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Old 12-24-2010, 06:12 PM   #11 (permalink)
ceej
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Join Date: May 2009
Location: Halsey Oregon
Posts: 37

Box - '99 Chevy Metro Base

Transit - '10 Ford Transit Connect Van XLT
90 day: 23.2 mpg (US)
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Sure. The way to do it would be to put a two stage power valve in. They are not suitable for power applications.

The problem is, with a 350 cfm holley, any time your foot gets into it even moderately with such a small engine, the vacuum is going to go away, and fast.

You will have to run a higher numeric number power valve, since the carburetor won't work well at such low signal levels.

As you come off idle, the transfer slots unmask. That's your first stage of enrichment, along with the pump shot. As vacuum drops out, the spring overcomes vacuum opening the power valve to add further enrichment.

If the circuits are too lean, you will have poor acceleration, and if your jets can't cover, lean surge.

Basically, under acceleration more than the most gentle tug, the engine will want something around 12:1 A/F. Basic driving around, 14.7:1. Set up properly with an engine capable of lean burn conditions, 17:1 is where most vehicles will run smoothly, lean of peak. The ragged edge of lean comes in higher than that.

If your particular location has mandated alcohol in the fuel, the numbers on the average meter will be lower. Cruise lean of peak with E85 comes in around 11:1. It's not really that accurate. A good digital lambda meter can be adjusted to read 1 at stoich. That will be more useful.
At the moment in Oregon, we are stuck with E10 in everything. Some places sell premium that has no Alcohol in it.

What is going to happen is, your power valve value will have to be high to allow you to accelerate while merging into traffic. I'd toss a WAG at a 10.5 Standard flow PV working with your engine size. A 12.5/8.5 dual range low flow or something of that range would probably work, though your acceleration will be notably less robust.

The 2300 has a lot more parts available than the 5200 series, so yes, it is more tuneable. Finding a 2300 series that is the right size to allow you to tune it without lots of patching to make the circuits work is going to be another animal. I don't know that it exists.
My second WAG is that you will find the 350 will lean surge on you unless you run pretty heavy jets, PV of course, pump cam, and shooters. I could not get the 500 cfm version to cruise on a 3.7 L engine. The 350 cfm is a tad big for a stock 3.7 as well though the circuits can be bandaided to work.

For the 2.0 Litre, an appropriate carburetor size is 196 cfm. That's with about 83% VE. That's probably about right. The 5200 is technically too large, even with a Volumetric Efficiency of 100% 233 CFM would be the peak flow a 2L would see at an engine speed of 6700 rpm. There is no economy running your engine anywhere near that fast.

For best fuel economy and acceptable power, smaller is better.

CJ


Last edited by ceej; 12-24-2010 at 06:16 PM.. Reason: Typo
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