Login    Forum    Search    FAQ

Board index » Racing Forum » Fuel Systems




Post new topic Reply to topic  [ 25 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: T slot 3310
 Post Posted: Mon Sep 17, 2012 5:41 am 
Offline

Joined: Sat Jan 07, 2012 5:22 pm
Posts: 63
OK.....this is gonna be long but here goes......

I pulled my 3310 apart and sent the base plate out to be rebushed and they milled it as they said it was warped.

Anyway i thought id do the Tuner trick and try and get the throttle plates to seal uniformly and im getting there slowly but what ive noticed is now i have No T slot exposed at all.

Tuner:
Quote:
As this procedure closes the butterflies tighter in the bores it lowers the edge of the throttle relative to the T-slot. If this is positive or negative in effect depends on where the original locations of the lower end of the slot and the throttle edge were. Some carbs are manufactured with the T-slot too long, exposing too much slot below the throttle at idle. Closing the throttle by this fitting process and using a hole in the butterfly can help that situation.

After the throttle plate fit is satisfactory, the lower end of the T-slots can be located to suit the particular throttle opening required for the desired idle speed. The engine has to be run until fully warmed up and adjusted to the desired idle speed and AFR and the carb removed and examined for the throttle opening and T- slot relationships. What steps to take next, are a judgment call based on the circumstances. To have reasonable control of the speed and curb idle mixture it is best to run the primary throttle opening in the range of less than 3/4 turn of the idle speed screw from closed tight in the bore and also have a minimum of T-slot exposure at the throttle opening for the desired idle speed. About .010” to .015” is highly desirable. Minimizing unnecessary T-slot exposure at idle will reduce the amount of fuel that passes through the engine when coasting with the throttle closed and the vacuum is very high.


So my question is When the butterflies are where i want them in the bores do i then need the T slot to be no more than .010 -.015 or does it have to be .040 like ive read else where?

Also he wrote that most holleys have a .025 t slot width. Mine measures .023, should i widen it to .025?

Hysteric


Top 
 Profile  
 
 Post subject: Re: T slot 3310
 Post Posted: Mon Sep 17, 2012 6:26 am 
Offline
User avatar

Joined: Wed Apr 19, 2006 8:20 pm
Posts: 5852
Location: N.J.
You should only be concerned with your T-slot after it's on the motor running and made your idle mixture adjustments. Set your speed screws then pull it off and take a look...From what I have read there does not seem to be much of an issue with the 4150 carbs like there is with the HP Dominators.

_________________
Image
running E85
Best ET 8.07
Best MPH 170.71
Barry


Top 
 Profile  
 
 Post subject: Re: T slot 3310
 Post Posted: Mon Sep 17, 2012 6:29 am 
Offline
User avatar

Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
Minimizing t-slot fuel requires more fuel from the idle port. The idle port sees manifold vacuum whereas the tslot sees relatively high vacuum even in a low vacuum hotrod cam engine. The idle port is lousy at fuel delivery the tslot is best.


Top 
 Profile  
 
 Post subject: Re: T slot 3310
 Post Posted: Mon Sep 17, 2012 4:29 pm 
Offline

Joined: Sat Jan 07, 2012 5:22 pm
Posts: 63
SHRINKER! Good to see you back.


Quote:
The idle port sees manifold vacuum whereas the tslot sees relatively high vacuum even in a low vacuum hotrod cam engine


Im pulling about 9 inches at idle in neutral and im fighting a rich idle condition when i looked into the carb the boosters were dripping so i reset the float bowls and it still ran rich so thats why i pulled the carb down to try and set it up properly. I had the base converted to 4 corner idle by a carb shop earlier but when i pulled it apart i noticed they only blocked 1 of the idle passages in the base.....not sure if this was the cause of the rich condition.

Ive converted one of my 12r 4777 bases to vac sec because its a 4 corner done properly.

My question is What should my starting point be the t-slot lenght and width? If i have NO t-slot

Shrinker wrote here:

Quote:
If the slot is widened to what Holley's used to be in the old days the jetting is less influenced by the slot exhaust area and more controllable via the jet and air bleed. The modern fancy carbs usually have too narrow a slot. Quick Fuel get it right, others stuff it up.

