Tech Tips:
Cylinder Head Improvements

From: Graham Robinson 62 Husky [Leslie3008(at)bigpond.com]
Sent: Thursday, September 30, 2004 11:18 AM
To: hillman@can-inc.com
Subject: "Hillman " Camshafts

This message forwarded by the Hillman List.

Jon, Jim, Keith, Rod and gentelmen, Comments please.
Camshaft Review prompted by the enquiry "Twin Carb enquiry".  Why?
Diagnosis as to why my engine and cam cut 'pinks/pings' under power and up hills.  Ignition is perfect with no drop off at >6000 RPM.  This is why I have been comparing/collecting camshafts for alloy heads.

Some cam specs : Minx III 14 41 50 5 S/Minx 14 52 56 10 C/I 1500 255 cam 37 64 67 22 260 cam 47 86 82 36 C/I, " and 51 89 82 36 AL 295 cam 38 72 72 38 AL 298 cam 57 91 90 44 AL My cam 20 66 66 20 AL

First number is: Inlet opens btdc, second is Inlet closes abdc, third is Exhaust opens bbdc, closes abdc.  C/I is cast iron head, AL is alloy head the rest are identified Humber, Hunter cams.
Hunter cams: 255 is 1500 C/I, 260 (two) one is C/I and 2nd is Alloy, 295 is single/twin carb and 298 is twin carb, both AL heads.
Minx III and Super Minx are docile compared to Hunter/Humber cams.  Humber possibly 295 with the GT possibly 298 cams.
Mine is relatively square as is the 295 cam.  My cam was cut for a blower application so I guess I won't know how it operates until I fit the blower but I can forsee exhaust problems from the above comparisons.  Fuel economy is good at 35 miles per IMP gallon (not US gallon) with twin CD150s fitted.
The 295 or 298 cam inlet opens 38/57 btdc with exhaust staying open longer.
My cam opens 20 btdc on inlet closing at 66 atdc and exhaust closes at 66 bbdc and 20 abdc and seems not enough duration for exhaust.  So I can see the engine getting hot and losing water coolant once blown because of that short exhausting period.  The short period for inlet doesn't concern me as the blower will fix that.
The 295 and 298 cams (probably) fitted to Humbers and GTs can be very thirsty but clears exhaust efficiently even with the standard 'extractor' manifold.  With normal aspiration mine is pretty docile until it gets up to 3000 RPM then it starts to take off but I am concerned that a recut to improve the exhaust will have to be done to improve exhausting or fit a 295 cam and don't worry about any economy or consumption.  Probably a profile cut 30 66 66 40 will improve mine no end.
The 'duration' of the Humber and GT cam is unknown to me at the moment but I hope someone can advise me what that figure is.  My 'duration' is rated at 266 which probably accounts for why compression test max is 150 lbs much short of the 180 lbs of the GT but once blown this compression will rise considerably.  The 295/8 inlet opens 30 degrees earlier and stay open longer so obviously more fuel, more stroke and far more power without 'pink/pinging' thus the increase in compression plus the cleaner efficient exhaust.

If all this gells and someone can confirm my concerns as I will have to recut my cam or fit a 295 cam when I pull the engine down to check a few items and fit the blower, best to do it all at one go, I guess?
Graham R..

From: Keith Johnson [keiths55(at)bigpond.net.au]
Sent: Friday, October 01, 2004 9:18 AM
To: minx [hillman@can-inc.com]
Subject: Re: "Hillman " Camshafts

This message forwarded by the Hillman List.

Graham I would need to sit down and draw out the cam duration figures to make some sense out of the "numbers" However the numbers I see don't tell all.  The wild card is the rate of lift and total lift on the cam. By relatively "square" I assume you are talking about the crest of the cam.  To do this the rate of lift would be faster but the total lift remains "sensible" so the cam profile fits within the cam base circle and the valves avoid hitting pistons.  The restricting of exhaust duration prevents effective scavenging of the burned gases and thus leaves less room for the incoming charge.  Ford Zephyrs of the fifties were set up this way.  Mainly as a result of that disgusting exhaust manifold system.  The "hockey stick".

