Topic: How much power does a CB400F sohc4 make?

[TomC]

Hi Small Four Lovers
      Tsflstb said "Anyway, not trying to boast here, as my dyno sheet would read maybe 29 horsepower on a good day." Tsflstb how did you come up with 29hp?
       Has anyone had there 400 dynoed? Stock? Modified? I think that the CB400F predated motorcycle magizens using dyno in there road tests. But maybe one did dyno one?
          TomC

[Lumbee]

...I seem to recall Hondaman making the argument one time that pound for pound the 400 has the greatest power to weight ratio...

[GroovieGhoulie]

37-38hp at the crank.  Bear in mind, that's with a new engine in perfect tune.   Most of ours are probably making a bit to a lot less.

392 pounds wet and ready to ride makes for 10.3 to 10.6 pounds per horsepower.

The 500/550 weighing a reputed 460 pounds with 50 hp gives 9.2 pounds per hp and the mighty 750 with it's 500 pounds of fun (give or take) and 67 hp gives 7.46 pounds per hp.

It seems the 750 is power:weight king with the 400 falling behind even the tuned-for-touring 500/550.

[Lumbee]

...I stand corrected Groovie...   

[GroovieGhoulie]

...I stand corrected Groovie...   

No biggie.  As a 400F Cultist, I'm a bit saddened by the numbers, but oh well, the 400 is the most fun to ride!

[tsflstb]

I just kind of pulled that number from my rectum as I do most of my facts.

Figured high 30's at the crank minus 10% driveline loss minus a few more HP for being a bit worn and not in a perfect state of tune.

[crazypj]

chuck a 500 kit in it and have fun.
The 750 is too wide and wears away the alternator cover.
 modded 550 is best
PJ

[aptech77]

Well,
 My 400F has had "some" work. I fig about 55HP@320(ish) LBS. That makes it 5.8LBS/HP..........

[DammitDan]

chuck a 500 kit in it and have fun.
The 750 is too wide and wears away the alternator cover.
 modded 550 is best
PJ

Everyone forgets the venerable and red-headed CB650 though... Best balance between the 750 and 550.  Mostly because it's the middle number between the two 

The CB650 ('79-'82) made 63HP @ 9k RPM, 485lb wet weight.

That gives it a ratio of 7.69 lb per HP 

[Pinhead]

Everyone forgets the venerable and red-headed CB650 though...

Why is that?? Best hp:weight ratio, best fuel economy, best suspension, best stock engine, best ignition, strongest alternator, and smartest drivers!! Why do we keep getting forgotten??

[eldar]

Hey you guys get forgotten, us 78 riders are ridiculed! 

[cb650]

The CB650 ('79-'82) made 63HP @ 9k RPM, 485lb wet weight.

That gives it a ratio of 7.69 lb per HP 

That was a factory rating and maybe a little much.       



                              Terry

[c_kyle]

The CB650 ('79-'82) made 63HP @ 9k RPM, 485lb wet weight.

That gives it a ratio of 7.69 lb per HP 

That was a factory rating and maybe a little much.       



                              Terry

Yeah, but it sounds good.

[cb650]

Yea so did the blond at the bar the other nite until she wanted money!

One of my friends that has a shop now has a dyno.  Maybe take the 650 over and see what it does one of these days.




                                                   Terry

[Kevin400F]

Going back to the original question, my stock '75 400F pulled 30.5 hp at the rear wheel on Honda of Houston's dyno.

[Sam Green Racing]

Going back to the original question, my stock '75 400F pulled 30.5 hp at the rear wheel on Honda of Houston's dyno.

That sounds about right Kev for a stocker. 

The CR750 with the stock motor puts out 60bhp at the wheel, it weighs in at 396lb, giving 6.6lb for each bhp to haul around.

The new 836 mildley tuned motor we are hopeing for 80bhp should give about 4.9 to pull.

But my none ohc single RS175 tops the lot, the 42bhp motor has just 154lbs to pull giveing 3.66.

Sam. 

