7 in the V750 Class
« Reply #1 on: July 24, 2020, 03:59:16 PM »
To be competitive the DS7 is going to need significant upgrades, but as Kevin Cameron said “Simplicity and light weight are never out of place in racing”. On the plus side the DS7 is much lighter than the CB’s (268lbs vs. 400+lbs), narrower, has better geometry, and is easier to make it handle well. The negatives are it is down on power (they make 80+hp), currently doesn’t stop that well, and gives up a huge amount of displacement for the 750 class. The strategy is simple: a well sorted disc front end so I can charge deep and trailbrake into corners while maximizing my theoretical mid-corner speed advantage AND enough smooth power to get after it before they do on corner exit and stay in the draft on the longer straights. A fairing is also in the works for eking out those last few mph.

The front end is pretty straightforward. I had found set of TX500 forks, triple, and front wheel a while back, so I re-laced the wheel with an 18” rim, rebuilt the forks, put a fresh Conti CR3 on there. Jamie @ Sonic Springs helped me choose a spring rate and they are winding those as we speak. For grins I went with a dual disc setup, mostly so I could use the spare 1st Gen SV650 brake setup I had laying around. We’ll see how it works, but I may go to a single disc/RD caliper later on to save weight. Those discs are heavy!!!!

Stephen Phillips
WMRRA #494
http://www.wmrra.com

Offline idr5c

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Re: 2020 WMRRA Season: DS7 in the V750 Class
« Reply #2 on: July 24, 2020, 04:34:29 PM »
For the engine I decided to seek professional help. I knew an R5 350cc top end was in order but I was unsure what direction to take the porting and how far. I initially thought about using the TR3 port specs as a starting point, but I was concerned with both the reliability of the engine and my ability to ride it. I reached out to Garrett (GRA2Strokes) for advice and after some conversation about what I was trying to achieve we settled on a plan: He would port the top end, not a full on roadrace port job but something to give me more up top and take advantage of my pipes and a bigger set of carbs. He would also cut the heads and make good use of the high octane fuel I run. Carbs are VM30’s, with the spigots turned down to fit in the stock boots.

Before


After, almost done

Stephen Phillips
WMRRA #494
http://www.wmrra.com

Offline Czakky

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Re: 2020 WMRRA Season: DS7 in the V750 Class
« Reply #3 on: July 24, 2020, 08:06:32 PM »
 ;D seriously love these updates. Thanks for sharing.

So much respect for club racers, even more for vintage club racers, Super extra respect for CB750 killers!

No disrespect to any cb750 riders....

Offline idr5c

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Re: 2020 WMRRA Season: DS7 in the V750 Class
« Reply #4 on: July 26, 2020, 09:37:03 PM »
Crankin'! I'm building the new engine on an RD350 lower end I had laying around.





This one was crusty as hell, but new parts are on the way to get it ready for a new life  :vroom:.
Stephen Phillips
WMRRA #494
http://www.wmrra.com

Offline 85RZwade

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Re: 2020 WMRRA Season: DS7 in the V750 Class
« Reply #5 on: July 26, 2020, 11:53:22 PM »
Watching from Washington with great interest  :pop: go get 'em!
Rubber side down!

Offline idr5c

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Re: 2020 WMRRA Season: DS7 in the V750 Class
« Reply #6 on: July 27, 2020, 05:59:36 PM »
Watching from Washington with great interest  :pop: go get 'em!