Intake and exhaust duration is important and cams need to be matched to the intake and exhaust systems fitted if you want the best results.  The 4 into 2 into 1 extractor gives good scavenging and boosts mid range torque.  The 4 equal lengths into 1 exhaust loses some mid range but will extend top end power.
My experience from the "suck it and see" university is that the extractor system is better on the street.  A reason for this is that we usually have very short intake lengths, which will have most benefit at the top end.  So the extractor gives a torque peak in the mid range that complements this and gives a broader power band.
Modern injected cars use long intake ram tubes after the throttle body and match these with different lengths of exhaust to give a very broad torque curve.  You can not do this with carbs, as the mixture tends to fall apart in the long intakes and you get erratic bottom end mixture distribution which causes rough running and leaning out on indvidual cylinders with valve burning consequences.

I have read that the use of a shorter exhaust duration is a USA technique that is used with forced induction (blower, turbo) to prevent over scavenging.  That is the blower is pushing fresh mixture in, and out past the still open exhaust valve.  In "stock" classes the trick is to set up the exhaust valve clearances very loose, thus reducing exhaust duration.  Early closing of the exhaust valve causes the fresh charge to "pack in" and give a usefull power gain.  I would have thought that reducing Blower presure would have the same effect and would also reduce the power taken to turn the blower.  The resulting net power would be the same but the internal stress in the engine would be less.

Your pink/ping problem under load is because the timing is to far advanced in those conditions.  On light loads you are probably OK but when the load on the engine increases by going up hill then you need to retard the timing slightly.
The vacuum "thingy" on the side of the distributor changes the timing as the intake vacuum changes.  If you drive with a vacuum gauge the intake vacuum drops when you encounter a hill.  On my old Ford with vacuum wipers the wipers stop working.  High engine vacuum gives further advance over the normal advance curve.  When engine load increases reducing vacuum the amount of vacuum advance decreases.  This is to prevent knock/pink/ping and /or engine destruction.  If ignored this makes unwanted holes in pistons :) So check that the vacuum advance is doing what it should.  The Hunter manual has a section on checking this operation.  For a modified engine you may want the centrifugal advance to come in quicker and more vacuum advance (hence more retard under load).  This will allow more total advance and more power.
Electronic engine management systems use a knock sensor to detect knock and the ECM retards the timing untill it stops.  This enables maximum advance to be used.  With the distributor system you need to make compromises.  This was the biggest complaint from those with performance cars when the unleaded peanut oil became our only available fuel.  The only way they could prevent knocking was to retard timing or have the compression reduced.  Both options losing bulk power.

So bottom line would be to get the distributor checked, perhaps with a view to changing the vacuum advance characteristics.  I think I suggested to Ian that he use the original 1390 distributor on his 1600 UTE as it was curved to suit the poor fifties regular fuels and would probably match the unleaded stuff we get these days.
It would be interesting to hear of his findings.  When setting up do your final timing setting with the vacuum advance connected.  If you then remove or block the vacuum line the timing should imediately retard.  If it doesn't something is not working correctly.

I haven't really addressed your cam questions :) the problem is there are so many other issues that have a bearing on cam profiles.

Remember the ultimate objective of all this blowers, intakes, cams, exhaust systems, is to get burnable mixture into the cylinder, burn it all and get the waste stuff out.  The more effectively you can do all of this the more power you will make.  It is of no use to have a monster blower on the in side if the exhaust system will not flow that much.  Improved breathing is the key.
I obtained tyre burning results (yes from a Hillman) by matching intake size, exhaust efficiency and a gas flowed cylinder head (iron) using a standard 1600 camshaft.  That engine would rev to 6500 in all gears and I am sure, under the heat of competition, it occasionally touched 7000 rpm :)
That cylinder head had Jag inlet valves Ferguson tractor (also TR-2 :) exhaust valves and radical porting.

