mods for the head

[pauljones]

Hi all,

Probably a question that will cause a bit of debate,

Im about to give my head to a local firm to port ect, so what details do I need to give to them?

the reply from them was port, polish, cc ing, flow balancing and a mild skim to ensure a gasket seal.

Does anyone have any specs or details that I should give them as I cant afford a new head from the usual suspects.

Many thanks,

Paul

[GrUmPyBoDgEr]

Hi all,

Probably a question that will cause a bit of debate,

Im about to give my head to a local firm to port ect, so what details do I need to give to them?

the reply from them was port, polish, cc ing, flow balancing and a mild skim to ensure a gasket seal.

Does anyone have any specs or details that I should give them as I cant afford a new head from the usual suspects.

Many thanks,

Paul

Paul,

I'd be very suspect of that reply, on the face of it, it sounds like they will do what anyone would wish for but the trouble is what specification do they intend to work to?
It all sounds a bit open ended if you know what I mean.

There will be other well informed guys here who will be able to provide some spec's for the porting, which in itself is a black art.
What makes me a bit skeptical is "flow balancing" do they actually have a flow bench for doing such work; I would be very surprised if they do or have the qualified people to operate one.
Maybe worth asking what their interpretation of that definition is.
If they have previous experience of Twincam heads they will have a "head" start, so to say; if not then I would probably be looking elsewhere.

In any case I hope you get the info' you need & that all works out well.
Cheers
John

[pauljones]

John,

Thats exactly what I was getting at.
As it happens they do have a flow bench.I did ask for a before and after print out of previous work,they have worked on twinks before,but I have no reply for that email.
The main thing is the price,?400+VAT.That seems ok to me and as I said they were local so no postage.Is this reasonable?Thats off course if theres no repair work needed,im sure there's not.
My understanding is the exhaust is far superior to the inlet,so a mild port match and polish is all thats needed on the exit.The inlet needs a bit more work to flow the required numbers,just to keep up,so to speak.

Perhaps this is a topic Rohan can help me on,please.

Paul

[jono]

I would speak with Dave Andrews, primarily a K specialist but a very well respected authority on head porting and he will understand the Lotus TC head.

A really nice bloke too, he's always happy to advise

http://kengine.dvapower.com/

Jon

[rgh0]

Hi all,

Probably a question that will cause a bit of debate,

Im about to give my head to a local firm to port ect, so what details do I need to give to them?

the reply from them was port, polish, cc ing, flow balancing and a mild skim to ensure a gasket seal.

Does anyone have any specs or details that I should give them as I cant afford a new head from the usual suspects.

Many thanks,

Paul

My comments on trying to expand the specification for the work would be as follows assuming the guys do know how to use a flow bench and have some knowledge of twin cams - i assume this is intended for a warm road engine not a full race engine.

Porting - The diagrams in the Vizard twin cam book have been posted before get a copy of those if the shop does not have it. Agree no porting needed on exhausts, just clean up and then play with your manifold to ensure a proper match. If they have a flow bench to test the work they do in line with the Vizard book all the better. Also they need an ultrasonic probe to measure the wall thickness as they port in the key areas of water jackets and the bottom of the spring pocket to ensure they maintain an adequate thickness. if they break through the cost for weld repairs starts to get very expensive very quickly

Polishing - no need for mirror finsh just ensure it is relatively smooth and well flowing using a carbide die grinder followed by a gentle application of a fine abrasive flap wheel is all that is needed

Combustion chambers - cc to same. Best place to take material off is around the inlet valves to unshroud them a little as this helps flow as well. You need to determine the compression ratio you want (say 10.5?) and gasket thickness you will be using but around 36 to 37cc is what you will be looking for I think if the rest of the engine is "normal"

Head gasket face - I would ensure has the right surface finsh for the gasket type you will be using ( the gasket manufactures normally will tell you what that is) and is flat to within a couple of thouandth of an inch only remove enough material to achieve that - dont forget to allow for this material removal in the combustion chamber sizing calculation.

