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Date: Fri Mar 4 18:44:20 1994   
Subject: Extrude-hone
X-Sequence: 3925

       Could you explain further this process and what sort of equipment is 
required to perform it and how much metal does it remove?
*  Peter Smith,Technical Services Manager  Internet *
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[It is a patented process that involves pumping a thick abrasive-laden
silicone putty at high pressure through the ports.  The abrasive
removes metal as the putty flows along.  The machine that does it 
looks like a stamping press.  It removes as much metal as you specify
and from where you specify.  As part of the setup, they install
baffles to direct the putty onto the surfaces that are to be machined.
The nifty part of this is it removes metal without changing the
general shape of the port and it leaves a VERY shiny surface.
Cost is in $200-300 range.  Seems high at first but the work involved
in taking a mm or two off of every surface in a Z manifold and head
by hand would be much more expensive and in the case of the EFI manifold,
would involve cutting it open, working the ports and welding it
back shut.  Get Dave William's vendor database from the
email file server for contact info.  JGD]

From: John De Armond
X-Source: The Hotrod Mailing list
Date: Aug 1992
Subject: Re: Extrude Honing

>I am looking for more information on extrude honing for ports and intake
>manifolds.  The adds I have seen seem to imply that the process does a
>pretty good job of changing the port topology to improve flow, as well as
>polishing the port.  Is this true, or should a person hand port the head
>before sending it off?
>The reason I ask is that I can imagine the abrasive taking a path that
>takes metal off the wrong places.

The only non-hype article I've read on Extrude-hone was in Stock Car Racing
awhile back.  The article mentioned that baffles are used to direct
the goo where it needs to go.  They're still not head specialists but
for many engines, just hogging out the stock manifold makes a world of


X-Source: The Hotrod Mailing list
Date: Apr 1993
Subject: RE: Head porting - dynamic flow
X-Sequence: 5161

>In everything I have read about cylinder head porting, the flow
>benches that are used (and the flow results) are based on
>a static valve opening and a 'constant' flow.  I was thinking about
>this the other day, and I wondered what the correlation was to
>the 'dynamic' (pulsed) flow of the port.  That is, will a porting
>mod that yields a 'constant flow' improvement still result in an
>improvement in the 'dynamic flow' of a running engine?

<stuff deleted>

>Based on that, I would expect that flowing port mods might come up
>with different information if the flow bench was set up to simulate
>the operating environment.  The flow characteristics should even
>change as the RPM changes - the 'resonant' flow pulse frequency (as
>well as the harmonics) should flow differently.

One of the problems with designing around resonance etc of exhaust systems is
the fact that every change in your exhausts systems restriction ( each bend,
T, muffler etc) creates a reflection.  Just imagine all the reflections and
harmonics.  Maybe with solinoid operated valves you could simulate the real
world situation.  What about fuel separation?  How would you model the
air/fuel mixture.  I still think that porting is more of an art than a

[One issue IS how to model the sonic activity in the system but the actual
waveforms can easily be determined by the use of pressure transducers.
As far as the porting (as opposed to intake and exhaust systems) is
concerned, fairly simple pulsating flow can simulate the environment
fairly well.  At least as important is flowing the same working fluid.
With carburators that means wet flow.  Even with port injection,
actual conditions are still important because of the disruption of the air
flow caused by the fluid injection.  I don't personally consider porting
as much an art as simply a process of trial and error.  JGD]

About extruded porting (I think thats what its called).  After it smoothed
out passages wouldn't result in worse flow?  Just like rivers - older ones
meander more due to the water eroding on the outsides of bends.

[Most engines that are candidates for the Extrude-hone process need
more flow capacity much more than they need refinements in flow patterns.
For racing engines, it has been widely held that a slightly rough
port surface aids runability in carburated applications.  My experience
with racing motorcycle engines tends to confirm that theory.  The theory
is the roughness tends to break up laminar flow near the wall which
aids the evaporation of the still-liquid gasoline.  This should not
be an issue with port fuel injection.  Avoiding turbulent flow should become
the dominant issue.  Smooth surfaces and gentle transitions are the rule.
Observation of a Camel Light fuel injected Chevy racing engine at the
Atlanta Grand Prix a couple of weeks ago tends to confirm that theory.
Intake ports were very smooth.  JGD]

Or don't I understand the process?


