I have a mystery 2.0L in my '79 Spider. I say that because the car has had several previous owners and no records of what they might have done to it. The woman that I bought the car from told me that the guy that she bought the car from put several thousand dollars into the engine. He wanted an Alfa that would be competitive against Porsches. Not sure if he was racing against 914's or what. He sold the car and bought a Porsche.
I d know that the cams are stock but both have been advanced.
I did a wet compression test, all plugs out, and throttle wide open this morning and came up with these numbers:
Cyl 1 240
Cyl 2. 230
Cyl 3. 250
Cyl 4. 230
Repeated the test with a second gauge and got the same results. I'm going to do a leak down test this week. Any idea what could have been done to this engine to achieve this high compression?
I used to wonder about this too. Atmospheric pressure is about 15 psi. At 9:1 compression 1/9 the volume would give 9 times the pressure or 135 psi. Where does the extra pressure come from? Adiabatic heating. Adiabatic means no heat lost to the surroundings. In a very short time the work done compressing the gas in the cylinder heats the gas and this heat makes the pressure go up even more. If the gas were compressed very slowly then the heat generated would be absorbed into the cylinder walls and the pressure would be near the expected 135 psi.
Two interesting examples of adiabatic heating are Diesel engines where the adiabatic heating is enough to ignite the fuel. Another is Chinook winds where in the Midwest winds blowing east coming to lower altitude from the Rocky Mountains can be very warm. The air comes from high altitude (low pressure) to low altitude (high pressure). The compression of the air by higher atmospheric pressure heats the air. Compressed air exiting the cylinder of an air compressor is very hot because of adiabatic heating.
In an older engine leaks around valves and rings might reduce the pressure a little bit. A performance camshaft would also reduce the compression at cranking speeds.
The opposite, adiabatic cooling, takes place when a gas expands quickly, like releasing air from an inflated tire.
230 psi does seem high though. The engine probably is in good tight condition, the starter motor spins it fast, and it doesn't have a racing cam. Maybe an experienced mechanic who has done many compression tests will chime in with typical values.
I was thinking that it must have been modified to run a much higher compression, but then the standard camshafts don't really make sense. Personally, I'd just be happy, or maybe your gauge reads high (test it on another engine, maybe).
Thanks folks. It's Spica. Wes rebuilt the pump a few years ago. My former mechanic could never get the car to run right. Just told me to drive it and enjoy it. Problem is that it is not enjoyable to drive. Idles at 2500. I don't know if the cams were swapped put it is possible.
The Marelli plex has a really short advance curve. So to get full advance at 4000 RPM the distributor is too far advanced at idle, and it will never idle properly. I ran into that problem on a Spider and finally ditched it for a stock distributor with a pertronix ignitor. That worked much better.
Swapping out your distributor for a stock unit or 123 would probably help. I agree having a car that doesn't idle properly quickly kills the joy
The Marelli plex has a really short advance curve. So to get full advance at 4000 RPM the distributor is too far advanced at idle, and it will never idle ptroperly. I ran into that problem on a Spider and finally ditched it for a stock distributor with a pertronix ignitor. That worked much better.
Swapping out your distributor for a stock unit or 123 would probably help. I agree having a car that doesn't idle properly quickly kills the joy
Thanks. Going to a 123 has always been on my plan of intent. I have a scope and will try to get it into cylinder 1 tomorrow. Will try to take some photos from the screen and post them.
I've never seen compression numbers that high, but there's no reason why they aren't obtainable. It's simply a matter of buying ultra high compression pistons and shaving the head until you get the compression ratio you want. I'm surprised that the engine doesn't detonate (ping).
You should talk to Wes about the engine see if he remembers it.
I know that 1960's era drag racers used to run their big V8s at 15 to 1 compression ratio using 100LL (100 octane leaded gas)
Bye
The Marelli plex has a really short advance curve. So to get full advance at 4000 RPM the distributor is too far advanced at idle, and it will never idle properly. I ran into that problem on a Spider and finally ditched it for a stock distributor with a pertronix ignitor. That worked much better.
