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Throttle Body Size? Reliant Kitten


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Ok Guy's my kitten is going into a fabricator to have a custom exhaust manifold made and efi plenum made in July. Question is what size throttle to go for. Engine only makes about 35bhp at the mo. The new inlet and exhaust will probably take that out to 40bhp. So it currently uses a hs2 on a crappy manifold so 1 1/4" but when you take into account the venturi its probably about 26mm. I'm planning on using a ATpower throttle body which is used in the Formula student class. Its a 28mm one (19mm restrictor removed) which will flow like a 30mm throttle on top but 28mm at part throttle. I'm not after making more power just to get more mpg but i'm sure more power and torque will result. Getting rid of the dizzy and carb is the goal and maximizing the engines efficiency. Question is will this be too big? or should I go bigger???

 

Fabricator wont know runner lengths or size till he has all the engine dimensions and cam timing etc to put the figures into the computer program. Any thoughts???

 

Chris.

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Unless you are anticipating a wild cam (>280º duration) there is no strong reason to use ITBs and some reasons why not.

 

Bike ITBs, especially those from the smaller displacement superbikes are all too big - even a bit big from Triumph 4s and 6s.  Smaller ones can be found on the big displacement touring oriented bikes (Suzuki GSX1400 = 34mm) which are tuned to grunt rather than scream.  Always bloody expensive though some reason and still too big for the Reliant.

 

I'd think anywhere in the 28 - 35mm range would be fine.

 

Nick

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I'm not after more power Nick so will probably go for the 28mm as I said earlier as it will flow like a 30mm throttle at WOT. Next size up on ATPowers range is a 36mm. I think its too big and didn't want to go ITB's with this car as its just not that kind of car. The fabricator says big improvements will be had as the system will be designed for the engine and the cam it has. Will let you know more when it happens. Once the rear axle is rebuilt and the new doors fitted I'll get the car on the dyno so a before and after can be had.

 

Chris.

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  • 2 weeks later...

Both Rebel racing and Reliant spares I know of, but neither do fuel injection as its not allowed in the race series. Rebel racing have a very good rep for good racing engines and rebuilds but I don't want a race engine or as rebuild. Just the engine I have, more reliable with correct fueling and spark to maximize its potential.

 

Chris.

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  • 10 months later...

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