Darrins 985 motor build with Dyno chart and 114.75 RWHP

Posted: Fri Apr 15, 2016 4:41 am

Hey guys,

It's been awhile since I have shown much (not much time) but here is a 985 that I recently built for a forum member Darrin G. Funny as I don't know Darrin's screen name on here.

Here are the details of the motor. It was not an easy one to do but I learned a lot and am very confident in my abilities after building it.

First of I lightened the 900 crank in my shop by 3lb 6oz's.
The cases got most all of Brents mods. 360 oiling mod, cam chain spray nozzle mod, windage windows cut in the cases and cylinder sleeves, cooling holes in the barrels and head plus widened the stock air ducts in the head. Oil filter air bleed mod, and of course his A guide, A tensioner and B guide. Borg Warner cam chains and primary chain.

Then It got a Headless oil screen and a banded clutch basket by Headless and I installed Wouts clutch rubbers.
The clutch is a 900 basket with a 1100 pressure plate as they are stronger and I removed the riveted steel plates and added an extra standard steel plate. Then I use Barnett clutch springs from a Honda CR500 (I like the feel and they are strong).

The primary shaft got all new rubbers.
New Yellow bearings in the mains and rods. I used stock 900 rods as Darrin didn't want to spend the $1300.00 for new rods but I did install new 1100 bolts.

For pistons I used some NOS old school Moriwaki pistons and they suck just as bad as the Wiseco 67.5mm pistons. Both of these pistons have too high of a wrist pin boss which makes for a low deck height. This means the pistons were almost 1mm low in the cylinders and that is a BAD THING. It causes the motor to ping badly and does not make a good burn.

To fix the low deck height, I took .013" from the case deck, and then removed the cylinder liners and took .013" from the base of the barrels. Then install the sleeves again and took .020" from the top of the cylinders and block. I then adjusted the height with the proper thickness base gasket.
This will be the last time that I will ever use Moriwaki or Wiseco pistons in a 900. I will use them in a 750 with 900 rods and a thick base plate to get my zero deck but that's another motor and it's starting in a couple of weeks.

Next I worked the head over pretty good. It got a full port job, I lowered the spark plugs in the chambers by 1.5mm, the valve seat throats got bored 1.5mm on the intakes and .5mm on the exhaust. The exhaust guides were shot so I installed new Bronze guides in them. I'm liking the Kibble White over size valves that are sold by Dynoman so those valves were used. 27mm Intakes and standard 23mm exhaust valves.
Then I welded up the combustion chambers and reshaped them. This is a game changer. Not as nice as one of Brents heads but the next best thing. The final head mod was to have it surface ground .010" and lots of holes drilled in the fin dams for better cooling.

For cams, I used a set of 1100F cams with 200 original miles on them and slotted gears to degree them in. It also got Kibble White dual springs.

Ignition is a Dyna 2000 with coils and wires and the exhaust is a Vance & Hines super sport model. Not the best and will be getting replaced soon with a JayGui racing exhaust that I am now the US distributor for.

For carbs Darrin is limited to 29mm smooth bores so a set of 29 Cr's were used. WAY TOO SMALL for this head and is limiting the power output but it's what we have to deal with for now.

Here is the Dyno chart. I'm pretty happy with how it turned out. I was shooting for 120 hp but the cams and carbs are hurting the outcome.

We got 114.75 RWHP and 75ftlbs of torque from a 985. That is pretty good in my book.

Posted: Fri Apr 15, 2016 4:44 am

I will show more of the build later. My internet connection is really slow tonight. It just took an hr to get what I did.

Peace and keep it in a Wheelie, Jim

Posted: Fri Apr 15, 2016 9:02 am

my take on your result is you've replaced the typical +/- 10% gain from CC (72mm piston) by working the head / compression, thats nice to see - especially without any cam variation - i.e. its a big fat broad gain - nice one Cool

CB1100F Joined: Jun 18, 2006 Posts: 2526 Location: UK

Looks very good Jim..i bet he is pleased as you with the result..when is the first outing for this race bike?

Keith

Posted: Fri Apr 15, 2016 10:14 am

That's nice work Jim! I always like seeing what the final result is after a build. Looks like this one got all the special treatments! Keep it up!!

Posted: Fri Apr 15, 2016 2:26 pm

krgood0 wrote:

Looks very good Jim..i bet he is pleased as you with the result..when is the first outing for this race bike?

