MicroSquirt.com read only forum (Jan.15,2018)

I'm working on collecting all the parts and I bought a set of throttle bodies and now I'm not sure I made a good choice.

I bought a full set from an 01 GSXR1000
They are sitting on the desk next to me and MAN...they look pretty big!
The GSXR redline is about 35% higher than the engine I'm working on.

Whereas the GSXR 750 (less displacement) but still 30% higher redline calculates at redline to move approx the same volume of air as my engine and the horsepower should be similar.

I'm fairly convinced I should downsize my throttle bodies to the 750 version to more closely match my engine??
I assume this would give me better low end performance and ride-ability?

Anyone have any experience with this dilemna?

Also the GSXR has a second set of butterflies to restrict air flow at low rpm (at least that's what I've been told)....is there an easy way to control the position of these with the microsquirt?

THANKS!

If your throttle bodies are for the FZR1000, then for a point of reference, the EFI detuned version (my GTS1000) has 34mm ventures. IIRC, the Thunderace & FZR1000 had 38mm, and I seem to remember an engine tuner that worked with Yamaha on the Superbike series who used 39mm flatslides. So a quick ball park would be compare the venturi sizes of your 750 to 1000 bodies. Generally throttle bodies are much bigger now compared to your pre 1990, but then there power output are much higher too.

FWIW, I would think the 750 ones would be adequate for your stock FZR1000 lump.

EDIT Grammar

GSXR 1000 K1 - K3 and GSXR 750 K1 - K3 have the same throttle bodies.

GSXR TB specs:

750 & 1000 from 2000-2003

750 & 1000 are essentially the same

80mm spacing between bore centres

270cc/m injectors

48mm ID, 54mm OD at inlet

42mm ID, 48mm OD at exit


600 from 2000-2003

As the 750 & 1000 except for:

230cc/m injectors

44mm ID, 50mm OD at inlet

38mm ID, 44mm OD at exit



Maybe you should consider the GSXR600 TBs

tubular wrote:...Maybe you should consider the GSXR600 TBs

Agreed.

Thanks for the specs Tubular...
The injector rate is a big help!

BUT you confused me the way you answered with comparison.

OH>>> Nevermind. I understand now! You list ID first and then OD of the bore....long day.

So, the 1000 and 750 bodies are identical...hmmm
and the 600 drops by 4 mm but the 600 only made 115 hp and the FZR1000 carb version made about 140 hp so I'm thinking the 600 TB would be on their very top end and most likely restrict the HP on my project.

Your information was EXTREMELY helpful!!!!
That would have been a big waste if I had bought the 750 TB and sold the 1000TB only to find out they are virtually the same anyway! I guess these TB on the 1000 is probably on the very max of their output and on the 750 they are on the low end.

SInce you certainly seem to know your way around these bodies, how critical is the second set of butterflies to performance. My set has the disks removed so someone apparently didn't like them. The positioner is still there but Matt (DIYautotune) indicated there wasn't an easy way to control them with the microsquirt. I figured I'd just ignore them for the moment.
And WHY were there two cable hook ups for the throttle? AN auto idle control maybe?

***EDIT** Dang...I just saw the top post in this sub forum and it lists all the sizes I was looking for. NOW I feel really silly

Designer_Mike wrote:...and the 600 drops by 4 mm but the 600 only made 115 hp and the FZR1000 carb version made about 140 hp so I'm thinking the 600 TB would be on their very top end and most likely restrict the HP on my project.

Never mind the horsepower, think of the airflow. What does your bike rev to, no more than 11000, and the 600 must be upwards of 14K, so it's a lot closer than you think. Then there is the restrictions within your standard carb set up, as in the venturi ones, the extra lumps of brass etc that you don't get with the injector set ups which translate to a bigger effective diameter.

Then go back to the horsepower, 34mm on my GTS gives me 118 at the rear wheel with no air box, your carbed FZR1000 in it's prime would only give 125 max and thats with better cams than mine, so the horsepower argument is diminishing. Secondly, a standard GTS1000 has 92 rwhp, and even with no cat etc produces just 100 rwhp, the biggest restriction is the air box and the long inlets. Thirdly, the 39mm flat slides gave 168 at the gearbox sprocket for an 888cc FZR1000 derived lump which hit 14K. Lastly the secondary chokes are used to help tractability with larger diameter throttle bodies (for high revving hp producing lumps), because if a rider gives the bike a fistful in too high a gear the engine baulks, so to sweeten the response the secondary chokes stay closed/open slightly to compensate and then open as the engine/ECU demands, all the time the hapless one is pinning his wrist to the stop. Nearly all race bikes junk this set up.

Conclusion, the 600s will be big enough, they will result in shorter inlet tract lengths and the restrictions will be elsewhere (air box/exhaust).

PS I am curious as to how you are planning to trigger the MicroSquirt on your bike if it is a stock FZR1000 with the B&G code, unless you are triggering off the coils/TCI unit.

I plan on a skip tooth 24 tooth (maybe 12) with a Hall sensor on the crank where the existing pick-ups used to be.
Drop the TCI completely (just to make it more challenging)

The 600 TB would be a bit easier to fit...and I'm more interested in lower rpm response along with the more casual rideability.

Damn you!....I thought I had made up my mind

24c nailed it down. I just might add that the GSXR TBs are tappered. For the GSXR600 the air intake is 42mm (ID) and tappers down to 38mm (ID). To put it simply, strange things will happen inside the TB with air flow and velocity. Maybe this compensates for bigger diameter TBs. Think the R&D dep at Suzuki has a good reason to do so.

The fact remains that these TB setups -both 600 and 750/1000- are designed for the specific Suzuki GSXR engines. So in reality neither is a perfect match for your -or any- efi conversion project. The 600 TB will much likely be more easier to install physically on your engine and more flexible at the later stage of tuning.

However, since you are in for challenges then I propose that you stick with what you allready have on your bench. At least I would choose to go that way. Think it is more fun to spend time try to tune the engine than trying to buy and sell stuff on ebay. But this is entirelly up to you...

Regarding the two cable hookups. It is a push-pull throttle arrangement, nothing to do with idle control.

OK.....FINE. I'll buy a 600 throttle body set up.

I know you guys are probably right.
Most likely what will happen is I will buy a 600 throttle body and the 1000 will sit on my shelf right next to a bunch of other parts I bought for this project and won't use.

Anyone got a set of throttle bodies to trade

**EDIT** now I'm really starting to hate you guys...the 600 fuel rail is not nearly as easy to modify as the 750/1000

Adds to the challenge I guess

The GSXR TBs are quite handy because they can be separated and respaced to fit the engine. However the fuel rail will need to be modified in 99% of the cases. Fuel rail is a critical part of the setup regarding project success and most important SAFETY. I suppose you don't want to be riding a flamethrower, so you need to fabricate or get somehow an exact suitable piece.

If the K1 gixxer 1000 TBs you have now are fitted with the modular fuel rail, then you could use this bits to fabricate a suitable fuel rail.
Check this: http://www.locostbuilders.co.uk/forum/4 ... tid=161445

it may give you a lead.

Good luck