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173 and a holley 350

Started by _Kevy_ , Sep 30 2012 05:43 PM

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#51 _oldjohnno_

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Posted 05 August 2014 - 10:03 PM

My partner has an auntie Flo. She was my dad's best mate's wife.

There's a joke in there somewhere, something about blowing and sucking. But I'm leaving it alone.

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#52 N/A-PWR

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Posted 05 August 2014 - 10:10 PM

Rob's Dad's Mate is his Father In-law,

and his Mother In-law Flo's well.

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#53 rodomo

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Posted 05 August 2014 - 10:15 PM

Wrong Dave. He was my partner's father's brother............but that irrelevant.

Auntie Flow is no relative of mine.....................at all....................................ever.

But I get what OJ is saying...................sorta.

Edited by rodomo, 05 August 2014 - 10:15 PM.

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#54 N/A-PWR

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Posted 05 August 2014 - 10:19 PM

Got a Flo to it still

Edited by GASPOWER, 05 August 2014 - 10:20 PM.

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#55 EunUCh

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Posted 06 August 2014 - 07:24 AM

I'll lay off the wall a bit now that helps heaps,obviously a bit more to it when it comes to numbers,i just try to simplify complex situations sometimes,obviously

not the best way to about things sometimes.

It sure would make things a bit easier if they did "standardize" things a bit,funny thing is thinking a bit more about it in our 2bbl example given here that

the number i managed to didle is close to 1psi in hg..good stuff,always been interested in how works.

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#56 _oldjohnno_

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Posted 06 August 2014 - 12:46 PM

We can boil the numbers down to something a bit easier to use. For a start we'll get rid of the the CID x VE x RPM bit and replace it with a single peak hp number, which is what the original numbers basically represent anyway. Then we can find factors that will give us carb flow figures for 1.5" and 3"hg - in other words 2 and 4 barrel carbs. What we end up with (for a common-plenum six) is:

peak hp x 1.8 = 4 barrel cfm, and

peak hp x 2.5 = 2 barrel cfm

Obviously there is a fair bit of variation from this possible, and it doesn't take into account things like plenum volume at all. So don't take it as gospel but it'll get you into the ballpark at least.

Auntie Flow is no relative of mine.....................at all....................................ever.

I think I may have met her once. Did she have cubic feet?

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#57 rodomo

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Posted 06 August 2014 - 10:34 PM

Did she have cubic feet?

No, but her hubbies name was Hans.

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#58 _Bluejinx202_

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Posted 07 August 2014 - 09:26 PM

True, but the different style of manifolding with the SUs means that the engine needs the extra flow.
Getting back to single carbs on a common plenum, I haven't tried a 500 Edelbrock on a 202 but I suspect that its secondary design would work very well on a six.

Was with a mate playing around with an edelbrock carb last summer on a chev, in the beginning it was looking promising as far as tunability went and we were starting to talk about trying one on my 202 when we had problems with the rods lifting (or not lifting, can't remember) something to do with low manifold vacuum out the carb on the shelf and replaced with a quickfuel

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#59 _Bluejinx202_

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Posted 07 August 2014 - 09:35 PM

Also, my 202 still has just under an inch of vacuum at WOT sitting at steady 6000 rpm full load and carb is holley 570, thought it was too big when I bought it but seems to be ok, and now after a lot of mucking around seem to have nice holeshot

Edited by Bluejinx202, 07 August 2014 - 09:36 PM.

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#60 _oldjohnno_

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Posted 07 August 2014 - 10:09 PM

Also, my 202 still has just under an inch of vacuum at WOT sitting at steady 6000 rpm full load and carb is holley 570, thought it was too big when I bought it but seems to be ok, and now after a lot of mucking around seem to have nice holeshot

Sounds like it's pretty well sized. Something to look out for with Holleys (and some Holley clones): as if having two different test pressures in use wasn't difficult enough, some of their carbs (the HP series for one) are rated at 28" of water, or about 2"hg. Why do they do this? I have absolutely NFI, and would probably have more chance of explaining the workings of a woman's mind than I would this. Just be aware that the HPs as well as a lot of the "performance" Holley lookalikes use the inflated cfm figures. I suspect that the deadshits in marketing would have something to do with it.

Also keep in mind that it's bloody hard to accurately measure pressure in a moving airstream; the pitot effect means that you often get a slightly lower-than-real reading (ie. higher vacuum number).

Edited by oldjohnno, 07 August 2014 - 10:10 PM.

