Transfer slot restrictors - Chevelle Tech
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post #1 of 39 (permalink) Old Apr 19th, 19, 8:29 PM Thread Starter
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Bill
 
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Who has tried them? Now since I changed overdrive gears in the TKO, the rpm at 70 is about 2750. I have the idle and slow speed about right at 13.8-14.0 but as the rpm increases it richens up. At 2750 its low 13's. It was worse and yesterday I went up on the iab from 73 to 75 and down on the mab from 28 to 26. Running a 70 jet in the primary with a 6.5 pv. Not sure on ifr size but it's stock size and down low. Yes t slot is square and it idles at 900 with 12.5 hg vacuum. I thought this might be a good time to try the t slot restrictor but not sure what size? Oh it's a 770 street avenger vacuum secondary.


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post #2 of 39 (permalink) Old Apr 19th, 19, 9:23 PM
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Re: Transfer slot restrictors

Quote:
Originally Posted by William Hennke View Post
Who has tried them? Now since I changed overdrive gears in the TKO, the rpm at 70 is about 2750. I have the idle and slow speed about right at 13.8-14.0 but as the rpm increases it richens up. At 2750 its low 13's. It was worse and yesterday I went up on the iab from 73 to 75 and down on the mab from 28 to 26. Running a 70 jet in the primary with a 6.5 pv. Not sure on ifr size but it's stock size and down low. Yes t slot is square and it idles at 900 with 12.5 hg vacuum. I thought this might be a good time to try the t slot restrictor but not sure what size? Oh it's a 770 street avenger vacuum secondary.
I would go up on the IAB more and see what happens. To easy not to try. try 78-80
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post #3 of 39 (permalink) Old Apr 19th, 19, 9:41 PM Thread Starter
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Bill
 
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Might be worth a try.I can drill a couple this weekend and try them.


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540 BB
10 to 4 comp.
Brodix Race Rite BB-2 Plus heads
Edelbrock RPM Air Gap
Quick Fuel 950 CFM Carb
Hooker Super Comp 2" primary headers
Straub hyd roller 236/[email protected] .050 646/623 107 LSA
Tremec TKO 600 .82 overdrive
3.73 Posi
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post #4 of 39 (permalink) Old Apr 19th, 19, 11:08 PM
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Gary
 
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Re: Transfer slot restrictors

at 2700 rpm you are on the main metering circuit
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post #5 of 39 (permalink) Old Apr 20th, 19, 1:35 AM
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Kerry
 
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I put transfer slot restrictors in the main body of my 770 street avenger. It was the only way I could lean out the 1200-2500 rpm range.
I also put them in my AED 950 HO Modified. Works perfectly.
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post #6 of 39 (permalink) Old Apr 20th, 19, 4:52 AM
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Geoff
 
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Re: Transfer slot restrictors

Reducing the MAB size will start the main system sooner. You may now have a rich overlap of the main + idle system; idle system controls lower cruise rpm.
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post #7 of 39 (permalink) Old Apr 20th, 19, 6:38 AM
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Re: Transfer slot restrictors

Quote:
Originally Posted by William Hennke View Post
Who has tried them? Now since I changed overdrive gears in the TKO, the rpm at 70 is about 2750. I have the idle and slow speed about right at 13.8-14.0 but as the rpm increases it richens up. At 2750 its low 13's. It was worse and yesterday I went up on the iab from 73 to 75 and down on the mab from 28 to 26. Running a 70 jet in the primary with a 6.5 pv. Not sure on ifr size but it's stock size and down low. Yes t slot is square and it idles at 900 with 12.5 hg vacuum. I thought this might be a good time to try the t slot restrictor but not sure what size? Oh it's a 770 street avenger vacuum secondary.
I feel like at 2,750 you are most likely into the main, and that PV might be a bigger issue than the t-slot. When you are at 2750, what does the engine vacuum look like?

T slot restrictors can be as small as .050 and up to .075 on a 4150 based on the ones i've experimented on.