Food for thought


From: murray gauld [eaglevis(at)bigpond.com]
Sent: Monday, November 29, 2004 10:27 PM
To: HillmanCars@yahoogroups.com
Subject: [HillmanCars] Fw: Cast Iron head


Goin' back to your email dated early Oct.. 04.  I want to modify our cast iron headed 1725cc motor.  Yes I know the alum. alloy one is better, but..........can you remember the work you had done on yours, what size were the new larger valves?  did you have valve stem bushes and valve seat inserts done so as to run unleaded?  Looking at our head (it is out on the bench at the moment) there appears to be room to enlarge the exhaust valves and port, even enough room to bring 2 and 3 closer together (hot spot?) or further apart.  A couple of millimetres would not hurt the rocker and push-rod set-up.

Also Holden 149 Pistons, any experience with them?.  What limits you from machining out bore size.  Ours is still 3.12 inches.  Crank shaft stroking for longer stroke, what advantage / disadvantage?


From: Keith Johnson [keiths55(at)bigpond.net.au]
Sent: Saturday, December 04, 2004 12:10 PM
To: HillmanCars@yahoogroups.com
Subject: Re: [HillmanCars] Fw: Cast Iron head

Been there, done that  :)

I should have been a mathmatician.
They work out funny formulas and tricks to avoid work.

I have "done" several heads in the past.
Read all the books, worked out the best profiles for ports and combustion chambers.
Then found a "good mate" who just loved to do the grinding stuff while I supplied liquid refreshments and light entertainment.  Nearly the worlds laziest man :)

Dave Wirram was the good mate he had the fastest 57 Minx I have ever seen apart from Dennis Marwood's 62 that was alcomer racing in the 60's.
After doing several the formula we found gave us the best results was fitting early Jag inlets and ferguson tractor (tax free TR-2) exhaust.  I think both valves required some machining attention, the Standard-Vangaurd ones definitely needed the stems shortened and a new retainer groove created.  We had a lathe so this was no problem.
Inlet ports opened up and polished.  Again from memory we increased the port diameter at the manifold face by about 1/8" which is a "tad" more than the manifold location ring size.  The metal around the valve guide was reduced on the inlet only.  The combustion chamber on Dave's 57 was opened up from the bath tub shape to a semi hemi concave shape which had the effect of reducing the "squish" area on the spark plug side.  All this required fairly radical head planing to get the compression up to something useful.  I took .100" off mine Dave removed .130" from his.  This amount of machining requires reworking of the side cover plate to get it to fit.  Both engines ran on super for street work.  Dave ran his on "Hot" avgas when racing and could dial in a lot more ignition advance.  Under racing conditions and even on the street it was vital with these compression ratios to avoid any low revs high load situations.  So no longer could you trickle along with the traffic in top gear as the engine would knock itself to pieces.  Being a rev head this was no hardship.

