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#Post#: 2008--------------------------------------------------
2ltr 8v Digifant power
By: JMR Date: December 12, 2014, 9:34 am
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We've done some work on Tim Hughes MK2 before, a lower F/D swap
& a Quaife diff, along with a tailbox swap from the previous
poor design which netted a 7hp peak power gain and 13hp (yep 1 &
3!) gain at mid range peak torque rpm.
Looking at the power curve the last time I saw the car, the way
it levelled off between peak torque and peak power was telling
me the engine was struggling to breathe as the revs rose. The
engine was also down on power overall considering the spec (110
at the wheels..133-134 at the flywheel), so my suggestion was I
take a look at the head and see what we had to start with and
look at improving the flow.
The previous owner, a friend of Tim's, had an engine kit
supplied and fitted along with, as we discovered, a 40.5 / 35mm
head. I've always seen improvements with these with some re
porting, but as we wanted to get the 2ltr breathing properly my
suggestion was we kept with the 35mm exhaust valve but re port
and add 42mm inlets. Now to cut a very long story short, as I
opened the last inlet throat it cracked through...I've gone much
bigger without an issue so this casting must have just been a
bit thin, nothing my alloy welder guru cant fix...normally!
After 3 attempts at grinding out and re welding it just wouldn't
take as the pressure test showed...it can happen but its
rare...so with time very much not on my side I started from
scratch with another casting. Now we had a dilemma, or at least
Tim did as I was confident I knew the answer. Tim had a budget
(as we all do) to fit the bigger inlet valves & new inserts it
needed as we were going to do on the original head, but bigger
inserts to support the 35mm exhaust valves from the old head
wasn't in the plan. It was simple in my head (pardon the pun!),
we'll just use the 42mm inlets as intended but keep to the std
33mm exhaust valves.
Tim had some reservations about my 42 / 33 combo as the word on
the street says a 2ltr needs a 35mm exhaust valve to make power.
I politely pointed out that his name sakes (Tim Moll's) 2ltr
race spec 8v crossflow made almost 200hp on 33mm exhaust valves
so I wasn't too phased about hitting the target I wanted to see
of around 150hp.
While the head was off Tim measured the piston deck height for
me so I could work out what needed skimming off the head to get
the C.R right. It was then we discovered 2 more reasons for the
engines lack of sparkle...the pistons were too far away from the
block deck for decent squish, which in turn, along with the deep
piston bowl, contributed to the C.R being roughly 1-1/2 points
lower than ideal for the 276 cam used.
With no perfect solution, I roughly closed the C.R deficit down
by half by skimming the head as much as I dared with a view to
maybe sorting the block at some point. The new 42 / 33 ported
head was then sent back to Tim for re fitting, followed by the
car heading back down to us to run up on the rollers for fine
tweaking.
However, at the end of the one and only power run, the rattle
from the bottom end told me we would be looking at the rest of
the engine sooner than planned! To cut another long story short,
Tim left the car with us and returned a couple of weeks later to
remove the engine for me to look inside. As I suspected, number
3 big end had gone, resulting in a scrapped crank and rod.
With a replacement crank found and some rods I had going spare
that we fitted with ARP bolts, I re built the engine after
correcting the squish & compression short fall while it was
apart with a good skim of the block. After Tim returned to fit
the engine, it fired up instantly for us to take straight over
to the rollers to finish what we started once and for all. With
time yet again not on our side, I bedded the rings and bearings
in during the 5 mile drive to the rollers to see how much all
the effort was worth....would we get close to our 150hp target,
would we gain any more mid range?
Well it certainly felt a bit stronger on the road, but with the
ignition and fueling set at a conservative estimate I didn't
push my luck too much. After some more running on the rollers
and some basic setting up the fresh engine was much more
responsive than the old, almost "open induction" like in
throttle response...not bad for digifant!
So the moment of truth had arrived...what would the so called
wrong valve size combo give us...the answer was more
power...everywhere. With 4 to 5hp more at 3 to 4000, peak torque
rpm was next up...an extra 10hp & 4500 from the new combo wasn't
to be sniffed at. With the old engine/head, power started to
flatten out shortly after peak torque, but not anymore. With
power now climbing much better than before we had an extra 12hp
@ 5000, 13hp more at 5500 and peak was now 17hp up over the
previous best @ 6K, with 127 at the wheels, around 152-153 at
the flywheel, with power at 6500 10hp up too.
With the car un-strapped from the rollers and a quick (quite
literally!) run up the road completed, I brought the car back
for Tim to try his new power unit....the grin on his face upon
returning said it all.
I feel there could be a little more to come as time didn't
permit any inlet manifold/plenum porting at all, but for now
Tim's 2ltr 8v is making the power it always should have.
The graph shows the progress from as we first saw it, the
tailbox change, and finally the current spec with the new head &
improved squish & C.R.
[URL=
HTML http://s66.photobucket.com/user/mrhillclimber/media/Mobile%20Uploads/2014-12-11121101_zps8e428b75.jpg.html][IMG]http://i66.photobucket.com/albums/h278/mrhillclimber/Mobile%20Uploads/2014-12-11121101_zps8e428b75.jpg[/img][/URL]
#Post#: 2165--------------------------------------------------
Re: 2ltr 8v Digifant power
By: Ganwinky Date: April 22, 2015, 4:55 am
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We can work with others.
#Post#: 2168--------------------------------------------------
Re: 2ltr 8v Digifant power
By: snowbopeep Date: May 6, 2015, 10:59 pm
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A good topic to learn a lot. A very rich data The lot
#Post#: 2180--------------------------------------------------
Re: 2ltr 8v Digifant power
By: toystoryful Date: May 25, 2015, 10:42 pm
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I read a very good post here. Read I was able to use really.
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