We'll see!!!! V750 has some serious competition: the combination of well developed bikes and experienced riders means I'll have to work my ass off to catch them. Mick Hart was collecting points and podiums on a factory Laverda long before I was even a thing. But they all do have valves and as we know in the enlightened 2T forum, valves are for toilets.   :dawg:
Stephen Phillips
WMRRA #494
http://www.wmrra.com

Offline 1976RD400C

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Re: 2020 WMRRA Season: DS7 in the V750 Class
« Reply #7 on: July 27, 2020, 09:57:40 PM »
  When I raced my modded RD400, way back when, I found the light weight (me and the bike) really helped. Just as much as horsepower for acceleration, slowing down quickly makes for a good lap time. A bike weighing 150 pounds less does that so much better.
  A little more encouragement. When my buddy brought his stock Laverta Jota 1000 to the track, the hot rodded RD could accelerate just as quick, if not quicker. Good luck. If those guys with valves are right behind you they are going to have a "holy crap" moment if they try to hold their throttle on as long as you entering a turn.  :righteous:
'76 RD400 green  '76 RD400 red   '84 RZ350

Offline idr5c

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Re: 2020 WMRRA Season: DS7 in the V750 Class
« Reply #8 on: August 04, 2020, 03:30:31 PM »
Things are happening fast now  :metal:. Garrett has been making chips getting my cylinders and heads together. He is planning to ship them Wed.

Port/sleeve alignment was terrible!




Ah, much better!




Also......






I too have been busy getting my crank together and trued. Cleaning up this case has been a major PITA. Whatever sealant the last person used was really hard to remove! Also this engine was apparently run on castor so it's got that gunk in the crank area.







Sorting jets is tedious..







Stephen Phillips
WMRRA #494
http://www.wmrra.com

Offline Czakky

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Re: 2020 WMRRA Season: DS7 in the V750 Class
« Reply #9 on: August 04, 2020, 09:19:53 PM »
Are you guys allowed to do any serious port work?

Offline idr5c

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Re: 2020 WMRRA Season: DS7 in the V750 Class
« Reply #10 on: August 05, 2020, 05:28:01 PM »
Are you guys allowed to do any serious port work?

Yes, engine modifications are open. They do need to be reasonable for the period (no flatslides, etc.) and adhere to the displacement limits. 
Stephen Phillips
WMRRA #494
http://www.wmrra.com

Offline idr5c

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Re: 2020 WMRRA Season: DS7 in the V750 Class
« Reply #11 on: August 10, 2020, 09:44:35 PM »
So, I got a box of parts from Garrett.......





Nothing too crazy here, but they do look nice! I wonder how they run? Only one way to find out  :vroom:





Assembly and squish measurements. My base gaskets were a little thicker so the squish ended up at 0.038" (was shooting for 0.030").




Got my carb situation sorted out using an RD350 high top throttle junction and cables, plus a spacer that I machined. I will be running the cables that John @EC sells specifically for this combination after the upcoming race round.






Then we were here! Did some jetting work today and I am pleased with the results. This thing rips! I can't wait to get it on the track. Now to get my numbers back on and finish the safety wire.

 
Stephen Phillips
WMRRA #494
http://www.wmrra.com

Offline pdxjim

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Re: 2020 WMRRA Season: DS7 in the V750 Class
« Reply #12 on: August 11, 2020, 12:10:25 AM »
Looking good!

Garrett does great work!  The porting and head work he did on the Kart Track Racer project bike ripped. :metal:

Can't wait to get back into the LC he worked on for me.
Wasting time on 2T forums since the dawn of the internet.

Offline 1976RD400C

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Re: 2020 WMRRA Season: DS7 in the V750 Class
« Reply #13 on: August 11, 2020, 11:53:31 AM »
Light weight, big ports and carbs, super brakes. That thing is going to perform.  :clap:
'76 RD400 green  '76 RD400 red   '84 RZ350

Offline GRA2STROKES

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Re: 2020 WMRRA Season: DS7 in the V750 Class
« Reply #14 on: August 15, 2020, 09:24:31 PM »
This has been a great project and will be a continuous effort to study different effect and gains. We started off with a very mild port job actually. Naturally there will be many gains just by removing bad miss matches. On the transfer the miss match was so terrible it actually barley blended at the desired height I set.

I have another set I will be much more aggressive on and of course my pipes will be going on as well. That’s the next immediate step.

Garrett