Triumphrat

BLS

So we post at great length about intake and exhaust modifications. I don't recall seeing much of anything about compression. The stock compression is fairly low (9.2 if I recall correctly). I know the big bore kits up the compression some, but what if you don't want to go that whole route. Anybody making high compression pistons at the stock bore (I've got an 01 w/ the 790). :hammer: :hammer: :hammer:

ohiorider

Yeah, I've had similar thoughts. Once the intake is made as unrestricted as possible, the correct pipes are installed, and it's jetted properly, aside from a big bore kit, there's only a few things left. One would be to raise the compression, probably conservatively, since I don't think the Bonnie has any kind of knock sensor to retard ignition timing. A change to higher test fuel would probably be mandatory.

The other would be to replace the cams with something a little more aggressive than the stock camshafts. I'm not a cam expert by any stretch of the imagination, but the Bonnie's cam specs look conservative even when compared with the W650. For example, the W intake opens sooner and stays open longer (duration) than the Bonnie's. The same holds true for the exhaust duration.

Perhaps the folks on this site who are working on hotter cams could speak to this.

The Bonneville engine certainly has the makings of a little powerhouse .... short stroke, large bore, dual overhead camshafts, dual carbs. Probably a slight increase in compression and wilder cams (plus appropriate carburation) would make the Bonnie a bit more powerful at the top end, perhaps at the expense of an engine that is currently flexible thru the rpm range. Again, I'm only documenting my thoughts. Maybe our resident experts can address this.

Maybe our member from Switzerland has the right idea ... turbo it. i've known guys who've turbo'd their BMW K bikes, kept the boost mild, the innards of the engine stock, and achieved a reliable 20-25% increase in power. Others were more aggressive.

- Bob -

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2003 T100 (790cc) Lucifer Org and Silv: 122/42 jets, TORs, 17T, UNI filter, no AI, Polaris bellmouth, Metzeler ME880 tires, Progressive 440 shocks (105/150 springs),11-1126 fork springs, gaiters, MotoTwin low bars, 6024 lamp, htd grips, 12v outlet.

widowmaker

Gentleman, our 904 bog bore is a 11 to 1 compression. I had a dealer up north dyno a 790 bonnie at 51 HP and when he did my pipes,airbox removal kit, and 904 big bore and got 72.8 at the rear wheel, ive got the dyno chart if you want to see it.... email me for details

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ohiorider

That's impressive! Makes me want to find an older Bonnie project bike and get out the wrenches. At a guess, how much of the 20+ hp would you attribute to the 114cc displacement increase and how much to the other modifications, like increased compression ratio? I guess what I'm asking is sort of the same question BLS asked, which was what kind of increase could you expect if you raised the compression while retaining stock (790cc) displacement?

- Bob -

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2003 T100 (790cc) Lucifer Org and Silv: 122/42 jets, TORs, 17T, UNI filter, no AI, Polaris bellmouth, Metzeler ME880 tires, Progressive 440 shocks (105/150 springs),11-1126 fork springs, gaiters, MotoTwin low bars, 6024 lamp, htd grips, 12v outlet.

ohiorider

That's impressive! Makes me want to find an older Bonnie project bike and get out the wrenches. At a guess, how much of the 20+ hp would you attribute to the 114cc displacement increase and how much to the other modifications, like increased compression ratio? I guess what I'm asking is sort of the same question BLS asked, which was what kind of increase could you expect if you raised the compression while retaining stock (790cc) displacement?

- Bob -

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2003 T100 (790cc) Lucifer Org and Silv: 122/42 jets, TORs, 17T, UNI filter, no AI, Polaris bellmouth, Metzeler ME880 tires, Progressive 440 shocks (105/150 springs),11-1126 fork springs, gaiters, MotoTwin low bars, 6024 lamp, htd grips, 12v outlet.

RedBird

For comparison: My 790cc with stock compression and NH Togas, Airbox removed dynoed at a little over 66 hp. I believe Tommyturbo got a little over 68 hp on his 790cc with similar setup. My guess would be that more of the 4--6 hp difference is due to compression ratio increase than the small increase in displacement. I believe the larger displacement will show up more in the torque values than in the hp values, and you will feel the torque values more in your "seat of the pants" dyno. :-D

Larry

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Larry
2003 T-100 (790cc), NARK, NH Togas, 8100 rpm rev limiter, 158 main jets, 42 pilot jets (less than 1 turn out on pilot screws), stock needles--no shims. 13 A/F ratio from 1100 rpm to 4000 rpm; 12 A/F ratio from 4000 rpm to 6000 rpm; 13 A/F from 6000 rpm to 8100 rpm.:D
2007 Tiger 1050--White:D--SW-Motech crashbars, Skidmarx rear hugger/chain guard, Calsci +7 windscreen.

BLS

So I know just enough to be dangerous but what the.....
I am thinking that the intake and exhuast improvements will primarily show up as improvements to high end hp. Camshaft changeout will likely be the same. Increased compression, say up to 11:1 like the big bore kit will not only help top end hp, but, with keeping the stock rather mild cams, improve mid-range tourque as much or more (relatively speaking).

But I was a liberal arts major, so I could just be making it up.

Roadglide

Volumetric efficiency is the key.