Booster Signal

[mike laws]

[Right hand drive]

[Right hand drive]

(Edit to above: .180” downleg boosters)

I forgot to mention earlier the AFR is not only a little leaner with the BLP booster carb and its calibration but a lot more steady AFR until mains start joining in. Almost fi like flipping between two AFR lambda numbers.

Took a look and a few measurements of the two different boosters between the two carbs. Both inserts same overall length. The Demon inserts are a bit taller out of the top of the banjo therefore a larger entry radius. Trailing edge shape the same. Demon trailing edge around .035”-.039” below minor diameter and BLP around .070” below.

So there are a few differences there but without being able to get in and measure actual discharge hole size in the Demons, step size and insert i/d after step for both insert brands and even internal channel dimensions in the Demon booster inserts it seems to be speculation as to low cfm sensitivity and effect on IFR/iab requirements between the two.

What raised an eyebrow and had me curious of hole size effect in annulars is out of about 12 Mighty and Race Demon carbs I have built and tuned with full recalibration this is the first that has needed as large as .035” IFR (low) and low as .067” iab and still be around 1.0 lambda (they are all tuned on the same engine). It may be some other idiosyncrasy of that particular carb leading to the tune state but learning of the effects of these types of variations helps the learning curve and component application and selection for the next street/strip carb build.

Being a fan of annulars I might have to get a bag of blank inserts and experiment.

They look ok in the black Demon too Mike.

[mike laws]

[Right hand drive]

So after another drive this morning the universe makes sense again.

It seems that the O2 sensor was telling lies last weekend. The way it wanted to center around 1 lambda my initial thoughts considering IFR/iab were that the sensor was on its way out. But I dismissed that because other than steady state cruising readings seemed to make sense. I have experienced it before where AFR readings become leaner with a lot of around town cruising, but again dismissed it in this case because that’s not what I was doing, just 10 min drives at least an hour or more apart. Maybe the O2 sensor got to a point where it wasn’t able to regulate its temperature as needed?

So this morning went for a drive on the usual route and this time lambda readings made sense consistent with .035” IFR and .067” iab. At 2000rpm .89 - .91 lambda. Other speeds I test at congruent with this. Replaced IFR/iab with .033” and .070” and curve for tested speeds is about where I expect shifting readings leaner by .4 lambda on average. Change MJ from 77 back to 76 and it’s ready for some WOT runs down the 1/8 next weekend.

So although the tuning irregularity was not as booster related as thought it still opened up thinking along those lines and has me considering booster design and placement in the venturi. Inserts still need reducing by .070”.

I’ll soon get back to the mini annular carb and hopefully by then have some more data acquisition fitted to compare x3 DL i/d boosters, the mini’s and the BLP .600” annulars in an 1.425” venturi x 1.75” throttle carb.

Thanks for your help thus far Mike.

*carb in the pic: Ultra sonic cleaned. factory chromate finish removed. Zinc plated. Black chromate dipped. All levers nickel plated. Metering blocks drilled and tapped for threaded IFR and emulsion. And of course threaded booster conversion.

[rgalajda]

Interesting. I have been trying to follow but maybe I have early dementia or some sort of lack of concentration . Anyway I am not sure what carb you were working on or what carb you are switching too. Maybe you can mention this in your posts for other readers ( meaning me )

[Right hand drive]

[rgalajda]

On the old forum I read where Mark had posted the booster leg inside diameter needs to be approximately .050" larger than the main jet you are using . So a #70 jet would require a .120" minimum leg diameter and so on. Can not remember what else he said but I would assume if the leg i.d. became too large for the jet relationship you could have a lack of signal resulting in late booster startup or/and erratic spitting ?

[Right hand drive]

[jmarkaudio]

Sorry I've been absent for a bit, day job has me hopping the last two years. Anything pass the jet less than double the diameter of the jet will start restricting flow, obviously the closer you get to the jet diameter the more significant it restricts. I always wondered why carb shops sent out methanol carbs with jets sometime .020 larger than the passages after it...

.600 boosters do signal more, but with a fuel channel on the small side it will become a restriction with any significant HP demands. I designed a .610, it signals harder than any booster from any other I've tried, and with a redesigned fuel channel the will supply about 700 HP worth of methanol in a 4150. For more HP I use a custom .545.