[aptech77]

Going back to the original question, my stock '75 400F pulled 30.5 hp at the rear wheel on Honda of Houston's dyno.

Sounds a bit low. HP loss should be around 10%.....right? Thats almost 20%. I would have expected something around 34/35HPRW.......

[tsflstb]

Honda of Houston (at least the new location) has a Dynojet 250i eddy current dyno.  I've read where HP numbers from those aren't typically as optimistic as the older types, but probably more accurate. 

We are pretty much at sea level, so that would boost the number if you're jetted accordingly.  What was the ambient temp when you had it done?  The air gets pretty hot and chewy in the summer time though...lots of factors go into that number...but 30 HP sounds pretty good.

[wardmoto]

10 % drive train loss is a stretch at best.  15-17% is realistic.  A crap rusty chain will soak up 2-3 hp.  When you start with 32 hp (bhp @ crank, according to Honda ona 350F)..that crap chain is 6-9% of your loss of hp!!!!!!

[heffay]

stock... yeah, hp loss will prob' be more than 10%
the more they get modded (for performance obviously) though, the less hp's they're gonna lose.  that'll bring that number a few percentage points down and more.

[Einyodeler]

But my none ohc single RS175 tops the lot, the 42bhp motor has just 154lbs to pull giveing 3.66.

Sam. 

Who says bigger is badder  

[Sam Green Racing]

It's little and wicked Steph. 

Sam.

[wardmoto]

More hp will lower the percentage of loss when compared to overall hp, but will not effect the actual calculable  loss.  Friction is friction regardless how hard you turn the parts...reduce the friction AND increase the hp.....AHH!!!!  Now we are talking.  And, on such a small bhp producing machine (stock), what better way to gain hp!!!  A new or well loved chain that can net you 5 or 6%hp!?!?!?! How easy is that?  Attack the motor for 5-6% increase and I bet you spend more money!  In the states (Carlisle PA) I cannot tell you how many bikes go by with screaming chains because they are bone dry!

[crazypj]

Post your dyno readout. should have A/F ratios as well so you can see where things are going wrong (if at all)
I picked up an extra 2.5 HP on Yamaha XS650 just by dropping needles (44.5 rwhp, up from 41.96hp) Still jetted slightly rich but didn't have half size I needed
30hp is a bit disappointing for a 400F as  a nearly stock  1970 CB350 Twin put out 34 bhp (changed carbs and pipes)
PJ

[Terry in Australia]

I always preferred the CB350F to the 400F, the 400 was always too "slab sided" for me, but I know how popular they are here, particularly with people of smaller physical stature. 30 BHP at the rear wheel seems about right, and while I could see maybe an increase of 25% with a lot of work, 50+ rear wheel BHP without some major engineering changes is doubtful, in the extreme.

By comparison, check the specs below for Honda's latest high tech "tiddler", with all the 21's century tech, it still only produces a couple more HP than the claimed BHP for a 400F from 30 years ago:

Model: Honda CBR250RR
Engine: 4-cyl, 4-valve, liquid-cooled, 4-stroke
Comp: 11.5:1
Power: 40ps @14,500rpm (claimed)
Torque: 2.4kg-m @11,500rpm (claimed)
Weight: 158k dry (348 pounds)
Wheelbase: 1345mm
Front tyre: 110/70-17
Rear tyre: 140/60-17
Fuel tank: 13lt
Top speed: 165kmh (100 Mph)

The biggest problem with both bikes, (the 350F and 400F) is that due to the 4 tiny pistons hanging off 4 tiny conrods attached to a longish crankshaft etc,etc, there is a lot of metal in them, and as someone has already said here, the 350 twin (which was only ever meant to be a cheap and cheerful commuter with no sporting aspirations) was quicker, and capable of better lean angles due to it's narrower crankcases.

Once again, on smaller bikes, weight is everything, so a skinny jockey sized guy on a 400F would probably keep a big fat bloke on a 750 honest, but seeings how I'm more of the latter than the former, I'll stick with my 750's. Cheers, Terry.