Author Topic: CB350 Racer (Read 7286 times)

kubricky · « **on:** November 12, 2016, 01:28:37 PM »

Hello folks.

I know there are articles out there and I don't mind reading them, I am just hoping someone can point me in the right direction.

Little background to start - I'm older than the average racer at 44 and started riding motorcycles late, on a whim. A few close calls on the street and 2 years later I was ready to give it up when a friend suggested "track days". A year later I was happy as a clam and thought maybe I can try racing and did so with the GSXR 600 I had at the time. I built it back to life from a salvage title and it did me good. that was 2006 and ten years ago. I did another season and then a few more races the following season but stuck with the track days and enjoyed it.

While sitting in the pits, all of my buddies would snicker at the vintage crowd, while secretly, I wanted to kick over the GSXR and go beg to have any of them vintage racers teach me the ways of their craft. I let that go and everything between then and today has put me in a position to pick up a fairly solid 1972 CB350F. I'm getting back to the grid next year on an R6 doing some endurance racing but I wont do it unless I have the CB350 with me.

The frame and motor are solid and I'm mocking up the frame in two weeks for the tail, riding position, and any braces I might need before it goes off to powder coating. I am wondering if there is a good "build walk-through" out there for a CB350Four which might show the location of frame "stiffeners" and braces. I've seen several comments but nothing concise, consistent, and detailed enough for me to understand exactly why I am putting the braces in the locations suggested. The fairly standard positions seem to be adding a tube between the upper shock mounts in the rear, adding a tube between the bottom frame tubes under the motor, and a seat loop. I've already welded the seams, would these three mods be enough for a first pass on the grid?

I don't have any performance expectations for first year on the vintage grid, I'll only plan to have fun, learn, and try to keep the bike running. Any articles or suggestions would be appreciated. Again, I certainly don't mind reading and apologize in advance for introducing myself and then asking questions that I am sure have been asked - I'm just looking for a link or 10.

best,
Kubricky

turboguzzi · « **Reply #1 on:** November 12, 2016, 07:22:20 PM »

welcome to the club... i have started vintage racing at 45, and still at it ten seasons on... so you are not alone

my only not so encouraging comment is that dont know how competitive the 350 four can be against the CB350 twins. There's a reason why there's a wealth of knowledge, aftermarket parts and links on how to build a fast CB350 twin, dozens have been built, not that much for the 350 four. sad but true. Im on this forum for a good ten years and dont recall even one member actually building and racing a 350f.....

so ask yourself if you want to start the more difficult path of tuning a bike thats not that common or known to be competitive, as much as you like your barn find. both the 500/4 and 400f are better starting points IMHO

i think that some people from ex hansen honda (or was it todd henning racing?) should have a link to a 350f build, but it was definitely a sort of a "GP replica" build for parading rather than a true vintage racer. google is your friend...

bwaller · « **Reply #2 on:** November 13, 2016, 02:27:49 PM »

I'm happy to hear you ignored your track day buddies. During track days most decent vintage guys on bikes half the size embarrass their modern counterparts in the cornering bits, but that's not worth discussing further. I'm glad people scratch their itch on the track, racing or otherwise, then ride sensibly on the street.

I don't want to discourage you but have to agree with TG that the 350 twin is undoubtedly more popular. These machines have developed a cult following and they have race classes everywhere. In our ass'n we had one 350F that was really well built and ridden by an awesome rider. It hasn't been out in a few years though. These are great little engines, like a sewing machine, but will be expensive to make competitive. Compression & tight squish for sure but the intakes are choked and valves are tiny. A good twin can make 50hp and are lighter with lots of available go fast parts like TG mentioned.

That said there's nothing saying you can't have fun. Stripping every gram of weight and focus on making it handle, add race rubber so it's easy & fun to ride fast first. Then if "it sticks" (the racing part that is) engine stuff can happen down the road.

The search function isn't working lately so it's a bit tough to find a lot of info on here lately.

Some fast guys will tell you there is no need for extra bracing, and it could well be. A lot of us do add some bracing, but maybe we're fooling ourselves! Certainly it can be easy to simply add weight and that is going backwards. I have a friend in the biz and here's what he did for me.

Forget the steering head section below, otherwise he prefers thin wall chromoly tubing and thin material forming "saddle tees" for bracing. On a single downtube frame, one cross member above the swingarm mount but as close to the pivot as possible, (I used an "X" pattern originally) and one between upper shock mounts. If you're using a race style seat there is no need for any loop deal, just tie the two sides together with a straight tube, keep it simple. Saddle tees stiffen areas as shown, and don't overdo those either. Don't weld the whole way around the original tubing for saddles but try to limit the weld to one side.