X-Source: The Hotrod Mailing list
Date: May 1993
Subject: RE: Head porting - dynamic flow
X-Sequence: 5188

> John has someone doing a flow bench article for PE now.  We've talked
>about doing a motored "bench" before, and I will probably be building
>one this summer.  With a motored bench you could also test the intake
>system as a whole.

Would it be possible to get a small camera/fiber optic device to
monitor airflow.  I'm thinking that something like what they do for
wind tunnels.  Maybe you can "see" trouble spotss in stead of trial and
error.  I have seen wind tunnel test with smoke injected into the

Would a similar arangement be possible or am I just blowing smoke?


[I've never had much  luck with smoke because of the problem of making
a smoke stream small enough to mean anything.  What does work, and what
comes with most commercial flowbenches, is a small hand-held pitot tube.
This can be used to probe around a port to see where the velocity profiles
are.  The problem with the commercial benches is they all seem to use
large Dwyer water manometers.  These devices are slow to respond to
begin with and when fed with a small bore pitot tube, are intolerably
slow.  A small pressure transducer close coupled to the probe and connected
to either a bargraph or an oscilliscope is vastly more responsive and will
allow one to see turbulence.  JGD]

From: emory!!frank (Frank Evan Perdicaro)
X-Source: The Hotrod Mailing list
Date: Jul 1993
Subject: Diacom on Saturn
X-Sequence: 5771

Can anybody tell me if the Diacom software currently runs on the
Saturn / Corvette ZR1 ECU?  Also, can somebody please post the address
for Rinda, and perhaps their telephone #.  Thanks.

Edge of charter warning.

Just got a new Saturn the other day.  I'm looking into doing some mods,
particularly a bit of cleanup of the sand-cast intake.  ( Why did they
not use foam cast, like the rest of the engine?  Grrr. )  Anybody have good
ideas?  Extrude-hone is too much, I think, and I am not too fond of the
bandsaw method.  There does not seem to be much in the way of aftermarket
or junk yard stock, either.  Factory racing team reports this to be a good
first step.  Thanks for any thoughts.

[I'm experimenting right now with electrolytic machining for opening up
my Zcar manifold.  This involves suspending a stainless steel wire cathode
in the runner, filling it with a suitable electrolyte and passing current
through the solution.  The rate of etch is dependent on the electrolyte
and the current density.  The finish depends mainly on the electrolyte.
I'm still searching for the optimum electrolyte.  Salt water works as
does sulfuric acid.  But I'm getting the finsh I think I should get.
There's a lot of literature on the subject if you want to play.  I think
I'm going to have to section the plenum before it's over.  No big deal
on the Z manifold.  The metal welds well.  JGD]

Frank Evan Perdicaro 			Dianippon Screen Enginerring of America
 Legalize guns, drugs and	   3700 Segerstrom Ave
  inhouse: frank@rebel, x210		      Santa Ana CA
   outhouse:, 714-546-9491x210	 92704

From: Dave Baker
Subject: Re: Proper cam for '84 GTi
Date: 13 Jun 1998

>Howdy, I'm looking for the right cam for my '84 GTi. It's actually a GTi
>motor/tranny in my '84 Jetta 2dr. I'm looking for more bottom end. "Low end
>grunt!". Also, any performance tips I can do. I've got a Bosal header, Audi
>throttlebody, K&N filter, I modified my airbox, Bosch plugs, NGK wires, Bosch
>pro-coil, distributor and rotor. When I do the cam I'm using a 1.8 hydraulic
>lifter head off my '86 Carat. I'll port it to the gasket but don't know which
>cam to use. Thanks for any help.

Lex - take some advice from a cylinder head specialist. Porting your head "to
the gasket" by which I presume you mean just opening out the areas you can
reach from the manifold end of the port will not help in the slightest and will
probably reduce bottom end power.

