Lotus Elan

Head work

PostPost by: steveww » Thu Nov 04, 2004 4:32 pm

I took the head off recently during a water pump replacement. While it
was off I thought I might as well do some polishing and porting to
improve gas flow and get a few more bhp. Closer examination of the head
showed the both in and ex valve guides to be shot plus the ex seats to
have seen better days. My local machine shop took care of those items.
Once I had the head back I set about is with a couple of carbide burrs
and some spirawraps all powered by my Bosch drill. The DPO had
previously had a bit of a go at it but it was not a good job. A couple
of evenings work soon had things looking much better. All it cost was
about 50 quid for the burrs and a box of spirawraps. If the engine
simulation software is correct this inexpensive tweek can be worth 10bhp
@ 6000rpm, a very good return on investment I would say.

It is really not that difficult to do, abit of nerve and a steady hand
is all that is required. Give it a go this winter.

--

Regards,

Steve Waterworth
***@***.***

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PostPost by: twincamracing » Fri Nov 05, 2004 1:02 am

Once I had the head back I set about is with a couple of carbide
burrs <snip> a couple
of evenings work soon had things looking much better. All it cost was
about 50 quid for the burrs and a box of spirawraps. If the engine
simulation software is correct this inexpensive tweek can be worth
10bhp @ 6000rpm, a very good return on investment I would say.
It is really not that difficult to do, abit of nerve and a steady
hand is all that is required. Give it a go this winter.

Indeed it is not all that difficult but I would urge due diligence
researching what works and what does not when starting to grind away at
these, not inexpensive, castings. There is as much to be gained by
having the valve seat sealing area moved further out the valve. The
quality of the valve seat machining operation can make or break your
port work. If any of you all feel hardcore enough to give it a go I can
post a Superflow manual to the group section, additionally I can post
part one of the text for a web site I'm building on DIY head porting
for the 2.5v6 Alfa engine.

Cheers,
Scott



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PostPost by: LotusRod » Fri Nov 05, 2004 1:11 am

Sounds interesting.
Sure would like to have a look.
Rod McIntyre
On 04Nov 2004, at 8:01 PM, scott potter wrote:

> Once I had the head back I set about is with a couple of carbide
> burrs <snip> a couple
> of evenings work soon had things looking much better. All it cost was
> about 50 quid for the burrs and a box of spirawraps. If the engine
> simulation software is correct this inexpensive tweek can be worth
> 10bhp @ 6000rpm, a very good return on investment I would say.
> It is really not that difficult to do, abit of nerve and a steady
> hand is all that is required. Give it a go this winter.

Indeed it is not all that difficult but I would urge due diligence
researching what works and what does not when starting to grind away at
these, not inexpensive, castings. There is as much to be gained by
having the valve seat sealing area moved further out the valve. The
quality of the valve seat machining operation can make or break your
port work. If any of you all feel hardcore enough to give it a go I can
post a Superflow manual to the group section, additionally I can post
part one of the text for a web site I'm building on DIY head porting
for the 2.5v6 Alfa engine.

Cheers,
Scott



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PostPost by: twincamracing » Fri Nov 05, 2004 1:22 am

Ok here's the part about doing the work using the Alfa head.
The techniques are similar:

Street Porting the 2.5 Alfa Romeo V6 Cylinder Head

This is a step-by-step guide to porting the standard 2.5 head as fitted
to the GTV-6, Milano and 75 models utilizing the stock valve sizes.



?The horsepower of an engine is directly proportional to the amount of
air drawn into the cylinder and retained until ignition occurs. By
reducing the air flow resistance of the intake and exhaust tract,
cylinder filling is improved and engine horsepower increased
directly.?1

Total flow through the engine is ultimately determined by the valve
diameters. Valve size is limited by the diameter of the cylinder bore.
Generally, hemi head engines permit valves up to .57 times the bore
diameter due to extra space in the combustion chamber.

?Tests indicate there is generally no power improvement as long as
exhaust flow is greater than 60% of intake flow. This would dictate an
exhaust valve diameter of .77 to .80 times as large as the intake
valve.?1

So let?s look at one of our favorites the 2.5 V6: 88mm bore, 41 x
36.5mm valves, intake manifold inside diameter ~34.67mm.

41mm intake is only .465 times bore diameter.
41mm x .85 = 34.85mm optimum venturi size.
36.5mm exhaust is .89 times intake valve diameter.

So our intake is too small, but efficiently sized and our exhaust is
too big.

Let?s look at what we can do to improve the efficiency of the existing
valve size combination.



