Problems with new set up

[Anonymous]

Hey,

I just got my new cam in and alloy head on my 250 crossflow falcon. It works smoothly until about 1700 rpm and it starts missing a bit. I think this is where the main jets come in (it's a 350 holley) and i'm wondering whether they are too small, or too big or what. Also, could it be a vacuum problem with this new setup?

Cam Specs

Crow 14771
Duration at .05 200/205
Lobe separation: 111
Timing: 4 advance
Total lift: .458/.471

The head has slightly bigger valves (1.8/1.6), with some work done in and around the valve and some port work on the exhaust side.

Thanks

 

[addo]

Check your idle speed - get it as low and stable as possible, note your vacuum readings and advance at that point. Make sure the ignition is advancing and firing satisfactorily, and the vacuum stable though dropping, with increasing RPM. How's the temp gauge?

Adam.

 

[xctasy]

Need more input brother! I've followed your XD project a little. Seems to be your on to a winner. You've got a 4-speed floorshift GL with a 2.92:1 diff that has an alloy head?

I could say:-
1.Exhast gas analyser it at a dyno shop, or get a mechanic to check it. 2.You need to know that its sitting at 13:1 air/fuel ratio at wide open throttle.
3.If its part throttle problem, the plastic cam can be changed to a different spring setting.
4. The squirter jets can be upsized,
5. the float level can be out,
6. the fuel pressure must be up to Holley spec,
7. there could be dirt in the fuel system. Holleys hate it!,
8. there could be an air leak, which isn't uncomon,
9. the ported vacuum on the ignition may not be showing enough advance.

10. I could be a dic|< head....

Checking it unloaded won't help.

I'm working on a flow chart for fault checks on Holleys.

Is this a part throttle problem at 65-75 km/h in top, or is it like at 15- 20 km/h in first as your going hard through the gears?

Sorry to be a clever dic|< , Cam. I can help out.

 

[Anonymous]

Hey again,

I think the problem lies with the power valve. The change in vacuum in the manifold due to the cam has caused a change in when the carby delivers the extra spurt of fuel. Which makes sense because it only starts to splutter when its under load or i'm opening the throttle up at about 1800 rpm or so.

 

[xctasy]

MustangGeezer, vlad
delt wit this.

The problem is more likely to be the pump squirter, in my opinion. The stock one is about 25 thou, and on a cammed machine, it needs more of a shot to richen things up. The drop in manifold vacuum is more or less instant off idle, and the power valve tends to come into play at wide open throttle regardless of the rpm.


First, there is a partial enrichement from the plastic cam which holds the spring on the throttle shaft. If you cange the spring position, this can provide extra fuel. Change this and see if it improves. There are 3 positions. I just grab the Holley book from Dave Emaneul, and change the spring to suit the diagram on one of the pages, about 55 form memory.

Secondly, if you realise any change in pump squirters is easier than a power valve swap if you have the tools, then you can go up to 28 or 31 squirters first up. Thats your next step. If there is still a problem, then you are right about the power valve. This is the focus of most of us, but Holley are more intersted in heavy intermediates with 283's, 302's or 318's on there 350 carbs, not guys like us who put fatter cams in sixes. The six has a high amount of wetted perimeter in the intake manifold...the petrol goes into the walls more than into the intake stream than on a V8 which have a better mixture distribution. So a six needs more of a squirt to richen things up than a V8.

Thirdly, a more aggressive power valve which 'pops' open at lower vaccum will allow the car to run richer more often. Any time you cam it up, it looses vacuum, so you should go for a lower number than the stock.

The stock power valve is 8.5" Hg. You can drop to 6.5 if you want to. 4.5 is comon for really big cammed up cars, but you really want a fairly conservative type, or your mileage will get killed dead.


Hope this helps.

 

[Anonymous]

I use a 32 pump squirter on my 250 .Came up from a 25 because of poor off idle response works great now!

 

[Anonymous]

Cam
Just as a side note your 350 holley may be holding it back a bit if 175 HP tops is the limit for a 350 Holley on a good six (as in previous post by Execute). Especially if youve got good extractors/headers. From what Ive seen 190 hp is not hard to make in a Crossflow even with a milder cam. Have a look at some of the old posts on this.
Cheers

 

[Anonymous]

Ive had to revise some of my oppinions after looking at the engine packages by Kostecki (as recently posted). I wouldnt like to guess at a power figure.
Cheers Tim

 

[Anonymous]

Hey again,

I changed the power valve and she goes fine now. I'm going to increase jetting size up to 65 though, as it feels a little lean to me.

Also, I realise the 350 holley is a bit too small for the setup I've got now. At the moment I can't afford it, but I would like to upgrade to a different carb later. What size/type of carb would you suggest?

 

[xctasy]

Ah, the 65 65 jet/ power valve combo! Most 202 Holden s with a 20/60 cam get 63 mains, and a 6.5 power valve, so 65 and 6.5 sound right on a mild 250.

The 500 is just a 350 with more venturi area and bigger throttle bores. The 350 cfm is a 155 hp max carb unless you have a custom cam. The 500 cfm is 220 hp max. In practice, the aussie7mains rule is cfm divided by 2. You wont see 175 hp from a 350, and you wont see 250 hp from a 500 cfm, but you'll get close!


(I did see a reputable source get 354 hp from 500 cfm in a 289 V8, so I won't say its impossible, but have you got 1000 bucks for a custom cam and dyno time?)

Get one of these 500 cfm suckers next time. A swap may happen.

The Holley has some nasty points, but nothing busy hands and a clear head can't fix. The information is everywhere, but few seem to realise where to find it.

You won't have any issues with the 350. It's a nice carb which is frankly too small for a 250, but it does a slightly better job than a 500 for fuel economy.

The ADM 34 is simply too small as well. Great for a non-Performance Forum, not ours!