///// How to test for restrictions ... Poor mans Flow Bench /////

Andyinchville1

Veteran Member
Joined
Apr 7, 2016
Location
Virginia
TDI
2003 Jetta TDI wagon, 5 sp, 226K miles
Hi All,

I know alot of us like to modify our cars for better performance and / or fuel economy so that got me to thinking about ways to quantitatively evaluate parts rather guessing and rating things subjectively.

With that in mind, and flow benches being super expensive , I though I could "make" a poor man's flow bench and wanted to run things by you all here to see if there is something I am not thinking of (after all flow benches are high $$ for a reason I guess?).

For my first test (and since I already bought it) , I wanted to see how much better an eBay side mount intercooler (about $100 , all aluminum, and slightly bigger (mostly thicker) than the factory intercooler.

My plan was to use my gas powered back pack blower (a Shindaiwa EB 630 blower rated for up to 651 CFM) and run the blower tube into one end of the intercooler .... I hope the blower tube is about the same size as the intercooler and my plan is to duct tape things to make sure air leaks are a minimum at the connections.

Using an inductive tiny tach , I can set the blower to a common RPM to do all the tests with.

One thing I am missing tho is a way to measure backpressure in the blower tube ( I think that would be the best place to put a guage?) .... what do you think I should use as a gauge or way to measure backpressure ? .... Ideally it should have a long sweep to make for accurate and detailed readings .... I'm not sure that an automotive boost gauge is detailed enough .

I suppose it may be important to have a way to accurately measure air temp and humidity too?

Anything else I may be overlooking? .... seems like this is almost too easy so I have a feeling I may be overlooking something.

With the right adapters , I'm guessing mufflers and exhaust pipes / systems could also be tested.

Thanks in advance for any and all help.

Andrew

PS - How many CFM exhaust flow does our TDI engines make a say 2500 RPM ? I guess boost may play into it also?
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
Northern MD (HAGERBUSH)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress)
what are you going to do with all this info if it works? My feelings on TDI mods is 2 schools, lots of cheap fuel, or $$$ to make it not smoke and we have done both. im 100% for you to make this work as it could help understand what issues could be resolved, BUT i go back to the video on motor trend where they crimped every downpipe before the collector on a 400hp v8 and basically lost only a few HP on a dyno
 

KLXD

Top Post Dawg
Joined
Aug 22, 2009
Location
Lompoc, CA
TDI
'98, '2 Jettas
Your leaf blower rating is based on its own plumbing. Doesn't mean it'll put that out with a restriction, that being your test article. Like an intercooler.

For measuring the pressure drop read up on manometers. A simple tube filled with liquid would be very accurate and cheap.
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
Northern MD (HAGERBUSH)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress)
Very true.
When it comes to air flow, it's considered a fluid. Measuring its volume and keeping things equal are probably the most important vs restriction.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis (where it's safe)
TDI
There are just too many to list....
Even the stock intercooler can move WAY more air than the ALH could ever require. Why do I know this? Because the 180hp 1.8t gas engine, which happily spins past 6300 RPM, uses what is essentially the same unit (only the connections to it are different.... the core itself is the same). And that gas engine is breathing through 2 exhaust and 3 intake valves and is using a larger diameter turbocharger. The advantage to using a larger intercooler isn't for air flow, it is for a broader area for heat exchange.
 

Andyinchville1

Veteran Member
Joined
Apr 7, 2016
Location
Virginia
TDI
2003 Jetta TDI wagon, 5 sp, 226K miles
Your leaf blower rating is based on its own plumbing. Doesn't mean it'll put that out with a restriction, that being your test article. Like an intercooler.

For measuring the pressure drop read up on manometers. A simple tube filled with liquid would be very accurate and cheap.
Yes, I realize any restriction in whatever the blower blows through will reduce its air output ....

I was guessing that the air output reduction would translate into some form of pressure that can be measured therefore determining how well something flows (like a muffler or something .... I have seem muffler tests where they typically show flow in terms of cubic feet per minute but since that would require higher tech equipment (i.e. more expensive) I though I would simply operate with units in backpressure since the equipment to measure that is probably alot cheaper.

I'll look into the manometer .... that does sound pretty cheap.

Andrew
 

Andyinchville1

Veteran Member
Joined
Apr 7, 2016
Location
Virginia
TDI
2003 Jetta TDI wagon, 5 sp, 226K miles
Even the stock intercooler can move WAY more air than the ALH could ever require. Why do I know this? Because the 180hp 1.8t gas engine, which happily spins past 6300 RPM, uses what is essentially the same unit (only the connections to it are different.... the core itself is the same). And that gas engine is breathing through 2 exhaust and 3 intake valves and is using a larger diameter turbocharger. The advantage to using a larger intercooler isn't for air flow, it is for a broader area for heat exchange.
Hi,

No doubt the stock intercooler probably flows well enough (after all it is the one the VW engineers put in), BUT , like so many things, typically more is better and admittedly my real quest was for more MPGs but any added power was OK too.