Besides the basics of a clean well lit workspace and a supply of
compressed air (this does give my tired little 5hp 60 gallon compressor
a workout) here?s what I use:

Dividers/calipers; a standard straight tip and an inside pair, 7? long

?? Die Grinder; straight

Carbide Burrs; a) ?? cylinder with ball nose, single cut, coarse flutes
for light alloy, standard shank; b) 3/8? flame, single cut, long
shank; c) ?? ball, double cut, long shank

Sanding Drums; ?? and 1? diameter with shanks to suit die grinder.
Additionally, I also keep an 8? long piece of ?? round stock with a
1?slot cut in one end to hold strips of sandpaper.

6? Dial Caliper

Neway Valve Seat Cutters; an assortment of diameters with 70, 45 and 30
degree cutting angles.

Prussian blue or machinists dye.

Clover brand fine lapping compound.

Safety Goggles; I really don?t like digging bits of debris from my eye.


Once the head is stripped of moving parts and cleaned up you can see
the valve pockets appear to have been roughed out at the factory , no
doubt by some one in a hurry, prior to the installation of valve seats.
Sometimes the pockets line up with the seats and sometime times they
don?t and I have seen them opened up larger than the seat insert.

The intakes tend to be especially dismal as the designed port does not
allow a straight shot to the valve like the old four cylinder heads.
The rough shaping of the casting along with the fellow in a hurry on
the assembly line conspire against a smooth transition around this bend
with turbulence and separation. As flow losses occur from changes in
direction and decreases in velocity I want to smooth the directional
flow and keep the velocity high. There is free power just waiting to be
unleashed with just a little bit of time and conscientious effort.
Follow me as I go along.

First I rough out the pocket with the ?? burr. Easy does it as the
coarse flutes can remove a lot of material in short order.

I follow with a 70 degree cutter to open the inside of the valve seat
to increase the net valve area . The inlet side I open from 1.44
(36.6mm), yours may vary, to 1.525? (38.7mm). Cool, huh? It?s like
putting in a 2mm larger valve. The exhaust side is opened from 1.218?
(30.9mm), again, yours may vary, to 1.30? (33mm). Another 2mm! For
those of you into building headers, 1 ?? head pipes are perfect.

One more time with the ?? and I do a rough cut on the inside of the
kink of the inlet port to give it the general shape of a curve. Again,
not too much as I?m not hogging this area out, just reshaping the
curve. I?ll get my inside dividers out and set them to 85% of my inlet
valve area so I don?t go too far as I don?t want to kill my port
velocity. Why 85%?

In the classic formula for maximum flow, the ideal intake system would
have a single carb throat per cylinder with a slide plate throttle and
a venturi equal to .85 times the intake valve diameter. Below the
venturi, the carb bore should gradually open up to the size of the
intake valve at the manifold entrance and gradually taper down to .85
times the intake valve diameter at a point about ?? or 13mm below the
valve seat.

Notice that 85% of the inlet net valve area is the same size as the
exhaust net valve area. Again, tests indicate there is generally no
power improvement as long as exhaust flow is greater than 60% of intake
flow. This would dictate and exhaust valve diameter of .77 to .80
times as large as the intake valve.

As can be seen, this exhaust is oversized in relation to the intake.
Work here will be limited to smoothing out the rough work done on the
assembly line and giving the entire port a consistent finish. Even
with a larger inlet valve the exhaust needs very little work and no
changes to the port dimensions past the pocket or bowl.

In fact our optimal inlet valve size in relation to the cylinder bore
works out like this: 88mm x .57 = 50.17mm; 50mm x .77 = 38.5mm.
These should be the optimum sizes, but I doubt there?s room for a 50mm
valve seat. Yeah, I know, you?re thinking about the spark plug hole?it
can always be reduced for a 10mm plug, gaining valve seat insert room,
but I?d be concerned with the seat protruding into the combustion
chamber. Using a 46mm intake would give us a good relationship with our
exhaust valve and maybe a seat will fit without fouling the combustion
chamber. I haven?t tried this yet, but it is known the 44mm inlet valve
and seat from a 3.0 litre will work, but that is for another article.
Let?s get back to the business of porting, shall we?

Next I chuck the 3/8? flame burr. The long shank lets me get well into
the port from either end. Now I smooth out my rough cut. The fine
flutes of the flame leave a good finish on the port walls. The kink
is made into a smooth contour watching to not open the throat more than
85%. The point of the flame allows me to get close to the guide. The
guides need not be removed unless they are worn enough to require
replacement.

