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924rennsport
Joined: 21 Oct 2008
Posts: 8
Location: boston, ma
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 Posted: Mon Feb 09, 2009 6:41 am Post subject: 924 on Bike Carbs |
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In the January 2009 issue of Practical Performance Car, there's an 81 924 running four "bike carbs"
Does anyone know what kind of motorcycle carbs would be suitable for use on a 924? Clearly, the intake manifold will have to be custom made.
But, if the whole conversion can be done for less than a pair of Webers would cost...
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Rich H
Joined: 10 Jun 2007
Posts: 2665
Location: Preston, Lancs, UK
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| Posted: Mon Feb 09, 2009 7:50 am Post subject: |
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GSXR 1000 K1 throttles are separate units so can be respaced easily.
No link, but might be worth looking at the forums on ppcmag.co.uk
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1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec |
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Mon Feb 09, 2009 8:40 am Post subject: Re: 924 on Bike Carbs |
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| 924rennsport wrote: | | But, if the whole conversion can be done for less than a pair of Webers would cost... |
Hmmm...that's probably a tall order, consider the Weber conversion can be done for ~$600-$700 depending on how much you end up paying for used carbs. There are a few of the 924 manifolds still floating around if you're persistent...which by the way, would make a great starting point for an ITB setup.
Do a search for daveo's threads, as he had a car setup this way, and I believe may still have the bits for sale. Here's a link to get you started:
http://www.924board.org/viewtopic.php?t=16654
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erstwhile owner of just about every 924 variant ever made |
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Martijnus
Joined: 29 Dec 2006
Posts: 2019
Location: Netherlands
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| Posted: Mon Feb 09, 2009 8:53 am Post subject: |
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| Rich H wrote: | GSXR 1000 K1 throttles are separate units so can be respaced easily.
No link, but might be worth looking at the forums on ppcmag.co.uk |
If the K1 units are the same bore as the K2 throttlebodies (which are fuel injection units) I'd rather look for some 750cc carbs.
I used the K2 ones on my engine and they're a bit too large imo... on the other hand, the low end is as good as before so it's not killer for the torque, but when I go 100% tps you can hear it's capable of getting more air than it needs.
My guess is that <40mm bores are best, but I can only speak from my experience above.
I went with 40-41mm ones because my complex calculations revealed that if a 1000cc can run 12000rpm with those things, my 2000cc engine can run 6000 rpm with the same air flow 
iirc the throttles from a 750cc FI bike are around 38mm, the carbs are probably the same bore.
Also think about the ports in the head, those are not really big in diameter and putting big bore carbs on it probably causes strange air flow (velocity) problems.
But 40mm does work.
What bore are those webers you can put on our blocks?
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"Rule: Turbo's make torque, and torque makes fun." (C. Bell)
924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment  |
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Chrenan
Joined: 15 Jan 2003
Posts: 3903
Location: Canada
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| Posted: Mon Feb 09, 2009 10:08 am Post subject: |
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Weber DCOE 40 is advised for a street car, 45 for track only.
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1987 951 - M193 Version for Japan |
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Martijnus
Joined: 29 Dec 2006
Posts: 2019
Location: Netherlands
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| Posted: Mon Feb 09, 2009 10:29 pm Post subject: |
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| Chrenan wrote: | | Weber DCOE 40 is advised for a street car, 45 for track only. |
so those are 4x40mm bores?
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"Rule: Turbo's make torque, and torque makes fun." (C. Bell)
924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment |
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bass gt
Joined: 02 Dec 2004
Posts: 971
Location: Johannesburg for now!!
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| Posted: Mon Feb 09, 2009 11:31 pm Post subject: |
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The "40" or "45"/"48" in the Weber nomenclature refers to the size of the main air venturi size.
45's work well for top end power vs the 40's, but do suffer with low speed air velocity, hence the preference for track usage.
I'm using 4 x 45mm taper throttle bodies, which taper from 45mm to 36 in the head. This should help the port velocity somewhat.
Steve
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Front Wheel Drive is the Devil's work. |
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Vince Ponz
Joined: 02 Nov 2002
Posts: 3581
Location: Florida
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| Posted: Tue Feb 10, 2009 12:54 am Post subject: |
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I have 45s and use it both for the street and track.
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"Never let them see you sweat"
77.5 924 modified track car
79 931 Euro stock
88 924S SE
87 911 Targa stock |
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daveo
Joined: 02 Sep 2005
Posts: 183
Location: GB
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| Posted: Wed Feb 11, 2009 9:02 pm Post subject: |
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yam R1 carbs work well. just sold my lot, sorry, full setup and fitting by Bog brothers £550. IF you put a add on piston heads for parts wanted the guy that got my stuff said he was not going use the manifold, long shot but you never know his name was tom
dave |
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benlg81
Joined: 12 Oct 2008
Posts: 204
Location: West Midlands UK
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| Posted: Fri Feb 13, 2009 1:47 am Post subject: |
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i have bought a set of cbr900 fireblade carbs and the fuel pump from these as well, i have a base plate for my manifold being made at the moment so i will just have to weld on some 41mm tubing and the manifold will be ready.
hopefully it will give a nice gain |
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daveo
Joined: 02 Sep 2005
Posts: 183
Location: GB
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| Posted: Fri Feb 13, 2009 9:14 am Post subject: |
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remember the the flote bowl has to be flat IE the line on the flote bowl has to be straght i think its 45 degre
dave |
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Martijnus
Joined: 29 Dec 2006
Posts: 2019
Location: Netherlands
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| Posted: Sat Feb 14, 2009 9:06 am Post subject: |
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most carbs on bikes are on an angle too... but the float bowl lies straight on those carbs.
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)
924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment |
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904kevinw
Joined: 16 Nov 2008
Posts: 4
Location: Jacksonville, FL
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| Posted: Sun Feb 22, 2009 11:59 am Post subject: |
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I just converted my '82 to a set of carbs off of a GSXR-750. I paid $80 for the set. I had to go through them to clean them up, and have fiddled with the jetting, but finally have a 924 that runs incredible compared to how it ran with the CIS setup. Of course, I did have to build a manifold from scratch, but with a little creativity, and knowing someone who can weld aluminum pretty well, it wasn't as tough as I thought it might be at the start of the whole project. Would I do it again?...absolutely!
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'82 924 with GSXR-750 carbureted custom intake |
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Sun Feb 22, 2009 12:14 pm Post subject: |
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| 904kevinw wrote: | | I just converted my '82 to a set of carbs off of a GSXR-750. I paid $80 for the set. I had to go through them to clean them up, and have fiddled with the jetting, but finally have a 924 that runs incredible compared to how it ran with the CIS setup. Of course, I did have to build a manifold from scratch, but with a little creativity, and knowing someone who can weld aluminum pretty well, it wasn't as tough as I thought it might be at the start of the whole project. Would I do it again?...absolutely! |
Pix?
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erstwhile owner of just about every 924 variant ever made |
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benlg81
Joined: 12 Oct 2008
Posts: 204
Location: West Midlands UK
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| Posted: Mon Feb 23, 2009 8:57 pm Post subject: |
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second the pix. also any more info like the bhp or drive gains?
Cheers
Ben |
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