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T slot questions

General engine tech -- Drag Racing to Circle Track

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mopardave
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T slot questions

Post by mopardave »

Can someone tell me what or how the t-slot operates? I understand it is a fuel passage at idle, but becomes an air passage once the blade is above it. At what rpm range is it fuel and how do you pick the t-slot jet correctly when that passage is fuel part time and air another time?
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Re: T slot questions

Post by Walter R. Malik »

mopardave wrote: Thu Oct 08, 2020 8:36 am Can someone tell me what or how the t-slot operates? I understand it is a fuel passage at idle, but becomes an air passage once the blade is above it. At what rpm range is it fuel and how do you pick the t-slot jet correctly when that passage is fuel part time and air another time?
That notion is backwards.
Usually, the SLOT, (sometimes a series of small holes), is a modulating area. A partial air-bleed at idle which turns into a fuel feed as the throttle plate goes past it.
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Re: T slot questions

Post by hoodeng »

As Walter said. The T slot, same as series holes drilled in line [there are carbs for methanol/fuel that have drilling's side by side to bring even more air/fuel into play] are transition from idle air/fuel circuit, to intermediate air/fuel circuit. As the blade passes the slot/holes more of the low pressure [manifold] side of the blade is bought online to enrichen the mixture conversant to the increased amount of air now passing the blade.

Cheers.
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Re: T slot questions

Post by mopardave »

Ok, so the t-slot would still be enrichening as the boosters come on and wot? I'm still chasing a very short bog when i jab the throttle wide open from low rpm while under a load (3rd gear). This is with a 511 with t ram and twin 750 holleys. I'v tried air bleeds, IFR, pv, float level adjustment, squirters and blue pump cams. Raising the float level made the best improvement. Bigger on the IFR and smaller on the IAB seemed to help a bit. Currently using 35 squirter. Also, i use a wide band and can see and feel a lean spot when i hold one gear(2nd) and wind it out to 4000+rpm. Starts getting lean above 3000rpm. Seeing high 15's and 16+ on wide band. Can feel the power drop off.
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Re: T slot questions

Post by Tuner »

That relatively large displacement probably needs 50cc accelerator pumps.
mopardave wrote: Sat Oct 10, 2020 9:29 pm Ok, so the t-slot would still be enrichening as the boosters come on and wot? I'm still chasing a very short bog when i jab the throttle wide open from low rpm while under a load (3rd gear). This is with a 511 with t ram and twin 750 holleys. I'v tried air bleeds, IFR, pv, float level adjustment, squirters and blue pump cams. Raising the float level made the best improvement. Bigger on the IFR and smaller on the IAB seemed to help a bit. Currently using 35 squirter. Also, i use a wide band and can see and feel a lean spot when i hold one gear(2nd) and wind it out to 4000+rpm. Starts getting lean above 3000rpm. Seeing high 15's and 16+ on wide band. Can feel the power drop off.
Also, i use a wide band and can see and feel a lean spot when i hold one gear(2nd) and wind it out to 4000+rpm. Starts getting lean above 3000rpm. Seeing high 15's and 16+ on wide band. Can feel the power drop off.
This ^^^ are you at WOT or part-throttle when it is lean? If it is not at WOT a lean A/F is not necessarily a bad deal as long as it is properly rich at WOT, 12.5/1 or so. A lean number at part-throttle, as long as it doesn't misfire, will burn less gas, and you can still got to WOT for the HP.

You need to do this tuning with a vacuum gauge along side the A/F gauge, so you can see when the power valve is in play at part-throttle and higher engine speed than idle and extremely low RPM. Pay attention to how the vacuum drops as you gradually crowd into the throttle at 3000 and 4000 RPM in higher gears.
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Re: T slot questions

Post by mopardave »

wot is currently 12.5 and i do have a factory vac gauge in the car. I need to watch it closer next time. I currently have 6.5pv's(4) now, just ordered 4 8.5's in case i need them.
The blue cams made no difference over the pink cams i have, so i put the pink cams back on. Do you think the pink cams will work good with the 50cc pumps? I can see the wide band flash 22 for just a micro second when i jab the carbs wide open in 3rd gear 30-50mph. Not sure what WB reads when i do this in first gear, but it spins the tire anyway, so no heavy load there and no bog either. Haven't been to a track yet.
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Re: T slot questions

Post by turbo camino »

Good job proving everyone wrong about how awesome the pink cams are.
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Re: T slot questions

Post by mopardave »

I get way more pump lever movement with the pink cams vs the blue it seems. I will get a little more time with it today, just trying to figure t-slot jet sizing thinking maybe this is the culprit. I currently have an .081 t-slot jet and thinking maybe it needs to be larger or smaller, but not sure which way to go with it trying to get rid of a slight lean condition a wide open jab with a load. Being that the t-slot is an air bleed at idle, i'm thinking smaller t-slot jet to richen it up down there?
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Re: T slot questions

Post by Walter R. Malik »

mopardave wrote: Sun Oct 11, 2020 10:03 am I get way more pump lever movement with the pink cams vs the blue it seems. I will get a little more time with it today, just trying to figure t-slot jet sizing thinking maybe this is the culprit. I currently have an .081 t-slot jet and thinking maybe it needs to be larger or smaller, but not sure which way to go with it trying to get rid of a slight lean condition a wide open jab with a load. Being that the t-slot is an air bleed at idle, i'm thinking smaller t-slot jet to richen it up down there?