if doing all of the above you also need to check the bucket bores and guides and ensure they are not worn outside of tolerances specified in the manual. I assume you may also be planning new cams, valves and springs and followers to make best use of this better breathing head. if so you may wish to consider bigger valves ? not critical but additional cost low if replacing valves and if seats needed anyhow

cheers
Rohan

[pauljones]

Rohan,

Once again,your a legend.Ive hunted around for the wizards details on the ports.not found it,could you post a link,i will admit to being a bit slow with computers so its probably my fault.
Thanks for the other replies too.
The engine will be road use only,perhaps the occasional track day,but not a race spec motor.
I was looking at keeping the standard,small,valves.Only to keep costs down.As for cams,im still not sure what to go for,upgrade to a cheep set of sprints was one option,but it can wait.
As a point,the induction will be Emerald/jenvey based,im told buy some that CR can be as close as 12-1 using management.Any thoughts on this?

Many thanks,

Paul

[twincamman]

THE FORD HEAD GASKETS ARE PRETTY GOOD lots of meat on them I would not skim a twink head untill its very warped so check the head with a straight. Edge and some feeler gauges --just where are you going to find hi test leaded gas to run 12 to 1 compression???? for the street leave well enough alone and run the head as close to stock because that will be fast enough to give you that warm brown feeling on occasion and ad some longevity to the motor -ed

[cabc26b]

Hi Paul,

I would be a little concerned that the shop chosen for the work is asking you for the specifications. Ideally their work bench should look this -
and they would have a clue to who Dave Vizard, Brian Hart, Gus Hutchinson etc are(were).

George

[pauljones]

Guys

Thanks for all the tips,just to answer Johns question.If I understood the answer directly,then flow balancing,is getting the exhaust to flow about 80% of the intake flow,why,I don't know.have I got this all wrong? Can someone shed some light on this "magic art",

[ardee_selby]

http://www.ebay.co.uk/itm/Tuning-Twin-C ... 3799551126

elan-f15/sectioned-lotus-twin-cam-cylinder-head-t22860.html

I've got a 3-parter by Vizard from C&CC. Will be posting them when they've been scanned.

Cheers - Richard

[SJ Lambert]

Hi Paul,

I would be a little concerned that the shop chosen for the work is asking you for the specifications. Ideally their work bench should look this -
and they would have a clue to who Dave Vizard, Brian Hart, Gus Hutchinson etc are(were).

George

You're right George, that is a good looking work bench!!!!

James

[rgh0]

Hi Paul,

I would be a little concerned that the shop chosen for the work is asking you for the specifications. Ideally their work bench should look this -
and they would have a clue to who Dave Vizard, Brian Hart, Gus Hutchinson etc are(were).

George

You're right George, that is a good looking work bench!!!!

James

A nice production run that John at Omnitech is part way through - 1 of them for me and 5 others for racers I know here in Australia out of the batch of 10 or so heads in the picture. Unfortunately 2 did not make it through the race porting as the cores not quite in the right place and broke through into the water jackets, a known hazard when pushing head development to the absolute limit and repair welding usually costs signifcantly more than the Stromberg head you started with. John substituted a couple of his spares in the batch at a very reasonable price -- Now that is customer service !!!!

cheers
Rohan

[GrUmPyBoDgEr]

Guys

Thanks for all the tips,just to answer Johns question.If I understood the answer directly,then flow balancing,is getting the exhaust to flow about 80% of the intake flow,why,I don't know.have I got this all wrong? Can someone shed some light on this "magic art",

Well I can't throw any light on the figures that should be expected because flow bench work was something that I never got myself involved with.
Flow bench work was done by some of the "performance engineers" at the company I once worked for.
Some of the results lead me to believe that some of them didn't know what they were doing
That company's interpretation of a "flow bench" was a large dedicated room where a cylinder head could be mounted on its corresponding block & all cylinders were individually connected to air supply ducts which had suitable flow meters fitted to them.
Those ducts were supplied with a massive amount of stabilised air whose flow could be accurately controlled.
I don't know what measurements were made during testing but I would stab a guess at pressure drop at various measuring points.

