OHG X-450 Mixer mounted Sidedraft to EFI Intake.

[Craigwell]

This mixer, able to be mounted for sidedraft operation, flows 450 cfm. I figure that's plenty of flow for my setup.

Wondering if I can just fab up a plate, center the bore over the divided plenum and go, or if this might flow uneven into the two collectors??

For the record, this is a carb engine, higher compression engine running on Propane (as the signature states)

I am looking for an ideal replacement for a stock carb manifold, which I am using with a 1bbl adapter for the OHG mixer currently.. no flow, no go. bad mileage.

 

[xctasy]

8) Keep on with your ideals, you'll enjoy the results because those long tracts will give brilliant low end torque compared to the stock piece of trash 1-bbl intake, and the whole set up will look killer! Additonally, the peak power will still be better than the 1-bbl intake. I love propane, it is a lot of fun because you really can't make a bad intake manifold.


The set up you propose will be fine so long as you ensure both plenumbs get the same amount of gas. You can set up a y-piece with a knife edged division, or a preferably a small log manifold. Either is easy to make, and if you don't like it, you can change it really easily. Propane is very forgiving to the right modifications.

The only issue is that the 4.9 EFI plenumb contains about 2.5 liters of gas not including the adaptor you'll have to make. That could be about 3 liters, which is 50 to 60% of the total capacity of the engine. This produces only one real problem in some circumstances. You might have to back off peak advance on over-run. Propane tends to bank up the inlet tract, and then ignite back up the tract from the intake valve when the advance goes stays at 25 to 35 degrees on over-run.

So just go ahead, and if you get a backfire, then back off total advance, and if it becomes a problem, then you'll have to fiddle around with the advance canistor, maybee fit a vaccum retard hose.

 

[fraso]

The OHG X-450 and Woodward CA475 mixers work best vertically rather than horizontally. The metering rod openings will tend to wear oval-shaped faster when the mixer is placed on its side.

Also, EFI intakes are best suited to EFI operation. Crown Victoria taxis commonly use Impco Model 200s mounted sideways similar to what you are proposing. Most of the time, they work fine. As xecute suggests, you could end up with backfires due to "fuel transport delay".

http://franzh.home.texas.net/fordbackfire/index.html

You could set up a propane injection system if you want to take advantage of the torque characteristics of the manifold.

As for your poor fuel economy, I don't think it is due to the way the mixer is mounted on the 1bbl intake. Do you have a copy of the Diagnostic Guide to properly set up your mixer?

 

[Craigwell]

I think that is a very interesting point xecute, the log might be the way to go. For the record, I could fab one up that would allow the mixer to remain vertical, and still have proper hood clearance.

I do already have the distributor curved to provide a total of 30 degrees.. 14 static, with 8R x 2 for 30 deg total. I can flip to a 10R and back off the static if necessary. Also can back the vac advance off.

The EFI 300 manifold, while long, isn't near as complicated. I can however see the risks of fuel transport delay. I think i would start with very conservative timing characteristics, and tune to suit from there.

I have Franz Hoffman's Guide, and also have Jay Storer's book. My OHG is in good repair (it is a gen II with adjustable 'power valve'. )

I recently tore it down and checked the metering rods, cleaned it out, verified all the o-rings were in good shape. I also rebuilt the X1 Regulator at the same time, new diaphragm, gaskets, springs. There was no problems beforehand or after, just wanted to do it.

I haven't given too much thought to changing out the springs, in either the mixer air horn or in the regulator. I figure i should see what my a/f mixture is like under load, cruise, etc before thinking of changing the setup. An o2 sensor and gauge are in my future, but not cheap.

These exact OHG pieces gave me 20mpg in a light 2wd with standard transmission. The heavy beast I have the gear in now wont see that, but i'd like to get to 15-17mpg.

The vacuum data is what's got me thinking intake / exhaust / valve rocker upgrade at this point:

60 mph in OD, 2000 rpm cruise. Vacuum 5" throttle 3/4 depressed
55 mph in 3rd 2800 rpm cruise. Vacuum 13" throttle 1/3 depressed

I want to be able to cruise at 65 mph in overdrive, turning around 2200rpm, with 13-14" of vacuum.

Feels like I need more tourque at lower rpm.

Thanks very much for the brainstorming.. much appreciated.