If you lower the slot you get more fuel at idle and all the way through the opening while the blade is close to the slot. If you widen the slot you get more fuel only as you open the blade but not at idle. If you widen the top of the slot you get more air leaking backwards into the drillings at closed blade positions. Its simple stuff. think of the slot as a small carby barrel and the blade as a slide throttle like a motorbike carby. Its like a tiny slide carby. The air bleed is the venturi and the edge of the blade is the slide throttle and the IFR is the main jet of a tiny carby. If you widen the slot you have just ported out the slide carby.


Hysteric


Top 
 Profile  
 
 Post subject: Re: T slot 3310
 Post Posted: Mon Sep 17, 2012 8:42 pm 
Offline
User avatar

Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
That comment I said about quickfuel getting it right with the tslot needs to be edited now. Saw some quickfuel carbys the other day and their quality has gone down a lot. Tslots different widths and lengths, boosters with dags on them and not straight.

If your boosters are flowing then it usually means that the idle is that inefficient that your throttle is open lots however you claim that you have no t-slot exposed so that means its fairly closed so I'm confused.
I have seen situations where the engine is idling and its running that incorrectly that pulsing air enters the idle circuit and enters the main well and causes the boosters to flow.


Top 
 Profile  
 
 Post subject: Re: T slot 3310
 Post Posted: Tue Sep 18, 2012 1:33 am 
Offline

Joined: Sat Jan 07, 2012 5:22 pm
Posts: 63
Quote:
If your boosters are flowing then it usually means that the idle is that inefficient that your throttle is open lots


When i pulled it off it was open a alot.

Quote:
however you claim that you have no t-slot exposed so that means its fairly closed so I'm confused.


After pulling it off and getting it bushed and attempting to fix the butterflies there is now no t-slot. So how much should i have exposed with the butterflies closed? .040 or less?

Shrinker this statement has been gnawing at me for a while
Quote:
Fix a Holley and it will work like a Carter.


Please elaborate why and which carb as Carter had a few different models?

Thanks again.

Hysteric


Top 
 Profile  
 
 Post subject: Re: T slot 3310
 Post Posted: Tue Sep 18, 2012 1:52 am 
Offline
User avatar

Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
Carters design philosophy is similar to other manufacturers. That is its to size the booster and channel so that there is no need for air bleeding. Air bleeding (emulsion) is a crutch to enable cheap manufacturing to function across a wide range of applications. A carby can be designed so that there is zero emulsion. People think that emulsion air creates some form of improvement to atomization, that is not the case, you cant actually emulsify a liquid and a gas, you can only emulsify like substances like liquids with another liquid etc. What other manufacturers of carburetors do is they design the booster as a 2 stage so its got lots of vacuum, and to stop the mixture going rich at the top end they reduce the size of the drillings etc so that friction and turbulent flow control the AFR. Doing it this way reduces changes to AFR from weather changes. A carby thats over reliant on emulsion air is over reactive to weather because the emulsion air is effected by the air pressure of the day. If you dont use it it doesnt screw it up.
Holley is a hotrodders carby but its not the best carby for someone who is seeking more.

Because you cant emulsify and liquid and a gas all you end up with in a holley is discharges of air and then fuel from the booster feed tube. Air travels in a reasonably constant manner down the venturi so any disruptions to constant flow caused by emulsion air is a disruption to the AFR thats delivered to any particular parcel of air. Boosters that are designed to use friction etc to control the AFR flow ina continuous manner just like the air does and the engine receives more consistent AFR to the air stream.

EFI is classic example of how not to do it. you open the intake valve for say 40 ms but only inject the fuel for 2.5ms. So WTF is happening to the rest of the air, how dry is it? Thats why good carbys make power.


Top 
 Profile  
 
 Post subject: Re: T slot 3310
 Post Posted: Tue Sep 18, 2012 2:07 am 
Offline

Joined: Sat Jan 07, 2012 5:22 pm
Posts: 63
Hmm.... While im pondering what you've written any chance on a t-slot size :-k

Were the Thermoquads the only Carters with double stage boosters? Can i make more power with a Carter as i have a few to experiment with but no Thermoquads.......yet =;

Hysteric


Top 
 Profile  
 
 Post subject: Re: T slot 3310
 Post Posted: Tue Sep 18, 2012 8:13 am 
Offline
User avatar

Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
T slots need to be .027 to .028" wide on average to work
I dont know if carter made other carbys with double venturi boosters. They probably did. I'm not concerned who makes what I'm just informing you of how the design should be done.
There are many abominations out there that were in production, just look at a VW beetle carby one day. BUT remember that the stock Beetle had an exhaust heat tube and its air cooled and runs higher cylinder temps than other engines and then think about why the carby is like it is.


