By Group K Technicians
The hull and driveline combination of the Blaster 2 boat is unlike any other high performance pwc to date. The apparent design intention was to make a pwc whose forte was strong low speed acceleration and excellent “lean in” turning abilities. In these regards, the Blaster 2 is a big success. The short, nose heavy, hull design allows for very aggressive and controllable “lean in” turning. However boats that turn in this way put a heavy load on the engine and driveline.
Aggressive turning causes a huge increase in the amount of water contact surface area (compared to the water contact of straight line riding). A tremendous amount of thrust is needed to drive a hull like this through, and out of, deep angled turns. To provide this needed thrust, Yamaha mounted the 155mm 1100/1200 pump behind a 753cc twin with dual 44 carbs. Even with this large displacement and big carbs, it’s everything this motor can do to turn the relatively large diameter impeller in this pump. To help with this task, the exhaust system of the B2 is designed to make the most of bottom end and mid range power. Yamaha decided that this low range power was so essential to the Blaster 2, that they knowingly made some significant concessions in high rpm horsepower. Besides, the job of pursuing higher peak water speeds with the B2 hull would have been made additionally difficult by the nose heavy high speed tendencies (unlike other pwc’s that have little or no nose contact a higher speeds).
While the large 44 mm Mikuni carbs allow the Blaster 2 to accelerate with great authority, they also consume gasoline at a rapid rate. This is not a big deal for riders interested exclusively in hard turning. However, it does become a problem for riders who need to cover a significant distance to get to their favorite ride area.
The main performance priorities of the B2 owners that contacted us were:
- Increase peak water speed, and
- Improve fuel range. More importantly these owners wanted significant improvements in these areas, without causing “any” losses in acceleration rate or turning ability.
While the stock B2 has outstanding turning and acceleration abilities, the total package has many traits that keep it from being a serious contender in any sort of IJSBA style competition. Given this, we found very few B2 owners that were willing to run the expensive $5 per gallon race gas to get a little more power. In short, most B2 owners wanted their modified machines to remain compatible with 92 octane pump gas. Our B2 Sleeper kit modifications have been focused to meet these afore mentioned needs and priorities. During the course of our testing, we found some other combinations that had some exceptional merits, but came along with slight compromises. The performance numbers of all these combinations are as follows :
- Impeller Exhaust Pipe Peak RPM Peak Speed (200 lb rider)
- Stock B2 Stock Stock 6420 – 6450 46.4 mph
- Sleeper B2 Stock Stock 6720 – 6750 52.2 mph (no compromises)
- Sleeper B2 Solas “S” Stock 6460 – 6490 52.3 mph (slight low end loss)
- Sleeper B2 Stock Pro Tec 6920 – 6940 54.5 mph (Requires 105 octane)
Package / Upgrade / Parts
Group K Price
BLASTER 2 “SLEEPER” ENGINE KIT
Includes cylinder porting and decking, cylinder head modifications cooling system upgrade, primer kit, and carb jetting. (send the cylinder head, cylinder, & carbs)
Recommended bolt on parts to accompany the SLEEPER kit
Group K Price
Boyesen Reed Stuffers
R&D Flame Arrestor
Ride Plate Pro Tec
Other Useful Modifications
Group K Price
Pump Blueprinting (send vain case and impeller housing)
Jet Dynamics Ride Plate
Scoop Grate Modification
Solas “S” Pitch Impeller
ProTec Exhaust Pipe
Call for Price
Top End Modification – All Group K kits include cylinder porting. In the past, cylinder porting has received an undeserved reputation as a modification that causes a loss of reliability and engine life. If the porting is performed by someone with very little Yamaha experience, that may be true. The porting mods used in all of our kits are the result of many months of performance and wear evaluation testing. We confidently claim that Group K cylinder porting will yield a wider power band and longer piston life than any other porting modification available anywhere. All Group K modified cylinders and heads are typically prepared as matched pairs to assure that you have the proper squish clearance and compression ratio for the quality of gasoline that you intend to use. These cylinder and head specifications play the key role in determining the amount of overall power that the engine can make as well as the quality of fuel that you must use.