Are you talking about distributor degrees or crankshaft degrees? I've been running 'Plex ignitions for years using a modified Plex distributor that gets it's max advance at about 3k. I have the max advance set at 36 crankshaft degrees (I never use the static timing marks, BTW). My much modified 2 liter in my Super idles smoothly at 700 rpm and runs equally as smoothly all the way to my imposed 7k redline. In multiple decades of Marelli Plex owning and driving, I've never encountered the problem you describe.
As far as compression ratio is concerned, the most important criterion is whether or not the engine can run happily on pump gas. If your engine runs happily, the actual compression ratio sorta becomes academic. If your engine was "built" at some point, my guess is that you have a combination of high compression pistons and a cut cylinder head. If you want to reduce your compression ratio you can fit a thicker copper-clad head gasket to get a few tenths lower compression. Or you can have an even thicker copper head gasket made.
Normally, this means you poured a small amount of light oil into each cylinder to seal the rings, then did your test to confirm you had no leaking valves.
If you pour a lot of oil into each cylinder you can artificially increase the CR to the numbers you quote. It’s a bad idea for a number of reasons.
Timing of the intake valve events will influence static compression. Closing the valve earlier results in higher pressure. So a short duration cam running with an advanced LC will make the highest pressure.
Thanks all. unfortunately my borescope camera is too big to get thru the spark plug holes. I was able to use it to look at the tops of the pistons. It looks like there are 3 numbers on each. Can't tell if they are 7's or 2's or some combination of both and then what looks like a /.
I use 93 octane gas and have never had a problem with pinging. When I did the wet test I only sprayed a small amount oil small amount oil into each cylinder and I will try the test again dry this time. I'm also going to do a leak down test this week. I'll post my results.
Hi there, the numbers likely line up with borgo 10.4 pistons, as others have said you likely have a shaved head as well. Redoing your compression test dry would be a good move, it will tell you if you need to be concerned about having to run super high octane gas. On the bright side having high compression already makes getting the engine to run correctly easier. Ignition timing set and spica reset to nominal throughout would probably serve you well.
Unfortunately it's too cold to try to work in my unheated garage today. Temp is down in the 20's with winds out of the north at 10 mph. They're saying that the temps will be be back up to the 50's by Friday. I'll do another compression test and a leak down test then and post the numbers. I just want to make sure that the engine is in good shape before taking on the Spica issue. The spark plugs do indicate that the engine is running rich.
O.K. It warmed up today so I was able to work on my spider. I did the compression test. This time dry, the engine up to temp, plugs out, and throttle wide open.
This is what I got this time:
Cyl 1. 200
Cyl 2. 200
Cyl 3. 200
Cyl 4. 200
Did the test twice and got the same numbers both times. The consistency is incredible so I'm not going to bother doing a leak down test right now. The plugs confirm that the Spica is set too rich. I have found a mechanic that knows how to properly tune a pump that Wes has rebuilt. The car has summer tires on it so I'll have wait until spring to have the car flatbedded up to him.
Hi there, good numbers on the compression test. Doing the compression test is about the same skill level as setting up the Spica, I would consider doing it yourself. Does it have a thermostatic actuator (TA)? Likely. You will need to know the T number off the spica pump to know if your pump wants a 27 or 29mm extension. Make yourself a dummy actuator, set the bell crank stops by borrowing the tool or use a digital protractor. Then pretty much most of it can be set on a non warmed up engine. It is a step by step process from beginning to end. Lots of help and support here.
Thanks. I thought about doing it myself. I even bought a crank stops tool. I decided not to for a couple of reasons.
First, my former mechanic, who has decades of Alfa experience, could not get the engine to run correctly with the pump that Wes rebuilt. He kept telling me that the pump was bad. I sent it back to Wes and he would test the pump a say that it was fine. Same result when we got the pump back. My former mechanic put his pump in my car and my car ran great. The rebuilt pump same problem. So back it went across the country. Wes tested the pump again and told us it was fine and sent it back. The T/A tested fine at 29 mm. My former mechanic put the pump back in and cranked it very rich to get it to at least run. It also idles at about 1500 rpm's. He told me to drive it the way it is and enjoy it. I don't think that my former mechanic followed the instructions that Wes provides tune the new pump.