Top 
 Profile  
 
 Post subject: Re: T slot 3310
 Post Posted: Tue Sep 18, 2012 10:00 am 
Offline
User avatar

Joined: Wed Apr 19, 2006 8:20 pm
Posts: 5852
Location: N.J.
hysteric wrote:
Hmm.... While im pondering what you've written any chance on a t-slot size :-k

Were the Thermoquads the only Carters with double stage boosters? Can i make more power with a Carter as i have a few to experiment with but no Thermoquads.......yet =;

Hysteric




Seem like you and Bruce have something going here but as far as the "size" of the T-slot goes if it's to large you will loose your ability to tune with your mixture screws...As it will draw excessive fuel from the slot. Correct me if I am wrong.. #-o

_________________
Image
running E85
Best ET 8.07
Best MPH 170.71
Barry


Top 
 Profile  
 
 Post subject: Re: T slot 3310
 Post Posted: Wed Sep 19, 2012 3:41 am 
Offline

Joined: Sat Jan 07, 2012 5:22 pm
Posts: 63
Thanks Shrinker

What do i set the Length at........ .040 with the butterflies closed? Remember i have NO transfer slot at all

Shrinker can you clarify which Carter to play with.....AFB, AVS or Thermoquad?

Hysteric


Top 
 Profile  
 
 Post subject: Re: T slot 3310
 Post Posted: Wed Sep 19, 2012 4:10 am 
Offline
User avatar

Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
The length of the slot is determined by the engines vacuum response. Vacuum response is determined by the interaction of cam and mixture and timing. You have to figure it out yourself.
You can play with any carburetor. Anything can be made into anything else. Ive made carbys from blocks of wood, old pistons welded together, aluminium tubing, Ive epoxied parts from one into another.
The most important thing is to ensure the needle and seat can flow the amount of fuel you need.


Top 
 Profile  
 
 Post subject: Re: T slot 3310
 Post Posted: Wed Sep 19, 2012 6:05 am 
Offline

Joined: Sat Jan 07, 2012 5:22 pm
Posts: 63
Ok Shrinker lets dance =;

I have both the AVS and AFB carbs and both look to be air bleed emulsion type or am i missing something here?

The Thermoquad differs in that it has a "Solid Fuel" type as well.

http://books.google.com.au/books?id=7UYdwPcl3xMC&pg=PA15&lpg=PA15&dq=what+is+Solid+Fuel+Thermo+Quad&source=bl&ots=qY8QUU-4K8&sig=utiTaukzEn-y_Lh2iPE4BPCkOgw&hl=en&sa=X&ei=gJNZULqyG82XiAe_6YGoDg&sqi=2&ved=0CDYQ6AEwBA#v=onepage&q=what%20is%20Solid%20Fuel%20Thermo%20Quad&f=false

Dave Emanuel writes:

The "Solid Fuel" design was implemented as a means of improving emissions. Carter engines(engineers perhaps) found that more precise fuel control resulted when the fuel was kept solid as it flowed through the main well and towards the discharge nozzle. The Solid Fuel design delayed introduction of emulsifying air until fuel entered the discharge nozzle tube.

Is this what you are alluding to?

Hysteric


Top 
 Profile  
 
 Post subject: Re: T slot 3310
 Post Posted: Wed Sep 19, 2012 6:22 am 
Offline
User avatar

Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
Yes. The reason why there is a air bleed at the end of the tube is to stop siphoning. The vintage cars did it by updraft carbys. Note the comment or explanation about the design of solid fuel. its a strange term to use but I guess the marketing guys have to do something. Anything that improves emissions also improves efficiency and thats how you make power.


Top 
 Profile  
 
 Post subject: Re: T slot 3310
 Post Posted: Wed Sep 19, 2012 6:25 am 
Offline
User avatar

Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
engines are not just air pumps, they are machines to condition fuel to optimum condition for combustion. Power doesnt come from air pumping alone it comes from chemistry.


Top 
 Profile  
 
Display posts from previous:  Sort by  
 
Post new topic Reply to topic  [ 25 posts ]  Go to page 1, 2  Next

Board index » Racing Forum » Fuel Systems


Who is online

Users browsing this forum: No registered users and 2 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