NOW bringing it up to date seeing as I have learned a lot since the old days.
I would leave the exhaust valves standard size and just polish the ports up to a smooth finish.
For the inlets I would try for a slightly larger inlet valve.  My approach to finding a suitable valve would be to note down all the specs from my engine manual and spend a quiet afternoon at the local library going through the car manuals section seing what late model unleaded versions come close.  I reckon you could squeeze about a 1.6" diameter valve in there.  Being a cast iron head and made of a better quality than the BMC heads you could possibly get away with machining the new seats straight in the head and using hardened valves for unleaded.  But insert valve seats are a common job these days to "unleadise" old engines.  The Rootes cast iron is quite a bit harder than the BMC stuff.  For the intake ports open them up by about 1/8" max, flatten out the "floor" area to allow a straight flow at the valve and polish to a mirror finish.
The valve seats should be a three angle cut and there should be no step between the port and the seat.  I would mildly reshape the combustion chamber out to match the bore size on the manifold side and round off the other edges of the chamber where the squish area remains.  Lumps and sharp edges are to be avoided as they will cause hot spots and pre-ignition.  If you use the premium unleaded then a slight increase in compression could be tolerated..
Obtain a burette from a scientific or school supply shop.  Doesn't need to be a super special one as we are interested mainly in comparing volumes.  Use this to check the final size of each combustion chamber after all your work (blue metho is good for this).  I haven't said it but all valves should be lapped in to the same level and avoid "recessing" the valve in the seat.  This is all pretty standard tuning stuff you will find in any generic tuning book.  All combustion chambers should be equal in size open up the smaller ones until they match.  With this level of combustion chamber modification a .030 to .050" head machine will bring the compression ratio up to something that will start making power.  Calculate compression ratio CR = chamber size plus swept cylinder volume / chamber size, these days anything past about 9:1 will cause problems with available fuels.
Valve springs use decent new double springs at least.
Valve seats the inlet can be narrower than standard with no problems but I prefer to use a slightly wider seat on the exhaust valve and also no reduction in the matrial in the port area around the valve guide.  Exhaust valves get a real work out so the more heat that can be coducted away in the short time it is on the seat the better. Again standard stuff that nobody thinks to mention, make sure the manifolds line up perfectly with the ports and that the intake passages in the inlet manifold are as good as in the head.

Not part of the head but my choices would be an interferance extractor exhaust 4 2 1 style.  again primary pipe size to match the ports.  I think 1.125" primary and 1.25" second part into a 1.75 or 2" collector and low restriction Turbo muffler and tail pipe.  Strangely enough you often lose power by making the extractor pipes larger as the gas velocity drops.  This sort of exhaust system matches the short intake lengths that we normally use with twin SU/Strombergs or Weber carbs.  If you play around with longer tuned intakes and fuel injection then you need further study.

The Rootes engine exhausts better than it intakes so working on the inlets pays dividends.

One of the reasons for getting all the combustion chambers the same and being consistent with intake ports from pot to pot is that it will smooth up engine operation.  You balance all the moving parts but when running variations in cylinder filling and compression ratio will also cause vibration and roughness.  This is one area where you can do a better job than most of the proffesionals as you really don't have time contraints so you can persist with it untill all the details are right.  With formula racing of any kind the attention to these small details is often the difference between winning and losing.  I once saw a BMC 1500cc engine that would idle at 100 rpm smoothly.  Just because of meticulous attention to every little detail.

Bigger size doesn't always go faster.  you could use standard valves with a decent port and polish and a slightly raised compression ratio and get excellent results.
The same goes for a cam to move all the parts, don't give away useful torque for a few horsepower more at the top end.  The Sunbeam group have some useful data on cams, the only thing to remember that saloons are slightly heavier and need more torque.

Something to digest and pull to pieces :)


From: Graham Robinson 62 Husky [Leslie3008(at)bigpond.com]
Sent: Saturday, December 04, 2004 5:42 PM
To: HillmanCars@yahoogroups.com
Subject: Re: [HillmanCars] Fw: Cast Iron head

