Topic: Fast 350 four engine - am I optimistic?

[morini312]

Hello

My limited ability to control my impulses have resulted in yet another motorcycle; an early 70ties Honda 350 four race bike. The idea is that I shall have it ready for the coming race season, but this plan is not very realistic given that I have lots of other projects, an active hunting dog eagerly awaiting skiing season and a 5 month old son commanding all my attention.

The bike has been raced in the 500 class with a set of 460 pistons, a Yoshimura cam and a flowed head, but the son of the previous owner, being used to modern race bikes, overrevved it resulting in an open block con rod failure.

The bike comes with lots of spares, 2 extra engines and a set of 466cc pistons. I plan to build a fast 350 to race in the 350 class and later do a 466 engine for the 500 class if my abilities and balls allow. I realise that the 350 four will never be a match for the much more popular 350 twins, but as a complete amateur I have managed to convince myself that I am only racing agains myself.

My normal routine for engine tuning is to optimise the head, camshaft, valves, high compression pistons, carbs, etc, but I am not able to find anything other than overbore pistons with standard compression on the net. I need to stay within max 1" overbore to be in the 350 class.

Does anybody in here race these bikes? How do they perform? What would be the best route for extra power? I have only owned the bike for a week and have not checked the Yoshimura cam profile, but if it is made for a 460, is it a known model and if it will fit a smaller engine?

Bike pics will follow. Eternal grateful for any tips.

[brooze72]

Hey Morini

Never heard of anyone racing an SOHC4 in a 350 class, seems those RDs are wicked fast, but I'm no expert on racing. 
550s are popular race bikes though, whatever you end up doing have fun & enjoy it!

[seanbarney41]

two stroke 350 usually goes in 500 class...but yeah, It really seems like the fours generally are not competive with the 350 twins because you don't see anyone trying to use 'em.  You probably would have to spin that tiny crank and cam reallllly fast to get comparable power, and then you got dependability/expensive problems...plus the 4 is heavier.  But maybe you can find some power somewhere that others have not...and have some fun

[bwaller]

I'd be interested in what assn. you'll be racing with. Normally we might be allowed between 1mm & 5% oversize depending on the rules. My first season I was surprised by a very fast 350F, that I haven't seen since. He had a set of Wolf pipes that sent exhaust note reverberating through my brain, awesome. 

These engines have to rev to make any juice, but please please install a rev limiter because this seems to be the way many of them end. If you want one opinion, save your coin for a set of Carillo's, balance the crank with all new crank/rod brg's. Build healthy compression and spend (most of) the rest of your fortune in the head. 

If money is tight, spend your dough building the best handling chassis & tires first, learn to ride & have fun. Then you can work an engine over.

[Tintop]

If I remember the VRRA rules correctly they allow you to use the 400 bottom end with a 350  top end.  The 400 being stronger.  As bw said what assoc. are you planning on racing with??

[turboguzzi]

hei morini (begs to ask which one you have...) your approach sounds about right, i.e., unless you believe you are a Valentino Rossi or Marc Marques in disguise, it will be initially about improving yourself rather than the bike. In that sense, starting from a bike thats already set up for racing is a good idea.

[HondaFreak]

Hi Morini, JD at Daviesmotorsport are building a Honda 350/4 and looks very good! I believe they never had time to do anything special with engine for last years I_O_M Classic TT but are having lots of work done on cylinder head for next year including new rods, new slipper type pistons, valves etc etc. They think it will be
quicker and more reliable than the twin! Lets wait and see!

[Kemp]

The 350/4 that Brent mentioned is Steve Canellos, a racer out of Toronto. That bike is quite well developed with rwh about 45. The guys are right, it is a lot easier and cheaper to modify a CB350 twin as opposed to the CB350/4. The big cost thing is rods. It seems that whether its a 350/4 or a 400/4 you will have issues unless you use Carrillo rods. I've heard you can shot peen the stock rods and that seems to be reliable but I don't know for how long. The Carrillo are about $1300. The other issue for engine life is modifying the oil pump for much higher capacity and pressure. You can use the impellers from the CB750 for that fix as noted by ttr400. I've seen CB350's that make in excess of 50 hp at the back wheel, not that uncommon while 45hp is easily achievable. So your up against it with the 350/4, a heavier bike with less hp.

I'm going to build a nasty 400/4 so I've been researching the issues for awhile. Daunting for the pocketbook BUT you just can't top the feeling when your "little" bike just slays the bigger machines!

[brooze72]

I'm going to build a nasty 400/4 so I've been researching the issues for awhile. Daunting for the pocketbook BUT you just can't top the feeling when your "little" bike just slays the bigger machines!

Looking forward to seeing that too!  Any timeline on the build or still in planning stages?

[bwaller]

Hey Kemp, you're right about Steve. He'd be fast on any damn thing.  I understand besides the 350 he has an ultra fast 400F, maybe you've seen it.

I've always thought it cool to do more with less. A good rider on a smaller displacement, lightweight, fast bike is a joy to watch and a headache for lots of bigger bikes.

Morini there are some here racing fast 350/400's. You need deep pockets to make them fast and hold together, but in reality it's true for anything raced! I think tintop is right about a 350 topend on a 400 bottom end, at least in our club. Having the 6spd will help.

You have my moral support sir! 

[iomtt9]

Brent hi hope all is well.... I have a feeling that the 350 and 400 are the same crank and rods. I might be wrong . Some one will put us right.  Its the sound of the 4 open pipes that makes me want to race a 4 instead of a twin, i'm to old to care about winning at all costs. A few beers and coming home with a smile on my face is more important  !!!!
All the very best in 2014
Col

[Kemp]

Brooze, will be building the 400F late spring I think. The plan is to have it ready for Barber Vintage Festival in the fall. I'm in a grudge match with Kiley in Alabama, to wit, 400F's at Little Talledega or at least on the backroads around Barber!!

I think the 350/400 crank and rods are the same. You might be able to put a 350 cylinder on the 400, I have a set of 350 and 400 cases and a 400 cylinder so I could see if they'll fit together. That could be cool. Even if they don't you could put the liners from the 400 into the 350 with some machining and then overbore to maybe 466. This might affect what class you'd be racing in though, still a bit of a sleeper!

[iomtt9]

You can put the 350 cylinders on the 400/4 bottom end, but the 2 middle front studs are a different length, and i think they may even be a different thread into the cases, iam very slowly putting one of these together and are just starting to come across some of the problems. One thing is for sure if you are going to bore 350/4 or 400/4 to a bigger capacity you defo need better rods. Will try and post some pics when i get a bit further on with my project.
Col

[Tintop]

The way the VRRA rules are written the 350/4 runs against the 360 twin (both allowed 5% over bore).  The 350/4 can use the 400/4 cases / crank / tranny (which gives you a 6 speed).  The 400/4 runs in the next class up.  I know Denis Curtis did a Drixton type frame for a 350/4 (used my lump), but I have never seen it racing with us.  Not sure where it went.