The critical areas in this head as in almost every other is what is done to the
valve seats and the throat and the short side port bend. Shoving a cutter up
the 2 inches of port you will be able to reach with a black and decker will
increase port area, decrease air speed, reduce low end power and do nothing to
increase flow at all. Get it done by a proper head shop who other people in
your area have a good word for. If the situation over there is anything like it
is over here in the UK then most head shops won't be much better than close to
useless. Shop around first.

Properly done a well modified std valve head on the GTi will give 15 more bhp
and grunt throughout the rpm range, not just at the top end. Our big valve
heads in race engine trim are making 180 bhp on the standard injection system
so it shows what is possible on the 8v motor. Sorry we are in the wrong country
for you or I would love to help.

Dave Baker at Puma Race Engines - specialist flow development and engine work.

From: Dave Baker
Subject: Re: Proper cam for '84 GTi
Date: 14 Jun 1998

>AFAIK any aftermarket cam you're going to find is going to give you high
>RPM power at the expense of torque.  Porting the head (intake side,
>anyway) will achieve the same effect.

>Subject: Re: Proper cam for '84 GTi
>From: Nathan J Nagel <>

Sorry Nate but thats a load of absolute bollocks. Properly ported cylinder
heads increase torque throughout the rpm range not just at the top end. Any
increase in air flow leads to better cylinder filling at all engine speeds. The
main misunderstanding about cylinder head mods comes about because so many of
them are done wrong. Increasing port size to a greater diameter than necessary
reduces gas velocity and can be bad for low speed torque. Proper mods which
increase flow by attention to valve seat, throat area and port bend radii
increase flow and therefore port velocity through the same size port.
Calculations and good flow bench work indicate the port size needed to cause
little or no restriction to the valve.

Also many cam manufacturers do short duration cams for towing and other uses.
However the GTi engine is pretty good on low rpm torque and going down on cam
duration is not necessary for a daily driver. Done properly an 1800 gti can
show 135 bhp, 125 to 130 ft lb peak torque and drivability better than stock
all through the range.

Dave Baker at Puma Race Engines (London - England)  - specialist flow
development and engine work.

From: Dave Baker
Subject: Re: gas flow head
Date: 09 Jul 1998

>From: TBerk <>
>I1000101 wrote:
>> ok,
>> now ive read about alot of cars in PVW getting there heads gass flowed,
>> What is this, and what are the advantages of this? Is it something that
>> i can do myself or is it something that best be left to the pro's.
>> Also anyone know of anyplace that i can get my 16V ported and polished
>> in the newyork area, the guy that was going to do it just dikked me
>> over
>I hope you won't take this the wrong way- I have come to understand that
>there is not much to benefit from with a port and polish on the 16v
>heads. Apparrently the heads are close to tollerence in some areas and
>also that they flow about as good as they are going to get. Sorry to be
>light on specifics, I'm an 8 valver by default.
>How's this for a an improvement:
>blueprint the engine. I'd think this would help a high reving engine
>like the 16v. With all that reciprication mass balanced out you get more
>bang for the cubic inches (millimeters).
>( In search of an inexpensive Audi 80 2.0l bottom end on the West

"Gas Flowing" is improving the port and valve seat shape to increase airflow
through the port. More airflow relates directly to more power. The 16v head has
great scope for improvement and is in no respect "close to tolerance" nor does
it in standard form flow anything like as good as it can get. Properly done you
can get 25 bhp extra from a head with standard valve sizes and more from big
valve heads.

Even an averagely well modified head should show 15 bhp although I have no
knowledge about how good the cylinder head specialists in the USA are or who to
go to. Without the right professional equipment and plenty of experience you
can't do this yourself.

Balancing the engine parts will achieve nothing whatsoever except a lighter
wallet. VW do a perfectly good job themselves and even if they didn't,
balancing of the reciprocat"ing" or rotating mass contributes only to engine
smoothness and not to power output.

Dave Baker at Puma Race Engines (London - England)  - specialist flow
development and engine work.

