Cylinder head and cams are stock, nothing fancy. Engine only has AEM
cam gears. Most engines respond very well to few degrees of intake cam advance
and exhaust valve retard. This allows for better cylinder filling at higher rpm
range due to intake charge inertia and some scavenging effect due to later
exhaust valve closing. It's good for high rpm power but can sacrifice some
midrange torque because of bigger valve overlap. Overlap causes dilution of
intake charge by exhaust gases at lower rpm range / small throttle opening
angle.
I had very good results with adjusting my cam gears when engine was lightly
modded. Used GTech Pro
Competition model for power/torque measurements, did 2 runs before and 2 runs
after every adjustment step to be certain results
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are repeatable. I ended with intake cam advanced 4 deg. and exhaust cam retarded 2 deg. On the screenshot black graphs are measurements before (cam gears set as per TSRM) and red graphs - measurement after adjusting cam gears. Probably my cam timing was too far off optimal due to the thick 2 mm MHG. I think adjustable cam gears are a must even for mildly modified motor with thicker than stock HG or aftermarket cams.
This summer I installed Toda camshafts
which were purchased 2 years ago. Cams are used, but in very good condition.
They came with set of JUN adjustable cam gears, I wanted to use this rare set in
place of my more common (and prettier) AEM gears but found that AEM are
considerably lighter and decided to sell JUN set.
Cams are very mild, 7.9mm lift and 272° of advertised duration. This is roughly
equal to 220 - 230° @ 0.050", depends on ramp profile of the cam. Stock cams are 7.5mm lift, 200° duration @ 0.050". So my
cams have only 0.4mm more lift and 20 - 30° longer duration. I
swapped my cams together with seriously worked cylinder head, they supplement
each other very well, I did not notice any loss in low end torque. engine pulls 10.5 in-hg
idle vacuum at 950rpm, still street friendly considering engine's 8.23:1 CR.
I was always fan of idea to improve flow potential of intake and head rather then pushing few more psi of boost. VE rules. Most of the people who know 7M engine agree that it has horrible head, but at the same time it is widespread opinion that 7M head does not need headwork unless your aim is 600hp or higher. Most common argument sounds like: "Person X pushes 600+ whp on completely stock
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head" I think the same person X would have dynoed at least
10% higher number at the same boost pressure if he had professional porting job
done and fitted oversize valves with multiangle valve job. Above you can see
flow comparison graphs taken from
mkiiitech.com Better flowing cylinder head is one of the
reasons why there are more 2JZGTE Supras making 1000+ whp then 700+ whp 7MGTE
Supras. 1JZGTE head fits somewhere in between 7M and 2JZ graphs. It was "common
knowledge" for long time that 1JZ head flows better than 2JZ head, hence 1.5JZ
hybrid. There was interesting discussion
on Supraforums recently which proved this myth wrong.
For myself I am considering two options. First is to buy
Standard Abrasives
porting kit and do the job myself. Second option is to have it done by
professional who can flow bench the head and achieve much better results. The
main point here is to increase flow without reducing air velocity, if ports
hogged out too much cylinders filling on low rpm will be very poor and engine
will loose torque on lower rpm, this is not good at all for street driven car.
Average DIY enthusiast can do few good things to his (her) head (i.e. cylinder head).
First - port match intake ports to head. Never port match exhaust ports, head
ports supposed to be smaller than exhaust manifold ports. It helps to prevent
exhaust flow pulses reversion and called reversion dam.
Second - smooth out sharp edges and rough casting marks to eliminate turbulence.
Don't polish intake ports to mirror-like finish, their surface has to be rough
to maintain some boundary layer turbulence.
It has effect of reducing port size at low flow condition, which is good for
bottom end power. Also this boundary layer turbulence prevents fuel separation.
Fuel separation is bad thing, similarly to poor atomization it causes fuel
droplets size to be inconsistent and leads to erratic combustion and slower burn
rate. Exhaust ports flow best with a polished finish, it also prevents carbon buildup.
Try to keep port cross section area of the port constant. Remember the principle
that it takes energy to accelerate air. If port expands air will slow down, if
port contracts afterwards air will accelerate (which takes energy). It will cost
you power because less air will make it's way into the cylinder.
Third - go further to short-side radius (the point where intake port floor
curves down), it is very critical area. Smooth that spot if it is rough or more
worse - sharp. Just think what you would do if you were air. If short-side
radius is not smooth and really radiused down but looks more like sharp object
sticking out from the port floor then air will separate from the port floor and
create huge turbulence in that area. Long-side radius (ceiling) normally doesn't
require any job.
Fourth - check valve throat area - this is the smallest diameter in the valve
pocket just above the valve seat. The most restrictive part of the intake tract
is intake valve. With well matched cams and good valve job it should flow as
much as open (unrestricted) port of 80% of the valve area. It is especially important if oversized valves used, they have to be unshrouded
to realize their full potential.
And last step - remove valve shrouding cast marks in the combustion chamber,
they block flow when air/fuel mixture enters cylinder, especially at low valve
lift. Though some engine builders have opinion that low lift flow may be not so
good like many people believe. Actually valves flowing a lot at low lift act
like longer duration cam, allowing more overlap and reversion.