Keep in mind that adding a member across the frame near the swingarm pivot must not be done unless the engine is bolted in, plus the swingarm is in place and properly tensioned otherwise getting the arm in place after might be more difficult!

kubricky · « **Reply #3 on:** November 22, 2016, 07:34:27 AM »

Thanks so much for the replies and the information - definitely a little different vibe here (call it refined/mature). I have the bike mocked up and I'm getting critical path items to get the motor running and stiffen the frame. I am going to add the saddles (great idea) and a brace between the shock mounts.

It seems like ignition system and headers are next for critical path. I have original points, plate, coils, and wires but I'm not sure if they are any good. I'm going to reach out to HondaMan to see if he still has the transistorized kits and if he recommends the dyna or other for a race bike.

I have a cb550 stock exhaust that is cleaning up pretty well, I'm going to see if someone needs it to offset the cost of a Mac 4 into 1 (any other suggestions? I think Kerker makes one too). I've been to airtech and a seat/tail is coming so I can mock up riding position. I have a set of woodcraft rearsets that I will repurpose.

turboguzzi · « **Reply #4 on:** November 23, 2016, 08:21:15 AM »

Brent and me thought we managed to put you off big time... so now that you showed some resilience, some tips:
dont get too hung up on frame bracing... Brent is a champ so puts it to good use, but seen enough totally unbraced frames in the vintage winning circle. would leave it for later in case that youll ride so hard as to feel the need. shocks, spring rates and proper brakes much more important

dont wan to say "best", but 90's GSXR electronic ign. boxes + pickup + coils are super reliable, ultra cheap and almost a bolt on. check out bwaller's threads and mine for "gsxr ignition".

carnivorous chicken · « **Reply #5 on:** November 23, 2016, 08:32:05 AM »

Interested to see where this goes -- 350F is one of my favorite bikes, but as others have said will be tough to keep up with 350 twins. 400F is a platform others use for racing though, extra 50cc, extra gear. If your 350F engine takes a dump, you can swap out a 400F engine with no difficulty, just a few minor mods. Regardless, good luck!

*** I should add: I've kept up with some bigger bikes through some twisties on my 350F, keeping it pretty wound up. While they're heavier than a 350 twin, they're not that heavy and they're pretty fun to toss around.

bill440cars · « **Reply #6 on:** November 23, 2016, 08:46:20 AM »

Quote from: carnivorous chicken on November 23, 2016, 08:32:05 AM

Interested to see where this goes -- 350F is one of my favorite bikes, but as others have said will be tough to keep up with 350 twins. 400F is a platform others use for racing though, extra 50cc, extra gear. If your 350F engine takes a dump, you can swap out a 400F engine with no difficulty, just a few minor mods. Regardless, good luck!

I agree, I am looking to see more, on this one. Definitely got some good advice given here, already.
So, I'm following this one, for sure.

iomtt9 · « **Reply #7 on:** November 24, 2016, 03:38:40 AM »

We did the 350cc Classic TT in 2014 on our little 350/4. We qualified for the race. The bike had 28bhp, It did 99mph flat out down sulby straight, and averaged 81mph, Unfortunatley it broke down at water works on the last lap.
We only did it for a bit of fun and the four pipes made a lovely sound.

turboguzzi · « **Reply #8 on:** November 24, 2016, 11:34:54 AM »

Colin, you are telling only half the story... tell him also huw much the 350K4 were doing down sulby!

bear · « **Reply #9 on:** November 24, 2016, 03:26:18 PM »

Doing PI this year Stockers?

Cheers,
Brian

iomtt9 · « **Reply #10 on:** November 25, 2016, 09:49:17 AM »

No Bri, its still there to do it again though,was made redundant after 34 years in my job.

bear · « **Reply #11 on:** November 25, 2016, 11:21:25 PM »

Bugger

Hope things work out mate.

scottly · « **Reply #12 on:** November 26, 2016, 07:03:29 PM »

Wouldn't a 400 have to compete with the 500s? A 350 top end should bolt onto a 6-speed 400 bottom end, since they share the same cylinder base gasket. As has already been mentioned, pay attention to removing weight; I would forgo the time and expense of powder-coating and put the money into alloy rims or port work, especially for a race bike in development.

turboguzzi · « **Reply #13 on:** November 27, 2016, 11:30:48 AM »

got a feeling that a 400 bottom end wouldnt be ahrma legal.... never mind that he'd need to get a second engine up front...
on the other hand, at least here in italy, ive seen the 400s can be made extremely competitive with (if not better than) the 500/4 and parts to do so are readily available, try and find just high comp pistons for a 350/4.

markreimer · « **Reply #14 on:** November 29, 2016, 09:37:47 AM »

Very cool, looking forward to following along.