During testing, we found that more radical porting specs could sometimes offer a slight improvement in peak water speeds, however the low end power delivery was seriously hurt. For our kits we always choose the port layout that offers the strongest possible acceleration along with good peak speed ability. We believe a tiny increase in peak speed is not worth any loss of acceleration or reliability.
Ignition – We consider the ignition system of the B2 to be of primary importance because it’s the first twin cylinder pwc to have different ignition curves for both cylinders. This is done to offer a more retarded timing for the rear cylinder (for more info on this, see our website document “Rear Piston Seizures”). This retarded timing, for the rear cylinder, helps to keep the operating temperatures of both cylinders more symmetrical when the drive live is heavily loaded. We found no advantages to changing these timing curves. Furthermore, the B2 driveline does not seem to respond well to being “revved” beyond the abilities of the stock limiter (about 7100 rpm). All of our modification sets retained the stock ignition curve and rev limiter.
Inlet System – In the past, we have not recommended dual 44mm Mikuni carbs for any of our Yamaha 633/685/701/753/781cc twin cylinder formats. We felt that the available dual 44 aftermarket systems lacked the inlet tract air speed and precise metering to be significantly better than other smaller throat systems. We still feel that way. However the design, and excellent metering, of the dual 44 Mikuni’s on the B2 are unmatched by any aftermarket arrangement we have seen. We still consider the 44 throats to be more than this particular engine arrangement needs, but their performance is great none the less. The inlet tract air speed (and authority of acceleration) of these dual 44 carbs can be slightly improved with the use of the aluminum Boyesen reed cage stuffers, and the R&D “Plenum” type flame arrestor. We recommend these two bolt on parts for every modification level of the B2. During all our tests, we used the stock reed cages and petals. These stock parts offered good performance along with excellent long term wear.
We consider the installation of larger carbs on this machine to be unwarranted and unwise. Larger carbs would not benefit the overall acceleration, but they would certainly harm the fuel range.
Exhaust System – While the stock exhaust system does have it’s high rpm limitations, it provides a very wide and strong powerband. Of all the aftermarket exhaust system modifications we tested on the Sleeper, we had the best performance results with the Pro Tec system. It turned the engine about 150rpm over our best stock piped combination. However the installation of this pipe, on our Sleeper equipped B2, resulted in an unexpected side effect.
The Pro Tec piped Sleeper could run full throttle all day long on 92 octane pump gas. However as soon as we backed off the rpm to 6100 – 6300, the engine would only run a few moments before scoring a piston. We immediately assumed that we would be able to fix the problem by richening up the (pilot jet) mid range fuel mixture. By the time we had gotten rich enough to abate the temperature problem, we had caused an unacceptable low speed carburetion “stumble”. After many weeks of testing with different combinations, we found ourselves backed into a technical corner. Anything we did that resolved the mid range overheating, would in some way harm the perfect low speed acceleration that owners mandated. At any point in the testing, we were able to immediately solve the temperature problem by running 105 race fuel. However, as we mentioned earlier, most of our recreational customers consider the cost of race gas to be prohibitive. Unfortunately we do not yet have any other better solutions.
We don’t believe that the design of the Pro Tec pipe, itself, is to blame for our temperature difficulties. However the combination of that pipe with our Sleeper modifications has (for the meantime) created a problem we can’t solve with 92 octane fuel. For the B2 owners who want a pipe to let their boat to deliver the “maximum”…race gas will be the order of the day.
We recommend that a stock waterbox silencer be used on all Sleeper kits. Contrary to common belief, the stock Yamaha waterbox yields excellent overall power levels in all high output applications. Unlike most after market waterboxes, the stock waterboxes can offer quiet sound levels along with strong power when water is diverted away (water diverters are a part of every Group K engine kit).