From: Dave Baker
Subject: Re: Head work on 2L golf
Date: 01 Aug 1998

>John Garrick wrote in message <>...
>>Hi guys,
>>I'm considering having some head work done on my 1995 VW Golf GL 8v;I
>>came accross a company here in australia that suggested they could do a
>>port and polish (MILD) on the head as well as matching the exaust
>>The car will have a NEUSPEED 276 degrees cam with ajustable cam gear as
>>well as air box mods & currently has a 2 and a quarter inchs exaust with
>>an american "hooker" muffler.
>>My questions are; is it safe for them to do head work on a head were the
>>valves are still on it.what could I expect form this engine once done !

Don't understand your question. You can't do anything to a cylinder head
without taking out the valves first. As to power increase it depends whether
they are any good or not. Zero bhp if they are useless and do nothing
constructive - up to 15 bhp if they are top notch flow specialists. Suggest you
get in writing exactly what they propose to do and the power gains they claim
before agreeing to anything.

That means specifying whether the valve guides will be removed and replaced
(you can't reach the critical areas in the ports unless this is done - lots of
cheapo firms don't bother and get no real airflow gains), whether the valves
will be recut and backcut at 30 degrees (critical for flow), whether the seats
will be properly cut with 3 angles (critical for flow), whether the gasket face
will be resurfaced (should be a std part of any head job), whether they use a
flowbench and what flow gains they claim.

Then go somewhere else and get a dyno printout in std form and go back after
the work and verify the gain. Don't rely on a dyno printout from the firm doing
the work - you can make a dyno show any before and after figure you like if you
have a vested interest in the outcome.

After all of that you may still end up in the situation where if you get no
good power gain they will claim one of the following:

A) - there is something wrong with the  rest of the engine preventing their
good work from showing extra power.

B) - The dyno prints from the other independent firm are rubbish and they only
back up power claims with results on their own dyno.

C) - Every other customer has been perfectly happy so you are just a whinging
bastard. (see I speak Aussie too)

D) - "Ah well sir - it takes at least 2,000 miles for the cylinder head to
carbon up again before any power gains are apparent. Bring it back in a month
if you are still unhappy" - by then hopefully you'll be too mentally exhausted
to bother and anyway you'll have forgotten how it used to go and will have
managed to convince yourself that it is a bit faster.

Caveat Emptor as they say in Rome

Dave Baker at Puma Race Engines (London - England)  - specialist flow
development and engine work.

From: Dave Baker
Subject: Re: WTB 2.0 16V 91GLI ported and polished head
Date: 07 Aug 1998

Please, please, please stop using the word "polished" in respect of modified
cylinder heads. Polish is actually bad for fuel drop out and therefore power.
Shape is what matters and how well the valve seats are cut. "Gas- flowed" is
fine. "Ported" on its own is fine. "Modified" is fine. "Polish" sucks.

Dave Baker at Puma Race Engines (London - England)  - specialist flow
development and engine work.

From: Dave Baker
Subject: Re: Ford colonge V6 performance
Date: 02 Oct 1998

>Subject: Re: Ford colonge V6 performance
>From: (Alan Eardley)
> Adding stage 2 heads (oversize inlets, ported exhausts) made it
>rev much more freely but suprisingly only reduced the quarter mile time by a
>tenth or so.

Probably because they actually had very little flow increase and didn't give
any real power. These heads are very tricky to port properly and need plenty of
flowbench time. When I did some flowbench work on this engine many years ago
the first result from fitting big inlets was to REDUCE flow. The port shape
needed to be changed considerably to make the big valves work. Once this had
been got right the flow went up in proportion to the increase in valve area as
it should do.

Most so called "Head Porting" out there consists of a quick flash up and down
with a flap wheel to make things shiny and no flowbench work at all. You get
what you pay for.

This engine is mainly restricted by the cylinder head and inlet manifold flow.
Properly done heads with a decent carburation system, (or even better, throttle
bodies) and power outputs over 200 bhp are easy enough to achieve.

BTW 103 degree lobe centreline angles sound a long way out to me. Closer to 110
degrees would be more normal to achieve a good balance of top end power without
losing low end tractability. Are you sure you aren't confusing the quoted inlet
timing at full lift figure with the LCA? These are two completely diffferent

Dave Baker at Puma Race Engines (London - England)  - specialist flow
development and engine work.

