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Dyno tuning a blown MGB

Subject: Dyno tuning a blown MGB
From: Larry Colen <>
Date: Thu, 5 Dec 2002 18:21:13 -0800
You all have heard various bits in the saga of my mounting a
supercharger from HP ( ) on Jasmine ( ) my 1969 MGBGT. It's very close, and
extremely promising. I've already seen an improvement of 86% (168/90)
in peak torque, and 45% (109/75) in peak horsepower. I still have a
few bugs to work out, and I'm sending this to people I figure would
either be interested in the status, or may have some suggestions for
the answers to my questions.

The good news is that the dyno run was very informative. I found a few
things wrong, figured out a few more things and on my best runs saw
168 lb-ft of torque at 4000 RPM and 109 HP at about 6000 RPM, just
before the headgasket blew. In contrast, my last motor, which was
about the same, except naturally aspirated and 8.8:1 compression made
90 lb-ft of torque at about 4000 RPM and hp maxed out at about 75 at
about 5000 RPM.

I'd like to give a plug for Randy at Integrity Automotive in Scotts
Valley California. He did a great job helping me tune the car on the
dyno. His number is 831-439-9631.


When I put this incarnation of the motor together, it was running
strong, but had a water leak and a busted water guage. Due to my own
stupidity, I seriously overheated it. While it was overheating, I had
some nasty problems with predetonation. I tried solving the
predetonation by playing with the timing, then by adding in race
gas. I finally reset the timing, and got it running well, despite a
blown head gasket.

Last Friday night, I replaced the head gasket. On Monday I drove the
car to work, it was running very strong. I saw 5000 RPM in fifth gear
overdrive, and she was still accelerating like I was only doing the
speed limit (rather than twice the double nickel). Monday night, I
determined that my temp guage was completely non functional, so I
didn't drive the car on Tuesday. Tuesday night I put in a new temp
guage, changed the oil, dealt witha  few other minor issues and drove
the car to work on Wednesday. The car was really sluggish, it felt
more like a Rubber Bumper B rather than the pavement pounder it should
feel like. I noticed that the belt (fan, water pump, and blower) was
loose and at the limit of adjustment so I swapped to a smaller
belt. Some of the power came back, but it was still weak. 

On Wednesday I had also ordered some richer needles (BCF & BCG) to
fatten up the midrange. They were supposed to arrive via UPS red,
i.e. by about 10:30 AM, so I set up a dyno appointment for 11 AM on
Thursday. At about 1PM I gave up and went to Integrity Auto in Scotts
Valley without the needles. They showed up at about 5PM on Thursday.

Things discovered:

She was running about 20 degrees retarded, this severely adversely
affected HP. There is something funky about the timing. What the dyno
shows to be the best setting is reading 28 BTDC on my degree
wheel. I've got to get the car up on the hoist to check that. My crank
pulley is too tight, and isn't going to come off the motor.

She was running way lean right off of idle up to about 3000 RPM. I
applied emory cloth to the needle and it's a lot better, but still
lean around 3000 RPM. Running it way retarted made the CO look way
low, advancing the timing improved that. I'll need to measure the
needle and get a better profile.

I ordered two needles from Joe Curto yesterday, to be shipped UPS
red. They've never shown up.  

I dunno if my head is warped, but I've ordered a solid copper head


According to Randy, between 4 and 6% CO is  optimal.
An early run, before I sanded the needle or Randy advanced the timing

stock BBC needle:

CO %    RPM
 2.6     974
 0.1    1287
 0.1    2379
 0.5    2477
 1.2    2574
 2.0    2691
 3.2    3091
 3.9    3216
 4.4    3338
 5.9    3917
 6.8    4629
 7.3    5126


On my best recorded run, I cut it short before seeing maximum power.
This is with the timing advanced, and a slightly reprofiled needle,
but it's not too far off of a stock BBC:

Readjusted timing
slightly reprofiled needle:

CO %    RPM     lb-ft   hp
 6.0    1678    20.5     4.3
 5.8    2225    145.8    36.9
 8.7    2549    156.1    48.3
 5.8    2765    159.5    53.6
 2.9    2928    161.8    57.4
 3.7    3515    166.1    70.7
 4.8    3792    168.1    77.2
 5.4    4000    168.3    81.5
 7.4    4652    167.8    94.7
 7.8    4957    164.3    99.0
 7.9    5125    164.6   102.7
 7.9    5464    156.5   104.4

I did another run where I ran the car up to about 6200, but didn't
realize I needed someone to click for each data point, so I didn't
collect any data. I saw about 109hp, and when I heard the engine
"stumble", at about 6200, still putting about 105 hp to the ground, I
backed off. 

On subsequent runs, at about 5500 or 5200, it would all of a sudden
just lose power, as the headgasket apparantly let go. We were getting
seepage around cylinder #2.

Randy measured my boost at 6.5 pounds.  

I bought an STI boost guage from a friend, but it's weird, "Zero" keeps
wandering around the guage.


Notes and Questions:

This time, when I have the head off, I'll check it for flatness.

If I have to have it milled, and I don't want to lose compression
chamber volume, where would be the best places to remove a little
metal to improve flow? My guess is around the exhuast valve. With the
blower, I can force as much air in as I want.

Various people have mentioned O-ringing the block. I've also heard
that this does not work well on MGBs. Does anyone have any experience? 

I noticed that the HIF comes with spring loaded needles. What are the
advantages/disadvantages of the spring loaded needles in an SU?

I've ordered a solid copper head gasket. Is there any special care and
feeding that such requires?  

What do the people who run high compression E-Prod, or Vintage MGB
motors do?

A lot of my difficulties have been due to rushing to meet deadlines,
causing stupid mistakes and me to miss even more deadlines. There are
all sorts of things that I should have done a lot sooner.

The Scorcher distributor I bought from HP uses Bosch Points:
GB700 / 1 237 013 121 
I want to replace them with a Pertronix Ignitor. Does anyone know if
there is one for this application, or what vehicle those points are
normally used in?

I've found something worse than oldies station that play the music I used to
listen to. Oldies stations that play the "new" music I used to complain about.                          

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