Customized Suzuki Intruder in French village
Photo: Copyright © 2014 Eelke Blok

Finding missing power

With all the new Mini stuff, it has been a while since I reported about the white Cooper. Last weekend, some stuff happened that is more than worth a report, though. More than likely, we've found what is causing the hole in the engine's power!

It's over a year ago that we went to the UK, to go to the IMM and
visit MiniSport for a rolling road session to see whether the car was
now performing as should be expected with the new engine, based on a
MiniSport stage 2 head and a MiniSport block (after the first engine -
the original, overhauled one - was found to considerably underperform
and above that, also drink oil far too much). Unfortunately, this
engine wasn't performing a lot better. Only 65 bhp was pulled out of
it, while the kind of setup I have (or was supposed to have) should get
to 75 bhp easy, if not 80 or more. For pictures, have a look at the
photo series about the IMM 2004 and SMOB in the picture section (temporarily down), there are a few about the rolling road session in there.

The verdict after the rolling road was that the car was low on
compression, and that the first thing to check would be the valve
timing. If that was OK, further investigation into the rest of the
engine would be required, to find out whether it has the correct
compression ratio.

It took a long time to have the valve timing checked and corrected, but this was done a few months ago, which I reported in this post on my blog.

However, as I wrote last time: "There's some bad news too,
though. The compression hasn't changed a bit since the last time, and
that shouldn't be a surprise according to my mechanic; if valve timing
would be as much off that it would start affecting compression, the
engine wouldn't even have run.

"It feels like the car has gained a few BHP, but due to the compression
that is still off, I doubt it is where it needs to be, which is in the
80+ BHP range. It might have entered the 70+ range now though."

So, we weren't quite there yet, and I wanted to get to the bottom of
the problem before taking the car to a rolling road again to get it
properly set up.

Luckily, a friendly visitor of the Mini Seven Club Forum
who is very much into head work and tuning engines, offered to have a
look. Joost, big thumbs up, you are already a great help! Dutch
visitors who are interested can check out his insights in this thread on the forum.

Last sunday was the day we arranged for Joost to come over, pull of the
head and see what was up. He already calculated that it was unlikely
that just the head would cause the loss in BHP and compression. So, we
were at that point already fearing that also the type of pistons used
was not right for the engine.

Well, he was right, here's the verdict, loosely translated from Joost's post on the Dutch forum.

First of all, indeed the wrong type of pistons is in the engine, P21251
where it should have been P21253. Compression is now more in the range
of 8.6, where it should be 10.38 for the camshaft.

The MiniSport stage 2 head really is quite dramatically bad. Keith
Calver had already said that these heads often have worse flow than
standard MG Metro heads, which wasn't a lie.

One of the inlet valve settings (is that the right word?) was cut 3mm
too deep, unless it has buried itself into the head (not sure of the
terminology), but it really doesn't look that way.

Apart from this, he has more comments on the porting and such, but I
don't understand it completely in Dutch, so there wouldn't be much
point in translating it to English. Bottom line is, the inlet valve
that is too deep will be corrected by fitting a valve seat (normally
only used on exhaust ports) and he will try and correct the porting as
much as he can. He reckons the head will give in about 3-5 BHP when
compared to a head that is done exactly as he would like it. With the
right pistons in the engine, of course. With the current pistons, it
should still make a difference, just not as much as it would with the
proper CR.

The get out of the engine what is in the parts, it will have to come
out again and the pistons will need to be replaced with the correct
type. I'm going to have to decide when to undertake this project. In
the meantime, it looks like I will be driving the engine with the
modified head and the wrong pistons for the coming summer and leave
this for a project for next winter. Before than, I hope to have moved
house and found some place to undertake this kind of job.

Although all this does not look good for MiniSport, it has to be said
that I am not going to try and find out how the experience will be
trying to see some of my money back, or a replacement head. Maybe they
would proove to be a reliable company ready to admit and act on their
mistakes, but I do not feel like all the hassle this would inevitably
present. It has been a long time since the head was bought, and also a
long time since it was found, on that one day in august 2004 on their
rolling road, that there was a problem. Also, I do not know on who's
account those wrong pistons went into the engine; whether the engine
came as a pre-assembled unit from the UK, or whether it came here in
parts and it was assembled by the company doing my Mini at the time
(the guys who did the restoration). It's clear someone screwed up
(well, that was clear really from the day the power output of the
engine was known), but I'm not going to try to find out who, and not
going to try to make any warranty claims (I've had enough of those with
this car). I really already decided that the day I decided to have
someone else investigate and correct the valve timing. On to actual
solutions. Solutions I have a little bit more control over.

Add new comment