From: Dave Baker
Subject: Re: port & polish
Date: 17 Oct 1998

>From: "Ryan Press" <>
>Hi all, I'd like to add a little more oomph to my stock 1600.  I would like
>to add a bigger cam and a slight port and polish of the heads.  I read that
>if you do this incorrectly, you loose intake velocity, and ruin your
>low-end.  <snip>

The majority of the flow gains from mild port work is in what you do to the
valves and valve seats and adjacent areas. Hogging metal out of the main part
of the port (especially the bits you can reach if you only have short burrs)
won't do you any good.

Unless you have long stem grinding burrs, high speed porting kit and valve seat
cutting equipment and the knowledge to use it I would stay well away. By all
means remove a few sharp edges in there and have a general clean round but if
you want decent flow gains - say 10% or more - then find a good head shop.

Dave Baker at Puma Race Engines (London - England)  - specialist flow
development and engine work.

From: Dave Baker
Subject: Re: VR6 - Max power?
Date: 19 Oct 1998

>From: "Joel Bell" <>
>How about a 3.0 or 3.1 conversion?  I'm not suggesting it increases flow,
>but if you want more power...more displacement is a sure bet...

I'm afraid not - or at least not as much as most people think. Lets do a little
thought experiment and I'll explain why. Imagine a 4 cylinder engine with fuel
injection and lets say 100 bhp. If we take two of those engines and bolt them
together to make a V8 it would be safe to assume we would double the
horsepower. We have after all doubled the capacity as well as the valve area,
induction capability, exhaust capability and everything else. You can probably
see where I am heading now.

Now lets go for capacity increases more in line with what we can achieve by
machining an existing engine. If we take that 4 cylinder engine and turn it
into a 5 cylinder engine with one more identical cylinder we have made a 25%
increase in capacity and again we would expect around 25% more bhp. But what if
we just increase the bore and stroke of the 4 cylinder engine to create 25%
more capacity without making any other changes?

We still have the same valve area, induction and exhaust capability etc as we
started with. If the additional cylinder of the 5 pot engine gives 25% more
power because it is one more cylinder identical in all respects with the
original 4, what power increase will just the extra capacity give us?

The answer depends on the state of tune of the engine. In all out race tune the
extra capacity will give almost no more power than we had with the smaller
engine and maybe less. What determines the ultimate power potential of an
engine is the amount of air that it can "process" per unit time. What
determines this is the flow capability of the cylinder head and that in turn
depends on the valve area and the efficiency of the port design. What the
bigger engine will do is produce its power at lower rpm and the max power rpm
will scale exactly with the capacity increase. There will, due to the lower
rpm, be lower frictional losses and these will show up as a slight increase in

In road tune we are not talking about the ultimate power potential of the
engine but similar principles will apply. We may, with no other changes, see a
small increase in peak power but NOTHING LIKE in proportion to the capacity
increase. Normally we might expect to see about 1 quarter to 1 third of the
capacity increase showing up as a power increase. So 10% more capacity might
show up as 3% more peak power. REMEMBER, we are talking about making, at this
stage, no other changes to the engine.

What we will see is more power in the low and mid range rpm band i.e greater
torque. This should scale very much more closely with the capacity increase so
we might expect say 8% more peak torque from a 10% capacity increase. Again
though, the usable rpm band will fall in line with the capacity increase so
peak power will be at 10% lower rpm and peak torque will also occur sooner.
What we end up with is an engine that lugs well low down but runs out of breath
very soon. Driveability will be better but ultimate point to point speed (like
1/4 mile performance) will not improve very much if at all.

However that is not the end of the story. We can take advantage of the extra
capacity to run a little more cam duration perhaps, because we can afford to
lose a bit of the new found low rpm torque. This may, in a perfect world,
bring us back to showing perhaps 4 or 5% more power from our 10% capacity.
Unfortunately in most cases we are stuck with the range of cams available to us
and the next cam up in a manufacturer's range will probably be too much of an
increase and we will lose too much low rpm torque.