In my experience with them, it's the last thing to get adjusted. When you have the throttle plates set correctly, then the correct combo of IFR and IAB plus the correct mixture screw position, correct powervalve rating to keep it closed until it's needed, then you find the t-slot enrichment is too much. I found it very frustrating to get improvement


Also your drop in MAB down to .026 is going to bring the main in earlier, but depending on what you're seeing elsewhere maybe it's needed. Sometimes I will cheat the primary MAB a little bigger to delay the main and make the secondary MAB a little smaller to bring it in as soon as the secondary opens. But those move effect the overall afr curve, so you might not want to do that.

1967 Chevelle Malibu 4 door


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post #8 of 39 (permalink) Old Apr 20th, 19, 8:46 AM
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Chris
 
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Re: Transfer slot restrictors

ran t-slot jets on my dominator when at drag week last. no way could I have completed it without them. I ran 0.045 to start and would be at 0.050 at the end of the day. Made a big difference all around. not only cruising but the way the car got up on RPM. anyone running rich under 3000rpm, I would recommend this mod to.

with them in my afr was reading 14.5 - 15.2 all the time in Georgia area. at home it would be around 13.5-14.0.

without them I was down at mid to high 12's

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502 big block
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post #9 of 39 (permalink) Old Apr 20th, 19, 9:26 AM
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Kerry
 
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Put your iab and mab back to where they were.

How many turns out are your mixture screws? If less than 1 turn, put a smaller IFR in first.

I use #48 bit .073” in my 950 HO. #51 bit .067” in my 770 street avenger with 4 corner idle.
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post #10 of 39 (permalink) Old Apr 20th, 19, 10:39 AM
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Re: Transfer slot restrictors

I did a fair bit of WB tuning on the 3310 on my BBC truck and documented progress along the way here.

https://www.tapatalk.com/groups/raci...alve-t960.html

Although I didn't try a TSR you might find some of the information useful.

With the amount of valve overlap your engine has the WB is not necessarily accurate at low speeds. The observed 14:1 AFR at idle is probably leaner than true AFR due to oxygen making its way into the exhaust during overlap. As you increase rpm and throttle the dilution effect is reduced. The true AFR may not be getting richer with RPM. The wideband is becoming more accurate. I mention this so you don't spend too much time chasing a number on the wideband. Give the engine what it wants.

At 2750 RPM the IFR still has some influence at very light throttle. I'd guess its insignificant when pulling a grade or accelerating. You were correct to reduce the MAB and increase the IAB to try and lean the cruise AFR in the 2,700 rpm range. You could also try reducing the emulsion bleeds in the primary metering block. These should be 0.028", and you can try 0.026". You might need to bump up the PVCRs to maintain WOT AFR. You might also need a higher # PV to keep from going too lean before the PV opens.

installing a TSJ might also work, but if you lean the top of the TS too much you might experience low speed bucking around town. I think its worth a try though.

After you get the low speed sorted out wire the secondaries shut and check WOT AFR on the primaries only and adjust PVCR to desired AFR. No need to run it to 6,000 rpm. A few short blasts in overdrive should do it. Reenable the secondaries and adjust secondary jetting to achieve desired WOT AFR.

If your 770 does not have the vacuum secondary signal tube, I recommend installing one.

https://www.tapatalk.com/groups/raci...tube-t205.html

I tap the vacuum passage in the vacuum pod for a set screw with a 0.055" hole and remove the check ball from the vacuum pod. Try a yellow secondary spring.
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post #11 of 39 (permalink) Old Apr 20th, 19, 12:30 PM Thread Starter
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Bill
 
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I opened up the iab to 78 this morning it leaned it slightly. I then went from 70 main jet to 68. That put everything in the 14-15 afr range but car didn't like it. The surge/bucking was worse at cruise. I went back to my QF 950 and it runs in the mid 13's on afr at cruise. Still surge/bucking. Changed plugs, even tried a locked mag on it still the surge/bucking. Some of my nightmare can be found here: Overdrive and camshaft selection https://www.chevelles.com/forums/sho....php?t=1084626. My comments start around post #14. I have had this issue for awhile. As in the other post I changed my overdrive gear and made things much better but my surge/bucking though much improved still exists. The simple fact is I have tried everything trying to improve things but I don't think I am going to get there without a cam change.