With my first reply I was really being a bit cynical about the flow bench; mainly because the large majority of "tuners" wouldn't recognise a flow bench even if it slapped them in the face & the term "flow tested" has been very much miss-used over the years.
Tuners that have their own engine test bed will use the results from them to judge the effectiveness of the "porting" that they have done on a cylinder head.

Sorry about my earlier posting, it was a bit obtuse & misleading.
Cheers
John

[rgh0]

Guys

Thanks for all the tips,just to answer Johns question.If I understood the answer directly,then flow balancing,is getting the exhaust to flow about 80% of the intake flow,why,I don't know.have I got this all wrong? Can someone shed some light on this "magic art",

Well I can't throw any light on the figures that should be expected because flow bench work was something that I never got myself involved with.
John

I probably cant shed much more light but In my simple understanding of the desired flow ratio between inlet and exhaust ports is as follows

1. If the exhaust flow is to high you loose scavenging effect due to low exhaust velocity and this costs power
2. If exhaust flow is to low the pumping losses of pushing the exhaust out are to high and you loose power

The magic number is typically around 70 to 80% but it varies from engine to engine.

All of this is based on low velocity steady stae ( below sonic velocity flow) tests on a flow bench versus in real life high velocity ( above sonic velocity) and pulsating flow in a real engine but the 70 to 80% rule seems to roughly apply between a flow bench and a real engines performance. However for any particulalr engine design it may be 60% or 70% or 80% or 85% so no real substitute for development work and lots of dyno tests. Even today in the world of computational fluid dynamics on super computers cant model it very well.

In a full race twin cam you work the inlets as hard as you can for maximum flow and put in a big lift and long duration cam (.49 and 310 to 320 degrees seat to seat ) but you need to hardly do anything in comparision to the exhaust and you can use a shorter duration lower lift cam ( .45 and 280 degrees seat to seat). The result is little if any hp loss compared to doing more porting or more cam on the exhaust and much better torque due to the right balance in exhaust versus inlet as the standard exhaust porting is well oversized compared to the standard inlets. Maybe this orginal design was possibly to compensate for a restrictive road exhaust system - who know?

cheers
Rohan

[msd1107]

This topic has seen much interest.

A previous post (elan-f15/line-twin-cam-porting-article-t16194.html) has a down loadable spreadsheet that allow the determined user to fiddle around with different sizes of valves and port sizes and see their effects.

The key figure is velocity as a percentage of sonic velocity (Mach%). This is limited to Mach1 but that figure is never achieved. At low valve lifts, velocity can approach that figure. At high valve lifts, the curve of mass flow versus Mach departs (substantially) from linear by Mach .5 to Mach .55. You get better torque at lower RPM by using smaller intake ports so that you get the benefits of high intake gas velocity at lower RPM and live with the greater losses at higher Mach% as the revs increase.

Since the exhaust flow is at a high temperature, the effective flow velocity at a constant Mach value is much greater. This implies that to minimize losses in the exhaust phase, you should use thermal barriers in the cylinder head, piston crown, and exhaust port to maximize exhaust temperature and minimize Mach value, a trend that is now becoming somewhat more recognized, although not mentioned directly.

Flow benches are only useful in the grossest sense, since airflow velocities in static measuring never get into the Mach range that is vitally important. CFD programs cannot deal with this either, so that the best results get produced by the tuner with an implicit understanding of what the airflow molecules do when dodging around all the obstacles in the intake system, intake port, combustion chamber, exhaust port, and exhaust system.

The bottom line is, I have been following this field in greater or less technical depth for more than 50 years now, have developed and applied some theories that seem to work, and continue to feel that the best of modern technology is far from reaching what I feel is possible to achieve. I wish I was in a position to undertake a proper development program.

(Said after imbibing the appropriate amount of high quality red!)

David
1968 36/7988