Keith

Darrin's racing it next weekend at Willow Springs. I bought a ticket to fly down and watch my efforts go around. I just wish we could put some real carb's on it.
All in all, I'm happy.

Posted: Fri Apr 15, 2016 2:47 pm

krgood0 wrote:

Jim I am in LA for that weekend, i will try to get to Willow Springs for a day

Kieth

Keith, it's 80 east of LA in the desert !!!! Wish I could be there myself to see Jim's work and Darren's ride as it sounds like a success. 114 HP is very good considering the 29mm carbs and cams. I'm picking that a little more tweaking with the exhaust etc and 120hp just might be achieved.

Good job all round.

Captain

Posted: Fri Apr 15, 2016 3:30 pm

Hi All,

I'm more than pleased to say the least. I'm more relieved that the build and tune are almost complete. Well, I mean..the tune is always ongoing but I'm happy to have it together. I say this because I'm not the worlds greatest mechanic as Jim would probably tell you. I have the aptitude, just have ZERO patience and that isn't a good combination.

Anyway, the overall number for sure suffers by my own hand and not a testament to Jim's (and Jett Tuning's John Ethell) ability to get power, I have the crappy ole Vance and Hines pipe (baffle removed), 29mm carbs (ahrma requirement for overbores), 530 chain, 1100 cams, and other small things that could probably eek out a few more HP's. Since the dyno run Jim put up, I dropped the pilot and installed stacks on the carbs and that number is up to 115.5 or something. I will be adding a jaygui exhaust or something in the near future but for now, I'm in a crunch to get this sucker to the track.

The stock engine ran on the same dyno with the same carbs and pipe two years ago and put out 92.1 or something. So as you can see, following the recipe that the Captain has perfected over the last however many years, significant gains are achieved. I'm very happy to have had Jim and the Captain in my corner and I'm excited to go try this new beast. It was difficult on the stock motor as the straights were loooong. I am not expecting miracles as it always comes down to the rider and I'm ok with my ability being the weakest link.

I'll get some notes and try to post up a ride report after. I'm hoping to see some of you folks from the LA area at Willow next week. And maybe from the bay area the following week in Sonoma.

Cheers!
Darrin

Posted: Fri Apr 15, 2016 3:52 pm

You're talking about 23% increase in power with Jim's work, using the same carbs and exhaust. Jim should be quite proud, especially using an OEM cam, degreed at OEM spec. If there's room on the exhaust valve, retarding the cam timing (at the A chain) a couple degrees will yield more top end.

CB1100F Joined: Jun 18, 2006 Posts: 2526 Location: UK

Captain wrote:

krgood0 wrote:

Jim I am in LA for that weekend, i will try to get to Willow Springs for a day

Kieth

Kieth, it's 80 west of LA in the desert !!!! Wish I could be there myself to see Jim's work and Darren's ride as it sound like a success. 114 HP is very good considering the 29mm carbs and cams. I'm picking that a little more tweeking with the exhaust etc and 120hp just might be passed.

Good job all round.

Captain

Yes i am staying in Long beach area about 100 miles away, not been to willow springs before, been to Road America and Daytona for the AHRMA in the past, be good to see Jim again and see his latest handy work in action

Yes 120 is not too far away, a few minor tweeks should get there

Keith

Twinstar Joined: Jul 06, 2010 Posts: 128 Location: Toronto

WOW - These are big numbers! I didn't think a 985 was capable of numbers like this...very impressed with everyone's work!

Posted: Wed Apr 20, 2016 7:19 pm

Well done Jim....
Smile

Posted: Wed Apr 20, 2016 8:11 pm

Cool! CR29s will do everything well, they just have less at wide open. Use the shortest velocity stacks you can. You might look around, people have been known to bore smoothbores. 29s might be able to open up to become 33s, or at least 31s... It was popular to bore VMs years ago... The critical piece is the jet block, if it gets too weak. Think oval bore...

Posted: Wed Apr 20, 2016 10:57 pm

lets see some pictures of this hot rod.