Second, although I have owned this car for years, I don't know enough about this engine. I knew that the compression was quite high but didn't know why. It appears that the engine has Borgo 10.4:1 pistons. I still don't know what else has been done to this engine other than both standard cams have been advanced. We are assuming that the head has been shaved put don't know if the valves are oversized. Would anything done to this engine require a higher performing Spica pump?
Hopefully this new mechanic will be able to get this engine running properly and make this car a pleasure to drive.
My former mechanic put his pump in my car and my car ran great. The rebuilt pump same problem. So back it went across the country. Wes tested the pump again and told us it was fine and sent it back. The T/A tested fine at 29 mm. My former mechanic put the pump back in and cranked it very rich to get it to at least run.
- Drew
Two things, if your mechanics personal SPICA pump ran your car perfectly, find out if his is a regular SPICA or a "performance". If it was a standard SPICA chances are thats what your car needs (in the end, whether it be this one or another).
Second, running a car rich for a while is a good way to eventually wipe out the piston rings from the gas washing off the oil, though I did catch that you are no longer driving the car.
Dumb question, when your mechanic switched the two SPICA pumps, did he switch the pump single or did he switch the manifold and other parts?
I find it odd that your car ran with his SPICA, but not with yours, and Wes has inspected your pump more than once.
I understand your frustration, faulty fuel systems on any car can make you want to pull your hair out and seeing as your Alfa mechanic gave up with it..you have good reason to be intimidated.
Your compression is something to be envied though! It will be a strong motor when you get it tuned right!
As far as I know my previous mechanic only swapped the pump. I can't distrust Wes though. He is a legend. There is another problem here that we haven't uncovered yet. You are correct that I haven't drive the car much since I bought it. Maybe 500 miles. I'm taking it that it is a good sign that I can somewhat read the numbers on the pistons with a borescope. That's how another forum member was able to tenitivly identify the pistons. I'm sure that my new mechanic will get this all strengthened out in the spring. Unfortunately, his shop is in the icebox part of the state and it appears that we have an early winter setting in.
I agree, something is amiss. I was partly wondering if maybe the manifold itself had a leaking gasket or the throttle butterflies are off in some way.
I am not one to offer SPICA advice however.
If I were you, waiting on the mechanic, I would probably wait a few days. Read up on the SPICA system here on the board, then I would get bored and decide that I must find the problem. Even if I dont drive the car, the suspense of not knowing why my car won't run correctly would drive me nuts LOL
Has your Alfa mechanic got a running car he could put your pump in to see how it runs?
This would be the best test of the pump, not putting another pump on your engine. If the other engine runs fine, then need to move on ... but its definitely the pump, somehow, if a good engine suddenly gets upset with this pump.
Pete
Thanks. I'll definitely talk to my new mechanic about that. Pretty sure that it isn't the pump. I'm in a holding pattern now until spring. The Spider is all tucked in for the winter. Hopefully we will see an early spring.
I think that you are correct. That's why he is my "former" mechanic. The spider will be flatbeded to my "new" mechanic once the snow melts in the spring. Probably be mid April.
Just a quick update. I have gotten a bit sidetracked with a few projects but I spoke to my new mechanic last week. He needs to finish up a few projects. We are talking again on September 1st. The good news is that he thinks he was the one who built this engine. Thinks he built it for a guy named Peter Bush. Won't know for sure until he sees the engine. If anyone knows Peter or how to get in touch with him, I'd like to talk to him. All of the records have been lost in the "ether". The good news is that the mechanic is now very interested in the project. I'll post another update in September.
One other note, when I started the engine this spring so I could move the car out of the garage, when up to temperature, the idle now drops down to between 5 and 6 hundred. So the plot thickens.
200 psi compression is what I had with a 2000 fitted with Motronic 10.4:1 pistons and stock cams.
A standard Spica pump can't cope with much changes.
What cams are in it and how are they timed?
200 psi compression is what I had with a 2000 fitted with Motronic 10.4:1 pistons and stock cams.
A standard Spica pump can't cope with much changes.
What cams are in it and how are they timed?
Thanks for your input. Wes identified the cams as stock from photos that I sent him before I had him rebuild the pump. They are both advanced. I think my old mechanic said 26*. There are more questions than answers about this engine. Hopefully my new mechanic will be able to provide the remaining answers and we will get a fun car to drive out of this.
- Drew
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