361 Shootout

[Terry Syd]

The guys at the local shop took their carb for x-rays. They had several shots done at different angles so they could see exactly where all the passages were and how much meat they had to play with.

I wouldn't call what they ended up with as a 'carburetor', it was more like a pipe.

Brian, looking at the extensive work did to open up those transfer tunnels, is that a stock jug or the BB?

 

[parrisw]

Yep, used a boring bar, but sometimes have ground a small 1/4 HSS tool with a profile to do the edges of the venturi when removing choke plate and reworking the entry for a race carb.

Cool thanks!

Say on a 372 carb? How much can you safely take out the venturi?

What are you indicating in the last pic? Is there really any room for adjustment?

 

[timberwolf]

I would have to look at a 372 carb, been a couple years since I worked one of those over, the are a few different carbs found on the 372.

Last pic was just checking centering of the carb.

 

[SpaayDawg]

Just subscribing to this thread. Great read and material content. Please keep it coming!!

 

[Grande Dog]

Howdy,
Back in the day when we were messing with velocity stacks, we used t-handled tapered reamer to adjust the venturi. It can be done without a machine tool.
Regards
Gregg

 

[AUSSIE1]

I had a pin hole through to a passage that wasn't visible to the eye and the only way to find it was by pressurizing the carb under water. A dab of the wife's nail polish sealed it up and doesn't break down with the fuel.

 

[timberwolf]

we used t-handled tapered reamer to adjust the venturi.

Yep, others pretty much must be done with a hand grinder due to odd shaped venturries or bulges over passages.

If you want to work over the diamiters under the throttle or choke plates though that needs a little mor precision.

 

[Tzed250]

Yep, others pretty much must be done with a hand grinder due to odd shaped venturries or bulges over passages.

If you want to work over the diamiters under the throttle or choke plates though that needs a little mor precision.

Do you mean like the WJ-69A has in it?

 

[Zombiechopper]

Brian, would you see any benefit in putting an 044 carb on the 361? I'm a little leary about grinding a carb, was just wondering if the larger carb would work well (aside from the expense of buying a carb). Or is it necessary to run the smaller carb for idle stability etc?

 

[timberwolf]

I was planning to try this, but there are some problems to overcome, it would be far from bolt on. The choke shaft is not indexed correctly to mesh with the 361 linkage, pulse line is fed through face of carb on 361 and direct to carb on 440, fuel curve may need some tweaking and a couple other issues. But I can't see any reason I can't make it work.

 

[Terry Syd]

I figured out from the bit of gasket material on the ported jug that it was the stock jug. That is a fair bit of work on the transfer ducts to get it to flow, I'm waiting to see what you do with the BB!

What is the material you used to measure the cross section of the ducts? It looks like some sort of material that will set and then can be extracted and measured. The guys in the Dolkita BB thread would probably find that stuff useful.

 

[timberwolf]

Just modeling clay. Works well for measuring and casting external transfers too.

Just moved flow bench to the basement, so will get some flow info going.

 

[Terry Syd]

Do you make a couple of runs, one without the piston in place and another with the piston set at BDC? I've always wondered how much, if any, restriction is caused by the flow around and through the piston.

 

[timberwolf]

Actually I have a positioner built into the bench so I can move the piston up and down and load flow info into computer as piston moves. It is quite a bit of work to set up though. So, for looking at port flow I am finding it more practical just to position the piston by hand and measure flow.

 

[timberwolf]

Flow tested a few carbs.

26.7 cfm @ 20 inWC - 361 stock
29.3 cfm @ 20 in WC - 361 moddified
30.4 cfm @ 20 in WC - 440 stock
32.4 cfm @ 20 in WC - 440 moddified

There is a bit of +/- on the numbers as the calibrated orifice was 1.500 and would get better resolution with a smaller orifice.

 

[mtngun]

Thanks for the excellent flow data, TW.

Any drawbacks to modded carbs, assuming it is done well ?

 

[timberwolf]

If it is done right and fuel curve tweaked back to shape there should be little drawback.

However at part throttle lower speeds (say 5-7k) there could be more difficulty with break up of fuel due to lower velocity.

New 361 air filter flows very well, ~63.9 cfm @ 10 inWC

Which actually outflows a new HD filter off the 440.

47.9 cfm @ 10 inWC with dust band on
56.4 cfm @ 10 inWC with dust band off

 

[2000ssm6]

I got a Maxflow kit I give ya for testing purposes if you think it is worth doing. Came off a 460, I know they work but they are dang ugly.

 

[timberwolf]

I might have one of the max flow filters about, not sure. They are ugly and likely not much need. One day when I get the dyno dialed in with some better electronics it would be a good test to see if any difference could be picked up between filters.


Just for the heck of it flow tested the mufflers though it really won't tell much accuratly about non steady state flow under running conditions.

12.1 cfm @ 20 in 361 stock muffler (screen made no measurable difference)
46.7 cfm @ 20 in 361 single port 21.1mm
50.0 cfm @ 20 in 361 dual port 20.5mm

 

[Trigger-Time]

I might have one of the max flow filters about, not sure. They are ugly and likely not much need. One day when I get the dyno dialed in with some better electronics it would be a good test to see if any difference could be picked up between filters.


Just for the heck of it flow tested the mufflers though it really won't tell much accuratly about non steady state flow under running conditions.

12.1 cfm @ 20 in 361 stock muffler (screen made no measurable difference)
46.7 cfm @ 20 in 361 single port 21.1mm
50.0 cfm @ 20 in 361 dual port 20.5mm

Have you ever tested 361 muffler after singel port.
Then removed muffler guts and re-tested?

Or stock muffler before and after guts removed, no MM


TT