I have a '74 cb350f and I love it. It's heavier than the twin, but not that much heavier. And it's slower off the line but once into the power band it's pretty close. Just chopping the 4-4 exhaust and switching to a 4-1 will save you a boatload of weight.

I installed 400F headers onto my 350F, and then used a cocktail shaker style Emgo pipe, which is really light. And it sounds MEAN rev'd up to 10k

I've done a bunch of spirited rides with guys on bigger bikes and as it's been mentioned earlier, it's not too much trouble to maintain the pace. I certainly wasn't the slowest rider, which I attribute to how easy it is to throw the little 350 into the corners.

The 350F is an uncommon bike already, even more uncommon as a race bike, that's reason enough to move forward with the project! If you just wanna go fast, stick with the R6. If you wanna have fun and ride in style... you know what to do.

01Thomas · « **Reply #15 on:** November 29, 2016, 01:32:42 PM »

Let's not forget about the Kaz Yashima CB400F racebike. In the right hands it was a real giant-killer. Not a 350, but definitely related.
"Ontario Motor Store"

iomtt9 · « **Reply #16 on:** November 30, 2016, 11:33:27 AM »

Think i have found a few short Vids about the 350/4 in the IOM. Not sure how they will turn out but will give it a go.
Col

turboguzzi · « **Reply #17 on:** November 30, 2016, 11:35:08 AM »

thomas, a bit of a misleading comment... the kaz bike was raced as a 492 c.c. not as a 400...and no, although related, the 350 and 400 are different enough for hop-up parts not to be applicable

if you know how to turn a CB350F into a 49hp/110kg race bike, i'd like to hear and im sure kubricky too

yep, that's the kind of level the 350K4 twins have reached these days. in the UK 350k4 tuning is a bit of a religion, but im sure that in AHRMA there are K4s with 45hp/120kg if not better. Achieve that with a 350F and yes, you'll have fun racing a rare bike.
small reality check :
http://www.daviesmotorsport.com/portofolio/davies-motorsport-350-honda/

iomtt9 · « **Reply #18 on:** November 30, 2016, 11:37:34 AM »

Just put a couple of vids on re 350/4 tell me if they come out Turbo guzzie,?
Agree with what you say to, if you want to be competetive you need the K4 twin,

754 · « **Reply #19 on:** November 30, 2016, 01:29:25 PM »

They are getting 45 plus hp out of XL 350, that are over 450 cc.... Buddy of mne is building one right now..
Bet they would do the job..

turboguzzi · « **Reply #20 on:** November 30, 2016, 01:37:51 PM »

he wants to race it as a 350...

neat videos colin, but hose beers arent doing the power to weight ratio any favors!

bwaller · « **Reply #21 on:** November 30, 2016, 05:05:46 PM »

Pretty sure Tim's 350T is pushing 50 at the wheel.

scottly · « **Reply #22 on:** November 30, 2016, 06:53:37 PM »

Quote from: turboguzzi on November 30, 2016, 11:35:08 AM

although related, the 350 and 400 are different enough for hop-up parts not to be applicable

Same crank, same cam. Does the 400 have larger valves, or better ports? They also share the same carb-to-head insulators. Granted, a 350-4 motor will never be as light as a twin, but I think it still has potential, especially for the OP's entry into vintage racing.

Colin, what was done to your 350 to produce 28 HP? If you have proper dyno charts, please share them.

iomtt9 · « **Reply #23 on:** December 01, 2016, 03:39:54 AM »

No Dyno charts for the 350/4, we took it to the IOM and ran it on a Dyno just to get carbs a bit better.
The bike is pretty standard, we put a mild cam in, race valve springs, CR26 carbs, and 4 pipes on, that was about it.
You are correct about the 350 head and pots bolting on to the 400 bottom end but you have to change 2 front crankcase studs because they are different.
Our little 350/4 is no longer with us, but hoping to put another one togeather for the Next season and run it at the IOM, Manx GP Classic TT.
Will keep you posted,
Col

turboguzzi · « **Reply #24 on:** December 01, 2016, 04:45:15 AM »

ASFAIK 350 has smaller valves, and worse, as a 350 hell be stuck to 47mm pistons, smaller than what even the pitbikes use, so very limited (if any) choice, but maybe Col knows better...

The way i look at it is that it takes about the same amount of effort and resources to build any racer (400 hours from my experience), but if the expected end result is 30hp versus 45hp, then you might as well start with the right base bike no? The fact that he happens to have a 350f has minor weight IMHO. the price of a title less 350K4 dog to build a racer with, will be a drop in the sea of other expenses.

News:

Author Topic: CB350 Racer (Read 7286 times)