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Old 08-07-2022, 05:21 PM
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Thanks for the kind words supporting my previous experiences on a dyno and in vehicle testing, Mike.

Tom V.

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Old 08-07-2022, 06:50 PM
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Will be a cool deal to see how it goes.

Some of the older Wide bands used a sensor that had to be fresh air calibrated. There are some newer ones that do not, I have one of the newer ones on the data logger on the IA Camaro.

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Old 08-08-2022, 10:09 AM
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Steve Morris used the Sensors that had to be fresh air calibrated before each run.
Not sure of the brand, many years ago.

A Lot better parts (if they come from a good source) vs the old days.

Tom V.

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Old 08-08-2022, 12:08 PM
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I have an even older K&N O2 monitor that used a narrow band sensor and tried to extrapolate from there.

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Old 08-10-2022, 07:56 AM
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I have a few preliminary results from a second dyno session with the replica bathtub intake and a pair of 750 AFB carbs. Total dyno time, about 9 hours. 20 gallons of what is called around here, recreational gasoline. 90 octane, zero alcohol. I am not going to post dyno sheets because the printer is dead and may need to be replaced on the dyno. I will take some screen shots and post next week. Bottom line, that intake with my engine combo at least wants TONS and TONS of fuel!. It's just crazy. The more fuel you throw at it, the more power it makes and I don't have jets or metering rods to make it "too rich". The largest jets for the AFB style carbs are 120's. I had some 116's and it was still pretty lean. Like 14.8-15:1 AFR in spots. So what's a caveman to do? Drill them out of course. So I ran a 1/8" bit through the secondary jets, to see what would happen. It loved it. Picked up 30 HP with that change. But still averaging 13.2-13.7 AFR. It's much smoother now through the pulls but still not rich enough. Also has one very lean spot between primary to secondary transition, when the velocity valve in the AFB is opening and secondary fuel begins to flow. Has a couple hundred RPM spread with high 15:1-low 16:1 AFR. So still some tuning to do. But it's getting close. Picked-up 100 HP yesterday and there is probably 10-15 HP more still out there. But that's just about it IMO. Will play some more after the Norwalk event.

I know people want to know HP and torque numbers so here the peaks so far. 452 Ft. lbs.@ 4800 RPM. 441 HP @ 5900 RPM. I think it's going to finish at about 460 HP.

Two things are really hurting it that were part of the Street engine compromise. Compression is low. Static: 10.1 with aluminum heads. Running on readily available pump gas was a must. The stock iron long branch exhaust manifolds are too small. I can just tell they are really bottled-up over 5200 rpm's or so. You can hear it on the dyno.

Overall, it idles nice @ 1000 RPM, is very snappy and sharp on the primaries with direct linkage, zero leaks, and it looks cool.

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Old 08-10-2022, 08:10 AM
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Mike,
If these are "SFD" files. If you email them to me I can print them to PDFs and posts the PDFs.

Stan Weiss <srweiss1@comcast.net>

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Old 08-10-2022, 08:20 AM
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And that's why chicks dig him.

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Old 08-10-2022, 10:49 AM
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The next step is clear.....take a drill bit to the primary jets!!

Eric

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Old 08-10-2022, 10:59 AM
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Quote:
Originally Posted by Stan Weiss View Post
Mike,
If these are "SFD" files. If you email them to me I can print them to PDFs and posts the PDFs.

Stan Weiss <srweiss1@comcast.net>

Stan
Thank you for the offer and I may take you up on this. I have to shift gears and get ready for Norwalk. But when I get back, I will either get a new printer, fix the old one or get the files to you. I don't have ready access to them at home.

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Old 08-15-2022, 08:07 PM
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I spent considerable time at the Norwalk event talking to people I thought might be able to offer a little assistance tuning my engine with the bathtub intake. Spoke at length with both David and Rodney Butler, Arnie Beswick, Dimitrie Toth, and others. All have experience with the various Bathtub replicas and original Bathtubs and AFB carburetors. Everyone i spoke to seemed to feel a 4-hole spacer was a must to make this set-up work better . So I ordered a couple spacers today. Was trying to avoid using any spacers due to limited hood clearance. But if needed, I will run them. Also, everyone agreed the iron long branch exhaust manifolds are not adequate for this displacement and cam, heads and induction system. So I borrowed a pair of Hooker competition 4 tube headers for dyno comparison purposes only. Plan to run again Wednesday or Thursday. I will share results. This will be my last dyno session as the engine will have to be removed for school to start next week. Hope to pick-up another 20 HP or so with the spacers, jetting and timing. Maybe another 20-25 HP with a good set of headers. We will see.

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Old 08-15-2022, 08:29 PM
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I'd be curious how the headers effect the jetting.

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Old 08-15-2022, 08:37 PM
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Mike,what about just a couple 4 hole gaskets stacked to save you some room?Tom

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Old 08-15-2022, 09:14 PM
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Quote:
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Mike,what about just a couple 4 hole gaskets stacked to save you some room?Tom
That's a great question Tom. I will start with the 1/2" spacers, since many were run that way. Then maybe try 1/4" worth of gaskets. I really wish I had more time to try all kinds of fun stuff. But unfortunately, one more dyno session is all I am going to be able to do. Want to get the most bang for the buck. I should mention, it is running very well now but of course I want to get the most I can out of it. Just feel like it's down on power based on the hardware in the engine. In my car, on the street, it's probably fine. But we always want more. Also, the better it runs, the more efficient it is.

