94mm - 652cc - OEM stock bore diameter
95mm - 666cc - First overbore size
96mm - 680cc - Second overbore size
97mm 0 695cc - Third overbore size.
Beyond 97mm - such as 98mm - requires a larger cylinder sleeve and then there is the issue with the cylinder head to cylinder bore area...you will have the edge of the cylinder head and head gasket slightly protruding into the bore....this creates a hot spot that will cause detonation.....sooo bores larger than 97mm will require a custom head gasket a custom piston and some combustion chamber work by a qualified performance shop to re-shape this area.
Remember MOST of the power increase comes from the compression ratio increase from the stock 8.5/1 to the Wiseco piston's 10.5/1....Is it really worth spending the $$$ on the custom head gasket, 98mm piston and larger 98mm cylinder sleeve and head work for a few more HP than what you get with the readily available 97mm piston?
As far as cylinder head work is concerned the 650 savage has a pretty good intake port only needing some smoothing and carb flange size matching A.K.A. blueprinting.
The 650 Savage exhaust port is very poor....it only flows about 50% of what the intake port does. The stock exhaust port has an ugly, narrow, sharp casting edge where the exhaust gasket is. I open up and smooth out the exhaust port as much as can be done safely without weakening the cylinder head and I match the exhaust port exit to the exhaust pipe gasket to eliminate that turbulence area...
With the cylinder head work and a performance cam & a 38mm Lectron carb (.354) lift my engine pulls strong right up to 8000 RPM...I won't rev it any higher than that.
These engines are so mildly tuned by Suzuki that they respond very well to performance work.
the stock 650 Savage puts down 24 rear wheel HP...with these mods you can increase this to 48 rear wheel HP without too much effort.
1) High compression big bore kit
2) Better flowing exhaust system
3) Better camshaft
4) Improved air flow through the intake & exhaust ports
5) Improved carburetion....you will NEVER get good throttle response
or power from the OEM Mikuni BS40 CV carb.
The BS40 Mikuni carb Suzuki puts on these bikes was originally used by Harley Davidson on their 1980's 1000cc Iron head Sportsters and it is way too large a carb for our 652cc Savage engine.
The formula used by engine builders to determine carb size is available here.....
http://www.csgnetwork.com/cfmcalc.htmlThe stock 652cc Savage engine requires at MOST a 80 CFM carb for a highly modified engine.
The Mikuni BS40 carb that comes on our 650 Savage FLOWS 140 CFM....this is way too much carb for this engine size and results in sluggish engine performance, poor throttle response & poor fuel economy.
Here are some CFM numbers for some popular Mikuni carb sizes ...........
33mm MIKUNI Carburetor 103 CFM
34mm MIKUNI Carburetor 109 CFM
35mm MIKUNI Carburetor 115 CFM
36mm MIKUNI Carburetor 119 CFM
38mm MIKUNI Carburetor 129 CFM
40mm MIKUNI carburetor 140 CFM
The smaller the carb the better the fuel economy, drive-ability, low-mid range torque and throttle response.
The larger the carb the better the high RPM performance.
There is always a trade-off here...you have to determine at what RPM your engine is going to operate MOST OF THE TIME !!
Street engines typically operate between 1500 and 5000 RPM so choose your carb size and engine modifications accordingly.
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