Some serious tuners go as far as changing combustion chamber geometry, picture
on the left shows TRD 7M head, on the right side - picture of stock 7M head with
+1 mm Ferrea valves (picture borrowed from topic on Supraforums - this is Slow 66's
head, he builds very nasty mk3 drag car). You can see he removed squish pads
near intake valves for less shrouding and better cylinder filling. And in the
centre - picture of the group A racing head. All squish pads gone, as far as I
know they don't offer any advantage at high load/rpm, but very good thing for
street engine because they promote turbulence in combustion chamber. One
interesting note -Nissan's RB26 head also doesn't have any squish pads, similar
to group A head. I would never risk to do such radical changes like removing
squish pads completely, it would make horrible street engine making power in
very narrow rpm range.
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There are many more secrets in building good cylinder heads, every professional
has his own tricks. I can advice some good reading on this subject:
http://www.gofastnews.com/board/technical-articles/979-porting-school-1-why-engines-need-airflow.html
- this is by far THE BEST resource for somebody interested in head
porting, intake manifold designs and combustion dynamics, written by great David
Vizard. On the bottom of the first post you will find many links to other
technical articles.
Secrets of Cylinder Head - article from Sport Compact Car by Mike Kojima
Do-It-Yourself Guide - porting guide from Standard Abrasives
4-valve head - optimum port velocity - some hardcore reading
with useful links from Eng Tips Forums
Port & polish to a mirror finish - some more reading from Eng Tips Forums
detonation and
preignition.pdf - how combustion chamber design affects
engine detonation resistance, article by Allen W.Cline
engine knock, and how to eliminate it.pdf - another good
article, by Ray T.Bohacz
Last spring I contacted Erin Carpenter from Revolutionary Performance to do headwork for my 7M. Revolutionary mainly specialize on V8 motors, but they also do porting of 7M, 1JZ and 2JZ heads. I asked to source used 7M head for me because to ship my head to States would be too expensive and cause big downtime. I purchased full set of Ferrea valvetrain parts (+1mm oversize valves, springs, titanium retainers and valve locks) from Titan and shipped it to Revolutionary. We agreed to do full effort porting with flow testing and matching individual cylinders. When job was
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done I received from Erin port flow data of
stock and ported heads, above are the graphs I prepared. Stock 2JZ head flow
numbers taken from
mkiiitech.com , I draw these graphs to compare my head with stock 2JZ -
our Big Brother. I imagine ported 2JZ head would do far better then on
illustration above.
When I received my head I found that Revolutionary cut valve guides to improve
ports flow, I did not like it, not too good for street motor, I should have
discussed it with Erin. Another big surprise was that it was not possible to set
proper valve lash even with thickest 3.30mm shims. Oversize valves were too
"low" in the head. Again, I should have foreseen this, but to send my cams to
States to do proper valve job was not an option for me. I had to give my head to
local machinist who milled valve seats and did standard Toyota 3-angle valve
job. He also fitted new valve guides.
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Before sending my head to machinist I
removed cast ridges shrouding valves and slightly chamfered squish pads in the
proximity of valves. Hope it helped valves to flow better, especially at low
lift. Another trick helping
to cool cylinder 6 which tends to overheat is to drill 2 additional holes to
improve coolant flow from the cylinders jacket to the head. If you want to do it
- just lay head gasket on the head and mark place where you want to drill. This
is so called Zooloo mod and it was discussed
here. I also removed climate control heater, this car never driven in
winter. Coolant outlet from the banjo bolt on the back of the cylinder head I
connected with upper radiator hose, it will significantly improve coolant flow
through the head.
Previously I used 2.0mm MHG, now after reading how important the squish is I
purchased 0.051" (1.295mm) Cometic gasket. It gave me squish clearance 1.2mm andcompression ratio 8.23:1. Squish is good thing, though it is still far from
optimal 0.8 - 1.0mm. Good squish makes air/fuel charge more homogeneous, it
burns faster and requires less ignition advance, improves mechanical efficiency.
As a rule of the thumb every 0.01" (0.25mm) reduction of piston to head distance
brings optimum timing requirements 1 deg. down which is very beneficial for
power and BSFC. Slow burning combustion chambers have disadvantage of high
ignition advance requirement, combustion starts early BTDC and completed late
ATDC. Combustion happening further from TDC occurs at lower effective
compression ratio and utilized less effectively. Usually with faster burning
combustion chambers octane requirements either stay the same or go down,
provided CR is constant. Squish band also cools down end
gases and helps to reduce detonation. Maybe next time I have to go with 0.045"
or 0.040" gasket. First result of
reduced gasket thickness what I noticed is my motor idles now happily at
14.0-14.2 AFR, previously it had hard time to idle even at 13.0 AFR, I had to
keep it 12.0 - 12.5. Another noticeable improvement - I can close now my cold
start idle-up solenoid valve at 40°C, this valve is controlled by AEM and
previously was set up to close at 70°C and rpm > 1500rpm, otherwise idle was
quite rough and engine used to stall at the drop of the throttle. Gas mileage
also improved, on highway speed 90-100mph with occasional blasts to 120-130mph
it is 21.5mpg (11ltr/100km). In-city mileage is 14-15mpg (16-17ltr/100km)