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Old 08-15-2022, 10:01 PM
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Arnie indicated that the bathtub + AFB combo took a lot of work to optimize. Mikes experiments will be a great baseline for the new users.

Eric

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Old 08-16-2022, 07:10 AM
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FWIW the factory inline dual setups mounted on the 542991 and 9770859 intakes had 3/8" spacers on them. I do not know the thickness of any spacers the factory put on bathtubs but found some 1/4" spacers that I've put on bathtubs sets I've restored for people. The next time you have the tops off of your carbs pull the rear boosters out and then the secondary air valves and weigh the valves. The problem may be that you need lighter secondary valves and I may/probably have a lighter set I can send you to try if you wish.

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Old 08-16-2022, 08:11 AM
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Thanks for the reply, 61-63. I will weigh the air valves after I take the engine off the dyno. Unfortunately, just running out of time . But actually, it is acting like they may be a little too light based on the air/fuel ratio when I first load in the dyno. It goes pretty lean then catches up after a few seconds. I have talked to a couple friends that dyno lots of engines and they say AFB's response is pretty unpredictable on the dyno as there is no way to really duplicate the load of a moving car with the static load a dyno applies. Those air valves probably need to be tuned once back in the car and driving. They said Q-jets can present similar challenges but are soooo easy to tune compared to AFB's. I am planning to try and get a Go-Pro camera mounted above the secondaries to take some video of how the air valves are operating on the dyno. Just to see how they behave. 61-63, I will be in touch after running it again. Thanks.

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Old 08-16-2022, 03:08 PM
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Quote:
Originally Posted by mgarblik View Post
That's a great question Tom. I will start with the 1/2" spacers, since many were run that way. Then maybe try 1/4" worth of gaskets. I really wish I had more time to try all kinds of fun stuff. But unfortunately, one more dyno session is all I am going to be able to do. Want to get the most bang for the buck. I should mention, it is running very well now but of course I want to get the most I can out of it. Just feel like it's down on power based on the hardware in the engine. In my car, on the street, it's probably fine. But we always want more. Also, the better it runs, the more efficient it is.
Years ago, Joe Zajac and Larry Kaufman were trying to get a bit better response out of their 750 cfm AFB carbs with the 'generation 3' intake that Randy Williams did for them for the NSS cars.
The 'generation 3' intake is very similar to the Intakes being produced today.

So they tried the mod I suggested.

Two AFB 4 hole metal plates 1/8th inch thick. Carb throttle bores for the 750 cfm carbs may be different vs the carbs you choose to run.

MATCH the metal plates to your carb throttle bore sizes.

Now for the Modifications:

Measure and cut 8 pieces of steel tubing so that the inside diameter of the tubing matches your throttle bore dimensions.

Bore the AFB 4 hole metal plates so that each machined bore just matches the outside diameter of the 1" long steel tubes.

Weld "in 4 places" the metal tubes to the plates. so now you have two 4 hole "inverse" inserts that do not raise the height of the carbs more than 3/16 of an inch and still provide the "4-Hole" SIGNAL you want the bottom of the carbs to see from the intake plenum.

Worked great on Larry and Joe's intakes and they were very happy with the better throttle response, lower ETs, and slight MPH improvement.

Tom V.

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Old 08-16-2022, 03:26 PM
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Quote:
Originally Posted by Tom Vaught View Post
Years ago, Joe Zajac and Larry Kaufman were trying to get a bit better response out of their 750 cfm AFB carbs with the 'generation 3' intake that Randy Williams did for them for the NSS cars.
The 'generation 3' intake is very similar to the Intakes being produced today.

So they tried the mod I suggested.

Two AFB 4 hole metal plates 1/8th inch thick. Carb throttle bores for the 750 cfm carbs may be different vs the carbs you choose to run.

MATCH the metal plates to your carb throttle bore sizes.

Now for the Modifications:

Measure and cut 8 pieces of steel tubing so that the inside diameter of the tubing matches your throttle bore dimensions.

Bore the AFB 4 hole metal plates so that each machined bore just matches the outside diameter of the 1" long steel tubes.

Weld "in 4 places" the metal tubes to the plates. so now you have two 4 hole "inverse" inserts that do not raise the height of the carbs more than 3/16 of an inch and still provide the "4-Hole" SIGNAL you want the bottom of the carbs to see from the intake plenum.

Worked great on Larry and Joe's intakes and they were very happy with the better throttle response, lower ETs, and slight MPH improvement.

Tom V.
Tom,
Unless I miss understand what you are saying. That sound like what many companies make and sell as "shear plates". I don't know that I have ever seen one made for an AFB.

Stan

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  #39  
Old 08-16-2022, 06:22 PM
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Agree Stan, and the plates being sold are made from aluminum and are typically 1/2"
thick.

That is why I posted the info on how we made our plates from steel and for AFB carbs.

Tom V.

And yes the Shear Plates have been around for a good number of years. They work.

We made those plates many years ago FOR AFBs.

Tom V.

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  #40  
Old 08-16-2022, 06:43 PM
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That's a nice idea Tom. We have a couple shear plates at the school but for dominator carbs. I like the idea. If I could have anticipated all the issues ahead of time, I could have had things like this ready to test on the dyno. No time now. I have one more shot to get it as good as i can with the parts I can get together very quickly. Engine has to come off after next session. Next chance to dyno test would be June, 2023. School starts next Monday. No faculty projects allowed during the school year, period. It's all about the students and their engines. If I can't get it to a level I am happy with, I could run it on the chassis dyno next spring. That may be the best way to continue this anyway. Thanks for the idea.

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