One of the most critical areas for optimal flow is known as the short
side radius. It is here is where the bottom of the port turns into the
seat and the incoming flow must make this turn with out detaching from
the walls and going straight interrupting the rest of the incoming
flow. This should be a nice smooth radius, Very little needs to be
removed here, just a smooth blending of the radius to allow the flow to
gradually make the turn, reducing flow loss.

The port walls can be gently opened where they meet the floor of the
port along the short side radius, widening the radius in to a slight
?D? shape where the straight back of the ?D? is the floor and the short
side radius.

If you are keeping the guides, you are nearly done here. This stage of
the porting and this finish of the port walls is a quantum leap over
the factory job you could go straight to a valve job and feel good in
the knowledge you have made a noticeable difference, from here on the
returns are less for the time involved. Skip on ahead to the matching
of the inlet face.

If the guides are junk, and these are, it is time to knock them out. A
big mallet and a proper sized driver (tool A.3.0134 or similar turned
on a lathe) makes easy work of it. No heating of the head is necessary,
drive them out from the seat side. Refer to the factory workshop manual
for more details.

Once the guides are out I use the ?? ball to smooth around the guide
opening. I also use the ball to smooth out any casting marks present
along the the port wall without changing the shape of the port wall.
The diameter of the ball and the double cut flutes enhances the overall
quality of finish in the port. I smooth the entire port without major
material removal and I will periodically check with my dividers to keep
my nominal dimensions intact through out this port and match the
remainder to this one.

Next I address the inlet face at the manifold where there is another
example of a rough job from the assembly line. Using the ?? burr I
blend the port wall to the inlet face without changing the opening of
the inlet face. By the way, I have seen cases where the manifold sits
askew of the port, check with an inlet gasket and scribe a new port
opening if necessary and blend to this new mark.

Note the port dimensions from inlet face to throat are basically
unchanged. This keeps the velocity high in the port, the throat acting
as a venturi to speed up the airflow to the bowl before passing through
the seat.



Now the sanding drums are used to give a consistent surface finish to
the ports. And there you have it. Install guides and a 3 angle valve
job in the next installment.

Note: the greatest flow loss in the inlet port is due to the expansion
of the air out of the valve. This makes the area from ?? below the
valve to ?? above the valve the most critical area. The valve seat has
a considerable effect on the flow.


1 Superflow 110 Operating Manual

2 For the purpose of this article the Net Valve Area is defined as the
inside diameter of the 45 degree angle in the valve seat.

3 For an interesting argument for a 65% cross section in 4 valve
engines I direct you to www.mototuneusa.com




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PostPost by: lotuselan2 » Fri Nov 05, 2004 4:56 am

Steve
did your machine shop do a multi-angle cut on the valves? Any good shop
would and that is worth a percent or two.
Ken
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PostPost by: steveww » Fri Nov 05, 2004 11:14 am

No I asked them not to cut the seats. I will cut 3 angle seats myself.

The theory from Scott is quite helpful. I have an old friend who has
a head porting business, he mainly does K-series engines but he got
me started with the Lotus twinc.

Just a few practical tips:

The ally will tend to clog the burrs, lightly coating them with PTFE
cycle chain oil before cutting significantly reduces this.
Additionally regularly clean out the burrs while cutting I used a
coper wire brush, then re-oil. I also had an extension shaft made up
to hold the burrs so that I could get deep in to the ports,
particularly the inlet port which is very on on the Lotus head.

When cutting keep the burr/spirawrap moving at all times. Be very
careful around the valve seats as it is very easy to under cut the
seats as the ally is a lot softer. Cut a small ammount and then run
your finger up the port, any lumps and bumps need to be smoothed out,
all turns should be smooth and prgressive. If you have never ported a
head before just use a drill not a die grinder. The die grinder has a
very high rpm and removes material VERY quickly especially on ally,
additionally if the burr digs in due to inept handling there is a
good chance you will damage yourself and the head. Tank tape and old
head gasket to the head, this will protect the machined surface while
you work on the head particularly the combustion chamber. Have old
inlet and exhaust valves turned down so that they fit flat in to the
seat, use these to protect the seats while you work the combustion
chamber.

If there is enough interest I can write all this up properly with
photographs.

--- In ***@***.***, "lotus" <[email protected]> wrote:
Steve
did your machine shop do a multi-angle cut on the valves? Any good
shop

would and that is worth a percent or two.
Ken



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PostPost by: twincamracing » Fri Nov 05, 2004 3:13 pm

The ally will tend to clog the burrs, lightly coating them with PTFE
cycle chain oil before cutting significantly reduces this.
Additionally regularly clean out the burrs while cutting I used a
coper wire brush, then re-oil. I also had an extension shaft made up
to hold the burrs so that I could get deep in to the ports,
particularly the inlet port which is very on on the Lotus head.

slower speeds reduce clogging and hard soap or wax works well on the
burrs, too. I have both std and extended shank burrs finding the
"flame" shaped burrs used most often. The coarse cut burrs for
aluminium are for rapid stock removal and not needed, the single or
double cut burrs for ferrous materials work great and give a much
smoother finish.

