Small Block Power Delivery

[GonzoB]

I've recently acquired a 07 Breva 750. My first one of these. Recent previous bikes have included 3 Harleys (Sportster, Dyna, Road King), Suzi 800 cruiser, and my most recent a CTX700 Honda. All of these have been vee-twins (yes, the Honda was a parallel twin, but it had a 270 degree crank, so I'm counting it)

The point I want to raise here is that the power delivery on the Breva is very different to the other twins. I find it so much more impulsive, as if the flywheel were much smaller. I can feel every power impulse as I accelerate. The compression ratio is comparable with the others, and the state of tune is similar. The torque reaction when I blip the throttle is strong, so I assume the flywheel is normal size.

So, am I deceiving myself? Or does the SB have something special?

Gonzo

[oldbike54]

 What RPM range are you operating the engine in . Your engine is a Heron head design , known for producing a nice torque curve , but it still likes to rev .

 Dusty

[Perazzimx14]

Wonder if it the transverse mounting of the motor making it feel different?

Is there something special about small block Guzzi's. There is for some.   

[John A]

When you are rolling across " fly-over " country , if a Guzzi is in good tune, it almost seems like you can hear two engines running together , in  sync perfectly.  Any body else noticed this?  Maybe Im imagining it, I used to be around helicopters a lot. Big blocks anyways, I think small blocks would be the same.

[Kev m]

It's definitely a smaller/lighter flywheel feel than your Harleys.

It tends to want more rpm than a Sporty, which wants more rpm than a BT.

Also if you ever ride a big block Guzzi you'll feel a difference as well. The big block having the feeling of a heavier flywheel.

[GonzoB]

What RPM range are you operating the engine in . Your engine is a Heron head design , known for producing a nice torque curve , but it still likes to rev .

 Dusty

Say 2500 to 4500, once above that it smooths out a lot.

Gonzo

[Kev m]

Say 2500 to 4500, once above that it smooths out a lot.

Gonzo

You're kinda lugging it at the bottom half of that range.

Generally speaking I would expect to be in the 4k+ range on that bike. The newer smallblocks tolerate a little lower, but definitely not in the 2's.

[oldbike54]

Say 2500 to 4500, once above that it smooths out a lot.

Gonzo

 Well ...

You're kinda lugging it at the bottom half of that range.

Generally speaking I would expect to be in the 4k+ range on that bike. The newer smallblocks tolerate a little lower, but definitely not in the 2's.

 What Kev says . It might need a good sync done , but even the SB's like a few RPM's .

 Dusty

[Guido Valvole]

I'm not familiar with the 750 smallblocks, but I have two earlier 500s. There, nobody home under 5000 rpm, especially in 4th or 5th. V50ii with tiny carbs and valves, not much above that either. Monza/V50iii, gets happy above 5500. With 50 percent more displacement, you should have more torque - but still it's a Guzzi and Italian so likes to rev. My Le Mans 1000 is the same way, actually. 5th gear there is useless under about 80 mph.
cr

[LowRyter]

Harleys top out at 5k rpms.

I think that's the answer.

[Kev m]

Harleys top out at 5k rpms.

I think that's the answer.

BT's

But Sportys are 6kish, 7k with a reflash.

Similarly where BTs tend to run 2-3k much of the time Sportys tend to run 3-4k much of the time.

[frozengoose]

The point I want to raise here is that the power delivery on the Breva is very different to the other twins. I find it so much more impulsive, as if the flywheel were much smaller. I can feel every power impulse as I accelerate. The compression ratio is comparable with the others, and the state of tune is similar. The torque reaction when I blip the throttle is strong, so I assume the flywheel is normal size.

So, am I deceiving myself? Or does the SB have something special?
Gonzo

The thing of it is, as they say up here, is that if it hasn't had a recent tune up by somebody who knows what they're doing, it's all speculation. I'm not sure if you like the way it runs or not from your post. If you do, then enjoy, if not, get a tune up. I have a v65 and it runs like an old Triumph 650, lots of low end and then runs out of power at higher rev's. My kind of bike!