With a Holley type metering system ...
Smaller slot restriction will richen idle and lean off-idle; larger slot restriction will lean idle and richen off-idle.
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Re: T slot questions

Post by ClassAct »

mopardave wrote: Sun Oct 11, 2020 10:03 am I get way more pump lever movement with the pink cams vs the blue it seems. I will get a little more time with it today, just trying to figure t-slot jet sizing thinking maybe this is the culprit. I currently have an .081 t-slot jet and thinking maybe it needs to be larger or smaller, but not sure which way to go with it trying to get rid of a slight lean condition a wide open jab with a load. Being that the t-slot is an air bleed at idle, i'm thinking smaller t-slot jet to richen it up down there?
If you don’t bend the accelerator pump arm so it’s flat on the blue cam you’ll lose a bunch of lift. The blue cam is far better than the pink cam, and I spent years using nothing but the pink cams.
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Re: T slot questions

Post by mopardave »

I will stay with the pink cams for now as i have a few more things to try first. I drove the car today and streetability is awesome. Idles and cruises clean and wide open throttle is in the mid 12 range on the wide band. The slight bog is almost nonexistant, but its still there and i noticed that when tipping throttle in to accellerate in 2nd or 3rd gear the wide band will go up into the 16-17afr range and i can feel some surging there. Also the vac gauge read 8 or 9" vacuum in the lean spot, so maybe a 8.5pv will cover that. Would like to try the 8.5pv's, 4 hole spacers and a .085 or .090 T slot jet. My thought is if i fix the lean spot in the transition it my also fix the other hiccup at wot jab.
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Re: T slot questions

Post by Tuner »

Both the pink and blue cams offer full displacement of the accelerator pump diaphragm, provided the angle of the pump arm lever where it contacts the cam is adjusted correctly for each cam. The lever may (will) require fine tuning for each different pump cam, no matter the color.

Part of the situation accelerator pumps must deal with is the first 1/4 of butterfly throttle travel gives near 75% of total flow capacity.

The pink cam, though it can displace 100% of the pump, has the least displacement of the pump, and so least pump shot, in the first 1/4 or so of the throttle shaft rotation of all Holley pump cams.

The blue cam has the most pump displacement in the first few degrees of shaft rotation of the 30cc pump cams .... provided the pump arm angle adjustment is correct.

When the throttle is suddenly opened the first source of enrichment fuel to the cylinders is from the puddle in the manifold on the floor and walls of the runners. The usual situation with the pink cam's weak pump shot during the first few degrees of throttle shaft rotation is it does not sufficiently replace fuel to the puddle and this causes the lean condition until the puddle can recover by acquiring some of the fuel issuing from the main nozzle.

A significant percentage of the fuel in the intake, approximately 50%, is in the "puddle" ... in the film on the manifold walls

You should be able to get the blue cam to displace near 100% of the pump at 1/4 throttle if the lever angle is adjusted properly. A pink cam upside-down, screw in #2 hole, can do the same with proper lever adjustment.

If this doesn't cure the hesitation, then 50cc pumps and 50cc pump cams may be necessary. Standard pump cams will not increase the delivery of 50cc pumps. 50cc cams have higher lift.

This is an interesting video showing the "puddle" of liquid fuel in an intake. Many thanks to Jon Kaase for the effort required to do this.

https://www.youtube.com/watch?v=7Iq1B-2 ... e=emb_logo
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Re: T slot questions

Post by mopardave »

Nice vid, thanks tuner. My set up is 2 billet 650's on a indy tunnel ram and 511 mopar. I previously thought i have 750's, but the veturi is a 1.325 making it a 650 with a 1 11/16 blade.
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Re: T slot questions

Post by mopardave »

couple vids of what i'm working on.https://youtu.be/9j2CXouWfmU
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Re: T slot questions

Post by mopardave »

Test drive today. https://youtu.be/Ke-MdKWufd8
I notice in the vid that the wide band goes kind of rich at the beginning of the hit, like 11's then evens out to 12.4. pvcr's are .058 and main jets .070, squirt is .035's.
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