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173 and a holley 350

Started by _Kevy_ , Sep 30 2012 05:43 PM

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70 replies to this topic

#26 _Bomber Watson_

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Posted 15 January 2013 - 08:26 PM

Knowitall.

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#27 _oldjohnno_

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Posted 15 January 2013 - 08:30 PM

Knowitall.

Nah, I just make this shit up..

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#28 _Bomber Watson_

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Posted 15 January 2013 - 08:31 PM

Very convincingly!!!!

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#29 N/A-PWR

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Posted 16 January 2013 - 01:47 AM

OK oldjohnno and Bomber Watson,
Let's say the 'Big Boy' Holley #6425 would be useful on a Fully Worked Six up to a point.
It's something to experiment with - I was leaning towards the 650cfm but the 735cfm has some goodies. Dave I

p.s. a custom manifold having the carb a Foot from the head.

Edited by TORYPOWER, 16 January 2013 - 01:49 AM.

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#30 _oldjohnno_

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Posted 16 January 2013 - 06:31 AM

OK oldjohnno and Bomber Watson,
Let's say the 'Big Boy' Holley #6425 would be useful on a Fully Worked Six up to a point.

I can't agree with that. Even if we ignore the obvious sizing issue, I just don't understand why anyone would want to use such a carb unless you were forced to by the rulebook. There's any number of carbs (either single or multiple) available that would do a much better job and at a lower cost.

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#31 warrenm

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Posted 16 January 2013 - 07:23 AM

I'm with you oldjohnno.^

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#32 N/A-PWR

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Posted 16 January 2013 - 09:55 AM

I can't agree with that. Even if we ignore the obvious sizing issue, I just don't understand why anyone would want to use such a carb unless you were forced to by the rulebook. There's any number of carbs (either single or multiple) available that would do a much better job and at a lower cost.

Thank-you oldjohnno for your great knowledge,
I suppose I am a 2bbl Fan and like to push their boundaries. Dave I

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#33 _oldjohnno_

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Posted 16 January 2013 - 10:26 AM

Thank-you oldjohnno for your great knowledge,

See post #27

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#34 _Bomber Watson_

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Posted 16 January 2013 - 07:20 PM

Peronsally i'd put a $50 4bbl on before a $5000 2bbl....

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#35 _Kevy_

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Posted 03 August 2014 - 04:40 PM

Bugga the 173. Iv'e just had a 202 (204) built by a mate that is the similar bottom end specks as a bathurst xu1 and the high compression 173 head has been ported to extremes with inlet posts removed but has not been on a flow bench , has flat top pistons blue motor rods and a crow xu1 street grind cam ( not sure of the cam number) and complete valve train too not sure of the brand but the largest valves that can fit ( not yella terra). But the second set of valve springs not in yet until run in, Has an Aussie speed four barrel manifold ( 9 port ) To run my 350 holley until i could afford to buy a 465 or 390 holley for it, We have had a 350 holley on it and it just run out of puff, Then put a 500 holley on it and it wont cruise but is the fastest thing iv'e ever sat my arse in, Everyone said you will never get a 500 holley to work correctly at low to cruising rpm's ( which the car will do 90% of the time) so i bought a brand new 465 holley and it's chocking this thing, cruises fine and is extremely economical but no fun factor like the 500, and the 465 makes this thing sound like a stock engine no lump at all . So my question is do i get a 500 holley and hope it will be ok or just go for the 600 with vac secondary's. I have to buy a 500 holley and money is running out and 600's there's plenty around. Would it be worthwhile stuffing around with a 600 on a 202?

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#36 _Bomber Watson_

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Posted 03 August 2014 - 06:05 PM

a 465 4bbl flows more air by a reasonable margin than a 500 2bbl.

Sounds like you might have a to stiff vac secondary spring in it?

Cheers.

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#37 EunUCh

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Posted 03 August 2014 - 06:51 PM

If the calculator is correct a 173 @7000rpm with a volumetric efficency of 90% will need 315 cfm of carb.

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#38 _Bomber Watson_

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Posted 03 August 2014 - 06:55 PM

Which calculator?

The holley one is useless, it doesnt take into account the pressure drop.

So, at what pressure drop is the 315 cfm?

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#39 _Kevy_

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Posted 03 August 2014 - 07:18 PM

The secondary's diaphragm spring has been changed to a much lighter one (Jets have not yet, neither has the powervalve been changed havn't tested the vacuum yet ) Vacuum was at 11 inch pounds with the 500 holley( 55 powervalve in that ) installed not sure on the 465 yet and the secondary's open at which seems like 3/4 throttle at mid rpm's but havn't done final tuning yet, to start with they would only open at full throttle high rpms which left the thing pinging until ya got ya foot flat. We should have got the head flow tested first might have been easier to choose a carb.

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#40 EunUCh

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Posted 04 August 2014 - 07:20 AM

Sorry bomber it was the calculator on my bench in front of me at the time that i put an equation in to find how much a 173ci engine

would flow,it may not be right hence the "if".

