Login    Forum    Search    FAQ

Board index » Racing Forum » Fuel Systems




Post new topic Reply to topic  [ 8 posts ] 
Author Message
 Post subject: Throttle Stop Carb
 Post Posted: Thu Dec 22, 2011 1:46 pm 
Offline

Joined: Thu Feb 12, 2009 7:52 pm
Posts: 348
I am looking at doing some throttle stop racing this year. I have always heard that a carb is set up differantly for throttle stop racing.

Anyone know what they do differently in those tunes?

Only thing I can think of is you would need to ensure the part throttle operation is right. Most carbs I see box stock are rich on cruise and and can see that causing issues trying to be consistant on a stop.

Thanks

_________________
74 Nova
Best 9.87@131 on the rev limitor 1 Feb 2013
1/8   6.15@110 NEW BEST 27 Nov 11
Image


Top 
 Profile  
 
 Post subject: Re: Throttle Stop Carb
 Post Posted: Thu Dec 22, 2011 4:41 pm 
Offline

Joined: Thu Jan 29, 2009 10:59 am
Posts: 438
Location: Auburndale, Florida
Bill, you can run your footbrake off the stop just fine. The O2s will look pretty odd, though. Let me see if I can dig up an O2 from one of my T-stop runs and e-mail it to you.


Top 
 Profile  
 
 Post subject: Re: Throttle Stop Carb
 Post Posted: Thu Dec 22, 2011 4:53 pm 
Offline

Joined: Thu Feb 12, 2009 7:52 pm
Posts: 348
If I do run it, it will be hotrod, off the t-brake, I was just curious if there was anything I need to pay attention to.

_________________
74 Nova
Best 9.87@131 on the rev limitor 1 Feb 2013
1/8   6.15@110 NEW BEST 27 Nov 11
Image


Top 
 Profile  
 
 Post subject: Re: Throttle Stop Carb
 Post Posted: Thu Dec 22, 2011 4:59 pm 
Offline
Site Admin
User avatar

Joined: Tue Apr 18, 2006 6:38 am
Posts: 11804
Location: Coming At Ya!
fourtenposi wrote:
I was just curious if there was anything I need to pay attention to.


FYI, guys that are successful at 10.90 are running 145/150 at the stripe. Having said that, you might want to get more mirrors so you can better judge their closing speeds. =;

_________________
Big Boyz Toyz!

Image

Necessity is the plea for every infringement of human freedom. It is the argument of tyrants; it is the creed of slaves.

William Pitt, British Prime-Minister (1759-1806)


Top 
 Profile  
 
 Post subject: Re: Throttle Stop Carb
 Post Posted: Thu Dec 22, 2011 11:47 pm 
Offline

Joined: Thu Feb 12, 2009 7:52 pm
Posts: 348
As long as I am where I need to be on the tree, I don't need to see them coming to know where to drop them, :-$

_________________
74 Nova
Best 9.87@131 on the rev limitor 1 Feb 2013
1/8   6.15@110 NEW BEST 27 Nov 11
Image


Top 
 Profile  
 
 Post subject: Re: Throttle Stop Carb
 Post Posted: Fri Dec 23, 2011 12:03 am 
Offline
User avatar

Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
Whats important with part throttle mixtures is the main jet size. If your tuning technique uses main well drilling diameter (read as restriction in the angle channel etc) as part of the mixture control for full throttle then when you go to part throttle it will run too rich. Part throttle operation increases the vacuum at the T-slot and it does that without supposedly altering the AFR from the booster. Obviously the CFM is reduced so the booster is supposed to flow less total fuel but its supposed to be at the same percentage (AFR) of the main venturi flow. The t-slot however is on the surface of the bore and it only reacts to vacuum. At part throttle (thats close to full throttle like say 3/4 open) this creates a situation where the additional T-slot fuel has to be controlled by the main jet. If the main jet is too large and the well too small the main jet will allow extra fuel from the T-slot WITHOUT restricting the flow from the booster. Part throttle running is all about managing the depression on the outlet side of the main jet.
The most obvious thing to do for part throttle running is use a smaller carby. That way the depression is concentrated at the main venturi. If the carby is too large eg the main venturi is too large, the depression concentrates at the butterfly and you have the problem of how to regulate the T-slot flow.
For best part throttle racing the tune has to be correctly done, not botched like some do for drag racing by having the attitude that nothing matters because we only use full throttle.


Top 
 Profile  
 
 Post subject: Re: Throttle Stop Carb
 Post Posted: Fri Dec 23, 2011 9:59 pm 
Offline

Joined: Thu Feb 12, 2009 7:52 pm
Posts: 348
I was also thinking that the smaller carb would be better of the stop.

I am planning on using a #1 stop which is a plate type stop. I was told that they were more consistant.

Any opinions?

_________________
74 Nova
Best 9.87@131 on the rev limitor 1 Feb 2013
1/8   6.15@110 NEW BEST 27 Nov 11
Image


Top 
 Profile  
 
 Post subject: Re: Throttle Stop Carb
 Post Posted: Fri Dec 30, 2011 3:03 pm 
Offline

Joined: Sun Nov 11, 2007 10:33 am
Posts: 1293
Location: Montgomery, Alabama
I have only used linkage stops. I kill it quick and hard. Then get the big run on the top end.

Haven't done it in years though. Now I hit the index with N2o =; =;


Top 
 Profile  
 
Display posts from previous:  Sort by  
 
Post new topic Reply to topic  [ 8 posts ] 

Board index » Racing Forum » Fuel Systems


Who is online

Users browsing this forum: Bing [Bot] and 4 guests

 
 

 
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
cron