The History of My Car & Engine

from Rally Bashing Hack to Weekend Racer

STAGE 3 - High Compression, Lumpy Cam, Weber Fed Screamer!

The power wasn't really there though, not anywhere near what I wanted.  So I bought a new crow camshaft, 284deg advertised duration.  This didn't make much difference at the time, it was lumpy at idle, and seemed to have a bit more in the mid range, but it didn't make much power at higher rpm.  There was an airflow bottleneck somewhere, likely the stock carby being a restriction.  

The car was getting a little bit quicker, but very minor improvements.  I thought more compression is probably the answer, so off came the head again.  I noticed there were some small marks on the top of the standard 1600 flat top pistons from where the valves had been hitting.  Would have been a combination of the higher lift cam, shaving the head, and valve bounce at over 6000rpm.  

I got the head shaved down to the valve seats which was about another 2mm off, and ended up with 40cc combustion chambers, giving  9.6:1 static compression with the stock 1600 pistons.  It now had a decent compression ratio as a base, and a big increase over the 8.7:1 stock ratio.  I also did a lot more porting of the head, and un-shrouded the valve seats in the combustion chambers.  I simply imagined how the air was flowing through the port, and tried to smooth or remove any restrictions.  This took about 30 hours.  I didn't have access to a flow bench at that time, but later testing has shown the head flows really well, it's head #1 on the 'stage 12' page.   

At the same time, out came the engine for new rings and bearings.  With the head shaved as far as it was, and fitted with the big cam, the valves were definitely hitting the pistons, so I had to machine some valve reliefs in them.  I did this myself by positioning each piston at TDC, and with a spare head fitted to the block, I would spin a special valve I modified with a drill, which grinded a valve relief into the top of the piston.  You can just make out the valve reliefs in the photo below.

I then got a 32/36 DGAV Weber and adaptor plate, hoping for a bit more flow and hp.  The DGAV has the hot water "aqua" choke, but I had to remove that as it was hitting the brake master cylinder.  I ported the plenum area of the inlet manifold as per this manifold page.   The engine was lumpy, sounded tough, and loved to rev.  It had more power right throughout the rev range, and was better at higher rpm too, where the stock Nikki carby had been choking it previously.

My little tacho often saw 7500rpm.  I never got it tuned properly though, which is why it would have been a bit down on power compared to what it could have made.  It was way too rich, and I couldn't seem to find a sweet spot with the ignition timing.  I could wind in around 50deg of static ignition timing, but couldn't hear the engine detonate, so I set it where I thought is should be.  If I had of put it on a dyno, I probably could have got an extra 20% power with the right air/fuel ratios and optimal timing.  

At this stage, I was running low 16's 1/4 mile time at 140km/h.  This was with old hard rear tyres, and a bit of wheel spin.  Slicks and softer rear suspension probably would have got the car into the 15's easily.  I am guessing I had about 90-95 hp at the flywheel.

I fitted a 38mm DGMS Weber which is a bigger carby and actually felt quicker, but I couldn't get any better than low 16's 1/4 mile times.  Again, the jetting was too rich for the engine and I never measured a/f ratios or had it dynoed.  It probably made an extra 5hp with this carby, but thinking back now there was potential for so much more.  The 38DGMS would have made an even bigger difference on an engine flowing more air than mine, like a G200 for eg.

Check out STAGE 4 - Low compression G200.