I had read that diesels gain efficiencies by NOT having the engine operate operate through a throttle plate like previous carb equipped engines (having to "work" to "pull" air through a relatively small restriction).

Given the same thinking but scaled up, it would seem to be reasonable that any restriction in the air intake system may "act" like throttle plate and cause the engine to work harder to " pull" air in thus reducing its efficiency.

I was thinking that the small intercooler (although made of many small passages) may not equal up to the flow of the "pancake" intercooler piping.
(I was blown away to read that a single 3" diameter exhaust pipe flows BETTER than true dual 2" exhaust pipes .... this made me wonder IF the many small passages in the intercooler may pose a restriction when compared to the relatively large diameter of the pancake piping of the rest of the intake system?

Originally I had planned on buying the upgraded intercooler piping , so at that point the intercooler would (in my mind) be THE restriction so I decided to go with the upgraded side mount to boot for about $100 off ebay (I would have gotten the upgraded piping also but it is out of stock at Kerma for now).

I came from mainly using trucks to pull trailers for work and exhaust upgrades for less restriction always seemed to help performance (lower EGTs (which is not a real issue in our cars unless really hot rodded but in towing heavy weights, even a relatively stock engine can get toasty! , better mpgs etc .... admittedly tho the sound of a 4" straight pipe from a 5.9 Cummins was a little excessive even driving easy).

Any idea on how to calculate the CFMs oour 1.9 engines can produce exhaust wise or need intake wise?

Best I could figure was 3.16" stroke times 3.76" bore is about 29.49 cubic inches air per cylinder per revolution times 4 cylinders but then it gets complicated in that exhaust only happens every other stroke , and boost plays a role in addition to all that .... hmmm

Andrew
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis (where it's safe)
TDI
There are just too many to list....
The ALH already runs without a throttle. Efficiency is gained by reducing fuel, not adding air. They are already running lean. So lean, they need less oxygen charge to keep the NOx down (hence EGR). If you want to make the engine more fuel efficient, you'd ditch the EGR, run a fixed MAF value (these two, collectively, are known as a MAF delete tune, but the MAF fixed value will determine to some extent the fuel map), run as small of a nozzle size as available (in the ALH's case, the stock automatic cars' units will do the job), keep the timing in the middle to bottom/middle part of the graph, and possibly for higher speed cruising swap in one of the available taller fifth gears.
 

noob_tl

Well-known member
Joined
Mar 30, 2012
Location
Central Indiana
TDI
2003 NB
It seems to me that the biggest air restriction is the ECM. It determines what pressure it wants in the manifold and adjusts the turbo to achieve that. Anything you do upstream of that won't affect the amount of air flowing through the intake ports, because the ECU will just compensate. The stock plumbing was designed so that it can flow more that the engine will use, so the ECM is always in control. Adding things like an aftermarket cold air intake (often implemented as a warm air intake) or larger piping have no effect unless you've modded the engine to make much, much more power than stock.
 

KLXD

Top Post Dawg
Joined
Aug 22, 2009
Location
Lompoc, CA
TDI
'98, '2 Jettas
Not disagreeing with you guys, just adding this for Andy's edification.

The intake flow even with boost would be relatively easy to figger but the exhaust which includes the burned fuel would be a bit more complicated. Getting deeper into thermodynamics along with fluid flow. I remember enough to know I'd have to dig out my text books from 30 years ago.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis (where it's safe)
TDI
There are just too many to list....
I'd also like to point out the teeny tiny turbocharger... the ultimate limiter of all the air going into and out of the engine. Since the ECU/turbo can through some fault actually quite easily OVER boost the engine, I'd say there is PLENTY of available air. And given the MAP sensor is on the outlet side of the intercooler, it isn't like the intercooler itself is restricting anything.

The intake ports in the head are tiny. Barely any larger than the older smaller displacement engines. They ever so slightly enlarged them as much as they could, but they are pretty limited due to the fact that it isn't a crossflow head. All the ports are side by side, fighting for the same real estate, and they really can't get any larger. The cooling system is very near them, the casting doesn't have anything much else to give up, aside from maybe polishing... but that alone won't do a whole lot as the inside of the intake manifold is even rougher. Not to mention, again, EVERYTHING has to wend its way through that little bitty turbocharger. If you've ever seen one cut open crossways, you'd see just how small they are inside. Your thumb could just about block it shut.
 
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