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Discussion Starter #1
looking to acquire a 1st-gen B12 engine and already have plans to turn it into a monster. Here's what I have in mind:
  • Hayabusa pistons and rods, it'll punch out the motor to a 1216cc while being stronger too. I've read that 81mm is the max you can bore the OEM sleeves to before needing new sleeves. I've also read that the 'busa pistons have a lower deck height than the original B12 pistons so to correct this you'd need to run the rods with them. How would I go about selecting the correct bearings? Is it the same process as usual for oilers? That's something I'll have to read up more on
  • 748cc DOT head. Might go towards larger valves, might not. Original intention is to get 38mm carb boots (so I can run 38mm or 40mm carbs) from a newer model and port-match the head as well as some porting for even flow to the valves. Yes I'm aware that the DOT head puts the carbs higher up but it also has the steepest and most straight runners to the intake valves. If I can source a late model 1100 head with 38mm ports and screw adjusters that would probably be better
  • part of the reason to run a DOT head is because they have smaller combustion chambers, which will aid in compression since the 'busa pistons are more "dished out" than the B12 pistons. I need to CC the piston domes and cylinder head to see what kind of squish area and volume I'll be working with, which will determine if I'll run a base gasket or not. I've got an '89 750 intake cam, I'll move the B12 intake cam to the exhaust side and slot the cam gears to properly degree them in. the cylinder block and the head will need to be resurfaced so they can mate with each other, depending on how much material would need to be taken off also depicts this
  • conversion of the diaphragm-style clutch to a coil spring-type. might not be necessary to some, but its for peace-of-mind. This engine once its all done will be making anywhere between 140-150 whp and 85 ft-lbs torque. I'll keep the original 5-speed tranny but might throw in a stiffer detent arm spring
I think the biggest question in the air at the moment is cylinder head options. I could always just get the B12 head flowed and ported, or I could do the same with larger intake boots and carbs, or source a late-model 1100 head that runs 38mm or 40mm carbs, or run a DOT head as-is or with minor port work/cleanup. How much time and money I spend on the head will determine how much power I'll make, but my target is the 140-150 range while spending the least. I think I can get that with a DOT head, they are widely available too which helps
 

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Discussion Starter #4
stock intake valve sizes on these motors are 28.5mm in diameter. doing some quick math, both intake valves combined have an area of 1275.88mm^2. even with 40mm carbs and intake ports, cross sectional area of the port entrance would be 1256.64mm^s. I know that there are many other factors in considering cylinder head airflow and one would be that these are side-draft engines and really most of the fuel/air mixture only contacts roughly half of the valves, which is why bigger is better. but I always thought that overall intake tract area would taper down, certainly an eye-opener
 

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I would wait increasing engine size till after good port job and larger valves is installed. 30/26 is max for the standard seats. Im not sure that it is nesasary to enlarge the exhaust valve but 275£ for a complete set with titanium retainers its probably the way to go. Remember to add gsxr cams or buy race cams for it. My 10 cents
 

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Discussion Starter #6
I would wait increasing engine size till after good port job and larger valves is installed. 30/26 is max for the standard seats. Im not sure that it is nesasary to enlarge the exhaust valve but 275£ for a complete set with titanium retainers its probably the way to go. Remember to add gsxr cams or buy race cams for it. My 10 cents
what would be the point of getting larger valves but not opening up the seats/ports? If I go that route I'll do everything at once and buy different carb boots to run 38 or 40mm carbs and port the head to match. I do plan on running slingshot cams in it, and I'll only do the 1216 with 'busa pistons and rods if the compression isn't very good and/or if the journal bearings need to be replaced
 

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you always do that when you make the new angles. its just the max size the standard seats can be made to suit
 

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abusoracing is probably cheapest and used to have a kit with 30mm intake and 26mm exhaust valves with titanium retainers for 275£. you can check en out on their website
 
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