In addition if we increased bore rather than stroke we might benefit from a
little more flow due to unshrouding of the valves but this depends on cylinder
head design. We might also take advantage of this bigger bore to fit more valve
area into the head and perhaps this will now scale better with the capacity

Hopefully we can now see that we only get a power increase in line with a
capacity increase if we also scale up the valve area and induction and exhaust
flow capacity by a similar amount. For most engines we tend to be limited in
what we can do in these areas by the design of the engine. Often we can
increase the valve size until the valves touch each other before they touch the
bore walls so a bigger bore makes little difference to what we can achieve in
terms of cylinder head flow.

Now go back and look at what happened to peak power when VW first increased the
size of the 8v and 16v engines from 1.8 to 2.0 litres. This was an 11% increase
in capacity but the cylinder head stayed the same. Peak power hardly changed at
all. In fact on the 16v engine in europe it went down from 139 bhp to 134 bhp
(if memory serves) until further changes were made later on with the tall block
engine. The 8v only went up from 112 to 115 bhp.

Finally, for anyone really interested in understanding engines properly, have a
look at Bill Jenkins book on the small block chevy engine. Many of the
principles in it are worth noting. For the drag engines where just peak power
was the main thing and tractability didn't some into it he used the smallest
engine sizes like the 327 cid. Only for track and street engines were longer
stroke cranks of use and the 350 and bigger engines performed better. It makes
you think!

Dave Baker at Puma Race Engines (London - England)  - specialist flow
development and engine work.

From: Dave Baker
Subject: Re: port & polish
Date: 19 Oct 1998

>From: Jeffry Johnston <>
>PumaRacing <> wrote:
>: The majority of the flow gains from mild port work is in what you do to
>: the valves and valve seats and adjacent areas. Hogging metal out of the
>: main part of the port (especially the bits you can reach if you only
>: have short burrs) won't do you any good.
>: Unless you have long stem grinding burrs, high speed porting kit and
>: valve seat cutting equipment and the knowledge to use it I would stay
>: well away. By all means remove a few sharp edges in there and have a
>: general clean round but if you want decent flow gains - say 10% or more
>: - then find a good head shop.
>: Dave Baker at Puma Race Engines (London - England)  - specialist flow
>: development and engine work.
>Cool Thread and post!  Dave can you tell me anything constructive I did
>to my heads?  I've ported 4 stroke motorcycle heads before and got gains.
>(we can go into that more if you want)
>What I did to my dual port heads was first pick some out that didn't have
>the extra metal surrounding the exhaust valve guides.  Next I didn't mess
>with the intakes as they looked about as good to me as I could figure out.
>What I did do is remove as much metal as I dared from the exhaust ports
>in the area of that "square corner"  I straightened the exhaust port out
>as much as I could.  The main difference could be seen and felt in that
>there was more open area near the end of the valve guide.  The metal was
>removed from the opposite wall of the ports from the vlave guides, see
>what I mean?  I also "made it a little bigger" all along the length of
>the ports but mostly from straightning out the "square corner side" of
>OK, my question for you is how bad did I screw up? ;)
>What advantage -and- disadvantage is there in, not so much totally
>removing, but certainly rounding of that dangged square corner in the
>exhaust ports?  What's it there for?
>I mostly used a pocket knife and carved out the metal.  It sure was
>nice compared to all that cleaning stuck aluminum from the burrs like
>I had to do before.  I guess a guy needs those special aluminum cutting
>burrs. :)  I also special-ground an old knife I had around here get to
>certain areas.  It carved out smooth and easy.
>Alvin Johnston  <--Libertarian

Sorry Alvin - it's been so long since I did anything on VW aircooled heads I
can't remember what they look like. I think though you might mean the shortside
of the exhaust port and that square bit which is common to many engines is a
good thing to work on. It's impossible for me to say though what you did from
description only.

Doing ports with a knife though - that's a new one on me. I have read Mark
Twain though and I do know how you yanks love to whittle. I think I'll stick to
the high speed carbides for now though unless someone gives me an ally
whittling knife for Xmas.

Dave Baker at Puma Race Engines (London - England)  - specialist flow
development and engine work.

