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If the bike puts out 130HP, then that's the most you can expect from a B20.
Are the carbies you have Mikuni BDSR40? If so, they are CV carbies just like SU's only smaller. Probably the best carb for one throat/cylinder operation these days is the flat slide Mikunis, but they are as expensive as Webers. VPD sells them to run on the Volvo SU manifold, but the problem with that is you are still stuck with the crappy 180 degree manifold. Both Webers & Mukinis need to run on an independent runner manifold to actually get tuned ram effect.
MegaSquirt with the D-Jet manifold: the problem with that is the manifold is sub par. It's a lot better than the SU manifold, but doesn't give the torque of an independent runner because it uses late '60's tuning formulas. It either needs to have shorter runner to tune to the 3rd harmonic for a very strong top end race only engine, or it needs to be longer & a little smaller in runner diameter to tune to the 2nd harmonic for a street/race engine.
What the go with your 93mm B21 pistons? Can you swap them for 92mm pistons? Can you get a refund or a credit & then buy custom pistons? You absolutely need a very good block AND 46mm inlet valves to make use of the bore. 93mm bore is a feeble 2% bigger in capacity than 92mm pistons, at most you get 2% more torque & without big intake valves & A LOT of very good porting, you won't get a single extra horsepower. Now compare 92mm to 90.5mm. That is only 3.3% bigger + you are forced to use Cometic or Custom headgaskets which is just a major PITA.
What sort of SU's have you got? HS6 limit your horspower a lot, but you can build a torquey & economical engine with them. HIF6 flow 14% more air which gives you a similar boost in power provided the head is good without loss of part throttle economy & they handle a lot better. HS6 & HD8's are a bit problematic when you toss them in to corners, but the HIF's with central float bowl are a big leap forward when tossing your car around corners.
What's your budget? Have you contacted Volpro for a price on a good head? You want to spend a great deal of money on the head because that's wear the power (& bonus extra fuel economy) is found.
What do you have for a gearbox?
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Three 164's, Two 144's, One 142 & a partridge in a pear tree.
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