Lotus Elan

TwinCam head flow data

PostPost by: rgh0 » Mon Nov 22, 2021 10:12 am

There is very little published data on original or modified heads or new ( SAS QED Bean) heads flow testing. If your into Chevys there are literally hundreds of head builders publishing data :) not so with our engines :(

So I thought its time to collect some data on twink heads. I have started with the flow testing done recently on a McCoy modified racing head of mine that I am rebuilding for my spare race engine. Its an early McCoy modified race head at No 34.

Running McCoy 450 cams , TTR exhaust, 45 DCOE with 36 mm chokes and 12.5 comp ratio with Avgas the 1600 cc engine made 175 to 180 HP at 7500 to 8000 rpm based on rolling road tuning with great mid range torque . This matches well the estimated head HP capability based on flow testing of 180 hp with 0.45 lift. With a higher lift and longer duration cam and bigger carb chokes a bit more top end power of about 10 to 15 hp is possible at the expense of midrange torque with this head.

Twin Cam head flow check Eddie Woods.jpg and


It would be good to see any equivalent flow data plus any resulting engine dyno data that people have for standard heads or for ported standard heads or for the new SAS or QED or Bean heads


cheers
Rohan
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PostPost by: rgh0 » Mon Nov 22, 2021 10:51 am

This site gives some flow data for a UK "CNC ported" head with standard big valve size inlet but a very strange overly big exhaust valve size so not sure how good this data is :roll: . This may be new QED or SAS head and the exhaust valve size just a simple error as no one else is doing CNC porting that I am aware of in the UK, unfortunately no details given? Note this data is at 28 inches of water gauge versus my previous post testing at 25 inches

http://users.erols.com/srweiss/tablehdc.htm#Lotus

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Rohan
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PostPost by: promotor » Mon Nov 22, 2021 8:33 pm

Some good info there Rohan. I haven't got anything of value I can add apart from that in the UK when you mention CNC Heads it refers to Ric Wood Motorsport incorporating CNC Heads.
His workshop is one of the most impressive places I've been to and his portfolio of work is pretty large to say the least. I would say the article you posted refers to him.
He's well known at Goodwood too.

Well worth a look around his websites :

https://ricwood.com/

https://www.cncheads.co.uk/

Check out the Cosworth GAA engines he rebuilds!
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PostPost by: rgh0 » Mon Nov 22, 2021 11:27 pm

It looks like CNC Heads has done development work on twincam heads as the web site gives a price for porting them. If anyone has dealt with them it would be good to see any before and after flow data on a twincam and the outcome in terms of engine dyno testing.

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PostPost by: lotusfan » Tue Nov 23, 2021 12:12 pm

Hi Rohan

That all looks very interesting but can you clarify what some of the row titles refer to please.

For the intake valve:

Lift is obvious - inches
Range - what is that?
Flow % - seem like very small percentages unless 0.48 means 48%?
CFM - presumably flow through the valve
Mean CFM - how is that derived? Presumably not a simple average?
HP - these presumably are what you achieved from your engine.

Thanks
Mike
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PostPost by: nmauduit » Tue Nov 23, 2021 12:54 pm

Thank you Rohan, most interesting...

Did you get a measure for each cylinder, then if so how close to each other are they ?
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PostPost by: rgh0 » Wed Nov 24, 2021 9:58 am

lotusfan wrote:Hi Rohan

That all looks very interesting but can you clarify what some of the row titles refer to please.

For the intake valve:

Lift is obvious - inches
Range - what is that?
Flow % - seem like very small percentages unless 0.48 means 48%?
CFM - presumably flow through the valve
Mean CFM - how is that derived? Presumably not a simple average?
HP - these presumably are what you achieved from your engine.

Thanks

I believe:
Range = setting data for the flow bench flow measurement orifice
Flow percent = a fraction of some calculated maximum theoretical flow for the selected measurement orifice setting.
Mean = some mean flow measure based on some "typical" cam profile for the head tested I think
HP = the maximum expected HP per cylinder multiplied by 4 in this case for a "well developed" racing engine thus representing what's possible for the head under test for a cam with the maximum lift at each quoted HP. The manual gives a formula for the revs required based on cylinder size under the head.

The Superflow SF1020 manual which I need to study more :) can be found here
https://superflow.com/downloads/
and gives more details

cheers
Rohan

edit ... done some more reading of the manual
Last edited by rgh0 on Wed Nov 24, 2021 11:04 am, edited 1 time in total.
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PostPost by: rgh0 » Wed Nov 24, 2021 10:01 am

nmauduit wrote:Thank you Rohan, most interesting...

Did you get a measure for each cylinder, then if so how close to each other are they ?


I am not sure if all cylinders were checked but the McCoy conversion head is CNC ported in both the new manifold and original head so each intake and exhaust are identical in shape and should flow the same unlike a hand ported head where its hard to get each port identical

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