From: Dave Baker
Subject: Re: how much power gain w/polished head?
Date: 23 Nov 1998

>From: (Samram3)
>I have a non-turbo 95 eclipse, and was wondering if anyone could give me an
>idea on how much of a power gain I would get if I had the head polished and

Polish - nil bhp
Porting - How long is a piece of string? It's not like buying a specific
component - it depends how good the person doing the work is. Between nil and
10% extra on std valves.
Dave Baker at Puma Race Engines (London - England)  - specialist flow
development and engine work. Puma billet aluminium throttle bodies from £390
per 4 cylinder set. Grooved brake discs coming soon.

From: Dave Baker
Subject: Re: Torque Curve explaination needed....
Date: 02 Dec 1998

>From: (Graeme J Quinn)
>Ok, so I understand that torque is the ability of the engine to turn
>the crankshaft, and that horsepower is the amount of torque measured
>over time.  I get all that...
>I also understand how volumetric efficiency affects the torque output
>of the engine, and how a restrictive intake/exhaust/head design will
>reduce the volumetric efficiency at higher revs resulting in a drop in
>torque as the engine speed rises...  Yes?
>Right, my question is, if torque is simply the ability of the engine
>to turn the crankshaft, why does it reach a peak at 2500-3000 revs,
>etc?  Surely it's not a volumetric efficiency thing?  Torque doesn't
>need momentum, so what's the deal?
>Is it that at very low revs the scavenging effect created by tuned
>intake runners is lost, and when the engine reaches a speed at which
>the scavenging effect created by pressure waves bouncing off the
>closing valves reflects off the throttle body and back into the valves
>as they open?
>The Taurus SHO has dual intake runners, with a set of one specifc
>length that are used at low speed, then a set of secondary intake
>runners that are opened by the computer at circa 4k rpm...  This is to
>take more advantage of scavenging at lower and higher revs, yes?
>What else is causing the low torque output at about 1500 revs etc?
>(I'll learn all this engine tuning stuff eventually!)

This is too big a subject to go into in depth (sadly we have to pay for local
phone calls to access the net here).

However - pulse tuning is part of the story but look at where the piston is
when the inlet valve closes. Anywhere from 50 degrees ABDC with a std road cam
to 85 degrees ABDC with a race cam. At low engine speed there is plenty of time
for the cylinder to fill and gas speeds are low. As the piston starts back up
on the compression stroke it pushes mixture back out of the still open inlet
valve. This leads to what is called low "trapping efficiency". Hence poor
volumetric efficiency and torque. The longer the cam duration the worse this
situation gets.

As engine speed rises a number of things happen. Gas speed in the inlet port
increases and it is harder to stop it and reverse flow. The time the piston
takes to get from BDC to the point of inlet valve close also drops in inverse
proportion to engine rpm. The rising piston starts to compress the fresh charge
but before the pressure pulse thus generated can stop the incoming flow and
force mixture back out down the port the valve shuts.

At some speed in the mid range of the engine's power band the effect of these
factors is such as to maximise trapping efficiency and hence you get peak
torque. At higher engine speeds than this the time available for the cylinders
to fill drops so much that volumetric efficiency falls again and eventually the
point of peak power is reached. To offset this lack of time and improve high
speed volumetric efficiency you need to improve the flow capacity of the
induction system or increase valve opening duration.

Scavenge during valve overlap also has a big effect on low speed torque and
some fresh charge is lost down the exhaust port with long duration cams.
Manifold runner lengths further complicate the matter due to pulse tuning
effects. Modern engines employ a variety of tricks to try and keep low rpm
torque while still keeping good top end power. Variable length and volume
runners, variable cam timing and duration etc. As with many things in life it
is all a matter of acceptable trade offs.

As a general rule it is far better to improve cylinder head flow as much as
possible and then use as little cam duration as you can get away with. That is
why manufacturers have gradually turned to 4 valve engines. In the tuning world
too many people fail to pay enough attention to head flow because it is hard
work and needs flow bench time and experience. It is easier to just put a
longer duration cam in there and tell the customer that he has to accept less
low speed torque.

Get the head flow right though and it is amazing how much power can be gained
without sacrificing any low speed manners at all.

