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1 Posts Member #: 11572 Junior Member |
31st May, 2017 at 07:35:19am
By intro I race a GPA metro Turbo (computervision) and have problems with power delivery on anything that is not full throttle or on boost above 5000 rpm. I am thinking that the dash pot that lifts as a vacuum is created by Venturi effect is reacting unpredictably as the airspeed goes up to way beyond that designed. At 250+ Bhp (1.5bar) the airspeed through the carb could require a rethink of the jet bridge and Venturi holes under the dash pot piston. Is the airspeed under the piston drawing it and the needle down more than the vacuum is pulling the piston up? I will try to rig a simulator so we can phisicaly see what's happening but have any members come up with a solution already? |
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 12307 Posts Member #: 565 Carlos Fandango Burnham-on-Crouch, Essex |
31st May, 2017 at 09:16:20am
well, i'd start here...
On 28th Aug, 2011 Kean said:
At the risk of being sigged... Joe, do you have a photo of your tool? http://www.turbominis.co.uk/forums/index.p...9064&lastpost=1 https://joe1977.imgbb.com/ |
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 8604 Posts Member #: 573 Formerly Axel Podland |
31st May, 2017 at 10:05:22am
The air speed is no higher than N/A with blow through, just the air density is higher. Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
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806 Posts Member #: 989 Post Whore North Yorkshire |
31st May, 2017 at 11:27:17am
Have you tried a stronger spring in the dashpot, as used on the Maestro and Montego turbo? People have had them running over a bar boost still using the single SU on a 2 litre engine. |
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 9502 Posts Member #: 1023 Post Whore Doncaster, South Yorkshire |
31st May, 2017 at 08:48:33pm
you need a stronger spring or springs, to make sure the needle doesnt rise to its maximum station before maximum air flow (not boost) is reached
Yes i moved to the darkside |
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Forum Mod 10980 Posts Member #: 17 ***16*** SouthPark, Colorado |
31st May, 2017 at 09:46:34pm
I doubt you're reaching the limit of the carb. More likely, you have a setup issue.
Edited by TurboDave16V on 31st May, 2017. On 17th Nov, 2014 Tom Fenton said:
Sorry to say My Herpes are no better Ready to feel Ancient ??? This is 26 years old as of 2022 https://youtu.be/YQQokcoOzeY |
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 1648 Posts Member #: 9038 Post Whore Carlisle, Cumbria |
31st May, 2017 at 10:11:42pm
On 31st May, 2017 TurboDave16V said:
I doubt you're reaching the limit of the carb. More likely, you have a setup issue. One of the USA based members spent a long time looking at needle profiles and the position of the dashpot piston for different load sites. Made for very interesting reading, but I can't recall the topic title or the guys username... Have you got a wideband to determine your fueling or are you guessing that you need to modify the carb? My experience is that the stock carb and plenum restrictor is basically as perfect as you'll get ( except for the poppet butterfly valve). The engineers didn't arrive at that by pure luck. http://www.turbominis.co.uk/forums/index.php?p=vt&tid=159683 |
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224 Posts Member #: 9987 Senior Member Amsterdam |
1st Jun, 2017 at 04:56:58am
On 31st May, 2017 TurboDave16V said:
I doubt you're reaching the limit of the carb. More likely, you have a setup issue. My experience is that the stock carb and plenum restrictor is basically as perfect as you'll get ( except for the poppet butterfly valve). The engineers didn't arrive at that by pure luck. Interestingly enough I noticed that the Grp A turbo running on swiftune's dyno recently doesn't use a plenum but had a boost pipe running straight into the carb's mouth. |
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3588 Posts Member #: 655 Post Whore Northern Ireland |
1st Jun, 2017 at 09:44:46am
On 31st May, 2017 Gpametroturbo said:
By intro I race a GPA metro Turbo (computervision) and have problems with power delivery on anything that is not full throttle or on boost above 5000 rpm. I am thinking that the dash pot that lifts as a vacuum is created by Venturi effect is reacting unpredictably as the airspeed goes up to way beyond that designed. At 250+ Bhp (1.5bar) the airspeed through the carb could require a rethink of the jet bridge and Venturi holes under the dash pot piston. Is the airspeed under the piston drawing it and the needle down more than the vacuum is pulling the piston up? I will try to rig a simulator so we can phisicaly see what's happening but have any members come up with a solution already? So why not explain your problem ? Your setup ? And what power do you believe you have, or want to have ? 9.85 @ 145mph
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3588 Posts Member #: 655 Post Whore Northern Ireland |
1st Jun, 2017 at 09:49:50am
On 1st Jun, 2017 Evoderby said:
On 31st May, 2017 TurboDave16V said:
I doubt you're reaching the limit of the carb. More likely, you have a setup issue. My experience is that the stock carb and plenum restrictor is basically as perfect as you'll get ( except for the poppet butterfly valve). The engineers didn't arrive at that by pure luck. Interestingly enough I noticed that the Grp A turbo running on swiftune's dyno recently doesn't use a plenum but had a boost pipe running straight into the carb's mouth. Running without the OEM plenum is with hindsight what caused me most of my problems some 20+ years ago when I ran mine. Back then I never fully appreciated what the restrictor/straight inlet section was for. I ran open plenum to enable IC fitment etc and it did take ages working with the carb to get it all to work well. It was never perfect, but it was pretty good. Havent a clue what AFR's etc were, as no such thing as widebands etc back then, but I drove it daily for a few years and could run 25psi without issue ( well other than expected clutch/gearbox/HG related problems ) So as others say, the chances of being at the limits of the carb here, are very unlikely. And I'm near sure some guys with the Maestro's or Montego's still ran a single carb near 300hp too ? 9.85 @ 145mph
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 1497 Posts Member #: 100 Parisien Turbo Expert Paris\' suburb |
6th Jun, 2017 at 04:54:11am
Hello, to start 250 bhp+.. mega lol , bref.
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