ianjenn
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| posted on 11/4/11 at 05:53 PM |
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supercharging and carbs
Hi All
Okay so my current engine is a zetec st170 running off bike carbs, think from zx6r or gsxr and the ignition is from a megajolt. In my forever search
for more power I stumbled across info about adding a supercharger. (it already has a 50hp shot of nitrous). So I have fitted an eaton m45 (think it is
?) from a mercedes. At the moment it is still on the same jets as the carbs were set at prior to supercharging.
The fuel is now fed from an MSD 2225 fuel pump to a mallory 4309 fuel regulator (which gives fuel pressure 1psi above boost). The regulator has a line
from the homemade plenum and the carb float bowls are pressurised using an 8mm pitot tube. I have lowered the floats by 1mm and set the baseline fuel
pressure to 2.5psi.
I had my first run out today and was surprised to find that the fuel pressure goes off the scale of my 15psi gauge on acceleration. I was expecting a
boost pressure of around 7psi Is this correct? My return line is 8mm and not restricting things.
Actually after checking I think I have miscalculated my actual boost. The crank pulley is approx 130mm and the supercharger pulley 70mm giving ratio
of 1 - 1.8 so 10-11000 revs of the supercharger at 0.7l per rev. Think that means I will get 12psi boost but I am confused about engine displacement.
Now I'm thinkin I might need an intercooler as the boost is higher than i thought?? and if I do have to fit an intercooler which one is best
there are thousands on ebay!!
I have a rolling road booked in for next week so just wanted your opinion on my set up. Is there anything I have missed? ?intercooler? The engine
seems to over rev at gear change a bit but otherwise runs okay? I have fitted a bypass valve from magnatec to ease the pressure at idle. Any other
suggestions will be most welcome?
Best wishes
alex
[Edited on 11/4/11 by ianjenn]
[Edited on 11/4/11 by ianjenn]
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ChrisL
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| posted on 11/4/11 at 08:22 PM |
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Excuse my naivety but how do you supercharge carbs? I'm guess with an air box but would love to find out more....
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ianjenn
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| posted on 11/4/11 at 08:54 PM |
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well I'm no expert and things could go hideously wrong. After much internet surfing there is loads of info about turbocharging motorbikes and I
have applied the same theory to my car. Using a pitot tube (type into google) I am pressurizing the float bowl so that the carbs can function under
boost. The rolling road will be very interesting!!
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Craigman9
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| posted on 11/4/11 at 09:05 PM |
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I also have a ST170 with ZXR9 carb's.
Would love to supercharge mine one day.... 
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ChrisL
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| posted on 12/4/11 at 06:42 AM |
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Some info on intercooler sizing here:http://www.unclebobsturbos.com/newbie.html
Given my above post I have no idea if it's any good...
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FASTdan
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| posted on 13/4/11 at 11:01 AM |
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Good work, I look forward to seeing how this one progresses As I've said before I'd like to swap the weber on my XR2 turbo for a set of
bike carbs.....
NEW danST WEBSITE NOW LIVE! Bike carbs, throttle bodies and more......
http://www.danstengineering.co.uk/
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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ianjenn
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| posted on 13/4/11 at 04:35 PM |
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Hi All
At my last rolling road the air correction jets were blocked off as I was running an air filter. I am wondering if the air correction jets now need to
be unblocked as the carbs have a plenum and are pressureised. Does anyone know if I am makin any sense. Just wondering if this is the cause of my over
revving atgear change
thanks
alex
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