Dave Baker at Puma Race Engines (London - England)  - specialist flow
development and engine work. Puma billet aluminium throttle bodies from £390
per 4 cylinder set. Grooved brake discs coming soon.

From: Dave Baker
Subject: Re: souping up 1.8l 16V engine - numbers please
Date: 28 Jan 1999

>From: (typhus)
>thanks for your reply!
>> 83mm is fine - 84mm seems to cause no long term problems even on
>> 200 bhp engines but thats as far as you can go.
>Okay, how deep would (in the worst case) a wear mark in the cylinder
>wall be after let's say 300.000 miles? Could it exceed a depth of

If you mean the lip at the top of the bore caused by the top piston ring over
time then no - 1mm is 40 thou !! If there were a 40 thou ridge at the top of
the bore then the oil you put in the sump would exit via the exhaust at the
rate of about 1 pint per mile. I once stripped an engine with a 10 thou wear
ridge and a couple at 8 thou. They didn't run very well either of them. Anyway
- why do you you ask ? - what has a 1mm wear mark got to do with the price of
fish ?

>> Don't be silly - you are thinking of spending £600-£800 on very
>> very slightly longer conrods rather than skim a bit off the block
>> or head ????
>DOH! I wasn't aware of the fact that they were so much.
>Skimming the head was an idea I had anyway but since I figure one
>headgasket on 100k miles is normal and re-leveling the head comes
>with it I don't like the idea that much - I'd hate to get stuck with
>too little material to work on.
>Nonetheless it is taken into concideration.
>> Depends on the cam you fit. Hardly the main thing to be worrying
>> about anyway if you want more power. Why fret about the 1 or 2 bhp
>> to come from increasing compression slightly rather than thinking
>> about the 30 plus bhp possible from a really well modified head
>> compared to the zero or less than standard bhp if the head is done
>> by a wally ?
>I figure "wally" means as much as amateur?

There are plenty of good amateurs in all walks of life but yes you get the
general idea.

>It is hard to prove it but
>the guy knows what he is doing. He has been modding heads for a number
>of Group H teams and has a lot of experience. The modded ducts have
>one diameter from the beginning to the end and are polished to
>absolute mirror finish.

That tells me most of what I need to know then. A mirror finish is about the
worst thing you can do to a cylinder head but then magpies are attracted to
shiny things !! You don't want polish - you want the correct shape for high

> I have seen Hartmann heads where the cast had
>cracked between the inlet valves, my bud only mods the seat itself,
>not the outer ring.

Not sure what you mean here by outer ring.

>As a matter of fact I fear the job he will do on mine will be too
>extreme, I have got to find a way to put some brakes on him before he
>turns the head into swiss cheese.

Dave Baker at Puma Race Engines (London - England)  - specialist flow
development and engine work. .

From: Dave Baker
Date: 18 Apr 2002 00:42:37 GMT
Subject: Re: Is a 5-angle valve seat better than a 3-angle?
Message-ID: <>

>From: "The Davenport's"
>"Thomas Hood" <> wrote in message
>> The Cylinder Head Shop here in the UK is offering this service on
>> their Serdi equipment but I have never seen this offered before. Does
>> it flow noticably better? Is valve seat life compromised?
>> If 3 angles is better than 1 and 5 better than 3 is the perfect valve
>> seat a radius?
>> Tom
>In theory, yes...but that is a pretty hard theory to hit.
>In a perfect world, a knife edge would be the best, but it's not going to
>last very race, no make it last longer, a radius with a
>very small, single angle would be best...small the contact, the better flow,

I take it you don't have a flow bench then or you'd know just how wrong that
was. I suppose I shouldn't complain that so many people get valve seats wrong
because a fair chunk of my work is putting previously modified heads right and
it's nice easy to find horsepower, generally with a customer who is then
astonished at how slow the car really was before.

What amazes me though is that there are so many books out there that tell you
how seats should be cut (like any of David Vizards or Bill Jenkin's excellent
book on the Chevy engine) and yet the tuning industry never appear to read them
and just churn out the same old narrow seats time after time that don't work
well at all.

Dave Baker
Puma Race Engines (

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