Compression Ratio

[Nitrate]

I have FI 81' 2000. I am wondering why the stock compression ratio is so low 8.1: 1? What was the ratio for European models? I'm thinking a 9 or 9.5 would be nice. Is there a head change or piston substitution for the 2000 engine that would increase compression? RDB

[zachmac]

Wasn't just the FI cars, some of late carburetor cars had low 8:1 compression. Not sure why? Trying to burn cheap gas and meet emissions?

In any case you a couple of options. An 1800 head for example will bolt on and the reduced chamber will increase CR. You can also of course mill your head to get a little gain. Pistons are available in several dome heights (stock are flat) and the 4 to 4.5 mm ones would put you in the 9.5 to 10:1 range. Pistons are of course a lot more involved to replace than just the head so a lot of people just do the 1800 head.

CR is also of course partly a function of valve timing and overlap. You could in theory boost CR with the right cams but in general hotter cams lower CR and you need to compensate with the head / pistons.

BTW, if you decide to go with an 1800 head I have one ready to bolt on for sale .

[Nitrate]

Thanks Jeff. Do you know of anyone who has done the piston change? Looks like it could be done with engine in car. Anyone have any additional info? RDB

[zachmac]

Thanks Jeff. Do you know of anyone who has done the piston change? Looks like it could be done with engine in car. Anyone have any additional info? RDB

I just swapped to 4mm domes in my 79 carbed car but I had the engine out for a rebuild. Getting the oil pan off without dropping the cross member can be done but you have to reach into the goo and unbolt the oil pump to do it and then reverse the process putting it back together. Plus, how do you know what you'll find cylinder wise? In most cases you'll at a minimum want to hone the cylinders to get the new rings to seat and that is doable engine in but not advisable. Lots of folks have changed out pistons.

[azruss]

low CR allows the use of regular. with FI and a cat, emissions were relatively easy to achieve. It also as the advantage of puting the torque in the midrange. This helps with fuel economy and engine life. I would enjoy more HP out of my FI, but not at the sacrifice of mid-range torque.
I seldom take my car to 5500 rpm and most of the time under 5k. My 1st spider was a 1438 and eventho it was fun to drive, you spent a lot of time working your tail off to get the max out of the motor. To me, a the stock 2L was a big improvement from that. I would be curious if anyone has dyno'd a 2L with just domed pistons to see what the torque and HP curve looks like.

[Nitrate]

Jeff, Could you describe the driving characteristics of the car with the 4mm piston change. Where do you notice the power increase. Low, midrange, upper end, or is it the same across the whole spectrum? Is this a seat of the pants noticeable change compared to the car before? Is it worthwhile , would you do it again? Thank You, RDB

[narfire]

1980 FI
I found the best bang for $ spent was a 1800 or 2L FI head that had a good valve grind, tidied/matched intake and exhaust ports with a set of little bit hotter cams ( bought from Allison's), adjustable cam wheels and an absolute must...degree'd in properly. headers with 2" exhaust helped a bit as well. Also shaved flywheel....
I did spend some loot on a re-bore with 84.4 pistons but the head and cams really woke the engine up... comparatively to stock.
What I did was source a decent 2L engine, put it on a stand and as $$$ permitted over time , I built it up to what I could afford then swapped it into my car.

[opus10583]

I have FI 81' 2000. I am wondering why the stock compression ratio is so low 8.1: 1? What was the ratio for European models? I'm thinking a 9 or 9.5 would be nice. Is there a head change or piston substitution for the 2000 engine that would increase compression? RDB

Hi,

Infant emissions and no-lead gasoline technologies. The pre-Fed cars maxed at 9.8:1, iirc.

A head swap may get you a couple of tenths, you need pistons to go up integers. Beware your sourcing.

I've had my '78 rebuilt with 9.8:1 pistons and a 34 DMS, after going to a 4-2-1 exhaust: It's a very different car, and now as intended.

CR gives you torque, more really wakes up the 1800, and yields that wonderful canzone Italiana!

Ciao,
Mark