Cylinder head adaptor query.

[4v6]

Good evening Guy i hope youre well.

My question concerns cylinder head bore adaptors and their effects upon accuracy when measuring airflow, specifically, will there likely be a large negative effect on accuracy if i utilise only the closest bore adaptor size i can get rather than one that is absolutely the same as the bore size?

In my case, the closest tube size i can get is 93mm inside diameter and the usual bore of the engine is 87.5mm.

Heres a photo of my (unfinished) home built flow bench that utilises digital electronics and pitot tubes for measurements.

Thank you for any advice you may be able to give.

[Guy Croft]

In my exp it will be fine, being 5.5mm or so bigger on diameter, 2.75mm on radius will not tend to give give an artificially high reading. The problem usually comes when it's smaller than the engine bore because the bore can shroud the valve.

You want the test bore (that simluates the cylinder) to be about 5" tall to stabilise the airflow into (or out of) the port.

GC

[4v6]

Many thanks for that reply Guy, it answers my question perfectly.

Best wishes, Tony.

[Guy Croft]

You're welcome Tony, and it is nice to be appreciated. All too often I answer questions (as best I can) and don't get any acknowledgement at all.

It's great to see you developing your own flowbench!

GC

[superbike]

Totally agreed

I have found on my own home made bench the height of the bore adaptor gives the greatest errors.

If i test a ducati head on a short 104mm bore adaptor i get a much lower reading than on a smaller 100mm adaptor wich is some 4 inches taller..

[trickymex]

Hi,

Sorry to high-jack this thread but would you be able to give me some pointers on making my own flow bench ???

Ricky

[Evodelta]

Hello,

Do a search on t'interweb for 'Tractorsport forum' .com.

Martin.

[trickymex]

thanks you:)

[superbike]

Hi,

Sorry to high-jack this thread but would you be able to give me some pointers on making my own flow bench ???

Ricky

Flow performance sell an electric box called an fp1 wich is really good. It as good or if not better than monometers.

I just purchased the box and made my own pipework and pitot tubes. Takes about 2 days to understand the software. If you dont quite have enough power to pull a test pressure you can have the box estimate it and its pretty close.

[dflinkmann]

In my exp it will be fine, being 5.5mm or so bigger on diameter, 2.75mm on radius will not tend to give give an artificially high reading. The problem usually comes when it's smaller than the engine bore because the bore can shroud the valve.

Hello Guy,

Thats a really interesting hint for me. I am despairing with getting the perfect tubes for my selfmade head adaptors. What is your experience with very small bore diameters ?

My engine heads do have typically 66 to 76mm bore sizes. The standard acryl/plexiglas tubes have inner diameteers of 60,62,64,70,72,74,80,82 and 84 mm.
These sizes fitting great for the 70 and 72mm bores and even my heads with 68mm could fit with a 70mm plexiglas tube.

I am unsure with the 66mm and 76mm cylinder bore heads. because using tubes of 70mm respective 80mm would result in an 12% (repective 10,8%) larger area than the real engine bore.

Could you hand out some experiences with oversize tubes which will still work fine ? (e.g. whats the original versus tube size when you are talking of 5.5mm larger diameeter)

Kind regards,

Daniel

[Guy Croft]

Hi Daniel,

"66mm and 76mm cylinder bore heads using tubes of 70mm respective 80mm"

That is perfect. Using a bigger bore than standard OE diameter for test will only ever yield an 'artificial' gain in flow if the original bore was too small and shrouding the valves. I have never found this to be the case except when extremely large oversize valves are used (which I did with a 49mm valve in a 2 liter TC motor a long time ago, on the dyno a waste of time really..).

G

[dflinkmann]

Sounds good, but what about blow testing instead of sucking ? The air would "hit hard" the edge, which wouldn't be there when the tube would align perfect.

Can I ignore that too ?

Thanks and kind regards,

Daniel

[Guy Croft]

A fair point, and one would have to test right size and oversize to determine that effect. I could not really offer a substantiable comment, sorry. I suspect that the effect of the overlap into the test bore might be quite modest if anything at all, but I may be wrong.

You'll understand that I use a range of my own modular aluminum adaptors that replicate the actual bore size pretty accurately so have not explored the limits of what will happen in that event.

GC

[SirYun]

if you need a more accurate approximation of the bore size you can glue in sheets (good quality heavy paper)on the inside untill you reach the desired diameter ( think wallpaper). add some clearcoat to seal from moisture.

I have just got my Flow Quik as well (the device in the picture) but yet have build some proper cabinets to house both vacuum motors and a settling chamber and get my valve opening fixture sorted so it is repeatable.