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540 BB
10 to 4 comp.
Brodix Race Rite BB-2 Plus heads
Edelbrock RPM Air Gap
Quick Fuel 950 CFM Carb
Hooker Super Comp 2" primary headers
Straub hyd roller 236/[email protected] .050 646/623 107 LSA
Tremec TKO 600 .82 overdrive
3.73 Posi
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post #12 of 39 (permalink) Old Apr 20th, 19, 2:02 PM
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Gary
 
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Re: Transfer slot restrictors

surging and bucking indicates its lean. what do you have the timing set at? i would forget about what your o2 readings are for the time being and just put 2 more sizes primary jet in and see what that does for the surging. im sure it runs killer with that cam but the 107 lca and the 12 degrees more exh duration arent helping it at low cruising speeds. the dual plane should help with the low speed reversion. that said you should still be able to tune it. first thing to do is give it more fuel.use the afr gauge as a reference . dont go at it with you have to make cruise 14.5 to one.
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post #13 of 39 (permalink) Old Apr 20th, 19, 2:14 PM
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Re: Transfer slot restrictors

Quote:
Originally Posted by William Hennke View Post
I opened up the iab to 78 this morning it leaned it slightly. I then went from 70 main jet to 68. That put everything in the 14-15 afr range but car didn't like it. The surge/bucking was worse at cruise. I went back to my QF 950 and it runs in the mid 13's on afr at cruise. Still surge/bucking. Changed plugs, even tried a locked mag on it still the surge/bucking. Some of my nightmare can be found here: Overdrive and camshaft selection https://www.chevelles.com/forums/sho....php?t=1084626. My comments start around post #14. I have had this issue for awhile. As in the other post I changed my overdrive gear and made things much better but my surge/bucking though much improved still exists. The simple fact is I have tried everything trying to improve things but I don't think I am going to get there without a cam change.
In my experience, 68 PMJ is too small for a 770. My truck has a smooth WB signal with a 70 PMJ, but cruise AFR is in the mid 13's. With a 69 PMJ the cruise AFR is mid 14's, but the AFR spikes quite a bit due to misfire. You have to keep the leanest cylinder happy. Say the WB reads 14 AFR average, the leanest cylinder might be 16 AFR and misfiring.
69-CHVL and anix like this.
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post #14 of 39 (permalink) Old Apr 20th, 19, 3:09 PM Thread Starter
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Bill
 
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I knew the 68 was most likely too lean but wanted to try it. I have had the timing all over including locked at 34,36 and 38. Right now timing at 18 initial 36 total mechanical all in around 2600. I have 8* vacuum hooked to full vacuum. 2 different carbs one in the low to mid 13's with no improvement. It shouldn't be that hard to make it run. My opinion is it's a waste of time. That overlap is causing a lot of reversion in the intake. Even if I do get it out which i doubt, I am sure it will suck gas and still be temperamental. I have had some big cams on the street before but never anything that tight on lsa. It was a bad decision on my part to run it and I just as well change it and move on.


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540 BB
10 to 4 comp.
Brodix Race Rite BB-2 Plus heads
Edelbrock RPM Air Gap
Quick Fuel 950 CFM Carb
Hooker Super Comp 2" primary headers
Straub hyd roller 236/[email protected] .050 646/623 107 LSA
Tremec TKO 600 .82 overdrive
3.73 Posi
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post #15 of 39 (permalink) Old Apr 20th, 19, 3:28 PM
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Gary
 
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Re: Transfer slot restrictors

Try throwing some jet at it just to see what happens. The only takes a few minutes
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