56 cubic inch engines

[Eric Bryant]

> From: Dave Edge [mailto:edgedj at yahoo.com]
> Subject: RE: 56 cubic inch engines
> 
> hmm, I think I'll get away with one of the issues you
> hit - induction. I've got a 32mm throttle plate and
> original (fairly) small bore inlets. Reason being that
> I'm bunging a turbo on this thing so I should get good
> mixing and the ram of the turbo should make up for the
> small throttle plate etc. - I hope!
> 

Well, if nothing else, the small TB will give decent part-throttle tip-in
response.  The big TBs on my bike open too quickly, and it's difficult to
get back on the gas after a low-speed corner without commanding too much
throttle opening.  

Seems like a 32 mm throttle body might be just a bit on the small size,
though.  My old Honda VF1000R had a pretty mild 1000cc motor (by bike
standards - it still managed 105 RWHP), and that had (4) 36 mm carburetors.
Modern 600 cc bikes run carbs at least that big.   Then again, it's a bit
more critical for NA applications. 


> Re injector sizing - aarrrgh, that's my main worry.
> I'm running the injectors from a Ford Fiesta xr2i (UK
> car) which had a 1.6 engine capable of about 120 bhp.
> "Oh, but that's way too big for your 930cc imp engine"
> I hear you all say. I hope not, afterall what can I do
> when I want 120 bhp with the turbo attached. 
> 

Well, considering that my bike produces 125 HP from only two injectors (if
Suzuki's service manual is to be believed, my bike runs only one set of
injectors at WOT), it's probably got injectors that one would consider to be
"too big" - they're probably in the 30-40 lb/hr range. 

> On the plus side, there is a vacuum/boost sensor of
> the fuel reg so the fuelling should go down at idle.
> How about extending that theory and providing an extra
> bleed valve to relieve more pressure in the fuel rail
> when the throttle plate is closed? sounds a bit rough
> and ready to me, anybody think it might work?

Personally, I'd avoid doing anything with the fuel pressure except
referencing it to the manifold vacuum.  But, if it comes down to it, maybe
dropping the FP at idle will be required for your motor.

Eric Bryant
mailto:bryante at ghsp.com
http://www.bryantperformance.com  
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