 

[fraso]

If you can get 20 mpg with your mixer in a light 2wd with a standard transmission, you've probably got it set up pretty good. The fact that you've got a heavy 4wd vehicle is the main reason you're getting poor fuel economy. There's not much you can do to improve this except drive slow and steady. Lower (numerically) gears can help to reduce pumping and friction losses but 2000 RPM at 60 mph is pretty good too.

Regarding your vacuum data, 5" Hg might be enough to get you into the mixer's power fuel mixture. The low vacuum reduces your pumping losses but the fuel mixture might be too rich for best fuel economy.

The O2 sensor would be handy to help you fine-tune your mixer but, as they say, the proof is in the pudding. I'm not all that familiar with the OHG X-450 and so I'm not sure how independent the power and economy settings are of each other. However, if you want the best fuel economy and don't have to worry about emissions, you can try to gradually lean out the cruising fuel mixture to an acceptable compromise of economy and power. I wouldn't worry about reaching the lean-backfire limit because your truck will lose too much power long before it reaches that point.

As you lean-out the fuel mixture, you also need to advance the timing a bit because the fuel mixture will burn slower and will need to be ignited sooner. This is done with the vacuum advance. The centrifugal advance should be set for maximum power with the power fuel mixture.

 

[80broncoman]

I like the long runner intake best, but if that doesn't work out at least fix a 4 bbl intake like I did this one here:
http://fordsix.com/forum/viewtopic.php?t=13456

and another:
http://fordsix.com/forum/viewtopic.php?t=26247

More info and theroy here:
http://fordsix.com/forum/viewtopic.php?t=40107

I can't think of who else here has done this mod, but I know I'm not the only one.

 

[Craigwell]

That is good information, thank you guys.

5" is meant to be the tip in point for the power valve. On my version of the OHG, I can adjust this.

I will try to lean things out a bit more, and dial in more vacuum advance. I will do it in a baby step or two, and monitor the results.

The best scenario is I get a wideband 02 sensor, and a decent numerical AFR gauge mounted in the dash.

Once I finish some prep work on the 2wd runner I just bought, I'll start driving it daily; which will put me in a better position to get the work done I need on the beast.

 

[Craigwell]

Well, I can confirm that driving with discipline doesn't matter to this setup.

I manually upshifted/downshifted between 3/OD, and kept my vacuum at at least 13" at all times for a week of highway driving. Speeds didnt exceed 60mph unless on a modest down grade.

Didn't make a lick of difference. I swear fuel consumption is better read by how long the engine's running, doesn't seem to matter what it's doing.

My compression being raised 1.5 points, timing curve re-done and vac advance made a good difference for power, but consumption is the same.

I can have it cooking at 75mph, 5" vacuum in overdrive, around 2500rpm, and I get the same 12mpg.

I really think the intake idea, and a swap to an overdrive standard are the only things that might make a difference mileage wise.

 

[fraso]

If you get the same fuel economy at 75 mph as you do at 60 mph, that would tell me that there is something that is not optimized at 60 mph.

Air resistance varies with the square of speed and power varies with the cube of speed. That means that the drag on your vehicle is 1.56 times higher at 75 mph than it is at 60 mph and pushing your truck through the air takes 1.95 times more power at 75 mph than at 60 mph. See air resistance on wikipedia for more information.

My guess is that there is room for improvement in fuel mixture and/or timing at 60 mph. You mentioned that vacuum advance made a good difference for power. Centifugal advance is there to provide maximum full throttle power while vacuum advance provides improved fuel economy at part throttle. With propane, you can't set vacuum advance by listening for part throttle knock and I find that over or under-advanced vacuum advance can significantly reduce fuel economy.

Can you try reducing your vacuum advance in small increments (like 1/4 of a turn)? If your fuel economy gets worse, try gradually increasing it.

 

[Craigwell]

my timing: static 14*
centrifugal: 16* (8R)

vac advance was ordered from rock auto and is the same as it came out of the box. Acceleration from stop much improved.

I did bend the spring holders in slightly when i recurved my centrifugal, i'm all in pretty early.

I do have good power, the truck will hold 80-85mph in overdrive, turning about 2600rpm. Vacuum drops to 0-5" though, throttle plate 3/4 open.

I will play with the advance. Backing it off a bit may be a good idea. I was getting the same mileage before recurving the distributor (it was a 16R!), and replacing the faulty vac advance canister. (it was toast)

I still find it remarkable that the mileage has never wavered, over 15000km with this beast. Doesnt matter if it's all highway, loaded or empty, fast or slow, or all city, etc etc. 12mpg. Almost dont need to look at the gauge on the tank.