Pump – The large 155mm diameter pump used in the B2 is, in large part, responsible for the terrific low speed acceleration of this machine. This pump loads the engine “hard” at all rpms and all water speeds. Because of this heavy loading, the slightest compromise in bottom end, or mid range power, resulted in a very noticeable weakness in acceleration. On most other machines, this issue is easily dealt with by fitting a slightly lower pitched prop. Unfortunately, this is not an option for B2 owners. The stock B2 prop is a much milder pitch than the stock impeller used in the 1100 Raiders. Nearly all the aftermarket props for this 155mm pump are made to a steeper pitch than the 1100 prop. The only exception is the Solas “S” prop, which is a slightly lower pitch than the stock 1100 Raider. However, even this “S” prop is much steeper than the stock B2 prop. The Sleeper pulls the “S” fine in the middle and upper ranges. But there is no denying that it also causes a momentary (yet always there) hesitation right off idle. The “S” prop would be a great choice for B2 owners that were interested in increased fuel range at cruising speeds, but we acknowledge that few B2 owners do a lot of “long distance cruising”.
Pump blueprinting offers much better “hook up” in rough water conditions and is an important asset to machines that will be run hard in rough water conditions. If your machine will be operated primarily on smooth water, the blueprinting will offer little improvement for the money spent.
Plates and Grates – When ridden at full speed, on glass water, the B2 “Sleeper” has a tendency to be a little unstable because the front heavy hull is “steering on the nose”. We found two good ride plate options for the B2 that resolve this problem. The best “all around” plate is the Pro Tec. This plate offers great turning and stability, along with a flat water increase of 1 mph. This speed increase comes as a result of the nose being lifted slightly out of the water at high speeds.
The other option is a “shimmed” Jet Dynamics Blaster 1 ride plate. Bolting this plate on to the B2 with no shimming results in uncontrollable proposing. However with some 2mm shims between the hull and the rear mounting faces of the plate, the porpoising is virtually eliminated. While you may still experience some slight nose bounce at peak speed with this plate, it’s still about 1 mph faster than the Pro Tec plate (again a result of the nose being lifted higher yet off the water). For owners that don’t mind fiddling with shims to get the perfect ride, the Jet Dynamics offers the most potential. For owners that just want to “bolt it on and go”, the Pro Tec plate is the one.
The Sleeper B2 hooks up so well that we never felt the need for a top loader type scoop grate. We removed the two center bars from the stock grate and got all the hook up our test rider wanted.
Assembly Information – All Group K kits are accompanied by a step by step instruction pamphlet that outlines the assembly, break-in, fine tuning, and maintenance of your kit. For any further questions you may have regarding your Sleeper kit, you’re welcome to contact us directly for assistance.
Reliability – With the oil injection premix, or a 40:1 mix ratio of Maxima Super M, a crankshaft can be expected to last approximately 300 hours. For the higher revving 105 octane engines, the piston rings should be replaced no less than every 80 operating hours and the pistons every 160 hours. The 105 octane kit can not, and should not, be operated at high rpm’s on pump gasoline’s. In like, the 92 octane kits should never be run on 87 or 89 octane regulars.
ORDER INFORMATION: SEND ALL PARTS REQUIRED FOR MODIFICATION VIA UPS TO:
GROUP K • 4597 CALLE DEL MEDIA • FORT MOHAVE, AZ. 86426 • (928) 763-7600
GETTING THE WORK DONE – Most customers send GROUP K the parts needed for modification via UPS, and then do the engine assembly work themselves. We also do complete engine and pump assemblies for customers who want a finished unit ready for installation. The 150-lb. UPS weight limit makes engine shipping practical and affordable. NOTE: Group K will bill an additional $25.00 handling charge for complete engine assemblies. All orders prepaid with a cashiers check or money order will be returned freight free via ups ground service anywhere in the continental United States. All other orders will be billed to a visa/master card or sent freight collect cod cash. If you would like to pay additional for 3 day, 2 day, or 1 day return shipment, please specify your preference in a cover letter with your parts. Be sure to include your return address and day phone information in case we have any questions regarding your order. PACK YOUR PARTS CAREFULLY !!