Posted: Sat Apr 23, 2016 4:31 am

It's my nature to share what little I know even if it could bite me.Bite me meaning it might get me beat on the track.Anyway,Darrin and JJam,I'm assuming this bike is an ahrma racer,the last time my partner Big Bore Mike R.I.P. ordered carbs for our old racebike,he ordered 29cr's b/c of the rules.He didn't read the rulebook........you are allowed to run bigger carbs,the inlet just has to be restricted down to 29mm.Hope to have my bike ready for Barber in Oct and hope to see you guys there.

Posted: Sat Apr 23, 2016 4:42 am

Double post.

Posted: Sat Apr 23, 2016 4:43 am

From the AHRMA rulebook....."A restrictor plate may be used where a minimum carburetor size is speci ed. A re- strictor plate must be at 1/8-inch thick with a constant diameter bore no larger than the required maximum diameter."........nice job on that engine!

Posted: Sat Apr 23, 2016 7:32 pm

I've known that at least one of my competitors have run bigger carbs with restrictor plates - it was several years ago and I can't remember if he ran 33s, 35s or what, and it was on a Z1 with a J-head. The rule book states the minimum thickness of the restrictor plates too. This guy had access to a dyno and did a lot of work tweaking his setup to get it to work well and while he didn't quantify what he ended up with he did say it was "a lot more" than running with 29s only. I was curious as I'd never seen a restrictor plate setup so I asked if he could let me look, and he said absolutely not. He was borderline offended because if I copied what he did it'd be like stealing his work for nothing. I was just curious... Honest! And I'm still curious.

Posted: Sat Apr 23, 2016 7:53 pm

a 29mm restrictor thats only an 1/8" thick isnt going to restrict very much at all. It'definitely be worth testing a set of 35's or even 37s. I bet there's another 15 hp in there. Not to mention the torque.

Posted: Sat Apr 23, 2016 8:10 pm

Hmmmmmmmmm........

Posted: Sun Apr 24, 2016 12:28 pm

Dennis,on a Z it would be bolt on easy,just get some nitrous manifolds,unless the id on those is already too big.......and off to the races.

Posted: Sun Apr 24, 2016 12:36 pm

Never knew Moriwaki and Wiseco apparently just use 750 kits for 900s......that means a lot of low comp 900's running around if they are .040 in the hole.I wonder if omt pistons are like that,when my 1002 last went together in 1985 I was a 19 yo kid and hadn't yet learned about checking deck and cam timing etc.

Posted: Sun Apr 24, 2016 12:57 pm

I thought it was the CBX that had the shorter pin to top of piston dimension.

Posted: Sun Apr 24, 2016 1:08 pm

900 and 750 have diff length rods,but I haven't had 750 and 900 Pistons side by side for over 30 years.Maybe the pin height is the same,and they just make the Pistons not to optimum,certainly wouldn't be an uncommon thing with Wiseco.

Posted: Sun Apr 24, 2016 4:37 pm

1100russ wrote:

I thought it was the CBX that had the shorter pin to top of piston dimension.

This is correct. The CBX pistons are "shorter"... I had posted pictures of the CBX piston, side by side with a CB-F piston.

Posted: Sun Apr 24, 2016 7:31 pm

ex-ama-superbike wrote:

From the AHRMA rulebook....."A restrictor plate may be used where a minimum carburetor size is speci ed. A re- strictor plate must be at 1/8-inch thick with a constant diameter bore no larger than the required maximum diameter."........nice job on that engine!

Right out of the AHRMA rule book for Vintage superbikes.

Quote:

3) All round-slide carbs are allowed (Keihin CR, Dell’Orto, Mikuni “smooth
bore” and like design). Flat-slide carbs are not allowed. Pumper carbs may be
used, but the pumper mechanism must be disabled. 1025cc four-cylinders may
use carburetors up to 29mm, or the stock constant-velocity carburetors that
were original equipment on that machine.

This limits you to 931cc, or 29mm carbs.

I think there's power to be had in the OEM CVs when setup properly at 1025 ccs.

Posted: Sun Apr 24, 2016 11:30 pm

Sorry for the hijack JJam,nice build.

Posted: Mon Apr 25, 2016 2:37 am

So what piston kit would be recommended? to avoid the deck height issue.

Posted: Mon Apr 25, 2016 3:04 am

Unfortunately there isn't one. You either do what Jim has done or find and modify a piston from some other model/brand. Or you commission a custom set that is correct in all areas.

Captain

Posted: Wed Apr 27, 2016 12:11 am

Good Job Jim !