Best 150-350cc fuel injected engine for small, light, aerodynamic reverse trike

[jkv357]

Originally Posted by P-hack

I'd have a hard time chopping up a cb250r, but no problem with an old $300ish bike. Consider one with a title to make it easier to get a plate.

True. It would have to be crashed or salvage to be worth it.

No CBR125s for us in the U.S.

[ScotD]

Both the Honda Grom (125) and Honda CBR250R could be the good choices for donor machine. Each has advantages and disadvantages; both are fuel injected and electronic ignition. The biggest difference is weight and power. The Grom is 225 lbs curb weight, the 250R about 360 lbs. I’d guess this means my finished trike would be under 300 lbs using the Grom vs. around 435 lbs using the 250R. I weigh about 175 and imagine often having another 25 lbs of baggage (500 vs 635 total weight).

Assume that aerodynamics are the same (same area and drag coefficient) and that they would be driven the same (NOT using the 250’s greater power for faster acceleration or cruising speeds) – what is likely to be the difference in MPG? For highway travel? For around town?

I expect most of my use will be highway, cruising around 55mph – traveling on the 2-lane highways of the less populated west, not freeways. Of course there would also be some use “around town”, though since I live in a town of under 1000 people with no stoplights, that’s not city driving, and generally I prefer to walk or bicycle. I will also use the trike for getting to/from trail heads and around local rural areas some, and, of course, occasionally for getting around a city during a trip.

I imagine I’ll get at least 125 mpg, and hope for much more, but I don’t know enough to be able to evaluate accurately, nor to evaluate the difference likely between 125cc & 250cc approaches.

Input appreciated.

Thanks, Scot

[user removed]

I don't think the Grom would have enough power. The CBR has been around for 3 years now so there will be much more salvage opportunities. If you find the power to be more than adequate then lower the overall final drive ratio.

regards
Mech

[ScotD]

Mech,

Thanks for your posts both to this and my aerodynamics thread. On that one you mention that your trike project is 1100 lbs, so I can easily see that you'd see the Grom as lacking adequate power! Since using a Grom I expect my trike's weight would be under 300 lbs (vs over 400 if using the 250); and since the Grom reviews suggest 60mph stock and my trike would be far better aerodynamically, I think it would have adequate power for my desires and use (though greater power would create additional versatility). Yes, final drive ratio is important . . . and yes, availability of a Grom is problematic.

The California Commuter, built in 1980 and setting world mpg records that year, started with a Honda Super 90 engine, and they got highway speeds and something like 186 mpg. To make it legal on the freeway they had to increase the power, using a stroke kit to bring it up to 130 cc. Though there was no significant weight change, the mpg went down to under 160mpg (they had expected an even greater change).

So since using a CBR250R would result in at least an extra 100 lbs weight, as well as twice the cc's, it seems very likely that mpg would be significantly lower than using a Grom . . .

But the truth is, that for me, this is all speculation - somewhat educated guessing!

Any further input???

[jkv357]

Grom's engine is ancient-tech, air-cooled, and has a 4-speed trans.

Look at the numbers that Ninja 250s have reached in the Vetter competitions and 3-wheel vehicles and compare the Ninja's engine design to the CBRs - the CBR is much better suited for F.E.

[renault_megane_dci]

Your best bet is the smallest displacement, FE and the most gears.
An engine designed for efficiency from low RPM rather than for top end power is also a big plus.
I think the CBR 250 fits in the "designed for efficiency rather then power" cluster (compared to a EX250 for example)
I wouldn't go for a 4 speed engine.

[P-hack]

You need to understand how to title a vehicle too. Even a salvage title in my state can be a PITA, for a few scratches. I bought a salvage bike, once, that was the last time.

Get a clean title, get it in your name, THEN convert it to a trike, and you are probably in business.

Get a salvage title, make a homemade trike, take it to the inspector to get it approved, and you might be pushing it to the junkyard.

An old thumper (with a carb for starters, can retrofit FI later) will get you rolling. 4 speeds would probably be adequate. I was getting like 100mpg on an old cb125 4 speed, carb, unmodified. Plus it was like $300

[renault_megane_dci]

The old thumper would never be watercooled.
I wonder if you can tin weld material to a head in order to water cool it ?

If it is the case then avenues are open.

Aim for the longest stroke it is a mechanical torque booster.

[mechman600]

Originally Posted by renault_megane_dci

The old thumper would never be watercooled.
I wonder if you can tin weld material to a head in order to water cool it ?
If it is the case then avenues are open.
Aim for the longest stroke it is a mechanical torque booster.

I agree, water cooling would be best. Generally, water cooled motorcycle engines have higher CR and thus higher efficiency. But if you are stuck, forced air cooling with small electric fans will work.

[jkv357]

Originally Posted by ScotD

The California Commuter, built in 1980 and setting world mpg records that year, started with a Honda Super 90 engine, and they got highway speeds and something like 186 mpg. To make it legal on the freeway they had to increase the power, using a stroke kit to bring it up to 130 cc. Though there was no significant weight change, the mpg went down to under 160mpg (they had expected an even greater change).

So since using a CBR250R would result in at least an extra 100 lbs weight, as well as twice the cc's, it seems very likely that mpg would be significantly lower than using a Grom . . .

I looked up the California Commuter (The California Commuter - World Record Holding 155 MPG Freeway Legal Car!) and read most of the info, and am surprised they only got 157 mpg on gas. The aero-modded Ninja 250s that Vic and Allan run in the Vetter Challenge are right in that range - even with speeds over 55 mph average and windy conditions.

I didn't see much info about the engine of the California Commuter. I'd like to know what RPMs they were running at 55 mph and at what % of throttle opening.

Here's info from Vetter's site about his competitions in the 80s - 1985 Fuel Economy Contest.

Best numbers were from Matsu Matsuzawa with 440 mpg. This page lists some of his mods - 1985 Matsu talks. In the results it says "Honda XL80", but in that page he says he stroked a 125 up to 185ccs. If Matsu was using 185ccs to get 440 mpg the CBR250's displacement shouldn't be a huge handicap - especially with newer-tech and F.I. in real-world riding where you will need acceleration at times. He also added a neutral available from top gear so he could coats freely - pulse and glide style.

Craig Vetter later commented (here and on his site) that he does not approve of P&G and will not allow it in the current competition.