Everything Keith tells us in his reply is correct for racing engines and CDI becomes practical to keep the spark active particularly if you have pre-existing spark problems or suspicions.
Port and polish chambers, particularly around the spark plug squish areas, matching manifolds to the head ports.  Larger 1.504" GT Hunter inlet valve might be sufficient.
The exhaust valve can go out to 1.204" and use dual valve springs instead of the single spring, but is effective as is but with designed extractors as Keith aludes to can be very successful plus a cam cut maybe to the 295 Humber version or consult your cam experts for torque performance with get up and go.  Not too thirsty as the GT 298 cam but maybe squared off a bit at max lift at the cam to increase duration!
Porting, polishing, balancing can make a lot of difference to a Hillman engine even with standard size valves.  Honeycombed cam followers helps rid the oil a bit quicker increasing RPM slightly.  Make sure you have good stem guides as worn ones cause other problems.  Valve inserts for unleaded in a cast iron head is not that critical 'Just Heads' in Mt. Druitt did a head up for Glen Davis and they said the inserts would handle the ULP fuels today with proper additives.  They also rebuild buggered alloy heads at very reasonable rates, for me anyway.  Cleaning oil channels by removing all plugs and chemical cleaning the block with new 'Welsh' plugs for the water channels is a must as are cam bearings.  Flat top pistons to max 3.30" size will help lift compression using whichever piston/ring set you feel fits your need.  I don't know much about stroking but I have seen them out to 2025cc and there is a company in Victoria that does this.
Research and read a lot and take your time with your calculator and measurements until you are happy with your decisions it will all work but depends if you want weekly racing engine or a torqued engine with longevity.
Then tackle gear and diff ratios, lower to move quickly or higher as a tourer.
1963 I built a 1390 to go in my Humber Vogue and I used a lot of options Paul Bolton (successfully raced Minx Specials) filled me in on and it went like a blurr with revs never peaking in third gear.  It went out to 6000 RPM with standard series distributor and gear with a nice set of extractors but I sold it didn't I!
Best of luck.

From: Keith Johnson [keiths55(at)bigpond.net.au]
Sent: Sunday, December 05, 2004 2:52 PM
To: HillmanCars@yahoogroups.com
Subject: Re: [HillmanCars] Fw: Cast Iron head

As a postscript to my earlier thoughts.
Often larger valves do not return performance improvements that reflect the higher cost of modifying the head.
Porting and polishing, better manifolding and upgraded camshafts often achieve results that make sufficient reliable power to meet our "needs".
From discussions on the Holbay alloy heads I seem to recall they had smaller valving than some of the other Rootes products.

We need to keep in mind what we do all these things for, apart from going faster :)
Power is made by getting mixture into the cylinder, burning it effectively and exhausting the burnt gases.
We can only make more power by getting more mixture in, harnessing the pressures from burning it and more effectively exhausting it.
An extractor exhaust gives free power with no loss of torque at low revs, fitting a pair of constant depression carbs (SU or CD Stromberg) will also alow more power without sacrafice of bottom end performance.  This is why these two bolt on modifications are the basics of hotting up your Hillman.  Using a camshaft that extends the power band higher up the revrange is the usual next step and probably the one that causes the most problem.  The "biggest" numbers for the cam don't always give the best overall performance.  Making 20% more power over 4000 rpm is not useful if the torque under 3000 rpm is down by 50%.  "Driveability" is less in this case.
Head porting, polishing and larger valves also gives improvements and usually without negative effects.
Balance is the name of the game.  You can't really go wrong with twin carbs and exhaust work but changes to cam timing, compression ratio and vale sizes change the overall dynamics so you need to learn more about how each modification works and how it interacts with the other changes to get best results.

Some of the V8 drag engines have been set up with the engine tuners restricting exhaust valve lift to give a presumed improvement in performance.  The low cost way was to run larger exhaust valve clearance.  If we ask why then it seems that the exhaust performance of the head is much better than the intake.  Result is overscavenging.  Lots of fuel and air going in but half of it kept going out the still open exhaust valve.  Makes great boy racer exhaust flames but not useable power.  Solution for these people was to make an early closing of the exhaust valve so this incoming charge was trapped and burned in the combustion chamber instead of out the exhaust.

