OF SOUTH AUSTRALIA INC |
Cylinder Head Improvements |
OF SOUTH AUSTRALIA INC |
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 |
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.
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 |
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
Keith
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?
Murray
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 |
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.
SUMMARY :–)
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 :–)
Keith
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 |
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 |
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
Keith
From: | murray gauld [eaglevis(at)bigpond.com] |
Sent: | Sunday, December 05, 2004 6:17 PM |
To: | HillmanCars@yahoogroups.com |
Subject: | [HillmanCars] Cylinder Head Ideas |
Many thanks for your experiences Keith and Graham. Have saved these in my Hillman Performance Notes "Folder" for future reference. Very much appreciated.
Murray
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 |
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 |
Keith,
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.
GR.