600 Holley on a 2V

[Anonymous]

After looking at all the old posts Im convinced it should work. I hope to get a 600 Holley in the next couple of weeks to put on my 250 2V. Ive just gone back through all the old posts on 600 650 mods to a 2V manifold ect. Even on "XT Falcons" engine with a fairly mild idle the 600 appears to work well.
Ill take the car out soon as it is and give it some curry and record times to see if the latter new addition does actually make a difference. If it doesnt work Ill move the timing gear around a bit (nine key way) to increase the duration. But Im expecting some gain without having to do this.
Only one problem I can see is that I will not be able to have the carb facing the normal way as its "wings" will stick out and hit my brake booster in the Cortina engine bay. Subsequently Ill have to turn it around which will mean the primaries will be off centre on the manfold and might prejudice the flow all to one side. I am hoping to get around this by trying to direct the flow toward the centre with a piece of half sectioned channel on an angle welded to the underside of the four barrel adapter to about 20 mm off the floor of the manifold?
I was considering dampening the secondaries but the carb re-builder I spoke to seemed to think that If I dampened the secondaries too much I may have trouble if I have innsufficient vacume to get the secondaries to work?
Just as a final note C.O.M.E racing recommend that a 465 or a 600cfm Holley be used in conjuction with the cams from their maximum efficiency range in a 253 Holden. The hottest cam in this range is a 204 at 50 which I estimate to peak at about 4000 rpm (although it will do more).I believe C.O.M.E come to a lot of there recommendations through stringent testing?
Any suggestions appreciated.

 

[xctasy]

Remember this rule, and stick with it. Carb cfm at 1.5"Hg divided by 1.6, gives the net flywheel hp. 390 = 244 hp, 465 =290 hp, 600 cfm = 375 hp. If its a two barrel, 350 is actually 247 cfm, and 154 hp, the 500 cfm is really 354 cfm, and 221 hp. A Weber DGAS 32/36 or US Holley Weber is pegged at around 230 cfm at 2"Hg. This is only 200 cfm at 1.5" hg, and 125 hp. Funny thing is, it works in every case. The ceiling limit only gets pushed when you have a volumetric efficiency of over 100%, like the NASCAR V8's. They run up to 3.8" hg at maximum power. A piddly 650 cfm double pumper carb with a restrictor plate does 650 hp.

You'll see that a 350 cfm Holley is only a 247 cfm carb at 1.5"Hg. To get 200 hp, the cfm flow is going to have to be 200*1.6, or 320 cfm at 1.5"Hg. In practice, the carb will have to suck close to 2.5" hg pressure. Over carbing is okay if its limited, Tim, and as long as it packages and works well on the primaries most of the time, and really well on the secondaries, then a 600 cfm carb isn't going to hurt performance of economy over a 500 cfm 2-bbl.

Example:-The Commodore Cup 253's have to run a 465 cfm Holley 4-bbl. They started off with 280 hp, and are now well over 300. 600's are illegal. The idea is simple, and it was discussed way back in 1988 on four cylinder Pinto engines all of 121.5 cubic inches. A single 2-bbl carb 350 cfm carb is more suseptable to surge from intake impulses than a 390 cfm carb. And any 2-bbl 350 cfm carb isn't a 350 at all, its a 247 cfm carb. A 390 or 600 cfm 4-bbl vac sec carb drives around as a 195 or 300 cfm carb most of the time, and then the vaccum secondaries only open up enough to feed the demands of the engine. Most of the time, a good six doing between 200 and 300 hp will only need between 320 cfm and 480 cfm to get that kind of power. The secondary ciruit is only there as a giant accelerator pump, and a little oversupply of fuel at wide open throttle does no harm to performance.

A 600 cfm carb is less restricted in the venturi area than a 390 cfm carb. The airflow is smoother and they are less suseptable to pulse waves from the intake reverting bacwards up the intake tract to upset the air/fuel atomisation. Plus, there is over 45 years worth of calibaration experiance with the carb.

On the race track, NASCAR, CAMS etc figure a restrctive carb is a good way of limiting the total $$$ people spend on there engines. If a 600 cfm carb was allowed, you can bet the 253 Commodores would be sailing on on towards the 375 hp zone

 

[Anonymous]

Its going to be fairly borderline on my 250 2V. But this is one reason I want to try it. I have gone from the stromberg 220cfm to the 350/250 cfm to the 500/350 cfm over the last 12 months (keep sending them back to the poor carb re-builder) and each time I seem to have freed up more and more power. But to go from a 350 to a 600 seems like a huge jump and I admit, I am a little apprehensive.
The only consolation is that I dont go very quick that often and If the secondaries give any benefit at all when I do then I figure it will be worth the effort and with future mods Ill never have to be concerned about the carb being too small.
Thanks for the above. Any thoughts greatly valued

 

[xctasy]

Well, one thing I'd like to add. The 1984 Mustang 5.0 got a 4v 4180 Holley 600 cfm carb on an unleaded, catalysed, 175 hp, IIRC, V8 engine that kicked out ~245 lb-ft.

What's the difference between that and yours? 175 HP with 600 cfm...I'll bet the secondaries were hardly ever open, and it ran on the front primaries most of the time.

Because it runs on a 300 cfm front set of barrels, its no jump at all. Ford Cortinas and Pintos ran the Holley 390 cfm carb on the Offenhauser twin plane intake manifold, and often never gave more than 150 hp. It gave better drivability than any of the 2-bbls. The Chevy Vega 2.3 alloy four had a Holley 390 4-bbl kit for use on a very nice alloy intake. If a rough pulsing four cylinder engine can take it, then so should a 250 cube engine. There should be no issues with reversion, even with the giant ports and intake runners.

If I'm wrong, I'll just have to threaten to eat my shoelaces again....

You'll possibly find an PN 8007 390 cfm carb is harder to find, but if you are worried, use one of these first.

 

[Anonymous]

Execute
Rang around today can get a 390 fairly cheap. Only one question the guy who ran one on his 4.0 litre AMG 6 and who recommended a 600 Holley said when he had tried the 390 he seemed to think it created to much of a restriction when going to the Secondaries.
Do you know what he means is this likely to be a problem on a 2V. I presume this is the same carb that the track pack used at Tonsley park without much success (for reasons you did mention) but has been used successfully on 253 racing.
I presume it will be OK just thought Id check.
Kind regards Tim.

 

[xctasy]

Tim said

I presume this is the same carb that the track pack used at Tonsley park without much success

The Mopar Men in South Australia used the American import Carter AVS carb. It was a bossom buddy of the AFB, perhaps a 500 cfm carb. The Pacer 245 4-bbl was quite a nice thing, but on the track, the smaller 2-bbl was a better deal. Dunno why asside from Mike Staceys team focus on the less powerfull 2-bbl.

Any ariel view of a 390 verses a 600 will show you the massive amount of venturi area restriction the little one has verses its bigger brother. Everyone with the smaller one seams to find that it's too restrictive on sixes. 465 cfm 4-bbls are the minimum Bill Shaw recomends for 4-bbl Hemi 245/265 engines. Its the signal hurting the smooth atomisation of the fuel air mix, I am sure from all the stuff I've seen and read. A smaller venturi just subjects the incomming mix to more turbelence. On a Pinto 2000, the air speed is likely to be higher as the idle is faster, and they rev more off line than a six.

Hope this helps. I'm putting the finshing touches on the Holley carb listings. Perhaps this will help you see what I'm prattling on about!