[SmithSwede]

You have simply discovered the magic of the Guzzi small block!

They are very eager off the line for such a “small” and lightly tuned engine.  Spunky feeling even at 2,000 to 2,500 rpm. 

Most of the time, though, I run mine no lower than 4,000 rpm.  They like to spin, so let them.  I’m usually surfing the engine between 4,000 and 6,000 rpm.   I routinely cruise at 5,000 to 5,500 rpm on the open road.

There is not much left above 6,500 rpm, so no need to go past that.

[GonzoB]

Thanks for all those thoughts.

To clarify, I probably should have phrased the question something along the lines of..

" In the around town rev range that I regularly used on my previous twins (under 4500) I find the Breva has a more impulsive power delivery. Is that a result of a smaller flywheel, or what?"

It sounds like it may be.

Gonzo

[rocker59]

You're lugging it.  You probably need to drop one gear for everything you're doing. 

Guzzis love to be ridden in the 4,000 to 6,000 rev range when out on the highway.

If you're in town and riding at revs in the 2000s, you need to drop one gear and enjoy the engine's power delivery.

I've owned Sportsters.  Riding around at 1800-2000 is normal.  The Guzzi is tuned to be at home at a much higher rpm.

Guzzis and Ducatis really are a lot different from Harleys.  Short Stroke vs Long Stroke, and other philosophical design differences.

[Kev m]

I've owned Sportsters.  Riding around at 1800-2000 is normal.

I guess things have changed in terms of gearing since you owned a Sportster, cause THAT'S LUGGING IT TOO.

For rubbermount sportys (2004+) and probably most EVO solidmounts (through 2003) you really should be above 3k most of the time.

BT's can run as low as you're saying....

[rocker59]

I guess things have changed in terms of gearing since you owned a Sportster, cause THAT'S LUGGING IT TOO.

For rubbermount sportys (2004+) and probably most EVO solidmounts (through 2003) you really should be above 3k most of the time.

BT's can run as low as you're saying....

I owned a 1974 XLCH in the late 1980s, then a 1994 XLH883 from new.  Things may have changed.

Accelerating away from a stop, I would shift around 3,000 and ride the bike in town in the low 2000s.  I mostly rode around town at that time, as I lived in a sprawling city.  (sucked).

I don't have much time on the rubbermount 2004-up Sportsters, they felt real similar to me, but I'll defer to you on that.

[rocker59]

???!!!???

V7 III Bore 80 mm, stroke 74 mm
883    Bore 76.2 mm, stroke 96.82 mm

Guzzis and Ducatis = Over Square, bore diameter larger than stroke length.

Harleys = Under Square, bore diameter smaller than stroke length.

Big personality difference in the two layouts.

[Kev m]

Guzzis and Ducatis = Over Square, bore diameter larger than stroke length.

Harleys = Under Square, bore diameter smaller than stroke length.

Big personality difference in the two layouts.

I deleted my edit because I realized where you were going.

There's a difference for sure, but in the big picture of engine feel is WAY more similar than dis-similar. But yes, the shorter stroke Guzzis CAN spin a couple thousand rpm more. And the difference in stroke, and engine timing, and flywheel do lead to the differences in feel.


EDIT - of course there are differences in Harleys too - I mean just the classic air-cooled stuff. I guess that's what I'm trying to say.

I find the Sporty is sorta middle-ground between a BT and a Guzzi (small block or big block) and that's what I meant about rpm.

From a very high level / typical running range, much below is lugging depending on conditions/load/gear/etc:

Harley BT - 2-3k
Harley Sporty - 3-5k
Guzzi Smallblock - 3-5k

The difference is that the Sporty runs out of gas sooner if you go beyond that 5k spot... the Sporty is done by 6k, the smallblock Guzzi by 7k.