What I am getting at here is each part of the tuning package must be considered together with all the other engine modifications.
Hillman heads of both alloy and iron persuasions breathe very well in stock form.  Far better than the obsolete (even in 1955) design used by Austin/Morris/MG etc.
A good port job just makes them better.  Extractors are usually "double tuned."  The short 18" primaries and the slightly longer 24" secondaries give a wider asist range.  This is also affected by the pipe diameter.  Larger tubing allows the exhaust gas to spread out and thus lowers the gas velocity and hence changes the time taken for the rarification pulse from the exhaust valve closing to reach the branch and reflect back up the other branch just in time for that exhaust valve to open, giving the extractor effect that makes for more efficiency.  My pipe sizes were based on short intake lengths.  If we use a longer intake we can tune intake and exhaust to broaden the power curve giving us extra power for "free".  Cam designers can only design the cam timing when they have all the information on what you have connected to it for intake and exhaust.

So what would I do today?
Well these days I don't race anymore so my requirement is for a smooth street engine.  If I was rebuilding I would give the head a minor port and polish and machine it about .030" to raise the compression, fit twin 1 3/4" CD Strombergs, extractor system and a GT style cam so that good torque is available across the rev range.
Valve springs and distributor advance characteristics would also get attention, perhaps with quicker adance curve.  This would need premium fuel to allow the best ignition timing settings to be used.
I would expect snappy acceleration and a top speed of at least 160 kph from this work with flexible top gear performance on the open road.  It should be able to rev to about 6500-7000 rpm through the gears.  This assumes a 1600cc or 1725cc short block under the head.  Cruising should return at least 26mpg (real gallons :)
With an existing sound engine I would just bolt on the carbs and extractor and enjoy :)

On the CDI issue what is forgotten by many is that it is harder to generate a spark as the compression pressure increases.  This is why racers always use some form of hotter spark, either spaorts coil or electronic.

Perhaps I should try some of this in my Californian


From: murray gauld [eaglevis(at)bigpond.com]
Sent: Sunday, December 05, 2004 6:17 PM
To: HillmanCars@yahoogroups.com
Subject: [HillmanCars] Cylinder Head Ideas

Hello every-one,

Many thanks for your experiences Keith and Graham.  Have saved these in my Hillman Performance Notes "Folder" for future reference.  Very much appreciated.


From: Graham Robinson 62 Husky [Leslie3008(at)bigpond.com]
Sent: Sunday, December 05, 2004 7:43 PM
To: HillmanCars@yahoogroups.com
Subject: Re: [HillmanCars] Cylinder Head Ideas

With all this inspirational data one also has to ensure the flywheel, clutch pressure plate and clutch will handle this intant power so you have to make sure these are up to near perfect condition as with the spigot pilot bush in the flywheel.
Also part of the overall balance process.  Go to stronger pressure plate springs or a later pressure plate, 8" clutch plate, throw out bearing or roller race, slave cylinder etc.  Clean radiator, thermostat and a good radiator cap also helps.

From: Graham Robinson 62 Husky [Leslie3008(at)bigpond.com]
Sent: Monday, December 06, 2004 4:51 PM
To: HillmanCars [HillmanCars@yahoogroups.com]
Subject: Re: [HillmanCars] Cylinder Head Ideas

I forgot to mention and Keith probably missed it too and that is when we did up the heads with port and polish etc.  We always opened the combustion chamber out to the profile of the head gasket with attention to the spark plug squish area.
Even some had the raised section around the valves cut away prior to polishing the whole chamber making each completely flat and shiny.  Ensuring each chamber had the same capacity for balance.  I would be wary of cutting too much off the head surface as you don't know how much it has been shaved in the past shld be 3.48" to start with anything less than 3.45" being a bit too much off shld be plenty of meat left near the side cover holes if too thin you will have to elongate these bolt holes so the side cover eventually fits or use a 1725 Hunter one that doesn't have a breather pipe and the holes are 5/16" clear.  Same problem happens with alloy heads but dims shld be the same.

There you go another difference maybe not sighted-side cover plate holes are larger on some also some later diff centers have smaller stud holes where most have 5/16" clear holes.  Becomes bummer when they wont fit and you are underneath trying to fit the diff center.

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