Never could get my head around the pressure drop verses flow stuff through carbs,never really bothered with it but no doubt there will be differences.

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#41 _Bomber Watson_

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Posted 04 August 2014 - 09:49 AM

Ressure drop is the vacuume at whih an orifice is tested.

Ie a cylinder head on the flow bench is tested at x pressure drop to get x cfm.

If you just work out the amount of air the engine needs, and get a carb of that size that is tested at 18", you will have 18" vac at wot....ie it wont get there.

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#42 _victor_

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Posted 04 August 2014 - 11:04 AM

I had 465 holey on 186/192 after rejeting ran fine, but nowhere as good as 3 x 150CD.

But one carby just less trouble to tune than 3.

350 should be fine until you do everthing you want to the motor, you then can pick the right carby when motor is done.

Victor

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#43 _oldjohnno_

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Posted 04 August 2014 - 12:05 PM

If the calculator is correct a 173 @7000rpm with a volumetric efficency of 90% will need 315 cfm of carb.

Most people seem to get the best results with a drop of 0.5" to 1"hg at the hp peak. So if we split the difference and call it 3/4" hg and use 315cfm as our raw flow number and then convert it to the 2 and 4 barrel standards we get about 640cfm for the 2 barrel and about 450cfm for a 4 barrel. Which to me sounds as if it would be at least in the ballpark. I've always thought that a pair of 350s end to end would work very well on a 202 with a tunnel ram style manifold. Size-wise they'd be very close to perfect.

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#44 _ljxu1torana_

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Posted 04 August 2014 - 03:27 PM

what about the 390 4 barrell holley.

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#45 _Bomber Watson_

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Posted 04 August 2014 - 04:01 PM

Its about 75cfm less than a 465?

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#46 EunUCh

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Posted 05 August 2014 - 04:46 PM

I still don't get the pressure drop/flow bit :banghead:

Does this mean same 173 engine at 6000 @ same VE will need about 549 cfm (2bbl)..or is there a bit more to it..i don't get it?

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#47 _oldjohnno_

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Posted 05 August 2014 - 09:18 PM

I still don't get the pressure drop/flow bit

Does this mean same 173 engine at 6000 @ same VE will need about 549 cfm (2bbl)..or is there a bit more to it..i don't get it?

Imagine you have a piece of steel plate with a 1/2" hole drilled through it. How much air can this hole flow? The answer is it depends on how much pressure is applied, or more precisely, how much pressure difference there is between the high pressure and low pressure side. There is no absolute number that will describe its flow capacity. If it's just sitting there on the bench it flows nothing, but if you apply say 5 psi to one side there'll be airflow through the hole. If you increase the pressure to 20 psi the flow will increase, and if you increase it again to 300 psi it'll increase again. But if you have 300 psi on both sides of the hole your flow will be zero - it's the pressure difference across the hole that matters. You can produce flow just as easily by reducing the pressure on one side - it still creates the pressure differential that produces the flow.

Obviously then we can't give our hole-in-a-bit-of-steel a flow rating without also specifying a pressure drop - the two are linked. But we might call it 600cfm at 150psi for example. A carburetor is the same, without specifying a test pressure the cfm number is meaningless. So we need a standard test pressure, and when carbs were first being classified by cfm that pressure was 3" of mercury, or about 1.5psi. Back in those days they were mainly 2 barrel carbs and 3"hg became the defacto standard, and it's still the standard today for 2 barrel carbs.

When 4 barrel carbs were introduced there was a problem though - most of the flow benches of the time simply didn't have enough capacity to pull 3"hg of suction through the bigger carbs. So the 4 barrels were tested at half the depression, just 1.5"hg and this became the 4 barrel standard. Obviously then it meant that because the 2 barrels and 4 barrels used different test methods, the cfm figures for each weren't comparable. They still aren't today.

But it gets worse. Say we calculate that our engine needs 315cfm of air at peak hp. Does that mean we choose a carb that flows 315cfm at 3"hg? Or 1.5"hg? Neither actually. We know from experience that a drag engine performs best if the pressure drop across the carburetor is somewhere between 0.5" and 1"hg at peak hp. So what we really need is a carb that flows 315cfm at say 3/4"hg. It'd make a lot of sense for the carb manufacturers to rate their carbs at this pressure but they don't, they stick with the traditional 1.5" and 3". Which means we have some sums to do to convert the flow @ .75" to the flow @ 1.5" or 3" so we can select the right carb. And to do this we just have to remember that the flow rate isn't in direct proportion to the pressure drop but to the square root of the pressure drop. In other words, to double the flow you need to increase the pressure by a factor of 4.

Just keep in mind that all this applies to a 6 or 8 cyl engine with all the intake runners linked into a common manifold. Once you divide the runners up into singles or sub-groups (eg. a V8 with a dual plane) a whole other set of calcs apply. And yes your sums for cfm at 6000rpm are correct.

Hope this helps.