can I get any useful flowbench data from a gauge? - newbie flowbench questions please

[diydyno]

hi, first post and trying to get started on understanding diy flowbench principles.

Is a 30"hg vacuum gauge going to show me any useful data when testing a carb or cyl head from a small single?

I was hoping to construct a dedicated cylinder barrel to act as the plenum and just bolt the cyl head to the barrel.

The gaps in my understanding have stalled my build.

Can I use gauges instead of manometers and where do I measure/what do I measure?( is it flow or differential pressure, or something else completely!)
I am confused and not sure what try next.

To help understand my project can I describe what I have constructed up to now...
# I had a damaged single cylinder 4 stroke engine that consists now of crankcase with internals removed and all holes blanked/sealed except for cyl barrel.
# I had hoped this could be the plenum chamber but maybe I am wrong on the principles.
# I fitted a bspt fitting to the side of the chamber to attach a flexi pipe, leading to a vacuum 30" hg gauge
# I fitted another bspt fitting to the chamber to attach the vaccum pump.
Now you all realise the low level of flowbench knowledge I have can you please help!
(here's a pic of the basic engine to show the crankcase/plenum chamber and a drawing of the original assembled engine) is it going to be possible to make a flowbench from the idea?


thanks for reading this far! Hope you can help me get started again.

[Tony]

I suggest you spend some time reading through a great many of the threads here, it is an absolute goldmine of information.

A mechanical pressure gage can certainly be used measure pressure instead of a manometer. But it would most likely be sadly lacking in accuracy, resolution, and repeatability.

Manometers are low cost, simple to make, extremely accurate, and easy to read. That is why we use them.

[diydyno]

thanks Tony.

Anymore thoughts anyone on my idea of using the crankcase as a flowbench? Where should I mount pressure sensors when testing a cyl head, attached to the flowbench?

cheers.

[bruce]

I just flowed some of those heads the other weekend for a kart racer. Showed him why bigger is not always better on his "hogged out" porting job he though would flow massive amounts of air. Filled in some areas with some clay, reflowed the head and picked up 2-5 cfms from .100 -.350 lift . . . when he left he had a big ole smile on his face!

Personally, I'd make a bench and seperate adaptor for testing. Making a bench would allow you to test anything that would come along later. The cost to make a bench is not going to be all that much more than trying to modify a block as a "dedicated" flowbench.

As Tony stated you can get ALOT(?) All(?) of the info you seek by using the search feature of this forum, most of your questions will be answered by reading the past posts.

[diydyno]

thanks for the input.