Tractorsport Flowbench Forum Archive

Posted: **Thu Jun 14, 2007 7:19 pm**

Hi
When making a perspex cylinder head adaptor to mount on top of your bench. How critical is the size of the bore/cylinder that the chamber of the head sits above ?
My engine has a 73mm bore, will a head adaptor with an 80mm bore affect airflow results dramatically ? How critical is it ?

Thanks
Phil.

Posted: **Fri Jun 15, 2007 11:29 pm**

I think that a 7mm difference may be fairly significant, depending on the particular cylinder head flow characteristics.

Looking up my steel pipe and tube catalog, closest standard off the shelf size I can find is: Three and a half inch (88.8mm od x 8mm wall) Boiler Tube to BS3059

In theory that should have an unfinished bore size of 72.8mm. It would be perfect, that is, if you can track down some.

Posted: **Sat Jun 16, 2007 7:17 am**

Agree with Tony....get closer to your bore size

Posted: **Sat Jun 16, 2007 2:25 pm**

The normal "rule of thumb" is that a bore cylinder .060" larger than the assumed bore of the engine will not greatly affect flow readings.

ANY dimension larger or smaller than that reading will either cause Valve Shrouding or artificially high readings vs the actual bore of the engine.

Tom Vaught

Posted: **Sat Jun 16, 2007 7:48 pm**

Thanks for your advise chaps.

Phil.

Posted: **Mon Dec 03, 2007 2:01 pm**

Back on this again. I've found some perspex tubing suitable for the adaptor. It has an ID of 74mm which should be spot on.
My question is, it only has a wall thickness of 3mm, will this be strong enough to withstand the vacuum of the bench ?

Posted: **Mon Dec 03, 2007 5:39 pm**

Posted: **Mon Dec 03, 2007 5:57 pm**

3mm wall thickness will be fine if you have a thick support on each side of the cylinder to support the weight of the head. If you have access to a Super Flow operator's manual in the back of the manual they give plans for a cylinder/ support structure for the head. Otherwise maybe someone can scan in the rough picture.

Tom V.

Posted: **Tue Dec 04, 2007 3:38 am**

Thanks ! Yes i was planning on having supports to take the weight. I have an idea of what they look like from some pictures i've seen. But anymore info/pictures are more than welcome.

Thanks.

Posted: **Tue Dec 04, 2007 11:54 am**

There are a number of pics in the "Readers Flowbench Projects" section threads started by Erik and blownalcohol.

Doug

Posted: **Tue Dec 04, 2007 12:11 pm**

Hi again, Starting "doing some numbers" right after the earlier post. If a slightly undersize bore adapter were tapered to match the bore, how far would the taper have to be carried out back to the standard size? Specifically, I have a 2.0 inch ID (50.8mm) acrylic tube and a 52 mm bore (49mm stroke), could I taper the .024 inches (on the radius) down into the tube in a quarter inch (10 times the depth) or do I need to go more? My alternative is to get a 2-1/4 ID (57mm), saw through the wall and remove a small section, then clamp and glue it back together (almost round). Thanks for any guidance!

Doug

Posted: **Wed Jul 02, 2008 3:26 pm**

I have a similar issue.

I checked out what kind of bores I would generally use and thats: 66mm, 68mm, 72mm, 76mm, 84mm, 85.5mm, 88mm and 90mm

Thats a quite bunch of different head adaptors and tubes I would need. Who could give me a hint which bores I could safely combine into one
tube diameter ?

Daniel

Posted: **Sun Aug 24, 2008 4:38 am**

I found this interesting info when looking for some adapters.

Posted: **Sun Aug 24, 2008 6:35 am**

some more discussion concerning sizing the adapters.

Posted: **Sat Oct 11, 2008 7:15 pm**

Sometimes you want to reply but cannot back up what you are going to say so I did not say anything when this discussion was going on. I felt it was very necessary to have the correct diameter cyl. Head adaptor to simulate "your" cylinder. I have two for my small blocks, one is 4.030" diameter and the other is 4.155" diameter. I knew I had a reason for doing this, just couldn't remember why it was so important to me :p - I have attached a bit of a discussion that Larry Meaux was having at Speedtalk.com
"Notice=> that on a larger 4.000" Bore, the Intake Flow went
turbulent near .550" Lift , and the entire Lift Curve was no better
on the larger 4.000 Bore -vs- 3.750 Bore

i see this happen sometimes on Wedge Head designs
and this is especially true if a Cylinder Head's Short Turn and Port
were Ported and developed on a Bore dia like 4.030,
then Flow tested on a 4.125 Bore ...Flow Numbers can go down.

thats why its always very important to develope your Ports
for the Engine's real Bore diameter.

On BBC Canted Valve type Heads, you don't see this effect very often.
Typically the Heads Flow more on larger Bores."
__
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers
www.maxracesoftware.com

John

Tractorsport Flowbench Forum Archive

Cylinder head adaptors