When cutting keep the burr/spirawrap moving at all times. Be very
careful around the valve seats as it is very easy to under cut the
seats as the ally is a lot softer. Cut a small ammount and then run
your finger up the port, any lumps and bumps need to be smoothed out,

perhaps the most critical area is known as the short side radius, the
point where the floor of the port blends into the valve seat, look to
make a nice gentle radius with out any edges

all turns should be smooth and prgressive. If you have never ported a
head before just use a drill not a die grinder. The die grinder has a
very high rpm and removes material VERY quickly especially on ally,

I find using pistol grip shapes to port a bit akward, you can put an
in-line regulator to reduce the rpm of the air powered die grinder and
a bit of rubber hose under the paddle helps with control. I would
recommend finding as clean junk non-Lotus alloy head to practice on

you work on the head particularly the combustion chamber. Have old
inlet and exhaust valves turned down so that they fit flat in to the
seat, use these to protect the seats while you work the combustion
chamber.

good idea, less is gained with chamber work tan the area 1" behind the
valve, bear in mind any chamber work requires the final volume to be
checked (actually a good idea for any performance head work)

If there is enough interest I can write all this up properly with
photographs.

I have photos of the Alfa heads but there simply isn't rooom in the
files section. Anyone desiring a copy of the Superflow manual drop me
a note off list and I'll get zip files posted out next week.

Now I'm off the the harvestclassic.org with one of the Laverda

Cheers,
Scott



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PostPost by: steveww » Fri Nov 05, 2004 5:09 pm

The drill works OK for me, no problems with the pistol shape. I guess
what it is your are used to.

The short radius is the most critical and the most difficult to work on.

On the Lotus twinc head there is quite a bit of shielding around the
valve seat close to the chamber edge, good idea to cut this back a bit.
The turned down valves are also useful for measuring chamber volumes.
Use a bit of grease around the seat to get a good seal.

Another good tip is to use some smaller valves or turned down standard
valves as port size guides, a lot less fiddly than calipers.

scott potter wrote:
> The ally will tend to clog the burrs, lightly coating them with PTFE
> cycle chain oil before cutting significantly reduces this.
> Additionally regularly clean out the burrs while cutting I used a
> coper wire brush, then re-oil. I also had an extension shaft made up
> to hold the burrs so that I could get deep in to the ports,
> particularly the inlet port which is very on on the Lotus head.

slower speeds reduce clogging and hard soap or wax works well on the
burrs, too. I have both std and extended shank burrs finding the
"flame" shaped burrs used most often. The coarse cut burrs for
aluminium are for rapid stock removal and not needed, the single or
double cut burrs for ferrous materials work great and give a much
smoother finish.

> When cutting keep the burr/spirawrap moving at all times. Be very
> careful around the valve seats as it is very easy to under cut the
> seats as the ally is a lot softer. Cut a small ammount and then run
> your finger up the port, any lumps and bumps need to be smoothed out,

perhaps the most critical area is known as the short side radius, the
point where the floor of the port blends into the valve seat, look to
make a nice gentle radius with out any edges

> all turns should be smooth and prgressive. If you have never ported a
> head before just use a drill not a die grinder. The die grinder has a
> very high rpm and removes material VERY quickly especially on ally,

I find using pistol grip shapes to port a bit akward, you can put an
in-line regulator to reduce the rpm of the air powered die grinder and
a bit of rubber hose under the paddle helps with control. I would
recommend finding as clean junk non-Lotus alloy head to practice on

> you work on the head particularly the combustion chamber. Have old
> inlet and exhaust valves turned down so that they fit flat in to the
> seat, use these to protect the seats while you work the combustion
> chamber.

good idea, less is gained with chamber work tan the area 1" behind the
valve, bear in mind any chamber work requires the final volume to be
checked (actually a good idea for any performance head work)

> If there is enough interest I can write all this up properly with
> photographs.

I have photos of the Alfa heads but there simply isn't rooom in the
files section. Anyone desiring a copy of the Superflow manual drop me
a note off list and I'll get zip files posted out next week.

Now I'm off the the harvestclassic.org with one of the Laverda

Cheers,
Scott



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