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#61 orangeLJ

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Posted 08 August 2014 - 07:33 AM

Hole in the steel plate analogy is the best, most simple explanation I've read. Thanks OJ.

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#62 EunUCh

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Posted 08 August 2014 - 04:42 PM

The pressure drop verses flow makes a bit more sense,but since we are talking about flo's rates,,,hear is a dumb question,when they flow a carb., is it done with an air cleaner with base and top with an element or just bolted up to flow bench?

Obviously a large cleaner offers more flow but does this somehow influence the way the air behaves considering it now has to enter from the sides and then'sees" the the air horn and needs to do some gymnastics to get over the "hump" , was just wondering if that there was a some sort of "smoothing" out of air flow over the air horn before it gets to venturi that it might affect air flow one way or the other.

Edited by EunUCh, 08 August 2014 - 04:43 PM.

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#63 UCgazman

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Posted 08 August 2014 - 05:25 PM

Isn't that why a lot of guys mill off the choke tower?

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#64 _oldjohnno_

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Posted 08 August 2014 - 05:50 PM

As far as I know they are tested bare, and dry. Whenever you pull air into an opening the majority of the flow comes from the sides anyway, so it doesn't make a lot of difference to the flow pattern. But a well designed base - eg. L88, Moroso, R2C - will help the flow. I don't think the flow difference with and without a cleaner is enough that you'd need to make allowances in your calcs. And besides, the range of usable carb flows/pressure drops is fairly wide so if I was say 30cfm bigger or smaller than optimum I wouldn't lose any sleep.

Keep in mind that different applications will work best with different sizings - a highly developed pro-stocker might run with only 0.25" pressure drop, a weekend drag racer 0.5", a circuit car 1" and grannies daily driver 2 or 3". Generally the wider the required rev range the higher the pressure drop - or in other words the smaller the carb. A small carb/large pressure drop arrangement will almost tune itself; at the other extreme it'll be much more difficult to get a decent curve.

The choke tower doesn't make as much difference as you'd expect, at least not until you get into the bigger stuff. I cut them off but I have to admit that on something like a 202 it doesn't achieve a thing.

Edited by oldjohnno, 08 August 2014 - 05:52 PM.

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#65 EunUCh

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Posted 08 August 2014 - 06:15 PM

Sounds like they are fairly forgiving apparatus in most cases

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#66 _Bomber Watson_

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Posted 08 August 2014 - 06:37 PM

Should probably point out to, oj hinted at it, they are flow tested dry.

So once theres a stream of fuel in the venturi it changes again.

Again probably not a huge deal.

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#67 N/A-PWR

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Posted 08 August 2014 - 06:40 PM

how does water injection, effect this DJ.

So once theres a stream of fuel in the venturi it changes again.

great information OJ too

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#68 _Bomber Watson_

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Posted 08 August 2014 - 06:42 PM

Water injectiin is generally put into the manifold so wont.

I have seen aperatuses on draw through turbo thigs with a nozzle above the carb, and as we can assune this woud reduce the real world flow through the venturis as well.

Cheers.

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#69 _oldjohnno_

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Posted 08 August 2014 - 07:02 PM

Should probably point out to, oj hinted at it, they are flow tested dry.

So once theres a stream of fuel in the venturi it changes again.

Again probably not a huge deal.

I think that because the pressure-drop rules-of-thumb are derived from experience the allowance for fuel is built in. But a lot of guys add up to 10% flow capacity to the entire intake tract when running methanol. Of course this doesn't apply to us 202 jockeys; we just have to grab as much flow as we can possibly get.

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#70 _oldjohnno_

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Posted 09 August 2014 - 12:14 PM

Here are a few more figures for anyone interested that show the drop in density (and therefore peak hp) with progressively smaller carbs and larger pressure drops. I've used 0.5"Hg as the baseline, the percentages shown are the approximate power decreases from there.

0.5"Hg--0

1"Hg--2%

1.5"Hg--3.5%

2"Hg--5%

2.5"Hg--7%

3"Hg--9%

The trick is in balancing the tuneability and drivability losses incurred with the bigger carbs against the potential power gains.

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#71 EunUCh

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Posted 10 August 2014 - 08:41 AM

Excellent oldjonno ,should be enough info in all that to give someone doing a bit of playing around that has a vac gauge ,lead foot and a bit of a hill to make a decent streeter drive

and behave not too bad even if a slight power loss is sacrificed.